Non ADA Gear > Effects
NPD - Mesa Boogie V-Twin Preamp
MarshallJMP:
--- Quote from: Systematic Chaos on July 02, 2018, 06:13:42 PM ---
--- Quote from: MarshallJMP on July 02, 2018, 01:23:50 PM ---SC, I saw it has 2 channels, a clean and a dirty or am I wrong, I'm guessing you want to alter the dirty channel?
--- End quote ---
MJMP, thanks for tyour reply and taking the time!!
It actually has 2 1/2 channels. Channel 2 can be switched (see the black switch in the middle of the pedal) from a low gain "Blues" to the high gain "Solo". I be interested in slightly altering/tightening up the dirty channel.
I'm nowhere near you in reading schematics but my take is that the initial dist/gain is produced by a TL072 going into an array of clipping diodes. I already though of maybe a 2604 instead of the TL072 to make that a bit more organic....
--- End quote ---
SC, I send you an email with some things to try out, if you like them you can post them here.
Systematic Chaos:
Got it MJMP, thanks.
Here's for all:
--- Quote from: MarshallJMP on July 03, 2018, 03:21:01 PM ---Well you could lower C22 and C23 to roll off some bass freq, or C24 (I would start with 1µF and go from there.
Gain wise, there is a lot to begin with (around 2000x with the opamps), you could raise R28 to get more. But you need to be carefull that the noise doesn't get too high.
You can also play around with the diodes, replacing them with led's.
--- End quote ---
I'll tinker around with it during my summer leave and I'll let y'all know
Short Qs:
- Do you mean C22, C23 and C24 altogether (C24 has polarity, right?) Any special recommendations on type/brand/value?
- By how much should I raise R28 to get just a tad bit more gain?
- Do you think I'll get some improvements if I swap U4 (TL072) for an OPA2604?
- Clipping wise I actually prefer the softer clipping Silicon diodes over LEDs...
Dante:
--- Quote from: Systematic Chaos on July 04, 2018, 03:24:52 AM ---Got it MJMP, thanks.
Here's for all:
--- Quote from: MarshallJMP on July 03, 2018, 03:21:01 PM ---Well you could lower C22 and C23 to roll off some bass freq, or C24 (I would start with 1µF and go from there.
Gain wise, there is a lot to begin with (around 2000x with the opamps), you could raise R28 to get more. But you need to be carefull that the noise doesn't get too high.
You can also play around with the diodes, replacing them with led's.
--- End quote ---
I'll tinker around with it during my summer leave and I'll let y'all know
Short Qs:
- Do you mean C22, C23 and C24 altogether (C24 has polarity, right?) Any special recommendations on type/brand/value?
- By how much should I raise R28 to get just a tad bit more gain?
- Do you think I'll get some improvements if I swap U4 (TL072) for an OPA2604?
- Clipping wise I actually prefer the softer clipping Silicon diodes over LEDs...
--- End quote ---
AaAAAAaaaaannnnnddd, right about here is where I get that look on my face like I need to droooool cuz I don't understand -SQUIRREL!- what's going on and -PRETTY BIRD!- I kinda have that blank look on my face like -BAHAMAS!- I'm somewhere else
R28, opamps, softer clipping Silicon diodes?!?!
SORCERY!!
MarshallJMP:
Don't say that too loud or the internet inquisition will lock is up and torture us >:D
Systematic Chaos:
Conclusion:
- changed R28 from 100k to 120k metal film
- swapped the TL072 (JRC072D) to a BurrBrown OPA2604AP
- lowered both C22 and C23 from 1µF to .33µF Mallorys
- lowered C24 from 22µF to 2.2µF Panasonic Gold
This thing delivers! You still have to use an OD set to Clean Boost settings up front to tighten it all up and make it sing....but then so it does.
The lead Channel is a mix between Recto and Mk, the Blues Channel is a Californian flavored Brown sound and the Clean Channel is dead on Blackface.
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