Volume lost debug on Mudbunny [edit] - Sound like a beast now :)

[Gledison]

hey guys, as usual i have to post some problems with my last build. It was working fine but i didnt know that the volume should be muuuch louder. I've read some posts and followed some suggestions.
i cann hear the full power on Q2 but in Q3 its the same as with my output, much lower.
ive changed transistors , 5088's and the same issue.
i was poking with the audio probe and i noticed a decay in volume on C8. One side is loud and the other side is quiter, but i dont know if this is normal or not.  Capacitors can reduce input volume or just filter frequences?
thanks for any help

[madbean]

Could you list the values used on the resistors on Q3? An incorrect value could have a big impact on output.

[Gledison]

Could you list the values used on the resistors on Q3? An incorrect value could have a big impact on output.

Hey Brian, thanks a lot for helping mate!
so, lets see if iget it right:
R15 has 0,60V on the Base of Q3 and 6,4V on the collector of Q3 conected to C8
R13 has0,60V on the base of Q3 and 0,60V on the lead connected to C7.
R16 has  0,07V on the collector of Q3 and 0V on the ground
Is it R16 too low?
[edit]: something weird in R15, when i mesured the resistance, it showed 80k, i removed, and the resistor was ok.
thanks again Brian!

[Gledison]

.

[muddyfox]

something weird in R15, when i mesured the resistance, it showed 80k, i removed, and the resistor was ok.

You can't measure resistances in-circuit (well, some you can but you need the schematic) because you're likely measuring some parallel or serial/parallel combination of that and other resistors and other parts of the circuit. Try going by color bands first and only remove if you're fairly certain that you have a wrong value in place.

[Gledison]

something weird in R15, when i mesured the resistance, it showed 80k, i removed, and the resistor was ok.

You can't measure resistances in-circuit (well, some you can but you need the schematic) because you're likely measuring some parallel or serial/parallel combination of that and other resistors and other parts of the circuit. Try going by color bands first and only remove if you're fairly certain that you have a wrong value in place.

Yeah, i was almost sure about it as well! in the end i removed it and installed a new one. i hate to see the colours on this tiny bastards , and on the metal ones, purple, red , wine, for me are all the same ,im not colour blind, but colour  lazy
Do you know if a capacitor can reduce Volume as well? i´ve noticed that after C8, my volume drops and wondering if that might be the problem.
thanks Muddy

[midwayfair]

Do you know if a capacitor can reduce Volume as well? i´ve noticed that after C8, my volume drops and wondering if that might be the problem.

Think of a capacitor as a short (a piece of wire) for all frequencies above a certain point. It's "frequency specific impedance" -- it impedes the passage of anything below its rating. Okay, it's not as sudden as a piece of wire, just that it doesn't start doing anything until you hit a certain frequency.

A resistor impedes ALL frequencies, just only by a certain amount.

Okay, let's open the mudbunny schematic and find C8. It's wired so that one side is on the base, and the other is on the collector, of Q3. What else is wired like that?
Our feedback resistor (R10) -- this is part of what sets the gain of the transistor.
Our clipping diodes -- this is what creates the distortion.

Let's break down what's happening here. The feedback resistor is pretty easy. It forms a divider with R9, which then provides a path to ground for voltage coming out of the collector. (If R9 wasn't there, we'd use the inherent input impedance of the transistor plus R11, which are the only other path to ground. R9 is actually in parallel with that resistance, but R9 is smaller and more predictable.) If we make R10 bigger, then less voltage will "escape" from the collector to ground. The collector voltage would rise and we could possibly squeeze more gain out of the transistor than we need. If R10 was too small, the collector voltage would drop.

Looking at your voltages, your collector isn't too far off from 6V. It's higher than other examples, but that could mean lots of things -- you are most likely using a higher gain transistor than some people, or parts tolerances mean that the exact ratio of all the resistors hanging off Q3 conspired to put your voltage a little high. So we can safely conclude that you probably used the right resistors.

Next let's look at the clipping diodes + C9. We're going to treat C9 as a path only for frequencies below a certain amount, remember. And then anything that passes is going to get clipped. It's a feedback loop, and it's in parallel with R10. D3/D4 will conduct if the signal gets larger than .6V on either side. That's a pretty big signal, so it's only going to happen after the signal is amplified a lot. Thinking about it a bit, you'll realize that this means large signals will get clipped by the diodes and become very distorted, small signals (if there are any left after being amplified by Q1 and Q2!) won't get clipped by the diodes, bass frequencies that are too low for C9 don't get clipped at all by D3/D4, and frequencies high enough to pass through C9 with large amplitude are happily going to go through the diodes and get clipped. What else does that mean? Well, you're going to lose some signal, because it's getting clipped. But the transistor is also amplifying your signal by a LOT. So it should sound similar to what happens if you audio probe the base of Q2 and the collector of Q2. After all, Q2 and Q3 are identical stages. But it's hard to tell because there's another element in the feedback loop ...

