Vintage amplifiers that could challenge or approach current state of the art amplifiers

[MakeMineVinyl]

Yah, but there's no easy way to do that (ideal, or reject odd order terms). I prefer to eliminate as much distortion as I can. You consider having more distortion an advantage?

I specifically said that NO distortion was the ideal.

 

[DonH56]

I specifically said that NO distortion was the ideal.

You said:

I wouldn't consider that an advantage. The ideal is no distortion, but I'd rather keep the even harmonics and reject the odd ones.

I would consider getting rid of some distortion an advantage but I understand even-order harmonics are preferred by listeners if you had to choose. I think we are talking past each other, probably my fault for browsing during a test run. Back to work...

 

[SIY]

I built a bunch in the 70's and 80's. Still have the preamp and the 30W ".01". Use the power amp as my test bench speaker amp.

And it hasn’t burned up? You lead a charmed life!

 

[DonH56]

This is what I said: >>>The ideal is no distortion <<< Is some part of that unclear?

Read all of it. You said you would not consider eliminating even-order distortion terms an advantage in response to my first post that listed reduction of even-order terms as an advantage. It's the first line in your response. I have no argument with the rest of it.

 

[anmpr1]

Are you old enough to remember Southwest Technical Products?

From slumming around the Net it appears that Jim Bongiorno's GAS Ampzilla was similar in design to some of the STP kits. One was called the Tigersaurus amp, which sounds like something Bongiorno would come up with. I vaguely recall hearing about the Tigersuarus amp but have no first hand experience with it or any of the STP products. I also missed out on Jim's Ampzilla kit. You snooze you looze as they say.

 

[bloodshoteyed]

The Kenwood power amps were very good, but had aggressive current limiting below 4 ohms and the Mk2 power amps are prone to going up in smoke due to stability issues. At one point, I had 7 of them. They are all sold and gone now. This is my pic from 2007. I kept the left hand pair up until a few years ago

as i was searching for old Kenwoods i stumbled upon this post of yours and i have a question - would you happen to know anything about the late 80s KA series? specifically the KA-1100D?
can't really find anyone with first-hand experience (besides the "i had it/loved it") let alone someone who was around back then servicing this stuff

 

[Doodski]

as i was searching for old Kenwoods i stumbled upon this post of yours and i have a question - would you happen to know anything about the late 80s KA series? specifically the KA-1100D?
can't really find anyone with first-hand experience (besides the "i had it/loved it") let alone someone who was around back then servicing this stuff

It appears to be a respectable amp from pics but it doesn't have the current capability from the pics I have seen.

 

[anmpr1]

It appears to be a respectable amp from pics but it doesn't have the current capability from the pics I have seen.

The idea of 'high current' is a somewhat 'new' idea in hi-fi, but one that has taken hold and is now pretty common. In the '50s and '60s an amplifier's low impedance current capability was not much of an issue because amplification was tube based, and well known electrostatics (such as the then 'high end' KLH Nine--16-30 ohms mostly resistive) and horn loaded loudspeakers didn't require that sort of power.

Early transistor amps were both voltage and current limited due to both parts availability and price considerations; they generally tended to be unstable with out of the ordinary loads, too. In any case most loudspeakers were going the 8 ohm 'nominal' route which accommodated the tube to transistor changeover. In the early days, a 60 watt/ch transistor amp was considered 'high powered'. The usual thing was probably 20-35 or maybe even 40 watts a side.

The first 'high powered' consumer amp I recall (Phase Linear 700) used Delco power transistors designed for automobile ignitions. It was good with resistive 4 ohm loads, however it's Audiograph Powercube capability into lower range capacitive/inductive loads was not impressive at all--certainly not by today's standards.

Japanese integrated amplifiers of the '70s were mostly designed with two and three way 'bookshelf' loudspeakers in mind. That was pretty much the only market they played in, and for that there was never a problem. The L100 didn't care. Even the AR3a (a 4 ohm speaker) could be driven to decent levels with a 60 watt/ch integrated amplifier, and most Japanese integrated amps were good for their rated power into 4 ohms.

A typical 'high powered' example was the mid to late '70s Pioneer SA-9500 integrated which was rated at 80 watts/ch into 8 ohms, and 100 watts/ch into 4. No lower ratings were given, because the amplifier would not pass the FTC schedule at lower impedances, and it really wasn't needed in the scheme of loudspeakers it played with.

The first time I recall 'current' being an issue was in the late '70s, and that was the Mark Levinson ML-2 class A amp, rated at 25 watts into 8 ohms, but was able to throw down 100 watts into 2 ohms. Others quickly followed. With that sort of power available, it was possible to design speakers such as the Apogee, rated at one ohm. Whether a one ohm loudspeaker represents 'progress' is another question, though.

