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: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:Since I had to take the unit apart anyway, here is a quick teardown: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.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.As usual we start with our dashboard of 1 kHz tone into 4 ohm load @ 5 watts: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:Signal to noise ratio is nothing to write home about either:Crosstalk is good (one channel bleeding into another):Frequency response is problematic, showing that it changes with your speaker load:Multitone shows frequency dependent error and high noise floor:Here are the power ratings:The regulated switching power supply allows no headroom:Not a whole lot changed with warm-up: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.------------As always, questions, comments, recommendations, etc. are welcome.The beheaded pink panther is demanding that I throw a funeral for him. I keep saying he is not dead so that makes no sense. He counters by saying that if a human had suffered the same, we would have said funeral. I guess he has a good argument there so pleaseas much as you can for a proper event using