Shop OBEX P1 Docs P2 Docs Learn Events
Amp/preamp design — Parallax Forums

Amp/preamp design

chemaniachemania Posts: 25
edited 2008-08-06 16:14 in General Discussion
Starting a thread to chat about amp/preamp designs.·
Chris, tell me about some of the things you have done before.

Jeff
«134567…11

Comments

  • Jonathan AllisonJonathan Allison Posts: 96
    edited 2005-03-01 16:57
    What kind of amps, like for a guitar or for a home / car audio?

    I'd be interested in gaining some knowledge on guitar tube amplifiers.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Johnny
  • chemaniachemania Posts: 25
    edited 2005-03-17 13:03
    I have built several home amps and preamps.· I have not tried car amps because of the need to build the switching PS.· One car design I did used a PS from a "dead" amp.· I just piggybacked the new amp onto the old amp's rails.· Tube amps are fairly easy although those high voltages can be "enlightening" if you stick your finger in the wrong spot!· I think there are some tube guitar amp designs floating around on the web.· There are even some vintage knock-off amps around.

    Jeff
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-03-17 17:33
    Jeff,

    ·· Sorry, I must have missed this thread at some point.· Just noticed it when a reply had been made.· Most of my designs started out as discrete designs, using MOSFETs and lots of glue (Parts).· Later I moved over to hybrid amps, such as the STK amp chips.· Finally National Semi came out with a series of Power Amp chips called the "Overture" series.· And I implemented a few of them.· At the time, National also had a nice Audio Switching chip, the LM1037, which could control 4 stereo inputs to one output, and had muting control.· You could also parallel the outputs to get more inputs.

    ·· I built my own LED input and power meters using the LM3914 and LM3915 chips (Also from National).· I have a nice circuit which makes them work like they're supposed to, but seldom do, due to the way an audio signal works.· It's kind of a quarter wave rectifier/buffer on the input, using a diode, resistor and capacitor.· It provides a nice fluid display.

    ·· I used to get my Power Transformers (Now harder to find) from Mark V Electronics, although I think they went under.· These were usually 24-0-24 on the secondary, or thereabouts.· My power supply provides +/- 37 volts DC from that transformer.

    ·· Then of course comes the fun part...Microprocessor control of everything!· LCD Display, etc.· Originally used the Z80 (Pre-Stamp days), but later BASIC Stamp 2.· Once I get through re-vamping code I will post one in the projects forum.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage

    Parallax Tech Support
    csavage@parallax.com
  • chemaniachemania Posts: 25
    edited 2005-03-20 02:55
    Chris,
    When did you become a forum moderator? Or did I miss that from the onset? About those chipamps, I just got done with a couple lm3875 amps. They sound much better than I thought any chipamp could. But my Big Gun is going to be a Class A Mosfet.

    Jeff

    BTW Johnny, www.apexjr.com has some salvaged Fender amp transformers. Good start to a tube guitar amp?
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-03-20 03:18
    Jeff,

    · LM3875 isn't too bad...I was using LM3886T/F and more recently LM4652TA/F.· They're really nice high-quality chips with a lot of features, and minimal external parts requirements.· In fact I am working on one now (As in, over time, but a current project).

    ·· As for the Moderator thing, it kind of comes with the job.· smilewinkgrin.gif·· Anyway, let me know if you do get to try an LM3886 or LM4652 and what you thought.· Remember to have at least +/- 35VDC!· And don't forget the muting circuit...You can end up scratching your head wondering why your amp doesn't work, only to find out the muting circuit is enabled by default.





    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage

    Parallax Tech Support
    csavage@parallax.com
  • Dave PatonDave Paton Posts: 285
    edited 2005-03-28 03:30
    Chris-

    IIRC, +/-35VDC is close to the safe limit for the 3886. Anothing over +/-42 will cook it outright, and into 4R, anything over about +/-29VDC will bounce you off the current limiters too easily. My $0.02, having played with the LM3886 in all it's varities since about '98 or so. The BPA200 is still a somewhat elusive beast for me unfortunately.

