PASS 50W single ended mosfet amp.

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pre65
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#1 PASS 50W single ended mosfet amp.

Post by pre65 »

First thing I need to think about is a power supply.

It needs 60v @ 3.5A, but it seems a total capacity of 3X is recommended. So a big transformer (or two) is needed.

My initial thought (for cost reasons) was to use my 1000va isolation transformers, one per monoblock. Parallel the two secondarys to get 120v AC then rectify and smooth.

Is this a good move ?
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#2 Re: PASS 50W single ended mosfet amp.

Post by Cressy Snr »

Cant see why not. Those TXs are big b'stards; more than man enough for the job.
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#3 Re: PASS 50W single ended mosfet amp.

Post by Nick »

Other than 120v giving you 165v
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#4 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Nick wrote:Other than 120v giving you 165v
Yes, understood Nick.

And getting down to 60v needs several meaty (and hot) resistors. :wink:

As usual, I like to try and use what is "in stock".
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#5 Re: PASS 50W single ended mosfet amp.

Post by Nick »

As usual, I like to try and use what is "in stock".
Well good luck to you, but consider what that cost saving will cost you.

On the one hand you save a transformer.

You need a 200v 10000uf (say) cap, say £35
You need to then drop 100v which at 3.5A will be 350w of heat, so thats maybe £25 of resistor on £30 of heatsink and a huge amount of heat
Then a 100v 22000uf cap, say £30.

So thats £120

Or you get a 45v 500va transformer to give you the 3 times over size, which you wont have in the first case because of the resistor. (though not sure why you need to overspec is there is a CCS in the circuit) say £50. Plus a 22000uf 100v cap, £30.

So you will be spending £40 more and have to buy a lot of stuff, and have a worst supply, and have a bigger electricity bill, and a hot room. Just to use one thing you already have in stock. Sometimes if you want good results, you need to use the right things.
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#6 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Point well made Nick (as usual). :oops:

I had tried PSU designer and found it might not be as easy as I thought.

So, onto plan B. :wink:
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#7 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Re the 22000uf @ 100V caps. I have some large Rifa 22000uf @ 64v caps and was thinking up using 2 in series.

I'll see how it looks in PSU designer when I've sourced the transformers.
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#8 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Question for Nick, where is a good place to get decent toroidal transformers in the UK these days ?

I have used Antek in the USA in the past, but prices have now risen (plus duty) and the delivery's take time.
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#9 Re: PASS 50W single ended mosfet amp.

Post by cressy »

Last toroids I got came from transtronic in Chesterfield
Dunno what their range is like these days as it was a few years ago
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#10 Re: PASS 50W single ended mosfet amp.

Post by Nick »

For this I would have said Rapid. A off the shelf Vigotronix should be fine.
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#11 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

OK, time to re-evaluate. :lol:

Bearing in mind Nicks comment about the CCS and doubting the need to overspec the transformers, I have decided to build iteration 1) with in stock parts.

Namely 2 X 250va 44v (two 22v secs) toroids and 2 X 195zj Hammond 5A chokes. These with a bridge rectifier and my 22000uf caps should see just shy of 54v @ 3.5A in cap input according to PSU designer.

I'm going to use one (two) of Mikes interstages as the input transformer in 1-2 mode, I have these, and the Jensen ones specified don't seem to be available in the UK.

This should give me an idea if the amp is to my liking without spending too much.

The heatsinks I have should cope, so the biggest expense is the Mosfets themselves.
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#12 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Here is the circuit.

Image
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#13 Re: PASS 50W single ended mosfet amp.

Post by Mike H »

Phil I've just had a radical thought, how many 1000VA transformers have you got? Cos if you've got four, then you could use two of them to drop the 240V UK mains to 120VAC, input that into the other two, and that will then give 60VAC from their secondaries in parallel. (?)
 
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#14 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

WOW.

Two 1000va transformers per monoblock.

I'm thinking about it. :wink:
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#15 Re: PASS 50W single ended mosfet amp.

Post by Mike H »

Well it'll make them look the dog's danglies anyway. :lol:

EDIT: has to be better than umpteen zillion very hot resistors.
 
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