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Old 14th September 2011, 10:59 PM   #281
ManicP is offline ManicP  Serbia
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One more amplifier done Few more pics at baby diya
Complete amp and case are home made. 4 pairs of output MOSFETS, 1,6A bias.
I'm waiting cold weather to fire up my new heater...
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Old 22nd September 2011, 05:30 PM   #282
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Wonderful amp Juma. I was worried that it would be cold or critical sounding, but it is not in the least. It has better control over the bottom end than the AJ mono's I have. Still comparing and have had little real time with it. Hope to listen more this weekend.
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Old 23rd September 2011, 11:17 AM   #283
juma is offline juma  Germany
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Thanks Buzz, glad you like it so far

In the first place, thanks to Mr. Pass for this nice topology - I just used somewhat better output devices...
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Old 23rd September 2011, 11:39 AM   #284
Tea-Bag is offline Tea-Bag  United States
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I've been playing with a few different of the Toshiba's and the older school fairchilds.
I will say (OT here of course) that the fairchilds with the R1 layout sounds a bit tamer. In a good way. It may be encouraging for someone to try a FQP variations (to-220) with a combo juma/papa layout. Just sayin.
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Old 23rd September 2011, 12:14 PM   #285
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Its interesting, there is o doubt that it has wonderful control over the speakers. This is shows up especially well in the low end. I also don't need to turn it up as much as the AJ's to get deep into the recording with clairty. One thing I am holding off on is whether or not it has the sweet top end that the AJ's have. I have ot heard it o my good speakers, as i finished the amp while on vacation and was only able to bring small bookshelf speakers. I also did not bring my DAC and have been limited to using the old chip in my CD player. THings should get interesting when I get home and can plug it into my reference system. I have the BA-3 boards waiting at home and have heard good things.
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Old 25th September 2011, 08:14 PM   #286
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More comments. I plugged the J5 into my main system. Sounds wonderful from top to bottom. I can only suggest you build it. After hearing it, I am looking forward to BA-3 and may even build a BA version of this with feedback. This may be a circuit worth X-ing. Had some trouble, but as always, mistakes helped me learn. I think these mosfets are a bit more sensitive than the IRF stuff I have used. Just speculation, no proof. Kudos Juma!
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Old 28th September 2011, 12:05 PM   #287
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Juma,
I am interested in you preamp and have a question. When adding extra source resistance, does this just increase voltage drop(negative voltage) on source, lowering the gain or, does it create a voltage divider, since if is attached to opposing rail, presenting different dc point to sourcehaving same affect affecring gain? The connection to the other rail is throwing me.
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Old 28th September 2011, 03:09 PM   #288
juma is offline juma  Germany
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Quote:
Originally Posted by buzzforb View Post
Juma,
I am interested in you preamp...
If you mean BF862 based preamp, let's talk about it in its own thread, ok?
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Old 28th September 2011, 04:14 PM   #289
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Nope, the preamp version in post 42, I think.
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Old 28th September 2011, 04:45 PM   #290
juma is offline juma  Germany
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Buzz, it's very simple - in standard F5, JFET's sources are connected to GND potential (0V). In the preamp from post #42 I connected k170's source to negative and j74's source to positive potential in order to bias JFETs with same, high current but with raised value of source resistors to allow for higher value of feedback resistors that will not overload the output.
Yes, it lowers the OLG (since JFET sources are being strongly degenerated this way) but it actually improves the total linearity of the circuit and you need less NFB through the loop.
Anyway, this is preamp (or headamp) and we usually need less gain (6-12 db) from it.
Prakit built it his way (post #188) and he liked it as well as I did...
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