[tomchr]

Here is a site that is very interesting that will help you determine how much distortion you can actually detect with your ears! And then can apply this in a meaningful way to a piece of gears distortion measurements and see if this will indeed matter or not in your listening experience:

http://www.klippel.de/listeningtest/

Here is a link to a discussion of the HPA-1 that speaks to this test and how it might
apply to whether or not these measurments have a correlation to what you hear or not.

https://forum.headphones.com/t/tom-christian-audio-tca-hpa-1-headphone-amplifier-official-thread/4982/40

You can read the entire discussion or scroll down to March 1 and read post 41. Very interesting read...

There's also this: http://harmanhowtolisten.blogspot.com

Tom

[adydula]

Thanks for that Tom, I posted this sometime ago as well...good information:

https://forum.headphones.com/t/listening-skills/4595

Alex

[tomchr]

I had about 100 participants in my market survey. I posted survey links about a year ago on ASR, DIY Audio, my Facebook page, and via my Neurochrome Newsletter. I ran the survey for a few weeks.

I see two directions from the HPA-1:

• Up: Prettier chassis, XLR and 1/4" output, XLR and RCA input. Maybe a preamp output. Maybe higher output power. Possibly some other surprises that I'll keep as surprises for now. Price target: Somewhere in the $1-2k range.
• Down: Cost reduced version with a lower quality volume pot (the ALPS RK097 is a pretty decent pot that is one tenth the cost of the RK271 "Blue Velvet" used in the HPA-1), lower output power, RCA only input, 1/4" only output, one gain setting. Smaller version of the "upper class military look" (thanks for that term) chassis. Price target: $499.

Tom

[Freo-1]

This will arrive on Thursday. I don't have a large collection of headphones,  but I've a few of different quality levels I'll try out as fo follows

• Sony MDR 7506
• Sony MDR V700 (early Japan made)
• Sony MDR Z7 (Japan made)
• Audeze LCD 3

If I can get a single ended cable, will also try a Abyss Diana.    Will spend most of the time with the Z7 and LCD-3.  Just want to see how this amp improves the 7506 and V700.


I'm interested to see how well this drives the planr cans (especially the Diana).  Should be fun. 

[tomchr]

This will arrive on Thursday.

Fantastic!

I'm interested to see how well this drives the planr cans (especially the Diana).  Should be fun.

Indeed. I'm looking forward to hearing about it. The only planars I've tried so far have been the Andover Audio PM-50 (https://www.andoveraudio.com/products/pm-50-planar-magnetic-headphones). They worked quite well with the HPA-1. I'll also take the opportunity to listen a bit tomorrow when I go pick up a loaner HPA-1 from Absolute Audio (https://www.absoluteaudio.ca) in town. They had the amp on display this weekend and have an extensive collection of Audeze headphones.

Tom

[Freo-1]

I (think) the LCD-3 will be OK.   I'm less sure about the Diana. 


My migration to planar is the reason I obtained a Mjolnir Pure Bipolar.   I was able to get a cable that will allow for audition of the Diana. 

[tomchr]

I (think) the LCD-3 will be OK.   I'm less sure about the Diana.

LCD-3: 110 Ω, 101 dB/mW -> 650 mW -> 129 dB SPL. That's instant permanent hearing damage.
Diana: 42 Ω, 91 dB/mW -> 1.0 W -> 124 dB SPL. So your ears may last a split second longer with these before permanent damage occurs.

120 dB SPL is the threshold for permanent damage within seconds. So I think you'll be fine with either.

I estimated the output power from the output voltage at the onset of clipping for the various impedances from the graph below.

Tom

[Freo-1]

Looks like the amp should have no trouble with the planar headphones then.   

There are two different issues.  One issue is possible hearing damage from playing headphones too loud, which I am very careful about not to get into that situation.  That can happen even with a phone driving headphones.


The other issue is one where while the amp is driving the headphones. the overall presentation can vary even with the same Spl level.  Transients, tonal characteristics, etc. can be different between amps.  For example, I've noticed that the balanced Pure Bipolar amp has better overall sound with the LCD-3 than the Dynalo amp.  I assume that is because the Pure Bipolar is balanced, and has roughly 5 times the available output power over the single ended Dynalo.  They both sound somewhat similar, but the difference in presentation is noticeable with the planar cans, less so with dynamic cans.

