Not industrial
My two cents:
We are not industrial producers, we don't split every cent or we don't buy thousands of trafos.
In fact, an amplifier is DC-supplier wich you can modulate with your audio signal. So you need the DC current.
Choose an appropriate size of the trafo. And still think about regulating the PSU ...
Franz
My two cents:
We are not industrial producers, we don't split every cent or we don't buy thousands of trafos.
In fact, an amplifier is DC-supplier wich you can modulate with your audio signal. So you need the DC current.
Choose an appropriate size of the trafo. And still think about regulating the PSU ...
Franz
Traffos when stressed will lower their output voltage, this is what the regulation factor is. If it says 5% then the output voltage will fall by 5% under max rated output power. This droop can effect the sound quality.
A larger transformer will reduce this effect two fold.
1) it will not be as stressed so therefore will not droop as much
2) larger transformers have better regulation not dropping as much under stress.
So if a DIY person can get a larger traffo for not much more money over a smaller one then they will go with the bigger one. Also as DIYer you never know when youll want to change something, say add on another two channels. If you have the bigger traffo in the first place youve always got some future proofing.
But from a technical point of view you dont need a traffo any bigger then is required for max current drawn.
It also depends on the application
My 4 channel 80watts amp has a 650VA traffo, now for max output from each channel into 4 ohm loads this is not enough, but im never going to drive each channel, full power into 4ohms plus each amp only receives a portion of the audio spectrum because its an active setup.
So if you are going to be driving the amps to max output into tough loads then a bigger traffo may come in handy. If your not a smaller one will probably be fine. Its similar with heatsinks, my sinks on the aforementioned amp are suitable for max output into 4ohms but in the application I use them in they never get hotter then slightly warm to the touch.
Matt
A larger transformer will reduce this effect two fold.
1) it will not be as stressed so therefore will not droop as much
2) larger transformers have better regulation not dropping as much under stress.
So if a DIY person can get a larger traffo for not much more money over a smaller one then they will go with the bigger one. Also as DIYer you never know when youll want to change something, say add on another two channels. If you have the bigger traffo in the first place youve always got some future proofing.
But from a technical point of view you dont need a traffo any bigger then is required for max current drawn.
It also depends on the application
My 4 channel 80watts amp has a 650VA traffo, now for max output from each channel into 4 ohm loads this is not enough, but im never going to drive each channel, full power into 4ohms plus each amp only receives a portion of the audio spectrum because its an active setup.
So if you are going to be driving the amps to max output into tough loads then a bigger traffo may come in handy. If your not a smaller one will probably be fine. Its similar with heatsinks, my sinks on the aforementioned amp are suitable for max output into 4ohms but in the application I use them in they never get hotter then slightly warm to the touch.
Matt
Transformers are rated full load. If the regulation is stated as 5%, then off load it will be 5% greater than the rated voltage. This is more noticeable on small transformers, like 5VA, such that a 12v transformer may measure 15v off load. (This makes replacing a burnt-out transformer a bit of a gamble, if a good one is measured off load). Then there is the peak-to-peak ripple voltage, which is determined by the load current and reservoir caps.
This is how I usually size a trafo (using the example of the GC i'll be building shortly using dual 25V secondaries).
34V Rail x 4A peak current draw = 136W instantaneous demand.
X2 Channnels = 272W for both channels.
Personally, I've found that to avoid voltage drop on a trafo at peak draw I need about a 50% overhead in the VA rating.
Thus 272 x 1.5 = 408 VA.
Now in my case, I had a great opportunity to pickup a 500VA at about the same price as a 400VA, so I chose the 500VA. That and I plan to do some playing around with some design variations which may have higher power draw.
Now, I am also ignoring that the PS smoothing capacitors will also reduce the voltage sag that occurs during transient peaks (rule of thumb: 1F = 1A draw for 1s with 1V drop), and the fact that the majority of the time all audio amps are trickling along at only 1-2W output, so it could be reasonably said that I take the overkill approach.
Just my two cents.
34V Rail x 4A peak current draw = 136W instantaneous demand.
X2 Channnels = 272W for both channels.
Personally, I've found that to avoid voltage drop on a trafo at peak draw I need about a 50% overhead in the VA rating.
Thus 272 x 1.5 = 408 VA.
Now in my case, I had a great opportunity to pickup a 500VA at about the same price as a 400VA, so I chose the 500VA. That and I plan to do some playing around with some design variations which may have higher power draw.
Now, I am also ignoring that the PS smoothing capacitors will also reduce the voltage sag that occurs during transient peaks (rule of thumb: 1F = 1A draw for 1s with 1V drop), and the fact that the majority of the time all audio amps are trickling along at only 1-2W output, so it could be reasonably said that I take the overkill approach.
Just my two cents.
DC it is.
2*22VAC reads ~61VDC idle ~52VDC full power just before clipping on 8Ohms load.
Seeing some more weird stuff like low freq oscillation ~2.3Hz and hi freq at the same time just before clipping. DC offset is very sensitive to IC cable capasitance. Haven't seen any posts on these issues not that I read every post.
Still working on them...
2*22VAC reads ~61VDC idle ~52VDC full power just before clipping on 8Ohms load.
Seeing some more weird stuff like low freq oscillation ~2.3Hz and hi freq at the same time just before clipping. DC offset is very sensitive to IC cable capasitance. Haven't seen any posts on these issues not that I read every post.
Still working on them...
Morfeas:
Maybe the funny stuff is the high ripple, althought the low frequency is a bit odd.
But your voltage sag is even worse than what I had, 400VA, 2x22v. I had no measureable drop in the AC but 10% on the DC
DDM no scope
This is what I ran into with GC of 1500uf on 2875 bd and 4.7 on PS. read some of the later posts on buffered and regulated GC.
It seems to have adequate filter supply at high demand you have to go to a regulated and at the same time greatly reduce the size of caps on the 3875 pcb. then you can add healthy amounts of filters at the PS.
http://users.verat.net/~pedjarogic/audio/gainclone/supplies.htm
has a good writeup.
nealb(sp?) had some similar experience.
Maybe the funny stuff is the high ripple, althought the low frequency is a bit odd.
But your voltage sag is even worse than what I had, 400VA, 2x22v. I had no measureable drop in the AC but 10% on the DC
DDM no scope
This is what I ran into with GC of 1500uf on 2875 bd and 4.7 on PS. read some of the later posts on buffered and regulated GC.
It seems to have adequate filter supply at high demand you have to go to a regulated and at the same time greatly reduce the size of caps on the 3875 pcb. then you can add healthy amounts of filters at the PS.
http://users.verat.net/~pedjarogic/audio/gainclone/supplies.htm
has a good writeup.
nealb(sp?) had some similar experience.
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