Phone Preamp PSU

[francoiacc]

Hello everybody,
I'm building a new phono preamp and I'm now working on the PSU, attached there is a first schema.
Based on your experience what do you think about it ? Moreover, since my brother has a lamp shop, I would use 2 lamp transformer (pri 220V sec 11,5V 4A) but I don't know how these can work. So... any suggestion or comment??

Thanks
Francesco

 

[Sheldon]

Hello everybody,
I'm building a new phono preamp and I'm now working on the PSU, attached there is a first schema.
Based on your experience what do you think about it ? Moreover, since my brother has a lamp shop, I would use 2 lamp transformer (pri 220V sec 11,5V 4A) but I don't know how these can work. So... any suggestion or comment??

I have no direct experience with back to back transformers, such as you have shown. But I've seen a number of schematics doing something similar. Conceptually, I don't see any problem with it other than some loss of efficiency. Actual noise performance will depend on construction of the transformers.

Sheldon

 

[Miniwatt]

I would add another choke and cap.

 

[DF96]

Use Duncan's PSU Designer (free download) to model it and see how much ripple you get. Or estimate using a calculator/spreadsheet.

 

[Joshua_G]

I'd suggest adding Salas HV Shunt regulator: http://www.diyaudio.com/forums/power-supplies/134801-simplistic-mosfet-hv-shunt-regs.html .

 

[Sheldon]

Use Duncan's PSU Designer (free download) to model it and see how much ripple you get. Or estimate using a calculator/spreadsheet.

I guess you'd model it as a 220/220 transformer to get an approximation. Not sure how you'd account for the filament draw or the copper losses in the 12V windings.

Sheldon

 

[Soonerorlater]

I would use uf4007's or similar fast diodes instead of in4007's to reduce noise

 

[azazello]

You can connect electr. cap 22 uF between diods and 100 ohm.

 

[DF96]

In series a cap here will block DC. In parallel a cap will negate the benefit of the resistor and increase peak currents. Which one do you mean?

 

[francoiacc]

Regarding the diodes I think I'm going to use the BY399, I've found them in a small shop close to me! They are fast recovery type therefore less noisy.
Joshua what is Salas HV Shunt regulator ??
Attached is the heater supply schema with 338K regulator, the zero is raised from the ground in order to reduce any hum due to ground loops.
I did some simulation with psu designer, and modeling the two transformer as a single 220/220 I've a good output without ripple. But this is only a simulation.. it doesn't sound!! My bigger concerning is about the transformers, any experience about using lamp transformer like this??

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thanks
Francesco

 

[azazello]

I meen cap to ground.

 

[DF96]

That will reduce ripple in the supply, but may increase induction into nearby circuits. On balance may make things worse, especially for a phono preamp.

 

[Joshua_G]

Joshua what is Salas HV Shunt regulator ??

The link I gave says it all. It may be worth your while to read that thread.

Attached is the heater supply schema with 338K regulator, the zero is raised from the ground in order to reduce any hum due to ground loops.

The heaters are raised about 100V above ground, it may be too much for some tubes, probably 70V is preferred.

 

[Brit01]

I'm currently building a SRPP headphone amp but with the same psu idea.

2 small transformers back to back (due to cost and space).

220/6 - 6/220.

Just make sure the second transformer that is in reverse has enough current as you will lose plenty.
I'll hang the heaters of the first tranny (AC) and then rectifiy/filter from the second to get around 300V.

I used a 2Amp for the second transformer which was an overkill, supplying around 100mA (but sounded great), so I'm trying a smaller one to supply around 16 mA.