Neovibe done. Cant get a slow speed. Help!

[FuzzAldrin]

Finished it up. Worked on the first try to my amazement. Everything sounds great, except that the speed knob only works on the last 1/2 inch of travel.
I cant get it slower at all. If I try, the lamp just dies out. Ive messed with the bias trimmer and the offset mod.
Im using the lamp from small bear, and the recommended pot as well.

Any help in getting the depth more shallow? If I even touch the intensity/speed knob, the bulb quickly dies off.
It sounds great, I just need it tweaked, I guess. 
Thanks!

[R.G.]

What do we do when something doesn't work right?

[FuzzAldrin]

   I will post some voltages in a few hours. I think that is what you meant.

[FuzzAldrin]

Using 18V PS...

All transistors are 5088 except Q13 (2N3904)
R35/36 replaced with 250K in series (offset mod?)

Q1
C = 1.908v
B = 1.308
E = 0.891

Q2
C= 4.99
B= 1.918
E= 1.415

Q3
C= 10.49
B= 1.918
E= 4.38

Q4
C= 15.04
B= 4.75
E= 4.37

Q5
C= 11.26
B= 4.37
E= 3.76

Q6
C= 15.04
B= 4.76
E= 4.36

Q7
C= 11.29
B= 4.36
E= 3.76

Q8
C=15.04
B= 4.77
E= 4.38

Q9
C=11.27
B= 4.38
E= 3.77

Q10
C= 15.04
B= 6.01
E= 5.51

Q11
C= 17.08
B= 8.25
E= 9.55

Q12
C= 17.08
B= 9.55
E= 8.95

Q13  (2N3904)
C= 15.87
B= 2.35
E= 1.692

D1
A = 8.80
K = 8.85

D2
A = 8.85
K = 8.90

[FuzzAldrin]

Im back. Here are some photos. Not the best. Sorry for the long as wires. I didnt expect it to work 100% off the cuff, but will shorten and clean them up once its fully functional.

[SonicVI]

I used that same photocell/lamp setup and couldn't get a good sound. The lamp just wouldn't get bright enough.  I had much better results with the the little grain of rice bulb from Radio Shack.
http://www.radioshack.com/product/index.jsp?productId=2102815   

[zeeman]

Why did you socket the transistors? Why not just solder them in?

zeeman

[FuzzAldrin]

Why did you socket the transistors? Why not just solder them in?

zeeman

Does it really matter if I used sockets?? As long as you properly insert them in the socket, it should be fine. I did that to ease debugging if I needed to replace one.

[FuzzAldrin]

I used that same photocell/lamp setup and couldn't get a good sound. The lamp just wouldn't get bright enough.  I had much better results with the the little grain of rice bulb from Radio Shack.
http://www.radioshack.com/product/index.jsp?productId=2102815   

Thats very interesting. Would you say it was a considerable difference in sound? Were you having the same problem as me? My build "works" and sounds great at higher speed, but once I start decreasing that speed, the light just dies off.

I called the shacks near me, and one of them have that bulb (last one). I will see if I can get one tomorrow and put it in.
But, does anyone spot anything bad in the voltages???
Any other ideas/advice/suggestions?

[R.G.]

The reason I wanted to look at it in depth is that it was possible that the speed pots were interfering with the operation of the LFO through misconnection. That seems to be eliminated by the voltages.

I think you may have a transistor gain problem a pot problem. What you describe, an LFO simply quitting, is what happens when it runs out of gain. In this case, current gain in Q11/Q12. I never use sockets any longer, as transistors are much cheaper than sockets, and I hardly ever replace one. But you may be lucky on this one. Swap a few spare transistors for Q11/Q12 and see if it changes.

What is the value and taper of your speed pot?
Check the values in the LFO again. All correct?
What "offset mod" did you use?

[FuzzAldrin]

The reason I wanted to look at it in depth is that it was possible that the speed pots were interfering with the operation of the LFO through misconnection. That seems to be eliminated by the voltages.

I think you may have a transistor gain problem a pot problem. What you describe, an LFO simply quitting, is what happens when it runs out of gain. In this case, current gain in Q11/Q12. I never use sockets any longer, as transistors are much cheaper than sockets, and I hardly ever replace one. But you may be lucky on this one. Swap a few spare transistors for Q11/Q12 and see if it changes.

What is the value and taper of your speed pot?
Check the values in the LFO again. All correct?
What "offset mod" did you use?

Awesome, thanks. Makes sense.
The speed pot is from smallbear. "Alpha Dual-Gang 24mm REVERSE Audio Taper 100K, For Univibe clones and repairs"
Im sorry, the offset mod isnt an offset mod. I just have a 250K trim in R35/36 to adjust the mix for the deepest phasing...
Ok... I replaced Q11 and 12. Same voltage readings.
I also reflowed the joints.
Im gonna dive in the LFO and check values now.

[FuzzAldrin]

<sigh>

Had the damn speed pot wired incorrectly. 

Im an idiot.



But, I tweaked the mix trim and dialed in the most beautiful, lush vibe sound Ive ever heard. This is so excellent. Thanks a milloin RG for your help and for rev. engineering it in the first place. Wow. This sounds incredible.