Hello Everyone,
This a review and detailed measurements of the Accuphase C-280 peamplifier.
Accuphase C-280 - Presentation
This unit is from a friend who wanted to know how it performs and is ok to let me report the results, thanks to him!
Released in 1982, the C-280 was the top of the line preamp from Accuphase. It was sold at a very high price, one that if converted to today's money would make it close to $15k!
The crazy weight of 18kg does not translate into an extremely busy front face, on the contrary. In their brochure, Accuphase said they minimized the controls to the bare minimum, meaning no tones control for instance. But, as always with Accuphase, devil is the details.
So, here are the available functions, apparent or hidden behind the front bottom door:
Detail of the details: The general gain attenuation button, not hidden, has two position on the right -20dB or -30dB, to allow attenuation when doing fast-forward/rewind of our ancient Cassette decks or R2R, when searching for a track. And, turn the same button on the left for instant infinite attenuation of the output, so that the owner can respond to a phone call, as the brochure says
But, but, but, no phones out? Oh come on...
The back of the C-280 shows the magnificent custom RCA rhodium platted connectors:
There's only one balanced output connector, while we get two for RCA, allowing to drive two stereo amplifiers at the same time from them.
At the time, an input named "Disc" meant turntable, nothing else. We get two here (MM and MC switchable), and three additional high level inputs, one labelled Tuner.
Oh, and before I go to measurements, I need to mention that Accuphase was providing a good set of them, in their brochure, as all brands should. Not only we get a very detailed set of specs, we also get equally tangible graphs like these:
Accuphase said all specs were guaranteed, meaning they are the minimum that the customer would get. We'll check if the C-280 still delivers more than 40 years later...
The build quality of this device is staggering, as always with Accuphase. And being a high-end one, it is further refined here.
There is something that looks promising below the wooden case:
Let's go inside, oh yeah:
Speechless, I am. I did this picture in black and white to add a little drama to it. Did you stop scrolling and pause on it for an instant? Yeah, I know
This device not being mine, I did not go too far in dismantling it. But here is another picture with the 3mm thick aluminium top plates removed:
So, as you guessed, I'm sure, this a dual mono preamplifier. The three encapsulated cards are for respectively low and high level preamp heads, and the RIAA curve correction + equalization functions. The logic board is hidden, and located behind the front plate.
User experience
Well, what can I say?
Hearing the relays clicking when going from one source to the other tells a story that systematically starts by "Once upon a golden hour...". It’s a finer indulgence than reaching for whisky.
Like I already explained, the volume knob whispers elegance, it feels like caressing silk and is a quiet celebration of craftsmanship.
Now, Gentlemen, start your engines, time has come for measurements:
Accuphase C-280 - Measurements (Line)
It was not an easy task for me to test this old legend, especially the Phono performances that has put to the limits my measurement set.
All measurements were performed with an E1DA Cosmos ADCiso (grade 0), and the Cosmos Scaler (100kohms from unbalanced input), for capturing analog outputs of the Accuphase. I used a high performance DAC, the Topping D50III, as the generator with REW Software from a laptop. All these devices run on batteries, and the D50III was behind a USB isolator, to prevent as much as possible any ground loops.
I won't be necessarily following Amir's way of measuring such an item because I don't use an AP, and I wanted to check and compare the claims of Accuphase. So you can't directly compare to what Amir shows here, although it's not completely deviating.
I feel it's not nice, for this more than 40 years old device, to treat it like I've done. But, hey, are we not on this site for that one reason? Does it delivers? And does it still delivers after more than 40 years of duty services? Let's find out.
Unless otherwise noted, all measurements are from RCA outputs. The two channels were matched a 0.1dB, which good. Phase is of course completely flat. And the two channels had the excat same performances.
----
So, let's start with the SINAD view:
Pushed hard, to the limits, we get 109dB SINAD, respectable. This is with the Topping D50III (set to 2Vrms output) delivering 0.5Vrms, meaning it is at -12dBFS output, which inevitably means it lost 2bits of resolution.
The above is an unlikely scenario though, because what amplifier needs 8Vrms at its input? Or maybe a low gain highly linear one?
