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Old 9th June 2003, 03:40 PM   #1
Vladco is offline Vladco  United States
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Question Chip (gainclone?) type headphone amp

Iím thinking about building op amp headphones amp and really lost in the variety of option. I would like to build a reasonably simple amp if it will provide good quality sound.
What changes should I make to use gainclone as headphones amp?
Should I put limiter as
http://headwize2.powerpill.org/proje...imiter_prj.htm
Or do nothing to amp and use this advice:
http://db.audioasylum.com/cgi/m.pl?f...iy&r=&session=
Which op amp will sound better in this application LM3875? Or LM1875 is better because it lower power chip? After reading posts on this board Iíve got impression what they provide some kind of magic if used correctly. Or even ad825 will be sufficient to drive sennheisers cans and sound better? Or ad825 with buffer?
What kind of buffer is reasonably simple? Some thing like
http://headwize2.powerpill.org/proje...=eaton_prj.htm
Or just bite the bullet and go for
http://headwize2.powerpill.org/proje...lerano_prj.htm
if I want really good quality amp.
Any ideas will be appreciated.
Vlad.
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Old 18th June 2003, 09:59 PM   #2
moamps is offline moamps  Croatia
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Default Re: Chip (gainclone?) type headphone amp

GC chips are not generally intended or designed to drive headphones so I wouldn't recommend any of the options you mentioned. The insertion of a limiter would only corrupt the sound and bring no improvement whatsoever. Limiters are used in extreme situations in which it is necessary to protect ears from excessive sound pressure.
No experience with AD chips.
I'd suggest you built a decent A-class amp with FETs or tubes. Headwize site is great and you can find several such projects there. BTW, I've built a preamp-phone amp based on "The Morgan Jones Mini Tube Headphone Amplifier" project. I've been using AKG240 headphones and I'm very pleased with the sound.

Regards
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Old 18th June 2003, 10:31 PM   #3
paulb is offline paulb  Canada
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Your choice depends greatly on what impedance your headphones are, and the usual stuff like how much do you want to spend, how big a cabinet, etc.
600-ohm phones sound great driven by an opamp like the OPA2134 (i.e. the "Cmoy" amp). 32-ohm phones need an amp with more oomph.
General consensus on headwize, I believe, was that the chip amp (gainclone) amps were too noisy for headphones. Not sure if true or not. I have an LM1875 amp, with a resistor limiter, driving Senn HD580s and they sound fine.
moamps, I'm not sure how a resistor limiter "corrupts" the sound. Are you referring to the headphone impedance variations with frequency, and resulting frequency response changes from adding a resistor?
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Old 18th June 2003, 11:09 PM   #4
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Default Hey Paul

I did not know your headphone amp was an 1875 based one. Where are the plans from? What value inline resistor is at the output? I got the Senn 433 phones only to find that they have lousy reviews universally. Oh well .... they are what I could afford. My Gainclone pics are still in the film camera so nothing to post yet but it looks and sounds great...I think. Also another speaker project done with Minimus 7s up top(>500Hz High passed with 22uF) and reflex boxed Radio Shack 40-1197s running full range down below. I don't know how well balanced it is for the technical purist but it sounds good to me.
Greg
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Old 19th June 2003, 05:06 AM   #5
PGW is offline PGW  United States
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A very nice IC headphone amp appeared in May 2003 'Audio Express', by Klaus Noll.

It uses AD744/AD811 line stage (op-amp + buffer) with Jung/Didden regulators.

PCB layouts are provided, along with what I presume to be where to get hold of them.

I would tend to agree with moamps that the GC has too much power gain for headphones.



-- John
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Old 19th June 2003, 07:09 AM   #6
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Hey,

GainMONEY** and all the gainclones are all opamp based amplifiers, right?

That makes Chu Moy's amplifier at HeadWize ... a small gainclone.

Which makes me admit that I do use a small gainclone to drive my headphones. I use THS4022 though. This thing drives my K240M very well.

LM1875 will fry the poor headphones. Headphones can just berely handle 250mW. Or, your ears get busted. Either one would look very bad. ...

T

** I am quoting from Rod Elliot.

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Old 19th June 2003, 11:49 AM   #7
protos is offline protos  Greece
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Did connect my Senn 600 to my GC without any limiter.A little bit noisy but the sound was great - really gets the bass down.I would be quite happy listening to it permanently like this , maybe add a switch between speakers and 'phones. The OPA 627 output of my DAC sounds pretty good but I think this was more satisfying.
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Old 19th June 2003, 01:50 PM   #8
paulb is offline paulb  Canada
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Default Re: Hey Paul

Quote:
Originally posted by GringoAudio
I did not know your headphone amp was an 1875 based one. Where are the plans from? What value inline resistor is at the output?
Hey, Greg. I have a composite amp, uses a FET opamp driving the LM1875. It was in my living room for years, I repackaged it to place beside my PC. I use it to drive my ELF1.5s or headphones. For the latter, I just used 330-ohm resistors in series. My HD580s are 300-ohm phones. I'm in the middle of changing the power supply for it, I was getting too much hummmmm.
The design was from a Popular Electronics article, probably at least 10 years ago. I'll show you it next time we get together.
Quote:
Originally posted by Tomo
LM1875 will fry the poor headphones. Headphones can just berely handle 250mW. Or, your ears get busted. Either one would look very bad. ...
Depends, depends. I don't think I can drive even 250 mW into my phones with the impedance levels and the power supply voltage I'm using. But yes, I could damage my ears. That's why I have a volume control.
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Old 19th June 2003, 10:29 PM   #9
moamps is offline moamps  Croatia
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Quote:
Originally posted by paulb
moamps, I'm not sure how a resistor limiter "corrupts" the sound. Are you referring to the headphone impedance variations with frequency, and resulting frequency response changes from adding a resistor?
Hi,

I replied to Vlad's post about the insertion of voltage (input signal) limiter at his amp's input because he referred to an article on that subject. The insertion of a current limiting resistor at the output doesn't seem to be a particularly good idea either, IMHO (for the reasons you mentioned in your question, among other things). If the resistor is to be inserted, however, I don't think its value should exceed 1/10 of the nominal impedance of your headphones, based on my own experience.

Regards
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Old 19th June 2003, 10:58 PM   #10
paulb is offline paulb  Canada
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Quote:
Originally posted by moamps
The insertion of a current limiting resistor at the output doesn't seem to be a particularly good idea either, IMHO (for the reasons you mentioned in your question, among other things). If the resistor is to be inserted, however, I don't think its value should exceed 1/10 of the nominal impedance of your headphones, based on my own experience.
The sound, and what we prefer, is what it all comes down to in the end.
I believe one of the headphone amp projects I've seen actually has two outputs, one with and one without limiting resistors. I can't remember if the author uses the different outputs for different headphones or different types of music...
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