audible hum with two Sure TA2024 boards on same source

[Hybrid fourdoor]

I have two boards, trying to make a multi-channel amp. They share 15V power source (the red/black cable). When I plug a source just in to 1 unit, everything is perfect...just the tiniest amount of hiss (ear inches from tweeter). But when I try to hook the same source up to both units I get a very audible buzz from 3-4 feet away.

I though it was my iPod having a shared ground on the 1/8" to RCA. But now I am using the pre-amp outputs from a receiver and I get the same effect.

Any ideas?

 

[Mayuri]

Maybe the PSU is insufficient for the amplifiers?

 

[djoffe]

A Guess?

I think it may be due to the fact that these guys are switch-mode amps. There are sum and difference frequencies generated between the two of them, since they don't have synchronized clocks, and that's causing audible birdies.

I looked for data sheets on these boards, but didn't find much detailed info...maybe a 10 micro-Henry inductor in the +15 V supply lead of one would help?

 

[Khron]

Are the red & black wires soldered to both boards, and you're basically daisy-chaining the power?

 

[turk 182]

15 volts supply but no curent rating given....?
two amps with a common ground and no provision for isolating input source grounds....?
sounds like another thread about ground loops...i'm sure the usual debate will insue.....
or research the topic a bit....it's background that you'll need if your eventual goal is to build a multichannel amp....

 

[turk 182]

and i wish people would stop using low impedance source outputs like Ipods and there ilk as a source device across amp inputs that are designed as line level and wonder why they are having problems or thinking it sounds good.

and what makes you think the pre out's on the receiver are isolated?

 

[Hybrid fourdoor]

Are the red & black wires soldered to both boards, and you're basically daisy-chaining the power?

Yes, I don't see any functional difference between having the same PSU connect to each of them separately. It's a direct connection through the board, there are lugs on either side, so you can connect on each side.

 

[Hybrid fourdoor]

I think it may be due to the fact that these guys are switch-mode amps. There are sum and difference frequencies generated between the two of them, since they don't have synchronized clocks, and that's causing audible birdies.

I looked for data sheets on these boards, but didn't find much detailed info...maybe a 10 micro-Henry inductor in the +15 V supply lead of one would help?

I was also thinking it had to do with the frequency generation of each one. But the only thing I can think of that would attempt to fix that would be op-amp buffers.

I will try separate power supplies and see what happens.

 

[turk 182]

does connecting your "source" across the two input of one board result in the same hum/noise?

 

[Grib]

You should probably try to split the ground of the PSU before reaching any of the boards.
So that each board has a ground wire coming to it, and no board act as a ground splitting point.

Simply make a Y with you PSU cable a connect each branch to your boards.
I guess you could do the same thing for the + wire, but its probably less important

 

[doctormord]

and i wish people would stop using low impedance source outputs like Ipods and there ilk as a source device across amp inputs that are designed as line level and wonder why they are having problems or thinking it sounds good.

and what makes you think the pre out's on the receiver are isolated?

What's the point here? Apple products, Iphone4+ have pretty descent output DACs. If the amplifier can't deal with this, it's not the sources fault.

 

[HumbleDeer]

I think that every one of those small chip amps has a "sync" line. If you put the correct resistor between the two chips, you can have them natively sync their clocks.

The same thing is done with the cheap TPA-based amps on Ebay. Those amps also have such sync line. Sadly, they don't use it very often or appropriately

This amp has 2 chips which is similar to 2 seperate chips, somewhat.

https://youtu.be/16k4goWRT4o

 

[Hybrid fourdoor]

Ya I had watched that video actually before I bought the boards, but I couldn't find anything about it for this chip.

Anyways, I ended up using 2 separate supplies and the buzz/hum is completely gone. So it has to do with sharing the power.

How can I strip "AC" out of the power? put an inductor inline, or would a capacitor across the red and black be better?

 

[djoffe]

You need both. Now, there's probably already some bypass capacitance on the board, so the inductance by itself would be a good start.

 

[Grib]

Anyways, I ended up using 2 separate supplies and the buzz/hum is completely gone. So it has to do with sharing the power.

Did you try that ?

You should probably try to split the ground of the PSU before reaching any of the boards.
So that each board has a ground wire coming to it, and no board act as a ground splitting point.

 

[Hybrid fourdoor]

I used a DC power Y cable that had 2x 2.1mm connections. I tried that from one supply and the pulsing sound was only audible if you put your ear right on the driver. But it was there none the less.

I stepped up to an 18.5V laptop supply and gave each amplifier module its own LM7815 15V regulator. With this, the high pitched pulsing was completely gone and only a faint <normal> hiss could be heard.

So I solved the problem.

 

[Hybrid fourdoor]

Oh and if you were wondering I checked the amperage of the board before going the regulator route. At idle and low volume it used 65mA (0.065A). At comfortable volumes it used 71mA. This was with both channels driven into an 8 ohm load.