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Old 18th November 2009, 10:56 AM   #1
Bertel is offline Bertel  Germany
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Default 'Best' amp concept for headphones w/ impedance ~8ohm

Dear experts and enthusiasts :-)

I'm looking for interesting concepts and circuits for my following setup and seek your valued advice:

I use Ultimate Ears UE-10pro in-ear monitors (that's how UE prefer to call their cans) and really love them for their accuracy and transparency, they are still my top choice by far - of course my completely subjective take :-) The source for listening is my computer audio transport system which "ends" at the I/V stage of my Twisted Pear Buffalo32. I currently have connected the UE10pros directly to the BUF32S' I/V stage's output and this works remarkably well, but I've come to feel in many respects that an amp to drive the UE10pros properly is missing...

What's special now is the UE10pro's impedance: it's between 5 and 14 ohm depending on the frequency. Attached is a plot of impedance and phase of one can (the other side is practically identical).

I have not yet found an amplifier designed for "normal" headphones with usually much higher impedance that can drive my UE10pros satisfactorily, and I think there are not many commercial products out there that can serve them best. In fact I have made the best experiences so far with low-output power amps designed for "normal" speakers with similar impedance, of which some worked really well but always had to fight with noise and hiss etc. due to the UE10pro's by far higher efficiency factor (in comparison to the average speaker).

So for this reason I'm asking for your advice and experience: Have you come across interesting and promising (diy) concepts lately that either can deal with such low impedance, or (even better) were specifically designed for this?

Any feedback, comments and suggestions highly appreciated! :-)

Many thanks,
Robert
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Old 18th November 2009, 01:14 PM   #2
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Quote:
Originally Posted by Bertel View Post
Dear experts and enthusiasts :-)

I'm looking for interesting concepts and circuits for my following setup and seek your valued advice:

I use Ultimate Ears UE-10pro in-ear monitors (that's how UE prefer to call their cans) and really love them for their accuracy and transparency, they are still my top choice by far - of course my completely subjective take :-) The source for listening is my computer audio transport system which "ends" at the I/V stage of my Twisted Pear Buffalo32. I currently have connected the UE10pros directly to the BUF32S' I/V stage's output and this works remarkably well, but I've come to feel in many respects that an amp to drive the UE10pros properly is missing...

What's special now is the UE10pro's impedance: it's between 5 and 14 ohm depending on the frequency. Attached is a plot of impedance and phase of one can (the other side is practically identical).

I have not yet found an amplifier designed for "normal" headphones with usually much higher impedance that can drive my UE10pros satisfactorily, and I think there are not many commercial products out there that can serve them best. In fact I have made the best experiences so far with low-output power amps designed for "normal" speakers with similar impedance, of which some worked really well but always had to fight with noise and hiss etc. due to the UE10pro's by far higher efficiency factor (in comparison to the average speaker).

So for this reason I'm asking for your advice and experience: Have you come across interesting and promising (diy) concepts lately that either can deal with such low impedance, or (even better) were specifically designed for this?

Any feedback, comments and suggestions highly appreciated! :-)

Many thanks,
Robert

Dear Bertel,

you can find zillion of headphone amplifiers digging in the diyaudio site.

I want suggest you the following links not so well known.

John Conover: Direct Coupled Stereo Headphone Amplifier
A high performance full documented and very didactic project

http://focus.ti.com.cn/cn/lit/an/sboa031/sboa031.pdf
The "classic" double opamp approach

High speed amplifiers for audio
scroll to the middle of the page to: THS6012 CFB Opamp Headphone Amplifier
A high speed high current op amp from Texas

Bryston Limited - Music For A Generation
A schematic from a leader audio manufacturer
(download B100 SST schematic and unzip the B100_Headphone-buffer file)

and least but non last

sjostromaudio.com - Hifi Projects
This is the very well known Per-Anders site with a lot of headphone amplifiers
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Old 18th November 2009, 01:37 PM   #3
Bertel is offline Bertel  Germany
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Hi,

many thanks for the links provided!

Although not specifically for low impedance headphones (the TI document e.g. explicitely mentions "above 40ohm") I'll read through them to see if I can adapt parts that are helpful in my case.

What I DO find very interesting is the THS6012 part! I'll definitely look up here on the forum what I can find on it too, and the schematic in the link you provided looks like I should give it a go! :-)

BTW I have come across the TubelabSE-based headphone amp (Headphone Amp), I'll have to try that! :-)

Many thanks,
Robert
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Old 18th November 2009, 01:57 PM   #4
Atilla is offline Atilla  Norway
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I've used my PIMETA v1 with similar in-ear headphones. And even small 8ohm speakers, as a test. It handles that pretty well and sounds fantastic, with the opamps I used. I've used with 300ohm cans as well, with the same results.

The version 2 of the PIMETA uses buffers that are rated for even higher currents, which would easily drive complicated loads.


You can find it here : PIMETA v2 Headphone Amplifier. Fairly simple, small and highly recommended, at least by me .
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Old 18th November 2009, 02:20 PM   #5
Bertel is offline Bertel  Germany
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Hi Atilla,

many thanks for pointing me to this! I'll look it up at your website.

Thank you,
Robert
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Old 18th November 2009, 10:54 PM   #6
Atilla is offline Atilla  Norway
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Oh, sorry, that post really did sound like that's *my* amp.

The website and the amp design are Tangent's of course, I'm merely a builder, following his design.

And I really thought this was in the chip amp forum initially. There are great discrete designs as well, some of the really nice ones were already listed here. Taking a look at AMB Laboratories DIY Audio Site might also be interesting to you.
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Old 19th November 2009, 02:28 AM   #7
Bertel is offline Bertel  Germany
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Default γ2 dac !!!

Hi Atilla,

thank you so much for pointing me to the AMB Laboratories DIY Audio Site !!!

The headphone amps there are not really interesting for me - but their γ2 DAC is a revelation for me! I have been looking for a purist implementation of the Wolfson top-of-the-line DAC chips WM8741 and WM8742, and I can everything I plan (i2s input, configure as NOS DAC, use separate I/V stage etc.) with the γ2 - fantastic :-))

Best,
Robert
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Old 19th November 2009, 09:10 AM   #8
h_a is offline h_a  Europe
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Hi Robert,

with such low impedance headphones the best option seems to me to look for a buffer; you don't need voltage gain, just the current, so that seems the way to go.

You can have a look at Patrick's DAO and rework it for higher current and lower rails (the used power jfets are however hard to get).

Grey's simple mosfet follower is also an option. In fact, any ClassA-follower should do very well.

Anyway, I was curious what Bryston offers: I have never seen an amp that was so full of complementary LTPs. They even use the same topology for headphones and for tape out (compl LTP+ compl. emitter followers). Phono uses the same basic structure. At least to me that's not particularly impressive, but ok if it works well?

Have fun, Hannes
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Old 19th November 2009, 09:30 AM   #9
Bertel is offline Bertel  Germany
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Default Interesting!

Hi Hannes,

many thanks for pointing me to Patrick's and Grey's approaches and projects, they are indeed very interesting! I have found the respective thread (http://www.diyaudio.com/forums/pass-...amplifier.html) and will give it a good and thorough read! Sounds promising indeed...

Thank you,
Robert
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