Class A Mosfet Amplifier and PS

[Kinnja]

Hello,

This is my first project built without a kit, and my fourth ever.

Here is the link: http://diyaudioprojects.com/Solid/ZCA/index.htm

I'll attach the amp schematic on this post, and the power supply schematic on the next one. The above web site has been unavailable at times the last few days.

I would be grateful for any answers or advice.

--One resistance is shown as 15R/40W, could I use four 60 Ohm, 10W resistors connected in parallel here?

--Where the wattages of the resistors are not specified, does it matter, or would a half or quarter watt be ok?

--What voltage should the capacitors be, or does it not matter?

--How important is it to match the exact capacitance on the schematic, is it ok to go a little higher or lower?

--Is it ok to connect smaller caps in parallel to get larger cap values?

[Kinnja]

Here is the Power Supply schematic.

--Same questions about the caps, would it be ok for example to replace the low ESR 450uF cap with a low ESR 470uF?

--And do the cap voltages matter?

--What specs to I look for in a transformer for this power supply?

Thanks

[Luke]

hi Kinnja

before you decide on this design, are you aware this thing outputs somewhere between 5-10 watts of power? That means you need really efficent speakers to get the best out this amp.

"--One resistance is shown as 15R/40W, could I use four 60 Ohm, 10W resistors connected in parallel here?"

yes

"--Where the wattages of the resistors are not specified, does it matter, or would a half or quarter watt be ok?"

The schematic says to use 0.5 watt reistors unless marked.

"--What voltage should the capacitors be, or does it not matter?"

The rails are 24 volts, so if you use 35V or more all should be well.

"--How important is it to match the exact capacitance on the schematic, is it ok to go a little higher or lower?"

yes can vary a bit and wont make much difference.

"--Is it ok to connect smaller caps in parallel to get larger cap values?"

yes

"--What specs to I look for in a transformer for this power supply?"

Typically you would use a transformer rated at minimum twice the power that a class A amp consumes, preferably 3 times. The author states the amp comsumes 60watts but i think its more like 40, so 120VA to 180va should work fine, even bigger is better.

good luck and hope it sounds good:-)

[Tom2]

Kinnja,

I believe there is a mistake on the power amp schematic.
The polarity of 33uF tantalum cap is backwards.
The positive connection of the cap should connect to the 100k wiper.
You should email (Mark Houston) to confirm this.

Tom

[Minion]

I think this amp actually only puts out 1w of power, at least that is what the Site says.....The Design is very simular to the Mosfet Headphone driver accept useing a Lateral Mosfet....

[Kinnja]

Originally posted by Luke
hi Kinnja

...before you decide on this design, are you aware this thing outputs somewhere between 5-10 watts of power?...

Typically you would use a transformer rated at minimum twice the power that a class A amp consumes, preferably 3 times. The author states the amp comsumes 60watts but i think its more like 40, so 120VA to 180va should work fine, even bigger is better....

Originally posted by Tom2
Kinnja,

I believe there is a mistake on the power amp schematic.
The polarity of 33uF tantalum cap is backwards.
The positive connection of the cap should connect to the 100k wiper.
You should email (Mark Houston) to confirm this.

Tom

Originally posted by Minion
I think this amp actually only puts out 1w of power, at least that is what the Site says.....The Design is very simular to the Mosfet Headphone driver accept useing a Lateral Mosfet....

All the info is very much appreciated. I'll send him an email about that cap. Its ok if the amp does only put out 1W, I want to hear a Class A amp, and I would like some high efficiency speakers anyway.

[Luke]

all that effort for 1 watt , hope its a good watt

[Kinnja]

Originally posted by Luke
all that effort for 1 watt , hope its a good watt

One watt isn't much is it? The actual number should be around 5W. On the web page he says he burns up over 60W to get 5W Class A.

[Kinnja]

Originally posted by Tom2
Kinnja,

I believe there is a mistake on the power amp schematic.
The polarity of 33uF tantalum cap is backwards.
The positive connection of the cap should connect to the 100k wiper.
You should email (Mark Houston) to confirm this.

Tom

I sent an email, I haven't heard back from him yet but its only been a couple days.

I also noticed that the positive terminal of the speaker is connected to ground. If I build it as is, I guess I can get a cheap speaker, and stand clear of that cap when I plug it in. Hopefully only the cap would get fried. On the web site, he has an article by someone who built the amp, and he didn't say anything about any mistakes on the schematic though.

http://diyaudioprojects.com/Solid/Cl...sfet/index.htm

[Tom2]

Kinnja,

The schematic on the website looks correct now. (fixed?)
The positive of the 33uF now goes to the 100k wiper.

Tom