As probably the last circuit we shall build for headphone amplifiers, we want to find out how they sound under current drive.
This is not only known for loudspeakers, but also for headphones, especially for planar magnetics.
The circuit is an evolution from our earlier Pioneer Super Linear Headphone Amplifier.
https://www.diyaudio.com/forums/headphone-systems/313163-pioneer-super-linear-circuit.html
Only now it has been modified to output current instead of voltage.
Many of the aspects of the SL Voltage such as device matching, etc. still applies.
You can read about the article here :
http://xen-audio.com/documents/cdha/Current Drive for Headphones Public 181006.pdf
Happy reading,
Patrick
.
This is not only known for loudspeakers, but also for headphones, especially for planar magnetics.
The circuit is an evolution from our earlier Pioneer Super Linear Headphone Amplifier.
https://www.diyaudio.com/forums/headphone-systems/313163-pioneer-super-linear-circuit.html
Only now it has been modified to output current instead of voltage.
Many of the aspects of the SL Voltage such as device matching, etc. still applies.
You can read about the article here :
http://xen-audio.com/documents/cdha/Current Drive for Headphones Public 181006.pdf
Happy reading,
Patrick
.
Attachments
Links for the References
1. Apogee Groove Current Source Amp Measurements | InnerFidelity
2. A First Look at Current Source Amp Performance | InnerFidelity
8. FAQ about current-drive | Current-Drive - The Natural Way of Loudspeaker Operation
9. 6moons audio reviews: Bakoon HPA-21
10.Joe Rasmussen "Trans-Amp" - 40 Watt Transconductance "Current Amplifier" - diyAudio
11. https://www.appletonaudio.com/ele-projects/my-headphone-amplifier/
12. http://dj-higo.cocolog-nifty.com/blog/2016/08/post-7caf.html
13. http://cat0048.my.coocan.jp/CURRENT_Headphone/current_headphone_amp.html
14. http://www.diyaudio.com/forums/headphone-systems/306350-uthaim-fun.html
15. http://www.diyaudio.com/forums/headphone-systems/313163-pioneer-super-linear-circuit.html
16. https://muzgdiy.wordpress.com/tag/hdam-sa2/
17. https://www.head-case.org/forums/topic/12438-transconductance-amp/
18. http://www.diyaudio.com/forums/headphone-systems/292681-xen-shpp-simple-headphone-protection.html
Patrick
1. Apogee Groove Current Source Amp Measurements | InnerFidelity
2. A First Look at Current Source Amp Performance | InnerFidelity
8. FAQ about current-drive | Current-Drive - The Natural Way of Loudspeaker Operation
9. 6moons audio reviews: Bakoon HPA-21
10.Joe Rasmussen "Trans-Amp" - 40 Watt Transconductance "Current Amplifier" - diyAudio
11. https://www.appletonaudio.com/ele-projects/my-headphone-amplifier/
12. http://dj-higo.cocolog-nifty.com/blog/2016/08/post-7caf.html
13. http://cat0048.my.coocan.jp/CURRENT_Headphone/current_headphone_amp.html
14. http://www.diyaudio.com/forums/headphone-systems/306350-uthaim-fun.html
15. http://www.diyaudio.com/forums/headphone-systems/313163-pioneer-super-linear-circuit.html
16. https://muzgdiy.wordpress.com/tag/hdam-sa2/
17. https://www.head-case.org/forums/topic/12438-transconductance-amp/
18. http://www.diyaudio.com/forums/headphone-systems/292681-xen-shpp-simple-headphone-protection.html
Patrick
The circuit was also successfully built by a Beta tester, who used the version with DC servo.
In any case, it is still recommended to use a protection circuit, especially when this is non-invasive.
All listening tested were using planar magnetic headphones, HiFi-Man HE500 & HE-400 respectively.
They have constant impedance over the audio band.
Patrick
In any case, it is still recommended to use a protection circuit, especially when this is non-invasive.
All listening tested were using planar magnetic headphones, HiFi-Man HE500 & HE-400 respectively.
They have constant impedance over the audio band.
