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Old 19th August 2003, 01:29 AM   #1
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Default running two voltages

Well, there comes a time when someone wants to make an amplifier that can be plugged into two different mains voltages with no internal alteration.

My idea is to build a 900W 2channel amplifier that will work on 110V as a 225W amplifier and then on 220V as a 900W amplifier.

I have already come up with a design similar to ESP's P68 300W amplifier. I designed my version to do 900W per channel output for a 220V power supply and I imagine that the circuit should still be stable to run at half the supply voltage.

Does this seem correct? Rod states on his site that the P68 design is stable with as little as +-5V split supplies. I think then, that a very closely similar design should cope at only half supply voltage.

My true reasoning for this is that I wish to be able to connect the amplifier to ordinary 110V outlets when a 220V outlet is not available. I will eventually be installing 220V in my listening room but also would like to use the amplifier at friend's places sometimes. Not many people have 220V anywhere besides their kitchen and laundry room, which neither of which would make a good listening room. Rather the fact of breaking dishes at that power, or getting in somebody's way in the laundry room.

Any information is greatly appreciated.
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Old 19th August 2003, 01:36 AM   #2
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You could always use a simple overvoltage / undervoltage circuit to switch the way the transformer primaries are wired so that you always have the same rails.
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Old 19th August 2003, 01:37 AM   #3
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Well, the only problem is that I will never get 900W at 110V without bridging, thus my amp becomes a monoblock which I need two channels.
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Old 19th August 2003, 10:37 AM   #4
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I think the idea AudioFreak was suggesting would be to use a power transformer with two 110V primaries. A relay could normally connect these in series for 220V operation. A control circuit could detect if the rail voltages were only around 50V instead of 100V, and switch the relay to reconnect the transformer primaries in parallel for 110V operation. Using a suitable break-before-make relay and and taking into account phase of the transformer windings, this could work quite well.

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Old 19th August 2003, 12:51 PM   #5
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I completely understand what AudioFreak is saying, however, I can't afford anymore transformers and the one I have will only give me the right rails for 900W if I feed it 220V. Normally I would implement such a circuit to automatically switch the power, but also, a single 110V circuit wouldn't suffice for 1800W output anyway. Your ideas are quite valid and thankyou, however, what I want to know, is how well do you think the amp would fair at half the power supply voltage that it was intended for??
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Old 19th August 2003, 01:05 PM   #6
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Just curious, do you have both 110 and 220 V in Canada?

Do you intend to this amp around?

EDIT: Do you have 3 x 110 V or 1 x 110 and 1 x 220 V.
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Old 19th August 2003, 01:28 PM   #7
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Quote:
Originally posted by peranders
EDIT: Do you have 3 x 110 V or 1 x 110 and 1 x 220 V.

IIRC, they have 2-phase 110V with each phase being 180 degrees out of phase with the other. The 220V outlets are then wired with 2 live pins (1 for each phase) and earth.
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Old 19th August 2003, 02:56 PM   #8
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I think your question is: "Can I run my amplifier with half the supply voltage?" and the answer would depend on your amp design. Will all the circuitry run correctly at half the supply voltage? Probably yes, I know my ESP P3A runs down to just a few volts per rail.
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Old 19th August 2003, 03:50 PM   #9
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YES! Now you guys have it!

Yes, here in Canada we get 2phase to the residential areas. Half of the phase is used for general purpose outlets and is 110V. Dual Phase is used for 220V where more power usage is needed but also so you don't need really fat wires and high current breakers.

It's not really called 2phase here, since they are really only 1phase from the power company and it splits at the pole transformer which simply has a single ended input at 2kv and a center tapped 220V output with the center being neutral and grounded at the pole and service panel of each house. The power company runs a single 2kv line through the residential areas and uses the earth ground for the other side.

My amp design on the other hand is extremely similar to a P68 by esp, in fact, almost identical. So I'm just wondering your opinions on running it half voltage since I re-designed it for 74.5 volt rails which is what I get if I run the transformer at 220V.

The idea is that this amp will be good for gigs at schools and things where they have 220V in most places anyway. However, at home in my listening room, I'll probably never need more than 250W per channel which 110V operation would do. I am still installing 220V in my listening room for other projects such as some of my tube equipment and the 400W MH projector ballast which I prefer to run at 220V because then it causes equal transients on both phases instead of just one line of 110.

Anyway, anyone who thinks this amp will not work at 110? Just wondering to make totally sure.
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