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Old 9th June 2010, 08:43 PM   #1
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Join Date: May 2010
Exclamation varying amp input voltage

hi every body
I have a new concept . how bout varying the amps input voltage according to the level of audio input ..... in this way we use amps more efficiently and heating of the o/p devices will a lot less as compared to a constant supply....
this can done by the following ways
1. Changing the firing angle of a triac according to the audio input level .... This triac will feed the transformer
2. changing the firing angle of A SCR on the secondary side of the transformer according to audio input level.....

I dont know how well these ideas can increase efficiency & decease O/p device heating....
Kindly comment on this idea as all of u know more than me .......
I will put up some schematic later

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Old 9th June 2010, 10:03 PM   #2
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Location: Carlisle, England
Using an SCR/triac will generate all sorts of noise on the input and output of the transformer.

You would need a cct that responded very quickly to transients.
Murton-Pike Systems PCBCAD51 pcb design software.
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Old 9th June 2010, 10:10 PM   #3
latala is online now latala  United Kingdom
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Location: staffordshire
it,s been done an example is Bob Carvers power cube and later sunfire amplifiers to name a few
The problem is as ever what is going to tell the power supply where it needs to be in time to respond to the required output signal! it would be more complicated than the actual amplifier
regards Trev
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Old 10th June 2010, 07:02 AM   #4
Mooly is offline Mooly  United Kingdom
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Well you could use a similar scheme to this, using the control signal to set the line voltage instead of bias,
New idea for low dissipation Class A amplifier.

at least that would offer stability as the voltage would be constant for a given volume control setting.

As to varying the voltage dynamically... yes it has been done (as Latala points out), but it's going to be one complicated beast. To know the history of the signal implies delaying that signal first... and using a conventional PSU, just how quickly do you think a rail could respond in practice... and think of the current flow in the PSU suddenly increasing as the caps charge to a new higher level. Would the amp reject the changing ripple and voltage ?

My own thoughts on this (at the risk of getting flamed ) is to pursue low bias designs that run inherently cool... and if you are finding the sonics poor for whatever reason, then tbh that's as much a failing of the whole design rather than just the the class of operation.
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