Patrick
Hi. I was the Beta tester 
and here my experience with this other great design from Patrick (EUVL). This design was interesting for me because at the time I just got a nice pair of magnaplanar HiFiMan HE-400 headphone and was using them with the Xen Audio Pioneer Ultra linear headphone amp, with excellent results. Patrick asked me if I like the HE-400 with the his amp, and I answered, Yes very much! He told me that even if the Pioneer Super Linear was a great amp, the magnaplanar HP could be driven with even better result with a current amplifier, not a voltage one, as the Pioneer, and guest what! he had a design that he wanted me to try. I was in!
and here my experience with this other great design from Patrick (EUVL). This design was interesting for me because at the time I just got a nice pair of magnaplanar HiFiMan HE-400 headphone and was using them with the Xen Audio Pioneer Ultra linear headphone amp, with excellent results. Patrick asked me if I like the HE-400 with the his amp, and I answered, Yes very much! He told me that even if the Pioneer Super Linear was a great amp, the magnaplanar HP could be driven with even better result with a current amplifier, not a voltage one, as the Pioneer, and guest what! he had a design that he wanted me to try. I was in!
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To make a long story short, my time as a beta tester was a short one, because out of the box Patrick design worked like a charm. I must confess though that I missed the time to fully tried all function, such as the voltage mode adapter, in part because I already had the nice Pionner Super Linear (voltage mode), and I was pretty busy at the time with other projects. Also I used my extra parts inventory from the Pioneer project to build this amp. The small smd transistor were not as perfectly matched as the previous project, and I was not sure if the amp would be as well balanced, so I used the servo from the start. Other can certainly comments on the kit others features if they have more time than me. Here the final result
Attachments
As some others members can see I'm using my own motherboard design for this built, see the original GB for detail: GB for Pioneer Super Linear Motherboard
If there is enough interest with this new project, and if Patrick doesn't offer his own motherbaord option, I may run an other batch, we'll see.
So this project is a breeze to mount. For better results you'll need Xen Audio great discrete regulators, and the little protection pcb is a must, because this amp has a large DC swing at start-up.
Also take note that the amp, in current mode can be use only with a magnaplanar headphones. For other headphone type, simply use the voltage mode small pcb adapter, to convert the amp to voltage mode. The protection circuit can protect with the both mode, see the excellent documentation for details.
So in my view it may be the perfect headphone amp, can probably used with all the headphone out there (naturally not the electro static ones, as Stax). and sound just great, here my listening impressions:
I replied to Patrick with this simple comment: Well this amp may well be my last headphone amp [not with tube] that I ever build, it is so good...
With my HifiMan the sound is gourgeous, huge bass, mids to die for, crystal clear highs, and the speed, the speed! As they say in the UK, Lovely...
This latest Patrick's design is very recommended. Thanks Patrick for sharing.
If there is enough interest with this new project, and if Patrick doesn't offer his own motherbaord option, I may run an other batch, we'll see.
So this project is a breeze to mount. For better results you'll need Xen Audio great discrete regulators, and the little protection pcb is a must, because this amp has a large DC swing at start-up.
Also take note that the amp, in current mode can be use only with a magnaplanar headphones. For other headphone type, simply use the voltage mode small pcb adapter, to convert the amp to voltage mode. The protection circuit can protect with the both mode, see the excellent documentation for details.
So in my view it may be the perfect headphone amp, can probably used with all the headphone out there (naturally not the electro static ones, as Stax). and sound just great, here my listening impressions:
I replied to Patrick with this simple comment: Well this amp may well be my last headphone amp [not with tube
] that I ever build, it is so good...With my HifiMan the sound is gourgeous, huge bass, mids to die for, crystal clear highs, and the speed, the speed! As they say in the UK, Lovely...
This latest Patrick's design is very recommended. Thanks Patrick for sharing.
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I am glad that you like it. And thank you for being brave to try.The reasons for using our regulator instead of others are that :
1) it has built-in current limit, which is essential when using voltage mode together with the current sensing shunt protection circuit;
2) it has been tested to be stable with both the current and voltage mode.
That is not to say that other regulators would not do. But you'll have to try.
I personally like the "original" Pioneer SL (voltage) HPA better, marginally.
But that is a matter of personal taste. On top of that I do not own a planar magnetic.
As Algar mentioned you can plug in the voltage-mode for non-planar-magnetic phones.
