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Old 12th June 2010, 04:10 PM   #1
THKL is offline THKL  Germany
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Default Building a high-quality headphone system

Hi guys,

since I am usually listening to music in the late night (and some people would even say early morning), my new neighboors are not that amused and I will probably have to change my listening habit a bit.
Of course my listening hours won't change and so I will change to headphones.
I therefore went to different retailers and found the Sennheiser HD800 to be what I was looking for.

Now I want to build a system around those headphones. It will consist of a Linux machine running brute-fir for high-quality correction, libsamplerate for best resampling and send the RAW PCM data to a CPLD that generates the I2S signal for the DAC.

Sounds easy enough, but reading through this forum, I'm in need of good advice, since the information is just too manyfold for someone that isn't that deep into DAC design.
I don't want to design everything totally from scratch - that might come later, but I would be very happy if you could point me into the right direction for the parts that I should be looking for.

Basically I was thinking of using a FTDI chip with USB2 and 8kb buffers (with asynchronous read) feeding a CLPD that generates the I2S-signals (one normal and one inverted source) driven by a low-jitter reference-clock.

And now the questions start...

1.) What lowjitter clock would you advice on? I read good things about Tent clocks - other advice?
2.) Which DAC? I have ordered a Buffalo II to test with it, but you probably have other devices on your lists, too.
3.) Which I/V stage? I have ordered a IVY III, but I read that it could be improved quite a lot. What would you advice? I read some good comments on the Erno Borbely all jfet I/V.
4.) Would you advice on a headphone amplifier? Or is the I/V stage good enough to drive the HD800?
5.) If I should opt for a headphone amplifier which one would you suggest?
I read very positive feedback on the fully balanced Beta22 from AMB.
6.) Another option I got presented with is to use two ES9022 chips with integrated I/V (one normal and one inverted for fully balanced). Could anyone comment on those?
7.) What about digital volume control: with 32bit DACs that should never impose a problem - how are your opinions on digital volume control with 24bit DACs?

A lot of questions for sure, but hopefully someone with more experience than I have, could give me some hints...

Many thanks in advance
Thorsten
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Old 12th June 2010, 04:45 PM   #2
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Thorsten

I understand the temptation to throw a lot of technology at your sound system, particularly if you have a fair bit of electronics expertise, as you evidently do.

What you are proposing is overkill if you simply want an excellent headphone system. It may give you a lot to talk about on diyaudio, and even create a lot of excitement, but you could well end up with a system with a lot of problems, and no clear idea as to where to look to solve them. Sometimes you can have just too many controls available to you.

Why not look at Seigfreid Linkwitz' site and the headphones and headphone amplifier he uses? I am not suggesting you should adopt his system lock, stock and barrel, the site is a little out-of-date now anyway, but it may give you some ideas about how to implement a simple system which nevertheless provides reference-quality reproduction.

Hi-fi audio design is, in many ways, a dead subject, despite the passion it excites here. You could turn your attention to some of the more demanding issues which exist in spread-spectrum radio, lo-cost instrumentation, control or micropower design, and just listen to the music. Better still, learn to play an instrument (quietly, at night), or if you can play, make some original recordings.

w

Last edited by wakibaki; 12th June 2010 at 04:47 PM.
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Old 12th June 2010, 06:01 PM   #3
THKL is offline THKL  Germany
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Hi wakibaki,

first of all: thanks for your reply.
I think I do understand what you want to tell me and at its core I do agree with you. However I'm a bit of a perfectionist - I work to improve on the situation and I'm definately not that hardcore anymore.
But since I moved and the whole situation with building a headphone-system arised, I have to do something about it. And because building something is a hobby of mine, I want to start working on a headphone-system.

I have some money to burn on the project and want to get the best out of it. I don't have much experience in designing analogue circuits (although I studied computer engineering and sometimes design microcontroller-boards, I'm mainly a software guy and I never liked the analogue electronics part during university).
That is the reason why I want to use tried and proven "building blocks" - similarly to what you suggest.

Now I went out and found a headphone that I thought was impressive and bought it: the Sennheiser HD800.

Obviously every system has non-linearities that can - to the most extent - be overcome by equalisation: exactly as Mr. Linkwitz describes.
Writing software is what I do for my living and since high-quality audio libraries are available as open-source it is not that difficult for me to link those together and throw a functional graphical user interface to build and select playlists into the mix.
Now I have a digital source that accounts for errors in the rest of my setup, but that digital info still needs to be converted to analogue signals and amplified to drive my headphones.

Since I want to get some info from the community on what components to use for that endeavour and in the process probably roughly copy the hard work others have done in the analogue area by using their schematics, I feel the need to give something back to the community.
What I could do is designing a board with a CPLD that outputs bit-perfect I2S signals from audio files readable with common audio-io-libraries under linux (or maybe with a ALSA driver if the project gains enough interest).

Now I still need advice which DAC, which I/V (if not integrated into DAC) and which amplifier (if the I/V is not capable of suitably driving my HD800) I could use.
Additionally power-supply and low-jitter clock need to be discussed, since they mainly contribute to the performance of the whole system.

Best regards
Thorsten

Last edited by THKL; 12th June 2010 at 06:03 PM.
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Old 12th June 2010, 07:29 PM   #4
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OK, I have made my pitch...

