Hello everyone,
This is a review and detailed measurements of the Revox B 126 CD stereo player and transport.
Motivated by the presentation of the Sony CDP-227ESD by @audio_tony, I went to grab this old Revox which uses the Philips TDA1541A, in a single chip. After the TDA1540 of the Marantz CD-73, I wanted to continue the journey of discovering Philips DACs.
Revox B 126 - Presentation
This CD player was released in 1988 at a relatively high price for the time. It features the Philips Oversampling filter SAA7220P/B and the DAC TDA1541A. I've read so many times that these are amazingly good sounding, best DAC, etc... We'll measure that. It came with a CMD-1 or CMD-4/27 mech.
The back shows the essential:
We get only Coax outputs for digital signal but there are two, may to compare DACs
You can't see on that picture, but the back panel hides two other analog variable outputs which were therefore not accessible on this version. This was the privilege of the B 226S.
Let's have a quick look at the inside:
Servo on the left side, drive and power supply in the middle, conversion on the right. This is neat.
The drive is extremely fast to skip one or multiple tracks, I think it's the fastest I have. Scanning a track is little slower than others, though
Revox still service these devices today, not cheap, but they do it. We can find regularly some for sale from their restoration department. The price remains high on the market.
Mine has been fully serviced, the picture above was taken before that.
Revox B 126 - Measurements
From now on, I will be consistent with my measurements as I described them in the post “More than we hear”, and as I reported them for the Onkyo C-733 review. Over time, this will help comparing the devices I reviewed.
The Revox B 126 outputs 2.15Vrsm, and there was a slight channel imbalance of around 0.04dB (which is very good). The single-ended outputs are non-inverting.
Here you go with the 999.91Hz sine @0dBFS (without dither):
THD at -102dB, wow! This is really an impressive result for the time, one that we don't always find in recent CD players... The two channels have near identical performances.
Let's quickly check what happens at lower level, that is same 999.91Hz @-6dBFS (without dither):
Yep, the distortion has increased by 10dBr. This is were these old R2R architectures were suffering (no trimming laser for Philips chips). At -16dBFS, the distortion reaches -82dBr.
You've seen a relatively quiet power supply section:
Not much leakage from the mains (50Hz in Switzerland).
The below is a new measurement with shaped dither added to the signal and compared to no dither, to see if the DAC has the necessary resolution to benefit from it:
Well, no, nothing to gain from shaping the noise unfortunately, at least at full scale, the conversion generates too much noise, I'd say.
That said, at very low level, noise shaping still helps to have a very decent linearity, here below a tone at -110dBFS which is correctly represented:
You might have noticed a small pitch error, which is 0.001%.
And that means we are way below the strict resolution of the CD Audio. The software calculates a resolution that is near 18bits in this context. Thanks to noise shaping!
Bandwidth (now measured from a long term average of periodic white noise) is nearly flat:
You can see the ringing of the oversampling filter at the upper frequencies. And we also find our 0.04dB channel imbalance.
Let's continue with the oversampling filter behavior (from white noise) and together with dual tones 18kHz+20kHz (AES17) :
Yep, filter is ringing, this is an old 4x. Attenuation, out of band, is -50dB minimum.
Multitone (1/10 decade) shows a happy CD player, not having issue to clear 16bits of data:
This is the Jitter test:
This is an overlay of Analog (blue) and Digital outputs (red). The Revox does not suffer much from Jitter, even if the trace could have been cleaner. The level of Jitter is very low and will remain hidden when listening to music.
Started with the Teac VRDS-20 review, and on your request + support to get it done (more here), I'm adding now an "intersample-overs" test which intends to identify the behavior of the digital filtering and DAC when it come to process near clipping signals. Because of the oversampling, there might be interpolated data that go above 0dBFS and would saturate (clip) the DAC and therefore the output. And this effect shows through distorsion (THD+N measurement up to 96kHz):
I kept some references and will keep the same for other reviews, so you can quickly compare. The results of the Revox B 126 mean the oversampling filter has roughly 1.5dB headroom, which is good because it will prevent intersample-overs and therefore clipping where it's most likely to happen. The Yamaha CD-1 shines here because it's old enough not to have an oversampling filter.
Stereophile was often using the 3DC measurement as a prof of low noise DAC. It is from an undithered 1kHz sine at -90.31dBFS. With 16bits, the signal should appear (on a scope) as the 3DC levels of the smallest sign magnitude digital signal:
Without dither, the Revox suffers and there's a lot of noise at low level. We can still recognize the 3DC levels though and they are at the right amplitude.
