[Contrails]

https://www.audeze.com/blogs/technology-and-innovation/sensitivity-impedance-and-amplifier-power

This is a good read when trying to figure out what sort of requirements most planars require.

 

[jonathan c]

To @Contrails and @JLoud: one can more directly compare the efficiency / sensitivity of HE6 to that of LCD-4 by a conversion to dB per volt. This does incorporate dB/mw and the nominal impedance of the headphone. The formula is:

dB/V = dB/mw - (10 x log(ohms/1000)).

HE6: 83.5 dB and 50 ohms == 96.5 dB/V
LCD-4: 97.0 dB and 200 ohms == 104.0 dB/V

The HE6 is substantially less efficient, much harder to drive.

 

[KaiSc]

COMPARISON,
OTL Tube vs. Solid State headphone amps
driving AUDEZE LCD-4


Symphonic Audio OTL tube amplifier.
ECC81 drive tubes and 6AS7G power tube.
Max available power ca. 800 mW.

- vs. -
RME ADI-2/4 Pro SE headphones amp.
One of the most “neutral” amps available, ideal for referencing.
Max available power ca. 900 mW.


DAC for both: RME ADI-2/4 Pro SE.


Listening levels and conditions:
•Sound Level ca. 102 dB SPL Peak, 86 dBA Leq (long term average), at the upper edge of what’s healthy.
•Measured maximum power needed for this sound level: 1-2 mW only !
•A/B levels for both amps adjusted for being the same within 0.05 dB.
•Immediate A/B switching, no interrupting replug needed.
•Sighted A/B - the difference is so significant that a blind A/B is not necessary, the tube amp can always be clearly identified anyway.


Frequency response measurement:
RME ADI-2/4: linear <5 Hz - beyond 20 kHz.
OTL tube: -0.5 dB @ 20 Hz (AC coupling) -0.1 dB @ 40 Hz, linear to beyond 20 kHz.
Comment: Both amps are linear in the relevant audio range.
Audible differences cannot be related to frequency response.

Playlist:
Automatically generated playlist by Tidal, mixed CD- and HiRes-quality.
Most tracks unknown to me, so no expectation bias “how they should sound”.


Comparisons result:

Symphonic Audio OTL tube amplifier:

•The OTL tube amp has a distinctive color that adds what can be missing on the LCD-4:
LCD-4‘s slightly laid back character is supplemented by some transparency and bite.
•At first it sounds like an upper midrange/treble boost (that objectively is not there, see measurements).
•Impulses and attacks are stronger throughout the whole range from bass to treble, except for the topmost octave, that sounds little more rounded.
•The bass trades the lowest sub extension for a harder, more defined punch.
•Instruments and vocals in smaller ensembles are better separated, easier to follow their line, they stand out more.
•Emotionality is enhanced.
•It’s like being closer to the artists.
•Ambience is more centered, concentrated.
•Dynamics are spread: Louder parts do sound more aggressive, quieter parts softer.
There’s a significant reaction on the volume dialed-down, the sound gets darker and softer, even thought the basic character isn’t lost.


RME ADI-2/4 Pro SE:

•ADI-2/4’s headphone amp sounds softer and clean on first impression.
•The sub-bass is stronger, deeper and fuller.
•On crowded tracks ADI-2 stays more transparent.
•If a lot is going on in the upmost treble range, like percussions, hihats, cymbals and vocal sibilants there’s better separation.
•Ambience is spread wider and deeper.
•It does not add an overall color of it’s own.
•Dynamics are more even, with dialed-down volume the sound stays constant.



Conclusion:

•For 7 out of 10 tracks the AUDEZE LCD-4 / OTL tube amp combination is preferable.
•The colors of the OTL nicely complement with the “King Of Darkness”.
•Interestingly, on some tracks the RME is very clearly better suited.
•This might partly be linked to the OTL tube amp’s strong reaction on in-track-dynamics and volume-dial-changes.

 

[Articnoise]

To @Contrails and @JLoud: one can more directly compare the efficiency / sensitivity of HE6 to that of LCD-4 by a conversion to dB per volt. This does incorporate dB/mw and the nominal impedance of the headphone. The formula is:

dB/V = dB/mw - (10 x log(ohms/1000)).

HE6: 83.5 dB and 50 ohms == 96.5 dB/V
LCD-4: 97.0 dB and 200 ohms == 104.0 dB/V

The HE6 is substantially less efficient, much harder to drive.

It is power and current that is the limiting factors for planar magnetic headphones. Voltage is the limiting factor for electrostatic headphones.
Test this https://www.hear.audio/2019/06/01/headphone-power-calculator/

 

[TheAbyss2022]

COMPARISON,
OTL Tube vs. Solid State headphone amps
driving AUDEZE LCD-4


Symphonic Audio OTL tube amplifier.
ECC81 drive tubes and 6AS7G power tube.
Max available power ca. 800 mW.

