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Old 3rd March 2002, 09:39 AM   #1
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Default Best Dynaco MKIII driver circuit for hobbiest build?

I have a pair of MkIIIs and another for experimenting on. I was wondering if anyone had a circuit (schematic) for the input/driver that's way better than stock?

I was thinking of rolling my own, using a 12AX7 with a 1.6 ma constant current diode to make a true diff input, then cap coupling to a driver stage with a 12BH7 or 6SN7.

It'd be a lot easier for me if someone just said "use this - sounds great".

I know I can buy replacement driver boards for these amps, to use someone else's design, at $250 a pop...

I'd prefer to not spend that kind of money. I'm an EE who can solder. I've owned and modified Acoustat direct drive amps, and I'm still alive typing this in.

If you'd like to help me out, but dont want to post something publicly for me to see, write me at joejas@ihpc.net

Thanks!
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Old 3rd March 2002, 02:07 PM   #2
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Joe

I know just what you're saying. In AudioXpress, March 2001, there is an article showing a simple $20 mod. I haven't tried it but will soon. The article claims to do just what you ask - do this and it sounds great.

Phil
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Old 3rd March 2002, 06:18 PM   #3
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Default Thanks, Phil

Phil,

The articles in the back issue CD seem interesting enough to purchase for $29.99. Thanks for the pointer!
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Old 3rd March 2002, 06:43 PM   #4
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Default Re: Best Dynaco MKIII driver circuit for hobbiest build?

Quote:
Originally posted by jjasniew
I have a pair of MkIIIs and another for experimenting on. I was wondering if anyone had a circuit (schematic) for the input/driver that's way better than stock?
The front end i'm planning on using in my ST70 (and a pr of monobloc SCA35s) is Allen Wright's differential cascode circuit -- it should work wonders for Mk IIIs too.

Click the image to open in full size.

All the schematics and picturescan be found way down the page on the Vacuum State schematics page (PP-1C Power Amp).

dave
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Old 4th March 2002, 07:43 PM   #5
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Default Website down

Well, Allan doesnt want anyone to see his site at this time. I always get "connection refused". Do you have the diagrams to share?
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Old 18th March 2002, 04:14 PM   #6
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You may want to check out our site. We offer two "drop-in" modules for the MK-3. One provides a cascode differential amp with current source- it is our premium driver). The other uses a cascode gain stage direct coupled to a split load phase inverter (it is our standard driver). You can obtain the description and schematics at our webpage - www.curcioaudio.com.

Joe Curcio
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Old 18th March 2002, 05:19 PM   #7
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Default Thanks, Joe

I still havent got my Audio Express CD for last year's article, nor the paper copy I've asked for to take a look at that circuit.

Your implementation brings the number of circuits to choose from to three! The response to this question has been great!

I wonder why no one has suggested some "single ended driver with interstage transformer" type circuit? Why would the MKIII iron be unsuitable for this type of arrangement?
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Old 18th March 2002, 05:26 PM   #8
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The se driver driving a interstage transformer I think would be a good solution - it all depends upon the quality of the transformer. I'm new to this forum so I don't know what may be available in the archives however I do know that there are many discussions on the audio asylum on the use of IS transformers as phase splitters in pp power amplifiers.

Joe
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Old 18th March 2002, 06:50 PM   #9
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Default PWB-1A

Joe,

I checked out your site and it's a no-brainer. For the money, The PWB-1A is a great deal. I'm filling out the order form now.

Thanks for answering my post - you've saved me a lot of PCB layout time!
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Old 12th January 2003, 07:45 PM   #10
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Default Differential input to ST70

Hope I'm not hijacking this thread but I have an ST70 I'd like to run balanced in. I noticed the offerings on Joe's site are different for the st70 and the MKIII. Should I try to replicate the premium MKIII driver or go with the standard ST70 model?
Thanks,
Charles
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