But that converts the SL Trans to a CFA amp with NFB (negative feedback). In doing so, its character also changes; more like the F5-HA.
As it is known, I personally prefer the ZGF (Zero Global Feedback) sound.
My own prototype is due for independent audition in the coming weeks.
Then you will hear another opinion. We'll see what he says.
He has better ears than I do.
For those guys into current drive loudspeakers, you can easily scale this up to drive 8 ohm chassis in Class A.
So all in all a very interesting experience to say the least.
Patrick
The load is of course not resistive in transient, due to back emf of the voice coil motors.
It has already been explained in great detail in the references in post#2, so I shall not repeat.
For one, the output impedance of a modern voltage headphone amp is somewhere between 0~5 ohm.
A transconsuctance amp is typically >> 10k ohm.
And the SL Trans in voltage feedback mode is < 0.1 ohm.
Patrick
It has already been explained in great detail in the references in post#2, so I shall not repeat.
For one, the output impedance of a modern voltage headphone amp is somewhere between 0~5 ohm.
A transconsuctance amp is typically >> 10k ohm.
And the SL Trans in voltage feedback mode is < 0.1 ohm.
Patrick
Reference 2, for example, has some very detailed explanations as well as measurements of current drive :
A First Look at Current Source Amp Performance | InnerFidelity
And here is an explanation on planar magnetic phones :
How Planar Magnetic Headphones Work | InnerFidelity
Patrick
A First Look at Current Source Amp Performance | InnerFidelity
And here is an explanation on planar magnetic phones :
How Planar Magnetic Headphones Work | InnerFidelity
Patrick
During a trip to visit my parents I had the opportunity to swing by Patrick's place to have a listen to the Current Drive.
I had brought along my (older) Hifiman HE-500 as headphones, source was my modded DV20A SD-card player, strong competition from Patrick's stable the Pioneer SL.
As one would expect the Current Drive is clearly from the same family of P's ClassA amplifiers. With the given source there is no trace of harshness or glare, treble is
in fact really sweet (although the HE500 can be bettered in that regard), the soundstage very clear and three-dimensional.
You can basically point your finger only at the bass region that is somewhat softer than the SL in direct A-B comparison. It does have the same extension (as one would expect)
but doesn't hit quite as hard when the material demands for it. Softer doesn't mean muddy, and tastes are different, but with such competition at hand it had to be noted.
For sure made for some fun listening, and when it suits your taste: go ahead!
I had brought along my (older) Hifiman HE-500 as headphones, source was my modded DV20A SD-card player, strong competition from Patrick's stable the Pioneer SL.
As one would expect the Current Drive is clearly from the same family of P's ClassA amplifiers. With the given source there is no trace of harshness or glare, treble is
in fact really sweet (although the HE500 can be bettered in that regard), the soundstage very clear and three-dimensional.
You can basically point your finger only at the bass region that is somewhat softer than the SL in direct A-B comparison. It does have the same extension (as one would expect)
but doesn't hit quite as hard when the material demands for it. Softer doesn't mean muddy, and tastes are different, but with such competition at hand it had to be noted.
For sure made for some fun listening, and when it suits your taste: go ahead!
Thanks for the visit; always a pleasure.
We both immediately agreed that the bass was the most noticeable difference.
The SL Trans IMHO goes a bit deeper, when for example playing the 1812 Overture.
But compared directly with the SL HPA, it is perhaps not as tight, or "dry", as they say in Germany.
I guess in the end it is a matter of personal taste, and also headphone combination.
Otherwise it carries all the positive attributes of the original SL.
The nice thing is of course, in case you get tired of current drive, one stack-on board will convert it back to voltage amp.
Be it then with global negative feedback.
Patrick
We both immediately agreed that the bass was the most noticeable difference.
The SL Trans IMHO goes a bit deeper, when for example playing the 1812 Overture.
But compared directly with the SL HPA, it is perhaps not as tight, or "dry", as they say in Germany.
I guess in the end it is a matter of personal taste, and also headphone combination.
Otherwise it carries all the positive attributes of the original SL.
The nice thing is of course, in case you get tired of current drive, one stack-on board will convert it back to voltage amp.
Be it then with global negative feedback.
Patrick