BJFE / BearFoot fx Guitar Effects Community

How did the sound of the stock unit need to be changed? Controls are only in and out level - does the input act as the threshold? I thought I might like to try it out in the next couple of weeks.

Threw this on the breadboard instead of working this afternoon. Mine was a little rough aroud the edges since I didn't have a ton of time to play around with it, but I'd say it has potential. As the article says, its good in the lows and highs, so I might think about some kind of tone control, but that's just me. An attack/decay control could be good instead if its not too much of an addition to the circuit. Otherwise, I limited the range on the input gain a bit. I didn't see the need for two controls that took the signal down to nothing.

And, the frequencies that are compressed could be altered by playing with C5 (the emitter capacitor on Q2) couldn't they?

I might not fully understand, but is the germanium transistor a necessity there or could an Si be made to work?

So here is my experiment today. Mine was a little noisy so I swapped all the resistors to metal film 1%, that helped a lot. I also socketed all the transistors and have tried a silicon trannie in Q5, works just fine, it acts as a variable resistor to control the gain of Q2 so the affect on tone is minimal. I have tried using lower gain trannies as well KSA1015 for the PNP and KSC1815 for the NPN with gains in the 140 Hfe range. A must is a control over the swell, I did this by putting a 47k resistor in series with a 1M log pot in R8.

I think having a certain amount of gain on tap at anytime (limiting R1 and R9) would be a worthwhile experiment. The input and ouput control more than just the threshhold or output gain they have an affect on the entire circuit. It's interesting that P1 of R9 goes to +9v instead of ground. I haven't taken measurements yet on how the output gain changes the voltage to the collectors of Q2-4.

Regarding the tone, messing around with C5 will change the release but I dont think it would affect the tone much, try messing with C8 or put a passive tone circuit in at the R8 Q3 C8 junction.

However I do see some advantage to putting a variable resistor in series with the collector of Q5 and C5 (perhaps 25KB) to affect the release.

here is the revised Schem

Thanks for the comments. I'll have to play with the timing a bit when I get a chance.

A quick question because I'm probably over simplifying things to try to understand whats going on... If I play with C8, that'll change the frequencies that control the compression, but not really the frequencies that get compressed? I guess its gotta impact the output as well, but I think I'd focused more on passing signal to Q4 to control Q5. I dunno... I could be way off base.

Any other thoghts on this? I have the cousin of the ACP-1 in the shop right now as well, it's called the ACA-1, it has a cool input meter. It was also publised in Popular Electronics and I have a vintage issue on the way to me to compare the schem with the ACP-1

jfromel wrote:Any other thoghts on this? I have the cousin of the ACP-1 in the shop right now as well, it's called the ACA-1, it has a cool input meter. It was also publised in Popular Electronics and I have a vintage issue on the way to me to compare the schem with the ACP-1

Not that this is a thought, but C3 on your schematic is reversed compared to the original schematic. I am thinking of trying this one out in the next couple of weeks. I'm revising my vero layout tonight.

ibodog wrote:

jfromel wrote:Any other thoghts on this? I have the cousin of the ACP-1 in the shop right now as well, it's called the ACA-1, it has a cool input meter. It was also publised in Popular Electronics and I have a vintage issue on the way to me to compare the schem with the ACP-1

Not that this is a thought, but C3 on your schematic is reversed compared to the original schematic. I am thinking of trying this one out in the next couple of weeks. I'm revising my vero layout tonight.

C3 is backwards in my schem, you would do just as well with a 1uf fillm cap there I think.

Anything new on this? I finally got to putting it together last week. Probably need to play with it a bit more - there seemed to be a good amount of sustain. But when not playing it really brought up the noise floor. VR2 didn't really seem to do much to the sound.