Mini-T amplifier and Linear PSU?

[Tim]

I have an Amptastic Mini-T amp which I am very pleased with and use it in my study area with an HRT DAC and pair of Celestion speakers. However, the SMPS it was supplied with is dire, it feels so light and cheap I can't help feeling its more than just a weak link, I reckon it could be drastically hampering the amp performance. So I'm considering trying this bench linear PSU from Voltcraft.

http://i173.photobucket.com/albums/w63/greatgig/voltcraft_zps8d3b3767.jpg

VOLTCRAFT FSP-1122 25W Fixed Voltage Linear Power Supply - 12Vdc, 2A (http://www.conrad-uk.com/ce/en/product/511410/VOLTCRAFT-FSP-1122-25WW-Fixed-Voltage-Linear-Power-Supply-Bench-12VdcVdc-2AA/2110320&ref=list)

This is under 20 quid and I know some others use bench linear power supplies from reading the Computeraudiophile forum and are reporting very good results. Item Audio also sell Voltcraft bench supplies and they seem very pleased with them as well. Its not pretty I know, but that's not an issue as I can hide it away or maybe even re-case it?

So the question is, has anyone here tried this already?

[John]

Not with that but agree a good power supply helps take it to another level

[Tarzan]

I have an Amptastic Mini-T amp which I am very pleased with and use it in my study area with an HRT DAC and pair of Celestion speakers. However, the SMPS it was supplied with is dire, it feels so light and cheap I can't help feeling its more than just a weak link, I reckon it could be drastically hampering the amp performance. So I'm considering trying this bench linear PSU from Voltcraft.

http://i173.photobucket.com/albums/w63/greatgig/voltcraft_zps8d3b3767.jpg

VOLTCRAFT FSP-1122 25W Fixed Voltage Linear Power Supply - 12Vdc, 2A (http://www.conrad-uk.com/ce/en/product/511410/VOLTCRAFT-FSP-1122-25WW-Fixed-Voltage-Linear-Power-Supply-Bench-12VdcVdc-2AA/2110320&ref=list)

This is under 20 quid and I know some others use bench linear power supplies from reading the Computeraudiophile forum and are reporting very good results. Item Audio also sell Voltcraft bench supplies and they seem very pleased with them as well. Its not pretty I know, but that's not an issue as I can hide it away or maybe even re-case it?

So the question is, has anyone here tried this already?


This is my experience too, that big PSU how would you connect it to the Mini-T?

Are there any images of this?

[John]

Using spades would work and easy to buy a connector for the Mini T

[DSJR]

It's "only" 2A rated though... isn't the supplied one rated at 4A?

Before one of the "ME TOO" chaps starts marketing a £200 "upgraded" power supply for the Mini-T, maybe someone could make their own high quality high current DC supply and make it public for others to do if they wanted?

[John]

I think they go up to 5amps if I remember right

[Tim]

The supplied SMPS is rated 12v 5A, but the draw is minsicule from my unit. You can get these linear supplies at various ratings if you want to beef it up. The front terminals take bare wire or 4mm banana plugs. Making a power lead is simple, you can use shotgun coaxial satellite cable which has the benefit of screening and either strip the ends or solder on some banana plugs to connect the PSU. I'm pretty sure the Mini-T takes a 5.5mm x 2.1mm plug (http://www.ebay.co.uk/itm/5-x-DC-Power-Plug-2-1mm-x-5-5mm-Jack-Connector-Laptop-Long-14mm-/181053128798?pt=UK_Computing_CablesConnectors_RL&hash=item2a279b805e), but I would need to check this, but they are not expensive.

[John]

http://www.ebay.co.uk/itm/8x-5-5mm-X-2-1mm-DC-Power-Male-Jack-Connector-Cable-Adapter-Plug-CCTV-DVR-Camera-/120872876766?pt=UK_CCTV&hash=item1c2495bade I used these in the past pretty sure you can buy these separate

[Krisbee]

Tim,

SMPS are not all bad, Temple Audio supply what they claim to be a "Exceptionally Low Noise" external 12v 1.2A power supply for their Bantam Amp witha 2.1mm standard DC socket.

http://www.templeaudio.net/accessories.html

[Ali Tait]

Their supplies are ok yes, but the Golds sound much better on the end of a decent linear supply.

[Krisbee]

Their supplies are ok yes, but the Golds sound much better on the end of a decent linear supply.

Fair enough, then it boils down to how you measure "decent" and the depth of your pockets.

[MartinT]

I was using a 2A linear PSU and my Mini-T sounded fine but broke up into distortion at quite early levels. I now use a good quality 5A SMPS and the amp can go much louder without hitting distortion. Since I use mine for computer sound, near field, I don't have any problems with volume but the sound quality is very good (running from a Caiman DAC fed optically from my desktop PC motherboard). It really does depend on the quality of the SMPS.

[Covenant]

I was using a 2A linear PSU and my Mini-T sounded fine but broke up into distortion at quite early levels. I now use a good quality 5A SMPS and the amp can go much louder without hitting distortion. Since I use mine for computer sound, near field, I don't have any problems with volume but the sound quality is very good (running from a Caiman DAC fed optically from my desktop PC motherboard). It really does depend on the quality of the SMPS.

