looking for opinions on amp design.

[armstrom]

To make a long story short, I picked up this power amp kit for $10 to meet a minimum order requirement .  I wanted to see if I could get any opinions on the quality of the design. It's sold as a 30W amp and takes a single +50V power supply. The kit included a couple of heat sinks for the output transistors but I may upgrade to something larger. Here's a link to the instructions with a schematic. Note: The component values are not shown in the schematic (I guess they want you to buy the kit, since they are listed in the printed version of the document included with the kit).

Here's the document:
http://www.mr2-power.com/FK656E-1.pdf

I can supply specific component values if it would be helpful.

I have a couple of specific questions:
1) Am I giving up anything by using a circuit with a single positive power supply rather than the typical bipolar supplies you see on amps like this?

2) Can someone explain how the power supply design they show in the drawing can result in 50V DC? They say to use a 31-0-31 center tapped transformer... Wouldn't that result in closer to 80V DC after it's rectified?
Edit: Nevermind... I think I understand.. Since they used the center tap as the ground reference the two ends of the secondary are tied together in parallel resulting in a +31V AC voltage potential before being rectified... that would result in somewhere around 45V DC after rectification... In theory I could probably get away with a 35-0-35 transformer.


I plan to build the amp regardless (it was only $10 after all) but I would like to know what I'm in for as far as sound quality and robustness of the design.


Thanks in advance,
-Matt

[J M Fahey]

1)Somewhat old design but should work reasonably well. However, no matter what the brochure says, it has *NO* short protection;so just be careful.
2) If you already have the transformer, use it. If you have to buy one, a single 30 to 36VAC ;  60VA or higher transformer, rectified with a bridge (4 diodes) will be more efficient and somewhat easier/cheaper to find.
Good luck with your project.

[armstrom]

Thanks for the reply!

Is there an easy way to protect the outputs with external circuitry?

I don't have a transformer yet so I will probably do as you suggest and just get a single secondary transformer.

What do you think of these more powerful designs from the same company?
"50W" http://www.futurekit.com/basic_elec/FK660E-2.pdf
"100W" http://www.futurekit.com/basic_elec/FK666E-1.pdf
-Matt