I don't have the numbers but this mono block is far from little.
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Vintage amplifiers that could challenge or approach current state of the art amplifiers
- Thread starter restorer-john
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restorer-john
Grand Contributor
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I wouldn't call it "little" either.
The POA-6600A design is virtually identical to the slightly lower powered 200+200W@8R/350+350W@4R POA-2800 I have here. Same opto-coupler bias, same output stage devices minus one pair of OPTs. It was around 1995ish IIRC.
The POA-6600 is more like the so-called no-NFB models POA-1500/3000 etc.
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EarlofChatfield
New Member
Still humming along in my equipment rack... Any opinions on how an Adcom GFA-555 stacks up?
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Nice! I own a 535 and 5400 and enjoyed both for many years.
According to this Ken Rockwell review, which includes plenty of measurements, it's a killer unit:
https://www.kenrockwell.com/audio/adcom/gfa-555-ii.htm
He reviewed the MKII version, but it's likely the original (which has a more vaunted reputation) measures very similarly.
I was also struck that the 555 he reviewed measured notably better than the 545 and the two 535s he also measured.
Only issue I'm aware of with these old Adcom amps is that they lack speaker protection.
In fact, aside from a lack of speaker protection (and the mechanics of the power switch, which apparently has a habit of going south), I would think this amp would tick all the boxes for the subject of this thread - it provides gobs of low-distortion power and an argument can be made that in terms of specs it's close enough to modern state of the art to be similarly audibly transparent.
@restorer-john , I hesitate to even ask, but would you agree that this is one of those amps that "could challenge or approach current state of the art amplifiers"? It seems like it is, yes?
The only historical knock I've seen on this amp is a series of subjective reports that it sounds "dry," "etched," or "unrefined." But surely that kind of subjective claim wouldn't disqualify an amp at this forum, yes?
I posted some measurements a few days ago. Good enough for audible transparency, but nowhere near current state of the art for measurements.
Ok...here's another one I dug out... Any experience with these?
Mitsubishi DA-A15DC
Pics with and without meters...those up the cool factor a bit...
Edit: One more from above...
Mitsubishi DA-A15DC
Pics with and without meters...those up the cool factor a bit...
Edit: One more from above...
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Vini darko
Major Contributor
I think XraytonyB had some of those for restoration recently. Very nice kit
Vini darko
Major Contributor
I have the 545 mk2 which I own, like it a lot along with the GFP565 preamp.
Maybe one day I will put my hand on 555mk2.
Enjoy
I need to figure out how to safely ship these heavier amps to @amirm for testing and I will wait until his back is better.
I am willing to bet that these amps will beat the average SINAD.
1960s era: American Mid-Century Craftsmanship
JBL SA600. At the time, performance exceeded the capabilities of instrumentation. They knew that it measured 0.2% THD with zero feedback up to about 10 Watts, and they claimed that with negative feedback, the THD should be 1/50th of that.
http://www.aes.org/e-lib/browse.cfm?elib=1091
100 dB SNR at 10W or lower.
Guesstimated SINAD of 84-88 depending if the THD really is as good as thought.
McIntosh MC2105. People love the blue meters, and the reliability of this amp is well established. This is also a vintage amp that continues to hold its value.
Not the same amp, but it does show that measured performance can be very good with auto formers
Mc2255 Measurements
I think we hit the threshold of audibility with these amplifiers in a listening positioning for recreational listening with normal ambient noise. You may gain more detail with newer amps and more power with newer amps.
