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Old 12th February 2009, 03:00 AM   #1
GeeVee is offline GeeVee  Australia
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Default The thought process of the DIY’er

There are many things that DIY’ers do, including myself, and it makes me wonder if we actually stop to think.

It usually revolves around “overkill”, and the perceived increase in performance that we are sure we will be able to hear.

One such area is power supplies.

I completely agree that a good solid-state amp needs a good, stiff, well-regulated power supply.

Let me elaborate, and use the Aleph 1.2 as an example.

I am currently building an Aleph 1.2 power amp, and on examination of the original service manual and schematics, it can be seen that Mr Pass has employed a standard bridge rectifier, with approximately 100,000uf of capacitor filtering.

(Mine has 120,000uf)

Now to my way of thinking, the original designer, Mr Pass, has deemed that 100,000uf of capacitor filtering is appropriate for an amp of this quality.

If it weren’t, surely he would have added more filtering etc.

Now we take a look at the DIY’ers of this amp.

On this site, and several others, power supply filtering has been increased to 200,000uf, and in some instances up to 600,000uf.

My question is: if the original designer deemed that 100,000uf was enough, what sonic revelation are the “lets increase the filtering by 6 times” individuals expecting?

Is there something that I am missing here?

I would really like to hear from others.

Regards

George.
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Old 12th February 2009, 05:23 AM   #2
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GeeVee,

The total capacity of the filtering caps is awesome. You may also need a big transformer. I have tried both in the picture below. They are of the same input and output voltages. The black one is a 750VA made by Plitron. The big one is a 2000VA custom ordered from Amveco. Below the transformer is a 12" ruler.

With the 2000VA installed in a 150W x2 power amp, the difference in sound quality was quite prominent. I could fell stronger low frequencies as if a subwoofer was added to the system.

My two cents.

Xtaltech
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Old 12th February 2009, 06:58 AM   #3
Nrik is offline Nrik  Denmark
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Biggger transformer = lower series impedance in the PS.
This should be noticeable.

My experiences with capacitor values are, that you can hear a clear improvement when you double the value.
That is: Two similar amps, with one that has double capacitance in the PS is clearly noticeable as better sounding.

Why did the original designer not choose this value of capacaitor? Probably a choise of price-vs-performance - the sound improvement is after all not double as good, maybe 5-10%. And you gotta stop somewhere, and even 100.000uF sounds like overkill.
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Old 12th February 2009, 07:33 AM   #4
Nrik is offline Nrik  Denmark
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...I should note that my experiments were with class AB amps, not pure Class A amps.

Anyway:
Here is some good reading:
http://www.fmacoustics.com/set_company.html
...scroll down to: "4. Power supply assembly"
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Old 12th February 2009, 08:25 AM   #5
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I believe it was Mission in the UK who first offered a beefed power supply upgrade option : the PSX for their Cyrus quasi-compl. amp, around 1985.
However, the PSX power supply add-on was not only meatier, but also raised the power output level, as in higher rail voltage.

Sven Berendsen from Germany was the first to offer a power amp in a regular and a Heavy-Duty version with equal power levels afaik, around 1987 : the ES120 Blue edition and ES120 Red edition.
Exact same amp, but with a power supply nearly twice as large, both a bigger toroid and nearly two times larger capacitor size.
Berendsen audio still does a larger lytic can size option nowadays with their STA150 and STA150 SE special edition models, see berendsen-audio.de

Both amplifier models operate in Class AB, which is (should be) considerably less critical than Class A with regard to power supply size.
The bigger the ocean, the less visible a ripple(wave) becomes, but also depends on whether you're floating in a dingy or a giant supertanker.
The loudspeaker behavior is the most dominant factor for how far power supply size should be stretched, imo.
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Old 12th February 2009, 09:40 AM   #6
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Correct me if i´m wrong.
Some amplifiers are calculated for voltage sag/drop to go with lower impedance speakers within SOA.

Bryston for instance (class AB), go conservative on transformer size and just 5600µF per rail.
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Old 12th February 2009, 09:49 AM   #7
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You can soften the suspension on your car, doesn't make it a better ride.
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Old 12th February 2009, 09:56 AM   #8
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Hm.. but a to big carburator make it slower.
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Old 12th February 2009, 11:07 AM   #9
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My nextdoor neighbor's daily drive is a 2008 M-Merc, '05 model.
In his spare time he's restauring an old VW Bug, sentimental lane stuff for him, the car is parked in the garage 24/7.
The second garage holds a Saab Aero V6 convertible, so the M always has to sleep outside.

Maybe someone with a youth crush on Bryston amps fancies building one himself.
This is DIY, anyone can do as he pleases.
Personally i see this hobby as building hotrods with big engines, big carbs and fat tires, not assembling Bugs.
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Old 12th February 2009, 12:18 PM   #10
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Hot rods ok.
I spent some 10 years on the dragracing strip and to get max performance it cost me more than some burnt outputtransistors to go for concept and then tweak it a little bit further.
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