Advice Needed: Preamp Power Supplies.

[Mus]

A few things (lots!), about preamp power supplies, have been unclear to me for a while. Hopefully someone can enlighten me.

Is it always best to have local regulation i.e. to have the regs inside the preamp? Is this the case even if the pre-regulator is much more sophisticated than the local regs?

Specifically, if I use an Avondale APX2, as a Hicap substitute, will putting regs inside the preamp as well, say 6 TPR modules, improve the regulation or make it worse? Is it wasteful using an APX2 as a pre regulator, would a pair of TPR modules work (nearly) as well?

Regards,

Mus

 

[LesW]

The strategy I've found the best is regulators at the power supply then simple local gyrators for the various components. I'm sure that Andrew's Superegs would be an upgrade on the gyrators but haven't tried them in this situation. TPRs would also work well as local regs - given enough voltage headroom.

You pays your money and takes your pick as the saying goes.

 

[Mus]

Hi Les,

Thanks for the insight, I guess I will have to experiment a bit. Is the little PCB you produced for the gyrator circuit available off the shelf now?

Regards,

Mus

 

[Mr Tibbs]

I'm with Les here.

I've tried all sorts of arrangements before settling on what I'm using now, which is basically to put the best regulation in the power supply.

A standard hicap feeding six local SR's in my 102 was found to be inferior to a modified hicap using two SR's, feeding six local LT1086 reg's in the preamp.

Now, the hicap has six SR's feeding the six 1086's in the 102 and it has never sounded better.

My advice would be to concentrate on building the best primary outboard supply you can, then increase the regulator count in that supply (or number of supplies) to cover each preamp stage fed. Increasing the number of transformers has the big advantage of allowing multiple 0V returns. In other words, don't common the 0V returns at the power supplies, but take them individually to the preamp star 0V point. After that, local regulation can be used to upgrade on the simple RC line filters at each stage.

HTH

Mr Tibbs

 

[LesW]

Is the little PCB you produced for the gyrator circuit available off the shelf now?

As I build some every day, they're stocked in quite some quantity Mus.

 

[Mus]

Originally posted by Mr Tibbs
Increasing the number of transformers has the big advantage of allowing multiple 0V returns. In other words, don't common the 0V returns at the power supplies, but take them individually to the preamp star 0V point.

Hi Mr Tibbs,

What is the advantage of doing this? I don't know for sure but I think the APX2 must common the 0V returns at the power supplies, as it is a drop in replacement for the Hicap (Les?).

I was planning on putting 4 APX modules a case with 2 transformers, each with dual secondaries, and feeding the preamp via a 5 pin DIN. Obviously, with one pin for each of the 24V rails the fifth pin would carry both the 0V returns. How would you recommend I made the connection, swap the 5 pin DINs for 8 pin DINs maybe? Is it worth the extra hassle?

Regards,

Mus

 

[Mr Tibbs]

Hi Mus,

Have a read at the pre-amp fun thread. Hopefully it will answer some questions for you, but feel free to ask away, I'll be glad to help if I can.


"What is the advantage of doing this?"

Dividing up the 0V returns has a dramatic effect on pre-amp performance. With a common return, the quality of the 0V point at the power supply is better than at the star point in the preamp- this is not the ideal situation. Multiple 0V returns all commoned at the preamp effectively shifts the the power supply star point to the preamp where it belongs.


"I was planning on putting 4 APX modules a case with 2 transformers, each with dual secondaries, and feeding the preamp via a 5 pin DIN. Obviously, with one pin for each of the 24V rails the fifth pin would carry both the 0V returns. How would you recommend I made the connection, swap the 5 pin DINs for 8 pin DINs maybe? Is it worth the extra hassle?"

In your case, a burndy type multi core lead would give excellent results. Alternatively, you could use two snaics and common the 0V runs per each transformer.

Anyway, have a read at the other thread and come back for more answers.

Mr Tibbs