1x Large Torroidal or Multiple ?

[NickKUK]

The system will be powering a DAC - (+ve & -ve) 5v dac analogue and (+ve) dac digital separate voltages as well as a (+/- ve) separate internal headphone amp board. Looking at a linear power setup a case that can take the sizes.

In my head I have that a larger transformer could supply the voltage, so could smaller separate torroidals. All of the PSUs aren't really going to have a flux issue in driving the current needed (they'd be spec'd accordingly to demand). So the main thought is noise.

Either;
* larger transformer, rectifier & filters supplying a common rail to smaller regulators.
* 2 or 3 smaller toroidals with tailored rectifiers, filters and regulators.

 

[Vovk Z]

Two or three can be easier to buy, but they take much space.

 

[Mark Tillotson]

What voltages and currents?

 

[NickKUK]

What voltages and currents?

Oversized current capacity:

+5V 3A analogue dac & output buffer
-5V 2A analogue dac

+5V 2A digital dac

28V 1.5A analogue headphone

 

[Mark Tillotson]

What does "oversized current capacity" mean? What are the actual currents?

 

[Vovk Z]

I don't know but can guess that actual values are ten or more times less.

 

[NickKUK]

2-2.5x the quoted current requirement.

The reason is to run the regulators 200-250mA each (LT3045) rather than at the maximum 500mA to reduce noise.

 

[Mark Tillotson]

To size the transformer(s) we need to know the actual currents. Generously rating the regulators is a separate issue. Over-large transformers put out more magnetic interference and being large will have larger range of magnetic influence.

 

[NickKUK]

The DAC will be Soekris' 1941. Specification states +5V max 0.6A, -5V max 0.1A but for this it would be:
VCC5D - Digital Power @ 5V. 350mA
VCC5A - Analogue +5V @ 85mA
VEE5A - Analogue -5V @ 85mA

Soren indicates that the output buffer is takes it's power from the Analogue +/- 5V lines and works fine (Q here is 85mA to drive all that lot seems asking for it).

Soren has indicated that a digital display may be 150mA extra, however I'd like to run a number of things in future including RPi (5V 2.5A), a TFT screen (5.5V 150mA), etc so that would be 3-4A total. Initially I would use a CPLD (50mA max) that would be switching relays (latching but say 100mA for a coil).

The headphone amp would be Ian's HP2 which is 28V 1A by itself (judging by the rear of the pre-built HP2.

I was thinking to run the analogue supplies using LT3045 (+ve) and LT3094 (-ve) at 5V 200mA. This would work for the DAC, but I would probably add a second pair in parallel for noise and ability to support the buffer board. The 28V 1A supply would be via an LM-series regulator as the LT30xx tops out at 20V.

 

[analog_sa]

With torroidals there is always the suspicion that noise from one winding can easily be coupled to another up to fairly high frequencies. What you propose is not a comparison i have actually performed but the multiple transformer route seems safer if ultimate sound quality is the goal.

 

[Mark Tillotson]

1.5A for headphone amp?


Anyway I'd say one >= 25VA transformer for +/-5V (centre-tapped and full bridge rectified),
perhaps rectified and smoothed to >= 8V and then use point-of-load 5V regulators for each component - certainly the heavy load of a future RPi shouldn't impact on the existing 5V rails or cause them to droop.


second 50VA transformer for 28V supply.