CRATE BV amp Ch1 prob- "Crunchy" Noises.

[Sea Chief]

By shorting across D7 or by grounding R52 we establish channel 1 without the switch or jack. If the noise stays, this theory is not valid. If it kills the noise, we are hot on it.

Shall I try this? which side of R52 do I ground? (I cant find D7).

Alas Im not up to speed with understanding the idea behind it (other than dirt s'thing.. it does sound like a dirty noise, rather than a steady nasty tone/hum.. tho my 2ps worth means jacksh*t of course.. we know this by now!) so its a Q of 'go poke that' then 'now prod this'. I can cope with that.

[Jazz P Bass]

R 38 is bad?
100K, 1/4 watt.
You could try jumpering it.
It may or may not be a good test.

[g1]

Shall I try this? which side of R52 do I ground? (I cant find D7).
.

Ground the side of R52 that goes to D7.


The side opposite Q10.

[Sea Chief]

Ground the side of R52 that goes to D7.


The side opposite Q10.

Done that: noise remains. hmmm.

Is it OC1?

[Sea Chief]

R 38 is bad?
100K, 1/4 watt.
You could try jumpering it.
It may or may not be a good test.

Haven't yet tried this- are you confident its an ok plan of attack?

Does the general consensus point twd one of the (transistors) Q's now then? they look proper fiddly to get between their legs I'd say.

Aside: I dont suppose not having the FS plugged in (I dont have one for it, or another that works with it like a PV for eg) will have any affect? Ive not had issue b4 with any amp re noise w'out its FS in.

[Jazz P Bass]

Haven't yet tried this- are you confident its an ok plan of attack?

Does the general consensus point twd one of the (transistors) Q's now then? they look proper fiddly to get between their legs I'd say.

Aside: I dont suppose not having the FS plugged in (I dont have one for it, or another that works with it like a PV for eg) will have any affect? Ive not had issue b4 with any amp re noise w'out its FS in.

Jumper the resistor.
It is pointing to that.

[Sea Chief]

Jumper the resistor.
It is pointing to that.

Done that: jumpered/ bypassed R38: noise remains (actually sounded a bit worse even).

[g1]

Is it OC1?

No. You have proven that it is after C19 (post 82), but before the master volume (post86) .
So the noise should be coming in somewhere between those 2 points.

[Sea Chief]

Yes sorry (humor doesnt travel well on the interweb) that was indeed a bit too droll really.

Really am grateful g-one for the help.. I do sort of feel like we're closing in on this b'stard little prob.

[g1]

Ah, deadpan humour, my favourite kind. That's why I use those smilies even though they do irritate some people. But then it's not deadpan anymore is it?
I'm hoping to hear back from Enzo as to whether he thinks it could still be the gate supply for the Fet's.

[Sea Chief]

[Actually Ive just had an email from the guy who sold me this only 2 weeks ago. I opened an ebay dispute on sun (reluctantly) as I dont believe "but I just recorded with it b4, it was fine" when he passed it to me. Crackly pots -to me- are symptomatic of not being used for a prolonged time if nothing else, so he was lying. He either couldnt be fkd to check it, or knew it had developed a prob and passed it on to me. Little sod. And I hope you're reading this too. I emailed him the thread as proof it did indeed have a bad fault, he replied -now he knew I had tried to swap a few pg 1 components- 'well you can return it for a full refund, unless of course its been modified'. (All adds up doesnt it? = a toe-rag).

[Jazz P Bass]

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).

[Jazz P Bass]

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).

I have also thought that you should rotate the MV pot full On & full Off when grounding the MV.

[Sea Chief]

Try grounding out the MZ middle leg.
I have also thought that you should rotate the MV pot full On & full Off when grounding the MV.

MZ.. you meant ground out the MV pot middle leg?

Lordy does this mean Im entering the dark-side of my amp? oh sh*tsters I thought the prob was nailed to before the MV but after V2 pin 7..
.

[Jazz P Bass]

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.