Exactly 11 years and 2250 posts after the original CEN IV, the simple circuit still have many fans and positive feedback.
But the difficulty of having to use floating power supplies remains.
Especially, if one is using 2 channel balanced mode outputs, 4 of these floating supplies are required.
https://www.diyaudio.com/community/...lution-of-a-minimalistic-iv-converter.195483/
The question has been -- is it possible to have at least similar performance but using fixed rails ?
In the original thread, the use of current sources between fixed rail and IV circuit has been discussed.
11 years later, with experience gained from the revised XCEN converter circuit, the puzzle has finally been solved.
So here you are. Happy Reading.
Patrick
.
But the difficulty of having to use floating power supplies remains.
Especially, if one is using 2 channel balanced mode outputs, 4 of these floating supplies are required.
https://www.diyaudio.com/community/...lution-of-a-minimalistic-iv-converter.195483/
The question has been -- is it possible to have at least similar performance but using fixed rails ?
In the original thread, the use of current sources between fixed rail and IV circuit has been discussed.
11 years later, with experience gained from the revised XCEN converter circuit, the puzzle has finally been solved.
So here you are. Happy Reading.
Patrick
.
Last edited:
Someone impatiently asked for PCBs :
https://www.diyaudio.com/community/...st-tht-i2s-input-nos-r-2r.354078/post-7111042
There will be 2 GBs given sufficient interest, one for through hole, another for the DIP8 SMD version.
Details will follow after Fran has published his audition.
Bear in mind the number of JFETs required for both versions.
It will not be the most cost-effective solution for an IV converter.
Patrick
https://www.diyaudio.com/community/...st-tht-i2s-input-nos-r-2r.354078/post-7111042
There will be 2 GBs given sufficient interest, one for through hole, another for the DIP8 SMD version.
Details will follow after Fran has published his audition.
Bear in mind the number of JFETs required for both versions.
It will not be the most cost-effective solution for an IV converter.
Patrick
They surround me from everywhere... ahhhhhhh, I need a torch-lance ...(for an average soldering). But thanks to Patrick we have a new Papy Friendly TO92 design. Hey !Don’t be scared of those little guys, Iggy.
No floating supplies, nice Patrick!
I have been lucky enough to have a listen to both the SMD and through hole versions of this - my thoughts are below in hopefully enough detail but not so long as to be boring!
Background system:
Stacked quad 57s (freshly serviced and sounding good)
01a preamp with Rod Coleman filament regs and Ale Moglia gyrator supply
Miro AD1862 dac with SD card player (this is an older “yellow” SD card player that was quite common on Aliexpress some time back, using STM32F processor and fitted with basic Mori clocks).
Output stages:
DHT 3a5 output stage, with filament bias and Moglia gyrator for the anodes
SMD version FC Cen (with input servo, necessary for smd jfets, and with Sallen Key filter)
New prototype through-hole FC Cen (without input servo, and without Sallen Key filter)
Both types of FC Cen built by Patrick.
A small group of diyers and I have had great fun over the covid period with Miro's AD1862 dac. Apart from the basic build, all using Miro's PSU boards we have experimented a small amount with different sources and clocks for those sources (mainly just for convenience for those who use a particular front end). However, our largest experimentation has been with current to voltage output stages. These have included:
A variety of opamps
XEN Current mirror (single ended operation)
Pedja Rogic discrete diamond buffer
Original SEN with LiFePO4 battery supplies
New version cascoded SEN with LiFePO4 battery supplies (unpublished)
SRPP 6n2
AC coupled cathode follower with 6n23
3a5 DHT stage
SMD FC CEN IV
Through hole FC CEN IV (Patrick’s prototype)
Through all of this listening over many sessions, the 3a5 DHT stage stands out as a real winner. Some others have more detail, or would certainly measure better, or may be less complicated builds with lower voltages, but it has sat at the top of the pile and it has been the benchmark - if a stage is at least as good as it, or better, then you know you have something that is really special.
