Maybe someone could help identify this SL6310-based headphone amp...

[Cloth Ears]

Hi,

I was looking for a headphone amp the other day and picked this up on the 'Bay. In theory, it's also a pre-amp. But, I don't know what it is based on, or if it is based on any design that I've seen before. And it's sooo small and fiddly that I'd hate to start playing and stuff it up. It's actually got quite a nice, fairly neutral, sound, but I barely use any of the 2 volume pots (my Audio Technica's are quite easy to drive) and it rolls off starting at around 50Hz (so there's barely anything left at 25). I guess I'd like to use more volume control (I'm currently scared to put it in my pocket) and I'd like to see if I can roll it off a bit lower down.

I've attached a full internal shot, plus close-ups of the two boards.

Some of those numbers seem to be:
(on the smaller board)
476A M2405 (x2)
613
and what looks like RIAE?
(on the bigger board - for each channel)
SL6310 PSSA
6 N 100 35v
473 (x2)
243
295 (or 562 - depending on which way up you are)

I can go in with a magnifying glass to look at anything else. I'm keeping it, but I'd like to know more (and all I got was the unit, no provenance).

[discrete]

I have a tube full of those 6310 chips in dip-8 somewhere. It was a gift/surplus stock, maybe 20 years old.

Did try it once on breadboard.
Nothing special, but did not do the trouble to actually measure it.

It is a 500mW op-amp, discontinued a long time ago.

http://radiomods.free.fr/doc/audio/sl6310.pdf

[Cloth Ears]

Originally Posted by discrete

I have a tube full of those 6310 chips in dip-8 somewhere. It was a gift/surplus stock, maybe 20 years old.

Did try it once on breadboard.
Nothing special, but did not do the trouble to actually measure it.

It is a 500mW op-amp, discontinued a long time ago.

http://radiomods.free.fr/doc/audio/sl6310.pdf

Thanks, discrete.

I found the sheet, but I'm hopeless at doing anything practical in electronics (why am I here? I like reading and understanding, but that's as far as it goes). I'm interested as to why it would be rolling off at 50Hz (about 24dB/oct-ish).

[nevermind]

the capacitors are too low. the input one gives a corner frequency of 15 hz, and the feedback one 28 hz, at high rolloff. the feedback one would improve things the most if changed, it is the one next to the 473 resistors (the bigger smd capacitor). you could solder a say 4.7-10 uF electrolytic right on top of it, noting the polarity. that should improve the bass to 15hz.

[Cloth Ears]

Originally Posted by nevermind

the capacitors are too low. the input one gives a corner frequency of 15 hz, and the feedback one 28 hz, at high rolloff. the feedback one would improve things the most if changed, it is the one next to the 473 resistors (the bigger smd capacitor). you could solder a say 4.7-10 uF electrolytic right on top of it, noting the polarity. that should improve the bass to 15hz.

Thanks, nevermind! I think I might have a couple of Black Gates 4.7's hanging around. I'll go and have a look!