Sunn beta lead - unstable sound Topic is solved

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vincea
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Post by vincea »

Hi all,

I recently purchased a Sunn beta lead kit (schematic pcb guitar mania here https://pcbguitarmania.com/wp-content/u ... g-Docs.pdf). After soldering everything, I just have a huge hissing sound, sometimes with kind of distortion, but nothing else, the sound is pretty unstable and reacts really bad to any note I can play.

The circuit is built around a charge pump that is supposed to deliver -15/+15 from a LT1054, and this component is really overheating as soon as I plug the pedal.

I checked the current delivered after the charge pump and where I'm suppose to have -15/+15, I get -2/+15.4 when all other chips are installed. If I remove the chips, I have something close from -16/+16, and I installed every chip one after the other to see if all is still correct. With only all the RC4558 installed, I still have something close from -15/+15 (exactly -14.5/15.4, but I guess it's ok?). At the moment I install the CD4069 chip, the voltage drops to -2/+15.4.

As experiment, I changed the LT1054 for a 7660S (compatible if you add jumper between 1 and 8 ). Same behavior, without any chip, I have what I need, with the RC4558, I have something close, but with the CD4069 installed, voltage drops again, and the LT1054/7660S is overheating.

I changed also the CD4069 for a new one, but same behavior.

I checked the compared from here ( https://pcbguitarmania.com/wp-content/u ... g-Docs.pdf) with the one proposed in this thread (viewtopic.php?f=2&t=25813&p=285584&hili ... ta#p285584) and I found only one difference, the pin 7 of the CD4069 is connected to the -15 in the schematic from pcb guitar mania, but it's not in the schematic from freestompboxes (connected to ground in this one). So I tried also to bend the pin 7 and to connect it to ground, this time, I have less hissing sound, but the LT1054/7660S is still overheating and the sound is pretty bad, extremely unstable.

I checked all my soldering, there is no "false contact" (not sure the name in english), diodes looks just fine, they are in the righ side and capacitors looks ok.

Is anyone had the same issue? Or does anyone knows what I could/should test/try next to make this pedal works?

Thanks!

EDIT> Here are pictures of the board, I dont know if it can help or not. This version is the version with the pin 7 of the chip connected to ground. When I try with another chip, I just removed this one and connect the other (could the fact that I keep it connected to the ground, but to nothing else, when I'm testing other chips introduces perturbations in the circuits?)
sunnbetalead-front.jpeg
sunnbetalead-back.jpeg

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FiveseveN
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Post by FiveseveN »

vincea wrote: 27 Feb 2022, 07:24 pin 7 of the CD4069 is connected to the -15 in the schematic from pcb guitar mania
I disagree :D
4069.png
4069.png (4.45 KiB) Viewed 302 times
The 4069 is 18V absolute maximum, so it will definitely fry at 30V. Since everything seems to work without it, I would try a different chip, maybe test it beforehand.
Do you have a scope/audio probe? How about a +/-15V power supply to check it without the charge pump?
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

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vincea
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Post by vincea »

Wow! Did my eyes betrayed me? I was sure...

EDIT> Ah, ok, I found the issue... The building document that was linked in the website where I purchased the kit is this one: https://pcbguitarmania.com/wp-content/u ... -Docs1.pdf where the pin 7 is hooked to the -15. This version is from 13 march 2021.

The one I linked (thinking it was the one I used) is actually from the 18th january 2022 and there is a special mention saying: "The first version of this board has a mistake with the path tracing that makes the power drop down once
the CD4069 chip is placed on board.
This issue no longer exists in the current 1v3 version".
Meaning, I have the first version of the board! I purchased the kit at musikding, it seems that they shipped me the first version of the board.

Consequently, I looked for the "in between" version of the document, which I found here: https://pcbguitarmania.com/wp-content/u ... Docs14.pdf (also from the 13th of march 2021). This document have the modification I need to do to fix the issue.

I just did the modifications and all works! Strangely, the 7660S generates less noise than the LT1054, no super high pitch annoying sound.

Anyway, thanks so much @FiveseveN !!! Without your comment, I would have never checked the document again and see the "Warning" section this revision! Again, thank you, this building is hauting me since 3 weeks!

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