another neovibe question

[dfarrell]

I've just finished putting together my neovibe. I haven't boxed it up yet, and I am in the process of testing it out. It seems to be working so far, but it is making a "wump wump wump" sound when it is turned on. You can't hear it when you are playing something, but it is noticeable when you are not. Is this normal?

[R.G.]

Perhaps leakage of the LFO into the audio path. Is this in synch with the LFO? Does it change with the speed pot?

If so, you have LFO bleed. Could be a number of problems causing it.

[Zedmin_fx]

mine does the same thing, its kinda cool

[dfarrell]

Yes , it is in sync with the LFO, and it does change speed when I adjust the speed control. Any ideas as to what I can do?

[R.G.]

As hackneyed as it sounds, go read "what to do when it doesn't work", follow all the instructions.

Check all the device voltages. And in this case, also check the voltages before and after the 7815 regulator. Post them here.

[dfarrell]

Here are some voltages:

Before the 7815, the voltage is 15.05 Volts. After it it is 22.08 volts.

For the transistors (all are 2n3904)
q1 c = 2.10, b = .88, e = 0.94
q2 c = 4.02, b = 2.17, e = 1.54
q3 c = 11.45, b = 4.00, e = 3.44
q4 c = 15.06, b = 4.26, e = 4.35
q5 c = 11.38, b = 4.29, e = 3.70
q6 c = 15.04, b = 4.25, e = 4.22
q7 c = 11.41, b = 4.25, e = 3.64
q8 c = 15.04, b = 4.27, e = 4.23
q9 c = 11.36, b = 4.27, e = 3.63
q10 c = 15.05, b = 5.29, e = 5.28
q11 c = 22.04, b = 4.01, e = fluctuates from 9.58 to 13.75
q12 c = 22.01, b = fluctuates from 10.01 to 13.08, e = fluctuates from 9.33 to 14.01
q12 c = 21.06, b = fluctuates from 3.70 to 5.51, e = fluctuates from 3.80 to 5.01

[yeeshkul]

the same thing was happening to me, when i turned a buffer on at the input and Neo was not boxed up. So i put the enclosure on, tighten it up and the sound was gone. I bet it is gonna disappear when you put your neo in a box.

[dfarrell]

That would be nice! It sounds fine otherwise. What size box did you use?

[R.G.]

Yeah, I think that the box is the next thing to try. I didn't see any gross issues in the voltages, which is a positive thing. Try boxing.

[yeeshkul]

don't freak out before you tighten the screws so the enclosure shields the circuit all around -  Mojo Vibe does the same thing by the way .. i thought i damaged my friends Mojo first because i put the enclosure on but no screws and the bloody thing kept howling 
any box that is low enough that you can stomp on it is without using a chair ok haha

[dfarrell]

I don't have anything around here big enough to put it in, so I thought I would make box out of wood to put it in. (I've got lots of that!)
but I didn't think about shielding it.  I do have a roll of copper shielding tape, I suppose I could line the inside of the box with that?!?

[dfarrell]

I think when I was boxing it up, I shorted something out.  I had to replace the wall wart because I wasn't get any voltage. Now that I've replaced it, I am getting power, but the light won't flash, and the depth control isn't having any effect on the brightness. I've gone through and checked my voltages, and they are the same as above, except for q11, and q12
which are:
q11 c=21.01, b=16.7, e=21.02
q12 c=22.1, b=21.1, e=20.07.
So something else must have fryed, could it have been the diodes? or . .?.
. . .  and now the light bulb which was working when I started typing is not working anymore 

[R.G.]

Q11 base-emitter is shorted - either the device itself or something outside it is holding its emitter at the same voltage as the base.

[dfarrell]

I've replaced q11, and there is no change. I have checked under the board to see if there is anything shorting it out, but I can't see anything. Should I try replacing components around it? Or is there something else I should try? This was working at one time. 

[R.G.]

How about using an ohmmeter to see what's shorted to what?

If it was working at one time, something has changed. I know it's frustrating. But patience and persistence is the key here. Pull the board out. Does it now work? Hmmm... maybe something about how it's mounted in the box is causing this.

I would not have guessed a bad transistor first.

[dfarrell]

It is not in the box. I took it out before I replaced the power supply and rechecked the voltages.  I am thinking that when I had it mounted in the box, something was touching the box and that caused the power supply to burn out. Now that it is out of the box with a new power supply hooked up and all the voltages are as before except for q11 and 12, I am wondering if something in that part of the circuit was also damaged. Could the diodes or maybe a capacitor have been damage, and maybe that is the the source of my problem?
Does that sound reasonable?

[R.G.]

It is not in the box. I took it out before I replaced the power supply and rechecked the voltages.  I am thinking that when I had it mounted in the box, something was touching the box and that caused the power supply to burn out. Now that it is out of the box with a new power supply hooked up and all the voltages are as before except for q11 and 12, I am wondering if something in that part of the circuit was also damaged. Could the diodes or maybe a capacitor have been damage, and maybe that is the the source of my problem? Does that sound reasonable?

Sure, it's possible. But you have a big piece of information - Q11 is shorted. If you have replaced it and the short is still there, it's probably not the transistor, but rather something on the board. And the short is between emitter and power supply. None of the caps, diodes, etc go between emitter and power supply. There aren't many things that do.

If it were me, I'd examine every bit of the copper between the emitter of Q11 and V+ for any possible short. Right at the transistor is probably first place to start. Use a magnifier. Use your ohmmeter.

Find the short. You can. You already know how.

[dfarrell]

It works! After much poking and proding, I replaced r40 (it's resistance was way off) and then q12.  I put a new bulb in, and gave it a quick sound test, and I am back in business. Thanks for sticking with me and talking me through this R.G. You were a big help!

[R.G.]

KEwl. You DID already know how to fix it! Now go make LOUD noises!