m800 spitty at low gain

[Danbieranowski]

Just built the m800 and it sounds pretty good... a little dark. Biased the J201s (guaranteed authentic by GuitarPCB) to 4.5v other than the tone trimmer which I did by ear. What’s odd is that at low gain settings it gets a little spitty like a fuzz. Is this expected? Any ideas? There’s not any issue with the soldering and such. It works and all that. Just sounds a little different than I thought it might.

 

[music6000]

Just built the m800 and it sounds pretty good... a little dark. Biased the J201s (guaranteed authentic by GuitarPCB) to 4.5v other than the tone trimmer which I did by ear. What’s odd is that at low gain settings it gets a little spitty like a fuzz. Is this expected? Any ideas? There’s not any issue with the soldering and such. It works and all that. Just sounds a little different than I thought it might.

The internal Tone trimmer works in reverse, I have mine around 9.00 O'clock to give a brighter tone.
This is very fussy with the J201's if they are not in spec, you may have to tweak the trimmers by ear.
My first Faitrchild set were so far out of spec & the voltages range from 2.5v to 7v to get it sound reasonable!
I revisited & used NOS Siliconix J201's & it was perfect with all the trimmers @ 4.5v

Here is my report :

M800 Overdrive

Awesome JCM800 Emulation !!! All the Trimmers were adjusted to 4.5v & it was meh, 4.75, 5v, 5.25v & 5.5v, Louder with no Gain! Old School, Strummed a Chord & tuned each Trimmer by ear. Critical Trimmer is the Tone trimmer, This effects overall EQ & gives it the Power of The JCM800 sizzle! The...

forum.pedalpcb.com

M800 Revised Build

M800 Latest Update : I revisited the pedal 2 days ago, https://forum.pedalpcb.com/threads/m800-overdrive.935/, as I had recently acquired some Genuine NOS Siliconix J201 with the Dot. I removed the Fairchild J201's & replaced with the Siliconix J201's. I set them all to 4.5v except Q4 which...

forum.pedalpcb.com

I made a jfet improved matcher 2 to check jfets for IDSS

Greatly Improved JFET Matcher

Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 1000 verified designs. DIY your own boutique effects!

tagboardeffects.blogspot.com

 

[Danbieranowski]

The internal Tone trimmer works in reverse, I have mine around 9.00 O'clock to give a brighter tone.
This is very fussy with the J201's if they are not in spec, you may have to tweak the trimmers by ear.
My first Faitrchild set were so far out of spec & the voltages range from 2.5v to 7v to get it sound reasonable!
I revisited & used NOS Siliconix J201's & it was perfect with all the trimmers @ 4.5v

Here is my report :

M800 Overdrive

Awesome JCM800 Emulation !!! All the Trimmers were adjusted to 4.5v & it was meh, 4.75, 5v, 5.25v & 5.5v, Louder with no Gain! Old School, Strummed a Chord & tuned each Trimmer by ear. Critical Trimmer is the Tone trimmer, This effects overall EQ & gives it the Power of The JCM800 sizzle! The...

forum.pedalpcb.com

M800 Revised Build

M800 Latest Update : I revisited the pedal 2 days ago, https://forum.pedalpcb.com/threads/m800-overdrive.935/, as I had recently acquired some Genuine NOS Siliconix J201 with the Dot. I removed the Fairchild J201's & replaced with the Siliconix J201's. I set them all to 4.5v except Q4 which...

forum.pedalpcb.com

I made a jfet improved matcher 2 to check jfets for IDSS

Greatly Improved JFET Matcher

Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 1000 verified designs. DIY your own boutique effects!

tagboardeffects.blogspot.com

View attachment 15247

This is great, thank you! I can tell just by tweaking the trimmers that they literally silence the circuit if turned too far in either direction. So it seems like the sweet spot shouldn't be TOO hard to find. But I also found that it would oscillate if the trimmers were set to certain values, which was also surprising. Just weird all around! Thanks for the advice! I'll goof w it.

 

[Danbieranowski]

The internal Tone trimmer works in reverse, I have mine around 9.00 O'clock to give a brighter tone.
This is very fussy with the J201's if they are not in spec, you may have to tweak the trimmers by ear.
My first Faitrchild set were so far out of spec & the voltages range from 2.5v to 7v to get it sound reasonable!
I revisited & used NOS Siliconix J201's & it was perfect with all the trimmers @ 4.5v

Here is my report :

M800 Overdrive

Awesome JCM800 Emulation !!! All the Trimmers were adjusted to 4.5v & it was meh, 4.75, 5v, 5.25v & 5.5v, Louder with no Gain! Old School, Strummed a Chord & tuned each Trimmer by ear. Critical Trimmer is the Tone trimmer, This effects overall EQ & gives it the Power of The JCM800 sizzle! The...

forum.pedalpcb.com

M800 Revised Build

M800 Latest Update : I revisited the pedal 2 days ago, https://forum.pedalpcb.com/threads/m800-overdrive.935/, as I had recently acquired some Genuine NOS Siliconix J201 with the Dot. I removed the Fairchild J201's & replaced with the Siliconix J201's. I set them all to 4.5v except Q4 which...

forum.pedalpcb.com

I made a jfet improved matcher 2 to check jfets for IDSS

Greatly Improved JFET Matcher

Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 1000 verified designs. DIY your own boutique effects!

tagboardeffects.blogspot.com

View attachment 15247

Ended up working it out by ear and I’m much happier with it. The trimmer causing the weird spitty sound was the presence trimmer. Thanks for the advice!

 

[Coda]

Pedals can be a dick sometimes…