Yeah, that was before I laid it down for the heatsinking. It got pretty stinkin' hot in that configuration, which is why I made the change. Of course, drawing near the rated max out of the regulators will do that.
Dan-
The LM12 is actually designed for linear motion control. As such, THD wasn't a primary concern of the designers, and it has a pretty nasty response (and sound) above the 800-1khz region. Chris Little (the original designer of the circuit) used them as the bottom of a tri-amped speaker setup. I used them for sub duty. I wouldn't recommend them for anything full range. For that, I'd check into the LM3886, which isn't quite as powerful, but is much more suited to audio uses.
I used a bridged pair on each side because subs are hungry beasts, and because the voltage swing of the LM12s isn't all that great. It does add some complexity, but it's worth it in my opinion.
The schematic in the datasheet for the audio amplifier is basically the same as the LM3886 and any other power op-amp. It should work, provided you bypass the supply correctly and make sure to account for input noise and things like that.
OK, I was replying to your post line by line. I think I'm going to change that to a basic summary now.
Don't use the LM12 full range. Please. Get some samples of an LM3886TF and use them instead. I've got a page on my site about using that chip too, and there's a bajillion others doing things with it under the name gainclone. The LM12 uses an oddball 4 pin TO-3 package, and no stock heatsink will fit it. As for your heatsink choice, that's woefully inadequate. The natural convection of that 'sink is 36degC/watt, and for the LM12 as an audio amp, you'll need something closer to 1degC/watt, which that sink won't achieve, even with fan cooling. The LM3886 datasheet has an excellent piece on calculating heatsink size, and there are app notes on the Thermalloy site that are pretty awesome too. I'd strongly suggest reading them all. Linear amps like the LM12, LM3886, and any discrete transistor or FET design are terribly inefficient, and need gobs of heatsinking to run cool, or very inventive methods of cooling.
A pair of LM3886s can be put in a nice small case, and run happily see here:
That's in a Radio Shack case that's all of 10" on it's longest side, and about 4" tall to accomidate the heatsink and the transformer. You can see the size of heatsink I used for the pair...that's about the right size. I built a 4ch version of the amp, with the same size heatsink, but I can't run it as hard before it gets too hot. Pictures 4 and 5 are roughly life size on my monitor. I used a salvaged transformer that's roughly 200VA, give or take. With the large filter caps I used for the power supply, that was plenty for normal use.
For your case, you'll want to look into toroidal transformers. They have greater power density (more output for a given size) and are generally wider than they are tall. Just be careful mounting them. I'll go into that later if you end up with one.
By now you're probably thinking that the LM3886 isn't powerful enough, and at ~60W per chip, it seems that way on paper, but unless you listen to rap or hardcore techno with the bass all the way up, most speakers will be just fine, and the dynamic ability of the LM3886 is impressive. The BPA200 is the best option with them, using parallel pairs to build a bridged amp, but it's not terribly easy to do right the first time.
That's all I have time to type right now...more later if you want it.
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Funny enough, I was just looking into the LM3886 last night as an alternative. For my budget, the LM12 is just too expensive. I would rather blow up a 5 dollar 3886 than an 35 dollar LM12. And I'm not much of a rap person, but techno is good sometimes...so the power shoudn;t matter. I was reading on the DIYaudio forums that you could put two 3886's in series to get more power out of them. What do you think about this? I will post some links when I get home later to the schematics I found.
In series or in a bridge configuration? You can bridge them…I don’t know if I want to do that but I am happy with the LM3886 as they are anyway. I have built several working amplifiers around them. Great hybrid amplifiers even if the specifications went down between preliminary and release (I had early engineering samples). If you read back a few pages you’ll see the current amplifier I am building uses 2 LM3886 chips for stereo output. Did you get your rotary encoder yet?
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I got it today. Thanks a bunch. Sorry I didn't say it earlier, I was at school and I had a free period.
I'm out all night tonight and gone tomorrow for Mother's Day with my family, but I'll do some more research on Sunday. I'll let you know what I come up with.
Check it out and see what you think. Most of the discussion is about improving the design, but I'm perfectly happy with the original (unless it has major flaws of course...)
My goal on this is to go the the local electronics swap meet (TRW) and buy what I can there. It's on the 26th so I have some time to make a bill of materials and determine what I already have.
I will post my front panel design in the next week. I'm being held up on the LED choices for the level (VU) meter. I cant seem to find something I like yet...still haven't decided b/w T1 LED's, T1 3/4 LED's, or a premade bargraph display. Oh well, well see what happens. So far, I have a nice switch (from a previous project), a LCD in mind (Serial, 20x4 from eBay), my button choices almost made, and a knob picked out for volume.
