Audio transformer specs

[fatmarley]

Hi All, . Want to get a transformer wound (2x15v) to power an AD815 pre-amp. What specs should i ask for, for audio quality?

[AndrewT]

Hi,
15-0 & 15-0 Vac about 3VA to 6VA bridge rectifier &+-1mF smoothing with 7815 & 7915 regulators.
It will be enough to get you going and probably not sound too good.

For better performance, consider upto 50VA, two bridge rectifiers, upto +-3.3mF, 2r2, +-3.3mF, 317 + 317 regulators with 100uF on the adjust pin.

If you want bells and whistles then ask for an electrostatic screen and gauss band. But I don't know if it will sound any better.

decision, connect screen to audio ground or to safety earth?

[fatmarley]

I was going to use some ALW super regs and a pair of 10000uF BHC 4 pole T-net caps.

[fatmarley]

This is what ive found out so far: low impedance secondaries, split bobbins, interwinding shielding, low interwinding capacitance.

[AndrewT]

Hi,

split bobbins, interwinding shielding, low interwinding capacitance

have you been searching through desired parameters for output transformers?

You are looking for power supply transformers? or not?

The impedance of the secondary is inversely proportional to VA rating. The higher the VA rating the lower the impedance. If you add a regulator (ALW) then regulator impedance is many times lower than the transformer or the supply caps.

[fatmarley]

I got this info from www. Acoustica.org.uk

[AndrewT]

Hi,
that's some reading you referred us to.
I found one of your references

Bear also in mind that Julian Vereker once stated that for power transmission low impedance is critical and for signal transmission low capacitance.

and it shows you have mixed up power with signal.

Very definately, low impedance is crucial to quality in a PSU.
That site confirms that the regulator stands head and shoulders above all else when defining PSU source impedance. It even goes as far as saying smoothing capacitance may not be important to audio quality IF a regulator is fitted. I'm not sure I would go that far but your transformer is even further back down the chain.
That's why I said

ask for an electrostatic screen and gauss band. But I don't know if it will sound any better

As an aside,
two units I have (Quad tuner & Conrad Johnson pre-amp), run their regulators very hot. This cannot be for reliability, I guess it must have something to do with their opinion on how to make a regulator sound good when listening to it through the output stage.