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Re: Obsidian 2HV

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1/20/2001 5:16 AM

Re: Obsidian 2HV

Joe,

Does the 36V Obsidian sound different in the higher gain settings? I have it breadboarded, so I might give it a shot. Unfortunately, already have a pcb ready for parts. Hmm, maybe I could do a little meatball surgery . . .

Another Q: How do you keep it a little more silent during higher gain settings? I assume being in a metal enclosure will help a bit. I recall someone mentioning shielded input wire for some other design (TB I think), and wondered if this really helps. BTW, what wire would one suggest for this. Salvaged coax?

Thanks,

Dave

1/20/2001 8:35 AM

Higher gain settings result in the "normal" tone. Lower gain settings have more treble and need a tone control to compensate.

To reduce noise:

1. Add small (100pf) caps from each MOSFET gate to ground.

2. Increase the 100pf cap to ground on stage #2. Or add a .001 cap on stage #1. That should cut any RF off at the input.

3. Increase resistance between stages to set the maximum gain just where you need it, but not more.

4. Breadboards often have small capacitances between rows. Building the circuit for real often results in less noise than a breadboard. Especially keep the output away from the input.

5. Shielded wire may help a tiny bit, but high-gain circuits (especially with those sensitive MOSFET's) are naturally noisy.

My breadboarded circuit really wasn't that noisy. But I have active pickups and that may account for some of that, because adding resistance before the MOSFET circuit increases sensitivity substantially, so I would assume higher-impedance pickups would do the same. Just increase the 100k coupling resistors until it tames the gain level to taste.

Are you powering with 4 batteries, or a power supply? The latter (including wall warts) will probably require voltage regulation. Good Luck!

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