Vibrato Question for RG/Mark ....

[MartyMart]

Guy's just finished the "Ersatz Vib" yesterday and I'm not getting any lfo just yet !
Used 5953's rather than 5952's - sheets look VERY similar, so just checking that the problem
isn't there ?
Matched pairs of 1.9v and 1.68 as required.
Vero built - own layout, have sound and have "vib/phase" if depth pot is moved around, just no
lfo or any action from the "rate" pot ( dual 100k )
My layout went "as schem" but I had to "reverse" the Q7/8/9 section from right to left, so perhaps I
screwed a "node" up here ..... it was a bit of a brain teaser to lay it up "on the fly"
All ground / power / nodes "look" to be good and test fine on DMM, perhaps the 1k's have locked up
the rate to "0" !!
Hmmm , I'll persue it some more, I think it's 95% there .


SUBS :
5953 for 5952
pair of 200k's for the 220k's
Input pulldown "r" 1m not 2m2 ...... that's it
Power switched via "normal" stereo jack not the 3906, 100ohm across 9v then reverse prot diode and 100uf filter.
Voltage divider gives 1.7v for the Vcc.

[MartyMart]

I'm reading Q5/Q6 as :
Drains from the 22uf's
Source has the 1.7v Vsrc
Gates have 1m's ground and 1 uf's off to Q9's collector and emitter respectively  ??  right ?
De-bug, can't find a single "wrong node" it's just not "lfo'ing" .....

[R.G.]

In any debugging problem except the most simple ones, the first step is always divide and conquer.

You're in luck (relatively...). The problem is entirely the LFO, not the JFET signal path. You divided that out by noting that the thing seems to do vib/phase if you diddle the depth pot. In fact, Q9 and Q8 are probably OK. It's likely that the problem is all with Q7.

If you are concerned about the layout on Q7/8/9 that's probably where the problem is. Check your layout and wiring again. The phase shift oscillator, of which this is one, requires some picky conditions to be just so to oscillate.

Check the transistor DC voltages for an obvious out-of-bounds condition, then check the wiring of the speed pot.

[markm]

My first build of this had the same issue......BAD Pot! 
Not saying that's the cause but, I didn't even think to check the pot out and that's what it was.
Like R.G. said though, you are so close on this it's not funny!
And on VERO?
You are Brave aren't ya Marty!! 

[MartyMart]

Thanks guy's ... yup it's SOOOooooo close to working !! damm it !
Got it down to 6.5cm x 4 which isn't bad, could be even smaller ( 1590BB is fine )
Could be pot, but it's a brand new alpha dual 100k log .....
I've fine tooth combed the board with mag glass and nodes/soldering are all A-OK
I'll check out that pot and wireup again ...
So the 5953's should be OK ??

MM.