300b lovers

Interesting circuit ... thanks for posting it, Ralph.

It’s kind of weird the actual gain/driver tube is a powerful 12BH7, while the cathode follower is limited to 1mA or so from the 12AX7, which is about the worst possible choice for a driver. Very strange. Maybe an intentional current-limit for the power tubes?

Also was not aware the global feedback network has its own winding, making four secondaries on the output transformer. Most everybody else samples the 16-ohm tap, which captures the entire secondary that powers the speaker. I kind of wonder if McIntosh did this to make the circuit hard to copy.

From this distance, I wonder about circuit stability. I see at least two feedback networks, one nested inside the other, and the outer loop not actually sensing the voltage on the speaker terminals, but a separate winding (which will never be exactly the same, especially at high frequencies). The circuit has a massive amount of forward gain (12AX7 -> 12AU7 -> 12BH7), so the feedback networks are definitely active.

I rebuilt a number of classic mac tube amps when I was restoring vintage gear.  They all sound very nice, but the mac house sound is a bit soft to my ear.  Sort of on the warm side.  Pleasant sounding, but not the absolute last word in detail.  The preamps sounded like that too.  Very good gear if you like that sound and very reliable, but warm....  CJ gear was also a warm sound.

They all had a different "house sound". Marantz was crisper and more resolved, a more hi-fi sound, and Fisher sounded like a really good console. Not sure if the H.H. Scotts had a consistent sound or not ... they were mostly known for their FM tuners.

Dynaco was always the "value for money" brand, like a VW Beetle.

The HK Citation gear was the most razor flat sounding, and the Fisher receivers were actually quite good.   The Scott gear was also quite good, and my favorite small integrateds were the Sherwoods.   Their little EL84 based integrated was quite good if rebuilt.  None of these are as good as the really good modern tube amps, but only the really good gear.  The transformers in the much of the old gear were really good, but they didn't have the quality signal path parts we have today.  Also, they had all sorts of features that robbed signal quality, like miles of wire in the signal path to support things like stereo/mono and phase reverse switches, and of course tone control circuitry.   Very long signal paths in many of the old integrated amps and preamps.

The Dynaco ST 70 had good transformers, but the driver section was barely adequate and if you replace it with one of the more modern boards, especially the all octal tube ones, the amp is greatly improved.  The small chassis limited the quality of the power supply you could fit in there though.  Still, if modded, the ST70 is a great little amp for the money.

Playlist

Here’s what I’ve been listening to for the past year. Probably zero percent overlap with Don Sachs, and only 10% overlap with the folks at Spatial. It’s a mix of dense heavily-produced rock, London Sound, and German techno.

Joywave: Traveling At The Speed of Light (7:34 version)

Joywave: Smokestacks

Big Data: Unglued

Big Data: Put Me to Work

Disclosure: Help Me Lose My Mind (featuring London Grammar)

Soul II Soul: Keep On Movin’ (demo quality)

Elderbrook: Inner Light

Elderbrook: I’ll Find My Way to You

Ulrich Schnauss: Far Away Trains Passing By (whole album)

Phosphorescent: Song for Zula

Tears for Fears: Elemental

Tears for Fears: Woman In Chains (demo quality)

Preferred Listening Format:

* Shadow Vector, Surround Master, or DTS Surround system

* Open-back planar headphones

* DHT triode system

Probably half these songs would get me thrown out of most hifi show demo rooms ... certainly the first four, for sure. They’re all really emotionally intense, which is why I listen to music. Both "Keep On Movin’ " and "Woman In Chains" have an unworldly beauty unlike anything else, and Ulrich Schnauss’ "Between Us and Them" is quite a sonic excursion.

I’ve been lucky enough to have several experiences that changed my life ... when I was ten years old and heard stereo for the first time, and heard a live performance of The Messiah the same year ... fifteen years later, hearing Shadow Vector quadraphonic for the first time ... twenty years later, hearing the Ongaku and Reichert DHT amplifiers on my new Ariel speakers ... and ten years after that, my own Karna amplifier. Profound, deeply moving, out-of-body experiences.

That’s why I find audiophile discussions of "accuracy" to miss the point. I don’t listen to music to sip a single-malt whiskey, smoke a Cuban cigar, scratch my chin, mark up a twenty-point checklist, and write long reflective essays about this or that subjective aspect of the sound. That’s silly. What’s the point? Who cares what XYZ critic thinks?

It either gets me flying or it doesn’t ... and if it does, how high?