[ 'Dead CRATE BV- need help! ]

[Sea Chief]

Jumper from C3/C4 junction to ground.

Done: noise remains.

[Sorry g-one: Previous v1 pin 7 > gnd WRONG (MV was down). I got a v loud hum/ I cannot tell if noise behind, its such a prominent 'durr'].

[g1]

You will have to play around with jumper length and how it is routed so you can discern definitely whether the crunch noise is still there or not. For both points, V2 pin2 to ground, and V1 pin7 to ground.

[Sea Chief]

You will have to play around with jumper length and how it is routed so you can discern definitely whether the crunch noise is still there or not. For both points, V2 pin2 to ground, and V1 pin7 to ground.

Ok, V1 pin 7 there is extremely loud hum even shorter lead/ differenent gnd point etc.. but there is -no- crunchy noise behind.

V2 pin 2: this ones interesting.. essentially quiet but that crunchy noise is just trying to squeak thru, intermittantly.

[Sea Chief]

driving me nuts this.

V1 pin 7 again, same extremely loud hum, but turned down the crunchy noise is there. Maybe 1/2 as loud tho.

[Sea Chief]

V1 pin 7 again: crunchy noise IS here (not as prominently/ resolutely there other tests as its more intermittant, but its defo heard here) with MV even at 0.

I cant turn MV up past 4 as the hum gets so loud with this test- its just not good to have this going. Tried all manner of shorter leads, different gnd points, different precise 'pin 7' point ie R12: I cannot rid the massive hum. But crunchy -is- heard here.

[Sea Chief]

Try jumper from V1 pin7 to ground.

Argh this is infuriating..

V2 pin 2 again: I hear the crunchy noise as said quietly/ squeaking in intermittantly even with MV at 0. Turn MV up and IS resolutely there, but 1/2 as loudly as often before (with the massive hum together with it).

I cannot shift this huge hum (with MV max) with these 2 tests/ Ive done everything I can to rid it. Basically tho I -can- hear the crunchy noise behind even if its not as prominent as previous tests (done around V2 for eg).

[Jazz P Bass]

I would expect to hear all sorts of noises when getting on the grid pin.
So expect it.

It appears that the noise is after V2 A.
If grounding Pin #2 did not get rid of it, then the issue is being caused after it.
In a previous post above, you stated that grounding V2 Pin #2 stopped the noise.
Now it is still there, albeit in a suttle way.
So you are refining your perception of the noise.
So it's back to V2 B.
If grounding Pin # 7 truly kills the noise, then that circuit is still suspect.

[Sea Chief]

Yes I thought this huge hum sounded/ likely to be expected of sorts. Difficult to hear the damn prob noise behind this, but, listening v hard I can hear. So albeit not as prominent/ loud as tests last week, the same crunchy noise -does- appear on V1 pin 7.. and V2 pin 2.

(Would the reason that its less loud be due to the further 'stage' of preamp ie V2b onwards amplified this quieter crunchings I find ^ here, to the bigger crunchy noise Ive heard so often?)

Ok so now V2 pin 7 grounded/ done: noise is there (1/2 bad as often before. But crunchy it is).

[Jazz P Bass]

Can you get on any of the preamp plate resistors (such as TP4) & measure the Volts AC ripple?
If you get some ripple, watch it & see if you get spikes that coincide with the noise.
After that, it's the same tests as before.
Keep going down the line until it stops.
C20, one side at a time to ground is a good start.

[Sea Chief]

Hi JazzP- do you mean measure AC across R33? or measure AC @ TP4 ie one probe to gnd one to TP4 > measure AC..?

And then I'll go onto C20 again. thx

[Jazz P Bass]

Put the red lead on TP4 & the black on chassis ground.
Set your meter to read Vac.

[Sea Chief]

Put the red leaqd on TP4 & the black on chassis ground.
Set your meter to read Vac.

Done: I measure 0.00V. Not a sausage. Not even shifting to 0.01V whatsoever. The noise is back to the steady stream of prominently heard crap/ crunchy white noise thing. So there are no particular audible 'spikes' to any of the noise, as it were.

[Sea Chief]

C20, one side at a time to ground is a good start.

Done:
C20 (@ R34 leg).. noise ceases.
C20 (@ R35 leg).. noise remains.

[Jazz P Bass]

We are back to the bottom of V2A!
What does this statement mean, from post #33:"maybe as at the mo Q4 is reversed 'cowgirl' but works, tracks bad so has to stay as is for now"?
Bad tracks can be jumpered with a fine pice of single strand wire.
Take the Jfet out.
Reversed Cowgirl?
What was wrong with the Jfet that you purchased?

[Sea Chief]

My new JFET was fine.. but orig Q4 was fine too (my tracks arent but as you say can do the wire thing tho- but pref leave it be).

Its in 'reverse cowgirl' at the mo (ie D and S legs round wrong way) as I had to be sure the new J176 and old Q4 didnt have opposite flat faces. I tried it same-flat face orientation as Q4 prior to this of course. Both ways round exactly same: noise remains/ no difference to orig Q4.

thx SC