    As for the rest of the stereo gear, I've played with that too. I like the Burr Brown MPC507U for input switching, and the Crystal CS3310 for level control. Infinitely out of date notes from the first go-round on the project are here:

    http://www.dpaton.net/audio/preamp/preamp.shtml

    -dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    This is not a sig. This is a duck. Quack.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-03-28 04:35
    Dave,

    ·· Welcome to the thread...You are correct...+/- 35VDC is darn close to the max voltage.· In fact my supply tops out at +/-37VDC.· It certainly runs hot, but this is the only way to get the maximum output power from the chip.· You can certainly run it on less...In fact, I mentioned the LM4652 without thinking, since it uses less voltage.· Bottom line is, I am using a smaller supply on my current project.· I think it's +/-27VDC, but I need to re-test it.

    ·· I too have built many LMxxxx amps, but going backward.· Like the LM386, LM1877 and LM383 (all published in Forrest Mims books).· I did try the LM3875, but didn't care for it.· One thing I disliked about the LM38xx chips was non-standard pin spacing.· At least the LM4652 has more standard staggered spacing.· I haven't fully implemented it yet though.

    ·· On the note of pre-amps and controls, I had never heard of the MPC507U.· In fact a Google search turned up nothing until I stripped the U from it.· I will have to check it out.· The CS3310 says it's a Cirrus Logic part, not Crystal, but then again I never knew Cirrus got into audio chips.· I will be checking it out·as well.

    · Checked out your website as well...LCDs are so 1995?· Hey now!· They're more popular now that ever!· Even more so than VFDs.· LOL· That line kinda reminded me of those kids in school who said, "That was so yesterday!"· I also liked the "SuperDave" thing...Where do you get your Power Transformers from?· And what happened to Jeff?




    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage

    Parallax Tech Support
    csavage@parallax.com
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-03-28 16:41
    Send Jeff a PM [noparse][[/noparse]private message] and tell him that we all miss him. That'll work wink.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    G. Herzog in Taiwan
  • Dave PatonDave Paton Posts: 285
    edited 2005-03-29 04:15
    Chris-

    Crystal is owned by Cirrus these days, so the distinction is purely on the letterhead I think. Crystal as a seperate entity ceased to exist around 1999 or so when they were purchased, if my memory serves me. There are some workalikes of the CD3310 from TI that offer a quad package as well as +/-15V rails, both things I wanted from Crystal, but never got. The TI parts are almost as good, and for folks less serious than I will probably do just fine.

    The VFD was about my only choice for the display, since I wanted visibility in a dark room, variable brightness, and easy readability at 10'. The LCDs I got just didn't have that, mainly because the background was lit and the characters were dark. I know things have gotten better these days, but I have a soft spot in my heart for glowing displays [noparse];)[/noparse]

    The LMxxxx chips have been at the heart of many of my projects, and I've asked for so many over the years, National won't send me any more free samples, ever. I suppose I deserve that though. There's a pile of LM3886s from almost 10 years of acquisition, due to my amazing ability to lose each and every rail they sent, which were only found (en masse no less!) when I moved. I have a pair of LM4652s I have yet to play with. Life hasn't granted me the time to lay out a board for them, and the last amplifier project I worked on was the neverending quest for a working BPA200. I have a part file for the LM3xxx chips for EAGLE if you're interested. Same for the MPC507 (-UA designates the A graded SO part, BTW) and CS3310, among others.

    The power trannys came from scavenged chassis mostly. The quad LM3886 amps used ones from a pair of junked Pioneer receivers, the LM12 amp used one I picked up as a surplus place for $10, and the preamp uses one from Digi-Key. I have a pair of dual 55V EI cores from apexjr.com that I'm holding onto for some reason I have yet to think up, and I have a pair fo 63VCT 1kW toroids I got on a super-sale that will...well..that's a secret for now. My only hist is 41hz.com [noparse];)[/noparse]

    Back to the 3886s, I found after much (destructive) testing that they need a heatsink rated about 30% better than the formula gives in the data sheet to run well. Bridged and paralleled pairs make for gobs of power driving higher or lower impedance loads respectively. Whatever you do folks, stay OUT of the protection circuitry. SPiKE works well for protecting the chip, but at high levels will happily toast tweeters. The vertical discontinuous transitions it makes put bad mojo into speakers. Always make sure you have at least 3dB of headroom.

