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Old 27th April 2010, 11:10 PM   #11
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Quote:
Originally Posted by OneyedK View Post
I don't see the high gain in the driver/phasesplitter?!
It's a cascode of JFETs and BJTs. BJTs are naturally very high gain devices. It makes them highly useful in certain applications such as solid state amps where you want to drive the NFB way up, or use small collector loads to give increased bandwidths, or as CCSs.

No telling what that front end will sound like, though it's used frequently in all solid state designs where it works quite well.

Another one of those cases where you probably won't know until you try.
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Old 28th April 2010, 12:16 AM   #12
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I have a P-P amp using JFETs cascoded with triodes that works very nicely - you can see it by checking the "Kingfisher" thread. This one takes the front end to its logical conclusion - why use the triodes just to cascode the JFETs? I needed the space on the top deck anyway...

Last edited by wrenchone; 28th April 2010 at 12:18 AM. Reason: sp
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Old 4th May 2010, 05:44 AM   #13
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Amp is proceeding at a slow and steady pace. Just about all the wiring is in place on the top deck and just about all the holes are in the case, except for the pilot light, which will be a deep red first-generation GaAsP LED. The wiring harness from the SMPS to amp top deck is done, and needs to be integrated with the top deck. The bottom plate needs some ventilation holes.

Tasks remaining (not an exhaustive list)

1) Finish top deck wiring, mate with output XFMRS and in/out connectors, and bring up amp with bench supplies to match output tubes, verify bias levels and tweak compensation.

2) Modify SMPS top shield to accept AC in/DC out connectors, perform EMI scan with resistive load with supply mounted in case with shield.

3) After amp is working, disassemble to paint case and top deck.

4) Reassemble, retest, and wreak havoc...

Last edited by wrenchone; 4th May 2010 at 05:46 AM. Reason: sp
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Old 4th May 2010, 05:57 AM   #14
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5) Take it to Burning Amp.
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Old 4th May 2010, 11:29 PM   #15
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That goes without saying - It'll have some company, too, both vacuum and sand state.
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Old 5th May 2010, 03:05 AM   #16
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Old 18th July 2010, 04:12 AM   #17
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This project has been chugging along quietly in the background, taking back seat at times to some wild-a** ideas. Case and top panel are assembled,and the wiring harnesses are finished. Next step is probably integrating the top deck stuff with output transformers and connectors so I can bring up the amp in a decorous fashion with bench supplies. I'll post pictures when appropriate, but the amp is going to look a bit strange, with four stubby little compactrons sprouting out of the top of a 6" cube.
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Old 30th October 2011, 10:24 PM   #18
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This amp has been sitting around in the basement waiting for me to finish it. In the meantime I've realized that the current design does not address blocking distortion, and have come up with a somewhat different front end that direct couples to the output stage and gets rid of the problem (still sand state, though). I'll post some schematics when I get something working. Though the approach looks straightforward, it's always the actual implementation (and fitting it into a 6" cube) that's the rub. It will also require a different SMPS design, and I'll have to come up with that as well. More later...

This amp will represent another in a series of approaches to realize a push-pull design that addresses blocking distortion and imperfect matching between output tubes. When all the dust settles and I get things finished, I think there will be three or four alternative approaches. All have some sand in them, and I am defiantly unapologetic about it.
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Old 31st October 2011, 05:03 AM   #19
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I'm going to try using the same approach as I'm trying with the Devil to retool the driver board on a modified ST70 that's in progress, eliminating a lot of parts.
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Old 31st October 2011, 05:04 PM   #20
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you leave your boards bare copper - no protection ?
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