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TedNugent's picture

Noise at idle

All right, going to try this again...

I've got a late 70's HD130 with a phase inverter. New tubes and caps. At idle there is hiss. High end. And it remains while playing, muddying up the sound.

Anyone have any advice or experience with this? Surely I can't be the first. . .

Please let me know if you have ANY IDEAS at all. I'm keen to track it down and get this champion 100%.


The Nuge

mm210's picture

My only comment on hiss is

My only comment on hiss is that you might have to audio probe the signal all the way through the system and find out WHERE it starts. Carbon comp resistors can be noisy but you don't want to just blanket replace every one as that's a good way to start more trouble. You would have to, in good conscience, replace every resistor one at a time and see if that cured it. That could take a LONG time. Chopsticking the resistors in circuit and hot might work. Does it do it when cold, hot, all the time?

TedNugent's picture

Yes, hiss/noise at idle and all the time...hot or cold

Thanks for the reply mm210. Great to hear back from someone. . .

The noise is all the time. Hot or cold. It seems pronounced during idle as there's nothing else to distract my ears but as stated, it colors a recording significantly. You couldn't mic it on stage because it would fill up the monitors with white noise when no one was playing.

As for chopsticking, I'll have to do some reserach before making the attempt. I've seen it done in videos but haven't had a reason to go there myself.

Fingers crossed!


mm210's picture

It may not help much with the

It may not help much with the chopsticks though. If the resistor is cracked or has a bad solder joint, it may help. If it's just plain ass noisy, you'll have to either audio probe it or get out the scope. At least that's the way I go about it. Also, you might try pulling the IC's one at a time and rubbing them in and out. Also, swapping the IC's around may help too if you don't have a scope to track it down.

TedNugent's picture


Hello Musicmen,

Just wanted to finish off this thread for posterity. After some comparisons etc I've determined the problem isn't the MM HD 130 after all. It's the speakers. The same amp will be quite 'loud' at idle on an one set of speakers vs another. I don't know if it has to do with speaker age or miles on the odometer or what. But as I'd already changed the capacitors it was too late to test how much those contributed to the issue. Who knows.

But at this stage speaker set A seems a fair bit quieter than speaker set B, i.e. I can turn the Amp up to a certain amount with set A and still record with it. Whereas set B is just too hissy at quiet times in the song and the mic pics everything up. Also background bleed which isn't good. No complaints though - who records at 105 db at home anyway?

As a reference, my 65 watt 2x12 of the same era performs similarly. Dead quiet up to a certain point and then hissy. But isn't this the case with amps in general? At least older/vintage models?

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