Pocket headphone amplifier advice ??

Hi all,

I am planning to have an iPod mod (for my old 60GB Photo iPod) from;
http://www.redwineaudio.com/iMod.html
This guy says very good things about this mod (I think its a bit expensive but hope it will worth!)

Anyway, after this modding my iPods headphone output will go to the hell. So I will need a really little headphone amp for my iPod. Of course it will work with some little batteries (may be one or two 9v ones)

I saw some projects in headfi forums with just one (or two in parallel) opamp like OPA134.

I have an Ultrasone DJ1 (64ohms and 103dB/1mW) and a Philips SHP805 (32ohms and 104dB/1mW)

So, do you think just one OPA134 will be enough to drive these headphones?

Thx..
 
Dxvideo said:
Hi all,

I am planning to have an iPod mod (for my old 60GB Photo iPod) from;
http://www.redwineaudio.com/iMod.html
This guy says very good things about this mod (I think its a bit expensive but hope it will worth!)

Why dont you "Imod" your ipod yourself.. its not that difficult and it will not cost you an arm and a leg.. :D .You can do it for $20 or less..

Check here on how to do it..
 
Re: Re: Pocket headphone amplifier advice ??

xaudiox said:


Why dont you "Imod" your ipod yourself.. its not that difficult and it will not cost you an arm and a leg.. :D .You can do it for $20 or less..

Check here on how to do it..

Woaw! :eek: Saving 250$ plus expenses.... But do you think I can do all these? I am not good at SMDs... :(


angchuck said:
Don't worry, i am not korean too. :bawling:

i know you want something a lil' more than a cmoy....

Sure... But Mini3 is a good alternative I gues..
 
Unfortunately I do things in my own unorganized noobish way.:eek:

I don't have a "complete" schematic for the amp as a whole. It is basically three different circuits all merged together.

The first would be just the standard data sheet circuit for the MAX629 DC-DC converter. The only thing I did differently is add a 100nf ceramic cap between REF(pin3) and FB(pin 4) that completely got rid of a faint switching noise I heard once the amp was completed.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1705

Next would be the "Sijosae discrete rail splitter".

[IMGDEAD]http://www.headphoneamp.co.kr/bbs/data/diy_sijosae/Rail_Splitter.gif[/IMGDEAD]

Lastly is the amp circuit which is basically just a "cmoy" but instead of using OPA(2)134 I used OPA551/2.

http://headwize.com/projects/showfile.php?file=cmoy2_prj.htm

It has incredible output power for it's size and I think it sounds very good considering the power supply caps are tantalums and the input caps are XR7 ceramics.:eek:

Of course I won't argue there are much better headphone amp and power supply circuits out there, but good luck fitting them in that tin.;)
 
here's a simple one
 

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If we will use a single battery, then isn't it better to use rail to rail opamps on left and right channel?
In fact my real question was; the standart audio opamps are (30-40mA per amp) enough to drive 32ohm headphones?
For example;
If I need 50mW into 32ohm, then the output swing must be 1,256mV RMS, that means 39,5 mA will be sinked by the headphone.... Thats limit for a lot of opamps.
Am I right?
 
Dxvideo, contrary to most folks experience, I found the OPA134 was not enough for the low impedance phones I tested on. I chose the OPA551/2 because of it's 200ma output current.

The amp was built for someone WITH hearing loss, so causing hearing loss was not an issue. Even with the special purpose of the amp in mind, I personally still found the output lacking with OPA134.
 
Dxvideo said:
If we will use a single battery, then isn't it better to use rail to rail opamps on left and right channel?
In fact my real question was; the standart audio opamps are (30-40mA per amp) enough to drive 32ohm headphones?
For example;
If I need 50mW into 32ohm, then the output swing must be 1,256mV RMS, that means 39,5 mA will be sinked by the headphone.... Thats limit for a lot of opamps.
Am I right?


You might want to try the TPA6102 -- this will do your required power into 16 ohms, it's a part which costs $1.00 and will run off a couple of batteries, delivering 50mW into 16R. It's SO-8 so not the tiny ball grid array which are devilish to solder. If you want you can mount it on a surf-board and set the whole thing up on radioshack perf-board.

I have been playing around with other Texas Instruments switching amplifiers -- the TPA2010 I spec'd had reported THD% of 0.2% I was able to get it to 0.02%.
 
theAnonymous1 said:
Dxvideo, contrary to most folks experience, I found the OPA134 was not enough for the low impedance phones I tested on. I chose the OPA551/2 because of it's 200ma output current.

The amp was built for someone WITH hearing loss, so causing hearing loss was not an issue. Even with the special purpose of the amp in mind, I personally still found the output lacking with OPA134.

I think OPA134 with a buffer may be with two BJTs will be a better solution... What do you think?

jackinnj said:



You might want to try the TPA6102 -- this will do your required power into 16 ohms, it's a part which costs $1.00 and will run off a couple of batteries, delivering 50mW into 16R. It's SO-8 so not the tiny ball grid array which are devilish to solder. If you want you can mount it on a surf-board and set the whole thing up on radioshack perf-board.

I have been playing around with other Texas Instruments switching amplifiers -- the TPA2010 I spec'd had reported THD% of 0.2% I was able to get it to 0.02%.

Do you mean TPA6102 or 6120 If its TPA6120 then I know that IC already. And I have some LT1210 in my drawer. It works like 1/2 of TPA6120 (current feedback amp) However this type of opamps sink a bit more current than the "normal" opamps. So if you take consider I will use just a 9v (and possibly it will be a 250-300mA/H one) its not a good idea.
And about the Class D amps. In fact I havent listened a Class D amp until now (but my shitty Philips mini CDP!) and I am not sure their quality.
As I mentioned in the first text; I 'll make some mods on my ipod just to have a better sound..... So the quality is the top imortant matter and the second is portability..
May be third is the security controls in the airports... Does anybody has any idea; how to explain this (possibly Hammod box) amplifier to security guys?