Run pre-amp on "Laboratory" power supply

[CageyH]

Just browsing the internet, and there seems to be an abundance of variable laboratory style power supplies.
Would these be any good to run a Pre-amplifier from? The "branded" linear PSU is horrendously expensive.

I'll contact MCRU about a LDA version to see how much that would cost.

[Firebottle]

There shouldn't be any problem using such a power supply, just make sure it is adequately rated for the required current consumption of the preamp.

The branded PSU is likely to have a lower output impedance over a wider bandwidth, but whether the laboratory style PSU degrades any fine detail in the sound of the preamp can only be ascertained by trial and error.

For the price probably worth a punt.

:cool: Alan

[dgolh]

Using a laboratory Psu brings a clinical sound ;)

[CageyH]

:lol:

[struth]

What is a Laboratory psu? is it just a variac?

[enbee23]

The OP has already posted in, and therefore presumably read, the 7 page thread on wigwam covering the Pro-Ject RS preamp where power suppliy options are discussed, including the expensive Pro-Ject ones and inexpensive alternatives such as "lab style" examples. People even bought them, tried them and reported back.

"Just browsing the internet...", why so coy?

[CageyH]

"Just browsing the internet...", why so coy?

The same PSU will delivered to France (with a UK plug) will cost me €80. A proper linear PSU will cost me €200, unless I build one from the parts linked in the other thread.

If I buy the lab style PSU a for €80, I want to make sure that it's a good investment. I don't think it is much more than an SMPS with a linear regulator. If it is not good, and I want to send it back, the cost of the postage will be more than the PSU costs.

Ideally, I want a PSU with a French plug. I can't find one in France like it, but I can find others. The others have not been used with the preamp, hence being "coy." I have no idea if it will work or not.

[StanleyB]

If I buy the lab style PSU a for €80, I want to make sure that it's a good investment. I don't think it is much more than an SMPS with a linear regulator.
The specs of the Lab PSU will clearly state if it a SMPS or not. If the seller doesn't mention if it is a SMPS or not, then get the information from him/her. No need to think if you can confirm for sure. The only SMPS Lab Power supply that I know of are the ones from Rapid electronics and Maplin. Everyone else offers a linear power supply. Mind you, even if they did not quote if it is SMPS or not, the ripple voltage will give you a clue if it is MSPS or not. Anything around 1mV or less ripple, and you are looking at a linear PSU.

I use A LAB psu myself, and have been using one for years. I also have a selection of expensive single voltage power supplies. They are all excellent performers, with the Lab PSU producing slightly better noise and ripple readings on my scope.. The choice can come down to whether you like the idea of a display on your power supply, or you prefer an unassuming black box. I myself need the display when I am working on something electrical.

[Firebottle]

Here is a lab psu from a French supplier. A bit over the top in terms of power capacity, but it would run cool powering the Project pre:

http://www.conrad.fr/ce/fr/product/513812/Alimentation-de-laboratoire-rglable-0-30-VDC-0-5-A-150-W-Basetech-BT-305?ref=list

Cheers, Alan

PS I looked to see if I'd got anything linear lurking with 18V output, but no joy.

[CageyH]

Thanks Alan. If I could find one that stopped at 20V, it would be better. If little fingers were to find it, it could pop the preamp. There is a nice 48V model for my mono blocks though. ;)

The PSU linked on the Wam has a ripple voltage of <15mV at 2A. I assume this is SMPS.

[Stratmangler]

Thanks Alan. If I could find one that stopped at 20V, it would be better. If little fingers were to find it, it could pop the preamp. There is a nice 48V model for my mono blocks though. ;)

The PSU linked on the Wam has a ripple voltage of <15mV at 2A. I assume this is SMPS.

You may well find the 48v model doesn't have the grunt to handle big transients and dynamics.
That's why your Proprius amps utilise SMPS - a linear PSU that can handle big transients and dynamics would be (a) very large and, and (b) expensive, both to build and run.

[CageyH]

I think the biggest cost is certifying a linear PSU.

