Electrovibe mini no effects

[guitarDan444]

My EV mini build went pretty well. Everything fit and visually works but I'm not getting any pedal affect. The bulb works. the bias pots work. the speed control works. The volume works. The bulb can be adjusted down to dim and up to very bright. The same goes for the pulsing , adjustable from very slow to fast.

There is a noticeable volume drop switching from corrus to vibrato.

I measured voltage in various locations. I've got 9.1 coming in but only 16.8 where the schematic shows 18 and 12.6 where the schematic shows 15. Could I have a defective LT1054 or 1N5817?

I did correct the switch PCB in the photo, upside-down oops .

 

[RobinMallard]

I finished my full size electrovibe recently and also didn’t have any effect at first, just clean. I’d suggest measuring the voltages on your transistors, that’s how I found a short to ground. That was on the dual pot, which shouldn’t be your problem here but I find that helpful in trying to isolate problems. Also I’d use an audio probe to see where you loose signal.

Vibrato cuts out the dry signal, so if you’re not getting effect that would make sense.

What’s going on with the resistors on the left side of the top board?

Edit: I think I used the same purple enclosure as you!

 

[andrewsrea]

You are getting the correct voltage from the 12V voltage regulator (L78L12), as I would expect 15V is a typo.
You should be getting around 17.4VDC at the juncture of D5 (1N5817) and R29 (47R), although 16.8VDC isn't unusual considering device tolerances and the current load on the 18V circuit.

The volume drop perceived is normal. Chorus is achieved by an equal part vibrato added to an equal part clean signal. The volume drop isn't exactly half, because some of the clean and vibrato frequencies (in chorus mode) are phase-cancelled or partially cancelled. My Fulltone Deja Vibe does the same thing,

 

[guitarDan444]

Thanks for the quick response. That gets me a little closer!

 

[guitarDan444]

I finished my full size electrovibe recently and also didn’t have any effect at first, just clean. I’d suggest measuring the voltages on your transistors, that’s how I found a short to ground. That was on the dual pot, which shouldn’t be your problem here but I find that helpful in trying to isolate problems. Also I’d use an audio probe to see where you loose signal.

Vibrato cuts out the dry signal, so if you’re not getting effect that would make sense.

What’s going on with the resistors on the left side of the top board?

Edit: I think I used the same purple enclosure as you!

The purple looks good right .
I didn't have a large enough resistor so I soldered 3 in a row to get the value. I since replaced it with a single 2.1M. it didn't change anything.
I like the idea of using an audio probe. I'll have to figure out how to rig that up.
My electronic trouble shooting skills are low. When you suggested to check voltage shorts to ground I assume the potential go to 0 at the short. Is that correct?

 

[RobinMallard]

When looking for shorts to ground, yes you're basically just trying to see if there are places that should have non-zero voltage, but show as 0 when you measure one of the legs to ground with you DMM.

I mostly pointed out the transistors in the electrovibe because there are a lot of them, and they do the signal amplification in the filter section instead of opamps in other phaser like pedals. In my case, I was looking for places where the collector doesn't have something around 12-15 V (probably 12 as discussed above), and then the emitters should also be non-zero since it carries the signal from the first transistor to the second in each pair or in the case of the second transistor, has a resistor before ground, so it can't have a zero voltage.

An audio probe is actually really easy to make, I have a spare jack, a 100 nF box cap and a bunch of leads with alligator clips. Clip the ground lug of the jack to a ground in your pedal, and then the tip lug to an alligator clip lead that attaches to the cap. Finally a lead from the cap to use as your circuit probe.

Also, make sure your testing with the cover closed as light impacts the lfo's interaction with the filters.

 

[guitarDan444]

Wow, what a great explanation!! Thank you.
I did a first pass checking for shorts, nothing yet. I'm almost as interested in figuring out the audio probe as the figuring out the problem. Well maybe not that level. I really am looking forward to my purple electrovibe!

 

[guitarDan444]

Solved! I was checking voltages on the ldr's and found ldr4 really low compared to the others. I traced out that part of the circuit and found an open between R54, R55 and C20 and soldered in a jumper. See picture. Everything works! I may have damaged the trace earlier, when I swapped out a wrong resistor value. My repair skills are awful. I'm amazed at pulling this off. Thanks for the help. Couldn't have done it with out it!