[Freo-1]

One question I have is as follows:


What are your thoughts regarding the gain switch?  When would a customer use one setting vs. the other? 

[tomchr]

I will always recommend using the lowest gain setting possible. Basically, only increase the gain if you can't get satisfactory SPL with the volume control maxed out.

The gain switch is just to accommodate low-output sources, such as phones, tablets, etc.

Tom

[Freo-1]

 The HPA-1 headphone amp arrived yesterday. .    The build quality is quite nice, and the controls have a nice feel to them.  Given the amp’s small stature, this would be a good candidate for a desktop system for use at work or at home.  I want to thank Michael for this opportunity to review this amp.  I’m sure he will be most happy with it once he gets it back. 😊
 
Some background is in order:  The input to the amp was via a Sony UBP X-1100ES, with the Digital Sound Enhancement Engine enabled.  This doubles the sample frequency to 88.2, 96, or 176.4 KHz to an Oppo Sonica DAC.  The Sonica DAC employs the ESS 9038 Pro DAC, and sounds very good.  The connection to the HPA-1 was via the single ended connection.
 
So far, have done the listening with the Sony MDR Z7, and the Audeze LCD-3 headphones.  Most of my observations were with the Z7 headphones, as that combination sounded very good overall. 
 
The music with Z7 sounded quite nice.  The Z7 is an interesting headphone from Sony, hand made in Japan.  The headphone demands that good electronics drive them, or it won’t sound very good.  The HPA-1 is an excellent match for the Z7.  Music was re-created with good depth, clarity, and space.  The bass is deep and powerful (a bit warm from the can), but not overpowering.  The amp does a good job of controlling the driver here.  The midrange sounds well balanced.  On good recordings, instruments such as horns sounded like horns, which a lot of headphones can’t seem to get right.  Vocals were clear, especially female vocals.  The treble response is excellent overall, with a slight tendency to sound a bit bright.  There is plenty of power to drive the Z7 cans to very satisfying results. 
 
The reason I didn’t do as much listening with the Audeze LCD-3 cans is that this combination was not as good as I had hoped.  Planar cans can be a tough item to drive.  While the HPA-1 can drive the LCD-3 cans, the sound from this combination came across as a bit compressed.  This was very noticeable with instruments such as piano and strings.  I tried using the gain switch, but all that did was make it louder, it didn’t resolve the issue.  I also noticed this issue to a slightly lesser extent with my Dynalo amp driving the LCD-3.  Wound up obtaining a Pure Bipolar balanced amp to resolve the issue with driving planar cans.  The HPA-1 and Dynalo amps can drive the LCD-3’s fairly well, but not to the can’s full potential.  Stax electrostatic headphones suffer from this same issue, and need a higher-powered amp than what Stax makes to get them to sound their best.  I view this as more of a headphone design issue. 
 
Will provide additional observations prior to sending the amp to the next member. 
 

[tomchr]

Fantastic. Thank you for your feedback and detailed writeup. "Horns sound like horns"... Yep. That's one of the things I listen for as well. I used to play the trumpet, so I have a decent idea of what one sounds like. Also snares on snare drums, cymbals, etc. Those types of sounds are often hard to reproduce accurately, so those types of sounds are what I listen for (along with other things, of course).

Yeah. I would not expect the gain switch to change the sonic character of the amp. That's by design, actually.

If you were to point at an amp that really makes the LCD-3 shine, which one would it be?

Tom

[Freo-1]

Glad you enjoyed the write-up.  Still need to listen with the 7506 and V700 to see what improvements are wrought.   The amp works very well with the MDR Z7, which is not an easy headphone to drive.


One amp I know works very well with the LCD-3 is the Mjolnir Audio Pure Bipolar:


https://mjolnir-audio.com/product-selection/


I have the black version.  I got it second hand for a very good price.  Here is some additional information on the amp:


https://www.innerfidelity.com/content/katzs-corner-episode-18-icelandic-wonder


Bob Katz loved this amp with the LCD-4, which is harder to drive than the LCD-3.


I personally have not heard this amp, but it should work well with planar cans: ( A wallet hit to be sure   )


https://www.headamp.com/products/gs-x-mk2


My experience with headphones is mostly Stax, which is how I came across the Kevin Gilmore/Spritzer connection.  My past experience with Stax is why I migrated to planar cans for the dynamic world.

