Shop OBEX P1 Docs P2 Docs Learn Events
Switching power to audio amplifiers — Parallax Forums

Switching power to audio amplifiers

SSteveSSteve Posts: 808
edited 2006-06-11 01:03 in General Discussion
Short version: What's a good way to control power to audio amplifiers? I looked at the RC-4 and Crydom D2W203F, but I don't think the 2 amp capacity is enough. One of the amplifiers has a 3A fuse and the other has a 5A fuse.

Long version:

I have two audio amplifiers and an active crossover that I'd like to be able to switch on and off with a BS2 or SX. One audio amp is a 70-Watt tube amp and the other is a 200-Watt transistor amp (I'm in the US, so they're 110V). The crossover is a modified car audio crossover that I'm running off a 12V lead-acid battery. Currently I have a DPDT switch that switches the battery between either the preamp or a trickle charger. I control power to the amps by turning on and off a power strip.

There are two problems I want to solve. One is that if the preamp is turned on or off while the power amps are on (or the tube amp is off but not cooled down yet), there's a huge spike which could damage the speakers. I want to control the sequence and timing of power on/off to the components to eliminate the possibility of the spike. The other is that I want to be able to be able to turn the rig on and off with my remote. (I already bought an IR Buddy, so receiving and processing the IR from the remote shouldn't be an issue.)

I'm planning on controlling the power between the battery, charger, and crossover with a pair of MOSFETs, probably the IRF510s I have on hand (unless there's a reason I should use something else).

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
OS-X: because making Unix user-friendly was easier than debugging Windows

Comments

  • Dave PatonDave Paton Posts: 285
    edited 2006-06-06 14:32
    Relays are your friend for the amplifiers. I'd look into the solid state kind, or perhaps some larger units from Potter & Brumfield. You should probably also look into building a different power supply for your crossover. There are a large number of 1A 12V regulators that have a shutdown pin, which is perfect for interfacing to a power control line (0/12V, pretty common in the industry), and that will also get rid of the worry of the charger.

    -dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    This is not a sig. This is a duck. Quack.
  • SSteveSSteve Posts: 808
    edited 2006-06-10 02:00
    I've got the SX software written so that it recognizes the on and off IR commands for my Onkyo receiver and runs the outputs through the correct sequence of events. Now I just need to figure out the hardware side.

    I ordered some 5A solid-state relays <LINK>. Can I connect them directly to the SX output pin?

    What's the best way to connect 14-gauge wire to the AC side of the relays?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    OS-X: because making Unix user-friendly was easier than debugging Windows
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-06-10 03:50
    Steve,

    ·· Yes you can, but you should check the current draw, then, depending on how many you are connecting you may want to be careful about drawing too much current from too many I/O pins at once.· See the SX Datasheet for current handling information.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • SSteveSSteve Posts: 808
    edited 2006-06-10 22:38
    Thanks, Chris. I'll check the current draw on the relays. I talked to an EE friend and he said I also need to watch out for inrush current into the amplifiers on the AC side. It could be a lot more than 5 amps.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    OS-X: because making Unix user-friendly was easier than debugging Windows
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-06-11 01:03
    Steve,

    ·· By the way, I have built many Custom Amplifiers over the years (used to be a big part of my business) and I have always used mechanical Relays in my systems.· In fact, the amplifier running on this computer works the same way.· You press a button (Which is read by the Stamp) and it turns on a Relay through a 2N2222 transistor.· Tried and true.· There are actually 4 relays in this amplifier.· The Tape Monitor circuit is identical except the relays are smaller and there are two of them.· The muting circuit uses a small PCB Relay like the Tape Monitor Circuit uses.· The Power Relay is the big one...10A contacts.··And your friend was right...Inrush current should always be taken into consideration when switching a load such as this.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
Sign In or Register to comment.