Author Topic: help troubleshooting  (Read 775 times)

mlhuff

help troubleshooting
« on: January 29, 2019, 04:19:07 PM »
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

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Re: help troubleshooting
« Reply #1 on: January 29, 2019, 04:53:30 PM »
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

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Re: help troubleshooting
« Reply #2 on: January 29, 2019, 05:14:08 PM »
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

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Re: help troubleshooting
« Reply #3 on: January 29, 2019, 05:19:45 PM »
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
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

Re: help troubleshooting
« Reply #4 on: January 29, 2019, 07:53:53 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

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Re: help troubleshooting
« Reply #5 on: January 29, 2019, 11:28:35 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

Re: help troubleshooting
« Reply #6 on: January 30, 2019, 05:31:42 AM »
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
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mlhuff

Re: help troubleshooting
« Reply #7 on: January 30, 2019, 06:09:06 PM »
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