 

[Doodski]

The first 'high powered' consumer amp I recall (Phase Linear 700) used Delco power transistors designed for automobile ignitions. It was good with resistive 4 ohm loads, however it's Audiograph Powercube capability into lower range capacitive/inductive loads was not impressive at all--certainly not by today's standards.

I had the Carver version of that Phase Linear in the Carver C-500.

The first time I recall 'current' being an issue was in the late '70s, and that was the Mark Levinson ML-2 class A amp, rated at 25 watts into 8 ohms, but was able to throw down 100 watts into 2 ohms. Others quickly followed. With that sort of power available, it was possible to design speakers such as the Apogee, rated at one ohm. Whether a one ohm loudspeaker represents 'progress' is another question, though.

Heheh... 1 Ohm is severely low impedance and I remember drOOling on the Krell amps for that reason.

 

[mhardy6647]

Pioneer, Kenwood "trash" and "dreadful sounding things

Not trash -- but not great, either, even by the (higher) standards of the day.
On the bright side, a generation of... well... dopers (and some other people without a penchant for recreational pharmacology) heard & developed a taste for decently-reproduced audio.

PS In my case -- guilty as charged! (although never any Pioneer or Kenwood in those days, nor Sansui nor Marantz, for that matter)

 

[sergeauckland]

US practice was always more 'adventurous' than UK practice, where in the late 1950s, the 20 watt Mullard 5-20 was described as being suitable for small halls, and the 5-10 (i.e. 10 watts) more than enough for domestic use.

Current output wasn't an issue, especially when loudspeakers of that era were normally 15 ohms, and 8 ohm was this modern new-fangled European fashion that good old UK didn't quite approve of. (the UK alternative was 3 ohms)

Then SS (Germanium) happened, and it was suddenly discovered that loudspeakers were nowhere near their 'nominal' impedance and this started to matter. Fortunately, Germanium was soon supplanted by Silicon, and that allowed loudspeaker manufacturers to pay less attention to impedance, and it's been a battle between amplifier power/current and loudspeaker impedance/efficiency ever since.

The ultimate, I suppose, was the Apogee Scintilla, with its 1 ohm impedance, which prompted Krell to rise to the challenge.

S.

 

[Doodski]

Then SS (Germanium) happened, and it was suddenly discovered that loudspeakers were nowhere near their 'nominal' impedance and this started to matter. Fortunately, Germanium was soon supplanted by Silicon, and that allowed loudspeaker manufacturers to pay less attention to impedance, and it's been a battle between amplifier power/current and loudspeaker impedance/efficiency ever since.

Old germanium doped transistors apparently have poor high frequency response. They sound to me, "Flat."

 

[sergeauckland]

Old germanium doped transistors apparently have poor high frequency response. They sound to me, "Flat."

The main problem with germanium power transistors was low ft, and the problem of thermal runaway that required bias current to be kept very low. This in turn caused crossover distortion, and some early SS amps, like the Leak Stereo 30, had decent enough THD at full power, but it didn't reduce at lower powers, and indeed increased due to crossover distortion. Frequency response to 20kHz was normally fine, but distortion increased significantly as frequency rose, so again, the Leak Stereo 30 claimed 0.1% THD at 8 watts output, into 15 ohms, not even at full power, but only at 1kHz. It was a lot worse than that at higher frequencies.

It was fortunately soon replaced by the Stereo 30+, which had 2N3055 output transistors and was a lot better.

As to sounding flat, don't know as I've never judged an amplifier by how it sounded, only how it measured.

S.

 

[Doodski]

The main problem with germanium power transistors was low ft, and the problem of thermal runaway that required bias current to be kept very low. This in turn caused crossover distortion, and some early SS amps, like the Leak Stereo 30, had decent enough THD at full power, but it didn't reduce at lower powers, and indeed increased due to crossover distortion. Frequency response to 20kHz was normally fine, but distortion increased significantly as frequency rose, so again, the Leak Stereo 30 claimed 0.1% THD at 8 watts output, into 15 ohms, not even at full power, but only at 1kHz. It was a lot worse than that at higher frequencies.

It was fortunately soon replaced by the Stereo 30+, which had 2N3055 output transistors and was a lot better.

As to sounding flat, don't know as I've never judged an amplifier by how it sounded, only how it measured.

S.

That makes sense. I've heard some old germanium doped transistor Sansui and other amps that I serviced and they all sounded flatter than say a new British integrated or receiver. Yes, the build quality was great but the sound was weak and flat.
https://www.whathifi.com/us/features/9-of-the-best-british-stereo-amplifiers-of-all-time

 

[anmpr1]

Current output wasn't an issue, especially when loudspeakers of that era were normally 15 ohm sand 8 ohm was this modern new-fangled European fashion that good old UK didn't quite approve of...

