2. amps-preamps
  3. 1145581104

Need help to trouble shoot the noisy amp.

Gentlemen,

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....
zt000
metro04
222 posts
 
Zt000,

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...

zt000 OP
30 posts
 
Metro04,
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...
metro04
222 posts
 

Zt000,

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,
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