I didn’t look at the design (must be a member), but I agree with Dave in that the most straight forward designs can be gotten from the datasheet/AppNotes for the LM3886. I noticed in that thread though that they were questioning his op-amp front end. I don’t know what that is all about…A few of my designs had specialty audio op-amps to isolate the level meters and tape monitor circuits. With careful designs there’s nothing wrong with an op-amp in your circuit. I think other people tend to be overly critical of someone else’s design because they wouldn’t do it that way. Dave, Junkie and I are a few of the people out there who are more open-minded about this stuff. I feel you have to do what works for you.
Dave,
I had every intention of hooking up that power supply this weekend but when I went to get out the rest of the parts for the power supply I ran into a half-completed project I started some time ago and decided to finish it first. As of late last night I was still fixing a few soldering issues I found but I believe I have the hardware done. What took me so long was milling out the panels (by hand, using a drill, nibbler and files) and trying to merge concepts from 5 years ago with current ones. What I mean is that lately I have been using LCD Displays with keypad decoders in them (Matrix Orbital) but I had already mounted a Parallax Serial 4x20 in the cabinet and soldered a socket for the EDE1144 onto the Super Carrier Board so I went with it. Results of this can be seen this week posted in another thread. Sorry for being off topic.
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Oh, sorry I forgot that you had to be a member to access it. I use an extension for Firefox called BugMeNot (www.bugmenot.com does the same thing) that finds login's that people submit to their site and lets you through most login screens without creating an account. I might consider making an account now if I pursue the design though...
I attached the PDF of the schematic so you guys could take a look at it.
EDIT:
I've found another really nice design. It's a bit simpler than the other one. It uses two 3886's in parallel per channel, giving about 50W @ 4 ohms and 100W @ 8 ohms. Just what I want. The instructions are really clear and it even uses a regulated power supply. I'm leaning towards this one now...
Here's the link: http://www.shine7.com/audio/pa100.htm
/EDIT
Also, a quick question. I don't really know what to do for a preamp. I'm not sure whether the LM318 in the design counts as one, of if I need a separate one. If I do, then I plan on using the Sony CXA1352AS. It's 5 band graphic equalizer, preamp, and volume control in one. I would just use a Maxim digital potentiometer to control the volume and slide pots for the equalizer. I plan on using the chip whether I need a preamp or not, as it does have a line out that doesn't put the signal through an amp, just the equalizer and volume control.
Thanks,
Dan
Post Edited (Ductapemaster) : 5/13/2007 11:36:13 PM GMT
I can tell you this…You don’t need a pre-amp for the most part. Are you building an audio controller? If so you almost certainly don’t need one. But if you do build one based on op-amp design remember this…There are Specialty Audio Pre-Amps and there are general purpose pre-amps. I look for op-amps designed for audio.
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I've built all 3 amps in that paper, and they all worked, but the BPA200 was by far the hardest to make happy. I'd recommend the PA-100 for most things. It uses the LM3886s in parallel to allow for more current to the load with the same output voltage. That will enable the amp to comfortably drive a 4 ohm load. Used alone, an LM3886 will hit it's current limit before full power with a 4R load. Some empirical testing I did showed the current limit was a paltry ~2A in steady state output, with dynamic limits around 5A. If you do the math, that limits you to 100W peak and 32W continuous into 8 ohms. Fine for small bookshelf speakers and loud computer setups, but for really loud stuff, you need more.
That said, most speakers are plenty efficient for that 32W continuous. If you take an average speaker efficiency of 89dB 1w/1m (it'll produce 89dB of sound pressure (SPL) when fed 1W of pink noise and measured at 1M, on-axis), that 32W will give you 104dB SPL. That's a little bit louder than an industrial jackhammer at 1m, and is plenty for most folks.
The reason I preach more power is that dynamic range is what makes things sound good, not constant loudness. Modern music is pitifully devoid of real dynamics, having only 1-6dB of range for the course of an entire CD. As a point of comparison, a live orchestra will have 20-40dB of dynamic range. Live performances of rock and techno will have 10-30dB of dynamic range, as do some movies. 30dB of dynamic range requires 1000 times the power at it's highest level compared to the 0 point (30dB = 10^3 = 1000x power). If you start with 1W, you can see why I have a 7.5kW stereo This is especially notable for subwoofers. I routinely listen at 85-90dB in my living room. The amp for my mains is putting out around 5W rms, with peaks around 35W rms, per channel. The amp for my subs is putting out between 50 and 100W RMS, and peaks over 1800W, per channel.
Ductapemaster said...
I'm not sure whether the LM318 in the design counts as one, of if I need a separate one.
