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Old 9th February 2003, 07:02 PM   #1
nikosgr is offline nikosgr  Greece
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Default New PSU for class A amp

Hello world!

Hi, this is my first post on this forum. My name is Nikos, I come from Athens, Greece and DIY audio has been my hobby for the last 6 years.

I am currently in the middle of a PSU upgrade process for a MF P270-2 class A power amp.

Changes in the new implementation:
1) Separate regulated supply for the voltage gain stage (the design is based on an LM318, 12V supply). 2x200VA toroids, 2x20.000 F
2) Separate unregulated supply for the current gain stage (5x2SK1058 and 5x2SJ162). 2x1500VA toroids (2x100.000 F / 63V per channel). 150W output. Transformer secondary rails 2x43V AC - after rectification, 58V DC.
3) First class materials have been used throughout

My first question is:
I am thinking of using chokes. Browsing through this forum, I've seen them used in several Pass designes, and I 'm wandering if you think it may be suitable for my particular case.

Second question: In case I go ahead and use this solution, I'd need to know the following-
1) the way to calculate the mH needed for the chokes
2) how many amperes (I assume over 15Amps)
3) what kind of choke would be more appropriate?

Looking forward to your comments!!!

Nikos
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Old 10th February 2003, 01:22 AM   #2
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I like chokes because capacitor-only psu's have a sawtooth shaped ripple voltage, but a choke type supply has an almost sinewave ripple at 100 or 120 Hz. Even if the ripple voltages were equal amplitude the sinewave hum from the choke version is much less audible than the sawtooth buzz from the capacitor type.

My class A has a 27.7 volt supply that delivers 7 amps total, and with 229,000 uF and a 1.35 mH choke (about 60mm cube) between the diodes and the caps reduced the ripple to 2/3 of what it was without the choke. Power transformer ran cooler to because of lower peak currents. Chokes are good value!!
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Old 10th February 2003, 01:25 AM   #3
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Not to mention the superior power factor with a choke input power supply relative to a capacitor input power supply. Actually if you use a choke and a relatively small cap, you can get power factor fairly close to 1.
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Old 10th February 2003, 09:14 AM   #4
nikosgr is offline nikosgr  Greece
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Default chokes in psu supply

OK guys thanks for your replies.
But what kind of chokes you recommend and what values(mh/A) are needed in my case?

2X1500 VA Toroids 2X100000 mf per channel 2X43V secondary rails after rectification 2X58VDC

Looking forward for your reply
Nikos
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