So, let's now increase the Topping output to 2.5Vrms, and send a 1kHz sine @0dBFS into the Accuphase, and ask it to output the same voltage, which means unity gain:
Yep, 1 bit lost. But you can appreciate the vanishingly low distortion. Actually, it's the one of the Topping, not the Accuphase. Every time I thought I found distortion from the Accuphase, it was the one of the Topping...
The reason for that degradation is that this preamp has been designed to increase the input voltage with a high gain. This is where it excels, and we'll see that when we go to the Phono stage measurements.
----
Note the very low level of power supply related leaks (below -130dBr), meaning a very silent device, especially after 40+ years!
I overlaid the two channels on that view. It is in linear frequency scale for compatibility with the same view from Stereophile (eg: Rotel Michi P5)
----
Let's continue with the famous Multitone that a lot of you, including me, like so much:
This is from the file that @amirm shared some time ago, created from the AudioPrecision. So with that one, you can compare. The trace is really beatiful and means a distortion free-range of nearly 20 bits. Gran dad is still in very good shape, I'd say.
----
I could not measure the bandwidth... because I strictly measured the one of the Topping, up to 350kHz! So only for illustration, this is the bandwidth of the Topping, with its filter set to MODE 1 and with a sampling rate of 48kHz, and measured at the output of the Accuphase, of course:
At least we get to see the channel imbalance of 0.1dB, but on a bandwidth perspective, the Accuphase is completely transparent.
----
Oh, yes, another measurement that you can use to compare with other devices. It is the THD+N ratio vs frequency, with an extended bandwidth to capture all distortion and noise components up to 90kHz:
In 1982, I'm sure nobody thought about such a punishing test. But the Accuphase stays at 0.001% (-100dB) which is much more than reasonable.
----
The below IMD SMPTE sweep vs input level is not comparable to the same test from Amir, because it is excluding noise:
The trace shows a sweet spot at 1Vrms, and note I was at unity gain on this test. This last test confirms that the Accuphase is free from any type of distorsion.
----
Other measurements (not shown):
The line stage of this preamplifier offers staggering performances, in today's world, and they were absolutely unnecessary at the time, since no source was anywhere close to these performances. I guess the C-280 was pleased to see higher resolution devices join his game, but had to wait 5 long years for that (with the Accuphase DP-70 here below). And even so, it had headroom for more than that. Incredible.
The Accuphase C-280 is the pure definition of a preamplifier: straight wire with gain.
Accuphase C-280 - Measurement (Phono MM)
Spoiler Alert: Ok, so, that thing has been designed to be a Phono preamp, before everything else, I tell you. Let's see what you have to tell us, Mister HEAD AMP:
For what follows, I will be talking only MM simply because my poor Topping D50III (used as the generator for these tests) is not linear enough to create a decently silent 0.5Vrms output that would suit MC input. So I measured only the noise of the Topping in that case. Boring. With MM, I got results I can use, since the noise floor was low enough to get good results.
Let's start with the standard SINAD, again not comparable to what Amir usually does and I'll explain why:
This is the signal as it comes out from the Phono preamp, meaning I did not compensated the RIAA curve. The results are staggering, I mean we are close to CD Audio!
Now, let's correct the RIAA curve, with the software, to simulate how a record would be created, with the opposite curve:
Ok, we lost 12dB because you see the noise after 1kHz being higher, which is what the RIAA curve correction does. Now this is also extremely good result, no cartridge offers that linearity. Look at the distortion nearly absent, and you know what? It's the one of the Topping that is providing the test signal!
Why 40mVrms input when Amir uses 5Vrms for this test? For two reasons:
----
Next important set of measurements for a phono preamp is related to the above. It is important to know at what point it will clip, depending on the frequency. We need a good headroom, and all ancient phono preamps where known to have very good headroom. That's measured with a sweep of THD vy input level, at different frequencies. Let's check what our big bo(y)x has to say:
When I first saw the results of the sweeps, they made me laugh. The Accuphase clips past 300mVrms at 1kHz. That is giganticnormous
And look, at 10kHz, it does not reach 1% distortion with 2.5Vrms input!!!
Not only that, but the level of distortion is very low, and again we actually see the one of the Topping D50III, one of the best in class most linear DAC in existence.
The Accuphase will never break a sweat - it makes the laws of audio look lazy.
----
Ok, bandwidth, as we need to check the respect of RIAA curve:
Accuphase said "guaranteed +-0.2dB", I see below +0.1dB. Well done. Don't forget, 40+ years old...