The LM318 in that design is fairly redundant. You can do just fine without it, using the schematics on the National site. A preamp these days is used for switching and volume control, and as Chris said, it better called an audio controller. I'd recommend using the highest quality op-amps you can afford. When the signal is small, abuse due to poor quality components is larger, as a percent of the total, than it is in the amp. Analog Devices and Burr-Brown (now a part of TI) are good places to go looking.
-dave
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Would you suggest that I use another 3886 in parallel with the other two? That would increase the power by 150%...and it's not too expensive. I'm driving some good sized speakers (the main speakers are 6 inches in diameter, and theres a 2 inch midrange and a 1 inch tweeter) and they're 6 ohms total (thats what it says on the back...I have yet to confirm that) so I should get 55-65 watts from the dual 3886 setup. Thats pretty good for me, but I wouldn't mind another amp in there. Eventually, the speakers will be replaced by something a but more...professional. But when the time (and money!) comes.
Also, do you have any recommendations for preamps that have worked for you?
EDIT:
I have decided to forgo the graphic equalizer, for the sake of simplicity. I just don't need it. It adds more work to the final product and it wouldn't add all that much functionality for the effort. So just forget I mentioned it.
Thanks for all your help.
Chris:
I just got my SX-Key back from Parallax today and I'm having the same problem as I had before. Only this time, it seems to be warm all the time (it should mean its working?) and I still get the same error "SX-Key not found on COM1". I tried both cables again, and I switched out the SX chip for another...and no luck. I will try it on the other computer tonight, but I don't expect much.
I really don't know what to do! Why would this happen? And twice? I really just want to use the darn chips...all this hassle isn't much fun.
Thanks.
-Dan
Post Edited (Ductapemaster) : 5/15/2007 1:19:37 AM GMT
I tested your SX-Key prior to it being shipped out. I don’t see any reason why you would be having this issue. I know it’s not fun, but when we verified a working unit went to you we’re left baffled at why you cannot get it working. There must be something missing in this puzzle. Please contact me via e-mail to discuss this further. Take care.
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Ductapemaster said...
Would you suggest that I use another 3886 in parallel with the other two? That would increase the power by 150%...and it's not too expensive.
Nope. You'll only be able to realize the extra power with a very low impedance load, something you want to avoid. If you were driving motors, I'd say go for it, but for noirmal speaker use, 4-8ohms, a parallel pair will be just fine. If you need more power, try the BPA200, but plan for a lot of work.
Ductapemaster said...
I'm driving some good sized speakers (the main speakers are 6 inches in diameter, and theres a 2 inch midrange and a 1 inch tweeter) and they're 6 ohms total (thats what it says on the back...I have yet to confirm that) so I should get 55-65 watts from the dual 3886 setup. Thats pretty good for me, but I wouldn't mind another amp in there. Eventually, the speakers will be replaced by something a but more...professional. But when the time (and money!) comes.
Nothing personal Dan, but those are little speakers A pair of parallel 3886s should provide you with more than enough volume for normal listening. Out of curiosity, who made them? 'Professional' doesn't always mean good, just loud. I spent enough time doing pro sound to say that just because it's a concert speaker, it doesn't mean you want it at your house. There are a few boxes I'd love to have in my living room, but the cost, size, and visual aesthetics aren't compatible with my life right now, so I have some speakers I built.
Ductapemaster said...
Also, do you have any recommendations for preamps that have worked for you?
I had a Marantz AV-500 for a few years that I liked, except for it's wonky motor driven volume pot (L-R balance was routinely off 10-20%). Before that, it was a Hafler DH100, which was nice but lacked a remote. These days, I'm saving my pennies for an Anthem AVM-50. Needless to say, I'm a high end junkie, and the Anthem is out of any sane person's price range, but there's a lot of good stuff out there. On the used market, for a non-surround unit, I'd pick up a Hafler Iris with the remote if I was looking for something like that. It's a nice piece of gear that works well, and sounds good. I suppose I should ask about your price range for the preamp though...
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Dave Paton said...
If you need more power, try the BPA200, but plan for a lot of work.
I think I'll be fine with the setup I picked. This is my first amp project, so I don't need a huge project to go through. All it's got to do is look and sound good.
Dave Paton said...
Nothing personal Dan, but those are little speakers
Ha, I know. They're not very big, but then again, I was comparing them to computer speakers...maybe I should have said that.
And by professional, I meant that when I went out and bought a new set, they would be a bit more professional than my current setup. My current setup is just a nice (at least I think it sounds good...) pre-built Phillips stereo. The speakers I plan on using are the ones that came with it, so they're not the best, but they work. I might consider building my own speakers when the time comes to replace these.
