Subdecay - Liquid Sunshine  [traced]

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coldcraft
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Post by coldcraft »

Brian M wrote: The new version is quite different. Still jfet based, but it has three gain stages. They are biased differently. One of the gain stages is also used to implement a faux active tone control.
It is still fairly simple and the new one does not require trimmers. I'm sure some will say "ah-ha... mu-amp." Not on this one. a single jfet for each stage, and a fourth to buffer the output.
Offset Biasing?
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Post by coldcraft »

I deduced this from the PCB posted on Facebook.

I've boxed the grounded end of C9 because its possible that it connects to either end of R21, or somewhere else entirely. It seems to me like all the traces are on the top side of the board and the bottom is mostly ground plane, with a few power runs, but I could be wrong. I also used the previous schematic as a reference. The builder stated that its using J201s, but on board Q1/2 are DSG while Q3/Q4 appear to be SDG. But, I reserve the right to be wrong. I'm mostly interested in the biasing.

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Post by friedtransistor »

Wow, looks complex. I take it this is an overdrive type effect? Got any sound samples? The reason I ask is that I've tried multiple OD circuits, but have always been disappointed for their lack of ambiance.
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Post by Brian M »

looks about right.

I'm not sure if R13 and R14 are quite right.

And it's not too complicated. This is probably our easiest build. It's rather simple compared to most of the stuff we make. :D

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Post by mmolteratx »

Yea, R13 is connected straight to the C10/R14 junction.

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Post by friedtransistor »

Brian M wrote:
And it's not too complicated. This is probably our easiest build. It's rather simple compared to most of the stuff we make. :D
well, you certainly are more experienced than I am at this stuff :thumbsup
the most complicated thing I've worked on is either the boss slow gear or the boss oc-2. those turned out to be disasters :blackeye . right now I'm rebuilding an amp, but I doubt it'll turn out right. breadboards and perfboards are alright, but a pain to work with.
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Post by coldcraft »

Brian M wrote:looks about right.

I'm not sure if R13 and R14 are quite right.

And it's not too complicated. This is probably our easiest build. It's rather simple compared to most of the stuff we make. :D

Do you have to hand select J201s in order to get it to bias, or will this work with any?
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Post by mmolteratx »

Looks like bias is set by applying a reference voltage at the gate rather than relying on the drain/source resistors and the FET's characteristics. Should have some variation, but less so than the traditional Dr. Boogey alikes.

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Post by coldcraft »

just got one of these for myself. I have the version 2 as well, this one is great, very lively and dynamic!
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Post by rocklander »

coldcraft wrote:I deduced this from the PCB posted on Facebook.

I've boxed the grounded end of C9 because its possible that it connects to either end of R21, or somewhere else entirely. It seems to me like all the traces are on the top side of the board and the bottom is mostly ground plane, with a few power runs, but I could be wrong. I also used the previous schematic as a reference. The builder stated that its using J201s, but on board Q1/2 are DSG while Q3/Q4 appear to be SDG. But, I reserve the right to be wrong. I'm mostly interested in the biasing.

[ Image ]
so I'm assuming that pad 2= input, pad 3=output.. (please tell me if I'm wrong there), ll does that make pad 1 = earth?
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Post by JohnDodo »

On the off chance that somebody knowledgeable may reply to this resurrection of a pretty dead thread:

Is the Q1 buffer stage supposed to have about unity gain (for the MkII – I built the tagboard version)?
Because I lose about 6db from gate to source, and get the corresponding symptoms (i.e., no drive to speak of except at full CW). Q1 Voltages (quiescent/no input): D 9.2V; G 0V; S 1.28V
On the other hand, I checked multiple times for continuity or accidental solder bridges, and can't find anything wrong; components seem ok too. I tried all four (lol) 5458s I have for Q1, same results with each of them...

I'm a bit stumped. Pity because it does sound good with the drives maxed...

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