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Old 31st October 2004, 11:48 PM   #1
Stubb is offline Stubb  United States
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Join Date: Oct 2004
Location: Atlanta, GA
Default Reducing preamp/amp voltage gain?

The preamp/amp combo in our system consists of an Adcom 750 preamp and Bryston 4B ST power amplifier. The overall gain of these two components is fairly high, so the volume control rarely moves more than a few degrees from zero. This makes use of the remote difficult: a single push usually goes from "too loud" to "too quiet" and skips "just right."

Any thoughts on reducing the gain of this combo? The warranty on the Adcom has long since expired, but I'd rather not mess with the Bryston. The easiest solution would appear to involve building a fixed passive attenuator between the preamp and amplifier. Are there any rules of thumb for choosing the impedance of such a component to avoid trouble? The output impedance of the Adcom is listed as < 600 Ohms (< 1200 Ohms balanced), and the input impedance of the Bryston as 50k Ohms (20k Ohms, balanced). They're currently hooked via the unbalanced connection. A quick test with a VOM indicates that 1015 dB of attenuation should do the trick.

Thanks in advance for your suggestions.

Cheers,

Andreas
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Old 1st November 2004, 08:35 PM   #2
Tim__x is offline Tim__x  Canada
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Join Date: Jun 2004
Location: Edmonton area, Alberta
No real rule of thumb, it's weaker than that, maybe 'rule of pinky'

Keep the resistors high enough that you don't strain the preamp
keep the resisitors low enough that you don't put excess noise into the system.

May I reccomend a 10k and 3.9K with the 3.9k being the one tied to ground. In your particular setup this will give you around 12db of attenuation
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