ImPASSe -- transformer transplant - diyAudio
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Old 13th August 2009, 09:09 PM   #1
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Default ImPASSe -- transformer transplant

The little DYNACO PAS transformer just isn't up to the task of driving the filaments of the 6SN7/6922, let alone the RIAA (and what to do with the elevated filament?) so I got a couple of the Allied Transformers SY mentioned in the article and fit it via the back panel of the PAS. The preamp worked fine when powered with my Heath HV supply:

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Old 14th August 2009, 10:43 AM   #2
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What kind of power amp are you driving with it?
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Old 15th August 2009, 02:54 PM   #3
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The problem is entirely related to the Dynaco transformer -- as soon as the preamp starts to draw some current the output sags -- with my Heath regulated supply it isn't an issue at all.

I have had it drive an Audio Research amp, but will be employed with 4 F4's !

the 5V secondary is going to drive the filaments of the RIAA section as I will put a doubler on it -- I think you can see the RIAA in the picture -- uses the stock board with a more accurate network.

At any rate, here's a board design which I worked out -- has the diodes and filter caps along with SY's non-Darlington MAIDA. I use a pair of 3W resistors on the ADJ pin of the LM317 as they are cheaper:

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I don't think I will be able to squeeze it onto to the PAS chassis.

I pull all the ground returns to the butt-end of C101 by using the top layer exclusively for Node "0" -- elsewise the design can be done single-sided.
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Old 17th August 2009, 03:51 PM   #4
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Well, I can't find a smaller 47u/450V cap so I've had to fit in one with 22mm diameter. the 100u/450V caps are 22 or 25mm -- the board is a bit bigger now 2.5 * 3.5 inches -- and it's pretty snug:

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Old 17th August 2009, 05:44 PM   #5
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With the new he-man sized electrolytics (and film) caps:

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Old 17th August 2009, 09:23 PM   #6
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what problem does adding the bigger caps address? I'm not sure I follow, or is this total non-sequitor
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Old 17th August 2009, 10:16 PM   #7
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Quote:
Originally posted by luvdunhill
what problem does adding the bigger caps address? I'm not sure I follow, or is this total non-sequitor
The 100uF/450V and 47u/450V caps are either 22mm or 25mm diameter -- I had a smaller one in the original design -- I have some skinny HV caps liberated from a switching supply, but can't find them.

Allied has the UF4007 rectifier diodes -- for the most part I have used 1N4007 as I got a thousand on EBay 8 years ago for $10!
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