It is a great little radio designed for music. It is wonderful to use, works exceedingly well, with delightful sound. Silly expensive for a mono transistor radio, but brilliant.
A number of people have bought one after seeing and hearing mine. A great introduction to enthusiast audio.
Excellent to hear that it does sound good. I had been intrigued (but not enough to invest) by it’s pedigree. Wonderful news.
Paul & team:
How will the variations of the headphone impedence be handled? For example, headphones like:
(there are more headphones and this is just a sample over the huge variations of headphones out there.)
These are huge variations in impendeces from ~35 Ohm to ~800 Ohm with high power requirements (especially for the HE-6). How is the team preparing for this? Are you grouping them with change in output power or will it be dynamically adapted depending on the sensed load?
=> I have not yet found information how the "King" is handling this or whether it was specifically "designed" for the Audeze headphones.
Expected output frequence range: ???
Total Harmonic Distortion (THD): ???
Do you allow for 2 headphone output: ???
You mentioned that PS Audio is considering a “headphone amp.” and a “pre-amp. with build in headphone amp.”. Will the internal design be significantly different leading to significant listening experiences? Probably impossible to say at this point.
Regarding Cross-feed:
The SPL Phonitor is such an outstanding device that is used in professional studios to mix. albums via headphones. A superb headphone-amp for the designed purpose (w/out cross-feed usage). Often overseen is that the advantage of the new “SPL Phonitor 2” is that the cross-feed can be transferred to the XLR output, which can then be used to feed a headphone pre-amp of choosing. And yes, the cross-feed handling of the Phonitor is easy to setup but extremely effective and it does make a difference for longer period of listening using headphones.
Welcome!
The Phonitor is a wonderful hoot. I also find Michael Grace’s crossfeed circuit quite nice. Generally however I prefer to listen to headphones without crossfeed.
NS said Paul & team:The good news about headphone impedance is that all the designer needs to do is make sure we can handle the lowest, and have enough output voltage to cover the highest. And we do on all accounts.How will the variations of the headphone impedence be handled? For example, headphones like:
- Hifiman HE-1000 (Impedence: 35 Ohm, Sensitivity: 90 dB),
- HifiMan HE-6 (Impedence 50 Ohm, which is hard to drive (Sensitivity: 83.5 dB), requires 1W-4W into 50 Ohm),
- Audeze LCD-4 (Impedence 100 Ohm, Sensitivity: 100 dB/1 mW, requires 1W-4W),
- Audeze LCD-3 (Impendece 110 Ohm, Sensitivity 102 dB / 1 mW, requires 1W-4W),
- Sennheisser HD-800 (Impedence 300 Ohm, Sensitivity: 102 dB)
- to headphones with an Impedence of 800 Ohm.
(there are more headphones and this is just a sample over the huge variations of headphones out there.)
Expected output frequence range: ???
Total Harmonic Distortion (THD): ???
Do you allow for 2 headphone output: ???
There seems a bit of confusion when it comes to driving headphones - some think the output impedance of the headphone amp has to match the input impedance of the headphones. That’s not true. As long as the headphone’s input impedance is above the lowest output impedance of the headphone amp, you’re in good shape. The BHK can easily drive a 10Ω load - we even power small speakers with it.
Sensitivity is another matter. Sensitivity requires enough voltage on the headphone amplifier’s output to drive the headphone. The worst we’ve seen is the Audeze which work spectacularly well on the BHK Preamp headphone output. So, no worries, yes we have this covered. Both Arnie and Bascom are diehard headphone aficionados and they make sure it’s done right and sounds as good or better than anything Bascom has designed.
We do not have more than one output jack for headphones. And, I am sorry, I don’t have the specs with me other than the frequency response, which easily extends past 50kHz.
You realize you just took away the endless looping discussions about headphone amps on HeadFi which comprise perhaps a third of the website.
Inquiring about headphone specs v. amp specs on HeadFi is like asking “What oil is best and how often should I change it?” on an automobile enthusiast site.
