OKKO Dominator  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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Saruman
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Post by Saruman »

YEAH...THE OKKO DOMINATOR
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RnFR
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Post by RnFR »

looks like someone just made Degoop Doctor. :thumbsup
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kusi
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Post by kusi »

nice, thank you!!

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Post by Güero 2.0 »

Thanks Saruman, the White
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kusi
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Post by kusi »

are you shure about R4 / R5?

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Post by hewie »

Brilliant! Looking forward to getting this one built up in the near future.

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Post by batteryacidtea »

Hell yeah! Now that's something to really care about and spend crazy time building and playing! :applause:

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Post by DimebuGG »

From the layout, the two Vref's(V/2) are tied together?
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Post by RnFR »

kusi wrote:are you shure about R4 / R5?

regards, kusi
I was wondering about the first stage, too. that does not look right.
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Post by Saruman »

are you shure about R4 / R5? - yes
From the layout, the two Vref's(V/2) are tied together? - no

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Post by kusi »

please check R4 / R5 again, its impossible that a 10k/5k voltagedivider makes 4,7V from 10,8V...;)

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Post by Saruman »

please check R4 / R5 again
R4=R5=10K I do a stupid thing :lol:

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Post by bajaman »

please check R4 / R5 again
R4=R5=10K I do a stupid thing :lol:
Yes :thumbsup
I was running some potential jfets on my simulator and to get the voltages on your schematic, I had to change the value of R4 from 5k to 10k :wink:
Incidentally the correct jfet type is critical to the sound of this pedal - I could not get the correct measured voltages with J201 or 2SK117 :shock:
It would be great if you could determine what these fets are!
In the meantime my simulations with the 2SK30ATM were right on the button - the same voltages as on the schematic BUT it has DGS not DSG pinouts.
Most of the non linear amplification occurs in this input stage - the 10k loading resistor (R4), draws nearly 4 times the current of the fet when biased on and limits the gain of the first stage by nearly 50%. The distortion due to this badly biased and "slugged" input stage depends very much on the Jfet type and is assymetrical in nature for some types more so for the J201 than the 2SK30
No clipping diodes further down the track either :hmmm:
Incidentally almost any n channel jfet should work for Q2 - it is configured as a buffer stage between the input tone shaping Q1 and the rest of the circuit - the gate is biased at exactly half voltage or 10.8 / 2 = 5.4 volts dc - the source sits at 5.65v dc
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Post by Saruman »

All nominals on all the details (except resistors) erased :(
Q1 is the most interesting.

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Post by bajaman »

the rest of the circuit is very similar to the Marshall Bluesbreaker / KOT etc. fopllowed by another buffer (op amp this time) and then a 3 way active tone control with switch selected mid frequency centres.
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Post by bajaman »

followed :wink:
where did the edit feature go :?: :?: :?: :?:
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Post by Saruman »

R4 - 10K, C5 - 220n Q1, Q2 - BF245A :thumbsup

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Post by DimebuGG »

Saruman wrote:are you shure about R4 / R5? - yes
From the layout, the two Vref's(V/2) are tied together? - no
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Post by bajaman »

BF245A :thumbsup :applause: :applause: :applause: :applause:
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Post by RnFR »

the first stage is still confusing me. this seems like a very odd way to bias a FET. it would obviously bias it close to 1/2 Vcc, but it also seems like you would be shunting a ton of signal to ground through that 10K resistor. I'm aware of what the 10k on the emitter is doing, and why there is gain reduction and distortion there, but why is the collector biased off of the divider like that?
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