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

[chrisp2]

Hi Felix,

very good audio demonstration, that's exactly the noise.

[MarkWG]

What's the noise like with a guitar attached with the volume pots on the guitar turned all the way down?

[fjonasch]

Hi guys,

the noise with a muted guitar connected is exactly the same. I'm still in touch with Blackstar support, they now mentioned that there are transistors in the power amp stage as phase drivers, if one of those is noisy, this could be the source of our problems. I'm also still waiting for an explanation on why this only happens in the clean channel (and asked for the schematic to figure this out).

- Felix

[MarkWG]

Ok, was wondering if it could be a fault inside the guitar, as I've had that before with the stupid button-strong fender Jag. But I guess that wouldn't matter if the pre- volume was all set to 0. Good luck sorting it, I'm going to try out a 20 (2nd hand) this weekend, and will make sure I check it over for this fault. If it's any use at all, the Ht-5 is supposed to be at least vaguely similar in circuitry, and partial schematics are available for that here:

will have to link yourself:

thegearpage.net/board/showthread.php?t=624537

[MarkWG]

Hey, I picked my second hand HT-20 up this weekend and have just had my first real play with it.

My clean channel also has slightly more noise than the OD channel, and displays exactly the same behavior when turning up the volume and gain as you describe.

Without knowing the precise volume of the noise on your amplifier, I can't say for sure it's the same, but for me it's in no way annoying. In fact, if I remember correctly, it's a fair bit less than the noise on my new (reissue) fender twin, though I sold that about a year ago so can't back to back.

Have you got a amplitude/decibel meter (I think there's an iphone app), to make a comparison?

Either way, I'm loving the 20, I paid £250 second hand for it, and it blows the £900 fender twin out of the water (in my opinion).

[MarkWG]

Just a small update - I've bought a full new set of tubes, including some Tung Sol 12ax7's and a NOS Philips 5751 for the preamp stage and two Tung Sol EL34Bs.

I'll see if these make any difference to the noise on either channel. I'm not bothered by it at the moment, just want to see what the amps like with fresh tubes (not 14month gigged tubes).

[fjonasch]

Hey there!

Thanks Mark for your update. I agree, the noise is nothing that will bother you when you're playing at certain volume, but it's still strange and rather unexpected for a brand new amp. I've poked Blackstar support again to see where this is coming from. I can't imagine why the phase drivers would be more noisy in the clean channel than in the overdrive channel... I'll keep you posted.

- Felix

[MarkWillGreen]

Hey, forgot to add that changing the tubes did nothing for the noise. It's still pretty low. Also, in comparisson to my Fender Mustang 3 it's incredibly low. That thing buzzes like noone's business when it's on one of the gainy presets.

[hedman71]

Hi
After reading this thread i want to share my story.
I bought a Ht-20h for about two years ago new not used.
I have been more than satisfied with it, and one of the good thing is
that it´s been veary silent amp.
Mostly i have used it at home, but sometimes at gigs and in rehearsals.

A couple of weeks ago when a started up the amp i hear this hum and it´s exactly the way
it´s descibed in this thread, only i think my hum is louder. It´s nothing i can live with if im gonna use
it at home on moderate volume, cause i can hear the hum in the background then.

I have tried diffrent cables, cabinets, locations were i plugged the power in and so on..

Before that day when the hum appeared I had used it in the rehearsal and transported it home in the car.

[Drew_SCS]

Old thread but any more developments on this?

My problem is exactly the same as what fjonasch has been posting.

It became far more obvious again after swapping the rocket 50 for a celestion vintage 30.

I've biased the amp (had never touched it), and it was around 12.5 volts, now down to 11.5 as per spec, but no fix there.

Was about to buy new power tubes but I've seen people have no luck with that.

Getting desperate now, it's quite loud, consistent and putting me off.

Thanks