Other measurements (not shown):
This is exactly why I like this test. It represents well the evolution of DAC performances over time. The plot is at 1kHz and the legend shows the distortion (5 harmonics only).
Revox B 126 - Measurements (Optical Out)
I've seen several of you reviewing CD players using their digital outputs, in case the results could be improved with an external DAC.
First the digital output (coax only) is as what we expect it to be, perfect (999.91Hz @0dBFS without dither):
It was difficult to get a stabilised reading from direct digital feed, and I had to reduce the FFT size to speed the calculation and be able to show an FFT without windowing errors.
To further test, I fed an SMSL PS200 with that digital output, and I no longer had the issue:
But you see that the tone is now at 1000.02Hz instead of 999.91Hz. So that's the reason why it was difficult to read from the direct digital stream, because of the pitch error, and the PLL of the SMSL can't filter all of that, I guess. I probably should have a look at the Xtal. If you have another explanation, I'm interested
Conclusion
I was positively surprised by this player, especially the first time I read the THD at full scale. Of course, as an old R2R not benefitting from laser trimming, it has its limitations, especially at lower levels without dither. We are far from what BurrBrown achieved at the same period.
But honestly, I don't see anything to be really worried of here. We do much better today, but it was already very good at the time. Hopefully, noise shaping technique of today saves this DAC at very low levels and since it delivers at high levels, and with a decent resistance to inter-samples over, well... quite modern after all, no?
I hope you enjoyed the review!
Cheers
PS: I add a link to the nice maintenance guide with many drawings that look to made by hand.
--------
Flo
This is a review and detailed measurements of the Revox B 126 CD stereo player and transport.
Motivated by the presentation of the Sony CDP-227ESD by @audio_tony, I went to grab this old Revox which uses the Philips TDA1541A, in a single chip. After the TDA1540 of the Marantz CD-73, I wanted to continue the journey of discovering Philips DACs.
Revox B 126 - Presentation
This CD player was released in 1988 at a relatively high price for the time. It features the Philips Oversampling filter SAA7220P/B and the DAC TDA1541A. I've read so many times that these are amazingly good sounding, best DAC, etc... We'll measure that. It came with a CMD-1 or CMD-4/27 mech.
The back shows the essential:
We get only Coax outputs for digital signal but there are two, may to compare DACs
You can't see on that picture, but the back panel hides two other analog variable outputs which were therefore not accessible on this version. This was the privilege of the B 226S.Let's have a quick look at the inside:
Servo on the left side, drive and power supply in the middle, conversion on the right. This is neat.
The drive is extremely fast to skip one or multiple tracks, I think it's the fastest I have. Scanning a track is little slower than others, though
Revox still service these devices today, not cheap, but they do it. We can find regularly some for sale from their restoration department. The price remains high on the market.
Mine has been fully serviced, the picture above was taken before that.
Revox B 126 - Measurements
From now on, I will be consistent with my measurements as I described them in the post “More than we hear”, and as I reported them for the Onkyo C-733 review. Over time, this will help comparing the devices I reviewed.
The Revox B 126 outputs 2.15Vrsm, and there was a slight channel imbalance of around 0.04dB (which is very good). The single-ended outputs are non-inverting.
Here you go with the 999.91Hz sine @0dBFS (without dither):
THD at -102dB, wow! This is really an impressive result for the time, one that we don't always find in recent CD players... The two channels have near identical performances.
Let's quickly check what happens at lower level, that is same 999.91Hz @-6dBFS (without dither):
Yep, the distortion has increased by 10dBr. This is were these old R2R architectures were suffering (no trimming laser for Philips chips). At -16dBFS, the distortion reaches -82dBr.
You've seen a relatively quiet power supply section:
Not much leakage from the mains (50Hz in Switzerland).
The below is a new measurement with shaped dither added to the signal and compared to no dither, to see if the DAC has the necessary resolution to benefit from it:
Well, no, nothing to gain from shaping the noise unfortunately, at least at full scale, the conversion generates too much noise, I'd say.
That said, at very low level, noise shaping still helps to have a very decent linearity, here below a tone at -110dBFS which is correctly represented:
You might have noticed a small pitch error, which is 0.001%.
And that means we are way below the strict resolution of the CD Audio. The software calculates a resolution that is near 18bits in this context. Thanks to noise shaping!
Bandwidth (now measured from a long term average of periodic white noise) is nearly flat:
You can see the ringing of the oversampling filter at the upper frequencies. And we also find our 0.04dB channel imbalance.
