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Old 18th August 2006, 08:16 PM   #21
Zen Mod is offline Zen Mod  Serbia
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are you sure that you'll have needed DC voltage on lower mosfet's gate?

anyway-seems that 5460 is also too wimpy for task - driving even one gate of mosfet; besides-I'm not so sure that you can believe in software predictions ,it's possible that plain resistor is better sounding variant than CCS (or CS,if you wish)........I tried both variants sometime (even if not in exact Babelfish prototype) and plain vannila resistor is better for my ears;

hehe,it's not likely that Papa is pinching two resistors and one lousy BJT to save and prolong his Lab for another decade;I'm sure that he listened (more than ) both variants.......

find Jfets capable of 10mA at least (look at Papa's post few numbers above ) and try with them ; it's pretty re-searched area before "us" ...JC,NP and other old ##### measured and listened all that......

anyway-if you wish,nobody can't stop ya to make your own variant of any amp,but law's of physics are still stronger than we are
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Old 19th August 2006, 12:48 AM   #22
flg is offline flg  United States
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I'ld like to ask this question, regarding driving the output transistors. At lower voltages The IRFP044 has been said to be better. Well where are we 15V? But, I can see where you might have trouble driving all that gate charge with JFETs. But, recently the 5th generation IRFP044N has come to my attention. Have I missed something? This part has a little trouble with the Pd and the RthJ, but check out the capacitance/Gate charge numbers. Isn't it very close to the 240 parts? With greater gain? Wouldn't that be a worthwhile device for this situation??? I haven't tried any sims yet or anything. I don't remember seeing any discussions regarding it? What would be wrong with the IRFP044N device
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Old 21st August 2006, 12:12 PM   #23
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Yeah, I understand what you're saying. The MOSFETs need some drive because of the gate charge. I might just go ahead and build a mini-A type of amp instead. I have the mosfets for that anyway. I just thought JFETs might be different. Then again, maybe I will build it, if only to see if the spice predictions are in the ballpark compared to the real deal.
About the IRFP044N... If that is the only difference, it might be a real winner. If I didn't have 50 or the 240's, I would definitely consider those. Are they readily available?
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Old 21st August 2006, 02:47 PM   #24
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by nobody special
Yeah, I understand what you're saying. The MOSFETs need some drive because of the gate charge. I might just go ahead and build a mini-A type of amp instead. I have the mosfets for that anyway. I just thought JFETs might be different. Then again, maybe I will build it, if only to see if the spice predictions are in the ballpark compared to the real deal.
About the IRFP044N... If that is the only difference, it might be a real winner. If I didn't have 50 or the 240's, I would definitely consider those. Are they readily available?

just use whatever you can find easy for output mosfets;
look for input capacitance,but also for transconductance;in any case-you can always change them for something :audio approved: hehe
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Old 22nd August 2006, 01:30 AM   #25
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Well, my first thought about the 60db of gain, was something more like: That's what they do over in the Solid State Forum... Not that you are wrong or anything. And I certainly don't want to make you feel bad. I'm sure it works. But, Zen Mod's comments regarding resistors sounding better are likely due to the Pass philosophy of simplicity, restraint with the gain bis, minimal Feed Back, etc.
I would suggest trying "degenerating" some of the gain of using the active load and linearizing it also at the same time. Enough current is difenately a requirement but, most or all the Alephs only had 10mA per leg right? Driving 2, 3, 5 or whatever, pair of gain transistors??? Getting closer to that number may be a good start. But getting the JFET stage gain closer to the 9610's stage gain would also be a good start.
Just a thought.
Another thought, Have you seen the Self "Blameless Amp"? He uses a follower, I beleive he may call it a beta enhancer, driving his voltage gain stage. Back when Ckoky did the jfet amp I played around with siming a follower like that between the JFETs w/active load and the output stage. Yes it's another stage, but a simple one...
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Old 22nd August 2006, 04:24 PM   #26
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Thank you for the comments.
I knew I would probably hang myself out to dry with the active load, as far as popular opinion is concerned. I'm not so sure that it's a bad idea, though. In my opinion (and I could be totally and completely wrong) the point is not to add more gain stages. More gain stages seem to push the harmonic balance toward the higher orders. But, why not try to increase the gain on a single stage, or two? Is an active load that much different than a cascode? Maybe it is, maybe not. I would like to hear comments on this either way. If it was all bad, would Nelson have used something similar on the Aleph P1.7? Correct me if I'm wrong, but aren't the upper current sources acting as an active load?
The simulations indicate the same type of harmonic balance with the active load as without- a falling series of harmonics, only much lower in level. I know we don't design with our meters, but I can't see how this would sound worse.
I really do like the degeneration idea... maybe there is a sweet spot to be found this way; the active load giving some room to play with the open loop gain, controlled by the degeneration. Interesting idea.
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Old 22nd August 2006, 06:39 PM   #27
BillWW is offline BillWW  United States
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Default jfet clarification

Before anyone buys parts, I just wanted to make sure everyone knows the 2sj174 is not a jfet, but a mosfet. The correct jfet does not have the prefix 2s in front of it.

The correct part is j176 from www.allelectronics.com.

5 for a $1.00

If you have the zvp3310a p channel mosfet that one sounds wonderful too. I have a hard time deciding which one I like better between the zvp3310a and j176 jfet. They both have their own unique sound.

I would need to build two amps with these front ends, to try and see which one I really liked, but off of my memory from listening sessions both had qualities I liked over each other.


Regarding Nelson's diyop amp article that has been a great inspiration to all of my variations on the Aleph front end. That has been one of my favorite articles of his offerings!

His jfet matching in this article applied to N channel jfets. Would that also apply to P channel jfets except for reversing the S and G? I get the pins mixed up so if anyone is familiar I would like the exact pins to swap and to verify if this would be the best for matching the j176 jfets?

I know they are not the same as mosfet matching already according to this diyop amp article.

Bill
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Old 22nd August 2006, 07:03 PM   #28
EUVL is offline EUVL  Europe
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Just a remark, without stating what is better or worst :

J176 is a JFET from Siliconex (Vishay), transconductance 4.5mS, Ciss 20pF, noise 20nV-sqrt(Hz).
2SJ74 is a JFET from Toshiba, transconductance 22mS, Ciss 105pF, noise 0.95nV-sqrt(Hz).

I use both, but Vishay mostly as cascode or current source.


Patrick
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Old 22nd August 2006, 08:06 PM   #29
Zen Mod is offline Zen Mod  Serbia
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complementary pair for J176 is?

if any....


5 for a buck.....
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Old 23rd August 2006, 12:46 AM   #30
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nobody special, Yes, I agree with everything you said, I think. Even regarding the beta enhancer... Your not hanging youself out your trying things. I like to try all these ideas on the sim too What sim do you use
I don't have to much to say about the active loading vs. the cascode. I believe the cascode idea relies more on the gain device and it's characteristics at a stable drain voltage. With the active load you are introducing an apposing load that tries to maintain a stable current By using a complementary device it would seem, it's the way to go. There is more to understand there but I'm not sure I do
Yes, the 1.7 uses this techniqe, along with many others. I think there is some publeshed Doug Self info(for free) regarding the Blamesess design that may be informative. I'm not sure where though... I may have it saved somewhere here. He goes through optimizing each stage.
Thanks EUVL, I know the ones I have are JFETS
BTW, Many JFETs drain and Source pins are interchangable That's weird I know, but try it on the simulator
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