----
Oh, yes, for the fun, as @amirm likes the below measurement. It is a sweep of THD only (no noise) with an extended bandwidth up to 90kHz to capture distortion at high frequencies too:
I did the above with two different input levels (5mVrms and 10mVrms), at respectively 52dB and 40dB. Well, the distortion we see does not come from the Accuphase, but one more time, you know...
The phono stage of the Accuphase C-280 is outstanding.
Conclusion
I've been preparing this review for weeks, spent countless hours performing measurements, and so many more to prepare the script and write this review. It was a personal investment, an adventure worth every single hour spent on this fantastic piece of engineering.
I initially thought it was unfair to torture this old device as we'd do on modern ones. But my friend convinced me to go for it. And oh boy...
This isn’t a preamplifier, it’s an artist in disguise. And it knows about architecture: I can't resist to share one last picture:
Yes, certainly, some modern devices can beat it, but you have to search hard for them. And what will remain of them in 40+ years? I'd be curious to know, but I'm unlikely to be around, considering my age and genes.
At the end of the day, Accuphase said the specs were guaranteed… and they could have added "for at least 40 years".
I hope you enjoyed this review as much as me writing it.
Happy weekend!
Flo
This a review and detailed measurements of the Accuphase C-280 peamplifier.
Accuphase C-280 - Presentation
This unit is from a friend who wanted to know how it performs and is ok to let me report the results, thanks to him!
Released in 1982, the C-280 was the top of the line preamp from Accuphase. It was sold at a very high price, one that if converted to today's money would make it close to $15k!
The crazy weight of 18kg does not translate into an extremely busy front face, on the contrary. In their brochure, Accuphase said they minimized the controls to the bare minimum, meaning no tones control for instance. But, as always with Accuphase, devil is the details.
So, here are the available functions, apparent or hidden behind the front bottom door:
- Volume button from the stars: Accuphase has been paying attention to the touch and feel of the volume button for years. This one comes from somewhere in our galaxy, and we got lucky it landed on earth. There are no words to describe the feeling of using it to increase/decrease the volume. Not only that, but it is of extreme precision, especially at high volumes which eased very much some of my calibrations for measurements.
- Subsonic filter: yes of course, it's coming from an era of Vinyl where this one was mandatory, and it seems new joiners of MM/MC phono preamp forgot why we needed it.
- Mono/Stereo switch: so useful!
- MC Load selector: 10 ohms, 30 ohms and 100 ohms for coupling MC cartridges.
- Tape monitor: the youngest of you will not know why, once upon a time, we needed to record on external medium
- Left and Right Channel gain attenuation: No balance available but these two allow for it. They will reduce the output gain of respective channels by an extremely precise 0.5dB (up to -6dB) or 1dB (beyond -6dB) per step, as I measured them.
- Loudness compensator: No tones control, but the loudness contour offers two positions that will vary with the position of the volume button.
- Gain attenuation: overall gain attenuation -20dB, -30dB or infinite
Detail of the details: The general gain attenuation button, not hidden, has two position on the right -20dB or -30dB, to allow attenuation when doing fast-forward/rewind of our ancient Cassette decks or R2R, when searching for a track. And, turn the same button on the left for instant infinite attenuation of the output, so that the owner can respond to a phone call, as the brochure says
But, but, but, no phones out? Oh come on...
The back of the C-280 shows the magnificent custom RCA rhodium platted connectors:
There's only one balanced output connector, while we get two for RCA, allowing to drive two stereo amplifiers at the same time from them.
At the time, an input named "Disc" meant turntable, nothing else. We get two here (MM and MC switchable), and three additional high level inputs, one labelled Tuner.
Oh, and before I go to measurements, I need to mention that Accuphase was providing a good set of them, in their brochure, as all brands should. Not only we get a very detailed set of specs, we also get equally tangible graphs like these:
Accuphase said all specs were guaranteed, meaning they are the minimum that the customer would get. We'll check if the C-280 still delivers more than 40 years later...
The build quality of this device is staggering, as always with Accuphase. And being a high-end one, it is further refined here.