    My current projects are a little different...the primary one is a microphone preamp for mobile stereo recording. DC to light in a straight wire with gain is the goal. I'm halfway there.

    There's also a V3 of the preamp in the works. I think it'll probably be in SX/B to take advantage of the interrupts (mainly for the optical encoder, but also for some other things I have planned) and the speed (realtime serial control, better remote control interface, realtime power measurement and display from the internal amplfiers, etc). I do C for work, so I like to use things that are more friendly for my hobby stuff. It was actually going to be my SX contest entry, but real life got in the way. The analog sections are going to get the most rework. The THD on two of the channels is astronomically high (3%, but it's all 2nd harmonic...) and phenomenally low (0.008%) on another. I need to get that balanced, hopefully around 0.01% or so. And there needs to be a serious layout change for the input sclaing and DC servos...the board is too big to fit into the 1U box I have planned right now. I think edgewise card orientation (per input of course) is the way to go. Or maybe not. We'll see. Enough rambling, I need to sleep.

    -dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    This is not a sig. This is a duck. Quack.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-03-29 06:22
    Dave,

    ·· I have to admit, you've put some serious consideration into your work.· I'm kinda surprised at the results with the LM3886 chips.· When they were first being tested, the specs changed several times on them.· They were originally rated at a much higher wattage, but someone must have found out what you did.

    ·· I myself waited until they were done figuring out what the true limitations of the chip were.· There's no doubt, it's not a perfect chip by any means.· But on the other hand, that's how hybrid chips are.· Simplicity in the external design has it's price.· So I kept my designs rather modest.· I never tried bridged mode.· Had no need, nor did I want the extra complexity or heat (Yes, they do get quite hot).

    ·· As a solution to my heat problem I implemented a cooling fan, rather than a larger heat sink.· The results were acceptable, and the only things was you had a nice heater at high volume.· But I never lost a speaker.· I did lose one chip, but I believe that was due to a faulty solder joint which made the chip intermittently contact on some important pin, like ground or something.· tongue.gif

    ·· I'm also surprised to hear about Crystal, since I still see Sound Cards being made in their name today.· However, I guess that's the way it is in the chip world.· Buy or be bought.

    ·· As for your suggestions on audio control, I haven't tried any of the TI chips, although about 5 years ago I gave them a quick glance.· At the time they didn't have anything with an easy interface.· I also dislike audio control chips that require more than 3 discrete components per channel to connect.

    ·· Are you currently working on an amp/pre-amp?· If so, I'd be interested in you posting your results.· I will be posting mine once I get the cabinets milled.· That will be my starting point.· I know what needs to go in there, and I just need to get the metal cut.

    ·· It was a good point on the VFD VS LCD displays, however, as you pointed out, things have changed, and LCDs can compete quite well for visibility.· Maybe not quick as good, but close, and let's not forget LCDs come in graphical versions.· I haven't seen a graphical VFD yet.· Not a cost-effective one anyway.· Besides, on this next amp, I think I am going to tone things down a bit...I actually don't have the demands/needs I once had.



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage

    Parallax Tech Support
    csavage@parallax.com
  • chemaniachemania Posts: 25
    edited 2005-03-29 23:56
    Sorry I have not been around lately guys.· Work has been too hetic.· I stopped my DIY audio project to start and finish a DIY bedroom project (totally analog).· Now that I have that finished (new 4 ft closet door, old was 2 ft, redressed all the drywall, and ceiling, and hard wood floors, and paint, etc, etc) that project I finally have time to sit down and start the really fun projects again!· I have had decent luck with the LM3785 but my problem basically falls around sound quality.· When listening with a Bride of Zen preamp, the soundstage and inner dynamics will just close down.· It will run this way for 5 or 10 minutes, then it will open back up again.· I think I might need bigtime EMI filters on the inputs.· I now have all but a few parts for the Class A amp and preamp and am going to go to WUSTL 2nd week in April and raid the CEE dept.· We are gonna barracade ourselves in there and not come out until SOMETHING is glorious!





