Yamaha A-S701 Stereo Amplifier Review

[TankTop]

How does it sound?

It doesn’t

That’s what you’re speakers are for but luckily it doesn’t screw that up in any way that you could ever imagine to hear

 

[Hipster Doofus]

I've owned this integrated amplifier for the last two years, and I could not be happier. Bought it second hand for €500 and they're well worth it.
I must say that the phono stage is pretty decent (moving magnet), I'm running a high output moving coil cartridge turntable through it, and despite having to raise the volume to almost half, the system output does not seem to add any perceptible noise to the signal (I'm 47 years old... take that into account for the high frequencies hearing loss).
It would be nice if @amirm had the time and product availability to measure it. I'm intrigued by what the results would be.

just turned 70...high frequency what did you say

 

[norman bates]

lol

Sitting 6' away from 6.5" 2-way, I can listen pretty flat.

But sitting 10-20' away, on a pair of 12" 2-way speakers without baffle step, listening far under 90db, my loudness knob is a welcome addition.

 

[capslock]

I just measured the AX-592. It looks very similar to PMA's results on an AX-396. Highest harmonics in the - 70s and one channel worse than the other.

Improve a Yamaha amp THD by 12 dB!

And now for something completely different … referring to the 2015 … 2021 thread “Improve a Rotel amp THD by 20dB! “ and also referring to Monthy Python, of course. Yamaha AX590 / AX592 / AX870 and AX890’s are not so bad amplifiers, but come along with some quite hefty flaws and quirks. E.g...

www.diyaudio.com

PMA, did you figure out if the was a problem with the relays? My amp is currently loaned out but I wonder if I should remeasure it right at the output coil.

 

[My adventures in stereo]

Thanks for the detailed review, used this & the 801 , was very happy with its performance & price.

quoting Amir, to point out a typo

Conclusions
The Yamaha A-S701 is a beautiful integrated amplifier with a lot of functionality. Its design is very robust and is cable of easily exceeding its specifications. Overall ranking is at the high-end of "very good," bordering on excellent. All of this comes at a reasonable cost.

 

[Leeken]

I had a Yamaha ax300 which only recently gave up,that’s a 1987-88 amp,looking at the innards on this it wouldn’t surprise you to get the same lifespan,how many times will I have replaced my current class d in the next 35 years due to beyond repair issues?
(incidentally the Yamaha could still have been repaired I just couldn’t be bothered and it had never been repaired once in all that time)

 

[capslock]

The schematics for 592 and 701 are readily available.

592 still had real pots rather than an integrated tone control / attenuator chip.

There is no bias control pot in either model. The 592 allowed 0.2 - 4 mV across 0.22 R (0.91 - 18.2 mA) per output pair. The 701 allows 0.1 - 10 mV across 2x 0.22 R (0.23 - 22.7 mA), an even wider range. Insanity! How should we expect any two amps to perform similarly?

The power amp board is largely unchanged. The small signal transistors got swapped out for newer models, the Sanken A1694/C4467 output transistors are still the same (decent, but not top notch Sanken models). The schematic seems to be exactly the same, even most component values are identical. The topology is:

- NPN long tailed pair with no emitter degeneration
- current mirror
- Darlington VAS single ended (working against a current source)
- EF2 output stage
- no Miller compensation (!)
- instead the current mirror is loaded to the upper rail with the series combination of 1000 pF and 470 R, and the VAS output is loaded with 100 pF each to the upper and lower rails
- the main feedback resistor is shunted with 22 pF in the 592 and 15 pF in the 701

So in summary, not using emitter degeneration on the input stage and only using a EF2 instead of EF3 are not state of the art, other than that, the topology is bog standard. The compensation scheme is unusual. Loading the VAS to AC ground is a bad idea as it throws away gain without having the benefit of local feedback in the VAS which would linearize it and lower its output impedance which is sorely needed given the EF2 output stage's nonlinear input impedance.