Also, I had a great idea today . The stereo is 4 years old, so I don't care much about it (my parents may think differently, however...). I was thinking I could just build a mono amp into the case of each speaker and have a small case outside as a power supply/volume controller. I don't know what you think about it, but it seems better than huge heat sinks hanging out of a small case. The heat sinks would just be on the back of the speakers. I need to do some investigating into the design of the speakers a.k.a. disassembly to find out the status of their...guts. The major deciding factor on this one is my parents will to let me do my thing with my stereo, but I can work with that.
Also, about the preamp situation. I was planning on building that also. The case that I am planning on was to have an LCD display and a nice volume knob for control and I was hoping to build my preamp inside. I read earlier in the posts that there are a few chips that do volume control, so I was planning on using one of those and some type of preamp (new suggestions?). I'm not even sure whether I can do this the way I want to, but I will do my best. If worst comes to worst, I can build a simple passive preamp.
No worries. My first set of 'real' speakers was made from found plywood and some Radio Shack closeout parts. Not special by any means, but functional. That's what really matters.
I'd recommend against tearing into the stereo. The speakers aren't made to come apart and go back together happily, and you'll be influencing the internal box volume if you stick your amps in there, which will alter the frequency response, and probably not in a good way. There's a pile of reasons that amps and speakers remain seperate, even today. There are powered speakers, but the really high end stuff still uses seperates.
As far as building a preamp, I think Chris, Junkie and I have hashed out the details enough times in this thread to give anyone with keen powers of observation a pretty complete plan for one. The cliff's notes version (sparknotes?) is this:
Crystal CS3310, TI/Burr-Brown PGA2310 or TI/Burr-Brown PGA2311 for volume control. TI/Burr-Brown MPC507s for input switching. TI/Burr-Brown OPA2602 or 2604 for misc. op-amp duties. Unity gain buffers all over. Stiff stable power supplies.
Active preamps are nice toys, and make life easy. I just wish I'd built a remote into mine. I'm sure with patience and effort you can build one. Mine only took me about 2 months of actual work...the rest of the year of hell was getting the processes set up, making the school happy, dealing with a murderous power supply, and not going insane in my last year of college. There's nothing particularly difficult, just time consuming.
-dave
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Thanks for the info Dave. I will look into the speakers and see if they come apart with screws, but if not, I won't mess with 'em. I would still like the stereo to be functional when I'm done here anyways.
And I have plenty of time to plan out my preamp. I will consult the thread for more info and I will post preliminary plans when I get around to them. I just finished up AP testing and finals are fast approaching, so I don't have a lot of time to do much of anything at the moment, but I'll fit it in where I can. Hopefully I will make it to the electronics swap meet in a couple weeks and see what I can scrounge up there.
Thanks for all the help.
Dan
Oh, and Chris, do you happen to have the pinout of that rotary encoder you sent me? I know the two pins by themselves are for the switch, but what's the order of the other three?
Also, I am going to try the SX-Key on the other two computers in the house and see what I can get it to do. I'll let you know if I get anywhere. I'm sure I'm just missing something ridiculously simple and it's screwing with everything...
I haven’t used these encoders yet but typically in the 3-pin design the center is common and the outer two are the A/B outputs. You could check with a continuity checker. Remember, the A/B outputs will need to be pulled-up or pulled-down before going into the BASIC Stamp inputs otherwise they’ll float when not selected. Which you choose (pull-up/down) depends on how you have the common lead wired (high/low).
Has anybody heard from Junkie lately?
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Back on page 9 he said he was back from his vacation...Ah well, he's probably busy putting the components into those amp boards and getting the programming in order. He is way ahead of us!
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Thanks Chris. All I needed to know was which was the common between the three. I check the pins briefly before, but I was expecting one of the outsides to be common so I didn't figure it out.
Sorry to have disappeared like .... (well govt in my country has developed the tools to make people disappear and people too have become used to seeing people just disappear from the face of the earth) well nothing of the kind happened to me actually I did switch job, with much better prospects and as one moves up the career ladder time becomes one of the most expensive commodities, same with me.
Anyways I am back and would contribute to whatever I could at this forum.
Well I did assemble the boards completely I took a few pics of them (which I ll post later) meanwhile I switched job and new one require lot of attention (being a Vice President & Regional Head in·an AMC·is not an easy job, believe me) so every thing regarding hobby project has come to a halt one due to time second due to the fact that two shipments of ICD2 have been lost and I have ordered another one with insurance this time so till then programming area needs to wait, once I get ICD2 hopefully I ll be able to debug the programme and hopefully complete the project..
Dave, for those who mind (I do)...These are pulls...Not new. I know many people won't care and will appreciate the information. It says they only have like 13 new ones left at $5+change each...
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Oops, I didn't even see the pull note. I got the link from their flyer which was light on details. Even as pulls, for 1.79, they're plenty good for experimenting, to me at least.
