Ohm Walsh Micro Talls: who's actually heard 'em?

Spoke to Matt at Bel Canto today. He says that what's called for is a preamp with an impedance output of between 50 and 100 ohms

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Rebbi, there are a limited number of tube preamps avaiable that will fall in the 50-100 output impedance range but if a Bel Canto rep says it, then its advisable to stick with that. I'd steer clear of preamps with output impedance in the thousands if I were you. The Juicy Music preamps do have variable output impedance that can be swithced to low output impedance.

If you don't need a phono section, the Juicy Music Peach I (or II) has a selectable output impedance with a low Z option of 50 ohms. It's a heck of a preamp if you can be patient and fine one used.

IMO, the 3.5k Ohm output impedance of the Blueberry is too high to match with most solid state amps because of the risk of rolled off bass.

Rebbe,

YEs, the Peach is the one without phono and apparently lower possible output impedance also, so that would be the Juicy Music one for you to consider.

Tvad,

I know you've heard a lot of combos and have a good handle on the matching impedance issue between amp and pre.

Do you find that the ratio of amp input to pre-amp output impedance is a reliable indicator of performance? If so, what differences do you hear consistently as this varies? Are there thresholds regarding this ration that can be identified that reliably predict actual performance in certain areas?

Thanks for whatever insight you might offer up on this topic.

The best indicator is bass extension and response (clarity, control).

I've found that 200 ohms or lower works best with most solid state amps having 23k ohm input impedance or higher.

Most preamp manufacturers I have asked have said that an output impedance of up to 500 ohms would be fine, but what I have heard in my system has not confirmed the advice.

In all cases regarding preamp output impedance when used with a solid state preamp, lower has been better.

I have found John Atkinson's test measurements section of Stereophile reviews extremely helpful on this topic. He always addresses output impedance in preamp tests, and input impedance in amplifier tests, and he suggests impedance matching thresholds.