help troubleshooting

Started by mlhuff, January 29, 2019, 04:19:07 PM

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mlhuff

I recently purchased and built a tycho brahe clone from general guitar gadgets. I get sound when the pedal is off. But when i turn it on, nothing. I am new to this and would like some help. I have looked up articles and videos but I havent found anything to help me trace the signal through the pcb and what voltages I should be getting.
Any help with this would be appreciated


GibsonGM

Hi ML, welcome!

Go here, read this, and see if you can provide the info requested back here in your post.  That will get us started   :icon_mrgreen:
These things are usually a builder error, poor soldering, the wrong part put in the wrong place and so on.  Taking it thru the process will help figure out what's going on!

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

Just noticed something odd, won't help OP though.  The GGG schematic has Q1 backwards (it works either way), but it is correct on the actual PCB they sell.

GibsonGM

Good find. 

Might as well toss this in here too, how to make an audio probe to trace the circuit, since OP asked about it.
https://www.diystompboxes.com/pedals/debug.html
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MXR Dist +, TS9/808, Easyvibe, Big Muff Pi, Blues Breaker, Guv'nor.  MOSFace, MOS Boost,  BJT boosts - LPB-2, buffers, Phuncgnosis, FF, Orange Sunshine & others, Bazz Fuss, Tonemender, Little Gem, Orange Squeezer, Ruby Tuby, filters, octaves, trems...

PRR

Quote from: thermionix on January 29, 2019, 05:14:08 PM...The GGG schematic has Q1 backwards...

The schematic is correct as drawn. The as-drawn power supply is Negative hot, POSitive ground. The gizmo is a feedback pair, complementary NPN-PNP, with a Darlington in the PNP position. Q1 should be a NPN and should be in normal mode (not inverted).

To show the action I have re-drawn without the AC parts, without the Darlington frill, so reduced resistors around Q1. It biases-up fine. Q1 forces Q2 Collector to follow Q1 Base, nearly. All polarities are correct.

Making the 2nd stage a Darlinton, making a 3-stage amplifier, allows making Q1 a higher impedance, more suited for guitar.

If you are saying Q1 should be "inverted" (C and E swapped), that would negate much of the advantage of a 3-stage amplifier, lower the input impedance. It may not be significant, depending what drives it.

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thermionix

Quote from: PRR on January 29, 2019, 07:53:53 PM
The as-drawn power supply is Negative hot, POSitive ground.

I'm aware, but the actual Tycobrahe Octavias had Q1 (NPN) installed the "wrong" way with emitter toward (+) ground.  The circuit runs either way.  This schematic matches the 70s originals, and the GGG PCB:



italianguy63

Quote from: thermionix on January 29, 2019, 11:28:35 PM
Quote from: PRR on January 29, 2019, 07:53:53 PM
The as-drawn power supply is Negative hot, POSitive ground.

I'm aware, but the actual Tycobrahe Octavias had Q1 (NPN) installed the "wrong" way with emitter toward (+) ground.  The circuit runs either way.  This schematic matches the 70s originals, and the GGG PCB:



+1

We had a thread on Q1 orientation sometime back..

Yes, the orientation works either way  (verified by me).. for what that is worth!

MC
I used to really be with it!  That is, until they changed what "it" is.  Now, I can't find it.  And, I'm scared!  --  Homer Simpson's dad

mlhuff

Thank you for the suggestions. I am reading up on what I need and building an audio probe. Trying to find an electronics store near me. Once I have this info I will post results