There is something that looks promising below the wooden case:
Let's go inside, oh yeah:
Speechless, I am. I did this picture in black and white to add a little drama to it. Did you stop scrolling and pause on it for an instant? Yeah, I know
This device not being mine, I did not go too far in dismantling it. But here is another picture with the 3mm thick aluminium top plates removed:
So, as you guessed, I'm sure, this a dual mono preamplifier. The three encapsulated cards are for respectively low and high level preamp heads, and the RIAA curve correction + equalization functions. The logic board is hidden, and located behind the front plate.
User experience
Well, what can I say?
Hearing the relays clicking when going from one source to the other tells a story that systematically starts by "Once upon a golden hour...". It’s a finer indulgence than reaching for whisky.
Like I already explained, the volume knob whispers elegance, it feels like caressing silk and is a quiet celebration of craftsmanship.
Now, Gentlemen, start your engines, time has come for measurements:
Accuphase C-280 - Measurements (Line)
It was not an easy task for me to test this old legend, especially the Phono performances that has put to the limits my measurement set.
All measurements were performed with an E1DA Cosmos ADCiso (grade 0), and the Cosmos Scaler (100kohms from unbalanced input), for capturing analog outputs of the Accuphase. I used a high performance DAC, the Topping D50III, as the generator with REW Software from a laptop. All these devices run on batteries, and the D50III was behind a USB isolator, to prevent as much as possible any ground loops.
I won't be necessarily following Amir's way of measuring such an item because I don't use an AP, and I wanted to check and compare the claims of Accuphase. So you can't directly compare to what Amir shows here, although it's not completely deviating.
I feel it's not nice, for this more than 40 years old device, to treat it like I've done. But, hey, are we not on this site for that one reason? Does it delivers? And does it still delivers after more than 40 years of duty services? Let's find out.
Unless otherwise noted, all measurements are from RCA outputs. The two channels were matched a 0.1dB, which good. Phase is of course completely flat. And the two channels had the excat same performances.
----
So, let's start with the SINAD view:
Pushed hard, to the limits, we get 109dB SINAD, respectable. This is with the Topping D50III (set to 2Vrms output) delivering 0.5Vrms, meaning it is at -12dBFS output, which inevitably means it lost 2bits of resolution.
The above is an unlikely scenario though, because what amplifier needs 8Vrms at its input? Or maybe a low gain highly linear one?
So, let's now increase the Topping output to 2.5Vrms, and send a 1kHz sine @0dBFS into the Accuphase, and ask it to output the same voltage, which means unity gain:
Yep, 1 bit lost. But you can appreciate the vanishingly low distortion. Actually, it's the one of the Topping, not the Accuphase. Every time I thought I found distortion from the Accuphase, it was the one of the Topping...
The reason for that degradation is that this preamp has been designed to increase the input voltage with a high gain. This is where it excels, and we'll see that when we go to the Phono stage measurements.
----
Note the very low level of power supply related leaks (below -130dBr), meaning a very silent device, especially after 40+ years!
I overlaid the two channels on that view. It is in linear frequency scale for compatibility with the same view from Stereophile (eg: Rotel Michi P5)
----
Let's continue with the famous Multitone that a lot of you, including me, like so much:
This is from the file that @amirm shared some time ago, created from the AudioPrecision. So with that one, you can compare. The trace is really beatiful and means a distortion free-range of nearly 20 bits. Gran dad is still in very good shape, I'd say.
----
I could not measure the bandwidth... because I strictly measured the one of the Topping, up to 350kHz! So only for illustration, this is the bandwidth of the Topping, with its filter set to MODE 1 and with a sampling rate of 48kHz, and measured at the output of the Accuphase, of course:
At least we get to see the channel imbalance of 0.1dB, but on a bandwidth perspective, the Accuphase is completely transparent.
----
Oh, yes, another measurement that you can use to compare with other devices. It is the THD+N ratio vs frequency, with an extended bandwidth to capture all distortion and noise components up to 90kHz:
In 1982, I'm sure nobody thought about such a punishing test. But the Accuphase stays at 0.001% (-100dB) which is much more than reasonable.
----
The below IMD SMPTE sweep vs input level is not comparable to the same test from Amir, because it is excluding noise:
The trace shows a sweet spot at 1Vrms, and note I was at unity gain on this test. This last test confirms that the Accuphase is free from any type of distorsion.
----
Other measurements (not shown):
- Input clipping at just above 20dBu (7.8Vrms).
