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Gyrator loaded Son of ZV9/F3
Gyrator loaded Son of ZV9/F3
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Old 4th January 2018, 08:55 AM   #151
juma is offline juma  Germany
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Seems like you are having a lot of fun..
Real chokes are (in my experience) inferior sounding solution, but many like them, so give it a try, you might like it.
Circuit from post #1 is nice, just take care about the parts you use in your build, some had problems with noisy resistors and similar stuff...
And yes, stay clear from BS170, if more people find out how good it really is, it will soon become much more expensive...
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Last edited by juma; 4th January 2018 at 09:03 AM.
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Old 11th January 2018, 07:34 AM   #152
Vix is offline Vix  Yugoslavia
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Hi Juma,

I am still playing with simple jfet and mosfet preamps. I have builthe one with BS 170, in fact I did the simplest version, I used the 4.4 K drain resistor (22k, 5 pcs in parallel) on a 60 V supply, 39 K from drain to gate, I also added a small gate stoppeer resistor, then a pot from the gate to ground to set the proper bias (around 20v at the drain, 40 v across the 4.4 k resistor). I can vary the input resistor from about 5.6 to about 12.4 k to vary the gain. (think of it as 5.6 k+ 6.8 K resistors in series, but the 6.8 resistor can be bypassed with a small switch for higher gain and vice versa). Since the input impedance thus varies from 5.6k to 12.4 k, I put 20uF cap at the input. To make sure it has low output impedance, I also added an output buffer (maybe it is not necessary). Currently it is driving F3, but could be needed to drive a Mosfet follower as well (Sewa- like Mofo, but with huge lighbulbs instead of an inductor and 40v supply). That's why I wanted to have a variable gain.
I did some listening to this preamp on F3. The sound is clear, neither cold nor warm. When not compared to anything, seems about right (on F3 amp).
But, then I reversed to the J310 Boz, this one:
Jfet BOZ

And...found that I like the J310 jfet Boz more. It is slighly less analytical and more warm sounding. I find it more enjoyable and less tiring than the one with BS170 mosfet.
But, it has just enough gain for F3, and certainly not enought for a Mosfet follower.
Now, my next step is to build the circuit as you presented on post nr.24. I guess that it should sound better than the variants I have built up to now.
But, since I don't have the BF 862 mosfet, I wanted to try that circuit with J310. Yep, I know it needs some modifications- that's what I am kindly asking you here
Also, instead of a gyrator with BS 170, could it also have a Jfet 310 CCS on top? Should be a tad simpler. Power suply is not a problem, in this case I can vary it from 20-40v (single rail)
If you are busy and don't have time to draw a schematic, maybe you could give me a few hints on what values to change? (source resistor etc)...

Thanks and regards,
Vix
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Old 11th January 2018, 12:07 PM   #153
juma is offline juma  Germany
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Quote:
Originally Posted by Vix View Post
... I don't have the BF 862 mosfet, I wanted to try that circuit with J310. ...
... instead of a gyrator with BS 170, could it also have a Jfet 310 CCS on top?..
You want J310 with occasional BJT to deliver clean and high voltage swing to drive the unity gain power amp - it's a no go here; J310 can not easily replace neither BF862 nor BS170 in this circuit, it's too different.

It would have to be a whole new circuit and I would have to build a prototype to test it. I could do it on commission but it would cost you much more than few pennies for appropriate parts.
Actually, for your needs, this (see attachment) is safest bet, stick to it ; #24 is too specific, no fooling around with it.
In attached circuit, you can use J310 instead BF862, but R14 should be 220R or so (for Id of 10mA or so), R20 should be 22k or so, and R27 should change to 56k. It will sound different, try it to find out if you like it
Attached Images
File Type: gif GF3-40V.gif (7.8 KB, 385 views)
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Last edited by juma; 11th January 2018 at 12:16 PM.
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Old 11th January 2018, 01:04 PM   #154
Vix is offline Vix  Yugoslavia
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Yes, it is doable, since I have all necessary parts.
Thanks Juma!
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Old 18th January 2018, 03:57 PM   #155
volavola is offline volavola  Italy
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Default Well I finish

Hello Juma
Finally I found them. Two jfet one 15,93 mA and the next 16.2 mA. The preamp sound very good. Round with B'52 rude with Ramones and sweet with the radio. My son love it
Thanks Juma
Attached Images
File Type: jpg 20180118_110950.jpg (334.4 KB, 342 views)
File Type: jpg 20180118_111042.jpg (304.1 KB, 324 views)

Last edited by volavola; 18th January 2018 at 04:02 PM. Reason: attach photo
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Old 18th January 2018, 05:06 PM   #156
juma is offline juma  Germany
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You are wellcome. Enjoy it
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Old 19th January 2018, 03:27 PM   #157
marconi118 is offline marconi118  Germany
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do you have the last schema of the Jfet BOZ with J310?
what is the gain and output impedance?

Can it be tweaked for 1K output impedance and still sound good?

Maybe using BF861C with higher Idss and lowering the Drain resistor
I need medium gain and low output Z
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Old 9th February 2018, 07:37 PM   #158
maouna is offline maouna  Greece
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Juma,maybe i am offtopic but some years ago i found this schematic of yours on the net but i have no info about it and i cant remember where i found it.Is there a dedicated thread with info on sounding impressions,improvements (if any)and comments etc.?
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Last edited by maouna; 9th February 2018 at 07:41 PM.
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Old 10th February 2018, 09:35 AM   #159
juma is offline juma  Germany
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It's a small MOSFET, common source connected, loaded with a CCS (JFET). Gain is defined through local, Schade feedback (R4/R5 ratio). R3 sets the Drain of Q2 at half of the power supply voltage. Any usual CCS (at about 10mA) can be used instead of JFET.
It sounds OK - I like the circuit from post #1 of this thread better, but it's easy and cheap to try both and decide for yourself...
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Old 12th February 2018, 08:28 AM   #160
maouna is offline maouna  Greece
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Quote:
Originally Posted by juma View Post
It's a small MOSFET, common source connected, loaded with a CCS (JFET). Gain is defined through local, Schade feedback (R4/R5 ratio). R3 sets the Drain of Q2 at half of the power supply voltage. Any usual CCS (at about 10mA) can be used instead of JFET.
It sounds OK - I like the circuit from post #1 of this thread better, but it's easy and cheap to try both and decide for yourself...
Thank you.I made a layout(not tested for errors yet) for this small MOSFET version to test.I read all posts from this thread and i saw on post #37 that you made an other version of schematic from post #1.Between those 2 schematics (post#1 and post#37) which one you like most in terms of sound?
Attached Images
File Type: gif bs170.gif (110.1 KB, 211 views)
File Type: gif pre-sch.gif (6.8 KB, 111 views)
File Type: jpg gf3-NoSchade-40V-post24 v2.jpg (441.9 KB, 108 views)

Last edited by maouna; 12th February 2018 at 08:31 AM.
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