This leaves C8. C8 is a smaller capacitor than C9 by a factor of 10. Again, we're going to think of the capacitor as a way to pass only certain frequencies. In the case of C8, those are high frequencies. They don't get clipped by D3/D4. They skip right past R10. In fact, they pass right from the base to the collector -- they NEVER get amplified by Q3! This is a big reason that the big muff has such smooth sounding distortion -- if you don't amplify the frequencies that contain a lot of harmonics, those harmonics won't be in the distorted signal to create a lot of intermodulation. You end up with lots and lots of gain without it sounding completely nasty and disgusting.

What are some things that could be wrong here?
-C8 could be MUCH too large -- like if you mixed up C9 and C8. (This is actually what I suspect has happened.)
-Your transistor could be bad, backwards, or otherwise not functioning properly.

[muddyfox]

Thanks for the play by play, Jon! I always enjoy reading your thoughts on stuff I really should know by heart by know. 

[madbean]

I suspect the volume drop after C8 is because the Tone control is loading down the output of Q3. But, Q3 collector might be a little high. Can we get a clear pic of the top of your PCB showing the resistors, please?

[Gledison]

Of courseeee!
John, im still reading at this moment your comment...im really into understanding what is going on..
just a quick update
the values of my trannies are here? the ones i posted before was a question if that should be the correct values...
here are mine:
Q1 E:6,73V / B:0,63V/ C:0,09V
Q2 E:6,8V/ B:0,60V/ C:0,07V
Q3 E:6,40V/ B:0,60/ C:0,07V
Q4 E:7,5V/ B:0,90V/ C:0,07V
Im using 2n5088's for all Q's! C8 instead of 560p, 470p. C9 instead of 50n, 47n.

[Gledison]

Ahhhhhhhhhhhhhhhhh I love Debuging!!!!
im not sure yet, but i was looking the schematics and it shows a NPN instead of PNP right?
i have followed the silkscreen with the suggested 2N5088. I believe that i have to turn them 180°.
It makes sense?
cheers

[midwayfair]

Ahhhhhhhhhhhhhhhhh I love Debuging!!!!
im not sure yet, but i was looking the schematics and it shows a NPN instead of PNP right?
i have followed the silkscreen with the suggested 2N5088. I believe that i have to turn them 180°.
It makes sense?
cheers

NPN vs. PNP does not tell you the pins of the transistor. You must check the datasheet against the schematic and the layout.

Always check the datasheet!

[Gledison]

Ahhhhhhhhhhhhhhhhh I love Debuging!!!!
im not sure yet, but i was looking the schematics and it shows a NPN instead of PNP right?
i have followed the silkscreen with the suggested 2N5088. I believe that i have to turn them 180°.
It makes sense?
cheers

NPN vs. PNP does not tell you the pins of the transistor. You must check the datasheet against the schematic and the layout.

Always check the datasheet!

Thanks John,
i understand that the NPN or PNP orientation does not shows the pinout.
What i figure it is that on the schematics, the emitter is showing as an NPN orientation.
I´ve checked first the datasheet and the 2n5088 was EBC, facing the flat side. What i think i did wrong is to use the silkscreen described on the picture of the pedal (pdf file) and even that the 2n5088 was suggested in the bill of materials originally, i think that the orientation is regarding a CBE transistor! , at least i hope!
will be home soon to check it out!
Thanks a lot for your help. It was a good kick in the But in order to look more critical to the schematics and datasheet.
Cheers

[Gledison]

Ahhhhhhhhhhhhhhhhh I love Debuging!!!!
im not sure yet, but i was looking the schematics and it shows a NPN instead of PNP right?
i have followed the silkscreen with the suggested 2N5088. I believe that i have to turn them 180°.
It makes sense?
cheers

NPN vs. PNP does not tell you the pins of the transistor. You must check the datasheet against the schematic and the layout.

Always check the datasheet!

hey John,
i've just turned the transistors and it seems that im having more distortion but not sure about volume. its not wierd that im having similar sounds with the transistor in one positio either the other one?
At 70% volume on the pedal engaged is similar to the pedal on bypass. the kick in volume stills come only after 90%.
Im not sure anymore if the Volume should actually works like this or not. The only reference i had is from reviews of other builders and they say that the volume, just turned a little bit up, get already very loud...
ah, and the values changed:
Q1 E:016V / B:0,7V/ C:4,5V
Q2 E:0,07V/ B:0,70V/ C:1,9V
Q3 E:0,15/ B:0,70/ C:4,7V
Q4 E:1,14V/ B:1,7V/ C:4,4V

[Blues Healer]

maybe I missed something, but is there a reason you left off R9 and C2?

OK, nevermind ... it's a Triangle version