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Hey all –
I’ve built up two Green Russian Muff’n fuzzes, and both have the same issue. There’s basically no fuzz, and a significant volume drop when they’re engaged. Both pass audio just fine. The tone knob seems to work as intended, the volume does its normal thing.
I’m going to start going through with an audio probe this weekend, but I’m wondering if I did something stupid easy to fix that someone could point me in the right direction (if you’ve run into the same thing).
I’ve had good luck with the one knob fuzz and rat deluxe kits, so this will be my first time debugging a build.
Hi Barry,
Apologies. Here’s the shots of the pedal.
For this one, I couldn’t quite the pot tangs through the holes, so I elected to just run some wires to them. The other one I did (which has the same issue) I did get the tangs through the holes, so the pots are on the board.
I’m not really sure what I’m getting through the audio probe. It appears that audio is getting through, and it’s just not distorting through the transistors?
Appreciate your help.
If it were me I would clean up all the solder joints on the back of the PCB.
Make sure you are using a cleaned, tinned, conical solder tip and make sure that the solder you are using is not too large in diameter.
While I would re-flow everything to simultaneously pull extra solder off the joint where there is too much and make sure that the solder flows into the joint. You solder joints should look like little Hershey Kiss candies. Nothing more or nothing less. If you get too much or too little you will end up with cold solder joints. I can tell you after doing support for 14 years here 80% of the time the issue is due to a cold solder joint.
Here are two areas of the PCB that have me especially concerned.
I am not sure if this will help but it shows what I mean by conical tip and proper solder diameter.
And one last thing is regarding shorting out the back of the PCB inside the enclosure. I do not see in your photo any kind of protection since you are not using right angle pots to mount the PCB safely to the enclosure. That may not be the case but I thought I would mention it.
Thanks!
Ok, I’ll take a look at those joints and reflow them to see what that does. I am using the pot covers, so I don’t think anything is shorting out to the board. For the other build, I was able to get the tangs through the holes, for this one they weren’t long enough to get through (they just barely poked through and I was worried they wouldn’t hold), so I just clipped them and ran wires.I do find it weird that both of the builds had the exact same issue, but perhaps I’m super unlucky and messed the same joint up twice.
R7 looks like a 100R (brown black black black brown) and not a 1K (brown black black brown brown) it may just be reflection but in the screenshot the 4th band looks black
This means that depending on the sustain pot position more signal would get dumped to ground
There are a lot of components in this circuit that can affect the gain so if you haven’t already check all component values and orientation are correct
Thanks guys. I went and reflowed some of the joints, and that improved the volume loss. It’s no longer below unity, so that’s cool. Seems like the gain is still not up to where it needs to be. Quick question – I’m not seeing the LEDs light up on any of the clipping mode toggles when I’m playing through it. Should they actually light up?
Billy – I did check that resistor, I think it’s just the light in my other picture. It appears correct I think.
I’ll probably just start de-soldering and reflowing everything from scratch. I appreciate all the help.
My continued advice would be to re-flow the entire project as you said. It isnt always necessary to suck up the solder since often you can pick up excess solder with your iron tip and then remove it on a wire scouring pad (like a brillo). This also prevents cooling down your tip. Then just clean and repeat. It also helps to tin the tip every once in a while.
After you do all of that then make sure all of your transistors are firmly seated in the sockets before you test. A loose transistor is as bad as a cold solder joint.
If that does not solve the issue then look carefully over your entire build by color band as Billy suggest for an error in resistor value which would explain a similar gain issue as well.
Beyond that an Audio Probe is also recommended.
An Audio Probe is a fantastic tool to easily locate a problem area
Audio probe the collector of each transistor stage ie the output
Start at Q1 with everything maxed in each switch position if that’s OK move onto Q2 etc that may highlight your problem area
As Barry advises reflow all solder joints It won’t take long just hold your iron tip on each joint for around 6 seconds until you see a nice solder flow that makes a good connection between component pin and solder pad
Post your transistor voltages for Q1 to 4 E, B, C pins
Reflowed the joints. Still have the same issue.
Transistor voltages are:
Q1: E 8.13, B .593, C .04
Q2: E 8.13, B 0.594, C .04
Q3: E 7.62, B 0.574, C 0.033
Q4: E 8.46, B .760, C .215
I didn’t socket them, but they’re all checking about an Hfe of 500, so I think they work?I’ll go start checking color coding now, I’m sure it’s possible I mis-placed a resistor. I appreciate your guys’ help. If you’ve got any other suggestions, please let me know.
Thanks!
-Peter
Hi Guys, I’ve checked all the color coding for each resistors / caps against the BOM Sheet, and Variant Sheet that are in the instructions. Everything appears to be correctly placed. I did notice that on the BOM sheet Readme instructions, it says to leave R27 blank (which i did), but in the variant sheet it has R27 listed as a 1k. I didn’t get a 1k resistor in the kit, so I assume it’s actually supposed to be blank?
In any case, I’ve ordered another kit, hoping that the third time is the charm. I figure that if I can get one working, I can use that to guide my audio probe of the other ones that aren’t currently functioning.
Your transistor voltages look off I don’t know if you’ve mixed your emitter and collector pins up but even if you have they’re not correct
Those readings you’ve given for the emitters are way too high are those readings with your black probe to ground and red probe to each pin
You’re getting audio through the circuit so they can’t be correct
What transistors are you using
R27 is the LED current limiting resistor only required if you mount your LED to the main pcb
Yea. I’m taking the black off the ground from the footswitch PCB, and measuring the DC voltage on the emitter leg (I think).
I’m using the BC549s that came with the kit.
Picture below is my reading off the first leg of Q1 using a battery to power it off the DC Jack.
The transistors are the wrong way around, the board, according to the build doc is laid out for 2N5088s afaik BC549s have the opposite pinout
But double check trying to work out pinouts by orientation from a datasheet isn’t my strongest point
That would make sense using the same transistors in each of your builds they’d not conduct properly I’d expect the output to increase significantly once you turn them around
With the current collector voltages at less than 0.7v the diodes wouldn’t conduct and clip the signal so hopefully that’s it
You’re right. They’re 100% reversed on the data sheets. And on the build that I didn’t clean up, I’d socketed the transistors. Flipping them made it work as it should. It’ll be more labor intensive to flip the ones on the board I posted the pictures of above (because I stupidly didn’t socket them), so I’ll get to that Friday.
Really appreciate your help! I probably never would have gotten there in my own. Rather frustrating that I didn’t see any warning about this anywhere in the build doc. Maybe I missed it. Either way, glad it’s working now. And I’m sure my bass player will appreciate having a couple spares 🙂
Glad it’s working Peter if I’m honest I rarely read the entire build document but I’ve got a DCA75, it’s on page 4 of the 2020 v3.5 doc page 5 of v2 doc
I’m sure you would have got there in the end it’s an easy mistake to make we’ve all done it
To remove the soldered in transistors if you don’t have a solder sucker just do one pin at a time or angle your iron tip on all 3 joints at the same time then you should be able to wiggle it up and out
If you have a solder sucker add more solder this way it melts much easier and is easier to suck out obviously be careful you don’t damage the pads only heat for a maximum of 6 to 10 seconds if you have a small croc clip, clip that across the transistor pins as a heatsink
Get yourself one of these cheap testers they’re pretty good gives you transistor pinout + hfe and tests diodes, inductors, capacitors etc
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