Pre-amp suggestions for Thiel 2.4/Pass Labs XA30.5

Al, do you think that McIntosh is on too something that other SS folks are not addressing? Obviously they have been doing this for a long time - is it a difference that makes a difference and all towards the positive, or a just a tradeoff like so many other things in audio design?

Hi Paul,

I have no particular insight into that. But I note that the MC402 and MC501 are both described as double-balanced, meaning that each channel consists of two fully balanced amplifiers that are bridged together via the autoformer. I'd expect that a key factor in the choice of design approach was that the hardware required to implement a fully balanced amplifier that could provide the current necessary to support those kinds of high power levels into low impedance loads, using conventional approaches that don't use autoformers, would result in a large increase in their already very hefty size and weight, with cost increasing commensurately.

Best regards,
-- Al

Thanks Al. Interesting how in the example you provided the dBW's go up and then down with impedance halving. Some how I get the sense that McIntosh just fell back on some of the technology they previously used with their tube amps, and that it's a bit of a cost cutting approach, to avoid spending on expensive heat sinks, etc. Interesting that in the decades following Mac's introduction of ss amps, very few (any?) seem to have followed this with approach.

It occurred to me that back when Mac first started building ss amps, the transistors of the time were not nearly as durable as they are today, and perhaps to maintain reliability they used autoformers to keep them from getting stressed. Speakers of the time were probably higher impedance loads designed for the tube amps that were prevalent at the time. Using the autoformers with the those high impedance speakers also permitted them run more power into them.

This thread is long since dead, but I thought I'd finish it off now that I've tried a Pass Labs X250.5 and compared it to my INT-30A.

The X250.5 had better bass, but in the end the 30A was just much more natural. Vocals (even on hip-hop) sounded more real, and the soundstage was better defined. So, after all the amp comparisons, I ended up keeping the INT-30A, despite the shortcomings. Although I did add a Thiel SmartSub to help put some additional bass in the system.