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In Reply to: Ming Da MC-2A3 preamp schematic posted by jwu - snoopy.org on June 13, 2008 at 18:47:41:
Found 2 major design flaws of the Ming Da:
1. Filament power supply in series, 2 supplies, one shared between 2 6SN7 and the other among 3 6922, non regulated.
Be prepared for it to sound good one day and bad on another.
2. Grid resistor from 6SN7 stage to 6922 stage is 1/10 of what it should be. In the unit and the schematic there is a 220Ohm resistor but with that you'd have to have a 6SN7 and the middle 6922 to perfectly jive with each other to avoid a high frequency oscillation which sometimes has the side effect of inducing a pronounced hum as if grounding is not proper.
This is why this preamp is both a tube-roller's dream AND nightmare.
Took me a while to figure it out. Swap in a 2-5k resistor and all is well.
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Follow Ups
- RE: Ming Da MC-2A3 preamp schematic - jwu - snoopy 11:54:54 07/26/08 (0)
- RE: Ming Da MC-2A3 preamp schematic - Argo 01:06:47 07/29/10 (0)
- RE: Ming Da MC-2A3 preamp schematic - phi70 13:46:44 05/18/09 (0)
- RE: Ming Da MC-2A3 preamp schematic - Frihed89 23:50:40 08/18/09 (0)
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