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


http://farm9.staticflickr.com/8538/8635844872_20c2e13e5a_b.jpg

[MartinT]

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

http://farm9.staticflickr.com/8535/8634737347_8b4141ee03_b.jpg

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.

http://farm9.staticflickr.com/8545/8635845398_de92e6c344_b.jpg

[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 :eyebrows:

[Tarzan]

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

:doh:


:lol:

[MartinT]

One observation so far: I've been running the levels up to as high a volume as I'll ever go and the PSU case is just not getting hot. So for any potential builders out there, the die cast case itself is probably sufficient heatsinking. I shall mount my heatsink anyway, since the damn thing is on order and I may as well finish the project as intended. I'll take a photo of the completed PSU then.

Meanwhile, latest system shot (with Sadé's Cherry Pie playing...)

http://farm9.staticflickr.com/8533/8639065898_dd37f38a5e_b.jpg

[Covenant]

That's a lovely photo Martin. You must have a good camera.
If it's not rude to ask, what did the PS cost to build?

[MartinT]

I'll leave you to ask Paul Hynes about the PR3iEHD module as I don't want to trample on his pricing.

The transformer, case, heatsink and other bits amounted to about £60. Of course, I re-used spare cables but I'm sure many constructors will have some bits lying around.


That's a lovely photo Martin. You must have a good camera.

Thanks - it's a Lumix GF1.

http://www.phototravelreview.com/wp-content/uploads/2010/07/648490.jpg

[MartinT]

One further mod: I replaced the 10,000uF Panasonic electrolytic capacitor (or additional energy storage, as Paul refers to it) with a 22,000uF BC cap with high ripple current rating (low ESR). I also added a snap choke to the mains power cable as the PC and ancillaries are putting out a lot of noise and hash. I'm not sure I can hear a difference at the moment, but I'll leave it for a day or so to let the cap fully form.

I'm still waiting for the heatsink to arrive, but the PSU really doesn't need it at the volumes I'm using.

http://farm9.staticflickr.com/8538/8651849221_d955b4d97a_b.jpg

[realysm42]

Cool project dude!

[Mark Grant]

One further mod: I replaced the 10,000uF Panasonic electrolytic capacitor (or additional energy storage, as Paul refers to it) with a 22,000uF BC cap with high ripple current rating (low ESR). I also added a snap choke to the mains power cable as the PC and ancillaries are putting out a lot of noise and hash. I'm not sure I can hear a difference at the moment, but I'll leave it for a day or so to let the cap fully form.

I'm still waiting for the heatsink to arrive, but the PSU really doesn't need it at the volumes I'm using.

http://farm9.staticflickr.com/8538/8651849221_d955b4d97a_b.jpg

Looks good.

I cant see an earth wire grounding the metal case, worth fitting if you have not done that yet.

Also some brown, blue and earth heatshrink on the incoming mains cable near the terminal block to finish it off nicely as at the moment they all look to be clear Teflon tubing.

[MartinT]

There is an earth wire, Mark: the twisted green coming from mains earth going to one of the heatsink mounting bolts.

I take on board the mains sleeving, I only have black sleeving but I triple-checked the cores before connecting them up on the terminal block!

[UV101]

Good call with that smoothing cap Martin. I often use good quality 22,000uF smoothers. You cant have enough in reserve I say! :)