Red House Forum Vibe debug help please

[tungngruv]

I built the "Redhouse" version of the Univibe. All trim pots and controls are working (Volume, Speed, Chorus/Vibrato switch, Intensity). No "Vibe" is happening though even though the bulb (Smallbear Lamp, 12 Volt 40 ma. Bi-pin # 7371 and Photocells Smallbear #338-54C679) are pulsing and reacting to all the trim pots and controls, When I switch it to Vibrato, the Vibrato is very wiggly and promising but has a huge volume drop. When I switch it to Vibe, it's much louder with no phasing at all going on. Almost like it's bypassing the effect entirely. Here is the link to the schematic/layout:

http://www.lynx.bc.ca/~jc/ForumVibe.pdf

The version I built is on pages 13 and 15. 

I used all 2n5088's except for Q10, 11 and 13, which are MPSA13's.

All jumpers are in place including the ones to allow using one power source, I also triple checked all resistors values, triple checked all transistor orientations as well as all cap values and all were OK. The 1uf's are all 50v non polarized. I'm getting 15.35 volts from my Dunlop adapter.

Here is the list of voltages in this order (E, B, C) using page 13 in the above link:

Q1 - .914, 1.35, 2.07

Q2 - 1.46, 2.07, 5.14

Q3 - 4.51, 5.14, 10.66

Q4 - 7.10, 4.85, 15.38

Q5 - 6.97, 7.11, 8.38

Q6 - 4.40, 4.82, 15.38

Q7 - 3.79, 4.40, 11.60

Q8 - 4.44, 4.86, 15.37

Q9 - 3.81, 4.44, 11.55

Q10 - 5.15, 6.19, 15.38

Q11 - the Emitter and Base jump from 4v to 9v and back down again, over and over. The Collector stays at 15.37

Q12 - the Emitter jumps from 5v to 7v, the Base jumps from 6v to 9v and the Collector jumps from 10v to 12v, all going up and down although this slowed down slightly with the intensity knob being turned.

D1 and D2 also jumped around the same voltages as Q12.

I hope this is enough information for someone to point out my error. I appreciate any help in getting this up and running. Also thanks to Brad for taking the time to put this together and everyone else who helped get this awesome project together.
   

[John Lyons]

Nothing stands out to me...hopefully brad will chime in with the expected voltages.
I'm sure it's something simple.

Bump!

John

[tungngruv]

OK, I rechecked everything and from looking at all of RG's posts, the most I can make out of this is that Q4's Emitter is higher than the Base, which shouldn't be happening.

Also, it turns out that I am getting the "vibing" effect, it's just a lot less volume than unity gain. When I switch it to vibrato, it's like running my amp with the effect bypassed, no effect whatsoever.

I'm really getting frustrated with this. This is about the first effect that I haven't been able to get right.

I think I may take a break for a few days....

[John Lyons]

I think the problem is somewhere in the mid section (phase stages) or in the mixing stage at the juction of the phasing and preamp stages.
If the vibrato is weak then it's not going to mix well with the preamp stages to create the chorus/phase.
Either the phase stages are not right or the mixing stage is off somehow.

EDIT:You  posted just as I was...
I overlooked that voltage reading on Q4.
If everything look ok component wise around Q4 then try swaping out the transistor.
Do the values measure ok for the resistors around Q4?
I'm sure you do it but I have become anal about measuring resistors before I put them it...

john

[tungngruv]

Yeah, I checked all the resistors before (and after) mounting them. I also replaced Q4 and got the same result. Thanks for the help anyway John, much appreciated. I think this ones going on the shelf for a while.

[R.G.]

The circuit around Q4 and Q5 is hosed. Just replacing Q4 or Q5 is unlikely to fix it.

Since there are so few parts there, meaure the DC voltages across each component, resistors and capacitors and report them. That will probably tell where the issue is.

I haven't examined the PCB so I don't know if the layout is correct or not. Let's presume it is until we find otherwise.

[RedHouse]

Sorry for the delay tungngruv, I've been out of the country for 3 weeks.

Send me a PM with your email address.

[RedHouse]

Ok Tony, here is a chart of the voltages from two of these boards I have running on my bench right now:
(using separate 15.4VDC supplys for LFO and Audio)

Q1-Q9 are 2N5088, and Q10 is an MPSA13:



Q1 - .92, 1.33, 2.03

Q2 - 1.45, 2.03, 5.19

Q3 - 4.5, 5.19, 10.6

Q4 - 4.45, 4.85, 15.4

Q5 - 3.85, 4.45, 11.6

Q6 - 4.46, 4.8, 15.4

Q7 - 3.85, 4.4, 11.5

Q8 - 4.46, 4.8, 15.4

Q9 - 3.85, 4.46, 11.5

Q10 - 5.2, 6.18, 15.4


As was said before somethings not right with your Q4 and Q5 voltages, look in this area...again.
(your emitter voltage seems high)

Q4
Your - 7.10, 4.85, 15.38
Mine - 4.45, 4.85, 15.4

Q5
Your - 6.97, 7.11, 8.38
Mine - 3.85, 4.45, 11.6

Doublecheck you have the right values for R13, R14, R15 and R16 as these set the bias for those transistors. Q5 looks specially bad.

When I switch it to Vibrato, the Vibrato is very wiggly and promising but has a huge volume drop. When I switch it to Vibe, it's much louder with no phasing at all going on. Almost like it's bypassing the effect entirely.

There should be NO volume drop as you describe.

It should be the same volume when in CHORUS or VIBRATO mode, there must be something wrong with the way the Chorus/Vibrato switch is wired.

Normally in the VIBRATO mode the volume is relatively constant level (when input is constant) and in CHORUS mode varies as the two signals start to cancell out in each sweep.

Note the univibe's "Chorus" mode is the phase-shifted/cancelled sound like in Robin Trower's "Bridge Of Sighs" or "Daydream", an oscillation between Thin-n-Fat sound, the VIBRATO mode has an actual pitch shift and has no cancellation (a warble sound).



-Brad

PS; I will update the PDF with a voltage chart when I can.

[R.G.]

As I said, tungn', if you can post the DC voltages across each component, it's likely that we can just tell you what part is bad or needs more work.

It's obvious from the first set of voltages that Q4 has some problems, and since its emitter is so much higher than its base, it can't be passing audio, hence the huge volume drop.

[RedHouse]

...When I switch it to Vibe...no phasing at all going on....Almost like it's bypassing the effect entirely.

I'm assuming you have put the light shield back on when testing this on the bench? if you leave it off the light in the room will cause the vibe to shift and stay shifted causing apparently no phasing at all going on allmost like bypassing the effect entirely. 
(don't laugh, we've all done it!)

[yeeshkul]

for Brad: great job! Thanks Brad for the great effort and the clean result  .

I have 2 questions:
1. In my build (Neo) i also noticed that the volume of the "funny" chorus(aka vibrato) was a bit above the vibe level. I picked the mixing 100k resistors from about 15 pieces, so they were the same value. What can be the other reason for the difference? I noticed in some Vibe clones there was 100k resistor at the output of the vibrato instead of 47k ... it looks like they wanted to put the vibrato volume a bit down ...?
2. How does the darlington at the last phase stage affect the sound?