[Colin151]

Hi there,
Don't know if anyone here might be kind enough to help me with something?

I wanted to make a headphone adaptor for use with a power amp from its speakers sockets, - obviously the power/voltage is too large for headphones so you must tone it down with resistors.

I found this voltage divider type schematic for a headphone adaptor circuit from a power amp on the internet.

http://cgim.audiogon.com/i/vs/i/f/1082826750.jpg

I soldered up this arrangement and it works fine, - the only problem is that it does not sound all that great, - quite thin. I note that this is a Grado schematic and the resistor values are probably therefor optimized for 32 ohms headphones, - my headphones are 300 ohm Sennheiser HD250II's so this might be the problem, - if so has anyone any ideas how I would do about calculating resistor values that would be better suited to my 300 ohms cans?

Any help would be really appreciated,
Cheers,
Colin

[coliam]

Hi,

I posted this to you thread on Head-Fi as well.

http://sound.westhost.com/project100.htm

He does what you want for the 'standard' 120 Ohms, which should be fine.

You'll also be able to use Metal Film Power Resistors, too, which will help your SQ issuues.

Hope that helps.

[Colin151]

Cheers for that Coliam,
This looks a bit different from the Grado schematic as it uses 3 resistors instead of two.

I had been using wirewound resistors (big block white resistors) for the Grado schematic, - I assume they are inferior sound to metal film and carbon film resistors. So you think I will be OK using say 2W metal film resistors from Maplin. Carbon film sound better but are not really designed for this type of use (dealing with a speaker level signal) I assume?

Cheers again,
Colin

Originally Posted by coliam

Hi,

I posted this to you thread on Head-Fi as well.

http://sound.westhost.com/project100.htm

He does what you want for the 'standard' 120 Ohms, which should be fine.

You'll also be able to use Metal Film Power Resistors, too, which will help your SQ issuues.

Hope that helps.

[coliam]

Yes, I think Elliot uses 1W, so 2W metal film should be fine.

... much better than the big wirewound 'coffins' , I'd have thought.

[Colin151]

Hi Coliam,
Many thanks for the info, - a bit of research around and yes, - coffin wirewound resistor have poor bandwidth and therefore are no comparison to metal films for sound, - so that must be my problem if the sound is thin. Many thanks for the help I mistakently thought is was the values causing thinness where it was probably just the type of resistor!

despite the lower power ratings of the metal films it should be OK, - I do not listen at mega loud volumes

All the best,
Colin

Originally Posted by coliam

Yes, I think Elliot uses 1W, so 2W metal film should be fine.

... much better than the big wirewound 'coffins' , I'd have thought.

[Colin151]

Hi Coliam,
I tried out the Elliot headphone adaptor schematic the other day, - it is better than the grado schematic I did with the wirewounds but the sound is still quite thin. Do you have any ideas how I can modify the schematic, - maybe change a resistor value or two, to make the sound fuller? I note the output impedance is 120 Ohms on this circuit and though this is supposed to be good with most headphones maybe my 300 ohm Sennheisers need a different output impedance?

Any help would be much appreciated.
Cheers,
Colin

[coliam]

Hi, Colin

I'm glad it works for you. I doubt it'll be an impedance issue, though, now. It should be fine at 120 Ohms.

It might be possible to add some sort of filter to it, but I'm not sure enough, myself, to give you guidance with that.