Quad 405 linear PSU replacement with switcher. - diyAudio
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Old 22nd December 2011, 02:02 AM   #1
errcl65 is offline errcl65  Canada
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Default Quad 405 linear PSU replacement with switcher.

Any experiences with the sonic quality of replacing the mains with
a switching supply like a Coldamp SPS30? It can also be ordered
with -/+ 15VDC to power the opamps in the 405/clones.

I have to switch out a noisy transformer in my unit and
am considering this as an option.
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Old 22nd December 2011, 05:48 AM   #2
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I have discovered over the past two weeks that contrary to popular belief an SMPS works and sound far better than conventional large transformer based supplies.
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Old 22nd December 2011, 06:38 AM   #3
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Chord Electronics seem to make a bit of high-end money out of switching supply amplifiers. among other gear.
Interviews with the designer showed earthing arrangements to be bigger than normal issues. Well, he would say that to promote his approach but the argument looked reasonable.
Hi-Fi and Home Audio, music systems, components, home cinema

Otherwise, have you exhausted the options of conventional, R-Core, C-core H-Core transformers which may fit the space available better?
It may be worth considering that 2 stacked toroids paralleled or seriesed can work just as well as a large one, Assuming the original transformer was probably under 200VA, why not a couple of say, 80VA size on the same mounting bolt? There are more ways than one to skin a PSU!
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Last edited by Ian Finch; 22nd December 2011 at 07:04 AM.
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Old 22nd December 2011, 08:07 AM   #4
errcl65 is offline errcl65  Canada
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Cost wise, I am finding a complete SMPS costs almost as much as the
toroid I would need.
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Old 22nd December 2011, 09:56 AM   #5
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Quote:
Originally Posted by Nico Ras View Post
I have discovered over the past two weeks that contrary to popular belief an SMPS works and sound far better than conventional large transformer based supplies.
I think there are good technical reasons why this should be the case. Just connect a scope to one of the rails of an amp under load, fed by an SMPS and then by a linear power supply. SMPS typically shows some switching fuzz above the audio frequency, but that is about it. Linear power supply sags under load, but not just that, it starts to produce a cross between a sawtooth and a sine wave at the net frequency. This produces a lot of harmonics, right in the audio band. In short, it makes a lot of sense to move the frequency at which the net voltage is transformed to outside the audio band.

vac
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Old 22nd December 2011, 01:06 PM   #6
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Quote:
Originally Posted by vacuphile View Post
I think there are good technical reasons why this should be the case. Just connect a scope to one of the rails of an amp under load, fed by an SMPS and then by a linear power supply. SMPS typically shows some switching fuzz above the audio frequency, but that is about it. Linear power supply sags under load, but not just that, it starts to produce a cross between a sawtooth and a sine wave at the net frequency. This produces a lot of harmonics, right in the audio band. In short, it makes a lot of sense to move the frequency at which the net voltage is transformed to outside the audio band.

vac
I would say this knocks the nail on the head. Conventional 50/60Hz transformer supply hum and harmonics lie inside the audio band.

We make transformers for all kinds of applications and I have tried most types and configurations. All my amps except for the class A I made in the last two weeks are big transformer driven until the SMPS arrived (US$50). The SMPS is from Mean Well Type S-350-27 adjusted to 30VDC/13Amp

My brother and I did some extensive listening over the past four days to evaluate the two set-ups and we both concur without any doubt, there is no comparison, SMPS is tonally far superior to conventional power supplies besides there is zero hum.
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Last edited by Nico Ras; 22nd December 2011 at 01:11 PM.
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Old 22nd December 2011, 03:04 PM   #7
errcl65 is offline errcl65  Canada
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Nico,

This is good news.

Is there any sonic benefit from additional capacitor banking
of the mains rail voltages?

Did you do any listening tests with and without the cap bank
attached to each channel?
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Old 22nd December 2011, 05:14 PM   #8
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Quote:
Originally Posted by Nico Ras View Post
....The SMPS is from Mean Well Type S-350-27 adjusted to 30VDC/13Amp...
This is a single rail, fairly large device and obviously 2 will be needed for the QUAD. MEANWELL offer multi output supplies but they seem to all be low power affairs and of the same polarity. Competing Chinese manufacturers seem to offer similar products, so perhaps this is not a suitable solution.

Does anyone know of such an affordable supply with dual, opposite polarity outputs or more compact types that could safely be stacked for the same purpose?
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Old 22nd December 2011, 05:32 PM   #9
errcl65 is offline errcl65  Canada
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I was going to get

SMPS500R with +/- 50VDC and +/- 15VDC aux. It can maintain 500W continously
and peak at 650W which is more current than the 2 x Q405 boards need.

It is 100mm x 100mm. Should be an easy fit to replace the factory transformer
and leave room for caps too if needed.

Google SMPS500R from (connexelctronic.com).

The unit is roughly $80USD. Which is about the cost of as replacement toroid.

I want to restore the 405 (stock as possible) to drive some ESL 63 so I get
some insight into Quad/Peter Walker's notions of acceptable sonics.
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Old 22nd December 2011, 05:43 PM   #10
ColinA is offline ColinA  United Kingdom
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I want to restore the 405 (stock as possible) to drive some ESL 63 so I get
some insight into Quad/Peter Walker's notions of acceptable sonics.


I think that is an insult to Quad and Peter.
In their day they were not " acceptable"
they were state of the art!!!!!!!!!
There were many other talented designers working at the same time either still with valves or with transistors, differences in tastes and hearing gave rise to many now famous brands.
No one then or now makes "Acceptable" HiFi!!!
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