![]() |
P3A Power supply
Roughly how many channels in the P3A amp (or any amp, really) may share a single transformer? I'm looking to build 8-channels of amplification based on the P3A and, ideally, use a single transformer (1x1kVA + 20,000uF per rail). Each channel will only be 40W continuous/8R (+/- 28.3v rails, 40v CT xformer).
Any thoughts? Thanks in advance. |
40VCT may be a little short for 40W/8R, is it OK to be 1dB low?
I would use 22-0 + 22-0, and use a one bridge for the + rail, and another for the - rail. One complete supply per channel. This will help avoid high current ground problems. The ATI multichannel amplifiers are built this way. For 8R loads and 60hz the minimum filter capacitance is 3,300µF per channel. Use 6,800µF for 4R. For 50hz the minimum would be 4,000µF and 8,000µf respectively. Each rail for each channel should have a 22µF ~47µF bypass cap. If you add 0.1µF film caps too, be careful as it may oscillate (try adding 2R2~4R7 resistors in series with the 0.1µF). The transformer should be 2VA for each W out at the lowest expected impedance. For 40W8R and 60W/4R that would be 120VA per channel, or 1KVA for eight channels. Use an inrush current limiter. |
You don't need anything like 1kVA per channel. That's just a waste of money, weight and space. I wouldn't bother with anything over about 200VA per channel, myself and even that is plenty.
If I was building this system, I would go with four 40VCT (20-0-20) 250VA transformers (one per two channels) and one bridge and cap bank per channel. You can go with bigger transformers if you use bad quality ones (bad regulation). Also, IMHO 20,000uF per rail is overkill - go with 10,000 per rail and save yourself some money. For what it's worth I can't ABX my 4,700uF per rail P3A from my 10,000uF per channel version and I would be happy to give a case of beer (Amstel or Windhoek) to the first person who can. You can go with more channels per transformer, but you will find that over about 300VA price doesn't scale linearly with VA (at least not in South Africa). Oh and as djk says an inrush current limiter is a must, especially if you are using toroidals. |
Quote:
The real question here is this : Though seperate bridges and capacitances are laudable for interaction of the various amplifiers it precludes the use of a single bridge and very large capacitor bank that under dynamic conditions will give lower ripple than seperate supplies. Each amplifier obviously must be separately fused. With just two channels playing for example, they would benefit from a way over specced power supply. I think it really depends on the intended use of the eight channels, unless there is a fundamental disadvantage of a single supply I am unaware of. :) sreten. |
Quote:
|
I might have misinterpreted. A single supply for all eight channels would be fine. The only reason I recommended four seperate transformers is that, around here, four 300VA toroidals are cheaper than one 1.2kVA toroidal.
Quote:
Quote:
Quote:
|
Thanks everyone for your replies.
First of all, I was asking about using one supply to be shared by all 8 channels :-D - so hell yeah I'm not using 1kVA per channel! I'm a student and do not have that kind of money! So basically I was asking if interaction between channels sharing a supply would be so bad that the idea isn't feasible. It's difficult to quantify 'so bad', but I'm not trying to eek the last final percent in performance. I just want a solid, good-sounding amplifier. BTW the 8 channels are for driving a pair of 3-way speakers (with the bass channel doubled up with 2 drivers per side... so 3.5 way? hmmmm dunno). Thanks |
Quote:
|
Quote:
Cheers Andrea |
Quote:
For music you don't need so much subwoofer power, but for Home Cinema a powerful sub is really nice (until the neighbours call the cops during Saving Private Ryan, that is). Wingfeather, have you been to Rod's forums? Follow the forum link on his page. There are a lot of guys their who are very knowledgable about his projects. Rod's forums are a good complement to diyAudio. |
All times are GMT. The time now is 08:40 PM. |
Search Engine Optimisation provided by
DragonByte SEO (Pro) -
vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 18.75%
vBulletin Optimisation provided by
vB Optimise (Pro) -
vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio