Blackout Effectors Mantra  [traced]

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neoflox
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Post by neoflox »

Not sure what you mean, there is no IN capacitor in this schematic :scratch:

Oh now I know. You're up to something. There are 24 caps in the gut shot, but only 23 in the schematic. Can someone verify this please?

box
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Post by box »

neoflox wrote:Not sure what you mean, there is no IN capacitor in this schematic :scratch:

Oh now I know. You're up to something. There are 24 caps in the gut shot, but only 23 in the schematic. Can someone verify this please?
Hi,
just as reference pls check:
viewtopic.php?f=13&t=4032&start=0
According to me : Cin (C1)=10nF.
Regards,
box

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coldcraft
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Post by coldcraft »

yes, we are missing an input cap. if you look closer at the schematic, you will see that the input has a DC voltage on it, which is not good for audio pops when switching. We are just missing the input cap, whatever it is
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Post by RnFR »

I was actually wondering the same thing when I was drawing it up. it should have an input cap. that superfluous post vol control cap made me scratch my head as well. maybe that's actually the input cap? if anyone can verify, I can fix the schematic tonight.
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Post by WhiteKeyHole »

It's not superfluous, just as there will be a DC voltage at the gate of Q1, so will there be at the gate of Q2.

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coldcraft
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Post by coldcraft »

RNFR is referring to C21, which is marked 100n, and is superfluous at the end of the circuit. That's probably the input cap.
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Post by box »

Hi,
Cin filters DC voltage from getting into your guitar. R1 and Cin also form a high-pass filter. R2 and C1 form a low-pass filter, which rolls off out the radio frequencies.
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box

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Post by WhiteKeyHole »

coldcraft wrote:RNFR is referring to C21, which is marked 100n, and is superfluous at the end of the circuit. That's probably the input cap.
:slap:

My bad.

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Post by RnFR »

i'd like to get this worked out, as it's the only thing holding up my pcb layout!
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KindaFuzzy
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Post by KindaFuzzy »

I think I boobed for sure, there's an extra .01 on the board that's not in the schematic, so that must be the input cap. I've already traded the pedal (will have another we've been waiting to trace shortly) so I can't confirm, but it makes sense.

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Post by neoflox »

So, 100nF input cap... :slap:

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Post by bubstance »

Well no, if it's the 0.01µF cap like KindaFuzzy said it may be that would be only 10nF.

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KindaFuzzy
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Post by KindaFuzzy »

bubstance wrote:Well no, if it's the 0.01µF cap like KindaFuzzy said it may be that would be only 10nF.
I think so, I remember there being two .1uf caps on either side of the output volume pot, because I thought it was weird while tracing, so it must be a .01 on the input. All the .1uf caps were blue, and the only blue ones that weren't .1uf were the three tone caps grouped all together up at the top of the board.

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Post by RnFR »

cool. I'll probably have the layout done next week when I get back to that job. I switched a few days to get some shit done. I'm going to make a minor adjustment, though. I'm going to move that 47p at the input to after the 10K resistor so it works properly, instead of possibly making RF worse.
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neoflox
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Post by neoflox »

Stupid me. Of course 10nF, not 100nF :whappen:

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KindaFuzzy
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Post by KindaFuzzy »

Here's a verified layout if anyone's interested, it'll fit sideways in a 1590BB. There's an error on RFnR's schematic as well, the 3n cap on the bass pot should go from pin 2 to 1, not from 2 to ground as drawn. I added the .01 input cap, and a 680p on the output pot to give a little more brightness at lower volumes. This pedal would be fun to play around with the tone stack to make it less bassy.
Attachments
Mantra layout.gif

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Mantra pcb.gif
Mantra pcb.gif (6.48 KiB) Viewed 1120 times

RnFR
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Post by RnFR »

here's mine.
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mantra schematic
mantra schematic
mantra pcb 600dpi
mantra pcb 600dpi
mantra layout
mantra layout
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Post by KindaFuzzy »

As usual I'm a bonehead, there's a mistake in the traced schematic, the signal should exit the tone stack from the treble wiper, not the bass wiper. I was on the tonestack calculator trying to figure out why there wasn't much trebble on my build and it hit me. I must have wired it properly on the breadboard without even knowing, sounds much better now please delete the previous version of my layout. Here's the corrected version.
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Mantra pcb.gif
Mantra pcb.gif (6.5 KiB) Viewed 1059 times
Mantra layout.gif

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gigelmargel
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Post by gigelmargel »

Hello all and thx for your work!

I've just finished my Mantra using RnFR's PCB and it doesn't work as I expected: the sound has a subtle grit...it has no "force". Moreover, the treble pot seems to do nothing and the bass pot influences very much the volume.

First 2N7000 don't have the voltages indicated in the schematic..it has something like 5.5V on drain and 4.5 on source. The second one is biased OK. Both FETs are biased at 6.2V, as in the schematic.

Anyone else built it using RnFR's PCB? It's the schematic verified?

Thank you very much!

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Post by auden100 »

Hey, Gigelmargel.

I haven't built it (I hope to soon), but from the looks of it, RnFR's schematic is an exact copy of the original traced schematic, which KindaFuzzy just said had a mistake in it. RnFR will have to answer if he's verified the layout though.
gigelmargel wrote:the treble pot seems to do nothing and the bass pot influences very much the volume
KindaFuzzy did make a mistake in tracing it: the output from the tonestack should be switched, so that the R16 is connected to the Bass wiper, and the output comes from the Treble wiper. Might be easy enough to just take one end of R22 and reconnect it to other side of R16.
gigelmargel wrote:First 2N7000 don't have the voltages indicated in the schematic..it has something like 5.5V on drain and 4.5 on source.
It's stated in both schematics that both 2n7000's sources should be 2.40V. Drains should be 7.45V. Perhaps try some other 2n7000's to see if you can get a pair with the right voltages.

Give that a try, and perhaps you'll have better luck.

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