The 3 devices being compared here were the 3a5 DHT stage, Patrick's prototype through hole FC CEN IV and the SMD version FC CEN IV. These were both powered from a diyinhk +/-15V supply (an older ultra-low noise unit). The IV is passive (500r resistor) for the 3a5 stage with voltage amplification by the valve.
The 3a5 stage first - you will already know the issues that exist with valve stages - they do not measure as well as solid state in general, and none more so than DHT valves which need either batteries for the filaments, or else a special supply. They are microphonic as well. However, in practice the sound is very appealing - deep holographic soundstage, very good resolution and spacing of instruments, full sound that is probably slightly on the warm side of neutral. It has a clean treble presence, and no hint of harshness or sibilance. It is especially good with vocals, and the projection from a centrally placed voice is really lovely. I suppose I can say it is a reference for me.
Next up is the SMD version FC CEN IV. Patrick built this for me, and as always did a really beautiful job in doing so. I set it up on a small piece of perf board, near the power supply so I could swap easily between stages. My test setup here is not ideal – long wires but that is necessary to allow change of stages. The SMD version warms up after a few minutes powered on and I waited for a few minutes before listening just to make sure everything was at equilibrium. In short, this output stage is at least the equal of the 3a5 stage which has been my reference. It does sound different than the 3a5, and is more neutral for sure, but it never strays into being hard or sibilant. For me, the key difference is that the vocals are just slightly more recessed with it compared to the 3a5 - but in saying that you have to understand that the 3a5 is probably more the odd one out here in that it is the unusual in how it projects vocals. If it makes my impression clear, I intend to replace the AC coupled output stage in a second build with this SMD version when I get a chance! It is very impressive.
On then to the through-hole FC CEN IV - how does it compare to the SMD version? It is very close indeed sonically, I would think that most people would not pick up on any differences between the two. I have convinced myself that it is just a tiny bit softer sounding, but do not take this as a criticism - there is full, accurate and deep bass, sparkling highs and everything in between. Soundstage is on a par with the SMD version. In truth I would fail a blind test miserably. So treat those comments with the skepticism they deserve - maybe this is a perfect example of confirmation bias. Also bear in mind this proto does not have the Sallen Key filter board either. If the goal of the through-hole version is to have an excellent sounding stage, that is on par with the SMD version, then I think that goal has been reached.
The comments above are based on my own listening – i.e. on my own, swapping between each output stage and also on a short listening session with a few friends from our diy group. Collecting their comments afterwards, I think they would agree with what I wrote above. Thinking back on our listening session, having lived with these output stages for a while, I think it’s only fair to add that they all sound fantastic – and I think we have to accept that any of us would have preference for one or another, or perhaps one might suit a listening use better than others.
As an addendum to the comments above, we were lucky enough to have a high-end commercial DAC here to compare in this same listening session - a DCS Bartok (€18k). The Bartok allows USB and network streaming and we also put that in the mix of what we listened to (using a second Miro DAC build with USB and bluetooth inputs and AC coupled 6n23 output stage). Although the AC coupled cathode stage is excellent, in my preferences it very slightly lags behind the 3a5 stage. The impression of the Bartok is that is presents a huge, really well resolved soundstage, with well separated instruments, each in their own space. I would say that the soundstage is probably bigger than with the Miro dacs, regardless of output stage. Is it better than the diy builds? Sonically it’s different but I find it hard to say it’s better. The streaming system works very well - it was easy to set up and use and allows for integration with Roon and all the major streaming services. The USB was picked up first time by my PC playback system (WTFplay, a bare bones linux system optimised for audio). Why do we include mentioning of this DAC here – it seems strange to include mention of a commercial unit with diy units. Well, ultimately, a benchmark is a nice thing to have, and I think it illustrates nicely the standard that the devices under test are held to. The point of DIY is not really to make something as good as a commercial unit, but rather to have something you built yourself that you cannot buy that sounds excellent. I think this has been achieved with the FC CEN IV and SMD FC CEN IV.