I wonder why the 701 measured so well. Amir, if you still have it, could you measure the bias current? And why did my 592 and PMA's 396 measure so badly? Mine was biased at 4 mA which is low but not catastrophically low. I really need it back and check if the relays have degraded.

Edit: I am just rereading PMA's thread. He did have a relay issue, but that was in one channel only and resulted mainly in HF (~ 10 kHz) distortion. So my bets are on either the bias current being right in the 701 Amir got or the CD direct input stage having been sorted in this newer model:

Review and Measurements of vintage Yamaha AX-396 integrated amplifier

A problem is that the "unity" setting may not measure flat, so there might be a frequency response change to take into account for perceived differences. There's so many different ways tone controls were implemented and also the hardware the manufacturers used. Some tone circuitry is...

www.audiosciencereview.com

I really need to get my unit back to measure upstream from the relay and to measure with CD direct engaged and not. I probably used CD direct, not knowing about above post that was an eye opener. On second thought, though, I tried two different output levels for my DAC and adjusted the output level with the volume pot, so the CD input buffer straining is probably not the issue here.

 

[Sokel]

The phono input circuitry is basically the same across the range from 300/301/500/501/700/701.

A-S701 phono stage:
View attachment 376028

The big issue of course is the overload characteristics due to the 5V supply rails and the following AVR chipset input limitation issues. The 701 phono overload is rated at 45mV (or more), which is absolutely atrocious. I tested the 300/301 -same circuitry but with much higher rails for the phono stage:

A-S300/301 phono stage (note the higher supply rails on the same circut):
View attachment 376030

It overloaded a 74mV@1kHz, which was dead last in a test of a dozen phono stages. To put in perspective, that is about half what even a cheap 1970s integrated would offer.

That said, the phono stage was very quiet (low noise) and sounded OK.

The entire range is built around 1990s Yamaha TopArt amplifiers (which is good), they've strapped on a cheapish D/A, used AVR chips for all the switching/routing and electronic volume (the volume pot is an input device to an A/D in the chipset) and run the entire thing from a custom uP.

They are great value and work well, but they aren't SOTA. You really have to step up further along Yamaha's range to get something special.

Quality and measurements aside,the fact that all schematics are available is a big plus.
Not so common these days.

 

[thierry moreau]

En fait, l’AS-701 est une version plus récente d’une lignée d’amplificateurs intégrés qui a débuté avec l’AX-590 :

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.

elektrotanya.com

En fait, l’AS-701 est une version plus récente d’une lignée d’amplificateurs intégrés qui a débuté avec l’AX-590 :

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.

elektrotanya.com

aLa lignée se poursuit avec les AX-592, AX-595, AX-596 et AX-597, tous prédécesseurs des AS-700 et AS-701. L’ONU

aLa lignée se poursuit avec les AX-592, AX-595, AX-596 et AX-597, tous prédécesseurs des AS-700 et AS-701. L’ONU

 

[xaviescacs]

I remember a pioneer amp also having overall lower volume when switching on the loudness mode.

 

[johnk]

Looks like I'll be staying with my A-S700 for a while longer and upgrading another part of my system ...

 

[WILL]

I had an AS-801(AS701 with USB dac) in the past and sold to an Youtuber.
The sound is very clean and natural, just like this measurement result.
Now is using AS-1100 just for its look.

 

[Moderate Dionysianism]

Would it pair nicely with Revel M16s? Is there a better choice for those speakers in the <2500€ (for an amp+speakers set) price range? And a noob question (never had a passive setup): what is the best impedance setting for 6 Ohm speakers like the M16? It looks like it says 'A or B' on the backplate above the switch?

 

[restorer-john]

Would it pair nicely with Revel M16s? Is there a better choice for those speakers in the <2500€ (for an amp+speakers set) price range? And a noob question (never had a passive setup): what is the best impedance setting for 6 Ohm speakers like the M16? It looks like it says 'A or B' on the backplate above the switch?