Still, I don't actually need them, since I have a pile left from when National had a more...er..liberal sample policy.
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Well, today was my last day of school, so my amp design/build can commence (finally)! I was thinking last night about other functions the amp could have and I thought I could replace something I already have by implementing it into the amp. At the moment, I control my music from my computer (it's hooked into my stereo across the room) but I have a special setup. I use my PSP (Playstation portable) to access a webpage from Wi-Fi that my music program (winamp) serves. It works OK and it allows me to do what I want to for he most part, but I have to have my computer on and Winamp started to use it. I would like to implement an MP3 player into the amp so I can clean up this whole mess.
The idea goes like this:
First, I need some interface to either an existing MP3 player (like an iPod for instance) that allows me to get a list of songs and control it using the SX, or I would need an interface to a hard drive (is there some chip that does this easily?) so I can control it directly. I know there is a serial interface to the iPod that one can use, but it's really slow and probably wouldn't work very well.
Next, I would use the PINK module to serve a webpage over my local network that allows me to browse and play the songs and control the amp functions (volume, etc.). This is the easy part of the design...
Well, there you have it. Am I getting into something I will never finish or is it possible to do this? Anyone done anything like it before?
I guess you have to set your own limitations for your projects…For myself I don’t think I have quite hit anything I couldn’t accomplish with the knowledge and parts I have, although I do have a design for a home/security controller which is beyond anything I have tried before. It will most definitely require the use of some Propeller chips. As for the PINK Module…The only thing I am using it for right now is both a demo box in Tech Support and a remote relay host for a Security System. For what I have planned on that system I am quite confident all features could be implemented.
On the audio amplifier side I haven’t thought of any reason to use a PINK Module in it so I don’t think that is something I will be trying anytime soon. You could let us know how that whole system turns out. I’m sure it will be interesting.
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Comments
Yeah, that was before I laid it down for the heatsinking. It got pretty stinkin' hot in that configuration, which is why I made the change. Of course, drawing near the rated max out of the regulators will do that.
Dan-
The LM12 is actually designed for linear motion control. As such, THD wasn't a primary concern of the designers, and it has a pretty nasty response (and sound) above the 800-1khz region. Chris Little (the original designer of the circuit) used them as the bottom of a tri-amped speaker setup. I used them for sub duty. I wouldn't recommend them for anything full range. For that, I'd check into the LM3886, which isn't quite as powerful, but is much more suited to audio uses.
I used a bridged pair on each side because subs are hungry beasts, and because the voltage swing of the LM12s isn't all that great. It does add some complexity, but it's worth it in my opinion.
The schematic in the datasheet for the audio amplifier is basically the same as the LM3886 and any other power op-amp. It should work, provided you bypass the supply correctly and make sure to account for input noise and things like that.
OK, I was replying to your post line by line. I think I'm going to change that to a basic summary now.
Don't use the LM12 full range. Please. Get some samples of an LM3886TF and use them instead. I've got a page on my site about using that chip too, and there's a bajillion others doing things with it under the name gainclone. The LM12 uses an oddball 4 pin TO-3 package, and no stock heatsink will fit it. As for your heatsink choice, that's woefully inadequate. The natural convection of that 'sink is 36degC/watt, and for the LM12 as an audio amp, you'll need something closer to 1degC/watt, which that sink won't achieve, even with fan cooling. The LM3886 datasheet has an excellent piece on calculating heatsink size, and there are app notes on the Thermalloy site that are pretty awesome too. I'd strongly suggest reading them all. Linear amps like the LM12, LM3886, and any discrete transistor or FET design are terribly inefficient, and need gobs of heatsinking to run cool, or very inventive methods of cooling.
A pair of LM3886s can be put in a nice small case, and run happily see here:
http://www.dpaton.net/audio/3886amp/3886amp.shtml
That's in a Radio Shack case that's all of 10" on it's longest side, and about 4" tall to accomidate the heatsink and the transformer. You can see the size of heatsink I used for the pair...that's about the right size. I built a 4ch version of the amp, with the same size heatsink, but I can't run it as hard before it gets too hot. Pictures 4 and 5 are roughly life size on my monitor. I used a salvaged transformer that's roughly 200VA, give or take. With the large filter caps I used for the power supply, that was plenty for normal use.
For your case, you'll want to look into toroidal transformers. They have greater power density (more output for a given size) and are generally wider than they are tall. Just be careful mounting them. I'll go into that later if you end up with one.
By now you're probably thinking that the LM3886 isn't powerful enough, and at ~60W per chip, it seems that way on paper, but unless you listen to rap or hardcore techno with the bass all the way up, most speakers will be just fine, and the dynamic ability of the LM3886 is impressive. The BPA200 is the best option with them, using parallel pairs to build a bridged amp, but it's not terribly easy to do right the first time.