1980s era: Japanese Economic Miracle “Bubble” Era
Accuphase P-266. Switchable Class A or AB. SNR rated to 120 dB. THD is competitive against modern Class AB amps. Lower power than today’s best.
http://www.accuphase.com/cat/p-266en.pdf
Kenwood L-08M. Final generation of the DC high speed amplifier backed with Kenwood Sigma Drive. 20,000 damping factor. Only 116 dB SNR and hiss can be heard with your ear directly to the tweeter of a high-efficiency JBL 4319. More noise than today’s best but still one of the highest damping factors of any amplifier.
https://1001hifi.blogspot.com/2018/04/kenwood-l-08m-rebirth-of-amplifier1980.html
2000s era: Audiophile Jewelry Era
McIntosh MC2102. The tube amp build to match solid state performance. Equivalent of a high-precision mechanical watch, it pulls out all the stops to produce an amplifier with no transistors in the signal path to achieve a measured performance that matches an average solid state amp. Imagine a mechanicslcwatch with the reliability of accuracy or a Casio solar. Tubes provide the benefit of the soft clipping and harmonics of tubes as you drive the volume up.
Devialet Phantom Silver: Not a traditional amp in the classic sense, but unlike the Devialet Expert that was measured here, a highly DSP’d speaker with superb bass extension at average listening levels of 80-85dB. Plagued by idiosyncratic software. The original firmaware allows it to be run in a pure direct optical, low latency mode which is where the speaker performs the best. The current generation Phantoms have dropped that low latency feature.
I am willing to bet that these amps will beat the average SINAD.
1960s era: American Mid-Century Craftsmanship
JBL SA600. At the time, performance exceeded the capabilities of instrumentation. They knew that it measured 0.2% THD with zero feedback up to about 10 Watts, and they claimed that with negative feedback, the THD should be 1/50th of that.
http://www.aes.org/e-lib/browse.cfm?elib=1091
100 dB SNR at 10W or lower.
Guesstimated SINAD of 84-88 depending if the THD really is as good as thought.
McIntosh MC2105. People love the blue meters, and the reliability of this amp is well established. This is also a vintage amp that continues to hold its value.
Not the same amp, but it does show that measured performance can be very good with auto formers
Mc2255 Measurements
I think we hit the threshold of audibility with these amplifiers in a listening positioning for recreational listening with normal ambient noise. You may gain more detail with newer amps and more power with newer amps.
1980s era: Japanese Economic Miracle “Bubble” Era
Accuphase P-266. Switchable Class A or AB. SNR rated to 120 dB. THD is competitive against modern Class AB amps. Lower power than today’s best.
http://www.accuphase.com/cat/p-266en.pdf
Kenwood L-08M. Final generation of the DC high speed amplifier backed with Kenwood Sigma Drive. 20,000 damping factor. Only 116 dB SNR and hiss can be heard with your ear directly to the tweeter of a high-efficiency JBL 4319. More noise than today’s best but still one of the highest damping factors of any amplifier.
https://1001hifi.blogspot.com/2018/04/kenwood-l-08m-rebirth-of-amplifier1980.html
2000s era: Audiophile Jewelry Era
McIntosh MC2102. The tube amp build to match solid state performance. Equivalent of a high-precision mechanical watch, it pulls out all the stops to produce an amplifier with no transistors in the signal path to achieve a measured performance that matches an average solid state amp. Imagine a mechanicslcwatch with the reliability of accuracy or a Casio solar. Tubes provide the benefit of the soft clipping and harmonics of tubes as you drive the volume up.
Devialet Phantom Silver: Not a traditional amp in the classic sense, but unlike the Devialet Expert that was measured here, a highly DSP’d speaker with superb bass extension at average listening levels of 80-85dB. Plagued by idiosyncratic software. The original firmaware allows it to be run in a pure direct optical, low latency mode which is where the speaker performs the best. The current generation Phantoms have dropped that low latency feature.
What about Avantone Pro CLA-200 Power Amplifier? Class A/B, 200wpc 8ohms, 300wpc 4 ohms?
Input sensitivity is 0.775volts, and it has gain/volume knobs in the front, one for each channel. Not sure if the gain knobs would help or hurt the overall sound quality if driven by a source outputting 2vrms....
If it says input sensitivity is 0.775v, does that mean when the gain knobs are turned clockwise to the max setting (+20 notches) or is that when the gain knobs are turned to the lowest setting (+1 notch?)?
