How do we remember 1970s amplifiers?

The music was so much better back then that we didn't know the equipment was lousy, and a good time was had by all.

Since everything is relative, and none of us had rigs much better or much worse than the next guy; we all thought our rigs were killer at that time.

My first stereo was an Altec-Lansing 911A compact in 1972 for $419 (about $2160 in today's money). It aspired to rare heights for a compact--it incorporated a (slightly de-tuned) Altec 44 wpc receiver, Garrard SL95B (their top line consumer deck until the Zero 100), Shure M93ED, and Altec 887A speakers, an 8" 2-way sealed cab. The tuner section was excellent and the amp section wasn't too shabby either.

A couple years later I was working at a hi-fi store in SoCal where our amps were Phase Linear (we needed their 700 to power the Ohm F's), Accuphase, Marantz Pro (a good lie at the time), Crown, and a few SAE's left over.

One day We hosted a Marantz clinic where an audio engineer would measure (for free) power and distortion on any unit you could lug in. I proudly brought in my Altec 911 and was disappointed to find that its 44 wpc at mid-band dropped off to 27 wpc at 20 Hz. Turns out Altec had shrunk the power supply (compared to the receiver it was based on) to fit it in the cabinet with the turntable.

There was an orphan pair of entry-level SAE components back in the storeroom--the Mk XXX preamp and the Mk XXXIB power amp. I picked those up and started using them instead. The amp was rated at around 50 wpc but the tests at the time indicated it put out more like 70, but the cool thing is it had textbook square wave response (even better than the Crown) in the bass. You could really hear that--any speaker it powered had cleaner, tighter, more extended bass with this thing than with a receiver.

SAE was also founded by James Bongiorno who founded G.A.S. and also co-designed the Dynaco 400. As I remember it, however, the treble was a bit hot. Still, I wonder how much our perception of the separates of the time is influenced by the way we used them. We had no awareness of a "burn-in" period, let alone a warmup period for solid state. We plugged things in and immediately started evaluating them. Now I never turn my power amp off, and it was pretty edgy when I first plugged it in and turned it on.

I also had the privilege of meeting John Iverson and spending a day with him as he demonstrated his incredible A-75 class A power amp into his own speakers. Until that day I'd never known that hi-fi could do *that*!

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.

Dynaco Stereo 300 / QSA300 Power Amplifier



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Description:

Specifications:

Rated 4-channel Power Output: 75 watts continuous average power per channel into 8 ohms (40 watts per channel into 16 ohms) 20-20,000 Hz, at less than 0.25% total harmonic distortion. Distortion reduces at lower power outputs.

Available 4-channel Output Power:

20-20,000 Hz, all channels driven, 0.25% maximum THD:

75 watts continuous average per channel @ 8 ohms;
100 watts continuous average per channel @ 4 ohms;
40 watts continuous average per channel @ 16 ohms.
Stereo Operation Available Output Power:

Low Impedance Mode Connections:

80 watts continuous average per channel @ 8 ohms;
150 watts continuous average per channel @ 4 ohms;
200 watts continuous average per channel @ 2 ohms;*
High Impedance Mode Connections:

80 watts continuous average per channel @ 16 ohms;
150 watts continuous average per channel @ 8 ohms;*
* 5 minutes sustained full power limit without a fan.

Power at Clipping, 1 of 4 channels, 2500 Hz, less than 1% distortion:

90 watts @ 8 ohms;
130 watts @ 4 ohms;
45 watts @ 16 ohms.
Power at Clipping, Each Stereo channel, 2500 Hz, less than 1% distortion:

Low-Z mode:

95 watts @ 8 ohms;
160 watts @ 4 ohms;
240 watts @ 2 ohms.
High-Z mode:

160 watts @ 8 ohms;
90 watts @ 16 ohms.
Intermodulation Distortion: Less than 0.25% at any power level up to 75 watts rms per channel into 8 ohms with any combination of test frequencies. Distortion reduces at lower power levels.

Half-power bandwidth: 37.5 watts per channel at less than 0.25% total harmonic distortion from 5 Hz to 50 KHz into 8 ohms.

Frequency Response: +0, -1 dB, 10 Hz to 40 KHz @ 1 watt into 8 ohms; ±0.5 dB, 20 Hz - 20 KHz @ 75 watts into 8 ohms.

Hum and Noise: Greater than 95 dB below rated output, full spectrum.

Input: 35,000 ohm load; 1.0 volt for 75 watts into 8 ohms.

Semiconductor Complement: 52 transistors, 40 diodes.

Slewing Rate: 7 volts per microsecond.

Damping Factor:

Greater than 80 to 1 KHz into 8 ohms;
Greater than 50 to 10 KHz into 8 ohms.
Channel Separation: Greater than 70 dB by IHF standards.

Connectors: Inputs: phono jacks. Outputs: Color coded 3-way binding posts with standard 3/4" spacing.

Dimensions: 18-1/4" wide, 14-1/2" deep;, 7" high panel, 17-1/2" wide. Add 1/2" for feet.

Shipping weight: 58 lbs. Net weight: 52 lbs.

Power Consumption: 120 VA quiescent; 10 amps maximum; 50/60 Hz, 120/240 VAC.

Designed by:

Harry Klaus

Year Introduced:

1976

Price:

$269.00 kit
$399.00 assembled

Comments:

Basically two ST-150 units in a single chassis, with separate power supplies. Usable as four independent channels or as a bridged stereo amplifier with 300 watts per channel. The MC2/MC3 meter kits provided output monitoring.

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This page created and maintained by Greg Dunn.
Copyright © 2000 Greg Dunn

I originally purchased this as a 4 channel amp which I used with my "Quad" Phase Linear 4000 pre. At that time, I thought it was "hot stuff".

Now, it is in use as a bridged stereo amplifier with 300 watts per channel. It sounds like what it is, "A big powerful mid fi amp". It works fine in our entertainment room where at least three conversations are always going on at the same time.

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.

One thing about the Dyna 400 and the GAS products was that they didn't skimp on the quality of the silicon . . . these were all fully-complementary output stages that used the transistors' characteristics very effectively. The GAS amps extended the complementary-pair thinking through to the input and voltage-amp stages, which IMO deserves respect for its conceptual elegance, even though there are some fundamental problems with its implementation. This fully-differential approach is also a hallmark of many of John Curl's designs, though I would hesitate to imply that the Levinson designs bore influence from the GAS.

But the Ampzilla was hugely influential . . . it did start out as a project amplifier with the schematic published in a magazine, and like the Williamson amp published 25 years or so before, bits of it seem to turn up everywhere. The current crop of McIntosh SS amps (from approx. the mid-1990s) use a front-end that strongly resembles Ampzilla's, with a few refinements.

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 remember my dad replacing his Fisher receiver (complete with built-in tape deck) and Fisher speakers with a new McIntosh 4100 receiver, DCM Time Window speakers, and a Nakamichi cassette deck. The difference in power and sound was incredible and formed the basis for my interest in audio. I have since moved the Mac/DCM combo to a second home, and it still sounds great.