Always the highest impedance setting in amplifiers with conventional transformer based supplies like this Yamaha. The lower 'impedance' setting will drop the rail voltages and/or change OC (over current) trip points.

Go with the highest rail voltages (8R settings) and enjoy the greater dynamic and continuous power from your amp.

 

[capslock]

Always the highest impedance setting in amplifiers with conventional transformer based supplies like this Yamaha. The lower 'impedance' setting will drop the rail voltages and/or change OC (over current) trip points.

Go with the highest rail voltages (8R settings) and enjoy the greater dynamic and continuous power from your amp.

In terms of dynamics and highest sound quality, yes. In terms of power consumption and reliable operations, no.

 

[trl]

Yamaha A-S701 Integrated Amplifier Measurements
As usual we start with our 5 watt dashboard after setting the volume control to get 25 dB gain:
View attachment 375868
This is better than I expect, landing the A-S701 in the upper range of our "very good" rating category as far as noise and distortion:

2V @ CD-input - CD Direct, SINAD: 90.5 dB @ 5 W / 8 Ohms

​

I'm glad to see that my measurements @2V - 8 Ohms from here are pretty similar with Amir's, thanks to the Cosmos ADC.

 

[AnalogSteph]

The phono input circuitry is basically the same across the range from 300/301/500/501/700/701.

A-S701 phono stage:

The big issue of course is the overload characteristics due to the 5V supply rails and the following AVR chipset input limitation issues. The 701 phono overload is rated at 45mV (or more), which is absolutely atrocious. I tested the 300/301 -same circuitry but with much higher rails for the phono stage:

A-S300/301 phono stage (note the higher supply rails on the same circut):

It overloaded a 74mV@1kHz, which was dead last in a test of a dozen phono stages. To put in perspective, that is about half what even a cheap 1970s integrated would offer.

74 mV + 40 dB at 1 kHz = 7.4 Vrms, which is about what I'd expect in terms of output at +/-13 V. The only way they could have increased the overload margin would have been by decreasing the gain. It baffles me that they didn't do just that on the A-S701. (But things don't always make complete sense with Yamaha. I have the feeling they like to use preexisting circuit blocks like Legos.)

Input filtering is also a fair bit better on the lesser model, 1k/470p seems crude and is unlikely to satisfy many cartridges.

One thing I do not like about the A-S301 circuit is its use of 100µ/16 V capacitors on rails of over +/-13 V. Those should have been 25 V types in the interest of reliability. Modern electrolytics' average actual sustained voltages tend to be much closer to rated voltage as a result of quality improvements. Where back in 1980 they may have needed to target a multiple of rated voltage to make sure that all reasonable outliers would still make the cut, improvements in manufacturing have reduced the spread considerably. That has brought down their size but also means the average capacitor of a given rating will sustain less voltage than back in the day, and degrade faster particularly in a no-voltage scenario. (Hence why I'd generally advise to match capacitance and size rather than rated voltage when recapping, unless it gets silly. For decoupling caps, about 3x rail voltage is enough.)

 

[BadAudioAdvice]

DAC or Phono. If I get time and owner can wait, I can test those as well.

Would be great to see this tested as well - hopefully they perform as well as the rest of the amplifier.

 

[beagleman]

I have the S501 precisely because of this:



Admit it - the variable loudness is effing awesome

And yeah, too bad the internal DAC wasn't tested. I use it, but I have no idea if it's any good.

I had an older Yamaha Pre amp from the late 80s with that same exact feature.
It worked great.

 

[peng]

I had an AS 500, the weaker brother of the 700.

At that time, I had a Klipsch speaker with all that brightness, and when I started using a Marantz NR1504, I felt the sound got warmer.

As someone who always trusts measurements, I’d like to ask: What indicates the difference I heard between those amps?

When I looked around, I saw a common belief that some Yamaha models are “bright,” which is something I experienced myself.

If it is operating well below its clipping point, frequency response performance should be main indicator of the difference you heard. It should be obviously anyway, I assume people who do "mixing" would concur.