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Yamaha A-U671 Integrated Amp & DAC Review

amirm

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This is a review and detailed measurements of the Yamaha A-U671 USB DAC and integrated class D amplifier. It is on kind loan from a member. The A-U671 costs US 499 but most vendors say it is no longer available even though it shows as current on Yamaha site. How fast modern gear becomes obsolete...

Yamaha has been clever to mimic the look of 1970s and 1980s switchgear:

Yamaha A-U671 USB DAC Integrated Amplifier Audio Review.jpg

Alas, the controls are plastic and don't have nearly the nice feel of their old brethren. The volume control is motorized though and is operable through the remote.

A built-in DAC and analog input would nicely satisfy many people. Unfortunately the unit arrived with something rattling in it. I took it part to find out it was a clamp of sort for the power supply bundle that had come loose. I put it back together and all worked except the USB DAC. I could control it, change its sample rate and such but it would not produce audio (with stock or Yamaha driver). Another one of the power supply screws was also loose. They should have put thread lock on them so that they don't come loose.

The back panel is as expected but with decent quality speaker terminals:

Yamaha A-U671 USB DAC Integrated Amplifier Back Panel Connectors Audio Review.jpg

Since I had to take the unit apart anyway, here is a quick teardown:

Yamaha A-U671 DAC Integrated Amplifier Analog In Audio teardown.jpg


The DAC is on top and the amp on the bottom of the green board. The yellow board is the switching power supply. And that black wrapper is what had come lose.

Yamaha A-U671 DAC Integrated Amplifier Analog In Audio teardown Class D Infenion IR4302M IC.jpg


In use the amp was very quick to shut down on overload. It would actually power off telling me it may be the power supply that is undersized.

Temperature rise is not remotely an issue.

Amplifier Audio Measurements
As usual we start with our dashboard of 1 kHz tone into 4 ohm load @ 5 watts:

Yamaha A-U671 DAC Integrated Amplifier Analog In Audio Measurements.png


I set the volume control manually to 29 dB as I normally do with integrated amps. SINAD which represents the worst of noise and/or distortion is dominated by distortion. At 70 dB, this is well below average:

Best sterep amplifier review 2020.png


Signal to noise ratio is nothing to write home about either:
Yamaha A-U671 DAC Integrated Amplifier Analog In Dynamic Range Audio Measurements.png


Crosstalk is good (one channel bleeding into another):
Yamaha A-U671 DAC Integrated Amplifier Analog In Crosstalk Audio Measurements.png


Frequency response is problematic, showing that it changes with your speaker load:

Yamaha A-U671 DAC Integrated Amplifier Analog In Frequency Measurements Audio Measurements.png


Yamaha A-U671 DAC Integrated Amplifier Analog In Frequency Response Simulated Load Measurement...png


Multitone shows frequency dependent error and high noise floor:

Yamaha A-U671 DAC Integrated Amplifier Analog In Multitone Audio Measurements.png


Here are the power ratings:

Yamaha A-U671 DAC Integrated Amplifier Analog In Power into 4 Ohms Audio Measurements.png


Yamaha A-U671 DAC Integrated Amplifier Analog In Power into 8 Ohms Audio Measurements.png


The regulated switching power supply allows no headroom:
Yamaha A-U671 DAC Integrated Amplifier Analog In Peak and Max Power into 4 Ohms Audio Measurem...png


Thermal Stability
Not a whole lot changed with warm-up:

Yamaha A-U671 DAC Integrated Amplifier Warm Up Audio Measurements.png


Conclusions
I have a soft spot for the look of the Yamaha A-U671. And inclusion of a USB DAC in a light and compact enclosure. Not much else to hang your hat on from there on. If you can find one at a yard sale for $100 it would be a good purchase. I don't know that I would buy it over so many other modern choices with Room EQ and streaming built-in.

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As always, questions, comments, recommendations, etc. are welcome.

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spacevector

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The power rating graphs shown are continuous ratings, right? The back panel shows only 30W rated mains draw.
 

restorer-john

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The power rating graphs shown are continuous ratings, right? The back panel shows only 30W rated mains draw.

It's a magic amplifier. Puts out more power than it consumes. ;)
 

restorer-john

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Sure is a very strange product. One analog input and USB- hardly comprehensive huh?

Compared to their own AS-300/1 integrated, there's no value proposition at all.

1581920475145.png
 
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amirm

amirm

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The power rating graphs shown are continuous ratings, right? The back panel shows only 30W rated mains draw.
They are continuous. I forgot to mention it comes with a tiny nuclear reactor so makes its own power partially.
 

pavuol

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Anyway, would be nice to know what the dedicated treble/bass controls do to response curve, is there some "industry standard" for it, or is it solely on the manufacturer?
 

restorer-john

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Real Yamahas are made in Malaysia these days.

I can tell you some stories about the QC in the Malaysian facility back in the day. It came on line in about 1990/1 and we had entire pallets of receivers that were faulty... Luckily, they ramped up production slowly and only with the low end products first.

It's been pretty good in the 30 years since to be honest.
 

StevenEleven

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Anyway, would be nice to know what the dedicated treble/bass controls do to response curve, is there some "industry standard" for it, or is it solely on the manufacturer?

It varies from brand to brand and from product to product within brands. A pretty descriptive spec is usually in the manual. I always have looked it up because broad based tone controls are very important to me.
 

restorer-john

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Anyway, would be nice to know what the dedicated treble/bass controls do to response curve, is there some "industry standard" for it, or is it solely on the manufacturer?

All over the shop. Some are +/-6dB. Others +/-8dB. Some are even +/-10-12db. The turnover frequencies also vary significantly.

It should be in the specs, but who knows these days.
 

gvl

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I can tell you some stories about the QC in the Malaysian facility back in the day. It came on line in about 1990/1 and we had entire pallets of receivers that were faulty... Luckily, they ramped up production slowly and only with the low end products first.

It's been pretty good in the 30 years since to be honest.

That was the beginning of the cost cutting era.
 

StevenEleven

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All over the shop. Some are +/-6dB. Others +/-8dB. Some are even +/-10-12db. The turnover frequencies also vary significantly.

It should be in the specs, but who knows these days.

Just looked it up, all they tell you is + / - 10 dB. So you don’t know what range of frequencies is affected at all. See page 3. Specs on page 17 don’t reference it. Really sad. This is a sad piece of gear, IMHO.

https://usa.yamaha.com/files/download/other_assets/3/795413/web_ZS22000_A-U671_om_UL_EnFrEs.pdf
 
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miero

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I set the volume control manually to 29 dB as I normally do with integrated amps.
To what level is relative the value 29dB?
 

restorer-john

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Just looked it up, all they tell you is + / - 10 dB. So you don’t know what range of frequencies is affected at all. See page 3. Specs on page 17 don’t reference it. Really sad. This is a sad piece of gear, IMHO.

If Amir still has it, he can run quick FR sweeps with the Bass and Treble boosted and cut. Assuming it's reasonably well designed the turn-over frequencies will be quite clear.
 

restorer-john

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To what level is relative the value 29dB?

Pretty straightforward. It corresponds to an amplifier that goes to 11. ;)

Seriously he's shooting for 29dB of voltage gain- a reasonable and typical representative value.
 
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