- Output voltage clipping: above 10Vrms (I can't measure more).
- Dynamic Range (CCIR 2k weighted): from 100dB at unity gain to 120dB at max gain.
- IMD AES (18kHz + 20kHz 1:1) : below -120dB from unity gain and above!
The line stage of this preamplifier offers staggering performances, in today's world, and they were absolutely unnecessary at the time, since no source was anywhere close to these performances. I guess the C-280 was pleased to see higher resolution devices join his game, but had to wait 5 long years for that (with the Accuphase DP-70 here below). And even so, it had headroom for more than that. Incredible.
The Accuphase C-280 is the pure definition of a preamplifier: straight wire with gain.
Accuphase C-280 - Measurement (Phono MM)
Spoiler Alert: Ok, so, that thing has been designed to be a Phono preamp, before everything else, I tell you. Let's see what you have to tell us, Mister HEAD AMP:
For what follows, I will be talking only MM simply because my poor Topping D50III (used as the generator for these tests) is not linear enough to create a decently silent 0.5Vrms output that would suit MC input. So I measured only the noise of the Topping in that case. Boring. With MM, I got results I can use, since the noise floor was low enough to get good results.
Let's start with the standard SINAD, again not comparable to what Amir usually does and I'll explain why:
This is the signal as it comes out from the Phono preamp, meaning I did not compensated the RIAA curve. The results are staggering, I mean we are close to CD Audio!
Now, let's correct the RIAA curve, with the software, to simulate how a record would be created, with the opposite curve:
Ok, we lost 12dB because you see the noise after 1kHz being higher, which is what the RIAA curve correction does. Now this is also extremely good result, no cartridge offers that linearity. Look at the distortion nearly absent, and you know what? It's the one of the Topping that is providing the test signal!
Why 40mVrms input when Amir uses 5Vrms for this test? For two reasons:
- The Topping does not provide a good enough signal at 5mVrms, simple.
- Because some dynamic cartridges (eg: Shure M44-7 - 9mVrms for 5cm/sec), together with over-cut records, would be reaching a speed velocity of 30cm/sec, meaning they'd be at or beyond 60mVrms.
----
Next important set of measurements for a phono preamp is related to the above. It is important to know at what point it will clip, depending on the frequency. We need a good headroom, and all ancient phono preamps where known to have very good headroom. That's measured with a sweep of THD vy input level, at different frequencies. Let's check what our big bo(y)x has to say:
When I first saw the results of the sweeps, they made me laugh. The Accuphase clips past 300mVrms at 1kHz. That is giganticnormous
And look, at 10kHz, it does not reach 1% distortion with 2.5Vrms input!!!
Not only that, but the level of distortion is very low, and again we actually see the one of the Topping D50III, one of the best in class most linear DAC in existence.
The Accuphase will never break a sweat - it makes the laws of audio look lazy.
----
Ok, bandwidth, as we need to check the respect of RIAA curve:
Accuphase said "guaranteed +-0.2dB", I see below +0.1dB. Well done. Don't forget, 40+ years old...
----
Oh, yes, for the fun, as @amirm likes the below measurement. It is a sweep of THD only (no noise) with an extended bandwidth up to 90kHz to capture distortion at high frequencies too:
I did the above with two different input levels (5mVrms and 10mVrms), at respectively 52dB and 40dB. Well, the distortion we see does not come from the Accuphase, but one more time, you know...
The phono stage of the Accuphase C-280 is outstanding.
Conclusion
I've been preparing this review for weeks, spent countless hours performing measurements, and so many more to prepare the script and write this review. It was a personal investment, an adventure worth every single hour spent on this fantastic piece of engineering.
I initially thought it was unfair to torture this old device as we'd do on modern ones. But my friend convinced me to go for it. And oh boy...
This isn’t a preamplifier, it’s an artist in disguise. And it knows about architecture: I can't resist to share one last picture:
Yes, certainly, some modern devices can beat it, but you have to search hard for them. And what will remain of them in 40+ years? I'd be curious to know, but I'm unlikely to be around, considering my age and genes.
At the end of the day, Accuphase said the specs were guaranteed… and they could have added "for at least 40 years".
I hope you enjoyed this review as much as me writing it.
Happy weekend!
Flo
Last edited:
