[jaxwired]

Hi everyone.  I need someone that is educated on this subject to help me out.  I've read that you have to be careful when matching preamps with amp to make sure the impendances are compatible. Can anyone expand on this for me?  What exactly should I be looking for when matching a preamp to my 4bsst2?   Thanks!

[wilsynet]

As I understand, rule of thumb is the input impedance should be 10-20x greater than the output impedance.  Some people say 10x, others say 20x.  You can be aggressive, you can split the difference or you can be conservative and assume 20x.

As a concrete example, with 20x as a guide, if the output Z of the preamplifier is 1K ohms, then the input Z of the amplifier should be 20K ohms or greater.  Same rule of thumb should be applied to source versus preamp.

[srb]

The "rule of thumb" for impedance matching preamp and power amp is that the power amp's input impedance be a minimum of 10X the preamp's output impedance, with 20X - 30X being even better.
 
The Bryston 4BSST2 has an input impedance 50K Ohm on the single-ended inputs and 20K Ohm on the balanced inputs.  The maximum output impedance for a preamp should therefore be ~ 5K Ohm single-ended and ~ 2K Ohm balanced.
 
You will not always find published input/output impedance specs on all gear.  I don't see output impedances listed for the Bryston preamps, but obviously you can be sure they are a good match.  Most solid state preamps will be a good match, but some tube preamps may have higher output impedances.
 
Also, the amount of gain may vary in a preamp and if the gain is too high this may result in a limited useable volume control range.
 
Steve

[jaxwired]

Thanks guys.

So a preamp as follows would be fully compatible since it's way under 5k ohms.  Right?

OUTPUT IMPEDANCE: 260 ohms Single Ended main; 20K ohms minimum load and 1000 pF maximum capacitance.

[James Tanner]

The Bryston BP26 preamplifier has 50 ohms of impedance on the RCA outs and 100 ohms on the Balanced out (50 ohms per leg)

james

[SoundGame]

Thanks guys.

So a preamp as follows would be fully compatible since it's way under 5k ohms.  Right?

OUTPUT IMPEDANCE: 260 ohms Single Ended main; 20K ohms minimum load and 1000 pF maximum capacitance.

Perhaps you have some leeway but sticking as close to the Bryston spec. James quoted might be the safest approach - though that may reduce your options.  I've heard of a lot of people matching ARC with Bryston with good results.  Not sure of the specs on the ARC preamps.

[schugh]

The ARC LS17 I am using with my 4B-SST2 says:

Output Impdence: 700 ohms Balanced, 350  Ohms SE Main. 20L minimum load and 2000pF maximum capacitance.

Seems to be working fine.

-- Sanjay

[wilsynet]

OUTPUT IMPEDANCE: 260 ohms Single Ended main; 20K ohms minimum load and 1000 pF maximum capacitance.

From an on-paper point of view, very compatible.  No issues there.