Electra distortion

[Denchy1]

Hi I have build my first pedal / amp. The amp is the chime amp circuit and is working well. I also have the Electra distortion circuit switchable by foot switch. This is based on the 10 min dirt pedal on YouTube, with the optional diode switching and the input resistance pot and volume pot. My problem is when I activate the switch volume drops a lot although the signal still passes and no distortions appears to happen even if I crank the amp stage. Any ideas why this could happen?

[GibsonGM]

Hi, welcome to the forum....go here, and post the information asked for back here.   We'll have a look for you!  Usually problems like this are pretty simple, often just wiring mistakes.

Can you also post the schematic you worked from?

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[Denchy1]

The switching error from the video schematic has been corrected so as not to output to ground on the boost setting
My lead to the output pot is on the back of the board after the output cap.

Any help much appreciated

[PBE6]

The switching scheme appears to be incorrect. As drawn, when the diodes are disengaged the output is sent directly to ground. Just snip those grounded wires (the ones NOT attached to the diodes) and you should be fine.


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[Denchy1]

Thanks PBE6 yes you are correct I had already changed this. My problem now is my signal is much lower with the Electra circuit on in either switch position than just the amp on its own?

[peterg]

The schematic calls for a 3M3 resistor but you have a 2M2 resistor on your board. Check the other component values to make sure they match the schematic. Please post a photo of the copper side of your board so we call see how the connections are laid out.

[Denchy1]

Please excuse the hot glue on the board as I had stuck it down. The wire goes to the output pot.

Yes I have 2M2 as this was what the guy had in the BOM on his website for the build. On circuit lab it works when simulated with these values. Cheers

[karbomusic]

I've seen Electra with both 2.2 and 3.3M and don't think that is your problem. You do want two 1n34a Ge equivalents for the diodes due to their low forward voltage. Silicon's (if I remember) may give less that satisfying results, via the circuit not being able to drive them hard enough and/or still have enough volume left over. Also if you are trying to switch between no diodes and diodes, you'll get some volume loss with the diodes in IIRC. I've built that exact circuit a number of times so I know it works.

[GibsonGM]

Do you have a DMM (multimeter)?  Some voltages would be helpful...that was what that 'debugging' page was about.

This could be as simple as your 3904 being in backwards, but without the voltages it is hard to say much...

[Denchy1]

Thanks for all your suggestions so far.
Yes I have one in my toolbox at work I'll probe some voltages at lunchtime and post them up tomorrow.

[brianq]

Have you tested without switch in circuit? +1 on measuring voltages Gibson.

[GibsonGM]

Just part of the debugging, it will tell you a lot...say the voltages are normal...tranny in backwards, or burned up?  Etc.

When I build anything, I connect in/out jacks to the circuit board, and 'try it out' before boxing it and wiring up the switch.  If the board works, it makes future debugging much easier!  Then you can blame the switch, or the old 'it's touching the enclosure' thing...

Electra is so simple, if the voltages are ok, and the transistor is in right and not dead...miswired switch or jack, something like that.

[Denchy1]

So all my transistor pins are high which is why i suppose when i play through i can get a very low signal only just detectable. as the signal is passed through the transistor loosing alot of voltage as it passes through.

Guess this means the transistor is either damaged or there is a short somewhere?

[Kipper4]

Is R1 3M3?
Those voltages dont look right at all.
even if the base was 7.9v the emmitter should be a diode drop (0.5-0.7v) lower than base

Edit
I just put it on the breadboard (no Clipping diodes)
subbed values 490ohm emmitter in place of 470ohm
3M2 feedback / base Biasing in place of 3M3
4k7 collector as per schematic
had to sub some values cause I have an ongoing large breadboard experiment going on,Thanks Duck Arse.

Voltages
C 6.7v
B 0.86v
E 0.24v

maybe you have a short?

[anotherjim]

Such a high value base resistor, the meters input impedance will load down the base voltage it measures - it could read lower than it really is while the others are true. Rather, probe voltage from transistor base to emitter. If that is a 2N3904, it looks to be the right way around in the picture - left to right ebc?

Check your 680R emitter resistor value with the meter resistance test - I can't see all of the body code in the pic'.

[Denchy1]

Thanks anotherjim, I think you've nailed it. I had 680 k not 680 I will try to find an resistor thats close and try. I had checked before the value but when .680 came up on the meter i had assumed it correct but on 2M setting this is obviously 680 k... Ill try this and then post the results.

Edit : just simulated on circuitlab and if i put 680 k all the pins of the tranny go high

[Denchy1]

I found a 470 R in the lab swapped it out and now the effect seems to work... Thanks guys will be more careful with my components next time

[GibsonGM]

Congratulations on your first debug, Denchy 

[anotherjim]

Cool

[Jamdog]

Now can we hear it?  😂