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previous: marleyman ray, here's a post about this amp fromawhile back -- 5/25/2000 6:30 PM	View Thread

From the Schematic Fellers

5/26/2000 11:33 AM
Graywater	From the Schematic Fellers All right - pulled the Crate schemo - but first, as to the "servo" bias, which I assume is a reference to the transistor regulated Crate scheme - this is primarily found on Crate's "doo-doo" series of amps. OK, VC5212 - bias is derived from a tap on the low voltage supply for the semiconductors - eventually the +/-10v supply. Anyhoo, neg voltage is tapped at the junctionof the anodes of D9&D11 which are connected to the junction of R63, C35 - side, and R77. R77(100 ohms) joins R78 (15K)(other end connected to ground) to create a voltage divider which sets the bias level - C49 is hooked across R78. Here's the rub: Since the bias is originally tapped from the unfilted negative rail of the low V supply (approximately 15.6 VAC) you can't increase the voltage much - next, since you want keep the balance in the +/- rails you want to keep the total resistance of R77&78 around 15K - prehaps changing R78 to a 15K pot. This enough to confuse you? GW PS: I remember providing this exact same info before - we need those archives!!

5/26/2000 11:33 AM

Graywater

From the Schematic Fellers

All right - pulled the Crate schemo - but first, as to the "servo" bias, which I assume is a reference to the transistor regulated Crate scheme - this is primarily found on Crate's "doo-doo" series of amps.

OK, VC5212 - bias is derived from a tap on the low voltage supply for the semiconductors - eventually the +/-10v supply. Anyhoo, neg voltage is tapped at the junctionof the anodes of D9&D11 which are connected to the junction of R63, C35 - side, and R77. R77(100 ohms) joins R78 (15K)(other end connected to ground) to create a voltage divider which sets the bias level - C49 is hooked across R78.

Here's the rub: Since the bias is originally tapped from the unfilted negative rail of the low V supply (approximately 15.6 VAC) you can't increase the voltage much - next, since you want keep the balance in the +/- rails you want to keep the total resistance of R77&78 around 15K - prehaps changing R78 to a 15K pot.

This enough to confuse you?

GW

PS: I remember providing this exact same info before - we need those archives!!

Replies:

Graywater Minor correction - 3rd paragraph sh... -- 5/26/2000 12:51 PM