I would say this amp seems like a worthy contender but I’m not sure if it’s input sensitivity is variable and compatible with streamers and av receivers and DACs. Wish they gave a range in the input sensitivity like the Hafler P3100 power amplifier does on its specifications sheet... if anyone has any experience with the CLA-200 power amplifier, please do share your thoughts on it as I would really like to know! Cheers.
Input sensitivity is 0.775volts, and it has gain/volume knobs in the front, one for each channel. Not sure if the gain knobs would help or hurt the overall sound quality if driven by a source outputting 2vrms....
If it says input sensitivity is 0.775v, does that mean when the gain knobs are turned clockwise to the max setting (+20 notches) or is that when the gain knobs are turned to the lowest setting (+1 notch?)?
I would say this amp seems like a worthy contender but I’m not sure if it’s input sensitivity is variable and compatible with streamers and av receivers and DACs. Wish they gave a range in the input sensitivity like the Hafler P3100 power amplifier does on its specifications sheet... if anyone has any experience with the CLA-200 power amplifier, please do share your thoughts on it as I would really like to know! Cheers.
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First time poster, long time lurker. Hi People!
Early Onix amps had a reputation, I have the OA21 plus SOAP power supply and find it to be clean and commanding. Any thoughts on this model?
It'd be interesting to see if the measurements stand up to the experience...
Early Onix amps had a reputation, I have the OA21 plus SOAP power supply and find it to be clean and commanding. Any thoughts on this model?
It'd be interesting to see if the measurements stand up to the experience...
OP
restorer-john
Grand Contributor
Have 1 in use with the preamp as my main system. Recapped, amazing performance.Yamaha M-85 is a classic of the day and has the grunt to back it up too.
It was in a thread discussing crossover distortion. Something like Class A vs Class D.
Sorry, on my phone so search is clumsy.
Likely not available but measuring it with modern tools would be interesting. Designed by Dick Burwen in the late 1950's
At Krohn-Hite Corp. Dick designed the laboratory UF101 Ultra-Low distortion Power Amplifier. Using type 6550 output tubes in a multiple-loop, high-feedback system, this amplifier, rated at 0.005% distortion was manufactured in small quantity for 20 years.
http://www.burwenaudio.com/Krohn-Hite_UF-101.pdf
At Krohn-Hite Corp. Dick designed the laboratory UF101 Ultra-Low distortion Power Amplifier. Using type 6550 output tubes in a multiple-loop, high-feedback system, this amplifier, rated at 0.005% distortion was manufactured in small quantity for 20 years.
http://www.burwenaudio.com/Krohn-Hite_UF-101.pdf
That's an amazing amplifier. It's indicative of the time that the manual even had a full circuit diagram and circuit description. Contrast that with today's products!
It does, however, go to show how far we've come that that performance can now be achieved for (relatively) pennies using a chip amp. Equally it goes to show that high performance isn't anything new and today's stuff is only 'better' when price (and reliability it has to be said), are taken into account.
S.
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Never heard of this before - very cool, and thanks for the link!
Two comments/questions from reading the spec sheet:
1. Feedback. It appears to be a high-feedback design, yes? It says it uses 80dB of feedback, and the voltage gain goes from 14dB all the way up to 30dB with "reduced feedback," suggesting that the feedback must be significant if it reduces the output that much. Thus feedback would seem to be a major factor in reducing the distortion, and goes against - or I would presume pre-dates - the audiophile distaste for feedback, especially among folks who would seek out tube-based gear. (To be clear, I'm not anti-feedback myself.) Very interesting.
2. Gain. The voltage gain figures are interesting, and I wonder if anyone more knowledgeable than me can translate them into more of an apples-to-apples comparison with modern gear. The stated gain is 14dB, which is very low, but that's into a 16 ohm speaker - would the voltage gain increase into a more typical 4 ohm or 8 ohm load?
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