new to amp design

neurot

Member
2001-07-08 1:57 am
TX
I have read Mr. Slones book and I will be taking more classes next semester about basic electronics, so I don't have boatloads of knowledge.

Regarding the power supply/transformers and calculations for VA ratings, I noticed that if the current was higher ( ex. 5A and 100V as opposed to 4A and 125V) the wattage output is higher. As I am new to this, I would just like to understand how this happens. But after looking at the Seal electronics site, the VA rating and the secondary voltage was lower than what I was calculating, which was odd to me because I just worked the problem both forward and back and was getting higher numbers. Is there a broad range of numbers to use for transformers for a specific power output?

Also, is it possible to increase the power supply, but leave the amplifier circuitry the same to increase output? Or is there something aside from power output thats dependent on an exact amount for the voltage rails inside the amp circuit?

Thanks for any help.
 
With a given transformer rating, specify the voltage
first and then you can change the current rating to
get the power output you want. Power is voltage times
current and can vary voltage and current in either
direction to get a given power rating for the transformer,
but not necessarily for a specific amplifier design.

You can increase the power supply voltage somewhat,
but run an increased risk of exceeding the voltage rating
of one or more components, and the current rating of
the output transistors (the Safe Operating Area) into
a given load.

Output power is a function of the load impendance and
the voltage swing; a solid state amplifier can deliver
roughly twice the power into a four ohm load than it can
into an eight ohm load. (A transformer-coupled tube amplifier can match itself to a load for a constant power
output.) Just don't expect to >reliably< get four times
the power into a 2 ohm load; even if the power supply itself
could deliver the power, the output stage might fail from
overheating.

When in doubt stick to the design, or ask the designer or
someone expert for help.