"SiC Puppy SE Amp Using Semisouth 085 JFET - Page 13 - diyAudio
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Old 25th October 2012, 08:47 PM   #121
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You should start another thread for this guy, as it has more aspects than a cat has hair. I've been thinking of doing a push-pull for quite some time myself, and there are many ideas from the tube world that could be adapted. I'm also awash in tube iron now, so I could throw a couple of pieces at a project like this. I'll probably wait until I flush all my single-ended projects through the system. The amp in my "Das Ist Aber Schade" thread hasn't even been powered up....

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Old 25th October 2012, 09:02 PM   #122
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Received a parcel today from DigiKey, with 4 x CMF10120D-ND, let's see... However, I would not run them below 40V D-S, though, but for 400V B+ they should be fine...
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Old 26th October 2012, 11:29 AM   #123
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Quote:
Originally Posted by wrenchone View Post
You should start another thread for this guy, as it has more aspects than a cat has hair. I've been thinking of doing a push-pull for quite some time myself, and there are many ideas from the tube world that could be adapted. I'm also awash in tube iron now, so I could throw a couple of pieces at a project like this. I'll probably wait until I flush all my single-ended projects through the system. The amp in my "Das Ist Aber Schade" thread hasn't even been powered up....
Hi wrenchone,

thats a good idea, in no way I meant to hijack your thread here... actually I like what you are doing and even quoted you in the article ;-)
Just wanted to add my experiences with the Semisouth JFETs...
By the way, the iron I used for the P-P output transformers are regular power supply toroids (2x 115V / 2x 12V / 240VA) , little cost but great results

will look for that other thread, the name is great!
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Old 26th October 2012, 06:06 PM   #124
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I wan't really peeved, but your effort is sufficiciently different that it deserves a thread of it's own. I think it's neat that people are finally getting around to dropping silicon (and more exotic materials) into traditional tube circuits. The "Das Ist Aber Schade" effort could be morphed into a push-pull topology without too much extra effort. I'll save more extensive comments for the new thread...
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Old 7th November 2012, 04:34 AM   #125
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I gave the Puppy some play in the living room last night, and I'm thinking it's special - that extra bit of clarity.
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Old 23rd March 2013, 08:18 PM   #126
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Attached is a photo of the first proto of an SE amplifier( the "SiC Puppy") using the Semisouth 085 silicon carbide JFET in the output stage. The front end uses the Supertex DN2540N5 depletion mode mosfet. I choose the Semisouth part over the IXYS depletion mode parts due to the extra headroom afforded by the 1200V rating, allowing me to choose B+ voltages with a bit more freedom. The circuit (to follow) is set up just as if the two parts were pentodes, with partial feedback from the output drain to the input drain, plus a limited amount of global feedback (disconnected at firtst. I used the One Electron UBT-1 1.6k transformer because I had a pair on hand. The output stage bias is set for the maximum primary current rating of the UBT-1 (150 ma). Next is a power-up with a DC supply to chcek stability of the output bias.
The heat sink is one of Papa Zen's giveaways from the very first Burning Amp in October 2007. I'm thinking of running the amp in a dual mono configuration using a pair of ~150VA step-up/isolation tansformers, which when configured for 230V output and rectified will give me ~320VDC B+. There is an on-board capacitance multiplier for ripple reduction, feeding a 270uF bulk capacitor.

More to come - this is just the first heads-up.
I would really love to see your schematic.
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Old 24th March 2013, 01:11 AM   #127
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Then you should read the whole thread. The schematic there is the only one that's available at this time.
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Old 23rd September 2013, 03:51 AM   #128
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I threw the SiC Puppy on the HP4194A gain-phase analyzer this afternoon, and got squirreley behavior near and beyond gain crossover, no doubt due to the output transformer. To add extra sauce, the scans for each channel were different, possibly due to changes in output transformers, even though they are the same vendor/part number (very different revs, obviously). Some extra compensation and a damping network will be needed so that things line up with my expectations. I'll document when I get results that satisfy me.
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Old 23rd September 2013, 11:58 PM   #129
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I added some compensation around the feedback resistors of the Sic Puppy and got the resulting gain-phase plots. Each plot shows one channel of the amplifier. The top plot shows the "good" channel, with a resonance appearing at somewhere between 3-4 MHz. The second "bad" channel shows a resonance occurring at ~500 kHz, and a second one in the same place as the good channel. In both plots, the gain crosses 0 dB, then pops up above zero at higher frequency. This is an indication of possible trouble with a difficult load (like a speaker, for example), and is something that needs to be fixed.
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File Type: gif Sic_Pup_G-P_NZ.GIF (47.8 KB, 150 views)
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Old 24th September 2013, 12:07 AM   #130
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This next set of plots shows the gain and phase with a 20 ohm + 33 nF Zobel network placed agross the output. The bottom plot shows the good channel. The Zobel has pushed the high frequency gain down such that it always stays below 0 dB after gain crossover. That's a good thing.

The top plot shows the bad channel. The Zobel in this case also keeps the gain below 0 dB after crossover, but the gain crossover frequency is defined by the first resonance, which is a problem. I was blaming this extra resonance on the output transformer, but there may also be a problem in that channel that I don't understand. Switching the transformers would be an easy way to ascertain that, and I may try it tonight.
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File Type: gif Sic_Pup_G-P_WZ.GIF (46.7 KB, 144 views)
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