Modwright LS 36.5 or BAT VK-51SE

Greg, I have no information specific to Lamm being noisy with other amps. However, you are correct to be concerned, and you should pay attention to this issue with a demo. Particularly with the Pass which are so quiet, adding a noisy preamp is one step forward, two steps back. If you can readily hear the difference in noise from your listening position in a quiet room with the preamp on vs. muted, then it may nag you in the end. I think noise destroys a soundstage.

In terms of mismatch, also consider that cabling is HUGE in defining bass and upper-end extension (PC, IC, SC). So many cables out there restrict both, or do one at the expense of the other.

Since the output impedance spec of the Dude is not provided, it seems to be a situation where you'd have to hear the preamp in your system to decide if it matches or not. You'd want to be listening for rolled-off highs. I don't know what a resistor pull-down XLR is.

The BAT VK-51SE was tested by Stereophile, and the output impedance was measured at 410 ohms (200 ohms spec'd by BAT), and rising to 4700 ohms at 20K.

Grant, I think you meant to say 20Hz, not 20K, and that what should be listened for is rolled off lows, not highs.

I don't know what a resistor pull-down xlr is either.

The posts by Atmasphere starting here provide some insight into the output impedance of the Dude. It sounds like a major contributor to its output impedance is the volume control and its setting (he indicates that the control is located at the output), with the output coupling capacitor perhaps being no more than a secondary factor.

Since the volume control is essentially resistive, rather than capacitive, its contribution to output impedance would be pretty much constant with frequency. So high output impedance would be much less of a concern than in the more common situation where it is due primarily to the output coupling capacitor, which would cause the output impedance to be much higher at very low frequencies than at higher frequencies. It is the DIFFERENCE in output impedance between those frequencies that causes low frequency rolloff when output impedance is too high relative to power amp input impedance.

Best regards,
-- Al

I should add to my previous post that high output impedance that is primarily resistive, and is therefore high at high frequencies as well as low frequencies, can result in upper treble rolloff due to its interaction with cable capacitance. But that is easily avoided by using low capacitance cables and/or avoiding long cable lengths, and is unrelated to which power amp is used.

Best regards,
-- Al

Roor, why the pre-amp search if you are upgrading your Pass pre-amp? It is my understanding that Nelson Pass creations are best if used together particularly in light of the impedance matching issues.

In terms of pre-amp options, I cannot speak to the BAT or Modwright as I have not heard them in my system. I would consider calling Dan Wright and seeing if any of his pre-amp owners also own Pass amps for more feedback. Otherwise, use your gut and buy something used for a trial.

I am a TRL Dude owner and love that unit, but also use their monoblocks and not Pass Labs. I don't know of any TRL who also owns the Pass Labs amps. The Weitzels might know.

Regarding "pull down resistors," that is simply studio slang for a xlr-rca adapter using a resistors to come up with a "phantom" negative phase. Cardas sells them. Nothing mysterious there.

"The posts by Atmasphere starting here provide some insight into the output impedance of the Dude"

Almarg, there is no insight there. Just misinformation.