This is important to keep in mind from an historical perspective. Anent the high current 'voltage limited' ML-2, the British loudspeaker scene, etc., an excerpt from a letter Julius Futterman wrote to Peter Aczel might be of interest--keeping in mind that Julius' amp would 'blow up' at 4 ohms, but could pump out 100 watts per channel into 16:

"Before transistor amplifiers the rated impedance of most high fidelity speakers was 16 ohms. In Britain practically all speakers were 15 ohms. There were sound reasons for this as, all other things being equal, a higher impedance speaker is more efficient and the crossover design is not as complex. We are referring, of course, to moving-coil speakers.

"The reason for the lower impedance of speakers today is, of course, the fact that transistor amplifiers, being voltage limited, provide more power for such speakers. As an interesting aside you implied in your review of the Tangent RS2 that it was an inefficient speaker as you were able to make the Levinson ML-2 clip on it with a master tape of piano music. On the other hand, I can make the Tangent RS2 play very loud with the H-3aa. The reason for this is simple : The impedance of the RS2 at 70 Hz, for example, is 11.5 ohms; at 500 to 2000 Hz it is 9 ohms, and it rises steadily to over 20 ohms at 6 kHz, which is well above the fundamental tones of the piano. With the ML-2's 14 volt maximum voltage rating you can see that there is very little power to drive the Tangent. End of digression.

"Electrostatic speakers are inherently of high impedance and this is lowered by means of a transformer. The Acoustat [here Julius is talking about the Acoustat X and not Jim Strickland's later transformer interfaced models] and Beveridge speakers use a different approach. They do not use a transformer; instead they employ very high voltage amplifiers to drive the speakers directly. The KLH-9, Quad, and Koss are examples of speakers using transformers. In general, the lower the turns ratio of the transformer the better the speaker because of tighter coupling and other factors that I will not go into here. The KLH-9 impedance is 16 ohms, the Quad 15 ohms and the Koss 4 ohms The KLH 9 and Quad were designed for tube amplifiers, the Koss for solid state."

PS: with this in mind, Harvey Rosenberg's team sold special order OTL amps specifically designed for the original Quad, and I think KLH loudspeaker. I don't know how they differed from the 'off the shelf' Futterman amps, though.

 

[mhardy6647]

Are you old enough to remember Southwest Technical Products?

Oh, yeah.

There's a SWTPCo preamp upstairs someplace. Afraid to even plug it in.
The amps were kind of notorious for failing dramatically... sort of like Bob Carver's early Flame Linears, but even somewhat more immolatable (immolatory? I do enjoy making forms of words ab initio)

I knew a guy in grad school with a couple (maybe four, upon reflection) SWTPCo Tigers (IIRC), and DIY Bose 901 clones. That hifi could raise a ruckus.
I also remember he had some sort of delay line -- I don't remember why though.

The mighty and terrifying Tigersaurus

Along these lines -- among the doorstops/paperweights in the basement -- a GAS Ampzilla (with profound issues in one channel) and a Dynaco ST-400 (which I would never plug in "as is").

 

[DonH56]

Oh, yeah.

There's a SWTPCo preamp upstairs someplace. Afraid to even plug it in.
The amps were kind of notorious for failing dramatically... sort of like Bob Carver's early Flame Linears, but even somewhat more immolatable

I knew a guy in grad school with a couple (maybe four, upon reflection) Tigers (IIRC), and DIY Bose 901 clones. That hifi could raise a ruckus.
I also remember he had some sort of delay line -- I don't remember why though.

I missed the SWTP diversion... Neat company, but my limited experience is the same -- the amps tended to blow up. Since I already had (and finally ditched) an infamous early model Phase/Blaze/Flame Linear 700 the only Tigers/Tigersaurus and such I had were the ones I was building (kits) or fixing for others. My very vague recollection is that the company was easy to work with though sometimes late with deliveries of parts.

They had a pretty big catalog before the end, including a function generator (not real clean but fairly cheap), frequency counter, and various computer kits. They defined their own bus IIRC, and used Motorola processors -- can't remember if they ever moved to Intel. I actually had a CT-1024 to use with my old COSMAC ELF (RCA 1802-based) computer kit.

 

[mhardy6647]

They seem to be better remembered for their 'putes at this late date than for any of their other products (kits).
There used to be a nice SWTPCo fanboy site, with several mostly complete catalogs, but I think it's gone other than a smattering of captures available via the Wayback Machine.

 

[DonH56]

Yah... IIRC they were actually pretty well-known for their computers and had some good ideas at the time. I lost track of the company many years ago. One of the local electronic labs had a bunch of their amps plus some other gear; I think the owner had a connection to Meyers, maybe from college days. Too long ago, don't remember now, but I do remember he'd come in with 4-8 Tigers at once for repair.

 

[SIY]

When they weren’t catching fire, the performance was excellent. Very advanced design for the era. I had a pair of heavily modified Super Tigers that went almost two years before conversion of all the silicon to carbon. They worked spectacularly well during their abbreviated life.