Background system:
Stacked quad 57s (freshly serviced and sounding good)
01a preamp with Rod Coleman filament regs and Ale Moglia gyrator supply
Miro AD1862 dac with SD card player (this is an older “yellow” SD card player that was quite common on Aliexpress some time back, using STM32F processor and fitted with basic Mori clocks).
Output stages:
DHT 3a5 output stage, with filament bias and Moglia gyrator for the anodes
SMD version FC Cen (with input servo, necessary for smd jfets, and with Sallen Key filter)
New prototype through-hole FC Cen (without input servo, and without Sallen Key filter)
Both types of FC Cen built by Patrick.
A small group of diyers and I have had great fun over the covid period with Miro's AD1862 dac. Apart from the basic build, all using Miro's PSU boards we have experimented a small amount with different sources and clocks for those sources (mainly just for convenience for those who use a particular front end). However, our largest experimentation has been with current to voltage output stages. These have included:
A variety of opamps
XEN Current mirror (single ended operation)
Pedja Rogic discrete diamond buffer
Original SEN with LiFePO4 battery supplies
New version cascoded SEN with LiFePO4 battery supplies (unpublished)
SRPP 6n2
AC coupled cathode follower with 6n23
3a5 DHT stage
SMD FC CEN IV
Through hole FC CEN IV (Patrick’s prototype)
Through all of this listening over many sessions, the 3a5 DHT stage stands out as a real winner. Some others have more detail, or would certainly measure better, or may be less complicated builds with lower voltages, but it has sat at the top of the pile and it has been the benchmark - if a stage is at least as good as it, or better, then you know you have something that is really special.
The 3 devices being compared here were the 3a5 DHT stage, Patrick's prototype through hole FC CEN IV and the SMD version FC CEN IV. These were both powered from a diyinhk +/-15V supply (an older ultra-low noise unit). The IV is passive (500r resistor) for the 3a5 stage with voltage amplification by the valve.
The 3a5 stage first - you will already know the issues that exist with valve stages - they do not measure as well as solid state in general, and none more so than DHT valves which need either batteries for the filaments, or else a special supply. They are microphonic as well. However, in practice the sound is very appealing - deep holographic soundstage, very good resolution and spacing of instruments, full sound that is probably slightly on the warm side of neutral. It has a clean treble presence, and no hint of harshness or sibilance. It is especially good with vocals, and the projection from a centrally placed voice is really lovely. I suppose I can say it is a reference for me.
Next up is the SMD version FC CEN IV. Patrick built this for me, and as always did a really beautiful job in doing so. I set it up on a small piece of perf board, near the power supply so I could swap easily between stages. My test setup here is not ideal – long wires but that is necessary to allow change of stages. The SMD version warms up after a few minutes powered on and I waited for a few minutes before listening just to make sure everything was at equilibrium. In short, this output stage is at least the equal of the 3a5 stage which has been my reference. It does sound different than the 3a5, and is more neutral for sure, but it never strays into being hard or sibilant. For me, the key difference is that the vocals are just slightly more recessed with it compared to the 3a5 - but in saying that you have to understand that the 3a5 is probably more the odd one out here in that it is the unusual in how it projects vocals. If it makes my impression clear, I intend to replace the AC coupled output stage in a second build with this SMD version when I get a chance! It is very impressive.
On then to the through-hole FC CEN IV - how does it compare to the SMD version? It is very close indeed sonically, I would think that most people would not pick up on any differences between the two. I have convinced myself that it is just a tiny bit softer sounding, but do not take this as a criticism - there is full, accurate and deep bass, sparkling highs and everything in between. Soundstage is on a par with the SMD version. In truth I would fail a blind test miserably. So treat those comments with the skepticism they deserve - maybe this is a perfect example of confirmation bias. Also bear in mind this proto does not have the Sallen Key filter board either. If the goal of the through-hole version is to have an excellent sounding stage, that is on par with the SMD version, then I think that goal has been reached.
