Author Topic: 8 ball - bluesbreaker like - oscillation?  (Read 138 times)

add4

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8 ball - bluesbreaker like - oscillation?
« on: June 30, 2018, 12:29:45 AM »
Hello guys,

So i am building a 2015 8 ball (i know, i know, i'm late in my builds).
The circuit is working, but unstable. When i push the gain up, D1 and D2 (LEDs) light up alternatively, like 10 times a second. And the circuit produce a kind of motorboating sound.

Funilly, I had the same issue with the same circuit when i breadboarded it, and with another bluesbreaker type circuit I built before. But not with madbean's King of klones which works perfectly. So i guess it's a common problem for this circuit topology

Does anyone know why this happens? and more importantly, how to solve this?

Thanks


add4

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Re: 8 ball - bluesbreaker like - oscillation?
« Reply #1 on: July 01, 2018, 02:38:54 PM »
anyone?
do you need something specific to help with this?

Tremster

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Re: 8 ball - bluesbreaker like - oscillation?
« Reply #2 on: July 02, 2018, 05:12:06 AM »
This seems to be a common problem with the 8Ball/Bluesbreaker:

http://www.madbeanpedals.com/forum/index.php?topic=17904.msg172052#msg172052

add4

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Re: 8 ball - bluesbreaker like - oscillation?
« Reply #3 on: July 02, 2018, 01:54:09 PM »
thanks, some things to try there. I think it's a common problem indeed.


madbean

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Re: 8 ball - bluesbreaker like - oscillation?
« Reply #4 on: July 03, 2018, 10:02:06 AM »
So, there are a couple mods I did on this circuit to try and squeeze as much gain as possible out of it. But, it seems like I went too far. The two changes are in the first and second gain stages.

To eliminate the problem try reducing R8 from 270k to 220k. If that solves the motorboating stop there. If not, either 1) replace R16 with 150k or 2) change the Gain pot to 100kB and remove (or clip one lead) of R16.

My apologies for the hassle. Please let me know what you find and I will update the build doc accordingly.

I own madbeanpedals (duh). I am part owner of Function F(X).

add4

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Re: 8 ball - bluesbreaker like - oscillation?
« Reply #5 on: July 03, 2018, 12:36:25 PM »
Thanks! i'll try that and let you know how it goes!