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Old 26th September 2012, 06:27 AM   #1
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Default Power source "adaptation" on guitar amp

I'm making a vox ac30, but I got a problem here. The transformer that I have here, is a full wave (275-0-275), and the transformer on the schematics is a half wave...

Schematics: http://www.voxamps.com/downloads/circuits/ac301986.jpg

Here say that must have 345V on C382, and I dont know the specs from this transformer of this vox, but I think that this value maybe can be wrong.

I tried to change here the circuit using full wave retification, but I got only 274V, with the amp warmed and playing a song... I cant say that is a problem yet because the amp sounds good here, but when I finish the pre-amps and etc, maybe the power source can drop too much this voltage ...

Anybody can help?
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Old 26th September 2012, 09:13 AM   #2
DF96 is offline DF96  England
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No, the transformer shown in the diagram uses a full-wave bridge. As you have a CT you only need two diodes to get full-wave rectification. Rectifying 275V rms will give you something like 388V DC offload, but less when loaded. This is consistent with 345V loaded.

If you are only getting 274V DC from a 275V rms transformer then something is wrong. Either your circuit is wrong, or your transformer is much too small.
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Old 26th September 2012, 10:37 AM   #3
palmas is offline palmas  Portugal
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Quote:
Originally Posted by DF96 View Post
No, the transformer shown in the diagram uses a full-wave bridge. As you have a CT you only need two diodes to get full-wave rectification. Rectifying 275V rms will give you something like 388V DC offload, but less when loaded. This is consistent with 345V loaded.

If you are only getting 274V DC from a 275V rms transformer then something is wrong. Either your circuit is wrong, or your transformer is much too small.
Even using half wave would get you near the target. So, please measure the Vac in the transformer when loaded (ist it really 275-0-275?).
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Old 26th September 2012, 04:44 PM   #4
kevinkr is offline kevinkr  United States
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Guitar amp threads belong in Instruments & Amplifiers per forum policy. Moved.
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Old 13th February 2014, 09:13 AM   #5
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would that schematic be correct also for a 73-75 Vox AC30?

J.
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Old 17th February 2014, 04:43 AM   #6
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J.
Best get the info from "the horse's mouth".
VOX | Vintage Circuit Diagrams
Cheers,
Ian
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Old 17th February 2014, 09:03 AM   #7
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Yes I already have that schematic, and as you can see, "the horses mouth" seems to be pretty dirty!
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