Hi
There is no rule for determining the uf value of a power supply versus the power in watts.
I recommend you go to Pass Diy and the read the article on Power Supplies. ( I recomend reading all the articles on that site. They are by Nelson Pass who generously provides a lot of help to audio diyers )
In general it is the transformer that varies in VA value as the amplifier watts increase. For a class AB power amp it is best to provide a transformer of at least 3 or 4 times the watt rating of the power amp and for a class A amp it is best to provide a transformer with a VA rating of at least 5 or 6 times the watts of the power amp. For example a 25 watt per channel power amp will need a transformer of at least 200va if operating in class AB and at least 300va if operating in class A.
The Capacitors do store a charge and you need to check that the capacitors store as much current as the power supply can deliver on transients. Howerer the capacitors smooth the dc supplies to the power amplifier output stage. In general terms you will probably need around 25,000uf for a 25 watt amp increasing to around 100,00 uf for a 200 watt amp. However as stated earlier the amount of "uf" is not directly related to the output in watts. Again I recommend you read the article mentioned above. For a pre amp a transformer of 60va is usually ok however 100va is better. A Preamp also usually needs around 3,000 uf. However with a pre amp the power supply design can get complicated as the designer tries to keep the power supplies in to the pre amp clean and stable as the voltages and currents in a preamp are small and power supply variations can cause distortion.
This should help you get started - but do read the articles.
Don
There is no rule for determining the uf value of a power supply versus the power in watts.
I recommend you go to Pass Diy and the read the article on Power Supplies. ( I recomend reading all the articles on that site. They are by Nelson Pass who generously provides a lot of help to audio diyers )
In general it is the transformer that varies in VA value as the amplifier watts increase. For a class AB power amp it is best to provide a transformer of at least 3 or 4 times the watt rating of the power amp and for a class A amp it is best to provide a transformer with a VA rating of at least 5 or 6 times the watts of the power amp. For example a 25 watt per channel power amp will need a transformer of at least 200va if operating in class AB and at least 300va if operating in class A.
The Capacitors do store a charge and you need to check that the capacitors store as much current as the power supply can deliver on transients. Howerer the capacitors smooth the dc supplies to the power amplifier output stage. In general terms you will probably need around 25,000uf for a 25 watt amp increasing to around 100,00 uf for a 200 watt amp. However as stated earlier the amount of "uf" is not directly related to the output in watts. Again I recommend you read the article mentioned above. For a pre amp a transformer of 60va is usually ok however 100va is better. A Preamp also usually needs around 3,000 uf. However with a pre amp the power supply design can get complicated as the designer tries to keep the power supplies in to the pre amp clean and stable as the voltages and currents in a preamp are small and power supply variations can cause distortion.
This should help you get started - but do read the articles.
Don
I like this power supply tutorial. Halfway down is an equation to calculate how much capacitance.
Power Supplies
http://www.eleinmec.com/article.asp?19
Power Supplies
http://www.eleinmec.com/article.asp?19
Last edited:
I am not an expert, but if this is your first SS Amp, I would read all of the links if you plan on building a monster. I am in the middle of building two 450watt mono blocks with the Blazer PCB. A friend of mine has an active 5 way crossover system and he had to build 10 of the amps with these same boards. He used Marchand's PCB for the active crossovers and construed 8 enclosures for the drivers. We just tweaked them a few hours ago and went over my power supply design that is still not complete.
The basic forumula is Q=CV=IT.
For a 200 watt amplifier I would use 10,000uF per rail.
That could get a 'little' expensive with a 400 watt amp not to mention the inrush current on power up.
G²
Most amps will be way underpowered following this rule of thumb.
Is this value the same for both linear and SMPS?Lets see, I got 20000uf shared between 2 channels, so only 10wpc? But don't think I listen half that loud anyway.
But AFAIK caps with bigger power density and lower size/cost have poorer performance compared to smaller caps? Am I right to say that? If that's the case, (unless going for the 100 caps in parallel approach) there'd need a big cap, some smaller ones closer to the load, some even smaller ones etc.
What's your take in the ratio of capactance and capacitor size in this case?
Some idle thought:
For same load
Power is proportional to V^2, charge is proportional to C & V
So in order to increase the power by increasing voltage, C needs to increase at the same rate as V to keep the ratio between V^2 and CV constant. This woud mean C is proportional to root of power
Or...
For same supply voltage
Power is proportional to current, so C is proportional to power for same time constant
Which is correct? Or they're both correct for the different scenarios?
(Oh nvm, I see why already - case 1 increases both current and voltage at the same rate, and charge increases along with voltage. Case 2 the capacitors don't get extra charge)
Or 3rd choice - just forget about maths and overkill the reservoir ^_^
For same load
Power is proportional to V^2, charge is proportional to C & V
So in order to increase the power by increasing voltage, C needs to increase at the same rate as V to keep the ratio between V^2 and CV constant. This woud mean C is proportional to root of power
Or...
For same supply voltage
Power is proportional to current, so C is proportional to power for same time constant
Which is correct? Or they're both correct for the different scenarios?
(Oh nvm, I see why already - case 1 increases both current and voltage at the same rate, and charge increases along with voltage. Case 2 the capacitors don't get extra charge)
Or 3rd choice - just forget about maths and overkill the reservoir ^_^
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.