| xyrion |
Hello,
I'm building an integrated amp from two bridged power amps, a volume control board and a line stage buffer. All the components have their own PSU-s so I need to provide a proper AC for the system using a toroid transformer ... or two? What solution would in your opinion yield the best results?
My volume control needs one 12V rail, line stage buffer needs another 12V and two power amps need four 22V rails. All AC.
From what I've read people generally agree that "pre" and "power" sections of the amp should have separate trafos, and when it comes to powering two bridged power amps it's much harder to find a consensus. Some say one toroid per power amp = better separation, others say one big toroid for both is more stable +one amp will always draw more current due to the nature of stereo so why use two trafos... What are your experiences and thoughts on this? Should I get one, two, three or four :cannotbe: ?
I didn't mention the VA ratings because I'm interested in finding the best configuration only and will buy a properly oversized toroid(s) anyhow.
Your comments and help is greatly appreciated and I'll be glad to learn something new. |
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| AndrewT |
Hi,
I would buy a smaller 12Vac transformer for the two lower current stages. Are these dual polarity stages or just single polarity?
For the power stage I would go with one large transformer. Dual 22Vac secondaries or 44Vac centre tapped. Both are equally good. Provided your PSU suits centre tapped, some don't.
The advantages of one large are less weight, less cost, less space and the best advantage is lower regulation.
I would run separate rectifiers and smoothing to each amplifier. If I read you right you have four amps bridged to give two channel stereo. That's four rectifiers for the four amps, all run in parallel from the same AC windings. |
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| xyrion |
Volume control and buffer are single polarity as oposed to +/- 22Vac needed per power amp. I will use one stereo power amp with bridged outputs per channel for my integrated stereo amp (IIRC it's called dual-mono configuration). Each one already has two onboard rectifiers, so I got that covered.
btw, if I order one toroid with only two windings on secondary (+22v and -22v) and split them in two wires to feed both amps will I loose anything compared to one toroid with four secondary windings? I'm asking this because if it's the same, I would prefer a torid with more primary windings(something like 220V, 230V and 240V) to better suit my home AC. |
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| xyrion |
| quote: | Originally posted by me
btw, if I order one toroid with only two windings on secondary (+22v and -22v) and split them ... |
Whoops, now I see this is called a center tap. :blush: |
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| AndrewT |
Hi,
you need to check inside your amp circuit.
If it already has two rectifiers, it could have either of two alternative connections into the PSU.
Is each rectifier feeding ONE bank of smoothing caps, producing ONE polarity of DC voltage?
Then the two rectifiers will produce the two DC voltages the amps need. There is no centre tap going from transformer to smoothing caps.
Alternatively, the rectifier could be connected across a dual bank of capacitors, with the common between the capacitors connected to the transformer centre tap. The second rectfier also produces a dual polarity +-V DC supply.
These two circuits operate completely differently. Do not mix them up or you risk blowing your transformer and rectifiers. |
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| xyrion |
| Second rectifier for my amp is provided as a part of a "hi power addon", so both of them produce dual polarity. |
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| DJ Exprice |
Most transformers have 3 or more secondary wires. AC1, 0v, AC2
Just do this to achieve 2 PSUs:
One rectifier board has AC1 and 0v.
The other has 0v and AC2.
Cheers! |
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| AndrewT |
Hi,
20-0 & 20-0 are two separate secondaries.
Because they are separate you can treat them as separate supplies and do things differently to either. You can connect a single rectifier and single polarity smoothing cap to the rectifier.
Do the same for the other and then use both DC supplies for what you want.
20-0-20 is a single secondary with a centre tap.
These are connected and you must treat them as connected. The PSU that you connect on the end must be compatible with a centre tapped secondary. Use a single rectifier into a dual polarity smoothing bank with the 0volt common connected back to the centre tap at the audio ground.
You can add a second rectifier to the secondary tappings, effectively the two ~ are in parallel with the original. It sounds like this has already been done to yours. The extra rectifier has it's own smoothing caps connected to the +&- for a second channel of amplification. BUT the two smoothed DC supplies are not independant. BOTH DC supplies are connected back to the SAME 0volt common.
DJ,
your suggestion sounds different.
Would you care to explain? |
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