That's all I have time to type right now...more later if you want it.
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Thanks for all the suggestions.
-Dan
In series or in a bridge configuration? You can bridge them…I don’t know if I want to do that but I am happy with the LM3886 as they are anyway. I have built several working amplifiers around them. Great hybrid amplifiers even if the specifications went down between preliminary and release (I had early engineering samples). If you read back a few pages you’ll see the current amplifier I am building uses 2 LM3886 chips for stereo output. Did you get your rotary encoder yet?
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Chris Savage
Parallax Tech Support
I'm out all night tonight and gone tomorrow for Mother's Day with my family, but I'll do some more research on Sunday. I'll let you know what I come up with.
-Dan
Check it out and see what you think. Most of the discussion is about improving the design, but I'm perfectly happy with the original (unless it has major flaws of course...)
My goal on this is to go the the local electronics swap meet (TRW) and buy what I can there. It's on the 26th so I have some time to make a bill of materials and determine what I already have.
I will post my front panel design in the next week. I'm being held up on the LED choices for the level (VU) meter. I cant seem to find something I like yet...still haven't decided b/w T1 LED's, T1 3/4 LED's, or a premade bargraph display. Oh well, well see what happens. So far, I have a nice switch (from a previous project), a LCD in mind (Serial, 20x4 from eBay), my button choices almost made, and a knob picked out for volume.
Thanks for all your guys help so far.
-Dan
I didn’t look at the design (must be a member), but I agree with Dave in that the most straight forward designs can be gotten from the datasheet/AppNotes for the LM3886. I noticed in that thread though that they were questioning his op-amp front end. I don’t know what that is all about…A few of my designs had specialty audio op-amps to isolate the level meters and tape monitor circuits. With careful designs there’s nothing wrong with an op-amp in your circuit. I think other people tend to be overly critical of someone else’s design because they wouldn’t do it that way. Dave, Junkie and I are a few of the people out there who are more open-minded about this stuff. I feel you have to do what works for you.
Dave,
I had every intention of hooking up that power supply this weekend but when I went to get out the rest of the parts for the power supply I ran into a half-completed project I started some time ago and decided to finish it first. As of late last night I was still fixing a few soldering issues I found but I believe I have the hardware done. What took me so long was milling out the panels (by hand, using a drill, nibbler and files) and trying to merge concepts from 5 years ago with current ones. What I mean is that lately I have been using LCD Displays with keypad decoders in them (Matrix Orbital) but I had already mounted a Parallax Serial 4x20 in the cabinet and soldered a socket for the EDE1144 onto the Super Carrier Board so I went with it. Results of this can be seen this week posted in another thread. Sorry for being off topic.
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Chris Savage
Parallax Tech Support
I attached the PDF of the schematic so you guys could take a look at it.
EDIT:
I've found another really nice design. It's a bit simpler than the other one. It uses two 3886's in parallel per channel, giving about 50W @ 4 ohms and 100W @ 8 ohms. Just what I want. The instructions are really clear and it even uses a regulated power supply. I'm leaning towards this one now...
Here's the link: http://www.shine7.com/audio/pa100.htm
/EDIT
Also, a quick question. I don't really know what to do for a preamp. I'm not sure whether the LM318 in the design counts as one, of if I need a separate one. If I do, then I plan on using the Sony CXA1352AS. It's 5 band graphic equalizer, preamp, and volume control in one. I would just use a Maxim digital potentiometer to control the volume and slide pots for the equalizer. I plan on using the chip whether I need a preamp or not, as it does have a line out that doesn't put the signal through an amp, just the equalizer and volume control.
Thanks,
Dan
Post Edited (Ductapemaster) : 5/13/2007 11:36:13 PM GMT
I can tell you this…You don’t need a pre-amp for the most part. Are you building an audio controller? If so you almost certainly don’t need one. But if you do build one based on op-amp design remember this…There are Specialty Audio Pre-Amps and there are general purpose pre-amps. I look for op-amps designed for audio.
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Chris Savage
Parallax Tech Support
I've built all 3 amps in that paper, and they all worked, but the BPA200 was by far the hardest to make happy. I'd recommend the PA-100 for most things. It uses the LM3886s in parallel to allow for more current to the load with the same output voltage. That will enable the amp to comfortably drive a 4 ohm load. Used alone, an LM3886 will hit it's current limit before full power with a 4R load. Some empirical testing I did showed the current limit was a paltry ~2A in steady state output, with dynamic limits around 5A. If you do the math, that limits you to 100W peak and 32W continuous into 8 ohms. Fine for small bookshelf speakers and loud computer setups, but for really loud stuff, you need more.
