First build

[Script]

And thanks for the walkthrough regarding calibration. I have to get the computer up and running. I changed machine and it's still awaiting complete reinstall.

What software did you use to get the THD graphs of the other units? Or is that excel fed by hand?

[Heikki]

Here is the libre office spreadsheet I used to create the curves

http://ghr.fi/proaudio/diodecomp/diodi.ods

[Heikki]

More accurate resistor values for the gain switches.

140
170
190
240
280
350
440
560
730
1k
1.4k

The values on the schematic have a tolerance of approximately +/- 0.1dB. Values listed here should be closer to +/- 0.02 dB

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[Script]

Thanks for the high-precision values for the Gain rotary. I soldered it, using up to two hand-matched resistors in series for a few values. Easy enough. The steps are spot on.

Otherwise I have been playing with pots to assess whether log (A) wouldn't suit me better.

THR A1k sure feels more sensitive than B1k
RAT A10k also feels better for dialling in more subtle settings

REL not decided yet, maybe log too, cos 350 or 400 or 450 ms are not that much different, 1s does make a difference though

ATT maybe log too, especially for fine-tuning to catch transients. Needs more testing.
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Overall, the same settings as on the dual comp (diode & vari) are very effective: ATT 1k, REL 47ms, RAT about half, THR adjustable for fine-tuning. If GAIN is stepped, I'll likely keep THR as a pot, or 24-step rotary maybe.

[yan6]

Hi folks, this is my first post here so a bit of an introductory. I'm excited to try and build one of these but this is my first venture out of the diy synth community. I was just wondering about the control wiring. In the schematic they are just blank resistors so I was looking for confirmation that I have these shown correctly.

Controls Question.png

What vu meter specs are suitable for the shown circuit

Finally I just wanted to confirm that 1n4007 is good for D73 & D74

[Heikki]

In the schematic they are just blank resistors so I was looking for confirmation that I have these shown correctly.

Those values look good to me. If your timing cap is 1uF your attack is approximately variable between 1 ms and 50 ms and release between 50ms and 550ms + attack time.

What vu meter specs are suitable for the shown circuit

Pretty much any 200 uA meter will work. 100 uA meters should work too.

Finally I just wanted to confirm that 1n4007 is good for D73 & D74

I used 1N4148. If 1N4007 has similar forward voltage at around 1mA current then it is fine.

Good thing to check is that the voltage across D73 and D74 is almost identical when when the threshold pots RV3 & RV4 are turned to max (500 ohm). RV3 & RV 4 should be matched since potentiometers usually have 20% tolerance.

[yan6]

Thank you Heikki, also what is the value of R93 & R94 in the CV section, 1K?

[Heikki]

For GR indication, I ran a cable on underside of board from sidechain CV1 out to onboard J13 (CV1 VU meter driver input). Stuffed R93 and R94 with resistors equivalent to VU meter resistance. Looking good for now.

Value of R93 and R94 will depend on what meters are used but probably resistor equaling the meters resistance is good starting point. With some meters D83 and D84 might have to be removed.