PSU for Mini-T Amp using Paul Hynes Regulator

[MartinT]

This straightforward project was to build a high current stiff regulation 14.5V DC power supply for my TA-2021 based Mini-T amp, using Paul Hynes' PR3iEHD regulator module. It could also be used to build a 12V DC power supply for TA-2020 based Mini-T amps (the regulator could probably be downgraded to the PR3i).

The idea was to replace the ubiquitous switched mode power supply with a linear PSU of much higher quality. It hasn't gone unnoticed that the PSU costs quite a lot more to build than the cost of the Mini-T itself. Such is the cost of getting the best from the class T circuit (more about that to come).

Parts List:

• Paul Hynes PR3iEHD regulator (a PR3i could be used for lower power TA2020 applications)
• Multicomp 15-0-15V 225VA toroidal transformer (oversized, per Paul Hynes' recommendation)
• Hammond die-cast aluminium case
• 10,000uF 25V electrolytic (Panasonic)
• Input power cable (re-deployed Connex silver cable)
• Output power cable (re-deployed Kimber PSB cable)
• DC power plug
• Strain relief grommets
• LED (blue, of course)
• Heatsink
• Heat transfer compound

[MartinT]

The power side completed, producing around 2 x 22V AC for direct input into the PR3iEHD.



Regulator bolted down with heat transfer compound (the heatsink will go on the 'underside' which will become the top-side). Wiring completed, including additional storage capacitor. LED is not yet inserted into its hole (drilled bottom-right). Adjusted and under soak test, showing a nice 14.49V without drift.

[MartinT]

I tried out the PSU last night in a temporary install (the heatsink is yet to arrive so I was careful to keep an eye on temperature). Swapping it in for the 14V switched mode PSU I was using was a bit of a revelation - bearing in mind that the PSU will need about 50 hours to fully bed in and the heatsink will reduce any possible thermal effects by maintaining temperature.

Using this setup with my Mini-T fed from a Caiman DAC, itself fed from my PC via optical cable, and powering my newly built Fostex-based speakers, I don't think I had fully comprehended just how good the TA-202x series circuits really are.

Firstly, there is a whole layer of subliminal grungy dirt missing from the music. This always gave me the impression of limited resolution and, most interestingly, a feeling that the amp was clipping when it was turned up. Possibly more like a class B amp's crossover distortion (although a class T doesn't have crossover distortion since the output stage is always either fully on or off). In any case, there was always a slight sense of unease which has now completely gone. Very fine detail emerges from a silent background, with deeper soundstage and very focussed instruments and voices.

Secondly, the bass now has proper clout. I had assumed that light bass was an attribute of class T operation but not so. We're talking about my small speakers here, but even so the frequency range seems better balanced and the music has a more structural feel to it.

Thirdly, the attainable volume has gone up considerably. No longer does it feel uncomfortable to wind the wick up (that feeling I had of reaching the clipping point) and I can get all the volume I will ever need while it remains clean and dynamic.

It's clear to me that the generic switched mode PSUs provided with the amps have poor regulation and response to current demand. The music ends up modulating the DC rail which is not a good thing, certainly not for the TA-202x circuit.

So, on first listening I am very impressed and will report back when the build is complete and the heatsink mounted.

[John]

Good result Martin
I think its pretty amazing what can be got from Class D amps, matched with the right speakers the results can be pretty stunning

[sq225917]

Nice...

[DaveK]

FWIW I've always powered my two Mini-T's from basic toroidal transformers and voltage regulators via JLH Ripple Eaters and never been aware of any lack of bass.
Dave.

[Tarzan]

Exellent job Martin, PSU's for T-amps are SO IMPORTANT, the mains lead looks familiar is it Connex Audio by any chance, keep the progress coming!

[UV101]

Nice one Martin.....I'm forever spouting on about the power supply being everything always!

I've never tried regulating the PSU in an amp let alone doing it with a decent reg...glad its turned out very revealing. Very tidy work too

[MartinT]

the mains lead looks familiar is it Connex Audio by any chance

Well spotted, Andy - as in the list in post #1

[Tarzan]

Well spotted, Andy - as in the list in post #1