CRATE BV amp Ch1 prob- "Crunchy" Noises.

[Sea Chief]

We will find that out as soon as you do it.
Rotate the pot when under test.
Full off & full on.
And, yes, MV stands for Master Volume Control.

Ok this is physically too difficult, IE middle leg of the MV pot is tucked right under. So, I was trying to find a suitable alternative, & on schematic it seems (if the line RHS of preamp page ''[point] H to page 1" is indeed the MV-middle-leg as it looks to be from a numpty's p.o.v) R6 or the - side of C14 I could use. Trouble is my tracks from MV-mid-leg dont follow to these two components. hmmm.

Is the line running off page 1 > onto page 2 (actually pg 2 is above pg1!) "to/from H page 1/2" the line for the MV-mid-leg?

[Sea Chief]

Try grounding out the MZ middle leg.
.

JazzP can you tell me: when you said "MZ" middle leg -did you mean MV middle leg?

And can you help me with an alternative point to the MV middle leg (if indeed that is what you meant) like say 'or the * side of R*' so I can do this test, but not direcetly onto a pot leg of MV (if indeed MZ is the MV) which I cannot phycically get to.

[Jazz P Bass]

Well what I was thinking was that grounding the bottom of the Master Volume did Not get rid of the noise.
But grounding R38 did.
But, was the MV control turned?
So, if you can get to the MV side of R38, ground that & rotate the Master Volume control.
I am hoping that the further the middle leg gets from R38 (which is grounded) the more it will hum.
If that is the case, then the problem is further down the line.
Which brings up 'Divide to Conquer'.
A guitar input into FX return will totally disconnect the preamp.
Turn the volume off on the guitar.
The amp should be quiet.

[g1]

Correct, R6/C14 junction connects to MV centre leg.

[Sea Chief]

Well what I was thinking was that grounding the bottom of the Master Volume did Not get rid of the noise.
But grounding R38 did.
But, was the MV control turned?
So, if you can get to the MV side of R38, ground that & rotate the Master Volume control.
I am hoping that the further the middle leg gets from R38 (which is grounded) the more it will hum.
If that is the case, then the problem is further down the line.
Which brings up 'Divide to Conquer'.
A guitar input into FX return will totally disconnect the preamp.
Turn the volume off on the guitar.
The amp should be quiet.

Ok Grounded R38 (MV side), rotated MV under test: noise ceases (well, innitially crunchy for say a sec then noise ceases).

Im sorry I cant remamber where I am with the tests now. MV mid-leg? (MZ?)

[Sea Chief]

O/K.
Try grounding out the MZ middle leg.
The wiper,which goes to the next part of the circuit (which has not been considered).

Done (@ R6): noise ceases.

Edit: MV turned both from 0 to 11.

[Jazz P Bass]

Ok Grounded R38 (MV side), rotated MV under test: noise ceases (well, innitially crunchy for say a sec then noise ceases).

Im sorry I cant remamber where I am with the tests now. MV mid-leg? (MZ?)

Follow this.
When we initially tried the ground R38 thingy, it got rid of the noise.
But where was the MV pot?
Probably all the way up. (CW full on)
So the middle leg (the wiper) of the MV 'saw' ground.
Now when you rotate the MV control CCW (full off) the noise returns.
The wiper is no longer grounded.
So we still have not divided the problem.
The problem is after the Master Volume.
That is why I asked you to plug a guitar (guitar volume off) into the FX Return jack.
I am attempting to rule out the whole power amp circuit.

[Jazz P Bass]

I have to apologize but I would like some clarification.
Your reply "Ok Grounded R38 (MV side), rotated MV under test: noise ceases " is too vague.
Please prove to me that , with R38 grounded, rotating the master volume contol makes noise when turned to one end & is silent when turned the fully other way.

[Sea Chief]

Follow this.
When we initially tried the ground R38 thingy, it got rid of the noise.
But where was the MV pot?
Probably all the way up. (CW full on).

Yes the MV was up.

So the middle leg (the wiper) of the MV 'saw' ground.
Now when you rotate the MV control CCW (full off) the noise returns.

I dont think it did, I rotated it 0-11.
Just done again, R38 (Mv rhs leg) to gnd: noise ceases turning MV 0-11 (ie ccw full to cw full).

The wiper is no longer grounded.
So we still have not divided the problem.
The problem is after the Master Volume.
That is why I asked you to plug a guitar (guitar volume off) into the FX Return jack.
I am attempting to rule out the whole power amp circuit.

So does that mean this is n/a yet, or now?

[Sea Chief]

I have to apologize but I would like some clarification.
Your reply "Ok Grounded R38 (MV side), rotated MV under test: noise ceases " is too vague.
Please prove to me that , with R38 grounded, rotating the master volume contol makes noise when turned to one end & is silent when turned the fully other way.

Yes sorry I was not 100% clear there. I realise this is an important point at which to be certain- thx for checking.

No, not noisy one way but silent the other.. the result was: turning the MV fully both/either ways: noises ceases.

Again: (R38 to gnd)..
If I turn MV CW: noise ceases.
If I turn MV CCW: noise ceases.

[Jazz P Bass]

Well F*** Me.

[Sea Chief]

Well F*** Me.

Now thats my sort of reply.

Is that you done then? thx anyway JP :-)

[Sea Chief]

Shall I throw it in the river now?

[Enzo]

Part of the challenge of this board, and its reward, for me at least, is to solve problems. We have to come up with strategies that we can translate into someone else's understanding. Believe me, I know how to troubleshoot. The challenge is to teach you to do it. So much depends upon our ability to communicate to you not only the techniques and procedures to find the source of the problem, but also to hopefully get across the understanding of why we do what we do. When I suggest shorting out some resistor or connecting a wire from here to there, I have a specific purpose. And when I do that, Jazz P and g-1 know EXACTLY why I asked you to do it and why. They understand troubleshooting as well. To you, some of these things are utter mysteries. That's OK, you do not have the experience we do. It can be frustrating when the communication breaks down. I accept the frustration as part of the challenge. Frustration is not the fun part, but what can you do? What might take me 5-10 minutes to sort out on an amp in front of me might take a couple weeks with this back and forth.

SO throw it in the river? No. But in any project, when progress stops, it might make sense to take it to someone who can do the job for you.


I used to do all my automotive work. I'd even pull the head off my truck engine and do a valve job. I once spent three days trying to install headers on a pickup. At this point in my life, I look at a project like that and think I could either take an entire weekend to do all this crap, or I could pay someone who knows what he is doing to just do the job professionally.

I need a new roof on my house. I can swing a hammer, but I guarantee you, ain't no Enzo going up no ladders. I called the pros.

[g1]

Well, as Enzo mentioned, you are free to bail anytime should you want to take it in to a tech. I'm not sure if it's been asked or answered yet, should a bad component be located, will you be able to replace it? In any case, if the problem actually gets found, it may be easier for you to understand a re-read of the whole thread.
Meantime, to carry on, I'm fairly convinced the problem is between C19 and the MV pot.
However I'd like to eliminate Enzo's hypothesis about the Fet control line. You will need 2 jumpers this time.
Remove V2. Use one jumper to short R37/Q5 junction to ground. Other jumper from MV/Q6 junction to ground.
Turn up master. Noise will probably still be there. Now rotate ch2 tone pots (low,mid,high) and see if any make scratching noises while turning or affect the noise in any other way.