I have an interest in an open source, well documented, high quality reference source. I have thought about building one on a number of occasions. I am only interested in a stand-alone device which would accept SD or similar flash cards. It would have a battery power supply as this would provide low noise. The data would be only 44k1 16-bit PCM and it would employ a NOS DAC. A very simple operating system written in VHDL would provide access to tracks, and would not operate during playback. Tracks would be recorded from a PC. This would still have required considerable work for one person to accomplish.

No-one really seemed interested in such a device at the time I proposed it, they all wanted something more complicated, they wanted multiple sample rates or 24 bits, or perhaps they just wanted to be able to continue to argue about jitter. I also found it difficult to get unequivocal recommendations about a DAC. I think there is such a project now, or perhaps more than one, but I grew disillusioned about 'the community', and ceased to pay attention to the issue, as anyway I think the concerns about jitter are exaggerated.

Be that as it may, I still have a standing search on ebay for TCXOs. You might be interested in this one @ 11.2896 MHz, good for 44k1...

Valab 1PPM 11.2896 MHz Low Jitter TCXO on eBay (end time 08-Jul-10 21:48:53 BST)

Good luck.

w
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Old 13th June 2010, 12:57 AM   #5
qusp is offline qusp  Australia
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you need to go over to head-fi.org to the DIY section over there. the beta22 is a very fine amplifier, definitely one of the best I have heard. I am in the middle of a similar project to yourself, but using the ackodac ESS9012 sabre dac, with D1 (or borbely) IV stage and 2 x peranders' QRV08 for headamps. i'm totally nuts about headphones, but I actually think you can possibly do better than either of us are going to end up with.

I dont know if you have caught the custom musicians monitor wave that has been happening this last year in portable audio (wait, read on I promise) jerry harvey makes JH16 and JH13 in ear monitors for musicians and us over at head-fi use them with our portable rigs, many like mine including a portable SD transport, feeding spdif to dac, then separate amplifier (well, i'll be honest, not many like mine )

I have been putting together a portable version of this using the buffalo II and a balanced OPA1632 opamp IV stage/headamp that is nearly finished

but last week at this years CANJAM in New York, Jerry Harvey Audio demoed a pretty insane and game changing new technology, these IEMs JH13 and JH16 are 6 or 8 drivers a side respectively, with a passive crossover in a custom molded shell, but he has just released the JH3a, which removes the crossover from the IEM and uses a 4 wire cable per side to connect a multichannel, phase aligned signal to them, yes, a fully digital XO with DSP, each one tuned for the persons specific ear canal shape response!!

so the room and resulting phase issues are totally removed from the system. the amp is transportable, has ADC and DAC with 6 channel amp, meaning there is a 3 way digital crossover for each ear.

this thing, apparently from reports at Canjam, utterly blows everything else away, including home headphone systems comprised of 10K+ worth of dac plus headphone amp (like the beta22 and even higher end electrostatic headphones)

now, is it as satisfying a diy project?? perhaps not, except for your digital source could still be used, but from reports from people I know and trust, ts definitely something to look into. the soundstage is apparently MASSIVE, larger than high end open backed headphones. and hell, by the sounds of it, you could get them (package deal with the dac/amp) and then buy the eval board for the cirrus chip they are using and develop your own DSP algorithm and MCU to drive it.

what you are doing already will sound well, sorry I dont know much about aftermarket clocks, i'm just using a 100mhz PCB mounted one in my dac.

I wouldnt use the 9022, its IMO not in the same league and also you are right, the volume control on 24 bits falls over

so there you gom that should be something to mull over, maybe post some questions over at head-fi too

good luck!! i'll be watching how your priject goes and once I have someghing to look at in a finished state for my 2 current projects i'll post some pics
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Old 13th June 2010, 01:02 AM   #6
qusp is offline qusp  Australia
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BTW I already own the JH13 and I actually prefer them to HD800, as do many, when pushed jery mentioned he thought the JH3a system was 50% better. that makes it better than any headphone I have heard at any price. i'll wait to make my own call on that, but its definitely something worth mentioning when someone posts a question like yours.

and yes the IVY will drive headphones reasonably well, but you can do better

Last edited by qusp; 13th June 2010 at 01:13 AM.
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Old 13th June 2010, 04:06 AM   #7
qusp is offline qusp  Australia
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Can Jam was in Chicago this year, for some reason I had new york on the brain
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Old 13th June 2010, 08:33 AM   #8
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Quote:
Originally Posted by THKL View Post
4.) Would you advice on a headphone amplifier?
I was considering this for the HD600.
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Old 13th June 2010, 11:55 AM   #9
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Quote:
Originally Posted by qusp View Post
10K+
I think this illustrates all too well that that whatever it is we are looking at it is is not 'community'. In all probability the advantages supposedly conferred by such systems are totally illusory.

Take a look at the other 2 designs from the Linkwitz headphone page by John Conover:

John Conover: Direct Coupled Stereo Headphone Amplifier

John Conover: Spatial Distortion Reduction Headphone Amplifier

The headphone amp I think is much better documented than the Gilmore design, which in any case is predicated on the philosophy of 'no high open loop gain' (no opamps), which I think is more an article of faith than a demonstrable fact. The Gilmore design might have some advantages when driving low-impedance Grados, but the Sennheisers have a much higher impedance.

w
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Old 13th June 2010, 01:30 PM   #10
SY is offline SY  United States
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The whole time I was reading this, I kept thinking, "Why is he doing this with opamps? Why doesn't he do it with software?" And of course, that's exactly where he ends up. Very nice project, thanks for the links!
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