[klao]

Any general guideline or recommendation on the preamp output impedance number to match with the 7B's balance input? 

Thanks all in advance.

[klao]

Published input impedance of the 7B's is 20K Ohms, but if I'm not mistaken, the latest Stereophile's measurement reported it to be 10K Ohms, so I'm not sure how low should a preamp output impedance should be to drive these monoblocks well.

I mean, what should be the acceptable ratio (amp's input / preamp's output).

Thanks you.

[raindance]

Most true balanced preamps should be 600 ohms or less output Z. If you are driving one amp, you are best with a preamp output impedance of around 10x less. If you are driving two amps, this value would be halved.

So, anything less than 1K should do for one amp.

If your cables are long, you will need to have a lower output impedance.

What preamp are you considering?

[vegasdave]

If you go with a Bryston preamp, that would make things a lot easier.

[klao]

I'm considering tube ones with HT bypass and two sets of XLR preouts, like Aesthetix Calypso, upcoming ARC LS27, and ARC Ref5 (used), although I really love the sound of BP26 & MPS2 + 7B/28-SST2 in dealer's showrooms.  If Bryston preamp, I'll have to toggle the RCA/XLR switches behind my 7B's if I hook them up with another AV receiver or processor when watching movies.  Just too lazy for that. 

Also, I prefer to have an extra pair of XLR rather than RCA preouts so that I can connect to a pair of subwoofers.

Since James has not commented on the new SP3 sonics as compare to the BP26, I might just go with 2-channel preamp + (cheaper) AVR/processor.