- vs. -
RME ADI-2/4 Pro SE headphones amp.
One of the most “neutral” amps available, ideal for referencing.
Max available power ca. 900 mW.


DAC for both: RME ADI-2/4 Pro SE.


Listening levels and conditions:
•Sound Level ca. 102 dB SPL Peak, 86 dBA Leq (long term average), at the upper edge of what’s healthy.
•Measured maximum power needed for this sound level: 1-2 mW only !
•A/B levels for both amps adjusted for being the same within 0.05 dB.
•Immediate A/B switching, no interrupting replug needed.
•Sighted A/B - the difference is so significant that a blind A/B is not necessary, the tube amp can always be clearly identified anyway.


Frequency response measurement:
RME ADI-2/4: linear <5 Hz - beyond 20 kHz.
OTL tube: -0.5 dB @ 20 Hz (AC coupling) -0.1 dB @ 40 Hz, linear to beyond 20 kHz.
Comment: Both amps are linear in the relevant audio range.
Audible differences cannot be related to frequency response.

Playlist:
Automatically generated playlist by Tidal, mixed CD- and HiRes-quality.
Most tracks unknown to me, so no expectation bias “how they should sound”.


Comparisons result:

Symphonic Audio OTL tube amplifier:

•The OTL tube amp has a distinctive color that adds what can be missing on the LCD-4:
LCD-4‘s slightly laid back character is supplemented by some transparency and bite.
•At first it sounds like an upper midrange/treble boost (that objectively is not there, see measurements).
•Impulses and attacks are stronger throughout the whole range from bass to treble, except for the topmost octave, that sounds little more rounded.
•The bass trades the lowest sub extension for a harder, more defined punch.
•Instruments and vocals in smaller ensembles are better separated, easier to follow their line, they stand out more.
•Emotionality is enhanced.
•It’s like being closer to the artists.
•Ambience is more centered, concentrated.
•Dynamics are spread: Louder parts do sound more aggressive, quieter parts softer.
There’s a significant reaction on the volume dialed-down, the sound gets darker and softer, even thought the basic character isn’t lost.


RME ADI-2/4 Pro SE:

•ADI-2/4’s headphone amp sounds softer and clean on first impression.
•The sub-bass is stronger, deeper and fuller.
•On crowded tracks ADI-2 stays more transparent.
•If a lot is going on in the upmost treble range, like percussions, hihats, cymbals and vocal sibilants there’s better separation.
•Ambience is spread wider and deeper.
•It does not add an overall color of it’s own.
•Dynamics are more even, with dialed-down volume the sound stays constant.



Conclusion:

•For 7 out of 10 tracks the AUDEZE LCD-4 / OTL tube amp combination is preferable.
•The colors of the OTL nicely complement with the “King Of Darkness”.
•Interestingly, on some tracks the RME is very clearly better suited.
•This might partly be linked to the OTL tube amp’s strong reaction on in-track-dynamics and volume-dial-changes.

Where can one find to buy the tube amplifier you have listed? can you even buy it new?

 

[KaiSc]

Where can one find to buy the tube amplifier you have listed? can you even buy it new?

The company is long gone - not mine BTW, to avoid misunderstanding.

I‘m currently thinking to hand the design to another little company for series production.
I had done some essential mods on it to better suit it to AKG K-1000 — a really “hard to drive” phone by today‘s measures, eating 200 times (!) the power of LCD-4, even more if some EQ is used.

The beauty of tube designs, they can be very simple and straight forward, even in this case.
Less parts = better signal, and higher quality parts can be used for the same money.

The core is the 6AS7G tube, which has a unique sound when used in an well done OTL arrangement.

 

[whirlwind]

Which tube amplifier is good to run with the LCD 4? Some recommended the ZMF Pendant but they no longer make them and getting them 2nd hand in the UK is nearly impossible. Therefore, if anyone knows any tube amplifiers that are currently being sold new I would appreciate it!

I am not to sure how far 2K would get you in the custom amp market these days.

If I was looking for a tube amp that could handle pretty much all types of headphones, I would be looking at having an amp built for that.

There are a few people on these forums that do just that. Never hurts to ask and communicate with a custom builder.

If you can solder or are not afraid to learn, there are also some kits you can build.

I know customs amps are not for everyone, but the bang for the buck is great.

 

[KaiSc]

I am not to sure how far 2K would get you in the custom amp market these days.

I know customs amps are not for everyone, but the bang for the buck is great.

Absolutely, and the pricing your find in the audiophile world these day is often hard to justify.

Even with exotic top notch components it‘s almost impossible to exceed 1K of cost for the materials of a basic tube headphones amp.
If you cross out “exotic” you will end below 250.

One thing to consider:
Tube amps work with high, potentially deadly, internal voltages.
So DIY is for skilled people only.

