BSIAB II, Stuttering sound

[b97pla]

I've just finished building the BSIABII using Torchy's vero layout, having it slightly modified to fit my components and I've also added a SPDT to switch power on or off and another SPDT to bypass the last filters (R17-C13 & R18-C14).
I wasn't able to pick up a 250 pF cap for C1 so I used a 330 pF polarized electrolytic cap with the negative pin going to ground.
I used polarized caps for C5 (470 pF, negative pin connecting to the "input" of the drive pot) and C3a (1uF, negative pin going to ground).

Anyway, bypass mode no problem but when engaging the circuit there is little sound and the sound "stutters". This is with my mp3-player as input signal, when using the guitar I don't hear any sound at all. When probing the circuit, the sound stutters right from the input tip. No matter if it's boxed up or spread out on the bench.

Some voltage readings (GGG values in parenthesis):

Battery: 9,10V
After D1: 8,42V

Q1:
G   0 V     (0)
S   0,46 V (0,95)
D   4,42 V (4,5)

Q2:
G   4,02 V (3,8 )
S   4,42 V (4,5)
D   8,43 V (8,0)

Q3:
G   0 V     (0,3)
S   0,05 V (0,75)
D   4,38 V (4,3)

Q4:
G   4,01 V (3,8 )
S   4,38 V (4,3)
D   8,43 V (8,0)

Q5:
G   0 V     (0,5)
S   1.09 V (0,9)
D   4,68 V (3,4)


Any ideas or hints at troubleshooting? Have I missed something obvious? I've done a couple of simple projects but this is my first "serious" circuit.
:roll:

[gotdabluz]

barring anything else you have welded into the circuit, have you tried adjusting the trimpot?

do this as you are running a signal (preferrably your guitar) thru it and make small adjustments in either direction to guage the effect on the output

I would guess that this is the probable root of your problem

[b97pla]

barring anything else you have welded into the circuit, have you tried adjusting the trimpot?

do this as you are running a signal (preferrably your guitar) thru it and make small adjustments in either direction to guage the effect on the output

I would guess that this is the probable root of your problem

Thank you, I have adjusted the trimpot so that the drain voltage on Q5 would be close to the GGG value... I will try playing around with it but my feeling is that the stuttering will be there regardless of the setting of the trimpot. Has anyone else experienced this?
Can it be the polarity of C5 that is wrong?
:?

[transient]

If you're not sure about the cap polarities, you can use two caps in place of one to get a non-polarized cap.

Simply use two polarized caps that are 2x the required value in this series configuration:

---[+ -] [- +]---

For example, you would use two 1000pf (1nf) caps in place of a 470pf cap.

...
emre

[Connoisseur of Distortion]

where on earth did you find a 330 pf electro?  

[b97pla]

where on earth did you find a 330 pf electro?  

Ok, now you're freaking me out..  :? Did I get uF? I'm gonna have to double check!

[transient]

I haven't seen any electrolytic pf caps either. But you seemed so sure that i assumed you somehow had 'em

The lowest value electrolytic cap i know is 1uf (one million pf).

.
e

[gotdabluz]

Thank you, I have adjusted the trimpot so that the drain voltage on Q5 would be close to the GGG value... I will try playing around with it but my feeling is that the stuttering will be there regardless of the setting of the trimpot. Has anyone else experienced this?
Can it be the polarity of C5 that is wrong?
:?

It could very well be something else, but you should still try adjusting the trimpot . . . the GGG values are close to ideal, and because of the variance inherent in FETs Q5 may not be completely happy with what you are feeding it.

I too had a stuttering problem at first with my BSIAB even though it was set 'properly' . . . a little tweaking to the trimpot eliminated my problem.

If that doesn't work, someone else here with more knowledge may be able to help.

Personally I would have built it as is first, and then add in tweaks once I knew I had it working properly.  At least then you may have been able troubleshoot a little easier.

[SaBer]

If you have a 330µF cap as C1, then you are basically shunting all of your signal to ground.  But, if its polarized, it might act strangely, when the signal coming in turns to the "wrong" polarity. Anyway I would check for C1 first...

[b97pla]

If you have a 330µF cap as C1, then you are basically shunting all of your signal to ground.  But, if its polarized, it might act strangely, when the signal coming in turns to the "wrong" polarity. Anyway I would check for C1 first...

Alright, now I've checked and of course I had soldered in a 330 uF cap... I guess that makes me the idiot of the day here..  :oops: I blame it on too much late nights breathing solder fumes.
Anyway, thanks for the help!