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Old 2nd March 2003, 09:13 PM   #1
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Default Leach power supply

What is better for SQ?

I will use amp for 8 ohm load.

2x6600uF per channel ( top quality caps Siemens Sikorel)

or

4x22000uF per channel (standard quality caps Jamicon)


Thanks for hellp.

janey
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Old 3rd March 2003, 04:34 PM   #2
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It is a matter of how much ripple current that you are allowing on your voltage rails. The higher the capacitance on the rails, the smaller the 60Hz voltage that will appear on them. The Leach amplifier has a high Power Supply Rejection ratio meaning that the circuitry can compensate a varying power supply voltage without the rail voltage signal appearing on the output as a signal. However high, there is still a finite amount which will appear on the output. So I always choose the higher capacitance at the risk of a higher volume occupance taken by the caps. My stereo Leach SuperAmp has one 55Kmfd per voltage rail. The stereo pair shares rails. Also, the higher the capacitance, the lower the rail droop will be under massive loading conditions.

BeanZ
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Old 4th March 2003, 12:04 AM   #3
Diode is offline Diode  United States
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Gee whiz beanZ,

Does your power-up sequence dim the lights in New York City?


What kind of switch do you use? Do you use a series triac to slowly power it?

YUP!!!! Big caps will do fine I hear multiple caps are better but I don't really know..........


Chris
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Old 5th March 2003, 05:23 PM   #4
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You are abolutely right!!! The lights do dim and occasionally if you catch it on an AC line zero-crossing, the breaker will trip. This is only because there is inadequate inrush current limiting. I use a very small switch for power (actually two switches). There is a smaller transformer inside my amplifier which is turned on first and which provides power for accessory circuitry such as LED VU meters, fans and fan controllers, and clipping indicators, and more importantly coil power for a small relay which is then turned on by the second small power switch. When this relay is energized, the contacts trigger the gate on a TRIAC which runs in the 1st and 3rd quadrants. The TRIAC is the main power switch which can be controlled with more attractive smaller, lower current switches preventing the use of a huge industrial rated power switch. In-rush current limiting will be added sometime in the future. I am a switching power supply designer and will eventually replace this large unregulated supply.

For less experienced players, in-rush current limiting is a MUST with this size of power supply.
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Old 5th March 2003, 09:39 PM   #5
Jeff R is offline Jeff R  United States
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BeanZ,
I would have thought using a triac would be a recipe for RFI. Do you go to pains to clean things up? Or is a triac a lot quieter than an SCR?
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Old 5th March 2003, 10:02 PM   #6
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My Leach amplifier is a dual-mono chassis, with two 30,000 uF capacitors per rail for a total of a quarter-Farad at nearly 60 volts.
Ripple voltage is gratifyingly low, and obviated any need for a regulated supply.

Needless to say, the room lights dimmed noticably when I turned
on the amplifier, and I was concerned about burning up the power switch contacts and blowing the rectifiers.

My simple fix was to use a double-pole center-off switch; one side has a 6 ohm 10 watt power resistor in series, the other side is
straight through. The Start position limits inrush current, and
the Run position of course doesn't; using both poles in parallel reduces stress on the contacts.

There are thermistors useful for this purpose; I simply used what I had in my collection. A 25 watt aluminum cased resistor bolted to the chassis would not be overkill, especially if you left the switch in 'start' position and proceeded to party all night at maximum volume.
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Old 5th March 2003, 10:27 PM   #7
UrSv is offline UrSv  Sweden
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Quote:
Originally posted by Jeff R
BeanZ,
I would have thought using a triac would be a recipe for RFI. Do you go to pains to clean things up? Or is a triac a lot quieter than an SCR?
I believe that problem only arrises when the Triac is used to regulate. In this case it just acts as a switch and once switched on there should be no noise created.
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Old 6th March 2003, 02:56 AM   #8
Diode is offline Diode  United States
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Hey BeanZ.

I used to be a power supply jockey for Lucent Technologies. I'm just a tech though.... The 2 projects I worked on were for Telecomm. and were 208VAC in 24V 100A out and 208VAC in 48V 50A out. We had PFC AC-DC supplies on the input and DC-DC on the output..... Let us know if you get a well regulated and protected supply from 110VAC input going!!!! We used full bridge topology! I don't know about the PFC section as I was responsible for the DC-DC side..........
Good luck!

Chris
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Old 6th March 2003, 04:11 AM   #9
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Diode:

In days long gone, I worked for Solid State Systems in Georgia;
we had lots of fun designing switchmode power supplies for
our telephone systems. I did all the test and repairs on the
power supplies, but alas, I didn't learn much about the
technologies. While there was a dramatic reduction in size
and weight over the ferroresonant-based linear supplies, getting
the switchmode supplies reliable took a couple of years.

Resonant mode converters looked interesting, though. But
business took a turn for the worse, the Class D ringer amp
got shelved, and I finally was laid off.

That ended my career in electroncs.

Certainy there are commerical amplifiers out there with switchmode power supplies, but experimenting with those
ideas has a necessarily low priority with me. I'm still very interested in the concepts.
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Old 7th March 2003, 12:17 AM   #10
Diode is offline Diode  United States
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I hear ya man......

I'm barely hanging on to my electronic career.... What are we coming to? Oh well....

Chris
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