gar2520 headphone amp

Hi,

So I spent this morning putting together a headphone amp with 2520. It works but doesn't sound right to my ears. I believe that it lacks bottom end and highs are too bright. I'll post schematic and some pics in the evening, but I followed a standard API312 schematic without transformers and added 1M resistor from +IN to ground. Powered with +-15V

any ideas how to improve it? or it is just 2520 sound?

ps. I didn't use any caps except of 330uF
pps. here's schematic from classicapi site, just for now so that we all know what we are talking about:
http://classicapi.com/catalog/product_info.php?cPath=22_47_55_91_93&products_id=158 (bottom of the page)

Is that link right? It's a design for a mic preamp.

I haven't played with that design, but it may simply not have sufficient drive to push a pair of headphones at low frequencies.

Maybe PRR will show up and shed some light...

According to the original API datasheet, it specifically lists "earphone and small speaker drivers".  It also says it can put out 0.8 watts, that's enough to blow your headphones and your ears along with them!

I'd say use a different schematic.  Maybe take a look at some opamp headphone amplifier schematics (headwise, headfi sites) and use one of those.  Some set the gain to a fixed value and use a pot on the input to vary the level of the input signal. (maybe a cmoy for starters?)

btw, are those 2520s known good and working?

Did you use the 330 uf capacitor on the output between the doa and the headphones? If so, that forms a high pass filter with the headphones impedance. If the headphones are low impedance, that might be the low frequency rolloff. The filter cutoff frequency is 1/(2*pi*C*R).

What's the headphone impedance?

Samuel