Guyatone's PS-021 Guitar Exciter/Compressor

[albru80]

Thank you for the schematic!
I want to draw a layout but I'm not sure about something:
to completely eliminate the flip flop switching from the schematic would you get rid of Q9, Q10, Q11, R15, R16, R20, R40, R41, R69 and C10?

[digi2t]

Hmmm, I see 3 jfets for the flip-flop bypass. Are two connected to the same side of the flip-flop?

Never mind. The schematic of the Boss OD2 just answered my question.

[aion]

Mark, thank you so much for that analysis! Such a great writeup.

[Mark Hammer]

My pleasure.  A whole lot easier to do with a nicely-drawn schematic to work from!

[gigimarga]

Hello all!
Anyone have built it? I've just finished (using this vero: http://tagboardeffects.blogspot.ro/2017/11/guyatone-ps-021-guitar-exciter.html) but it didn't work as I heard in demos: it has a low level and distorted output. All the pot seems to work OK.
In the schematic, the 22K trimpot looks strange to me. In all Dynacomp variants, it is only 2K. Maybe this could be a problem?

Thank you!

[R O Tiree]

Hmmm, I see 3 jfets for the flip-flop bypass. Are two connected to the same side of the flip-flop?

Never mind. The schematic of the Boss OD2 just answered my question.

It's been a while since I did any of this stuff... but I'm not seeing what Q9 does.

[aion]

It's been a while since I did any of this stuff... but I'm not seeing what Q9 does.

I think it's just a second turn-off point because it's such a large circuit. They mute the signal in two places in bypass, which happen to correspond to the input of the first half and the input of the second half, although there isn't any way of tapping into just one of the effects.

[R O Tiree]

Thanks, aion.

But how cool would it be to have the facility to select "Dynacomp" only (insert compressor circuit to taste), "exciter" only or "both"... ?

A couple of flip-flops + LEDs and associated momentary push-to-make switches, another JFET or 2 (I'd need to work that out), and Robert is one of your parents' siblings.  You could have the comp part of the circuit as a daughter-board, so people could choose from a variety or roll their own.  A standard Orange Squeezer is a very sweet circuit as is and (having built lots of comps) doesn't seem to have anywhere near the noise associated with a CA3080-based topology (never built a 13700-based one, so I don't have a feel for noise on those).  Optos are also nice-sounding... You could have all the components of the switching system on the main board, leaving only V+, GND, V_in and V_out as the only connections needed to the daughter-board.

[aion]

Thanks, aion.

But how cool would it be to have the facility to select "Dynacomp" only (insert compressor circuit to taste), "exciter" only or "both"... ?

A couple of flip-flops + LEDs and associated momentary push-to-make switches, another JFET or 2 (I'd need to work that out), and Robert is one of your parents' siblings.  You could have the comp part of the circuit as a daughter-board, so people could choose from a variety or roll their own.  A standard Orange Squeezer is a very sweet circuit as is and (having built lots of comps) doesn't seem to have anywhere near the noise associated with a CA3080-based topology (never built a 13700-based one, so I don't have a feel for noise on those).  Optos are also nice-sounding... You could have all the components of the switching system on the main board, leaving only V+, GND, V_in and V_out as the only connections needed to the daughter-board.

It would be pretty tricky to retrofit into a real PS-021 with the FET switching and all. But I may end up doing just the exciter portion as its own board (alongside the full PS-021 circuit) depending on how different I feel it sounds from the BBE Sonic Maximizer, which uses some of the same principles but is a lot more flexible (see my Lumin project).

[digi2t]

I went through my unit, and I took the liberty (using Aion's schematic) to fill in the rest of the blanks...



What I find really interesting is the indicator LED circuit. Personally, I find the color representation backwards (red = good, green = bad), but maybe it's a Japanese thing, or they simply inserted the LED backwards on the line.

[tokenofdevotion]

Did we ever find what was the difference between this and the ps-020 bass version? I recently got one and was wondering how to convert it to a 021. I'm pretty sure it's just a resistor or capacitor, but have no idea where to look at

[Rob Strand]

Did we ever find what was the difference between this and the ps-020 bass version? I recently got one and was wondering how to convert it to a 021. I'm pretty sure it's just a resistor or capacitor, but have no idea where to look at

Aion's document shows a table of the part values for each model.
He also mentions where the meridian differs from both the PS-020 and PS-021.

Six part differences between:  PS-020 Bass Exciter and PS-021 Guitar Exciter.

Designators reference aion's meridian schematic:
https://aionfx.com/app/files/docs/meridian_documentation.pdf

Code Select Expand

Part PS-021  PS-020 Function
(GUITAR) (BASS)

R8 560k 470k OTA control current (LM3080 pin 5)
R17 39k 43k Exciter gain resistor
C10 33n 68n Exciter phase compensation cap
C11 2n2 4n7 Exciter high pass filter cap
C16 10n 100n Tone control "bass" cap
C17 220n OMIT } Same part position.
C23 OMIT 22uF } electro/film and value change

I don't know if the Guyatone PCB's have designators but they definitely won't match the aion designators.
If you want to check if the values on your PCB match aion's values you will need to find where each component is and check the value.   It should be fairly easy.  If you can find a part with that value just check the connections to the other parts.  However, the opamp pins probably won't match aion's schematic either so use the pin function (input output) and not the pin numbers.

If you wanted to verify aion's tracing you could check more parts.   He could have missed one.