How do we remember 1970s amplifiers?


I would be curious to hear some of the memories and impressions associated with the following short list of 1970s amplifiers:

- McIntosh "first generation" SS amps, MC2105, MC2505, MC2300, MC250, MC2100
- Dynaco Stereo 400 and Stereo 120
- Phase Linear 400 and 700
- Bang & Olufsen "slide rule" receivers (i.e. especially blackface Beomaster 4000)
- Original Ampzilla (not Son of Ampzilla)

I've chosen this list mainly because they cover a wide range of approaches to solving the issues of early semiconductor technology, and they were all pretty mainstream products in the U.S. I'm excluding the Japanese receivers/amps not out of predjudice; it's simply that the circuit designs varied quite a bit with each model, and thus harder to broadly classify their characteristics.

I'm interested in impressions of both sonic and non-sonic attributes, and a preferred ranking of the above, if you like.
kirkus
Pubul57, aside from tons of repair and modification, my audio design experience revolves mostly around small-volume or one-off custom stuff for pro audio applications . . . various iterations of analog and mixed-signal "preamp"-type stuff. This has included mic preamps, electronic crossovers, long-line drivers and receivers, active bandwidth-limiting filters, small low-noise mixers, etc. etc., and various combinations of these building blocks combined into a single chassis. I used to get a lot of requests like "We need these PA systems to be at least 8dB quieter at the inputs to the mid- and tweet-amps, and get rid of that 'clippy sound' in the bass when it's really loud. Can you build something to do that?" And I would . . . and all kinds of similar stuff in FM broadcast and recording.

But I'm not an EE - my education is in classical music, and the way we learned about harmony, part-writing, counterpoint, form, etc. was to study the works of the masters (and the also-rans, too). I tend to take this approach to the study of audio design . . . since it's much more informative to analyze the harmony in Schumann's "Ich grolle nicht" than a silly textbook example, I'd rather listen to i.e. a DC-300 or whatever, then measure it and study its circuit design, than simply read about hypothetical circuits (and equations simply for their own sake) in a typical undergraduate EE text. The repair process is a natural method for analysis and measurement, and since I like to listen to music while I work . . . I've always kept a well-set-up amp/speaker system on my test bench, so I'm always trying to correlate what I hear to what I see and measure.

And I'm also generally a sucker for history, and love hearing/reading people's stories and narratives . . . hence this thread. Again, thanks to all for the contributions!
I had fun building the hafler pre and power amp kits;dh101 and the dh500 power amp.At this time of my early audio hobby the dh500 I thought was just awesome and produced the best sound driving my infinity speakers;the 500 still surfaces now and then with mods from musical concepts;
it was a pretty good performer for its time.
The DynaKit 120 circuit is a preamp on steroids. Output through a big capacitor: no transformer. Its sound quality was critisized until they come out with the conventional 150, which made the 120 sound good. I had both.

The Kenwood L-07M is a direct-coupled amp, input to output. It is really an analog-programmable DC power supply, with response time fast enough to play music. Response is DC to 100KHz. You have never heard bass until you try the L-07M.
Siliab, I am still running the 630,620, 600 Nakamichis. Bought them in 1977 and using Totem Mani's as speakers and Oracle Alexandria MKIII with B&O EN20 cartridge.

All sound great in my room, still!

Salut, Bob P.

11-29-11: Kirkus

--->SAE was also founded by James Bongiorno who founded G.A.S. and also co-designed the Dynaco 400.

I thought Bongiorno was just one of several people who designed different SAE products (not one of the founders), but I may be wrong. I had forgotten his connection to the Stereo 400; thank you.
You're right. I knew he was involved; I thought he had founded it, but that was Morris Kessler, with whom I'm not familiar. It looks like Bongiorno was an early advocate for bigger power supplies and wider bandwidth for better behavior into reactive loads and better dynamics. Bascomb King was also a collaborator on Ampzilla, according to a conversation I had with his son. It may explain the rave review Bascomb gave Ampzilla in Audio Magazine at the time.

--->Currently my #1 power amp is just past the '70s--the 1981 Heathkit AA-1600. I got it used for $239 and it makes my jaw drop. Just two years into the '80s, it is so far beyond the amps of the '70s. It reminds me a lot of the 1990-ish Jeff Rowland Design Group amps.

I remember these from the Heathkit catalogs, and dug up a schematic . . . and from the way it looks on paper, I'm not surprised that you like the way it sounds. It's kinda like a simplified Dynaco 400, but with the biggest flaws fixed (esp. the intermediate stage with its current-mirror).
I'm stunned every time I listen through it as I am right now. There is none of the edginess or midrange/treble harshness that described the typical '70s big power amp.