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

[chrisp2]

Hello,

I got me a new Blackstar HT-20 Combo. I'm quite happy with sound and quality but there's one thing that bothers me:
There's a remarkable background noise hearable in the clean channel. The guitar is plugged in and it doesn't matter if the volume on it is turned on or off, the noise is the same.
I already got me a replacement amp and the background noise on the second amp is the same as on the first one.
I have to say that the HT-20 is my first tube amp and I don't know what level of noise is normal for such an amp.
But what's really strange, at least for my understanding, is that the background noise in the overdrive channel is much lower. Normally I would say it should be the opposite way.

What are your experiences concerning this matter? Did you also notice a louder noise in clean than in overdrive?
I just can't believe that I received two amps with the same manufacturing error from two different dealers.
What can I do?

Thanks for your answers.

cu
Chris

[Beejer]

Hi Chris - More than a few folks have had new Ht's shipped with bad tubes, so I have read.

What kind of background noise? Low hum? High pitched hum? Loud Hissing? Clicks/pops? Radio channels? Volume drop?

I would try swapping out V1 with known good 12ax7/ECC83, if you have a friend with one handy. I don't have an HT-20, but V1 is usually furthest away from the big Power Tubes. Be careful and note where the gap in the pins are when you remove it, as you will put the new one in the exact same way. Do not force the pins in.

Just as likely you are getting interference from bad wiring, or simply being on the same house circuit with a nasty appliance.

Try moving the amp around the house . I would try this first.

[chrisp2]

Hi Beejer,

thanks for your answer.

It's not a low hum, no clicks/pops or radio channels. More of a medium pitched buzz or hissing. Not easy to describe when german is your native language

I tried different guitar cables, also quality ones but it didn't change.
I also thought of trying a power line interference filter to cancel possible interferences in the house circuit. Maybe that's a point.

Unfortunately I don't have a friend with ECC83 tubes around. What brand/type are known good ones for example?

[ronnie robinson]

Hi

The Clean channel should be very quiet even at high volume

Blackstars stock tubes are shockingly unreliable and by far the majority of problems with these Amps is the (stock) tubes but obviously any tube can go bad - assuming of course it not a prblem with building electrics .

Is this problem only on the clean channel? As Beejer suggests look at the PreAmp tubes (especially for the clean channel). It is worth before you buy any, to have a look at each tube, take each out, one at at time, do a visual check (any discolouring or loose bits inside) and then replace ensuring each tube is seated correctly.

JJs and tungsol are popular choices with the Blackstars


Let us know how you get on

[Beejer]

I also thought of trying a power line interference filter to cancel possible interferences in the house circuit. Maybe that's a point.

Ronnie's suggestions for trying a JJ or Tungsol in V1 are good. They are not too expensive and is is always good to have an extra preamp tube around when you own a tube amp. He is also correct that the clean channel should be quiet.

I had a thought: maybe try taking the amp to another location (friends home) and try it there to see if is your house wiring that is the issue.

Personally, I plug everything I use into a Furman Power Conditioner, just the basic MX8-2 model. In Europe, they must have a model for your voltage requirements.

Let us know how things work out.

[chrisp2]

Thanks for your suggestions. I will try new preamp tubes first and let you know what happened.

cu
Chris

[fjonasch]

Hi guys!

I recently bought a HT Studio 20 head and experience the same behavior. What I see is:

- Amp switched on, cable connected to input
- Channel and master volumes on 0
- Higher noise level in the clean channel than in the overdrive channel

Is this what you see (or in this case hear) too? I have already tried replacing the preamp tubes with a pair of 12AT7 I had around, no improvement. I also tried muting the preamp section by connecting a mute switch to the effects loop, no improvement again. This noise seems to have it's source somewhere after the return jack of the effects loop then... What I hear is a low frequency hum as soon as you switch the amp on (probably the 50Hz mains frequency) and then a higher frequency hiss as soon as the power tubes are warming up. Any other suggestions are very welcome. Did someone already try swapping the power tubes?

Cheers!

[Beejer]

Hi guys!

This noise seems to have it's source somewhere after the return jack of the effects loop then... What I hear is a low frequency hum as soon as you switch the amp on (probably the 50Hz mains frequency) and then a higher frequency hiss as soon as the power tubes are warming up. Any other suggestions are very welcome. Did someone already try swapping the power tubes?

Cheers!

I'm not a tech, but if you have isolated the problem that far down the circuit, if I am not mistaken, the next circuit would be the reverb unit, then the PI valve, then P1/P2.
I have read of numerous issues with the stock tubes, so it could well be the power tubes or the PI.

[chrisp2]

- Amp switched on, cable connected to input
- Channel and master volumes on 0
- Higher noise level in the clean channel than in the overdrive channel

Is this what you see (or in this case hear) too?

Exactly! That's what I hear too.

Ok... than it seems that the preamp tubes I orderd won't fix the problem... well...
What I noticed too: Checking with a headphone at the Emulated Output the Clean Channel is silent, no noise there.
Is that helpful to further diagnose the problem?

[Beejer]

Sorry Chrisp2, but without the schematic I do not know where the emulated output circuit is in the chain, so I regretfully have no input on this.