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 Post subject: Re: 12AU7/IRF612 updatePosted: 04 Dec 2008, 00:18
 Project Author

Joined: 03 Aug 2008, 20:22
Posts: 386
Well the correct way is to determine how much ripple is acceptable on the output. So lets go with 1%, and for 12V 12 * .01= .12 rms x2.828 = .339 p-p of ripple. For C = (load current x charge time / V rip) x 1E+6.

The amp draw about 500mA and the charge time in the US is ~8.3mS

C = (.5 x .0083 / .339) X 1E+6 = 12241.8 Uf

That is a large cap so you could go with a 10, 000uF 25v or as I did in my other amp use a pi network of 3300Uf -- 47R -- 3300UF, remember the resistor will drop some of the voltage. The higher the capacitance the more it will filter, but then there is reactance involved as well.

In short 3300uf 4700uF should be ok for a Pi filter 10,000 for a single cap.

After playing with ps for a little bit I like to take the pi filtering out to three stages.

If anyone else have better values for a three stage please chime in.

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 Post subject: Re: 12AU7/IRF612 updatePosted: 22 Dec 2008, 17:43

Joined: 01 Dec 2008, 10:38
Posts: 14
Location: Georgia
You have to excuse my ignorance
What is the advantage of going with a the pi setup as opposed to a single cap?
Thanks for the help, not sure if I will build the PS for this I found a medical grade PS thats has .05% ripple so might just go ahead and use it.

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 Post subject: Re: 12AU7/IRF612 updatePosted: 22 Dec 2008, 23:25
 Project Author

Joined: 03 Aug 2008, 20:22
Posts: 386
The advantage of a pi filter is that you can reduce ripple with smaller value caps. This saves space and cost. Dont get me wrong I am all for using a good power supply if it is available, but now that I am building higher voltage gear it is more practical. The good thing is if there is still a little hum add another rc stage, just not enough that it effects the plate curve.
Medical grade? Are you a biomed?

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 Post subject: Re: 12AU7/IRF612 updatePosted: 24 Dec 2008, 18:19

Joined: 01 Dec 2008, 10:38
Posts: 14
Location: Georgia
Im not, I am an EE student so I am still learning this stuff.

My father works in biomed at a local hospital so anything that is scrapped I end up with it. I got some nice wima caps for the headphone amp cant wait to put this thing together.

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 Post subject: Re: 12AU7/IRF612 updatePosted: 30 Dec 2008, 21:26
 Project Author

Joined: 14 Oct 2008, 17:35
Posts: 906
Location: Dartmouth, Nova Scotia
I guess I had better start gathering parts to build my amplifier, hopefully it will work with the IRF630 since I've got a dozen of them laying around, hmmmm I wonder If I have any other large fets. I just bought this mini case from Hammond to have some fun with!

_________________
My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700

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 Post subject: Re: 12AU7/IRF612 updatePosted: 01 Jan 2009, 01:36
 Project Author

Joined: 03 Aug 2008, 20:22
Posts: 386
I ran the IRF630 through the sim and it actually has a flatter curve on the high end. Should be a nice improvement.

Rogers

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 Post subject: Re: 12AU7/IRF612 updatePosted: 01 Jan 2009, 22:35
 Project Author

Joined: 14 Oct 2008, 17:35
Posts: 906
Location: Dartmouth, Nova Scotia
Really! I salvaged many of them from old computer monitors. I also have IRF610 x2, IRF640's and who knows how many other versions I have, lots of large fets from dead computer monitors and power supplies.

I'm also guessing it is possible to use Gio's CCS using the LM317 regulator?

_________________
My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700

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 Post subject: Re: 12AU7/IRF612 updatePosted: 01 Jan 2009, 22:44
 Project Author

Joined: 03 Aug 2008, 20:22
Posts: 386
Yes it will bump the efficiency of the amp up significantly, and if you can source a clear top 12AU7 it sounds the best in this amp.

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 Post subject: Re: 12AU7/IRF612 updatePosted: 01 Jan 2009, 22:58
 Project Author

Joined: 14 Oct 2008, 17:35
Posts: 906
Location: Dartmouth, Nova Scotia
Hmmmm, I think I have a couple of RCA 12AU7's and from what I remember they were clear tops!

When I finish my mini headphone amp I shall begin building and expearmenting with this one.

_________________
My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700

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 Post subject: Re: 12AU7/IRF612 updatePosted: 02 Jan 2009, 11:18
 Editor

Joined: 28 May 2008, 21:53
Posts: 4592
CrazzyAbtTubes wrote:
I'm also guessing it is possible to use Gio's CCS using the LM317 regulator?

You could, but check your stash of mosfets for complimentary pairs ... they usually have a 9 in front. So a IRF9610 is a P-Channel mosfet you could use with the IRF610. That should work better than a LM317.

_________________

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