HT-20: More Background Noise in Clean than Overdrive?

[thephantum]

My first call would be output tubes....but reading this thread, that is not the problem.

I will say that my HT-20H is dead silent, even at gig levels. Coupled with that is: this an old thread and no one has complained about it recently. So it's not a common issue, but it's obviously affecting a subset. That tells me a batch of bad components during a particular manufacturing run.

What it sounds like is AC noise getting induced into the signal path, so if I had to guess it's the choke resistor or something else just forward of the rectifier (possibly even something in the rectifier itself). Fact is though, it needs to get traced out with an O-scope to definitively make a diagnosis. Otherwise your just stabbing in the dark replacing stuff...

[noise7r]

Friends, someone solved it? I have the same problem on the clean channel on my ht-20h studio..

[thephantum]

This is a very old thread and from what I read, it was for a barely perceptible hiss on the clean channel that I'm not even sure was ever an actual problem. All tube amps will have some level of hiss. There are multiple posts stating that it was barely perceptible, could not be heard when gigging and that it was quieter when compared to other tube amps.

Specifically what kind of background noise are you hearing? Is it a low or high pitched hum or is it a hiss/buzz? Are there any clicks or pops? How loud is it? Can you hear it while you are playing? How old is the amp? Have the tubes ever been changed and, if so, have they been properly biased? Are you using a AC power filter or not?

[noise7r]

Here my video with this problem https://youtu.be/v7QPQ0x4MAw
I changed all tubes, but it changed nothing. On the overdrive channel this problem isn't present. I live in Ukraine and language in video not English, please excuse for it. but on video everything is clear

[noise7r]

I use the power transformer with 220 on 110 volts. Changed all tubes, a cable, the transformer of a power changed (220->110), a guitar also changed - changed nothing. I didn't set up bias of tubes yet

[thephantum]

Since the OD channel is so quiet, it could be some kind of a ground loop issue inside the amp...but it's so low level it's not worth worrying about. That level of noise is not unusual for a tube amp...the fact is the click of the power switch is louder than the hum. I highly doubt you would even notice it if you stood more than a few meters away from the amp. Tube amps make noise.

I use the power transformer with 220 on 110 volts. Changed all tubes, a cable, the transformer of a power changed (220->110), a guitar also changed - changed nothing. I didn't set up bias of tubes yet

What does that mean? You changed the power transformer from a 220V to a 110V but run the amp on 220V?

[noise7r]

What does that mean? You changed the power transformer from a 220V to a 110V but run the amp on 220V?

No, I thought that the problem can be in the step-down transformer which I use with the amp. (We have networks of 220 volts) Therefore I replaced it on better. However, it didn't solve a problem. In the amp changed nothing.

In the beginning this noise wasn't in the clean channel. Once I switched on the amp and heard it.

[thephantum]

That noise is most likely AC hum/ripple. I would say try a different step down or use filters, but the noise is only on the clean channel. Like I said, the only thing that makes sense would be a ground loop. Engaging the OD channel probably closes/eliminates the loop, thus stopping the noise.

It could be a lot of different things: cold solder joint, bad cap, bad transistor, etc. To track it down you'd need an O-scope to determine where the hum is getting injected. So unless the hum gets worse, I don't think it's worth going on a hunt for it.

Our of curiosity, why didn't you replace the power transformer with a 220V unit when you swapped it?

[bobspr26]

I have reduced a great amount of noise on my son's new HT20 head by inserting a small capacitor somewhere in the middle of elecronic board. It is not compromising anything and sounds wonderful. The noise is a result of a power supply buzz sneaking through electrical circuit paths.
If interested I can send a picture of what I've done bobdan26atyahoodotcom.