The comments above are based on my own listening – i.e. on my own, swapping between each output stage and also on a short listening session with a few friends from our diy group. Collecting their comments afterwards, I think they would agree with what I wrote above. Thinking back on our listening session, having lived with these output stages for a while, I think it’s only fair to add that they all sound fantastic – and I think we have to accept that any of us would have preference for one or another, or perhaps one might suit a listening use better than others.
As an addendum to the comments above, we were lucky enough to have a high-end commercial DAC here to compare in this same listening session - a DCS Bartok (€18k). The Bartok allows USB and network streaming and we also put that in the mix of what we listened to (using a second Miro DAC build with USB and bluetooth inputs and AC coupled 6n23 output stage). Although the AC coupled cathode stage is excellent, in my preferences it very slightly lags behind the 3a5 stage. The impression of the Bartok is that is presents a huge, really well resolved soundstage, with well separated instruments, each in their own space. I would say that the soundstage is probably bigger than with the Miro dacs, regardless of output stage. Is it better than the diy builds? Sonically it’s different but I find it hard to say it’s better. The streaming system works very well - it was easy to set up and use and allows for integration with Roon and all the major streaming services. The USB was picked up first time by my PC playback system (WTFplay, a bare bones linux system optimised for audio). Why do we include mentioning of this DAC here – it seems strange to include mention of a commercial unit with diy units. Well, ultimately, a benchmark is a nice thing to have, and I think it illustrates nicely the standard that the devices under test are held to. The point of DIY is not really to make something as good as a commercial unit, but rather to have something you built yourself that you cannot buy that sounds excellent. I think this has been achieved with the FC CEN IV and SMD FC CEN IV.
Many thanks for all the effort you put in for the auditioning, and of course making that public with the write-up.
For all others, Fran is just a good friend over the years. He is NOT part of the XEN team.
But Fran only showed you the top of the iceberg.
How about the comparison with the original SEN he built with batteries, the Xen CM IV, etc. ?
With his consent, here is the missing part (what he wrote to me back in April).
Would be wasting his effort back then not to publish.
21 April 2022
This amounts to a first pass only at this - more time is needed for proper comparisons over a longer period.
The descriptions below read like the worst of magazine audiophile BS, but I hope give some flavour of what I'm hearing.
Front end - Miro DAC powered by Miro PSU, yellow SD card player with A. Mori clocks and re-clock at the DAC.
After the DAC the system is a 01A valve preamp, Aleph J and Stacked quad 57s. In time I will try this with other amps and speakers.
(In the meantime, he is very very close to completing a new amp called F5-EXC.)
Sen IV - powered by 16.8V LiFePO4 battery floating supply
Really smooth presentation, lots of detail, bass impact a tad soft but not lean sounding. Side to side soundstage is very good, but front to back not as discernible. This is a sound that is very liveable with, not fatiguing, and not "digital". Criticism maybe is that it's not "exciting", but certainly this is a lovely listen and you will never feel tired of listening to it, you just float along listening to the music.
Cascoded Sen (Onsemi JFETs) - powered by 16.8V LiFePO4 batteries, floating supply
Within a few seconds, you can hear more precise soundstage and depth with this compared to the Sen. It's a similar sound, but has more detail and a bit more depth. Piano key strikes for example have more of a percussive feel than with Sen. On a second track (David Byrne, Glass and concrete and stone) the bass percussion is just heavier and has more impact. His voice hangs closer to you in the soundstage and so it feels like there are more layers to the music.
3a5 DHT stage
This is a soundstage king - big holographic soundstage with lots of impact but without any smooth edges and is my reference. It's the ultimate in non-fatiguing sound, and more than one (audio) educated visitor has said it;s the best digital sound they have heard. Voices in particular seem to take a step forward closer to the listener which is very attractive.
SMD FC CEN IV - powered via diyinhk ultra low noise supply 15V
Really excellent sound here Patrick - on a par with the 3a5 stage. Voices are nicely forward, great impact on piano, very nice nimble but hefty bass weight, Superb detail. Zero fatigue. You really have something here Patrick - this is the first output stage that has been at least the equal of the 3a5 stage. This is very impressive.
