Attenuator recommendations

Tonyptony: Thanks for asking for clarification, I've had too much espresso today.

I had one of Guy's Excellent Placette Active Preamps but it was impedance mismatched with my high sensitivity Lamm M1.1 amps. He suggested either adding his dual control volumn or just simply plugging in some 10dB shunts he would build for me. It might have been two Vishay, but his point was that this would be a very clean way to address the issue without modding either component.

There is a reason I just listen to the stuff and don't design it.

Tboooe, gain is gain no matter what the maximum output is so that would not be the issue. Input voltage times gain = output voltage.

However, the stated gain is with the volume control all the way up. The taper of the volume control is usually not linear and may be different for the 2 preamps. For instance, one preamp with the volume control halfway up could be near full volume and the other one only at half volume.

Tony, an attenuator can indeed by made with a single resistor in series with the input. As you conjectured the input impedance of the amp is the other resistor in the divider.

Although I would prefer not using one if I don’t have to, I’m not as dead set against using an attenuator as some. After all, the volume control is simply an adjustable attenuator. In most cases I would use one at the input of the preamp though instead of the input to the amp. The signal from CD into pre is much hotter than from pre into amp, the input impedance of the pre is usually much higher than the input impedance of the amp, and Pass amps are among the lowest. If you find a pre you really like any competent tech should be able to pad the gain either at the input or at the volume control.

Excellent point Herman. There are pre-amps with input gain switches. The manufacturers saw nothing wrong with putting the reduction ahead of the pre-amp line stage. ARC did this and others I'm sure.

Actually, although no one has mentioned this (I didn't read all of the posts so maybe I just didn't see it), don't most amps have the attenuator between the source and the line stage and the signal thats being attenuated is the signal from the source to the pre-amp, not the pre-amp to the amp?

Thanks for asking for clarification, I've had too much espresso today

Not a problem. :) I may call him about this. I wonder if he builds the shunts in the same sort of RCA M-F assembly as Rothwell. I'm dying to find out where to get that kind of thing so I can try to build my own. I've asked here and on AA and no one seems to know. Checked the usual electronics parts websites, too.

In most cases I would use one at the input of the preamp though instead of the input to the amp

Yeah, I'd have to agree with that, Herman. Makes it more complicated for me, though. First I'd have to build or buy multiple pairs. And second, my main source (D/A converter) runs to my pre over balanced ICs.

Maybe I should just send my pre back to Pass to have them mod it. The cost to get all those external attenuators would probably be about as much as just having the internals adjusted.