SOLVED M800 problems..

Idroj

Idroj

Active member
Hi, here we go again..

I finished building this PAL 800, and when I first turned it on I got some intermittent overdrive sound but only responsive when I strummed hard, if I played soft no sound... It almost sounded as if it was gated... Went back to it and now I have 0 sound when on and full normal sound on bypass.

This time I cleaned the pcb board 2 times before installing it... Maybe the problem is these J201s I bought on eBay? I also bought the presoldered ones from pedalpcb, just haven't put them together yet.. wanted to try the regular ones first.. Should I start there?

Any help would be greatly appreciated.

Thanks in advance.

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IMG_7794.jpg
 
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Idroj said:
Let me correct myself.. (had the jacks backwards) ? When ON, sounds goes through but it sounds like is gated, you have to hit the strings really hard to be able to get sound.. when fingerpicking soft, nothing.. sounds like it’s “trying” to work
Click to expand...
Turn all your knobs to 12.00 O'Clock, with your Digital Multi Meter set on DC Volts, Black Probe to Ground, Red probe to Drain, Adjust each jfet to 4.5v. By the time you get to the last one, Go back & do it again, Q4 is fixed but the Tone Trimmer control effects overall sound also so adjust that
after you dial your Knobs to where you like it while playing Guitar.
 
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music6000 said:
Turn all your knobs to 12.00 O'Clock, with your Digital Multi Meter set on DC Volts, Black Probe to Ground, Red probe to Drain, Adjust each jfet to 4.5v. By the time you get to the last one, Go back & do it again, Q4 is fixed but the Tone Trimmer control effects overall sound also so adjust that
after you dial your Knobs to where you like it while playing Guitar.
Click to expand...
Worked out perfectly! Thank you so much @music000 ! Q4 reads 8.6 no matter how I turn it. And I can’t hear any difference in sound while I adjust it while playing... I like the sound of the pedal, it’s robust, I was expecting it to be a bit more aggressive and brighter.. a little too dark/dull, but sounds good enough!

DC815338-79C8-42E2-943D-C9DD9E40B357.jpeg
 
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The Internal Trimmer definately effects the tone & Gain on the pedal.
If you say you can't notice the difference from Min To Max, it's Faulty!
Q4 is fixed voltage, The Trimmer is purely for EQ' ing the pedal!
 
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music6000 said:
The Internal Trimmer definately effects the tone & Gain on the pedal.
If you say you can't notice the difference from Min To Max, it's Faulty!
Q4 is fixed voltage, The Trimmer is purely for EQ' ing the pedal!
Click to expand...
I just fired mine up going into a 22w Clean Fender based amp.
With all controls at 12.00 O'Clock, BASS at 10.00 O'Clock & Gain at 2.00 O'Clock.
Internal Trimmer set nearly full CCW 8.00 O'Clock, It's BRIGHT & IT ROCKS!
Turning Trimmer Clockwise will darken the overall Sound!
 
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music6000 said:
I just fired mine up going into a 22w Clean Fender based amp.
With all controls at 12.00 O'Clock, BASS at 10.00 O'Clock & Gain at 2.00 O'Clock.
Internal Trimmer set nearly full CCW 8.00 O'Clock, It's BRIGHT & IT ROCKS!
Turning Trimmer Clockwise will darken the overall Sound!
Click to expand...
I just fired mine up again too. I don’t know if earlier I was turning it clockwise or what, but I turned it counterclockwise and HERE IT IS!! Nice and crisp!! Thanks!! Quick question: why, before adjusting all trim pots to 4.5v, I was getting that interrupted, intermittent gated sound? I just want to make sure it is 100% good and nothing is faulty. Also thinking about testing those other eBay J201s one more time, with the 4.5v adjustments.. to see if they were fakes or not..
 
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Best place to get good jfets is Smallbear Electric.....if he's got them in stock. Also the have converter boards that convert smd to through hole: https://www.pedalpcb.com/product/mmbfj201-jfet-pre-soldered/
and I'v had good luck so far with the ones from Tayda, but you have to solder them yourself. The board: https://www.taydaelectronics.com/smd-toto-92-diy-pcb-guitar-effect.html and the jfet: https://www.taydaelectronics.com/mmbfj201-jfet-n-channel-amplifier-transistor-sot-23.html
They aren't that hard to solder and they are in production so you don't have to worry much about fakes.....unless you are buying from ebay ?
 
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Idroj said:
I just fired mine up again too. I don’t know if earlier I was turning it clockwise or what, but I turned it counterclockwise and HERE IT IS!! Nice and crisp!! Thanks!! Quick question: why, before adjusting all trim pots to 4.5v, I was getting that interrupted, intermittent gated sound? I just want to make sure it is 100% good and nothing is faulty. Also thinking about testing those other eBay J201s one more time, with the 4.5v adjustments.. to see if they were fakes or not..
Click to expand...
With Jfets, That is just the general rule of thumb, 9v Pedal = 4.5v jfet Drain.
Alot of builders will use 4.5v as a reference point & then tune by Ear, some like 5v.
Just like Fuzz pedals with bias control, The more you starve it for Power, the less sustain & gated it sounds.
 
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Ohhhh ok I see I see... ?? Can I then, by providing a little more power on all JFETS, obtain a more sustained overdrive? Also, could you help me understand why are there 6 transistors and what is the purpose of each one? It sounds great now with the Q4 all the way turned CCW it has some bite! Only wish I could turn the gain knob, just a couple of notches further... Maybe experimenting with the trim pots I can make it even a hair more aggressive?
 
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Idroj said:
Ohhhh ok I see I see... ?? Can I then, by providing a little more power on all JFETS, obtain a more sustained overdrive? Also, could you help me understand why are there 6 transistors and what is the purpose of each one? It sounds great now with the Q4 all the way turned CCW it has some bite! Only wish I could turn the gain knob, just a couple of notches further... Maybe experimenting with the trim pots I can make it even a hair more aggressive?
Click to expand...
Try it at 4v on each jfet, It should get more aggressive & sustain.
If you get a negative result, Try at 5v on each trimmer, this will also effect the Tone Trimmer!
 
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Thanks! I'll test it with these suggestions and I will also test it with the "suspicious eBay J201s" I had on it before replacing them for these smd presoldered ones from pedalpcb. I'm just curious to see if those were indeed fakes or not, or if they'll sound any different. In theory, if both are authentic, should they sound and perform exactly the same?
 
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Try measuring Vp and Idss. There are instructions on how to do that elsewhere in these forums. Spec for J201 is Vp between -0.3V and -1.5V. Idss is between 0.9mA and 4.5mA. If either measurement is out of spec, then return 'em.
 
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I’d love to learn how to measure Vp and Idss. I looked for instructions here in the forum and and google and I couldn’t find clear and simple (at least to me ?) instructions... I read something about using a 9v battery and a 1k resistor but no instructions.. ☹️
 
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