Xen CM IV stage - powered via diyink ultra low noise supply 12V
Very clean sound with this - but to my ears and set up it is more 2 dimensional than the depth and feeling of reality that you get with the DHT, or new all-FET stage. There is also just a tiny little bit of sibilance that is more noticeable with this compared to the others. Now, these are all tiny differences, it's not anything huge but when you are critically listening and playing one after the other, you are listening for every tiny change. It does have the same impact on bass notes/percussion though so that is there in spades. I remember when you first sent me the one you had built, and thinking it was clearly ahead of the opamps I had used up to then. Just shows how far this has come.
So I need more time and more listening with them all, and also try them in other people’s setups.
I can say that the new SMD FC CEN is really promising given this first real listen. I think you have something special here.
I'm going to spend a bit more time tonight swapping back and forth between it and the DHT stage.
Good and all as the others are (and they are very good), these two are what I will focus on tonight.
22 April 2022
On further listening:
Two things that stand out a bit. I sense a bit more texture in bass .
For example Miles Davis, In a silent way, shhh-peaceful track - there are a few bits on that where there is a very slight vibrato in the bass.
That is more discernible with the FC CEN IV compared to the DHT setup.
Also, on some tracks there is an impression of greater dynamic impact/snap.
The DHT still maybe shades it out on vocals, but I think if I put people sitting in a room,
and swapped back and forth they would be hard pressed to tell them apart.
Patrick
For all others, Fran is just a good friend over the years. He is NOT part of the XEN team.
But Fran only showed you the top of the iceberg.
How about the comparison with the original SEN he built with batteries, the Xen CM IV, etc. ?
With his consent, here is the missing part (what he wrote to me back in April).
Would be wasting his effort back then not to publish.
21 April 2022
This amounts to a first pass only at this - more time is needed for proper comparisons over a longer period.
The descriptions below read like the worst of magazine audiophile BS, but I hope give some flavour of what I'm hearing.
Front end - Miro DAC powered by Miro PSU, yellow SD card player with A. Mori clocks and re-clock at the DAC.
After the DAC the system is a 01A valve preamp, Aleph J and Stacked quad 57s. In time I will try this with other amps and speakers.
(In the meantime, he is very very close to completing a new amp called F5-EXC.)
Sen IV - powered by 16.8V LiFePO4 battery floating supply
Really smooth presentation, lots of detail, bass impact a tad soft but not lean sounding. Side to side soundstage is very good, but front to back not as discernible. This is a sound that is very liveable with, not fatiguing, and not "digital". Criticism maybe is that it's not "exciting", but certainly this is a lovely listen and you will never feel tired of listening to it, you just float along listening to the music.
Cascoded Sen (Onsemi JFETs) - powered by 16.8V LiFePO4 batteries, floating supply
Within a few seconds, you can hear more precise soundstage and depth with this compared to the Sen. It's a similar sound, but has more detail and a bit more depth. Piano key strikes for example have more of a percussive feel than with Sen. On a second track (David Byrne, Glass and concrete and stone) the bass percussion is just heavier and has more impact. His voice hangs closer to you in the soundstage and so it feels like there are more layers to the music.
3a5 DHT stage
This is a soundstage king - big holographic soundstage with lots of impact but without any smooth edges and is my reference. It's the ultimate in non-fatiguing sound, and more than one (audio) educated visitor has said it;s the best digital sound they have heard. Voices in particular seem to take a step forward closer to the listener which is very attractive.
SMD FC CEN IV - powered via diyinhk ultra low noise supply 15V
Really excellent sound here Patrick - on a par with the 3a5 stage. Voices are nicely forward, great impact on piano, very nice nimble but hefty bass weight, Superb detail. Zero fatigue. You really have something here Patrick - this is the first output stage that has been at least the equal of the 3a5 stage. This is very impressive.
