Diezel VH4 hum/hiss problem

jake5150

New member
Hi,

I recently bought a VH4. I'm not able to open it up much at home because of neighbors, so I only found out at rehearsal that as soon as you move above bedroom level there is a very loud hiss, but only with a guitar or patch lead plugged in. It's silent without anything plugged in. It's so loud that it's going to be unusable live as the hiss will be too loud during parts where I'm not playing.

Does anyone have any advice?

Thanks in advance
 
Also, just to note that this is with the guitar volume knobs on full or off. Even if I just connect my TU-2 into a planet waves patch lead into the input I get the hiss. It's loudest on channels 3 and 4, but still audible on 2.
 
Did it have problems with the power tubes before? Like blowing the tube fuses?

If yes, the hum trimmer needs to be replaced.

If not, please hook the guitar into the serial return (crank master full). If you don't have hiss: preamp tube problem, if there also is hiss: power amp problem, f.i. (again) the hum trimmer caused by faulty power tubes.
 
Thanks for the reply. Yeah, the previous owner did mention he had a problem with the power valve fuses bowing.

I'm in the UK (London), do you know who I contact for the part and installation?

Thanks again.
 
I agree with replacing power tubes (get the EL34 BHT or BG type) PLUS getting rid of the hum trimmer and replace it with 2 pieces of 100 Ohm Resistors (I use 2 Watt as per Peter Diezel). The hum trimmer are too sensitive and can blow easily with the VH4.

If you can afford it I would also get a new preamp tube set while you're at it. It most like has never been changed. Get the recommended set from Peter Diezel .

Kind regards,

Jens Kruse
 
Thanks for all your help so far. I emailed Diezel UK (the tech service email address) a few days back but I am still waiting for a response. I know a Mesa tech locally, (please excuse my lack of technical knowledge) is the hum trimmer replacement a job I can take to any tech or should I go specifically to someone who deals with Diezels?
 
The trimmer is labelled on the board (pots facing you, right side), so IMO yes, any good tech is able to unsolder it and replace it with two resistors. Also install new tubes and rebias the amp.
 
It really is not a big deal to replace the hum trimmer. I have done it once in my VH4 as malfunctioning (actually "exploding" C-Svetlana) KT88 wrecked mine.

Just for the future record, is replacing the hum trimmer by resistors an official recommendation from Diezel nowadays?
 
YES ! We strongly recommend replacing the hum trimmer with the 2 100W resistors. Especially when you gig/tour with the amp you want to eliminate potential problems and these hum trimmers do blow with the VH4 models.

Jens Kruse
 
Thanks. Been there and very likely will find myself in the same situation again someday.

About the parts themselves, any other details than 2 pieces of 100 Ohm / 2 Watt resistors? No difference for the Euro-versions (230/240V)? Any recommended (tested and "Diezel-approved") brand? I might do this next time I retube my amp to prevent future issues.
 
Spoke with Peter Diezel last night. To replace the hum trimmer he now recommends a 47 Ohm/2W resistor on left side and a 100 Ohm/2W on right side (pots/knobs facing you) . This will bring the hum on ch4 to it's lowest .

Any resistor brand is fine. No difference for different voltage version amps like 230/240V .

Cheers,

Jens Kruse
 
Hi - I do have the manual. I just want to make sure I am ordering the right resistors for the person I am taking it to. I can't say I know what I am looking at.
 
Back
Top