Blackout Effectors Mantra  [traced]

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KindaFuzzy
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Post by KindaFuzzy »

Here's a sneak peak of latest acquisition before it gets traced. Looks like a pair of 2n7000 and a pair of j201 so far.
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KindaFuzzy
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Post by KindaFuzzy »

OK, here we go. Just finished the trace, lots of hidden grounds and 9v connections like the fix'd fuzz. Never seen a circuit quite like this with the two mosfets on the input. There were a couple of empty component places on the board which I labeled with question marks.

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culturejam
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Post by culturejam »

Yep, that looks to be fairly original. Not just a typical knockoff circuit. :thumbsup

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KindaFuzzy
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Post by KindaFuzzy »

OK, there's a bunch of errors in the first schematic, here's the proper verified one I figured out after bread boarding (I was doing a lot of document review last night) And I figured out what the T1 and T2 points were too, they're for biasing the J201s, which were around 6.1-6.2v with a 9v battery.
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Post by roseblood11 »

Great work!

Could you add the orientation of the pots please?

And have you tried this pedal with a 18V power supply? (I'm planning to put this in one box together with a Catalinbread CB30 and a voltage doubler...)

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Post by RnFR »

that looks more like it! thanks for doing this one, I've always liked the sound of It. mixing and matching types of trannies is something I love doing, and it's cool to see it happening here. what's up with those extra unmarked resistors on those jfets(R16,R25)? that looks odd. they definitely aren't necessary for biasing, and I've never seen resistors in that position before. could they be similar to the gate to Vcc resistors on jfet buffers that are used to reduce distortion due to high voltage swings on the input? that's just a guess. or maybe they just did something to the tone he liked? I haven't looked at the pics, why can't you get the value?
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KindaFuzzy
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Post by KindaFuzzy »

Pot orientation is 321 top to bottom on all the pots in the schematic. I wonder if there were different transistors in the circuit before, and it was just easier to use the same board and remove a resistor. I've got it on the breadboard still, I'll have to try adding some resistance and see what it sounds like. I've tried the pedal with a 12v and a 9v supply and didn't notice a difference, but it did take a minute to switch the power supply, and I was playing pretty quiet, so who knows, I'm sure it makes a bit of a difference.

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Post by RnFR »

ah, so there aren't any resistors, just spaces on the board? they were probably MOSFETs or Ge. I don't really think that protection diode on the second MOSFET is really necessary, either. if i have some time at work tonight, I'll try and knock together a digital copy.
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Post by KindaFuzzy »

Yeah, no resistors there, same with that cap on the last stage, just an empty spot on the board. I'd like to try it with germanium, lots of extra mojo points.

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Post by RnFR »

alright, i got this done right before i had to leave work. if there's anything wrong, let me know and i'll fix it tomorrow.

i just noticed that i missed a couple junctions. i'll fix it the day after tomorrow. no comp at home right now.
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KindaFuzzy
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Post by KindaFuzzy »

Looks good all I noticed after a quick glance was c8 should be 47p not 470p.

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Post by coldcraft »

the extra resistor spots on the jfets could have very well been for an alternate version using BJTs or maybe just a different way of biasing JFETs. If blackout comes out with a GE Mantra sometime soon, we'll know whats up.
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Post by Cannibal »

I have bredboarded a fetzer valve (the only variations from ROG schematics are: 1uf as output cap and 100uf as bypass cap) and then i have tried to add various resistors between gate and drain. When 've dropped in a 10 meg resistor it seemed to me that the circuit became more dynamic. This seems quite odd to me so i really like somebody else to try to confirm (or confute) this.
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Post by Nocentelli »

I'm going to have a go at breadboarding this tomorrow, but I've only got BS170s and 2N5457s: I have an idea that the mosfets are a direct replacement (is that right?) but can anyone suggest how to adapt it for the 2N5457s? Is it just a question of adjusting the drain resistors to get the reported voltages, or is it likely to be a bit more complicated than that? Thanking you in advancve,

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Post by RnFR »

KindaFuzzy wrote:Looks good all I noticed after a quick glance was c8 should be 47p not 470p.
got it. I'll try and get that fixed at work tonight.
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Post by coldcraft »

C14 and C18 look funny to me. I've never seen caps between gate and drain like that, only gate-source.

thoughts?
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Post by RnFR »

it's the same sort of thing, except it's shunting to gr instead of negative feedback. miller effect works both ways.
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Post by roseblood11 »

Does anyone have a veroboard layout? I'm to busy over the next few weeks...

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Post by neoflox »

I made one but it's unverified :horsey:
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box
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Post by box »

Hi,
I guess that on the IN capacitor (0.01uF ) or value like 0.022uF (0.047uF) is missing.
Please check.
Regards,
box

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