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Tom Christiansen Audio HPA-1 Headphone Amp Review

tomchr

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Yeah... This is why I try to use positive communication. Negations are processed slower by the human brain and are often missed.

Tom
 

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tomchr

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Topping D30 (connected by RCA cables to the HPA-1)
RME ADI-2 DAC FS (connected by XLR cables to the HPA-1)
Sennheiser HD-650
Focal Elex

I also brought a pair of Sennheiser HD-580 as a backup but they never made it out of the suitcase.

Both setups had a MacBook Pro delivering CD quality or better streamed from TIDAL (and some iTunes with local files). The connection from the MacBook Pro to the DAC was an optical link (TOSLINK).

Tom
 

tomchr

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Can you add your own channel imbalance measurements?
I turned the volume control by hand with as constant rotational velocity as I could. Like Amir, I measure a channel imbalance of less than about ±0.5 dB within the attenuation range of 0-60 dB. Within a few degrees of the minimum position on the volume control, the channel imbalance does get a bit worse than the ±0.5 dB. If 7 o'clock is the minimum position, the volume control will have excellent channel balance once it's turned past 7:30 o'clock.
HPA-1 R1.0_ Channel Imbalance vs Volume Control Attenuation.png


Tom
 

Music1969

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I turned the volume control by hand with as constant rotational velocity as I could. Like Amir, I measure a channel imbalance of less than about ±0.5 dB within the attenuation range of 0-60 dB. Within a few degrees of the minimum position on the volume control, the channel imbalance does get a bit worse than the ±0.5 dB. If 7 o'clock is the minimum position, the volume control will have excellent channel balance once it's turned past 7:30 o'clock.
Thanks!
 

tomchr

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NOT directly related to the HPA-1, but I thought I'd include it for reference. Here's the imbalance vs pot rotation for the ALPS RK097 (the less expensive green ALPS pots). It's quite good (within ±0.6 dB) in the 0-40 dB attenuation range, but degrades quite a bit closer to the minimum volume setting. The RK271 "Blue Velvet" used in the HPA-1 is much better as it tracks well to 60 dB attenuation.

Interestingly, the RK097 reaches 40 dB attenuation at about 8 o'clock (assuming 7 o'clock is minimum), whereas that's about 50 dB attenuation on the "Blue Velvet" RK271. In other words, the RK271 provides a much smoother transition from minimum volume to 40 dB attenuation than the RK097. The RK097 is still a pretty decent pot - especially considering it's roughly one tenth the cost of the RK271.

I'll obviously be using the RK271 "Blue Velvet" in my high-end amps. The RK097 remains an option for a low-cost amp.

Tom
ALPS RK097 Channel Imbalance - Annotated.png
 

Doodski

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NOT directly related to the HPA-1, but I thought I'd include it for reference. Here's the imbalance vs pot rotation for the ALPS RK097 (the less expensive green ALPS pots). It's quite good (within ±0.6 dB) in the 0-40 dB attenuation range, but degrades quite a bit closer to the minimum volume setting. The RK271 "Blue Velvet" used in the HPA-1 is much better as it tracks well to 60 dB attenuation.

Interestingly, the RK097 reaches 40 dB attenuation at about 8 o'clock (assuming 7 o'clock is minimum), whereas that's about 50 dB attenuation on the "Blue Velvet" RK271. In other words, the RK271 provides a much smoother transition from minimum volume to 40 dB attenuation than the RK097. The RK097 is still a pretty decent pot - especially considering it's roughly one tenth the cost of the RK271.

I'll obviously be using the RK271 "Blue Velvet" in my high-end amps. The RK097 remains an option for a low-cost amp.

Tom
View attachment 51594
I had no idea the cost disparity between the two pots could be so much.
 

tomchr

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I had no idea the cost disparity between the two pots could be so much.
Yeah. The "Blue Velvet" is not cheap. The RK097 isn't exactly cheap either, but if you buy enough of them, their cost becomes more reasonable. I guarantee you that the el-cheapo amps by Schiit et al. use pots that are even lower cost than the RK097.

Tom
 

Doodski

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Yeah. The "Blue Velvet" is not cheap. The RK097 isn't exactly cheap either, but if you buy enough of them, their cost becomes more reasonable. I guarantee you that the el-cheapo amps by Schiit et al. use pots that are even lower cost than the RK097.

Tom
I'm seeing how your HPA-1 amp costs $899.00 US. Excellent specs, high quality components even though you could have scrimped, 4-layer PCB, last headphone amp in one's life perhaps if the owner wanted it that way and should have a good resale value too. I closely follow the headphone amp sales at Canuck Audio Mart. Lots of junk, tube amps, Sennheisers and very few of the good stuff but what good stuff there is there apparently holds it's value so I expect your's will as well.
 

JohnYang1997

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NOT directly related to the HPA-1, but I thought I'd include it for reference. Here's the imbalance vs pot rotation for the ALPS RK097 (the less expensive green ALPS pots). It's quite good (within ±0.6 dB) in the 0-40 dB attenuation range, but degrades quite a bit closer to the minimum volume setting. The RK271 "Blue Velvet" used in the HPA-1 is much better as it tracks well to 60 dB attenuation.

Interestingly, the RK097 reaches 40 dB attenuation at about 8 o'clock (assuming 7 o'clock is minimum), whereas that's about 50 dB attenuation on the "Blue Velvet" RK271. In other words, the RK271 provides a much smoother transition from minimum volume to 40 dB attenuation than the RK097. The RK097 is still a pretty decent pot - especially considering it's roughly one tenth the cost of the RK271.

I'll obviously be using the RK271 "Blue Velvet" in my high-end amps. The RK097 remains an option for a low-cost amp.

Tom
View attachment 51594
Your rk097 looks really good. On the other hand I just randomly picked one. And it looks like this. :facepalm:
-6b42c8202f0f3aa9.png
 

tomchr

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A 2 (less than) dollars implementation.:p
The RK097 is less than $2 if you buy enough of them.

I suggest running your recorder a bit longer. I used 30 seconds in my plots. The slower pot rotation makes it more likely that you'll catch a discontinuity or spot with severe channel imbalance.

And, yes. Part-to-part variation (and with this test, test/retest reliability) are known issues.

Tom
 

JohnYang1997

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The RK097 is less than $2 if you buy enough of them.

I suggest running your recorder a bit longer. I used 30 seconds in my plots. The slower pot rotation makes it more likely that you'll catch a discontinuity or spot with severe channel imbalance.

And, yes. Part-to-part variation (and with this test, test/retest reliability) are known issues.

Tom
The first one is a novel connection of pot.
On the rk097 I have run it a few times as I couldn't believe it's that bad but it was.
 

tomchr

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Cool. My suggestion of using a 30-second sweep and slower pot rotation still stands.

Tom
 

T.M.Noble

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Yeah. The "Blue Velvet" is not cheap. The RK097 isn't exactly cheap either, but if you buy enough of them, their cost becomes more reasonable. I guarantee you that the el-cheapo amps by Schiit et al. use pots that are even lower cost than the RK097.

Tom
As a policy, we never comment on other manufacturers. Just for the record, we use an Alps RK 09 in both Magni3+ and Magni Hersey. We also use the RK 27 in our headphone amp Asgard. We agree, those are definitely quality parts.
 

tomchr

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Ah. The RK09 not the RK097. It looks like the RK09 is the same pot as the RK097 with a different (better, probably) mounting bracket. I stand corrected.

I'm glad we agree that the RK09/097 and RK27 are different levels of quality. :)

Tom
 

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