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Old 20th February 2009, 11:09 PM   #121
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Do we have an image of the finished beast?

Any measurements at all?

How about a picture off a scope of the square wave at say 10kHz into a 4 ohm load??

Came over here today to look at it a bit from the Blowtorch thread... = <bump>



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Old 21st February 2009, 12:17 AM   #122
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Bear,
I thought I mentioned some specs somewhere...if not, I'll try to scratch up some notes or toss one on the bench and re-fiddle. I'm at work (slow night, cross fingers it remains so) and can't just scamper off to look for paperwork. Given that it's been a year or so, I might have to dig.
From memory, the distortion is just under .1%, the primary culprit being the MOSFETs' Gate capacitance. Increasing the current in the driver stage drove (couldn't resist...) the distortion down something like .1% just for that one tweak.
I don't have a picture of the 10kHz square response, but it was essentially perfect. If I get one on the bench, I'll try to coerce my wife into taking a picture of the screen, as she's the one with the camera.
Bandwidth...oh, bother...I don't remember. 300kHz, maybe?
They still look pretty much the same as the pictures on the first page of the thread. I related this story somewhere, perhaps in this thread, perhaps in another, don't remember: Living where I live, metalwork is hard to come by and I've got a pretty clear idea of what I want--don't want an off the shelf sheet metal chassis. Those two factors are in conflict, unfortunately. I'd spent a week calling around before finally finding a shop that would even talk to me about a small job like this. They wanted drawings before they'd talk price--not an unreasonable request--so I started setting out what I wanted. I was just about ready to go when my wife came to me and said that her tooth hurt. She ended up needing a crown. For some reason only an accountant could love, insurance didn't cover it, which meant the money I'd set aside for metalwork went into porcelainwork in her mouth. I've not gotten back to the chassis aspect since.
I believe I mentioned that I was going to try bipolars. I am currently working up a line stage using JFET complementary differentials at the input, followed by bipolars. A variation on that will, in time, become the Version 3.0 front end (still MOSFET outputs). If nothing else, I'd like to get away from the Vgs variations that led to the adjustment pots in the front end--even though I Vgs-matched the MOSFETs. It works just peachy the way it is, but I'd like to make it more user friendly and those pots are a pain in the butt.

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Old 21st February 2009, 12:29 AM   #123
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Post 13 you talk about the specs.

JJ
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Old 21st February 2009, 01:06 AM   #124
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Thanks.

Grey
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Old 21st February 2009, 06:54 AM   #125
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Quote:
Originally posted by bear

How about a picture off a scope of the square wave at say 10kHz into a 4 ohm load??

Bear -
would you mind to see mine? Scale per division in left top corner, it is 10kHz into 4 ohm. Non-global feedback power amp, 1A idle current.
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File Type: png a1_double_step_s.png (27.0 KB, 463 views)
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Old 22nd February 2009, 03:27 AM   #126
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A "pinup"

Pavel, no output inductor?
Or, how does it look with a capacitive load... maybe this belongs on a different thread though...

That's the type of picture I would love to see posted for any amp project. The specs are nice, but being "old school" I like to see the square wave.

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Old 22nd February 2009, 09:35 AM   #127
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Quote:
Originally posted by bear
[B]... maybe this belongs on a different thread though...
definitely ....

About power amp step response etc. :-)
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Old 23rd February 2009, 09:03 PM   #128
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Dear Grey,
I just read with interest your GR-25 thread. Have you ever gotten to the 100W one?
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Old 23rd February 2009, 11:38 PM   #129
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Afraid not. Not that I don't want to, but I'm in such dire condition time-wise that I've only managed about 20 minutes at my bench since December. And most of that twenty minutes was spent trying to figure out where I had left off because I had changed things since my last known configuration. I usually try to leave a trail of breadcrumbs for myself, knowing that this sort of thing happens, but either I didn't get a note written or the note got lost.
Or maybe it was the mice who sewed the cobbler's shoes...maybe they were trying to tell me something. Perhaps I should become fluent in Mouse.
At this point, I might as well wait until I get the Ver. 3.0 front end ready, as it will have some bells and whistles that will make the front end easier to work with.
I spoke with my wife this weekend about taking a picture of a square wave for you folks. She agreed, but all three young 'uns are sick and it didn't get done, due to all the fetchin' and totin' and runnin' around.

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Old 24th February 2009, 12:04 AM   #130
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Okay,
Please hold your fort and please drop us a word once there will be some news.
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