YAMAHA A-S701 - tear-down, thoughts about the internals & few measurements

[dgk]

So I had actually dabbled in this FR deviation a bit already but didn't know what to make of it. To compare the HD650's nominal and peak impedance I used -5dbFS (just happens to be very close to +0dbVU) sine wave files at 1000kHz and 85kHz. I matched the RMS voltage the CD6006 and S700 were sending to the HD650's at 1000kHz then measured same at 85Hz. The RMS for both channels went up +0.1db from the CD6006 and +0.8db from the S700. I know RMS does not represent the in-can sound level entirely but is there a relationship that does? I certainly can hear the difference in volume between the two inputs to the headphones, might I be hearing the +0.8db??

 

[audio_tony]

might I be hearing the +0.8db??

I'd be surprised if your headphones are balanced to within 0.5dB in manufacture (I'm sure there must be a spec somewhere)

So with an accumulative error I guess it's possible you are hearing some imbalance at a very low level.

 

[dgk]

Well, I certainly can't hear any difference using music content of any flavour at normal listening volumes as I originally shared. With tone files at -5dbFS I kind of thought that the measured +0.8db Vrms increase at 85Hz between the S700 / CD6006 I got was the result of what you talked about regarding the HD650 impedance. Maybe this sort of increase in Vrms results in the sort of FR increase (in the cans) shown on the graph restorer-john shared?

 

[AnalogSteph]

Given the known 470 ohm output impedance on the A-S700, the difference between 1 kHz and 85 Hz on HD650s should be well above 2 dB on this amp. Not sure why you're only getting 0.8 dB. I'd suggest measuring DC resistance of both headphone drivers as seen by the output, just to make sure you don't have a bad contact with a few hundred ohms of series resistance hiding somewhere in your measurement setup. It could be as simple as the earpiece connectors that would like to be replugged (I certainly have to do that with my HD580s every once in a while).

 

[dgk]

I'll take another look before I get into troubleshooting the S700 for that balance problem this weekend. I have added a few things to my switchbox since doing doing this so maybe that'll yield the expected result.

 

[knownunknown]

how's the phono stage on the 501 ? would a rega fono mini a2d (or similar priced phono stages) be an upgrade or completely unnecessary?

 

[zepplock]

the phono on s701 is pretty poor, way worse than my little emotiva unit.

 

[ripmixburn]

the phono on s701 is pretty poor, way worse than my little emotiva unit.

This aligns with my experience of the A-S801 as well. I was ready to sell my turntable until I figured out how to use my Klipsch Powergate as a phono pre-amp (PRO TIP: unplug the speakers to enable the pre outs). The Yamaha phono preamp is lifeless and thin with a low rumble. Between that and the lack of bass management (sub out is fixed at 100hz, no high pass option) I am very tempted to upgrade to latest Outlaw receiver. Very disappointed this hasn't really been covered in the many reviews of the unit.

 

[trl]

the lack of bass management (sub out is fixed at 100hz, no high pass option)

But this is the high-pass frequency of the amp: 100 Hz, I see no problems with this fixed frequency setting, given that most subs will never be setup to higher than 80 Hz anyway. I was actually set my subs to around 40-45 Hz and I am perfectly fine with that.

If anyone found any phono measurements for A-S701/801 please post the links here. Thank you!

 

[ripmixburn]

But this is the high-pass frequency of the amp: 100 Hz, I see no problems with this fixed frequency setting, given that most subs will never be setup to higher than 80 Hz anyway. I was actually set my subs to around 40-45 Hz and I am perfectly fine with that.

The sub out is low-pass filtered so only ≤100 Hz frequencies can pass, which true, is fine for most people. What what I'm looking for is the option to high-pass filter the speaker outputs so I can avoid sending low frequencies to my small speakers. They can play louder more safely when the ≤100 Hz are not being sent there. The Outlaw receiver does this, as do most AVRs.

 

[trl]

What what I'm looking for is the option to high-pass filter the speaker outputs so I can avoid sending low frequencies to my small speakers.

You will probably not find such feature in a home audio system, so you should try studio monitors and their dedicated subs that can do that (not all of them, but selected equipment can do).

 

[trl]

I was able to measure the PHONO Input at the REC-Output from the backside of the amplifier. However, due to mV measurement, without an Audio Precision the THD+N will not compare with what Amir does, but however my Motu M4 is still decent after all.

From the below specs I see that for getting over 2 V RMS on REC-Out the input voltage for PHONO should be much higher than 5 mV RMS. From what I measured with an input of 45 mV I got 2.2 V RMS on RCA Output, while with 5 mV input signal I got 280 mV RMS on REC Out.

For 5 mV input I get 280 mV output and SINAD is about 64.5 dB, although the THD and noise floor seems pretty low on the graph. Not sure if it's ARTA that measures a bit odd the THD+N or it's my Motu M4 that simply can't work well with so low voltages

Despite having al distortions below -100 dB, for 45 mV input I get 2.2 V output, so SINAD is about 77.7 dB

Frequency response and THD for 5 mV input

Frequency response and THD for 45 mV input
​

However, the THD of 0.03% for 45 mV input from the specs is way higher than the 0.0025%. Too bad they don't specify the THD+N as well, so I can compare the numbers.

P.S.: I might redo the above graphs with the Clarett, maybe I'll get better figures due to a bit lower internal noise.

 

[trl]

I was also able to perform some measurements for 5 W @ 8 Ohms pure resistive load.

2V @ CD-input, SINAD: 88.5 dB @ 5 W / 8 Ohms

2V @ CD-input - Pure Direct, SINAD: 89 dB @ 5 W / 8 Ohms

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

1V input @ CD-input, SINAD: 88.5 dB @ 5 W / 8 Ohms

1V input @ CD-input - Pure Direct, SINAD: 88.5 dB @ 5 W / 8 Ohms

1V input @ CD-input - CD Direct, SINAD: 92 dB @ 5 W / 8 Ohms
​

What I see is that pressing CD-Direct button is decreasing the background nose with about 10 dB, while increasing the 3rd harmonic with about 8 dB. If THD+N is what it matters, then CD-Direct might need to be pressed for best results.

I realize that the input stage increases the harmonics when approaching the 2 V RMS on it's input. This means that the internal gain is a bit higher than regular line level voltage (2...2.2 V RMS), the "sweet spot" being around 1.2...1,5 V RMS. Good thing for Benchmark guys that did the trick on AHB2 with the selectable gain, this way remaining on top of other manufacturers in respect with THD+N.

By looking to Amir's graph for 5 W, the A-S701 is a bit better than NAD320BEE and Yamaha WXA-50 RCA for 2V RMS input and identical with Yamaha R-N803. Of course, with Audio Precision equipment and proper cables this amp will definitely measure better.

 

[Willem]

So basically good enough for transparency.

 

[ripmixburn]

I know the phono input measurements are not standardized here, so it's hard for the uninitiated like myself to compare measurements, but does provide any indication that the Yamaha phono is better than the Klipsch Powergate? https://www.audiosciencereview.com/...asurements-of-klipsch-powergate-dac-amp.7376/

 

[trl]

Well, ideally would be that both devices under test to be measured by the same audio analyzer and under exact same conditions. In this case they're not. However, the distortions on Klipsch are at -80 dB, while on Yamaha under -100 dB, although I am not sure I fully understand the poor THD+N provided by ARTA.

If I'd ever purchase a turntable again, I will definitely look over a dedicated phono preamp and I'll not rely on a built-in amplifier only phono preamp (as a backup perhaps it might work).

 

[Polar]

I found one "modding"

http://www.hifi-forum.de/viewthread-26-25705.html

 

[trl]

OK, so from my understanding the guy swapped the original 470 pF caps from the input stage low-pass filter with 100 pF or 125 pF. This will probably change the frequency-cut to way above the original and way more above the human audible limit, but nothing else.

Maybe this helps if very high impedance input cables are used, but without proper measurements this mod is just for fun.

This mod also involves a slight risk of getting some oscillations into the amplifier (very unlikely, but you never know without a scope or some sort of measurements).

I see 1 kOhms resistors and a 470 pF caps that create a low-pass filter. Based on http://sim.okawa-denshi.jp/en/CRtool.php the cut-off freq. is around 338 kHz. Changing the cap with 125 pF will increase the max. freq. to about 1.3 MHz, quite high and unsafe for audio use.

Maybe I'm wrong, maybe I don't see the entire picture here, but at first view of the Phono-input schematic I don't think this is a good mod.

 

[MacCali]

Few basic measurements done with Xonar U7 and Focusrite Solo 3.

First measurements were done with my Picoscope that showed a 35mV DC voltage on output. This is a respectable value for an amplifier that is able to push over 30V RMS on 8-Ohms speakers. I've seen headamps with 20-30mV of DC.

View attachment 36396
Ruler flat from 10 Hz to 22 KHz


View attachment 36397
Impulse response of the built-in DAC (optical input from Xonar U7 used as USB transport)
​

The below measurements were done without vs. with speakers connected, to show the influence of the 3-ways speakers for the output stage and the measurements values differences. The voltage used was around the value of 4.5V RMS, so a 5 W was used as reference here, as Amir suggested in his own power amps reviews. However, increasing the volume will lower the THD+N and increase the final SINAD. External DAC used was Conductor V2+ on DAC-Out (PRE-Out is too noisy due to the internal pre-amp chip).

View attachment 36400
External DAC used on CD-input, CD-DIRECT pressed, no speakers connected, 1 KHz


View attachment 36398
External DAC used on CD-input, CD-DIRECT pressed, real 4-Ohms speakers connected, 1 KHz


View attachment 36404
Built-in DAC (COAX-input), CD-DIRECT pressed, no speakers connected, 1 KHz

View attachment 36402
Built-in DAC (COAX input), CD-DIRECT pressed, real 4-Ohms speakers connected, 1 KHz
​

Seems that the Conductor V2+ has a better DAC inside than the A-S701, because with speakers connected I was able to get a THD+N of 0.0046% vs. 0.0071%.

Usually, when speakers are connected, the low-end of the audio band is more impacted, so below tests are with 50 Hz sines.

View attachment 36401
External DAC used on CD-input, CD-DIRECT pressed, no speakers connected, 50 Hz

View attachment 36399
External DAC used on CD-input, CD-DIRECT pressed, real 4-Ohms speakers connected, 50 Hz

View attachment 36405
Built-in DAC (COAX-input), CD-DIRECT pressed, no speakers connected, 50 Hz
View attachment 36403
Built-in DAC (COAX input), CD-DIRECT pressed, real 4-Ohms speakers connected, 50 Hz
​

Again, the external DAC connected to CD-input was measuring a bit better than the built-in one for 50 Hz test signals as well, with a THD+N of 0.0052% vs. 0.0080%.

So, for 5 Watts of power on 4-Ohms speakers connected and external DAC playing sines I got a THD+N of 0.0046% with 1 KHz and 0.0052% with 50 Hz.

The internal dac is basically burr brown? Doesn’t TI manufacture burrs

 

[trl]

https://www.nytimes.com/2000/08/26/technology/texas-instruments-completes-purchase-of-burrbrown.html