Thanks Elk. Yeah, headphones are just tiny speakers. There’s a lot of misconception about impedance. It’s instructive for our readers to understand that as long as the impedance is high enough, relative to the lower output impedance of the amplifier, then it just doesn’t matter - the only caveat is you need enough voltage to move the speaker’s diaphragm (headphone’s diaphragm).
In fact, one of the keys to make a great headphone amp, or loudspeaker amp (big loudspeaker), is low output impedance of the amp - zero being preferable. Of course zero impedance is a fairytale but good design can get close. The downside is how you achieve it. Use of large amounts of negative feedback helps lower output impedance but at a sonic cost.
In the BHK headphone amp, Bascom keeps the output impedance around 1Ω without negative feedback.
It always hits me when I read about matching the output impedance of an amp to headphones that they are trying to accommodate the foibles of poorly or improperly designed headphones. It is unfortunate that this can include a number of high end and/or boutique headphones. That, or we are reading the intimate discussions between fanatically crazed tewakers that are so often seen in our audio obsessed community.
J.P.
My intend was to ask if the pre-amp can handle low impedance headphones (Answer: yes) [not all head-phone amps can do that] and the other, more important for me, was whether the pre-amp can drive the headphones (answer: >100 dB/mW tested).
The answer received are not fully satisfying but are general enough, for instance, for the low impedance & low sensitivity headphone HE-6: the SPL Phonitor 1 (unknown for version 2) can support lower impedance (>0.18 Ohm – driving towards Paul’s mentioned ideal state of 0 Ohm) but it does not have the power to drive the low sensitivity headphone very well (in complete agreement with Paul’s answer). On the other hand, the April DP-1 lowest supported load is 75 Ohm (spec sheet) but it is one of the few that can drive the HE-6 (50 Ohm) headphone extremely well.
So, my question was not there to entertain folks but was an honest question to understand the expected capabilities of this future PS-Audio device, a pre-amp. paired with a head-phone amp. I want to understand, learn, apply and enjoy (not working in this field at all: optical engineer).
So, my take away is that: sensitivities below ~100dB/mW, like the HE-6 with 83dB/mW, are uncertain (not yet tested) to be driven extremely well. The other specs are not yet to be revealed with the exception of the frequency response (answer: ??? > Frequency > 50kHz) [=> SPL Phonitor 2: 10Hz to >200kHz] , which provides some knowledge of the frequency cut-off – Fourier Transformation – band-limitation and its implications when transforming between the two domains.
Is there an actual headphone you need to drive or is this simply a theoretical, albeit amusing, discussion?
I am certain the Audeze King headphone amplifier was not designed to drive only Audeze headphones, with a compromised ability to drive other 'phones.
Similarly, Mr. King is certainly well aware of the present audiophile obsession with planer headphones and has thus designed a headphone circuit for the BHK sufficient to drive the current crop of toys.
Perhaps Mr. King will see this thread and will comment.
Elk said Is there an actual headphone you need to drive or is this simply a theoretical, albeit amusing, discussion?I am certain the Audeze King headphone amplifier was not designed to drive only Audeze headphones, with a compromised ability to drive other 'phones.
Similarly, Mr. King is certainly well aware of the present audiophile obsession with planer headphones and has thus designed a headphone circuit for the BHK sufficient to drive the current crop of toys.
Perhaps Mr. King will see this thread and will comment.
Regarding what I consider the current important crop of toys, the HiFiMan HE-1000 and the Audeze LCD-4, I can say for sure that both the Audeze King headphone amp and the headphone amp in the upcoming BHK Signature Preamplifier drives them both with ease - and both of these new phones are major good!
BHK
It is time for some more information about the headphone amplifier in the upcoming BHK Signature Preamplifier. Circuit wise, it is a N channel MOSFET source follower running at about 150 mA idling current with a complementary phase modulated current source load. Gain of the headphone amp circuit is unity but with the gain of the main preamp output driving it. The output stage voltage is about +/- 12V which is going to limit the output power into higher impedance headphone loads - but that’s true for any design, it’s just where you draw the line. It is definitely at it’s best driving the lower impedance headphones.
