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

[AnalogSteph]

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.

This is the phono MM input, where capacitive loading of the cartridge is critical and very much affects its frequency response well within the audible range. Try modeling an MM cartridge as about 750 ohm + 440 mH and you should see the problem - these buggers are super inductive and their source impedance has climbed to >10 kOhms at the upper end of the audible range. The standard value for input impedance these days is 47k || 220 pF, and even that does not go down too well with quite a few higher-end AT cartridges once you add cable capacitance (~130 pF, typ), so it is common practice to reduce input resistance to 36-39k for these. With a total of 600 pF, not too many cartridges will be playing as intended.

Whacking in a 470 pF may have been needed to pass EMI testing but from a functional POV it's clearly a fail.

Using 47 kOhms has always been a compromise between noise performance and practicality. Going higher would enable a few dB lower noise still, but capacitance would have to be even lower then. This is only feasible if the preamp can be mounted inside the turntable, or even more radically, a tiny, super lightweight SMD buffer circuit can be mounted at the cartridge itself. (An idea that turned out to have been pioneered decades ago, if I remember the diyAudio discussion correctly...)

 

[trl]

I do see your point, thanks for sharing, but will AP equipment change the measured SINAD after swapping the values of these passive components? If yes, then how much?

 

[Overseas]

Hi, what specifications do I need for a headphone to optimally match the AS701 output? What models for example? Thanks.

 

[trl]

Well, there's not a dedicated heaphones amplifier in there, only A-S1000/2000/3000 or the newer high end series have a headamp inside. A-S701 has couple of resistors connected directly to the output stage, to lower the voltage.

Any mid-sensitivity headphone should do fine, but don't expect miracles in the output sound. High sensitivity IEMs will have hiss, low sensitivity planars (HE-5/6) will overdrive the output stage and you'll only listen to a distorted signal.

However, for a better performance you can always buy an external headamp.

 

[knownunknown]

maybe a little off topic but i could get a good deal on a yamaha a-s1000, but i don‘t know if it would really be an upgrade over my nad 316bee soundwise. don‘t want to spend 500€ only for a better looking amp. can someone maybe explain the benefits of the yamaha (in combination with some wharfedale dentons 85 in a small room)

 

[Overseas]

AS1000 is in the beast league, the beginning of the hardcore category.
It lacks gizmos and digital entries I think.
Probably very small difference in sound - it should have no DAC anyway.
Great difference in how it behaves as a workhorse under intense utilization, long term.

 

[knownunknown]

thanks, that‘s kinda what i wanted to hear and what i initially thought. i‘ll save my money then

 

[Overseas]

Yeah, if it is very good condition I would take it for my collection, here in Europe
However, my wife would kill me...

 

[trl]

maybe a little off topic but i could get a good deal on a yamaha a-s1000, but i don‘t know if it would really be an upgrade over my nad 316bee soundwise. don‘t want to spend 500€ only for a better looking amp. can someone maybe explain the benefits of the yamaha (in combination with some wharfedale dentons 85 in a small room)

It is definitely an upgrade, that's for sure. It plays in a different league, has a higher price and way better internals. It also has more power, a better look, but also a better resale value too.

 

[Overseas]

Regarding
'On the same board there is a clean +5V/0.5A USB power "outlet" (done with TPS2051CDBVR) for use with external devices like BT streaming or transport devices.'

In simple terms, what entry should I use for an external DAC or BT device?

 

[trl]

This +5V is for powering an external device, so if you have an external DAC that requires +5V/0.5A then you can use this, although there should be no audible benefits comparing with the original power supply provided by DAC's manufacturer. This port is there mostly for powering ON BT devices, in case someone wants to transmit audio via BT.

 

[tasotse]

hello!i have the same amp.i have a pair of 6ohm speakers and i want to put another pair.im thinking putting another pair of 6ohm too.the load that the amp will receive will be 3ohm per channel?i saw in your post that inside the amp is in parraler.i want to play a+b channel all the time and i dont know if it is safe for the amp.

 

[trl]

hello!i have the same amp.i have a pair of 6ohm speakers and i want to put another pair.im thinking putting another pair of 6ohm too.the load that the amp will receive will be 3ohm per channel?i saw in your post that inside the amp is in parraler.i want to play a+b channel all the time and i dont know if it is safe for the amp.

This amp was not designed to drive 3 Ohms speakers! Now, of course, it's all about how the impedance graph looks like, so feel free to let us know the exact Type & Model of your speakers, just in case anyone will be able to find the impedance measurement graph for them.

My recommendation is to purchase an identical amp to drive the 2nd pair of speakers and a pre-amp to control the volume adequately: leave the volume pots in the same position (to the max. output power you'll ever need, like 1 or 2 o'clock for example) to match the perfect channel balance and adjust the output volume from the external pre-amp (or from a DAC that has volume control).

 

[tasotse]

This amp was not designed to drive 3 Ohms speakers! Now, of course, it's all about how the impedance graph looks like, so feel free to let us know the exact Type & Model of your speakers, just in case anyone will be able to find the impedance measurement graph for them.

My recommendation is to purchase an identical amp to drive the 2nd pair of speakers and a pre-amp to control the volume adequately: leave the volume pots in the same position (to the max. output power you'll ever need, like 1 or 2 o'clock for example) to match the perfect channel balance and adjust the output volume from the external pre-amp (or from a DAC that has volume control).

the speakers that i have are dali spector 2.i was planning to buy the spector 6 too.as i see i will purchase another speakers that have 8ohm.perhaps the
whardale diamond 11.3 that are at the same price point.thanks for the reply!

 

[trl]

Nevertheless, you shouldn't pair different speakers on a stereo amplifier, unless you have access to their impedance graph. However, if you do that, try not to increase output power above 100W/ch. or at least set the impedance switch from the backside to 4-Ohms speakers to ensure amplifier will not overheat and get defective earlier (or monitor amplifier's temperature after 1h of continuous playback). Some 8-Ohms speakers might get their lowest impedance to 4-Ohms, while 4-Ohms speakers might have their lowest impedance point to 3-Ohms or even lower.

 

[Zaratustra#31]

This +5V is for powering an external device, so if you have an external DAC that requires +5V/0.5A then you can use this, although there should be no audible benefits comparing with the original power supply provided by DAC's manufacturer. This port is there mostly for powering ON BT devices, in case someone wants to transmit audio via BT.

This 5V port is only powered-on if you select the coax or the optical inputs. I though about using it for my Sanskrit MKII: useless since using an external DAC means selecting one of the line or CD as an input :-(

 

[trl]

Thank you for the update. I really think this is a marketing decision, too bad then.

Source: https://europe.yamaha.com/en/products/audio_visual/accessories/yba-11/index.html​

 

[peng]

thanks, that‘s kinda what i wanted to hear and what i initially thought. i‘ll save my money then

Unless you need a little bit more power output. The C316BEE, imo is as good as the A-S700 (both are pure bred/old fashion integrated), and aside from being less powerful, better than the A-S701 and S801 that share parts with their AVR cousins, so to me they are more like a receiver without the tuner, but though that doesn't mean its bad, just not a pure bred integrate.

 

[trl]

C316BEE is way cheaper and plays in a lower league from all perspectives (feel free to check both schematics too), not just output power, which is a bit over 1/3 of A-S701/801's output power (check audio.com.pl and audioholics measurements). You might need to compare the A-S701/801 with a more expensive NAD, if you really want to go this way.

 

[Willem]

And the AS701/801 also have digital inputs.