Let's continue with the oversampling filter behavior (from white noise) and together with dual tones 18kHz+20kHz (AES17) :
Yep, filter is ringing, this is an old 4x. Attenuation, out of band, is -50dB minimum.
Multitone (1/10 decade) shows a happy CD player, not having issue to clear 16bits of data:
This is the Jitter test:
This is an overlay of Analog (blue) and Digital outputs (red). The Revox does not suffer much from Jitter, even if the trace could have been cleaner. The level of Jitter is very low and will remain hidden when listening to music.
Started with the Teac VRDS-20 review, and on your request + support to get it done (more here), I'm adding now an "intersample-overs" test which intends to identify the behavior of the digital filtering and DAC when it come to process near clipping signals. Because of the oversampling, there might be interpolated data that go above 0dBFS and would saturate (clip) the DAC and therefore the output. And this effect shows through distorsion (THD+N measurement up to 96kHz):
| Intersample-overs tests Bandwidth of the THD+N measurements is 20Hz - 96kHz | 5512.5 Hz sine, Peak = +0.69dBFS | 7350 Hz sine, Peak = +1.25dBFS | 11025 Hz sine, Peak = +3.0dBFS |
| Teac VRDS-25X | -30.2dB | -24.2dB | -27.9dB |
| Yamaha CD-1 (Non-Oversampling CD Player) | -86.4dB | -84.9dB | -78.3dB |
| Onkyo C-733 | -88.3dB | -40.4dB | -21.2dB |
| Denon DCD-900NE | -34.2dB | -27.1dB | -19.1dB |
| Revox B 126 | -60.9dB | -41.3dB | -23.3dB |
I kept some references and will keep the same for other reviews, so you can quickly compare. The results of the Revox B 126 mean the oversampling filter has roughly 1.5dB headroom, which is good because it will prevent intersample-overs and therefore clipping where it's most likely to happen. The Yamaha CD-1 shines here because it's old enough not to have an oversampling filter.
Stereophile was often using the 3DC measurement as a prof of low noise DAC. It is from an undithered 1kHz sine at -90.31dBFS. With 16bits, the signal should appear (on a scope) as the 3DC levels of the smallest sign magnitude digital signal:
Without dither, the Revox suffers and there's a lot of noise at low level. We can still recognize the 3DC levels though and they are at the right amplitude.
Other measurements (not shown):
- IMD AES-17 DFD "Analog" (18kHz & 20kHz 1:1) : -94.6dB
- IMD AES-17 DFD "Digital" (17'987Hz & 19'997Hz 1:1) : -92.3dB
- IMD DIN (250Hz & 8kHz 4:1) : -87.8dB
- Dynamic Range : 97.2dB
- Crosstalk: -119dB (1kHz), -99dB (10kHz)
- Pitch Error : 19'999.15Hz (19'997Hz requested) ie +0.001%
This is exactly why I like this test. It represents well the evolution of DAC performances over time. The plot is at 1kHz and the legend shows the distortion (5 harmonics only).
Revox B 126 - Measurements (Optical Out)
I've seen several of you reviewing CD players using their digital outputs, in case the results could be improved with an external DAC.
First the digital output (coax only) is as what we expect it to be, perfect (999.91Hz @0dBFS without dither):
It was difficult to get a stabilised reading from direct digital feed, and I had to reduce the FFT size to speed the calculation and be able to show an FFT without windowing errors.
To further test, I fed an SMSL PS200 with that digital output, and I no longer had the issue:
But you see that the tone is now at 1000.02Hz instead of 999.91Hz. So that's the reason why it was difficult to read from the direct digital stream, because of the pitch error, and the PLL of the SMSL can't filter all of that, I guess. I probably should have a look at the Xtal. If you have another explanation, I'm interested
Conclusion
I was positively surprised by this player, especially the first time I read the THD at full scale. Of course, as an old R2R not benefitting from laser trimming, it has its limitations, especially at lower levels without dither. We are far from what BurrBrown achieved at the same period.
But honestly, I don't see anything to be really worried of here. We do much better today, but it was already very good at the time. Hopefully, noise shaping technique of today saves this DAC at very low levels and since it delivers at high levels, and with a decent resistance to inter-samples over, well... quite modern after all, no?
I hope you enjoyed the review!
Cheers
PS: I add a link to the nice maintenance guide with many drawings that look to made by hand.
--------
Flo
Last edited:
