Mad Professor Forest Green Compressor  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
User avatar
jsaily
Information
Posts: 23
Joined: 18 Jun 2011, 16:05
Has thanked: 7 times
Been thanked: 19 times

Post by jsaily »

I finally finished my latest FGC build based on daimondamps's PCB. Thanks for providing me with the Eagle files so I could generate gerber files. I made also some slight modifications like a ground fill around the board. The compressor effect is very low noise and works nicely now, much better than the vero board versions I've built before. This could also be to the use of the NSL-32 optocoupler, my earlier attempts were based on self-built optocouplers which didn't work well :-/ My friend has the original pedal so I need to borrow it and make some comparisons ;-)

One note about the component placement, the JFET orientation in daimondamp's figure is correct for 2SK170 (which I used). If the specified 2N3819 is used you should flip the component. Also be careful with correct component placement because some reference numbers are overlapped with component pads. I had to look very carefully from the PDF file. Some resistors in the layout are marked like jumper wires but have a reference number next to them. Of course I first put jumper links there and had to remove them ;-)

The layout is verified, thank you very much! Hopefully you have some time to make the small adjustments for making it easier & more convenient to build.

User avatar
ch1
Information
Posts: 28
Joined: 27 Sep 2009, 14:37
Has thanked: 2 times
Been thanked: 5 times

Post by ch1 »

Hi!
Good to see that my initial layout is appreciated and used. But why don’t you just post your new working pcb here instead of asking Daimondamp to update the other one.

Look forward to hear how it sounds compared to the original.

User avatar
sentimentalbob
Information
Posts: 1
Joined: 16 Sep 2009, 21:50

Post by sentimentalbob »

daimondamps wrote:Ok- so i've updated schematic and board with my values of components.
You can use NSL-32 optocoupler.
If you use Q1 2SK30A you must rotate it by 180.

Sustain mode disconnect original uncompressed signal so basically you have only compressed signal like in Pine Green compressor.
How to setup custom optocoupler?

1. Connect output jack to the center pin of volume pot
2. Set compression pot to max value
3. Remove R19 and connect 100k potentiometer in place the R19
4. Experiment with Pot to get nice sounding compression.
5. If release is too fast increase C13 value from 22u to 100u and again try to use R19 pot
6. Measure the value of the pot ant find resistor with similiar value and put it back in place R19 (or use 1 k resistor in series with 100k pot for release time regulation:)

Bellow are schematic , PCB and component placement.
Partlist

C1 47n
C2 22u
C3 47p
C4 1u
C5 100n
C6 220n
C7 1u
C8 22u
C9 100n
C10 100n
C11 100n
C12 22u
C13 22u
C14 1u
C15 220n
C16 100u
C17 47n
C24 100p

D1 1N914
D2 1N914
D4 1N4007

IC1 NE5534
IC2 78L05

LDR1LED1 NSL-32 silonex optocoupler

Q1 2N3819
Q2 BC550
Q3 BC550
Q4 BC550
Q5 BC560C

R1 1M
R2 1M
R3 5k6
R4 10k
R5 43k
R6 2M
R7 4k3
R8 6k8
R9 51k
R10 150k
R11 14,7k
R12 5k6
R13 200k
R14 200k
R15 10k
R16 110R
R17 110R
R18 5k6
R19 42K
R20 10k
R21 22k
R22 22k
R23 220R
R24 470R
R25 5k6
R26 1M
R27 51K
R28 27k
R29 27k

SW1 SPST

TONE 2 x 20KA (dual pot)
VOL B50K
COMP A500K
Cheers!
R22 22K or 47K?

User avatar
daimondamps
Information
Posts: 33
Joined: 09 Jun 2014, 08:38
Has thanked: 17 times
Been thanked: 34 times

Post by daimondamps »

sentimentalbob wrote: R22 22K or 47K?
22K

User avatar
jsaily
Information
Posts: 23
Joined: 18 Jun 2011, 16:05
Has thanked: 7 times
Been thanked: 19 times

Post by jsaily »

Sorry for the delay, but here are the updated layout and placement files based on daimondamps files. Use the schematic and components values from there. The new layout with ground fills is a big large for the 1590B box, but can be cut to fit although you need to make a gnd jumper link. I've built two of these now (one in 1590BB and one in 1590B) and they work well! Also played one bass gig with it successfully ;-)
Attachments
FGC_placement.pdf
(37.14 KiB) Downloaded 462 times
FGC_layout.pdf
(39.69 KiB) Downloaded 449 times

User avatar
jsaily
Information
Posts: 23
Joined: 18 Jun 2011, 16:05
Has thanked: 7 times
Been thanked: 19 times

Post by jsaily »

I found out that Q3 (lower BC550 transistor in LED driver circuit) is flipped in the schematic and in layout too. Emitter should point towards 110R + ground and not the LED. Funnily, it works quite nicely both ways ;-) If it's the wrong way around, only positive spikes are compressed.

When building another unit I noticed that it's quite picky about the NSL-32 optocoupler selection. I found out by measuring the diode threshold voltage over the LED that around 1.58-1.59V works best (I had a handful of optos to select from). Probably you can tune the circuit to accept others by altering the 42k resistor like in daimondamps instructions. The second unit is not so strong as the first one, so if you have output level problems the opto is the likely culprit! I'll look into this more afte Christmas...

User avatar
ch1
Information
Posts: 28
Joined: 27 Sep 2009, 14:37
Has thanked: 2 times
Been thanked: 5 times

Post by ch1 »

I’ve just finished my build of the FGC using my own layout posted earlier in this thread. As for many of you I have trouble with calibrating the LDR/LED combo. The main problem isn’t in the compressor mode but rather in the sustain mode(original + compressed signal). When I have the volume at min setting I get unitygain but then of course no sustain effect. Which means I can only get volumes over unitygain when I use the sustain mode. Should it be this way? My question is how it works for you who have built this or maybe have the original pedal? Maybe there are some components round Q5 that needs to be tweeked?

I have also found out that there seems to be no standard in how they specify the resistance of the LDR, so I’ve tested with a couple of them. But I think if you alter the R19( even over 100k) you can use almost any LDR as long as dark value is a bit larger than the resistance of the potentiometer. But the best of course must be to find one LDR that works with the original value of R19.

User avatar
whitemarker
Information
Posts: 1
Joined: 01 Jul 2013, 14:51
Has thanked: 1 time

Post by whitemarker »

@jsaily would you be able to provide your eagle file? I would just go over it again and clean it up just a bit.

would be aweseome!

User avatar
jsaily
Information
Posts: 23
Joined: 18 Jun 2011, 16:05
Has thanked: 7 times
Been thanked: 19 times

Post by jsaily »

Here is the whole directory containing all Eagle and layout files.

Jussi
Attachments
FGC.zip
all Eagle and exported layout files
(1.01 MiB) Downloaded 288 times

User avatar
Nixen
Information
Posts: 1
Joined: 16 Aug 2012, 21:21
Has thanked: 3 times

Post by Nixen »

daimondamps wrote:
ch1 wrote:Nice, well done! Think I have to try this out if I get some sparetime.
What about the distortion, is it gone now? Where and why did it occur?
I've build it thanks to you:)
The distortion occur on Q5.
I've changen values of R27 andR11 to those from pcb version.
R27 from 147k to 51k
R11 from 56k to 14,7k
This reduced the Q5 gain .
Hi all.
First of all I would like thanking the great work developped in this project. Thank you very much.
I am going to make this pedal using latest version of the pcd designed by daimondamps, but I have serveral doubts.
1. I am going to use a AD797 instead NE5534 in IC1 position.
2. I am going to use a 2SK170-G instead 2N3819 in Q1 position.
3. I am going to use a 20K pot instead 2x20KA (dual pot) in tone position. In electrical schematic I can´t see dual pot.

Must I modify other components in electrical schematics because the changes I have introduced?
I understand that BOM has not changed since the last publication of daimondamps, right?

Thank you very much.

Post Reply