[A_shah]

Got a email for Michael , I am next  on the list  !
 Happy on getting an opportunity to listen to the HPA-1 -Thanks Michael U are a GR8 Audio Buddy !
OK Just read the whole thread for the 1st time I am GR8 fan of Amir at ASR believe in measurement but they don't tell the whole story .
I am certainly looking forward to listening and Enjoying the HPA -1 please don't expect any critical listening reviews on the HPA although I am very capable of creating great reviews if need be.
Any way here  is what I have- it's  a partial list !
Head phones among others
1. Audeze LCD -X ( easy to drive ) even though it is Planner
2. Audeze iEM LCD 4I
3. Audeze ISine 20  IEM
forget the Boses & Beate etc etc etc

HP. Amps:
1. QuickSilver audio  SET Tube Amp:  my most favorite non fatiguing listening amplifier, I can never give that up. !  others may come and go 
2. Audeze Deckard
3. Chord Mojo /DAC /HPAmp
DAC's
1. Schiit Gungnir
2. Chord Mojo
3. Directstream PS Audio DirectStream DAC ( I could try listing to this unit with the HPA -1 , Do own a OPPO 205 which has a headphone out I believe comparable to Sonica DAC ( but won't have time for that !)
. Misc.
JCAT USB reference  Cable
Silver plated Audeze cable that came with LCD 4i
Solid Silver HP cable from Larvicables  from  Poland
Wywire Red HP cable made for me by Alex of WYwire GR8 chap !
ISI Purifier 3 ( into Schiilt Gungnir inputted by JCAT reference USB cable )
 all outlets are PS audio , Clean electricity, no hum anywhere in the circuit semi dedicated wring both to my DEsktop home office system and Main system

thanks 
Asghar
 

[mresseguie]

Ashgar,

Aw, shucks. You're very welcome. 

Enjoy!

Michael

[ServerAdmin]

This thread is now in All Solid State. If you have questions specifically for Tom, please ask him in his Industry thread -> https://www.audiocircle.com/index.php?topic=168574.0

[mresseguie]

Admin,

Thank you. 

I anticipate receiving my amp in approximately two weekss and I'm looking forward to it!

[A_shah]

Hi,
just my personnel impressions of the HPA-1, Of course these are subjective and personnel  , I have used two DAC's with the system , I find the better combination and pairing with the Schiit Gungnir & the LCD-X . My impressions are from  listening classical to POP music including piano recitals  & violin. The amplifier is very neutral and " DAC"  & source dependent .With  the Shiit Gungnir DAC and streaming( Tidal & Quboz)  it has a very good dynamic range, the layering & separation  of instruments is very distinct & clear , females voices sound as they should . however one gripe I have with the unit is that the volume knob is small for a high end headphone amp . 

Asghar

[mresseguie]

Thanks for your impressions, Ashgar.

I'm looking forward to listening to this soon. 

Michael

[mresseguie]

Well, I finally retrieved my HPA-1 from my cold garage where it had been sitting in its shipping box for a few days. I was too busy to hook it up till now, but I also wanted to make damned certain any viruses died before I risked drooling on the box or amp.  Ashgar told me he made an extra effort to disinfect it - just in case. Thank you, Ashgar!

I've got my 2014 Mac Mini feeding my dB Audio Labs Tranquility SE DAC which is feeding my HPA-1 via a pair of Triode Wire Labs RCA ICs. My HD650 cans are plugged in and I have MUSIC! The amp is still quite cold, so I will give it a bit of time to warm up before I get too picky about what I'm hearing.  I don't even know if I have the settings correct for my cans. 

I'd like to thank all the guys who participated in this tour, and to Tom Christiansen for agreeing to ship it off to someone other than the guy who purchased it. It is in remarkably good shape considering it skipped across North America to 5(?) locations before landing on my front porch. Thank you. My hat's off (revealing my bald pate). 

A special thank you goes to Alex (adydula). If it weren't for his enthusiasm and freely offering help, advice, and friendship, I quite likely would not have hosted this tour.   

I'll be back before too long with my impressions. Stay tuned.

Stay well.

Michael