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Preamp with LS Jfets
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Old 30th March 2018, 08:35 PM   #21
Telstar is offline Telstar  Italy
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Specs are great. How easy would be to lower gain and Rout?
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Old 30th March 2018, 09:00 PM   #22
Zen Mod is online now Zen Mod  Serbia
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gain is matter of R6 value

Rout is , well , matter of JFet drain sissyness ......... no way to go low , without buffer
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Old 30th March 2018, 09:14 PM   #23
Telstar is offline Telstar  Italy
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Thanks ZM
Rout isn't a problem in truth. The buffer I have planned is the F4, so it should be fine.

Someone got good spice models of lsk parts?
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Old 30th March 2018, 09:48 PM   #24
Zen Mod is online now Zen Mod  Serbia
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just use Toshiba models
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Old 30th March 2018, 10:23 PM   #25
Telstar is offline Telstar  Italy
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Originally Posted by Zen Mod View Post
just use Toshiba models
That's what I was planning to do.
I'll check datasheets and adjust something while duplicating those models, since these are C grade while the Toshiba models refers to BL.
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Old 31st March 2018, 03:11 PM   #26
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by Zen Mod View Post
gain is matter of R6 value
I played with it and lower I could get was 3,5X, but not in a very linear way. Not satisfied, I played with R3 instead, and I'm not sure how to interpret the results of the simulation. It should affect the currents, but dissipation of the 4jfets was basically the same. Hummm...
Distortion follows the output voltage (therefore keeping Vin fixed it seems lower with lower gain) and is very close to the one measured by Papa, except THD20>>THD1. I think the "C" version of Linear jfets improves linearity a bit especially at high frequencies (very important for me). I had to use j74/k170 models.

I also played with the rail voltages, which showed that the 18V chosen value is ideal (shouldn't have doubted that, but hoped to run it lower) and correspond to about 45V for the rails.

Anyway, I do like this circuit very much, I love the offset cancelling behavior (had to add only 7 ohm on upper rail to make it virtually 0 in sim). It looks like the perfect linestage to put in front of an F4.
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Old 31st March 2018, 03:18 PM   #27
Zen Mod is online now Zen Mod  Serbia
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just fiddle with it to your liking , and it'll sing
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Old 31st March 2018, 04:37 PM   #28
6L6 is offline 6L6  United States
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Quote:
Originally Posted by Nelson Pass View Post
Oh yeah, I mis-titled the thread. No balanced here.
Fixed.

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Old 31st March 2018, 06:24 PM   #29
vdi_nenna is offline vdi_nenna  United States
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What's up with Linear Systems?
The web site is not working and they don't answer emails.
Site move?
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Old 1st April 2018, 11:35 PM   #30
woofertester is offline woofertester  United States
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Originally Posted by vdi_nenna View Post
What's up with Linear Systems?
The web site is not working and they don't answer emails.
Site move?
I have emailed Linear Systems a couple of times with zero response.

On the other hand, I have traded emails with Central Semiconductor and have received a not-so-polite rebuff.

My gut tells me that money talks and semiconductor companies may tend toward being hard of hearing. You have to shout money-wise.

I have dropped back to punt and ordered some parts from a broker. If it turns out to be wasted money, it will not impoverish me but merely disappoint. If the parts turn out to be useful/genuine, I will buy enough for many DIY projects and call that good. The other option is to switch to BJTs.
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