Xen CM IV stage - powered via diyink ultra low noise supply 12V
Very clean sound with this - but to my ears and set up it is more 2 dimensional than the depth and feeling of reality that you get with the DHT, or new all-FET stage. There is also just a tiny little bit of sibilance that is more noticeable with this compared to the others. Now, these are all tiny differences, it's not anything huge but when you are critically listening and playing one after the other, you are listening for every tiny change. It does have the same impact on bass notes/percussion though so that is there in spades. I remember when you first sent me the one you had built, and thinking it was clearly ahead of the opamps I had used up to then. Just shows how far this has come.
So I need more time and more listening with them all, and also try them in other people’s setups.
I can say that the new SMD FC CEN is really promising given this first real listen. I think you have something special here.
I'm going to spend a bit more time tonight swapping back and forth between it and the DHT stage.
Good and all as the others are (and they are very good), these two are what I will focus on tonight.
22 April 2022
On further listening:
Two things that stand out a bit. I sense a bit more texture in bass .
For example Miles Davis, In a silent way, shhh-peaceful track - there are a few bits on that where there is a very slight vibrato in the bass.
That is more discernible with the FC CEN IV compared to the DHT setup.
Also, on some tracks there is an impression of greater dynamic impact/snap.
The DHT still maybe shades it out on vocals, but I think if I put people sitting in a room,
and swapped back and forth they would be hard pressed to tell them apart.
Patrick
Hi thanks for tests.
.
FC Cen from the PDF seems to be a Current Device. If it is no I gin this is sort of Current buffer. If it is some Current amplifiacation that is sort of Current amplifier.
And I to V conversion happening at "external" R, with Idevice in between. Direct implementation on DAC Iout is avoided.
.
Q1: Is there some current amplification?
.
Q2: What phase is in Voltage @Riv at the output on FC Cen?
.
(Simple Riv @DAC-Iout turns the phase opposite, by 180deg... So optional SE gain stage have a same shift and brihng back the phase in 0 deg)
Thanks
.
FC Cen from the PDF seems to be a Current Device. If it is no I gin this is sort of Current buffer. If it is some Current amplifiacation that is sort of Current amplifier.
And I to V conversion happening at "external" R, with Idevice in between. Direct implementation on DAC Iout is avoided.
.
Q1: Is there some current amplification?
.
Q2: What phase is in Voltage @Riv at the output on FC Cen?
.
(Simple Riv @DAC-Iout turns the phase opposite, by 180deg... So optional SE gain stage have a same shift and brihng back the phase in 0 deg)
Thanks
It is a current conveyor circuit, just like the original CEN IV, or the XEN current mirror IV, or the AD844 used as IV converter.
A current conveyor only convey the DAC current to pass through the IV resistor to generate a voltage.
So no current gain, Vout = I_DAC x R_iv.
A current flowing into the IV converter will generate a positive output voltage.
Patrick
A current conveyor only convey the DAC current to pass through the IV resistor to generate a voltage.
So no current gain, Vout = I_DAC x R_iv.
A current flowing into the IV converter will generate a positive output voltage.
Patrick
We found a possible supply of those SMD JFETs.
But they need curve tracing first to verify genuine (end of September as I am out of town).
If lucky, then Ripster has promised to take on the mammoth task of matching all devices.
Some component values can only be finalised after that.
He will then make available complete kits of 20 pairs including all components.
How to minimise shipment cost to outside EU still needs working out.
But at least that is (still) the plan, unless he changed his mind in the meantime.
And he will need time to do all the matching.
Patrick
But they need curve tracing first to verify genuine (end of September as I am out of town).
If lucky, then Ripster has promised to take on the mammoth task of matching all devices.
Some component values can only be finalised after that.
He will then make available complete kits of 20 pairs including all components.
How to minimise shipment cost to outside EU still needs working out.
But at least that is (still) the plan, unless he changed his mind in the meantime.
And he will need time to do all the matching.
Patrick
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