Strange sound disappearing

[iulker]

Hi everyone,
I have a problem with one of my built tube amps, which is, somehow, a clone of a Fender Vibrochamp, but without the vibrato circuit; having a solid state rectifier, not tube. So it's just 2 tubes in there, one 12AX7 and one 6V6.
I also added a digital reverb circuit made with Belton Digilong module, with the schematic from GGG site. This is placed between the tonestack and the volume, meaning right between those 2 triodes of the preamp lamp.
The whole amp is power scaled with a VVR circuit, similar with the one that Dana is selling. It's made by me, different transistor, no problem, I put the same circuit on another 3-4 amps, without any problem, until now.
The problem is tricky because it's happening randomly, when playing the guitar, the sound suddenly disappear without notice, and reappear after a while by himself, or after I hit the strings with some force ... I've noticed that no matter what level of the VVR or volume is, this behavior occur at apparently random times.
The interesting thing is that when I play some music through the same input jack, the music is playing fine, at any level, for hours, without any problem, the sound is not disappearing, no matter what level is on the mp3 player, or what level I set at the VVR or the volume!
Can somebody explain to me why the music is different from the guitar plugged in, and is not acting in the same manner ? And what could be the problem when playing the guitar and the sound stops ... ?

[iulker]

I attached a schematic based on the vibrochamp with the modules I put in.
The reverb circuit is powered by a auxiliary transformer with his own rectifier circuit, so it's not interfering with the power supply of the amp ...

[surfsup]

I had the exact problem. I found it to be a bad cap near v1 is there a swooshing sound too?

[iulker]

The sound is very good until it's gone
The voltages in different points are fine, in the range, no changes from when sounds good or is without sound ... strange motherfucker ...
I also changed both tubes with similar ones, replaced the volume and VVR pots, no changes ...

[Structo]

What happens when you take the Belton brick out and just go straight to the next stage?

[Firestorm]

If the dropout is truly random, it is an intermittent connection: a bad ground; a faulty wiper; a cold solder joint; even a marginal connection in a tube socket. If it is input-level driven, it's something else. Try to establish if it's really random or not.

[iulker]

The sound disappear, then I hit strings harder and it's back to life! What this mean? it's somehow related to the input level of the guitar ?? The grid of the preamp tube must have something to do this, it seems ... wrong biasing of the decoupling cap ... ?
I'm thinking loud .......

[JazzGuitarGimp]

Have you tried a different guitar cable? And a different guitar?

[dorrisant]

Have you tried a different guitar cable? And a different guitar?

+1... bad battery for my active EMGs can play tricks like this.

Tony

[iulker]

3 different guitars, and at least 2 different cables ... same behavior ...

[ampdoc1]

Try paralleling your reverb block with an alligator cable. I'd bet on problems there. Music probably doesn't activate the problem because most of it is very compressed vs a hard peak when hitting the striings.

Another thing to try is my "all around" bad part finder,...a can of freeze spray. I'll bet a shot to your reverb IC will kick it back on.

a'doc

[rock_mumbles]

Try paralleling your reverb block with an alligator cable. I'd bet on problems there. Music probably doesn't activate the problem because most of it is very compressed vs a hard peak when hitting the striings.

Another thing to try is my "all around" bad part finder,...a can of freeze spray. I'll bet a shot to your reverb IC will kick it back on.

a'doc

I agree that you should jumper across the input and output of the reverb circuit and see what happens ...

Did you use the exact circuit for the D-verb pedal?

If so you'll need to make sure you don't overdrive the module by using a voltage divider on the input, I'd also consider putting a resistor across the reverb input/output so some dry signal goes straight through (look at a Fender reverb)

[Aleksi]

Hi,

I've built two amps with the Belton reverb module (1st version). I think the maximum input signal level is only about 1.5V for the Belton. I'm guessing hitting the strings causes a bigger signal to be generated and the Belton doesn't handle bigger signals exactly gracefully... it will cause strange delay, fuzz and modulation noises to appear.

BR,
Aleksi

[iulker]

Thank you, guys.
Last night I was thinking at the reverb block, also ... it's the only thing I put in this amp for the first time, never worked with the reverb brick before ...
The problem is that the amp is not at me now, I make'it for someone else, in another location, so I will need to deal with the person to make some tests, otherwise he will need to send the amp back to me ...
Yes, I did the D-verb circuit, with the Belton brick on it, I inserted between the 2 triodes of the preamp tube, as I draw on the picture above.
I hope I will convince the man to make a shortcut between the input and the output of the reverb, see what's happening.
I'll put the result here as soon as I find something.

[iulker]

Hi,

I've built two amps with the Belton reverb module (1st version). I think the maximum input signal level is only about 1.5V for the Belton. I'm guessing hitting the strings causes a bigger signal to be generated and the Belton doesn't handle bigger signals exactly gracefully... it will cause strange delay, fuzz and modulation noises to appear.

BR,
Aleksi

You are the guy who started this: http://www.ax84.com/bbs/dm.php?thread=436251 ?
If so, please post a schematic with how you end-up with inserting Belton reverb and how you succeeded with the power problem, rectifier for the belton brick ...
Thanks.