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.
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...
In the first place, thanks to Mr. Pass for this nice topology - I just used somewhat better output devices...
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.
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.
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.
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!
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.
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.
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...
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...
I built both versions. The version optimized as a line amp is a clear improvement. The gain is about right. Everyone who build this F5 with K2013/J313 should build this pre too. You will love it! 
:up to Juma
:up to Juma
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ManicP,
Nicely made chassis. Very generous HS. It shouldn't be too hot, isn't it?
What did you use to cut square holes on the top plate? CNC? And how did you fix the grill to the top plate?
Best regards
Nicely made chassis. Very generous HS. It shouldn't be too hot, isn't it?
What did you use to cut square holes on the top plate? CNC? And how did you fix the grill to the top plate?
Best regards
So this just increases Vgs, which increases current and gain, which is then thrown away through degeneration.
There is no increase in both Vgs (of JFETs and MOSFETs) - it stays the same as in power amp version. That is the whole trick - to keep the same working conditions and be able to use higher value source and feedback resistors. Only thing that has been changed is OLG but we don't care about it since linearity is preserved and we don't need much gain anyway...
So most of the voltage potential that is added is just immediately thrown away with the extra degeneration. Vgs stays the same, but how you get there changes. It would seem this could be used in a no feedback setup like BA-3, but that is perhaps a misunderstanding on my part. Looks like I will have to build it to really get a handle on it. I learned quite a bit when building the power amp version, but apparently not enough.
Please, rad the post #290 once again, but carefully and compare the schematics of the post #42 preamp and the power amp. Keep the Ohms Law in mind all the time...
Thanks for taking the time Juma. Just got done listening to your F5 and Symphonie Fantastique. Now listening to Joni Mitchell.
On power amp version with source tied to ground, all voltages must sum to 15V. With source tied to negative rail, voltages must sum to 30v. In grounded, power amp version, limited voltage drop available to source for degeneration, but with preamp version more voltage available to source for degeneration.
All the above is the answer you gave your teacher that was in the form of a question rather than an answer.
Either way, the components are in the mail to build the thing, so I will know soon enough.
All the above is the answer you gave your teacher that was in the form of a question rather than an answer.
Either way, the components are in the mail to build the thing, so I will know soon enough.
Link in post #1 works all right (copy and paste into the new browser tab/window):
[special=http://www.diyaudio.rs/topic/1991-novi-amp-sa-2sk20132sj313]%[/special]
It's the thread that is being locked, but you can browse through it without problems (posts #1 and #25)
[special=http://www.diyaudio.rs/topic/1991-novi-amp-sa-2sk20132sj313]%[/special]
It's the thread that is being locked, but you can browse through it without problems (posts #1 and #25)
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