Germanium Tchula boost debugging

[Reg18]

This is my first post here and probably no surprises it's a debugging one!
I am new to pedal building and have no experience in electronics but have been really wanting to build a great fuzz with a boost.
After successfully building a Fuzz Face, Tone Bender Mk1.5 and finally settling on a Zonk Machine MK2 germanium fuzz as my favorite of them I have been working on a good boost to go in the enclosure.
I've built a lovepedal Tchula with a pnp germanium transistor and although it sounds just fine it drops out when engaging or disengaging. Any suggestions?
Example of the boost here
https://www.youtube.com/watch?v=ZfWWcMwEsx8
And here is the Zonk Machine MK2 with bass and bias as well.

https://www.youtube.com/watch?v=zbYpqCMJyh0

[antonis]

HI & Welcome.. 

Dropping out (in case you refer on Volume..) is caused due to shunt to ground diode pair..
Output signal amplitude is restricted to diode(s) forward voltage drop..
(any voltage coming out of transistor Collector of amplitude higher than the above mention value is "clipped"..)

P.S.
All schematics refered on Tchula include hard clipping diode pair but (of course..) they don't call it "boost"..
Could you plz post a schematic of your particular build..??

[iainpunk]

welcome to the forum,

what antonis said makes a lot of sense, we need the schematic and we would also like the voltages on the 3 transistor legs before and after bypass, my suspicion is that those are different fore some reason, which in turn makes the sound cut out.

cheers, Iain

[Reg18]

This is the schematic I used, I only used one electrolytic and swapped that to suit the pnp germainium transistor. I think I swapped a couple of values as I didn't have exactly the same, the output cap used was an 80nf, and the 3.3m was 3m. I might try removing the clipping diodes and see what that does from
What your saying.

[PRR]

....I only used one electrolytic ..... I think I swapped a couple of values...

There's two e-caps on the plan; which one did you skip?

You can't tell us what values you "swapped"?

But yes, this plan does have a problem when gain is switched from low to high. Add a 5k to 10k resistor directly across the switch so the 47u cap holds a charge.

[Reg18]

....I only used one electrolytic ..... I think I swapped a couple of values...

There's two e-caps on the plan; which one did you skip?

You can't tell us what values you "swapped"?

But yes, this plan does have a problem when gain is switched from low to high. Add a 5k to 10k resistor directly across the switch so the 47u cap holds a charge.

The 47u was changed for a 33u and is not electrolytic, I also didn't add the switch in so the gain pot is always engaged. This sounds like it could be my issue,I'll first try removing the diodes as they are socketed so an easy first step, then I'll try and find a 47u electrolytic for that spot. I'll report back.

[Reg18]

So I removed the diodes, still the same.
I switched out the cap for a proper electrolytic 47u cap and it still does the same.
I did notice it only does it on when disengaging though, not engaging.
It cuts out and slower rises back up to volume.

[antonis]

I still can't get your issue..

When you say "engaging - disengaging" do you refer on switch or complete effect (pedal)..??

P.S.
I think your old radio spares junkbox might include some degraded items..

[Reg18]

I still can't get your issue..

When you say "engaging - disengaging" do you refer on switch or complete effect (pedal)..??

P.S.
I think your old radio spares junkbox might include some degraded items..

Have a look at the first linked video, when you engage (click the footswitch) it is fine but when you disengage (hit the footswitch to turn off pedal) the volume drops out and slowly fads back in. Does that make sense?

[PRR]

We do not usually kill power to a pedal to disengage it; only switch the signal to go "around" the pedal.

Actually killing power is liable to make ugly turn-on/turn-off sounds.

[11-90-an]

Hi and welcome....

Can we see your footswitch wiring diagram? Also, pictures of your off-board wiring

[Reg18]

Hi and welcome....

Can we see your footswitch wiring diagram? Also, pictures of your off-board wiring

I essentially copied this off board wiring, I haven't added an LED yet though. And the positive from battery snap is linked to the grounds and negative is where the positive is in the diagram.
In my pic blue wires are input, green is output and the black is ground (joined to all the other positive grounds)

[willienillie]

I see 2 transistors, a 680K resistor, a 100K trimmer...these things don't jive with the schematic you posted.

Nevermind, more than one circuit in the box.

[willienillie]

And the positive from battery snap is linked to the grounds

Normally it would go to the ring terminal of a stereo (input) jack.  That disconnects the battery when you pull the plug, if you don't have a power on/off switch.  That wouldn't cause your volume drop though.  Can we see more of your wiring?

[iainpunk]

... we would like the voltages on the 3 transistor legs before and after bypass, my suspicion is that those are different fore some reason, which in turn makes the sound cut out.

i'd like to restate this here! what are the voltages on the transistor and the switch, if there is a DC on there, that would induce some problems like these. especially in this situation, both engaged and in bypass, that would probably help us a lot.

cheers, Iain

[Reg18]

... we would like the voltages on the 3 transistor legs before and after bypass, my suspicion is that those are different fore some reason, which in turn makes the sound cut out.

i'd like to restate this here! what are the voltages on the transistor and the switch, if there is a DC on there, that would induce some problems like these. especially in this situation, both engaged and in bypass, that would probably help us a lot.

cheers, Iain

I'm fairly new to measuring voltages so you may have to guide me through it a little bit.
Here's my first attempt, 9v battery putting out 7.89v
Collector 6.65v base 0.23v emitter 0.11v
Footswitch 6.65v on output to circuit board and 0v on output to output jack, 6.65v on both when footswitch is engaged.
I have hardwired the 47u to ground to try and elimatnate the whole gain pot part of the circuit to see if that was the issue, still no luck. The gain pot didn't appear to be working when I had it connected anyway so I think I've done something wrong in that area.

[willienillie]

Did you forget your output cap?

[Reg18]

Did you forget your output cap?

Yep you were right! I did have it in but the output wire wasn't connected in the right spot, not even sure how it was working at all but it works now and no drop out!
Thanks for help guys!

[iainpunk]

Did you forget your output cap?

Yep you were right! I did have it in but the output wire wasn't connected in the right spot, not even sure how it was working at all but it works now and no drop out!
Thanks for help guys!

that's exactly why i asked for the voltages, there shouldn't be any DC on the switch, ever.

willie nillie, was this what gave it away?

6.65v on both when footswitch is engaged.

cheers

[willienillie]

willie nillie, was this what gave it away?

6.65v on both when footswitch is engaged.

cheers

Well, same voltage on collector and output wire.