Some essential measured characteristics of the headphone amplifier circuit include:
Clipping power output at about 1% distortion vs. load impedance:
8 Ohm 0.6W, 16 Ohm 1.5W, 32 Ohm 1.8W, 50 Ohm 1.3W, 150 Ohm 0.46W, 300 Ohm 0.25W, 600 Ohm 0.11W (I heard that PS Audio plays speakers with the headphone amp on Bob Stadtherr’s test bench)
Frequency response:
+0, -0.25 db 10 Hz - 50 kHz -3 db at 170 kHz
Output noise:
< 25 uV 10 Hz - 22 kHz BW, , < 6 uV A wtd
In short, these specs are quite admirable and I would put the sound of this amplifier up against the best out there with results I am proud of.
Bascom,
It is very much appreciate that you revealed technical details. The fit “y=aexp(bx)+cexp(dx)” with (a,b,c,d = 2.875,-0.02663,0.6306,-0.002996) where x is the load impedance and y the power was well suited over the range (32-600) Ohm. Fit-wise, it would hit ~2W near 0 Ohm but the power will start to drop below ~32 Ohm (0-32)Ohm.
Am I wrong to interpret that this is roughly the point where the 1% distortion point was reached? Is the distortion then correlated to the load sensitivity, i.e., the more power it requires to drive it (i.e. increase in current), the more signal distortion (and noise) ? (questions from a non EE)
Thanks again for your ultra kindness to share the details with us – the specs look very promising indeed.
I might have missed it but is there a rear panel of the preamp?
I currently use an Audio Research Reference 5SE and I really like that it has both XLR and single ended inputs for every input - including the HT Bypass aka PROC input.
Does the BHK Pre have balanced inputs for the HT bypass?
EDITED - Re-read some of the old posts - so it seems that the BHK Pre will be similar to the way the ARC Ref 5/5SE worked - 5 inputs which can be balanced or single ended, and unlike the ARC, ANY input can be the PROC input. That is really neat. Add in per input volume memory and we have a real winner esp since my turntable is always a lot lower in output levels.
Re the volume control - I have always been a big fan of the way Ayre does volume control on its KX-R and KX-R20 where the input impedance is not affected by the volume level - so even at low levels, the Ayre preamp has the dynamics and pace as when it is running at high levels. With my ARC Ref5SE for instance, it really comes into its own when I can push the volume knob to around 40+ and this has always been a challenge when I used higher gain power amps with the preamp.
DoggieHowser saidRe the volume control - I have always been a big fan of the way Ayre does volume control on its KX-R and KX-R20 where the input impedance is not affected by the volume level - so even at low levels, the Ayre preamp has the dynamics and pace as when it is running at high levels. With my ARC Ref5SE for instance, it really comes into its own when I can push the volume knob to around 40+ and this has always been a challenge when I used higher gain power amps with the preamp.
Thanks Paul.
ps could have sworn I replied to your message before… hmm but it seems to be gone.
Anyway, I hope you will be producing another series of videos with Bascom regarding the design of the preamp. I loved the ones on the power amps. His frank, down to earth and open discussion was just such a breath of fresh air 
I’d love to hear this preamp against the best of SS and tube preamps like the Ayre and Audio Research.
I hardly dare to ask…there’s no optional integrated phono stage planned for this preamp, is it? 
I always tried to avoid the effort of all that cabling and in my opinion avoidable cost for an external phono stage…
I know and no, there’s no built in phono stage. If you see the insides of the new BHK preamp you’ll understand why. Chock full to the brim. The headphone amplifier, a true work of art, is enormous and takes up a lot of the room - but the main preamp stage is huge - tons of power supply to make it as good as it is.
Paul McGowan said I know and no, there's no built in phono stage. If you see the insides of the new BHK preamp you'll understand why. Chock full to the brim. The headphone amplifier, a true work of art, is enormous and takes up a lot of the room - but the main preamp stage is huge - tons of power supply to make it as good as it is.Are you just gong to sit there and tease us like that or actually show us a picture of the insides?
(Did you ever have a part-time job in the torture business?)
–SSW
Drip…, drip…, drip…
Paul has always been a master at dribbling out information to build suspense. And the pre-order list.