[Stratmangler]

When I last saw and spoke with Graham he said that a linear PSU capable of driving the amp properly would be large and complicated to build.
The SMPS he supplies is man enough for the job. I believe he also spent a goodly amount of time filtering out the very high frequency switching noise from the output, and also from being injected back down the mains.
SMPS done properly are perfectly alright.

That's not to say that it's not possible to build a linear PSU capable of doing the job, but you're talking big, as in Krell monobloc size big. Krells are as big as they are because of the size of the PSU and the amount of ventilation required. The massive heatsinks are for the power semiconductors they use in the amplification stages.
They run warm to say the least.

[CageyH]

Thanks for the info.
I am really only interested in the PSU for my preamplifier. The Amp PSU was a bit of an afterthought.
The Linear supply that Alan linked to looks good value, but I will keep searching for a 20V linear at a good price.

[StanleyB]

You can of course build your own or modify an existing one.

But 20V regulated is not a common type of output. Voltage regulators don't come in a 20V output configuration, unless it is based on something like the LM117 etc with a variable setting.

[Firebottle]

Agreed 18 to 20V fixed linear output is not common.

An alternative approach could be to use a 21 or 24V SMPS followed by an active filter, designed to drop 3 or 6 volts.

:cool: Alan

[CageyH]

I was toying with the idea of making one.
Audiophonics have a 20V linear dual output module, and a 2 x 20V transformer. It would just need to be put in a box., with a couple of plugs fitted. I would need to read up on this, to make sure that what I did would be safe. It may just be easier for me to buy a ready made, certified supply.
Audiophonics do one for €199.

[StanleyB]

I was toying with the idea of making one.
Audiophonics have a 20V linear dual output module, and a 2 x 20V transformer. It would just need to be put in a box., with a couple of plugs fitted. I would need to read up on this, to make sure that what I did would be safe. It may just be easier for me to buy a ready made, certified supply.
If you haven't done any previous DIY project that involved mains voltages, then I would strongly advise you to stay well clear of trying to build your own. Even an expert PSU DIY builder can tell you stories of the death defying near misses from the accidental incorrect wiring of mains.

If I were you, why not PM Lurcher, to name just one of our own members who have a world wide reputation as power supply designers. I am sure others can suggest other AoS members who are capable of building you a tailored solution within your budget, instead of you buying a generic one that is a compromise in one way or the other?

[CageyH]

I have plenty of experience of mains, and higher voltages.
I am just not sure about encasing a PSU in a box, which is why if I was unsure, I would buy a pre-made PSU out of preference. It's not worth risking anybody's life for a couple of hundred Euros.

[Firebottle]

Encasing a mains psu safely is by either Double Insulated or in a correctly earthed conductive enclosure.

For a small psu in a plastic box then it is usually double insulated. For a metal box the following applies:

For a fixed mains lead the lead must be secured by some form of clamp, to withstand a defined pull strength, can't remember the exact figure.
The earth conductor must be secured by a dedicated bolt (not one securing any component within the box), usually with a crimped or soldered connection to a ring tag.
A serrated or spring washer should be used to ensure good electrical connection and prevent loosening of the connection.
The connection must be made to bare metal.
Any removable panel should have its own earth conductor which connects to the dedicated bolt of the enclosure.

With correct fusing as well you have a safe unit that meets the Norms. Hope this helps,

:cool: Alan

[CageyH]

Any thoughts on this - http://www.audiophonics.fr/en/power-supply-kits-full-power-supply/alimentation-stabilisee-lineaire-15v-25a-m2tec-young-black-v3-p-8479.html

They will adjust it to 20V DC, and it will also allow me to run a couple of other devices. Seems a reasonable price too.

[Firebottle]

That looks excellent :thumbsup:

:cool: Alan

[CageyH]

Thanks for the feedback Alan.
It's cheaper than other linear supplies I have found, and safer for the preamp as it's not as easy to adjust as a lab supply and throw 30V through it.

[dowser]

Not read every post - but be wary of anything offering current limiting. I tried a bench supply to power a Naim preamp in the early days; dreadful compared to even a basic DiY linear supply. I was surprised given the Naim's only need around 200mA in total, but complete overkill is always better IME :)