Nelson Pass headphone amp for HD600s

[ak_47_boy]

Hello Pass Labs subforum. I am a newbie here looking for some direction.

I have just started a thick film design project for college. Rather then do the standard LED light flasher or FM transmitter i have opted to make something cool that i will get some use out of, a headphone amp.

What i am looking for is a tried and true zero feedback directly coupled schematic for an amp that will drive my HD600 headphones using an iPod or computer as a source. Does not have to be portable so i won't be using batteries. I need the basic schematic asap or else i would research this myself. Some variation of the Zen i am thinking?

Any input would be appreciated.

[DougL]

Cool Project. I have some thick film experience, and I am sure I am not the only one.
My professor advised us to build a published circuit, so we didn't have to struggle with design and build problems at the same time.

How about a B1 in thick film? Simple, well documented and useful.

Good luck.

Doug

[fitzfish]

ak_47_boy,

Yes, interesting project.

If you are using bare dies and wire bonding it also might help to know what small signal and power devices you have access to in die form.

How about a high power version of a dc coupled, B1 like follower, perhaps with N-MOSFETs and the necessary gate bias components. There are some variations on this theme - EUVl's DAO follower is one. It is optomised for 62 ohms. The HD600s would likely be easier to drive than the AK701s he's using because of the higher impedance. It would be cool if you could drive 15 to 300 ohms effectively though with one amp.

The new BA3 front end might also make for an interesting head phone driver biased up a bit. Too complex?

Either way, the headphones are expensive so some form of protection might also be in order...

One last thing - and this one is just my opinion - it would be very interesting to see a comparison of one built with high metal, low glass pastes laid out in lazy serpentine patterns or lines in a thin film like configuration vs bulk square resistors using higher glass content, higher ohms per square pastes. The point would be to to ensure low TCR, VCR, and to minimize resistor noise from the thick films. You can add a trim pad to one or both ends of the serpentines. The example picture below is done with penning, not screening, but it gives you an idea. Not sure if you can even print it but might be good for some extra points.

Happy firing,
Dave

[qusp]

cool project indeed!!

@ Dave: yes but the dao is a follower only with less than unity gain, you would need to have a pretty hot source for it to be useful with hd600 and hot iPod is NOT, or add a voltage gain stage.

i also thought headphone amp when i saw the BA3 front end, i think this would be a great choice, just watch the output impedance

[fitzfish]

Hi Jeremy,

Good point. With a 4 wire cable for the SENs he could build something along the Son of Zen line. Are they 4 wire stock? I don't own a pair.

Just suggestions stuimulate some ideas... perhaps others will chime in as well.

Dave

[merlin el mago]

I see this schematic in the headphones thread for Sennheiser HD600, there are also 2.2uf film caps on the output.

I need to know if schematic is Ok & LEDs value?

[qusp]

Originally Posted by fitzfish

Hi Jeremy,

Good point. With a 4 wire cable for the SENs he could build something along the Son of Zen line. Are they 4 wire stock? I don't own a pair.

Just suggestions stuimulate some ideas... perhaps others will chime in as well.

Dave

hey Dave, sorry mate, totally faded on this thread. yeah the stock cable is 4 wire by design, also has detachable cables, so any changes need not be permanent. the HD600 needs around 4vrms minimum, with up to 7vrms preferred for certain really dynamic passages/types of music. so really with an ipod as source he would need roughly 3-5x gain.

i was in no way shutting you down, i think you were headed the right direction, the DAO is a nice amp, coupled with a nice VAS would make it more universal and more appropriate for HD600 with sources lower than line level

pity the OP didnt come back, it would have been quite an interesting thing to see the result. what sort of dissipation can you have with thick/thin film concoctions though? how do you go about enlarged power handling?

[merlin el mago]

What's happened with this interesting thread?

[AndrewT]

Two of those post1 squiggly PCB traces connected in series and folded back to back would make a good low R, low inductance, medium power resistor.
Copper will have it's usual tempco, but for low temperature changes probably good enough.
Thoughts?