where to put superegs

[Mr Tibbs]

"can you just update us on anything alse you have changed from standard - coupling or decoupling caps, any of the gain cicuit mods that Les W shows on the Avondale website, etc."

The one thing I changed in the circuitry was adding a simple RC filter to the input biasing resistors. There are two of these circuits per channel, one at the input of the filter/buffer stage and one at the input of the output VA stage. From memory (I really should take notes ) the RC values were something like 10K/100u - These values are not critical though.

These filters help prevent power supply modulation (from other stages) reaching the input bias, where they would be amplified along with the input signal. Typically this results in reduced resolution, or 'smearing' of the signal.

I haven't touched the coupling /decoupling cap's. Hell, it looks like the 552 still uses those damn tant's, so that's good enough for me - for now (never say never)

"Are you using one transformer to power all the SRs in the HICAP, or many? Frame or toroidal? (I would think you are using the original transformer)."

I'm using the original hicap transformer/rectifiers/cap's. The 0V rails have been separated and kept separate up to the star 0V point in the 102- a really big lift in performance from this simple mod.

"The local 1086 are non-volagte ref ccts?"

Yeah, no Vref add on - just the standard LT data sheet implementation - I really like these 1086's!. (Naim RC filter removed from each stage power input)

Mr Tibbs

 

[ced]

Mr Tibbs,
I finally got round to doing your psu earthing mod, and it truly is superb!!!! So a big thank you for sharing that which I can recommend as a A++, 10/10 bang for buck must-do mod. And the best bit is its free apart from a couple of snips, dab of solder and foot of hookup wire.

Back to the thread's theme, I've also been mulling on why you and ron have hiss with onboard regs whereas I don't- Its a shame you can't get 3 - 5uf polyprops in place of the normal 47uf electrolytic decoupling cap (i'm assuming these don't work with normal monolithic regs as Mr Weekes stated though never tried it) as the gains are similarly huge IMO, though in different areas, to your earthing mod.

Anyway, 2 staring-me-in-the-face implementations I've got on my superregs are a 100uf electrolyic INPUT decoupling cap on the lm317 pregulator- a) because the walt jung 2000 article schematic had such and also b) because the lm317 datasheet says to use at least a 0.1uf tant for input decoupling if reservoir caps are more than 6 inches from the reg to ensure stability.

The other thing I've done to my regs is to put a ground plane covering the TRACK side of the superegs. I just used a square of pcb cut to the size of the reg and fixed in position using the stadoff holes of the superreg and plastic standoffs, then soldered the copper side to the superreg ground point with a small link wire. Again the walt jung article said reg noise was lower if the bottom side was shielded though he suggested just mounting the reg on the preamp case so the case metal acted as shield. However if the top plane is so important then maybe a bottom plane would be also.

And come to think of it the only time I ever had problems with the superegs was when I used them onboard on my cdplayer with neither of these 2 things. My cd psu still has these in the psu where they seem to be fine though afterwards I attributed the problem retrospectively to the pass transistor probably shorting to the case because of shoddy mounting. Maybe it was and maybe it wasn't.

So, don't know if either of these are relevant to the hiss problem or not and dont know if you ever tried them. You sound currently very contented but if not it might be worth investigating sometime.
cheers
Ced

 

[Fatmarley]

The other thing with raw DC supplies is to be very careful how you connect the diodes and output wires to the reservoir cap(s) - it' s easy to end up with extra noise induced because the impedance of even very short bits of wire really makes a difference at the peak charging current.

I just want to reinforce this comment because i had problems with the PSU i built for my Arcam, the sound became very confused with busy music, after a bit of head scratching i decided to beef up the 0v link between the main capacitors and now the problems gone.

I also beefed up the star earth in my pre-amp by drilling holes through the PCB, right up tight to the star earth, i fed solid core, tinned, copper wire (1.25mm) through the holes and soldered the wire to the star earth and to the track under the board.

 

[Mr Tibbs]

"I finally got round to doing your psu earthing mod..."

Cheers Ced

"So, don't know if either of these are relevant to the hiss problem or not and dont know if you ever tried them. "

To be honest, I tried all of those ideas and more - but no joy It's probably something to do with the circuit layout in the 102, making the stages slightly more prone to instability.

"You sound currently very contented "

You've nailed it there, Ced.

Mr Tibbs