Author Topic: Mudbunny farting out  (Read 3092 times)

TNblueshawk

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Mudbunny farting out
« on: June 27, 2012, 08:37:37 AM »
Well, seems I get 4 working builds to 1 with an issue. Frustrating but what am I gonna do. Dirtbag fires right up and then this low part build....arghh...  :-[

Anyhoo built the 'old' Mudbunny board to Creamy D specs. Works fine in bypass. When engaged I get that farty sound. You know the one where when you build a fuzz and bias trimmer is all geeked up until you adjust it sound. Problem here is there is no bias trimmer.

Q4 is the issue as you will see from the voltages. Problem is I don't know where to go next. I put a few days between the build and troubleshoot to hit it with a fresh brain but I think I need a jump start. I've reflowed and no bridges anywhere.

Voltages for all the 5088's are:

Q1  through Q3 all the exact same     
C: 0             
B:.57     
E: 4.08   

Q4:
C: .16
B: .75
E: .22

So I worked back from Q3 and checked voltages for those parts from there to Q4 as I'm losing something.
Voltage on each lead

C10v 1.01-4.05
R19v  3.16-4.02
C12v 1.89-.75
R20v 9.36-.75
R21v 0-.75

Tone pot:
1 = 3.16
2 = 1.89
3 = 1.01

Mids pot
1 = 0
2 = 0
3 = .15

Any one have any thoughts on where to concentrate? I'm not sure on what the norm should be for voltage drop but R20 sure looks screwy and C12 doesn't have much going into it.

John

mgwhit

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Re: Mudbunny farting out
« Reply #1 on: June 27, 2012, 10:20:43 AM »
Search the Tech Help forum fpr 'creamy dreamer q4' and you'll get at least three threads all saying the same thing -- something around Q4 makes it sound awful.  I don't know if anyone has successfully built the Mudbunny according to the Creamy Dreamer specs from the build doc and have it work without some tweaking.

TNblueshawk

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Re: Mudbunny farting out
« Reply #2 on: June 27, 2012, 12:10:40 PM »
Search the Tech Help forum fpr 'creamy dreamer q4' and you'll get at least three threads all saying the same thing -- something around Q4 makes it sound awful.  I don't know if anyone has successfully built the Mudbunny according to the Creamy Dreamer specs from the build doc and have it work without some tweaking.

Wow thanks Matthew. Just read all 5 threads that pop up on the search and frankly I'm a little pissed. I'll leave it at that.

Well at least I have 2 options to try now to get it working off those threads.

Thanks for the heads up.
John

TNblueshawk

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Re: Mudbunny farting out
« Reply #3 on: June 28, 2012, 07:16:23 AM »
In case someone uses the search button like I was advised this is fixed. I simply inverted Q4 and all is well. Of course I don't know how true to CD specs it is with that reversed but it works and sounds like a Muff. I did not do anything with the resistors as suggested in some of the other trouble shoot threads.

Big thanks to Matthew for alerting me to this issue as I had already spent a few hours scratching my head.
John

mgwhit

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Re: Mudbunny farting out
« Reply #4 on: June 28, 2012, 07:40:42 AM »
Glad you got it working!

I wish we knew more about what's happening at Q4 in that circuit.  Is there just too much gain for that transistor to handle?  Would another transistor handle it better?  Obviously others have fixed the problem by lowering the gain in previous transistor stages.

And why does inverting Q4 fix the problem?  Does that make it act like a cathode follower (buffer)?  Or is Q4 completely off and the signal is just going through R20 and R22 to the output?

LaceSensor

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Re: Mudbunny farting out
« Reply #5 on: June 28, 2012, 07:47:47 AM »
had this same issue. flipped q4 fixed it.
q4 should just be an output buffer I think.
worst case is the overall volume wont be as loud, but I recall it being fuck loud anyway, so this isnt losing anything. I used 5088s

greysun

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Re: Mudbunny farting out
« Reply #6 on: June 28, 2012, 08:07:21 AM »
So this seems a little crazy... However, I have to ask the question (Blueshawk, we'll talk outside of the forum about your issue)...

Does the new 2012 layout have the same issue? I was planning to try a CD, but also got all the parts to build a Mayo and a Violet Rams head. I was gonna just swap out the different parts once I figured out which one I liked most.

Has anyone tried the 2012 layout with the Creamy Dreamer Specs yet?

Let us know - let's get the issue fixed for the future generations...

... and the children of the future generations. ;-)

plesur

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Re: Mudbunny farting out
« Reply #7 on: June 28, 2012, 08:23:54 AM »
Try changing R22 to 2k2 instead of 22k. The orientation of the transistor is correct on the silk screen for Q4 for a 2N5088.

TNblueshawk

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Re: Mudbunny farting out
« Reply #8 on: June 28, 2012, 12:40:56 PM »
had this same issue. flipped q4 fixed it.
q4 should just be an output buffer I think.
worst case is the overall volume wont be as loud, but I recall it being fuck loud anyway, so this isnt losing anything. I used 5088s

Your old thread is the one that made me flip it. And yes, it is loud like a Muff should be.

Q4 must still be in the circuit thoug because when I pulled it out it went dead....hmmm...that didn't come out right  :P
John

TNblueshawk

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Re: Mudbunny farting out
« Reply #9 on: June 28, 2012, 12:41:41 PM »
So this seems a little crazy... However, I have to ask the question (Blueshawk, we'll talk outside of the forum about your issue)...

Does the new 2012 layout have the same issue? I was planning to try a CD, but also got all the parts to build a Mayo and a Violet Rams head. I was gonna just swap out the different parts once I figured out which one I liked most.

Has anyone tried the 2012 layout with the Creamy Dreamer Specs yet?

Let us know - let's get the issue fixed for the future generations...

... and the children of the future generations. ;-)

Sounds like your going to be the first  ;D
John

plesur

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Re: Mudbunny farting out
« Reply #10 on: June 28, 2012, 02:47:22 PM »
I got my suggestion about R22 from this vero layout by IvIark
http://tagboardeffects.blogspot.co.uk/2011/05/sustain-punch-creamy-dreamer.html
It says that it is farty because Q4 is misbiased.

TNblueshawk

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Re: Mudbunny farting out
« Reply #11 on: June 28, 2012, 02:58:18 PM »
Ah, good info.

You notice in my post that this is how it sounded...like say a one knob fuzz that you first fire up before it is biased, so this would be in line with that.

Hmmm, I hate to mess with it now that it is working (I'm not superstitious but ....) but maybe I should swap out the resistor just for poops and giggles to see what it does.
John

LaceSensor

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Re: Mudbunny farting out
« Reply #12 on: June 28, 2012, 04:27:41 PM »
I used the transfer artwork in the new 2012 document to etch my own, so ....

TNblueshawk

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Re: Mudbunny farting out
« Reply #13 on: June 29, 2012, 07:01:32 AM »
In the interest of science I popped in a 2.2k and flipped Q4 back to how it should be per the PCB and that worked. I'm unable to compare the sounds as I would have to have played it the other way for a while to get it into my head. A smart man would have socketed R22 but no, I'm not very smart.

So, is it something as simple as Brian only needs to change the BOM and it might have been an error all along? Sure would save a lot of frustration.

Just my 2pf's.
John

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Re: Mudbunny farting out
« Reply #14 on: June 29, 2012, 07:44:28 AM »
According the the tracing schem I have 22k is correct. I've added a note to the project doc that it may be incorrect and to substitute 2k2 instead. I suspect 8k2-10k might be fine, as well.
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