That said, most speakers are plenty efficient for that 32W continuous. If you take an average speaker efficiency of 89dB 1w/1m (it'll produce 89dB of sound pressure (SPL) when fed 1W of pink noise and measured at 1M, on-axis), that 32W will give you 104dB SPL. That's a little bit louder than an industrial jackhammer at 1m, and is plenty for most folks.
The reason I preach more power is that dynamic range is what makes things sound good, not constant loudness. Modern music is pitifully devoid of real dynamics, having only 1-6dB of range for the course of an entire CD. As a point of comparison, a live orchestra will have 20-40dB of dynamic range. Live performances of rock and techno will have 10-30dB of dynamic range, as do some movies. 30dB of dynamic range requires 1000 times the power at it's highest level compared to the 0 point (30dB = 10^3 = 1000x power). If you start with 1W, you can see why I have a 7.5kW stereo
The LM318 in that design is fairly redundant. You can do just fine without it, using the schematics on the National site. A preamp these days is used for switching and volume control, and as Chris said, it better called an audio controller. I'd recommend using the highest quality op-amps you can afford. When the signal is small, abuse due to poor quality components is larger, as a percent of the total, than it is in the amp. Analog Devices and Burr-Brown (now a part of TI) are good places to go looking.
-dave
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This is not a sig. This is a duck. Quack.
Would you suggest that I use another 3886 in parallel with the other two? That would increase the power by 150%...and it's not too expensive. I'm driving some good sized speakers (the main speakers are 6 inches in diameter, and theres a 2 inch midrange and a 1 inch tweeter) and they're 6 ohms total (thats what it says on the back...I have yet to confirm that) so I should get 55-65 watts from the dual 3886 setup. Thats pretty good for me, but I wouldn't mind another amp in there. Eventually, the speakers will be replaced by something a but more...professional. But when the time (and money!) comes.
Also, do you have any recommendations for preamps that have worked for you?
EDIT:
I have decided to forgo the graphic equalizer, for the sake of simplicity. I just don't need it. It adds more work to the final product and it wouldn't add all that much functionality for the effort. So just forget I mentioned it.
Thanks for all your help.
Chris:
I just got my SX-Key back from Parallax today and I'm having the same problem as I had before. Only this time, it seems to be warm all the time (it should mean its working?) and I still get the same error "SX-Key not found on COM1". I tried both cables again, and I switched out the SX chip for another...and no luck. I will try it on the other computer tonight, but I don't expect much.
I really don't know what to do! Why would this happen? And twice? I really just want to use the darn chips...all this hassle isn't much fun.
Thanks.
-Dan
Post Edited (Ductapemaster) : 5/15/2007 1:19:37 AM GMT
I tested your SX-Key prior to it being shipped out. I don’t see any reason why you would be having this issue. I know it’s not fun, but when we verified a working unit went to you we’re left baffled at why you cannot get it working. There must be something missing in this puzzle. Please contact me via e-mail to discuss this further. Take care.
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Chris Savage
Parallax Tech Support
Nothing personal Dan, but those are little speakers
I had a Marantz AV-500 for a few years that I liked, except for it's wonky motor driven volume pot (L-R balance was routinely off 10-20%). Before that, it was a Hafler DH100, which was nice but lacked a remote. These days, I'm saving my pennies for an Anthem AVM-50. Needless to say, I'm a high end junkie, and the Anthem is out of any sane person's price range, but there's a lot of good stuff out there. On the used market, for a non-surround unit, I'd pick up a Hafler Iris with the remote if I was looking for something like that. It's a nice piece of gear that works well, and sounds good. I suppose I should ask about your price range for the preamp though...
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This is not a sig. This is a duck. Quack.
I think I'll be fine with the setup I picked. This is my first amp project, so I don't need a huge project to go through. All it's got to do is look and sound good.
Ha, I know. They're not very big, but then again, I was comparing them to computer speakers...maybe I should have said that.
And by professional, I meant that when I went out and bought a new set, they would be a bit more professional than my current setup. My current setup is just a nice (at least I think it sounds good...) pre-built Phillips stereo. The speakers I plan on using are the ones that came with it, so they're not the best, but they work. I might consider building my own speakers when the time comes to replace these.
Also, I had a great idea today
Also, about the preamp situation. I was planning on building that also. The case that I am planning on was to have an LCD display and a nice volume knob for control and I was hoping to build my preamp inside. I read earlier in the posts that there are a few chips that do volume control, so I was planning on using one of those and some type of preamp (new suggestions?). I'm not even sure whether I can do this the way I want to, but I will do my best. If worst comes to worst, I can build a simple passive preamp.
