yrh0413 Have you tried the OPA 2134 instead of the OPA2107 ? It is quieter,wider bandwidth, and extremely low distortion.I have also tried the LM4562 in a preamp, but found it fatigueing,despite all the extra detail. For this reason, I fitted a SOIC OPA2134 in my X-FI soundcard with excellent results. IMHO,in a dulller sounding piece of gear the LM4562 could be worthwhile, but it isn't a good universal choice. SandyK
IIRC OPA2107 (one of my favourite BB chips) sounded pretty chocolaty and congealed in the Heed, the AD-823 offered up a bit more sparkle and zing though not enough to make it sound bright.... more organic and raw sounding with the AD-823 on board.
You could try the opa2134 it's one of the best drop in replacements for the 5532 you can get and is one opamp that never really offends. Opa2132 is another good one from the same stable.
I really love the Opa 2107 and have always classed it as sounding "as good as damn it close to two OPA627's on a Bdog" but in the Heed it really didn't perform at its best simply "dropped" in with no additional circuit tweaking.
I think Nigel went through quite a few opamps in his Heed 0pa627 (B-Dog), Lm4562, DY2000 etc. etc. and has ended up where he started with the AD-823, hopefully he will chip in with his impressions.
Another one you may wish to try is the OPA-2111, one of my all time favourites from BB but nobody else seems to share my opinions.... a beautiful sounding chip if implemented correctly and I'm surprised it isn't used in a lot more amps. Spec sheet here: focus.ti.com/docs/prod/folders/print/opa2111.html
I'm back with the DY2000 at the moment. It doesn't sound bright to me anymore with my HD650's, (lid removed, with my current isolation fetish) I love the AD823 though in the Heed & could easily live with either. In fact, if some gremlins swopped op amps overnight, I probably wouldn't notice the difference.
I'm very interested in any potential power supply improvements & have mentioned it before. I know Mike was looking at the possibility of a better transformer amongst other things. In fact, I'd love an ultimate power supply for the Heed in a different enclosure.
Nigel, i'm going to mount some regulators and tantalums at the rear of the transformer (as you can see from my picture above, the rear of the tranny has quite a big space), and perform P2P soldering on the components. Going external is the best solution, but i can't stretch my budget that far though .
Now i'm still cracking my head figuring how should i mount the Nichicon KZs LOL!
Surprised to see the Heed uses a raw supply. Regulation should certainly make quite a big difference, if it sounds better or worse in this amp is hard to say. If your going to add regulation to the existing circuit I'd use a transformer with higher secondary voltages and then drop this down to the Heeds original voltage through the regs. I see your using higher capacitance in the supply, the standard transformer is only 6vA per winding so a higher current transformer would be better anyway with higher uf's
Wish I had one of these amps, theres quite a lot of things I'd like to try with it, say regulation for the op-amp and raw supply for the driver transistors, or even VBE's which would clean the supply
Looking good mate, what voltage out you set the regs? just a couple of volts drop? Its hard to see the track from the picture but are those two electrolytic caps at the front of the amp in the feedback loop? it looks like C1 and the cap behind the vol pot are input DC coupling caps? Only local decoupling capfor the op-amp I can see is that 100nf that seems to have track that goes across the +/-v of the op-amp
yrh0413 Try to allow for a minimum of 3V DC above the regulators rated voltage output.Using ceramics as a parallel bypass usually results in metallic sounding treble. Better to use ordinary polys, unless you are using premium type electros. Even then you can try it and see. SandyK
I have the DY2000 ceramic, as recommended & first pioneered by dc. The metal version is said to be much superior, however, it is not easy to fit. It doesn't look like a usual opamp & will require a degree of skill to fit inside the amp.