What make is the 5 amp one Martin?
I have a 3 amp one feeding my Tamp by the computer. Sounds good but don't think an expensive linear PS is justified.

[synsei]

This (http://www.ebay.co.uk/itm/5-7-AMP-POWER-SUPPLY-LIMITED-QUANTITY-STOCK-CLEARANCE-/300561743930?pt=UK_Mobile_Phones_Communication_Rad io_Parts_Accessories&hash=item45fae0403a) may be a better bet for not that much extra, limited stocks though. It does appear to be solidly made...

http://i.ebayimg.com/t/5-7-AMP-POWER-SUPPLY-LIMITED-QUANTITY-STOCK-CLEARANCE-/00/$(KGrHqYOKiQE3f!ZON,OBN4!BR1N4g~~_35.JPG

[MartinT]

What make is the 5 amp one Martin?

It's an AP1203UV, 12V 5A, made in China.

[Ali Tait]

Fair enough, then it boils down to how you measure "decent" and the depth of your pockets.

I was using a good high grade SMPS which was a big improvement over the stock supply.Cost? nowt, liberated it from work.

Nick then offered me a simple supply he had made for someone else, just a toroid, bridge rectifier and big smoothing cap. Nowt fancy but it easily beats the SMPS. Not too pricey to do but well worth doing IMHO.

[lurcher]

Yep, you don't need to worry too much about regulation, just a low impedance passive supply with low ESR caps to allow a good peak current capacity.

[monkfish]

Hi
I replaced my Muse M20 power supply (Toshiba 12v 5a) with a 14v 5a Muse supply which I got from Ebay for 8 squids delivered.
More headroom, lower noise floor,bass more defined, happy bunny.

PS I know there are quality control issues with some stuff from China but the power supply has now been on for about two weeks with no probs, no heat, just a bargain I would say.

[Krisbee]

While opinions bounce back and forth, I have to ask just what is the most undesirable aspect of SMPS in this application? The high frequency switching spikes, the AC ripple, poor regulation, or other nasties?

I can't speak for others, but my understanding of Linear PSUs is rather basic. At it's simplest a step down transformer, a full wave rectifier to go from AC sinewave to a DC level with superimposed AC ripple and smoothing capacitor(s) to approach the ideal linear DC output. Then there's the behaviour of supply under load which introduces the whole subject of regulation.

Nick says regulation is not paramount in this case, and I can only guess that this might be because of the limited current draw on the supply, and/or the fact that the T-amp can tolerate small variations in DC voltage level.

Nick knows his business, selling some of his designs through Mains-R-US, but I can't imagine him sitting in a shed knocking out basic Linear PSUs for the benefit of all and sundry. Which leaves the no DIY-ers amongst us casting around for suitable commercial products, looking for recommendations and the facts by which to judge what's on offer. For example, when is regulation and when it is not, important. How good should the voltage tolerances be? Is, say, -/+ 5% under load good enough? What level of ripple is acceptable? Etc.

The last time I looked, anything remotely aimed at, or supposedly of, audiograde was typically twice of the price of the amptastic mini T-amp. Hence people have turned to bench supplies.

[lurcher]

While opinions bounce back and forth, I have to ask just what is the most undesirable aspect of SMPS in this application? The high frequency switching spikes, the AC ripple, poor regulation, or other nasties?

When I did some measurements and listening to them, the biggest problem was the HF noise from your typical SM supply appears on the speaker terminals, there seems to be very little PS rejection. And if you are real unlucky you will get interaction between the switching freq of the power supply and the amp.


I can't speak for others, but my understanding of Linear PSUs is rather basic. At it's simplest a step down transformer, a full wave rectifier to go from AC sinewave to a DC level with superimposed AC ripple and smoothing capacitor(s) to approach the ideal linear DC output. Then there's the behaviour of supply under load which introduces the whole subject of regulation.


Yep thats about it, I would add a CRC with as larger value and low ESR caps you can afford. Have a look at some of the simple power supplies Nelson Pass uses with his First Watt amplifier. Regulation is nice, low noise is also nice, but current capacity is what you want. Even though the idle consumption of these amps are low, start playing music and the demands on the supply changes altogether. They are very efficient, but not magic, if you want 20W out you need to put in at least 20W.


but I can't imagine him sitting in a shed knocking out basic Linear PSUs

No, not worth doing, I have little enough time as it is, but simple to do it yourself, or find someone near who would do it for beer money.

[synsei]

Nick, will the Eagle PS I linked to do the job? If so it's beer money so I may grab one ;)

[lurcher]

Nick, will the Eagle PS I linked to do the job? If so it's beer money so I may grab one ;)

It should do, can't say for certain just how quiet it is, but I think it would make an improvement.

[Sovereign]

Nick would you be able to tell us what we need for a linear power supply and how to do it? or is it too much of a faf?

[DiveDeepDog]

I recently hard a Muse T-amp, what a shock into a high sensitive open baffle array.

What really opened the sound though was a fully black gated uber power supply was swapped for the standard one.

Afraid I don't have details, but enough to say its worth optimising the power supply:)

[lurcher]

Nick would you be able to tell us what we need for a linear power supply and how to do it? or is it too much of a faf?

I will try and sort something out, give me a few days, still spending all free time writing dac software and building m-dac supplies :-)