Experiments of the DAC kind

[NRG]

I've implemented the pretracking supply for the -5 and +5v TDA feeds. Only thing left to-do is a couple of pretracking regs for the CS supply and I'm done....I think! Can't see what else I can do with the current layout / board, so time to case up and enjoy!

[freddiecas]

e really informative thread Neal The pre-tracker must have a much better performance than 2 regulators in series and the 317/337 is so cheap there seems to be no reason not to use it whenever possible.

I count 4 elecs, so one of them is decoupling R1 or R2? which one and which way round please?

[NRG]

Hi Fred, yes, I have a 47uf bypassing the set resistor R2 and also the LED's/Zener...and 100uF on the o/p of each regulator.

Ah! you noticed I rotated the R2 bypass cap on each of the first regs. There's a small offset voltage across these (the 1.25 reference voltage) and as the 'ground' is now derived from the o/p of the second reg the orientation needs to be correct. The Adj pin is therefore 1.25 above the 'ground' so for the negative regulator the negative leg of the bypass cap goes to the Adj pin and for the positive reg the positive leg of the cap goes to the Adj pin...

Hope that makes sense...

--Neal

[NRG]

I have a bit of temperature problem with the leading 5v regulators...more heatsinking required!

[leo]

Thats coming on really nice Neal!

[freddiecas]

Hi Neal,
so you have an elec on the pre Vref resistor R1 ("other way round"), one on output, one across Vref zener or leds, and the last is C2 decoupling between the 2 regulators? if I've got that right
and nothing on the input if short and straight from the large decoupling caps.

The ground sense from zener//cap is particularly good advice, I shall connect seperate wires to my "star" ground at the parallel circuits output.

I found your link to acoustica - very good reading, look forward to the 4th part - thanks for your patience.

[freddiecas]

I have a bit of temperature problem with the leading 5v regulators...more heatsinking required!

do they have more volts across them in this application than the second regs which don't require sinks? I see they had one bigish heatsink on the original board.
cheers, Fred

[NRG]

Hi Fred, hope the attached diagram makes it a bit clearer, this is for a positive regulator. R4 in my diagram can be replaced with the diodes or Zener. I have a small 0.1uF Wima right in front of each pre reg to bypass the supply as theres a few inches of wire between them and the supply.

The + / - 5v regs are having to drop 20v or so with the Alpha board, previously they where fed from the 15v regs so had an easier time! The second reg only drops 2.5v so does not need one.

--Neal

[NRG]

I've also added larger heatsinks and had a good listen tonight, the presentation is very easy to listen to, there seems to be no nastiness or edginess to the sound and yet there's loads of detail and depth... very good for long term listening...I'm liking it a lot!

[freddiecas]

Hi Neal,
that's brilliant, thank you very much for your trouble. I had got the output decoupler wrong as it needs to be on the sense gnd with R4/zener/leds etc.

Hmmm, 20V across that reg, a lot more power than the other one!

This has got to be one of the most cost effective "super" regs around. I'm really glad all your efforts have paid off in the listening

cheers,
Fred