Author Topic: Mudbunny VRH - no output.  (Read 1065 times)

Superstereosix

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Mudbunny VRH - no output.
« on: January 28, 2014, 02:32:06 PM »
Hey guys, finally got this muffer together and got nothing when I put it through the test rig..
Q1: Vc=3.8v, Vb=0.62v, Vc=0.03v
Q2: Vc=4.12, Vb=0.65v, Vc=0.06v
Q4: Vc=4.53v, Vb=1.73v, Vc=1.16v

I think I've located the problem around Q3.
Vc= 8.49v
Vb= 0v
Ve= 0v

R15 has 8.49v on the collector side and 0v on the other.  I figure it's open; R14 and R16 both read 0v on both sides..
I'd like to know what do you guys think before I start.. 

Any other readings I should take?  I switched the 5088 I had in Q4 with Q3 initially and got the same basic readings.
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Superstereosix

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Re: Mudbunny VRH - no output.
« Reply #1 on: January 28, 2014, 06:11:16 PM »
Took a couple of pictures after I reflowed everything around Q3.
R15 is the 470k metal film 3rd up from the bottom right hand side.
I'm gonna take it out and see if I get the same results. 

I'll also check the continuity of the traces while its out.
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madbean

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Re: Mudbunny VRH - no output.
« Reply #2 on: January 28, 2014, 06:30:33 PM »
I would also check for continuity on pads near that resistor to make sure there is none where there should not be. It's always (though rarely) a possibility.
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Superstereosix

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Re: Mudbunny VRH - no output.
« Reply #3 on: January 28, 2014, 07:09:45 PM »
Lifted one leg of R15 and it measures 466k.  So its not open.
Checked all continuity and everything is where it should be.
I'm gonna take an old tooth brush to it.  Wash away some flux..

Anybody have a Violet and could take some readings?

Might have to put this down till after work tomorrow..
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Superstereosix

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Re: Mudbunny VRH - no output.
« Reply #4 on: January 28, 2014, 07:33:38 PM »
Possible C10 issue?  Loosing current into the next stage?
Not shorting out with continuity tester.
This is the one mod I made in the circuit.  I couldn't get a 4n cap so I put a 3n9 in there.
Don't think it would cause this.

Gonna put R15 back in.
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Superstereosix

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Re: Mudbunny VRH - no output.
« Reply #5 on: February 07, 2014, 09:54:07 AM »
Finally figured out what I did after inspecting everything.
Had a 100ohm instead of 100k in R14..
Ain't gonna get any gain like that… Hate those dumb mistakes.  Hopefully the 2 double flushes have simple issues…

Q3 now reads:
Vc: 3.76v
Vb: 0.62v
Ve: 0.03v

Still kinda low maybe.  I'll have to try to get some sound out of it.

Found some good analyses of the big muff like this:
http://www.electrosmash.com/big-muff-pi-analysis
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Superstereosix

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Re: Mudbunny VRH - no output.
« Reply #6 on: February 08, 2014, 07:29:05 PM »
another issue: really low output.

seems common, gonna track the signal when I get the chance during the week.
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Blues Healer

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Re: Mudbunny VRH - no output.
« Reply #7 on: February 10, 2014, 01:33:22 AM »
Please check the orientation of D4.

Also, I've looked at some of my notes ... although I haven't built the violet version,  your voltages appear OK to me: the emitters and bases all have the correct swing, and the collectors are about right.
« Last Edit: February 10, 2014, 10:03:10 PM by Blues Healer »
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