I've built a ZenDrive clone from a kit and there is something wrong with it (it's the 9:th build, and first one to malfunction :icon_mrgreen:). The Volume goes from nothing to about unity and the Gain does nothing, so I guess there's something wrong with the gain part of the circuit. ::)
(https://s17.postimg.org/q1xy0qwh7/page2image9336.png_kopia.png) (https://postimg.org/image/q1xy0qwh7/)
I've tested the diodes and transistors with my multimeter (diode test setting), not removed from the circuit. Diodes shows 419-422 (ohms?) and transistors S+ to D- 687/686, S- to D+ 1291/1140 (S to G the same), G to D 0 (beep).
Are both transistors blown (static shock?), or have I toasted them (in previous pedals I have managed to solder 7 germanium transistors without destroying them, using same method with heatsink) or is it something else going on?
Quote from: voskarp on March 24, 2018, 12:48:28 PM
the Gain does nothing
Have you checked the gain pot itself? That's the first place I'd look.
Yes, measured from 1 to 2 & 3 0-0.45 M ohm, about as it should.
Bad soldering on R3 or the Voice pot, perhaps? If there's a broken connection in that string of components to "Va", then that op-amp is basically an unity-gain buffer built with far too many parts ;)
That was my first thought. There are other possibilities, I'm sure.
Tom
OK, I'll look for that.
The Voice pot changes the sound though, but I don't know if it is like it's supposed to be.
Here are some voltage measurements.
(https://s17.postimg.org/c9o4ihkp7/page2image9336.png.png) (https://postimg.org/image/c9o4ihkp7/)
I get 0v at 1, 2 & 3 on the Voice pot. ???
At R3 it's 4.78v.
Deeply suspicious!
Sounds like you're getting warm to me.
T.
I can't see any bad solder joints and the Voice pot measures (in circuit):
1 to 2 0 Ohm
1 & 2 to 3 0-9.7 kOhm
The strange thing is that on the VA side of C3 I have 4.88 v but on the Voice pot side (and on all pins of the pot) there's 0 v, so 0 v on Voice pot pin 3 BUT 4.77 v on both sides of R3! :o
Broken strands and short circuit to GND at the Voice pot?
(https://s17.postimg.org/fwq3jfjmz/schematic_text.png) (https://postimg.org/image/fwq3jfjmz/)
(https://s17.postimg.org/5zf2qfh6z/BOM_Circuitboard.png) (https://postimg.org/image/5zf2qfh6z/)
Quote from: voskarp on March 24, 2018, 01:30:08 PM
OK, I'll look for that.
The Voice pot changes the sound though, but I don't know if it is like it's supposed to be.
Yep that's the idea. It's an RC filter to tune the distorted signal.
It's a wierd one.
Did you swap the tone and gain pots by mistake?
Are the IC1B pins all around 4v5?
Gain 500k and Voice 10k.
IC:
1. 4.8 v
2. 4.78 v
3. 4.58 v
4. 0 v
5. 4.76 v
6. 4.78 v
7. 4.79 v
8. 9.8 v
Quote from: voskarp on March 25, 2018, 04:56:24 AM
(https://s17.postimg.org/fwq3jfjmz/schematic_text.png) (https://postimg.org/image/fwq3jfjmz/)
There's no way you've got 4.77V at one end of R3 and 0V at the same end of the Voice pot! They're connected together!
Unless they're not? Is that a clue?
Tom
Yes! 8)
But I really can’t see that the solder joints are bad.
Could just resolder anyway, no big risk of toasting resistors I guess...
Otherwise it must be the PCB track that is broken, or..?
<The Volume goes from nothing to about unity and the Gain does nothing>
That shows a unity gain non-inverting buffer on IC1A - something in the R3-Voice-C3-VA order is "open"..
Try to disconnect C3 upper leg from VA and connect it to any convenient GND..
(although I agree with you and Tom for a broken connection between R3 & VOICE pot so just place a wire jumper between them.. )
Thanks for the tips, I'll try that.
The jumper wire between R3 and Voice pot worked, now I'm off to play some guitar... ;D
Thanks everybody!
Excellent! Glad to hear you got it sorted!
T.