Need help to trouble shoot the noisy amp.


Not too long ago, I bought a pair of hybrid monoblock amp. One is dead quiet and the other is noisy but still plays good music. 90% of the amp is point to point wired so very easy to compaire the two. The noisy one is also running bit hotter and vibrates bit more on my touch.

Upon careful inspection, I've noticed that the power supply wires are connected (bunched up) differently. The quiet one is joined with (thick red + brown + black) & (thick white + white + light brown) combination. The noisy one is joined with (thick white + brown + black) & (thick red + white + light brown) combination. It has one big toroidal transformer and on small one connected to the input tube.

Could this be the problem? All other wirings are same on both. I'm tempting to re-wire the noisy one to see what happen. However, I don't want to distroy the amp either.

Big TIA for your kind advise....
did you contact the manufacturer for advise? I wouldn't think that the color of wires is important. Most likely it's a bad transformer. If you put your ear next to where the power supply is on this amp and it buzzes and the other one doesn't, my guess would be that it's a bad transformer.
Perhaps the best thing to do is go back to the manufacturer and provide the same description and ask the same question. Are the amps consecutive serial numbers? Who is the manufcaturer?
Ask the manufacturer of this amp before swapping anything. You could harm it (or worse), yourself.
If you cannot identify a problem, you cannot fix it. Please leave it alone. Power supplies are dangerous even with the unit disconnected (those big capacitors can pack a lethal punch).

I agree with albertporter about calling the manufacturer first, as it just takes a few minutes to verify. If not obtainable, and you have even basic electronic trouble shooting skills, and can locate a cheap volt meter (Home Depot, Radio Shack, etc), at least take some measurements before swapping the wiring. Mr. Porter and Gs5556 are right about their warnings, so, at least verify and discharge any HV caps before tinkering.
remove the output fuse.
Try swapping tubes, as a microphonic tube might just be your problem.

Unless you are a qualified technician i would not recommend rewiring the amp yourself. As stated by others power supply capacitors can store electricity for months. Unless you know how to drain them i would recommend you defer to someone else. As for the amps noise problem. Have you switched IC inputs to verify that it is the amp you are describing. My point is have you verified that the stated amp is noisy or not?? Also you may want to check your grounds on your fusebox to verify that it has a ground rod. Also, as others have stated call the manufacturer and see if they can offer ideas. It may be possible to "lift" the ground on the amp.

hope this helps,

Do you hear this noise through the speakers or is it just the amp (tranformer(s)) buzzing. If the former, it is almost always associated with a ground loop. If the later, it could be the transfomer but more likely it is a bad capacitor in the power supply. I am not a technician - just going on a similar experience not too long ago.
Thanks All!!
I wasn't getting a response back from the manufacturer. But, finally got the response back from the original builder.

Here is what he says:
I dont know what sort of transformer they are using now. But it seems that would be the cause of it. You could rewire the noisy trans same as the quiet one, use a 3-5A fuse , and monitor the amp as you switch it on. If it blows the fuse, or is even noisier, then turn it off immediately. If it is quiet, you can call yourself a fine detective. MickMN

Though, I have a felling that I can do this task, if a qualified tech is near So. Cal. area I'd rather take it to him. Any one of you know of any tech around So. Cal. area?

Big thanks to all your kind reply......

I am a tech, but in Chicago.

Before going any further, remove all interconnect and speaker cables from both amps. Plug them into the same wall outlet, one at a time, and examine/compare them again.

Next, individually swap the tubes and perform the same exam. If both act alike, connect a speaker load to one amp and note opperation. Now swap to the other speaker for comparison. Do these steps with the other amp for comparison against the first.

If both amps act similar, plug them both in while verifying performance without speakers, then with.

Still matching in performance? Start connecting them back into the source component, and swap chnls if needed, should differences be detected. It could be the amp, but making sure through deduction.

Based on these test results, I'll have more info.

Let us know...

Thanks for your kind and detailed instructions. I've tried all. Basically the only time that makes any difference is when speakers are connected. First, let me qualify the level of noise. The amps are rated at 112db s/n. The quiet one is very quiet no matter what I do to it. The noisy one is about par with low quality tube amp with about 80db s/n.

One interesting finding is that when input in NOT connected the noise level drops quite a bit. About 95db s/n (still not like the quiet one). However, if I connect the source, source is on or off makes no difference, I hear the noise again.

I've anylized the wiring again and noticed the real difference. The thick red wire is from the one end of the AC and the thick white wire is from other end of the AC. The Brown and black wires from one end of primary winding (trans) and the white and light brown wires from other end of primary winding. So, each cycle, one tranny is going through one direction and the other is going through opposit direction. So it seems.

Thanks again and looking forward to your next instruction...


I'll e-mail you and we'll further this off line, due to trivial technical correspondance. It'll be your choice to post any resolvement/findings.

In touch,