Power source "adaptation" on guitar amp

felipemuniz · 26th September 2012, 06:27 AM

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?

DF96 · 26th September 2012, 09:13 AM

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.

palmas · 26th September 2012, 10:37 AM

Quote:

Originally Posted by DF96

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?).

kevinkr · 26th September 2012, 04:44 PM

Guitar amp threads belong in Instruments & Amplifiers per forum policy. Moved.

26th September 2012, 06:27 AM	#1
felipemuniz diyAudio Member Join Date: Mar 2012	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?

26th September 2012, 04:44 PM	#4
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Guitar amp threads belong in Instruments & Amplifiers per forum policy. Moved. __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

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26th September 2012, 09:13 AM	#2
DF96 diyAudio Member Join Date: May 2007	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.