 

[whirlwind]

Absolutely, and the pricing your find in the audiophile world these day is often hard to justify.

Even with exotic top notch components it‘s almost impossible to exceed 1K of cost for the materials of a basic tube headphones amp.
If you cross out “exotic” you will end below 250.

One thing to consider:
Tube amps work with high, potentially deadly, internal voltages.
So DIY is for skilled people only.

Well, an SET amp is only as good as the trannies used, so whatever that may be...it can easily be over 1K for just the transformers.

 

[leftside]

Well, an SET amp is only as good as the trannies used, so whatever that may be...it can easily be over 1K for just the transformers.

Some custom OTL amps also have rather big caps And the power supply section of an OTL amp will also use transformers (well at least mine does, but I'm not 100% sure about "all" OTL amps?). Not as important as the transformers in a SET amp, but still important.
https://www.diyaudio.com/community/threads/power-transformer-for-otl-headphone-amp.298256/

 

[tumpux]

Well, an SET amp is only as good as the trannies used, so whatever that may be...it can easily be over 1K for just the transformers.

True.
Quality output transformers are something that rarely appreciated in a tube amplifier. It also the component that get skimp on in “budget amplifiers”.

 

[tumpux]

Some custom OTL amps also have rather big caps And the power supply section of an OTL amp will also use transformers (well at least mine does, but I'm not 100% sure about "all" OTL amps?). Not as important as the transformers in a SET amp, but still important.
https://www.diyaudio.com/community/threads/power-transformer-for-otl-headphone-amp.298256/

I think he’s talking about output transformer, not power transformer.

 

[KaiSc]

The AUDEZE LCD-4 200 Ohm is a great candidate and fit to be driven out of an OTL tube amplifier.
https://www.head-fi.org/threads/audeze-lcd-4.782442/post-17365451


Below I try to give realistic figures for sourcing of small amounts of components for a single DIY OTL tube amp project, from quality western providers.

Of course there’s no upper or lower limit if exotic audiophile or almost no $$$ chinese comes into play.


The power transformer in a tube amp is largely decoupled from the amp itself by the filtering.
The audio part of the amp doesn’t ”see” it, only sees the filtering circuit.
100 for the transformer would be premium, can be had for 30 too.

1K for the output transformers is quite a word - in headphone amps they are relatively small compared to speaker amps, where they go for 200.
Typically they are around 50-150 a piece from specialized companies like Tubeland, Lundahl etc.
In OTLs there aren’t any.

OTL’s pair of output coupling caps are quite big indeed, typically 50 - 200 uF / 160 V.
50 uF would be 16 Hz with AUDEZE’s 200 Ohm LCD-4.
Larger than 200 uF doesn’t change anything, as the OTL amp‘s output impedance is the limiting factor.
PP types go for ca. 20 a piece, less if you go for electrolytic + MKP/MKT/MKS bypass,

Tubes vary a lot, 2x ECC82 + 1x 6AS7G starts at 40.
NOS / New Old Stock doesn’t exist, once they are burned in or used some time they are no longer New, this is a typical thing to face using a tube amp, and that’s no problem at all.
Old Stock is a way to go, the mentioned standard types from Telefunken, Philips, Sylvania, Valvo, Mullard etc. don’t cost a fortune.

Casing is where DIY shines, either bought prebuilt up to various stages, or all DIY.


Finally, for those who want to try, there are assembly kits giving a starting point.
This one contains all parts except the tubes and case.

Electronic parts and circuit board for 50:
http://www.tubeland.de/product_info.php?products_id=58

PSU goes for 23:
http://www.tubeland.de/product_info.php?products_id=155

Power Transformer goes for 92 (encapsulated ring core):
http://www.tubeland.de/product_info.php?products_id=63

 

[leftside]

I think he’s talking about output transformer, not power transformer.

Yeah I know. Maybe I should have been more specific and said "the power supply section of an OTL amp will use (power) transformers"

 

[leftside]

The AUDEZE LCD-4 200 Ohm is a great candidate and fit to be driven out of an OTL tube amplifier.
https://www.head-fi.org/threads/audeze-lcd-4.782442/post-17365451


Below I try to give realistic figures for sourcing of small amounts of components for a single DIY OTL tube amp project, from quality western providers.


OTL’s pair of output coupling caps are quite big indeed, typically 50 - 200 uF / 160 V.
50 uF would be 16 Hz with AUDEZE’s 200 Ohm LCD-4.
Larger than 200 uF doesn’t change anything, as the OTL amp‘s output impedance is the limiting factor.
PP types go for ca. 20 a piece, less if you go for electrolytic + MKP/MKT/MKS bypass,

How about these caps We got the output impedance down to 15 ohms on this OTL amp. Power supply is separate (on the bottom in this photo).