    Jeff
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-03-30 03:40
    Jeff,

    ·· There you are!· Wondered what happened to you.· Congrats on finishing your analog project!· LOL· Now you can get to the real meat & potatoes!· On your amp problem, are you sure you're not experiencing thermal issues?· Not necessarily with the amp chip itself, but perhaps with the surrounding components or especially the solder joints.· You wouldn't believe some of the stuff I've seen bad solder joints do.· The effects can be quite amusing.· They can also be hair-pulling!

    ·· I'm going to guess that you have no newer pictures of your project since you've been busy with the other project.· Keep us up to date though.· I have 4 projects I'd like to get done in 6 months.· I don't know if it's going to happen or not.· I may only get two done, and I'm not sure where the Amp fits in as far as priority.· But I will let you know here.



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Tom WalkerTom Walker Posts: 509
    edited 2005-03-31 14:20
    With all of the wood in Jeff's project, would it not be more apropriate to call it an anaLOG project. :^)

    (Ouch!)

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Truly Understand the Fundamentals and the Path will be so much easier...
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-03-31 17:06
    Tom Walker said...
    With all of the wood in Jeff's project, would it not be more apropriate to call it an anaLOG project. :^)
    (Ouch!)
    I was guessing that was what he meant originally...lol


    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • chemaniachemania Posts: 25
    edited 2005-04-01 17:33
    OH boy,· You guys are a lot quicker that I am.· I had not considered anaLOG, oak floor.·· Although I was thinking if I used a·BS2 in my beltsander then it might be considered a DAC???

    I have the last of the parts ordered to actually build the pre and amp now.· I am going to probably pic up an OEM bs2 and a backlit 16x2 lcd to imbed into the project.· I am tempted to put the buttons and the lcd in a pendant so that the front of the pre only has one power LED showing.· I will have an RF remote in there and that should be along in a couple days.· I am going to load the whole thing and run to WUSTL next week.· We are probably going to make a run to a HS manuf in Chicago and get $1000·worth of heatsink (never can have too much, especially for Class A). ·

    The problem I am getting into now is that I am having to do some sweeps of prototype cabinet/driver combinations for a company that I do some consulting for so this stuff might get pushed even farther back.· Money comes first though and it is still a fun experiment -- annoying the neighbors with 120db, 30Hz at 20m!

    Talk at ya soon,

    Jeff
  • chemaniachemania Posts: 25
    edited 2005-04-01 17:35
    PS - I will pull out the IR thermometer and also do some rechecks of the solder joints on that amp. Thanks for the tips Chris.

    Jeff
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-01 18:13
    Jeff,

    ·· No problem.· As I said, my Amplifier project is going real slow right now too, mainly because I have 4 current projects.· But I will get it done eventually.· I am going to see if I can draw some graphics of the projects so you can get an idea what I doing here...· smile.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Dave PatonDave Paton Posts: 285
    edited 2005-04-02 02:01
    Chris Savage (Parallax) said...

    I have to admit, you've put some serious consideration into your work. I'm kinda surprised at the results with the LM3886 chips. When they were first being tested, the specs changed several times on them. They were originally rated at a much higher wattage, but someone must have found out what you did.
    Hehe...The LM12 has the same history. There was a version around for a little while that was named the LM12CS-80, which was tolerant of 80V rails and had some insane burst output capabilities. Alas, they are no more, but I did build a sub amp out of a bridged pair which worked very well until I acquired a multi-kilowatt replacement for it (first a Phase Linear PL700II, then a Crown K2, and now a Lab.Gruppen fp6400)
    Chris said...
    As for your suggestions on audio control, I haven't tried any of the TI chips, although about 5 years ago I gave them a quick glance. At the time they didn't have anything with an easy interface. I also dislike audio control chips that require more than 3 discrete components per channel to connect.
    The CS3310 (and pin-compatible PGA 2310) are standalone mixed-signal ICs. The only external parts you need are local filter caps, and a good PCB layout. They speak something like SPI, and it's blindingly easy to use. The BS2 code for updating the CS3310 looks like this:
    LOW CS
SHIFTOUT Dout,Sclk,1,[noparse][[/noparse]I\8,I\8]        ' Update CS3310
HIGH CS


