Tycobrahe - Parapedal  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
armdnrdy1
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Post by armdnrdy1 »

Did you read Jim's post?

I never thought to check your resistor values because ...I thought you would have double checked that before ever asking for help.

with R14 a 1K instead of a 1M pull down...you are pulling the signal down to ground! No wonder the signal disappears at the beginning of the circuit!
R15 at 1M instead of 1K will effectively block the signal as well.
Then the signal will get sucked to ground at the end of the circuit with R15 as a 1K.

Check ALL component values and change them to the correct, listed values.

armdnrdy1
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Post by armdnrdy1 »

Not Jim's post... Intripped's post.

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Post by JimSalabim »

Oh no!! Seems I really swapped the 1K and the 1M resistors …
I have just put them in the right place, but still no sound. I’ll do another check with the audio probe in a few hours and also check all other resistors again…
Thanks so much so far!!

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Post by JimSalabim »

OK. I have checked the values of all components now and hit every solder connection again.

The result of the audio probe:
Bildschirmfoto 2015-06-13 um 13.40.21.png
The voltages at the opamps are now:

U1:
Pin 1: 3,77 V
Pin 2: 2.32 V
Pin 3: 1.368 V
Pin 4: 00.1 mV
Pin 5: 1.368 V
Pin 6: 2.83 V
Pin 7: 2.38 V
Pin 8: 7.80 V

U2:
Pin 1: 7.05 V
Pin 2: 1.335 V
Pin 3: 1.368 V
Pin 4: 00.4 mV
Pin 5: 1.368 V
Pin 6: 1.363 V
Pin 7: 7.07 V
Pin 8: 7.78 V

armdnrdy1
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Post by armdnrdy1 »

Okay...

You still have something going on.

The voltages from your reply @ 17:15 had the reference voltage at 2.9V...now it's down to 1.3V.

Pull the op amps and take voltages again.

Take a close up picture of the whole component side of the board.

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Post by JimSalabim »

Voltages without op amps:

U1:
Pin 1: 4.43 V
Pin 2: 2.60 V
Pin 3: 4.82 V
Pin 4: 00.0 mV
Pin 5: 4.82 V
Pin 6: 4.75 V
Pin 7: 4.78 V
Pin 8: 8.37 V

U2:
Pin 1: 4.81 V
Pin 2: 4.82 V
Pin 3: 4.82 V
Pin 4: 00.0 mV
Pin 5: 4.82 V
Pin 6: 4.82 V
Pin 7: 4.75 V
Pin 8: 8.37 V
IMG_5456.jpg
On the left in the heat shrink tubing there’s a a 180 K and a 470 K resistor in series to get the desired 650 K for R1. I also tried it with a single 680 K, but it didn’t change anything.

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Post by JimSalabim »

Do you think the op amps are damaged, since there is no signal at output B at U1 (pin 7)?
Should I just get new ones and try again? Or could there also be another problem (more damaged components)?

armdnrdy1
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Post by armdnrdy1 »

At this point....I'm out of ideas.

I would get rid of the sockets for the resistor and diode. Solder those components to the PCB directly.

There seems to be intermittent bias voltage issues at pins 3 and 5 of the op amps.

Some voltage readings are in the ballpark and then next readings the bias is off.

You can try new op amps but....I think the problem is elsewhere.

Keep on it and if you don't get it going soon...I would start from scratch with a new board.

It's not that large of a circuit so...strike this one up as a "ghost in the machine!"

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Post by kymar »

I think you turned this thread in Pedal Debugging & Troubleshooting Support.

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Post by JimSalabim »

OK, thank you so much for all the help!
I’ll have another try with new op amps and soldering the components to the PCB directly. And if it still doesn’t work, I’ll try to get the layout on a breadboard and then on a stripboard.
I could also try the positive ground schematic then.

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Post by armdnrdy1 »

kymar wrote:I think you turned this thread in Pedal Debugging & Troubleshooting Support.
Was that really a necessary comment?

Are you the forum police?

:horsey:

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Post by kymar »

Unfortunately there is no any police here

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Post by JimSalabim »

I think I found the mistake. My pot wiring (I had posted a pic of it here) is completely wrong. Pot A is Pot B and Hot is Cold ... :slap:
I'll change it tomorrow and let you know if it works.
Maybe this was not the only mistake, but perhaps the last mistake left :)

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Post by JimSalabim »

Since the board is still not working, I have reconstructed daverdave’s vero layout based the geofx schematics and the small preview image of the vero layout which was still on Google.
This one’s positive ground now.
I’ll build this next week.
Parapedal.jpg

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Post by JimSalabim »

YES! It works! Sounds amazing! :D
I have added a negative voltage inverter to the stripboard (http://tagboardeffects.blogspot.de/2012 ... erter.html). Daisy chaining on the pedal board also works fine now.
Thanks again for all the help!

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Post by JebemMajke »

What other diode i might use?

Great work btw

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Post by JebemMajke »

It has been almost 3 years since I made it.

It is like ... wow ... the greatest wah for what i need. :)

Guys, what pots do you use?

I've been through all kinds, cheap, expensive, plastic, metal ... they all go bad after 2-3 months of usage.

I've read on the other forum that some guys suggest led/ldr conversion.

How?

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Post by JimSalabim »

Yes, that would be interesting. I have tried 3 or 4 Alpha pots and It always sounds a bit scratchy while moving the pedal in the lower range. I don’t know if the pots are the problem.

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