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Old 18th August 2009, 04:11 AM   #1
speedie is offline speedie  Australia
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Default budgets for mosfet amp construction

Hello all fellow fanatics
I have surfed around this site for some time and have an interest in the solid state amps that you are tinkering with
My back round is in diagnostics for air-conditioning and refrigeration, the current trend is more towards electronic control etc.
I do not have in my tool line up such things as oscilloscopes frequency generators etc but would still like to try my hand at amp building I am sure that a lot of you are self taught techs
My question is what an expected budget would be for a 100-300 watt mosfet amp in complete form cost, having never attempted these projects before it would be helpful if you could advise on expected costs etc.
Regards Speedie
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Old 18th August 2009, 06:56 AM   #2
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It would definitely cost several times more than factory built in China mass production one.
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Old 18th August 2009, 07:23 AM   #3
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I control cost by purchasing used or NOS heatsinks and transformers.

It's easier to fabricate a low wattage amp if it's your first attempt. Success build success.

If you're into class A, you can offset the lower wattages with higher efficiency speakers.
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Old 18th August 2009, 12:07 PM   #4
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Hi Speedie, as allways it is going to depend The problem with projects is that things can get out of hand. you start to think, I'll just add this it isn't that much more, and then that, and something else, and before long the total has ballooned.

As a Ball park I'd budget for between $500 and $1000 AU. for a 100-300W mosfet. Note I haven't built a new amp (apart from my gainclone) for over 20 years. My main amp is a 100W/ channel (into 8 ohms) Playmaster series 200, which is a mosfet amp. The kit originally sold for nearly $500 in 1987! (I think I picked it up for $399 on a run out sale).

The most expensive bits will be:

The transformer(s) Seriously consider getting two 300VA's for 100+ watts per channel., you can get away with one, but it will suffer if pushed hard. Dual mono will help with channel separation too.

The capacitors for the power supply. Cheap ones are cheap, good ones are expensive, epsecially here in AUS!!

The mosfets themselves, add more if you buy matched pairs (which is reccommened). Again expensive here in AUS..

The case. A nice case could easily set you back $200 or more. If you are handy with metal work you might be able to buy some nice heatsinks (there is a great aussie manufacturer who's name escapes me) and some aluminium plate, and fabricate your own case.

for transformers I'd recommend Harbuch in Hornsby, they manufacture ANTRIM transformers under licence, this is what I used in my gain clone. My 25-0-25 300VA was about $75 4 years ago... for a 100W or higher you will be looking at higher voltages and probably higher cost.

Try and keep the rail voltages down to maybe +- 50V (not sure if there are mosfets around at this voltage.. This will allow you to use 63V caps in the powersupply, which will reduce cost. 80V or 100V caps are much bigger and much more expensive!

Take a look at Rod Elliot's P101 http://sound.westhost.com/project101.htm I don't know what this amp sounds like and haven't read any reviews of it, but if you look at the ciruit it should allow you to price some parts and get a rough estimate of what it will cost to do a non kit type amp he does sell the circuit boards (something that is probably essential as layout is usually very important!).

I'm sure others can give more recommendations (and listening impressions) of various Mosfet amps you might wish to try. You might want to check out the pass labs forum. Nelson pass does lots of mosfet stuff, though I think it is pretty much all class A which won't meet your power requirements unless you have a small substation powering your house and don't mind the massive heat sinks required

Tony.
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Old 18th August 2009, 03:05 PM   #5
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Quote:
Originally posted by wintermute
nice heatsinks (there is a great aussie manufacturer who's name escapes me)
Conrad:
http://www.conradheatsinks.com
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Old 18th August 2009, 03:46 PM   #6
jcx is offline jcx  United States
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Quote:
Originally posted by Wavebourn
It would definitely cost several times more than factory built in China mass production one.

in fact it appears that buying New a cheap higher power PA (EP2500 for US$ 270 ?) would give you the chassis, Iron and lots of hardware already assembled in the right order for less than you can buy the parts alone - throw out the original amp circuit board and hack away

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Old 18th August 2009, 09:25 PM   #7
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Quote:
Originally posted by Diomedian


Conrad:
http://www.conradheatsinks.com

Yep that's the one thanks Diomedian!

Tony.
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Old 18th August 2009, 09:52 PM   #8
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As Carpenter alluded to, transformers and heat sinks are going to be your major costs up front (and then casing/ cosmetics on the back end). So it depends on which design you've gone with and your abilities to scrounge for cheap parts.

Why in particular do you want a MOSFET amp? Perhaps a 'class D' amp is a cheaper and simpler way to enter DIY?
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Old 18th August 2009, 10:11 PM   #9
ChrisA is offline ChrisA  United States
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Default Re: budgets for mosfet amp construction

Quote:
Originally posted by speedie
.....
My question is what an expected budget would be for a 100-300 watt mosfet amp in complete form cost, having never attempted these projects before it would be helpful if you could advise on expected costs etc....
There is the direct cost of the parts. Others have given estimates. But there are other start up costs too. For example you would need to buy wiire, solder and at least a few tools. This stuff can be used to built several amps. So you pay about double for the first amp. By the time you are building a third amp you have many extra parts on hand and the cost is much less.

But the real question, that is driving the cost is your spec. Why build a 300 W mosfet amp? Is the goal to learn about amps or to you really need to fill a large room with a very loud sound level. Why mosfet? There are "chip amps" and tubes (valves) that you can build with too.

If cost is an issue and the goals is education then the best plan is to build with salvaged parts. You woudn't care so much what you build so you can select a project to suit your parts. I just took home another load of junk PC power supplies. In each one are a few large capacitors and good heat sinks. I've got a transformer from an old battery charger that will make a greast power source for a solid state amp.

My advice is to build some small audio amps. Maybe a headphone amp with op amps that can run on battery power. Then move on from there while keeping an eye out for low cost parts
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Old 18th August 2009, 10:15 PM   #10
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Default Re: budgets for mosfet amp construction

Quote:
Originally posted by speedie


I do not have in my tool line up such things as oscilloscopes frequency generators etc but would still like to try my hand at amp building I am sure that a lot of you are self taught techs
My question is what an expected budget would be for a 100-300 watt mosfet amp in complete form cost, having never attempted these projects before it would be helpful if you could advise on expected costs etc.
Regards Speedie

I bought my test gear off ebay, 60 scope and 30 signal generator. For me they are vital as I make and sell amplifier modules.

As others have said its cheaper to buy a ready made one than build your own.

There are plenty of kits around for MOSFET amplifiers on the Internet.

Making your own can give a great buzz especially if you get across the high volts ! If you decide to build your own then play safe. Even +/-60 volts can give you a belt if you are not careful.
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