    Dout is the serial output pin, Sclk is the serial clock pin, but that's probably obvious. I is the volume variable (0-255) and it's sent twice, once for each channel. In my case, this went to two parallel-connected (on the serial interface anyway) CS3310s because I used them for a balanced line, and they only have 2 sections per chip. It would also make sens if you were using one chip for steteo, and wanted to make both channels the same, although if I were doing that I'd add an offset for a digital balance control.
    Chris said...
    Are you currently working on an amp/pre-amp? If so, I'd be interested in you posting your results. I will be posting mine once I get the cabinets milled. That will be my starting point. I know what needs to go in there, and I just need to get the metal cut.
    I'm currently doing the 3rd rev of my preamp. The second rev began shortly after I got my diploma, but was soon scrapped for a more or less complete rework. It's been in process for a skotch over three years, due mainly to work taking over my life. Right now I'm keeping the design pretty close to my vest, because I'd like to get it published at some point, and I've had my web-based publication work theived more than I care to count (My LM3886 page ranks highly in Google, and I've found dozens of directly copied versions, complete with my typos). I will be sharing tidbits as things go along tho, I'm sure.
    Chris said...
    It was a good point on the VFD VS LCD displays, however, as you pointed out, things have changed, and LCDs can compete quite well for visibility. Maybe not quick as good, but close, and let's not forget LCDs come in graphical versions. I haven't seen a graphical VFD yet. Not a cost-effective one anyway. Besides, on this next amp, I think I am going to tone things down a bit...I actually don't have the demands/needs I once had.
    Well, I don't really want a graphical display, but that's mainly a personal choice for me. I prefer to see 40 segment LED meters bouncing around and a line or two of text letting me know what I'm listening to and just how close to clip I'm running my stereo smilewinkgrin.gif

    -dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    This is not a sig. This is a duck. Quack.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-02 05:53
    Dave,

    ·· The CS3310 looks promising for the volume control, but I still need an updated chip to handle input switching.· I still need to lookup that other chip you mentioned.· Oh, and speaking of LED Meters, I have a nice circuit that works great for LINE LEVEL input meters, using the LM3915N.· I don't use 40 segs...Just 10 + 1 power LED.· But the input buffer not only 1/4 wave rectifies the signal, but makes the input more fluid, instead of jittery as the datasheet specs use.



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Dave PatonDave Paton Posts: 285
    edited 2005-04-02 16:53
    Chris-

    The MPC507 is a really cool switch. It looks like it was originally designed as an input mux for high accuracy ADC measurements. There are both differential 8ch and single ended 16ch versions as I recall. THD thru the beastie is very low, and it takes up so much less space than a bank of relays it's amazing. Charge injection is also phenomenally low.

    On your LM3915 circuit, is that little rectifier a variant of the oft-overlooked but handy 'active diode' concept? I'd love to see it. Side note: from what I remember, the 3915 was conceived as a PPM, or peak program meter, which by definition should follow every little peak and dip in the input signal. Further digression: I really wish National would do a SMT version of the LM391x series so I could pack my meter boards a little tighter. Right now I'm using a bunch of quad comparators for the meter on my mic preamp, because it's the only way I could get the density I need. Someone, somewhere, has got to make a small but mighty VU driver in SMT, no? a 16 pin SSOP would be just perfect.

    -dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    This is not a sig. This is a duck. Quack.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-02 17:11
    Dave,

    ·· Let me dig out one of my meters here...Okay, you want the secret?· idea.gif·· Basically the driver circuit itself is built to the specs in the datasheet (I believe).· I don't think I changed anything there.· But when you do that the display is erratic at best during normal audio.