Let me know what you think.
Thanks again,
Dan
No worries. My first set of 'real' speakers was made from found plywood and some Radio Shack closeout parts. Not special by any means, but functional. That's what really matters.
I'd recommend against tearing into the stereo. The speakers aren't made to come apart and go back together happily, and you'll be influencing the internal box volume if you stick your amps in there, which will alter the frequency response, and probably not in a good way. There's a pile of reasons that amps and speakers remain seperate, even today. There are powered speakers, but the really high end stuff still uses seperates.
As far as building a preamp, I think Chris, Junkie and I have hashed out the details enough times in this thread to give anyone with keen powers of observation a pretty complete plan for one. The cliff's notes version (sparknotes?) is this:
Crystal CS3310, TI/Burr-Brown PGA2310 or TI/Burr-Brown PGA2311 for volume control. TI/Burr-Brown MPC507s for input switching. TI/Burr-Brown OPA2602 or 2604 for misc. op-amp duties. Unity gain buffers all over. Stiff stable power supplies.
Active preamps are nice toys, and make life easy. I just wish I'd built a remote into mine. I'm sure with patience and effort you can build one. Mine only took me about 2 months of actual work...the rest of the year of hell was getting the processes set up, making the school happy, dealing with a murderous power supply, and not going insane in my last year of college. There's nothing particularly difficult, just time consuming.
-dave
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This is not a sig. This is a duck. Quack.
And I have plenty of time to plan out my preamp. I will consult the thread for more info and I will post preliminary plans when I get around to them. I just finished up AP testing and finals are fast approaching, so I don't have a lot of time to do much of anything at the moment, but I'll fit it in where I can. Hopefully I will make it to the electronics swap meet in a couple weeks and see what I can scrounge up there.
Thanks for all the help.
Dan
Oh, and Chris, do you happen to have the pinout of that rotary encoder you sent me? I know the two pins by themselves are for the switch, but what's the order of the other three?
Also, I am going to try the SX-Key on the other two computers in the house and see what I can get it to do. I'll let you know if I get anywhere. I'm sure I'm just missing something ridiculously simple and it's screwing with everything...
I haven’t used these encoders yet but typically in the 3-pin design the center is common and the outer two are the A/B outputs. You could check with a continuity checker. Remember, the A/B outputs will need to be pulled-up or pulled-down before going into the BASIC Stamp inputs otherwise they’ll float when not selected. Which you choose (pull-up/down) depends on how you have the common lead wired (high/low).
Has anybody heard from Junkie lately?
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Chris Savage
Parallax Tech Support
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This is not a sig. This is a duck. Quack.
Back on page 9 he said he was back from his vacation...Ah well, he's probably busy putting the components into those amp boards and getting the programming in order. He is way ahead of us!
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Chris Savage
Parallax Tech Support
Thanks,
Dan
Let me know when you have it working. Take care.
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Chris Savage
Parallax Tech Support
Dave, do you know where I could get a Toroidal Transformer (Audio) whose output is <=24V per secondary? For example 24-0-24. Thanks.
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Chris Savage
Parallax Tech Support
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This is not a sig. This is a duck. Quack.
Sorry to have disappeared like .... (well govt in my country has developed the tools to make people disappear and people too have become used to seeing people just disappear from the face of the earth) well nothing of the kind happened to me actually I did switch job, with much better prospects and as one moves up the career ladder time becomes one of the most expensive commodities, same with me.
Anyways I am back and would contribute to whatever I could at this forum.
Let me know if I could be of any help.
Last I heard you were assembling your boards…How did they work? Any new pictures?
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Chris Savage
Parallax Tech Support
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=11881
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This is not a sig. This is a duck. Quack.
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Chris Savage
Parallax Tech Support
Still, I don't actually need them, since I have a pile left from when National had a more...er..liberal sample policy.
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This is not a sig. This is a duck. Quack.
The idea goes like this:
First, I need some interface to either an existing MP3 player (like an iPod for instance) that allows me to get a list of songs and control it using the SX, or I would need an interface to a hard drive (is there some chip that does this easily?) so I can control it directly. I know there is a serial interface to the iPod that one can use, but it's really slow and probably wouldn't work very well.
Next, I would use the PINK module to serve a webpage over my local network that allows me to browse and play the songs and control the amp functions (volume, etc.). This is the easy part of the design...
Well, there you have it. Am I getting into something I will never finish or is it possible to do this? Anyone done anything like it before?
Thanks in advance,
Dan
On the audio amplifier side I haven’t thought of any reason to use a PINK Module in it so I don’t think that is something I will be trying anytime soon. You could let us know how that whole system turns out. I’m sure it will be interesting.
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Chris Savage
Parallax Tech Support