help with gain recovery stage

[Derringer]

What values would you use for R1, R2, R3, and R4 as labeled in the schematic here?

Right now I have r1= 330k, r2=82k, r3=10k, r4=2k2 .... based loosely off the big muff gain recovery stage (I don't have any 390k R's otherwise I would have just copied it 100%) It sounds pretty groovy but I don't know all that much yet about signal impedance and wanted to se if I was overlooking something critical. I don't know how to figure the impedance of the signal coming into the final stage there what with the T-notch filter along with the tone control.

I don't need a lot of extra gain here. Without the stage the pedal works and sounds fine but you have to crank the volume. Lower settings of fuzz don't have the beef to really stand out. "If" I calculated it correctly, this stage should have around 10dB of gain ... which seems fine ... maybe even more than enough. I don't know if I'm figuring the equations right though as there's no way for me to check against a known correct value.

Thanks for any help you can give.

Bill

[John Lyons]

If you make R4 larger you will get more volume output.
Try a temporary 5K or 1K pot there and adjust to taste.
Set the volume pot to half way up or a little more.
Twiddle the 5K temp. pot until the volume is good and then
measure the temp pot and put a fixed resistor with the value you measured.
Ta da!

john

[frequencycentral]

The gain recovery stage looks like an LPB: http://www.montagar.com/~patj/ehbsters.gif

Usually in the LPB R1 is 10 times the value of R2 to correctly bias the transistor. So - 390K and 39K, or 470K and 47K. I've seen a few different variations, but the ratio is always the same 10:1.

[Derringer]

cool


thanks folks!

[Dragonfly]

What values would you use for R1, R2, R3, and R4 as labeled in the schematic here?

Right now I have r1= 330k, r2=82k, r3=10k, r4=2k2 .... based loosely off the big muff gain recovery stage (I don't have any 390k R's otherwise I would have just copied it 100%) It sounds pretty groovy but I don't know all that much yet about signal impedance and wanted to se if I was overlooking something critical. I don't know how to figure the impedance of the signal coming into the final stage there what with the T-notch filter along with the tone control.

I don't need a lot of extra gain here. Without the stage the pedal works and sounds fine but you have to crank the volume. Lower settings of fuzz don't have the beef to really stand out. "If" I calculated it correctly, this stage should have around 10dB of gain ... which seems fine ... maybe even more than enough. I don't know if I'm figuring the equations right though as there's no way for me to check against a known correct value.

Thanks for any help you can give.

Bill

the schematic looks similar to a few things ive messed around with

look at Mark Hammers "scoop mod" for the Shin-Ei FY-2 ...it makes for a really flexible tone control....which would make the SWTC control you have on there unnecessary.

Also - the 27k between Q2 and Q3 emitters - if you are not going to do a "production run" of this design, a 30k - 50k trim pot would work better here, so you could dial it how much of the hfe is "bled off". It will add flexibility.

looks cool - keep us informed

[Derringer]

well ... here's where I'm at now



it actually all started with this design
http://www.diystompboxes.com/smfforum/index.php?topic=68673.0
and I had it nice an neatly boxed up like this




The original design sounded great when I and my band jammed in my garage ... it was my main distortion. It had a great defined chunk to it. Anyway ... that was in my garage before I did this to half of my garage ...




So I turned on, plugged in, turned up, hit the strings and it made a sound like BLAHHHHHHHHHHHHH ... totally undefined over-bassed-fizzy-farting-out-crap!

I tried a different amps and guitars ... same thing ... I rebuilt it to spec on breadboard .... same thing. The sound insulation in the room completely changed the sound ... plus I was now standing at about 15 feet directly in front of the amp as opposed to about 6 feet away diagonally. The difference was day and night.

So I redesigned it. The scoop circuit was because I had originally cheated a bit and used the 5-band active EQ on my amp to bring down the 1.5Kh a bit.


Now I don't have to cheat anymore!

Funny thing about the scoop too. I posted the question about how to scoop a specific frequency, was given the equations and figured out exactly what I wanted ... it didn't sound as good as what I had done by ear previously ... so that's why the scoop I ended up with resembles the superfuzz scoop so much. I kept the 22k and 10k resistors but opted for the 0.047uf with a 10k resistor between it and ground over what the equations had told me. .... Go figure


Concerning the 27k resistor ... I had fiddled with a 50k pot in there and always kept coming back to @25-30K so that's why I just went with the 27k R.

Is the scoop mod of Mark Hammer's that you're referring to the idea of a variable resistor between the bottom cap of the T-notch filter and ground? I'm about to search for it if I can find it. I'm pretty happy with how it's working now though with the fixed filter in conjunction with the SWTC. You'll notice that I increased the SWTC cap a hair as well as added a 100pf cap from b to c on the final Q ... there were some high harmonics coming thorugh on the treble strings that needed a bit of attenuation.