    ·· What I have done is buffered the input line to the LM391x by using a 1M resistor and a .1uF· capacitor.· This doesn't affect the functionality of the input, but buffers the input for so the display doesn't drop-out during negative swings.· Now, this wouldn't do any good if we didn't add a diode on the input to rectify the input signal just a bit.· I used a 1N914.· The Cathode is connected to one end of the .1uF Cap and one end of the 1M resistor, and these are tied to the input.· The Anode end is connected to your audio signal, and the ground is common.

    ·· Check this thread back in a little while and I will add a picture to this post of one or two of the prototypes.· They work awesome!· And are perfect for line level signals, in that a peak line-level signal (Around 1V P-P) will peak the meters.



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com


    Post Edited (Chris Savage (Parallax)) : 4/2/2005 5:28:30 PM GMT
    Level Meters 03.jpg
    1332 x 916 - 300K
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-23 20:16
    Dave,

    ·· Did you ever try the circuit I mentioned above?· If you want to see the effect of the buffer circuit, I could do a small video of it in action and post it.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-06-05 04:26
    Hey,

    ·· Did everyone give up on their BS2-controlled Amplifier projects?· Everyone seems to have disappeared!· shakehead.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-06-08 00:58
    Hello,

    ·· If anyone's interested, Nuts & Volts magazine had an interesting circuit posted in the "Electronics Q&A" section for an Audio/Video Switching Circuit.· The Audio section was the noteworthy part though, as there is a chip being used that could easily replace the one I was using in my old Pre-Amplifier designs (Discontinued).· Looks interesting, and I just got the parts in the mail, so I will have to let you know how they work.



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Dave PatonDave Paton Posts: 285
    edited 2005-06-08 01:06
    Chris-

    Mine has turned into an SX based preamp project, as I think I mentioned before. It's on hold, pending free time from work, and maybe that thing that Ken didn't tell me about (but vaguely hinted at) at Sensors Expo this afternoon wink.gif I haven't had a chance to test your meter driver, but a recent acquisition may have made it moot anyway- a pair of Dorrough's broadcast meters.

    I'll be posting an update to my LM3886 amps this summer I hope. I also will have some things on a Tripath kit I bought a few months ago.

    -dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    This is not a sig. This is a duck. Quack.
  • paysonbadboypaysonbadboy Posts: 81
    edited 2005-06-08 01:43
    I'd like to build a digital amp if possible. But from what I read, they are HARD to design and you have to use specific impedance speakers on them. You can't swap whatever you want like you can with most analog amps.
    Here's an interesting article I read http://www.psaudio.com/articles/sdat.asp

    The outputs are pure digital. either on or off, only varying using PWM at a very high rate.
    Very LITTLE heat generated from one of them amps.

    Wish it was simple enough to BUILD one [noparse]:p[/noparse]


    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    http://www.paysonarizona.net/
  • Dave PatonDave Paton Posts: 285
    edited 2005-06-08 03:10
    paysonbadboy said...
    Wish it was simple enough to BUILD one tongue.gif

    A digital amp is a misnomer. Every amplifier has an analog waveform at it's output, because that's the only thing that can drive a speaker.

    I think what you're thinking of is one of the many versions of switchmode amps, which operate much like your power supply, but with a much higher switching speed, lots and lots of filtering, and an output that's proportional to an input.

    National Semi makes a chipset that works OK for sub amps, and Tripath has some eval kits that will put you on the right path to their stuff.

    As for the specific impedence thing, the only place I've seen that bandied about was on car audio forums. The only limitation of the speaker's impedence is the design limits of the amplifier. I have one next to me right now that will put out about 2.6kW when bridged into a 4 ohm load. It'll do the same when drive 2 ohm stereo, which is what it's seeing with my subs right now. It never complained when driving an open, or 32 ohms either.

    One caveat: It takes some really amazing engineering to make a swictchmode amp sounds as good as a linear amp. I've been building amplifiers of one sort or another for auto for a decade and a half, and I still haven't done a switchmode amp I'm truly happy with. I've only met TWO that were commercially manufactured that I liked for that matter. TWO! (Caveat: I have really tweaky ears. I record orchestras and jazz quartets. My hearing is as perfect as it can be.) There are limitations to the performance due to the interaction of the signal waveform and the switching frequency, filter artifacts, and RFI issues to deal with. It's an exercise in compromise.

