This is a review and detailed measurements of the Yamaha A-1 vintage integrated amplifier. It is on kind loan from a member. He tells me that it has been serviced and restored a couple of years ago. The Yamaha A-1 came out in 1977 during a competition to produce the best spec audio products.
Most of the controls are hidden behind a drop down door:
On touch of the volume control and you are taken back to golden age of such mechanical controls. Boy, had I forgotten how good these used to feel compared to garbage that passes from mass market audio companies these days.
The buttons have the most solid feel, reminding me of ones we used to put on pro video products. Solid as a rock with positive feedback.
The "DISC" button is the equivalent of "pure direct" on modern AVRs and such and bypasses much of the circuitry internally. Alas, it is designed for LP playback to the phono equalization remains in the path so I did not test it for this review (may do later).
There are tone controls (but no balance). I set it to off of course for my testing.
The manual hearkens back to an area when performance indeed did matter including measurements that remind one of chip specifications:
The rest of the manual is full of diagrams clearly showing circuit flow and topology of various stages. Shame on the audio industry for forgetting its roots.
The unit is for Japan market and as such, is rated at 100 volts. To test it here in US, I used a variac to dial down the voltage to 100. This is a beefy 2000 volt-amp unit so should not impede power. But may be responsible for some mains leakage (which I could not lower with playing with grounding).
Speaking of beefy, the A-1 is massively heavy on the left side, sporting two independent transformers, one for each channel.
The components inside are quite rusty as you may be able to tell, having enjoyed some time in a damp shed no doubt. Despite that, at no time did the unit complain by shutting down or anything. It does have a high pitch whine if you stress it though or during warm-up.
Those metal components in the middle of the heatsink are the power transistors using the "TO-3" package. During that era, anytime you saw these transistors you knew that good money was spent on the components. TO-3 transistors with their large metal enclosure dissipate heat a lot better than the TO220 and other alternatives. Alas, they cost a fortune so they were phased out over time.
The power supply capacitors are top-brand japanese Nichicon. They did not look very fresh to me though even though they were supposed to have been replaced two years ago. Wonder if they used older parts.
One of the things I did not like was the flimsy speaker terminals that you could barely get to tighten on bare wire. I soldered my wires to give them more girth and they still barely held on to them.
Pre-amplifier Audio Measurements
The Yamaha A-1 has preamplifier out but unfortunately no input to the power amp. I thought we start with how the preamp perrforms then before testing the whole unit:
View attachment 37042
Looking to the right of our 1 kHz tone, we see that the only harmonic distortion visible is the third harmonic at -110 dB! That is very good.
Alas, SINAD which looks at both distortion and noise suffers from the power supply spikes, lowering to 90 dB or so. Still respectable but a loss of 20 dB.
FYI, 1 volt is the maximum usable input on this amp. Going beyond that severely clips. Rated input is actually much lower than this and being before the CD era, this is understood.
Amplifier Audio Measurements
I set the gain to 29 dB using the volume control and ran our usual dashboard at 5 watt into 4 ohm using a 1 kHz tone:
View attachment 37043
I should note that I had to let the unit come up to temperate at 9 watts or so for a few minutes. Prior to that one channel had a lot more distortion which gradually reduced. The A-1 has massive heatsinks and the temperature sensor is placed on the opposite side of the transistors, requiring a while for it to get a more accurate snapshot of the transistor temperature to set bias.
Once there, we see again that our harmonic distortions are quite low at below 100 dB. What is there are power supply components which heavily derate SINAD. As is, the A-1 doesn't place very high in our list of amplifiers:
View attachment 37044
Note that from audibility point of view, the power supply spikes don't matter much since our threshold of hearing is quite high there. So this is a case of SINAD showing us something that is not very representative of audible performance. Alas, we have made our bed and have to sleep in it with respect to SINAD.
Drilling more and only looking at harmonic distortion we see a far prettier picture:
View attachment 37045
Distortion products are at or below -105 dB which again, is very good. Our threshold of hearing is only -115 dB or so meaning these distortions are all but inaudible.
Alas, noise is the problem as we can see with no input to the A-1:
View attachment 37046
How much of this is due to age of this unit is hard to say. Perhaps whoever restored it did not pay enough attention to power supply output. There is no equivalent measurement from Yamaha to know for sure. The kind of FFT analysis we can do today would have been unheard of when this device came out.
The higher noise floor hurts baseline performance at 5 watt:
View attachment 37047
The owner told me that the SNR is around 112 dB or so. Clearly we are missing that by good bit but what is there is good enough at full volume to clear the 16 bit CD hurdle.
1 kHz spectrum naturally shows a very clean output:
View attachment 37048
THD+N versus level and frequency is I think the cleanest I have seen:
View attachment 37049
All the lines land on top of each other as if the frequency doesn't matter. Note however that due to high noise floor, we don't get to see the true distortion metric so perhaps that is helping here. Yamaha measurements show more of a differentiation so perhaps our sample unit is noisier than it should be.
Let's look at our power output versus distortion and noise into 8 ohm:
View attachment 37053
We meet the specification for power and do better in distortion by a mile.
Here is the same for 4 ohm load:
View attachment 37054
We clock a lot better here beating both power rating and distortion level Yamaha used.
I did not attempt to measure peak or maximum power as these keep the amplifier at full power for a while and I did not want to chance damaging the unit. Likely could have handled the load but I just did not want to take a chance of blowing the output stage and searching for devices that may not be manufactured anymore.
Conclusions
The stories of these hero amplifiers of the 1970s beating the distortion devil seems to be true. The Yamaha A-1 aces such tests, beating vast majority of amplifiers today and putting many to shame big time. What keeps it away from achieving top status is the high power supply noise. As mentioned, I am not sure if that is due to the sample I have or typical of the unit. With that included, our state-of-the-art amplifiers like Hypex/Purifi and Benchmark AHB2 provide a wide gap in performance.
I don't know how much these units go for but if they are reasonable in price, they would make a good alternative to modern amplifiers.
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As always, questions, comments, corrections, etc. are welcome.
Seeing the vintage amplifier, the panthers are demanding vintage clothing to fit in! I think they have a point so like to get them all new, 1970s era outfits. So appreciate kind
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