    As an amplifier designer I respect more than almost anyone I've met said: It's easy to build one. It's hard to build one really well.

    That applies to linear as well as switchmode amps BTW. The nuances are many. Don't be discouraaged if it down't work quite right on the first few tries. You'll get there eventually.

    As for PS Audio, they're not bad, but their marketing department had a lot more to do with the content of that page than their engineering department. take it with a grain of salt. Check out the white papers at: http://www.labgruppen.se/?Id=1831 The Lab guys have a lot more engineering in their tech notes than marketing.

    -dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    This is not a sig. This is a duck. Quack.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-06-08 05:08
    Dave,

    ·· Will be interested in seeing your project when done.· I thought I'd mention the circuit from Nuts & Volts since I hadn't heard about those Audio chips until then.· Thanks for the extra information though, stuff to mull over.



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • paysonbadboypaysonbadboy Posts: 81
    edited 2005-06-09 01:19
    Dave, that's about it. i think the digital amp switched the output at like 250Khz or something silly. Then it's filtered. Because it's filtered, THAT is why it needs specific speakers.

    Car amps don't care as long as it can handle toe load. 2.6K watts should be a MONSTER amp. I've got a 600 Watt ZEUS that I decided to stop fixing. It has 12 Mosfet's in the power supply, and s6 out put transistors just for two channels. My Kenwood is supposedly 800 Watts that i use now. I think more like 500 would be RMS. I have not taken it aparts. But it does have a cooling fan. I think the technolodgy in it is probably better than the 10+ yr old Zeus.
    Interesting thing is a month or so ago I had a long drive and was playing my music loud in my truck. The amp for the sub never overheated. But the amp driving my door speakers and tweeters DID once and shut down on me!
    That amp has no fan and is UNDER one of the seats in my Quad Cab Dodge. The Kenwood is under the other seat as well. But like I said, it has a fan and did ok.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    http://www.paysonarizona.net/
  • Dave PatonDave Paton Posts: 285
    edited 2005-06-09 03:47
    The things that determines what speakers an amp can drive are it's frequency response and its output capability, ie, how many volts at how many amps (at a particular phase angle) into a given load. Period. Filters have nothing to do with that unless they limit one or the other. If anyone tells you differently, they're either lying or they just changed the laws of physics. Car amps, home amps, digital amps, tube amps, pro amps, guitar amps, whatever. It all comes down to voltage, current, and frequency response. Always.

    As for the amps overheating, if you listen to pop or modern rock, or really anything on broadcast FM, it's so heavily compressed now (<3dB of dynamic range, TOTAL), that the amps for things above a few hundred Hz effectively see a 100% duty cycle. Sub amps, because they work on a limited subset of lower duty cycle frequencies (typically less than 10%) have much lower average dissipation, and thus overheat a lot less. When I used to mix concerts for a few thousand people, I had more power on the mids and highs than the subs, by a factor of 3. For subs, they only need to go boom from time to time. A voice that's heavily compressed (because the manager wants me to make it sound "just like it does on Clear Channel") is asking the amp for power several thousand times a second, instead of 30 or 40. That has a real impact on the overal power consumption, and the dissipation of an amplifier. BTW, that overcompression is why live music sounds so much more, well, live, than CDs. The 'loudness wars' on FM are killing the music industry, one track at a time.

    That sub amps of yours? I bet it's a "digital" amp. My MTX 500d is. They're wonderful for low frequency stuff, when implemented with some common sense on the part of the designer.

    As for the 2k6W amp, it's a Crown K2. It has no fan, it plugs into the wall, and it's heavy. I have a more powerful one. It weighs 20lbs, uses a 30A mains circuit, and packs 6.4kW into a box that's 3.5"x17"x15". Power density is easy. It's quality that's hard.

    -dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    This is not a sig. This is a duck. Quack.
Sign In or Register to comment.