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Old 3rd April 2012, 05:16 PM   #71
Skorpio is offline Skorpio  Denmark
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Quote:
Originally Posted by juma View Post
Hi Wrench,
here is my take on "turning a (MOS)FET into a SIT/triode". Fair Zin, low Zout, BW(-3dB)=1MHz, rail-to-rail swing (almost), high PSRR, Id about 15mA, sounds wonderfull - what more could a man want ?

Built, tested, measured (except for THD) - here is the schematics:

I like this one

How would you evaluate it between all those fine circuits you and others have made in the past? I am thinking power follower driving duty...

Just to name a few:

-BoZ
-JBoZ
-B1 (sound character)
-Triode with CCS load
-Other relevant



Na, building will be done nomatter what within a few weeks
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Old 4th April 2012, 07:01 AM   #72
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I'll be starting another thread in the Pass Labs section called L'Fake, a response to the L'Amp featured there that uses the scarce Yamaha SITs. The mosfet/jfet combination I showed at the beginning of this thread is perfect for making a fake SIT with a largish mosfet like the IRFP140/240 or the IRFP044/044N, among others. I also have in mind some largish TO-247 Fairchild "house numbered" devices I got for a relative pittance from Electronic Goldmine. The nice thing is that this setup will work with just about any mosfet that's large enough to dissipate the required power. They just about all turn on substantially at 4V or so, so setting up the bias current and output centering is relatively straightforward.

Anyway, I've done sims with both resistive and current source loading - the current source load sims better in terms of THD. For someone that wants to mess around with a simple SE Class A amp using readily available parts, this could be the ticket. All sims I've done so far are dominated by 2nd harmonic, with the 3rd down 10-20 db, and the rest much lower.
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Old 4th April 2012, 07:15 AM   #73
Skorpio is offline Skorpio  Denmark
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Originally Posted by wrenchone View Post
I'll be starting another thread in the Pass Labs section called L'Fake, a response to the L'Amp featured there that uses the scarce Yamaha SITs. The mosfet/jfet combination I showed at the beginning of this thread is perfect for making a fake SIT with a largish mosfet like the IRFP140/240 or the IRFP044/044N, among others. I also have in mind some largish TO-247 Fairchild "house numbered" devices I got for a relative pittance from Electronic Goldmine. The nice thing is that this setup will work with just about any mosfet that's large enough to dissipate the required power. They just about all turn on substantially at 4V or so, so setting up the bias current and output centering is relatively straightforward.

Anyway, I've done sims with both resistive and current source loading - the current source load sims better in terms of THD. For someone that wants to mess around with a simple SE Class A amp using readily available parts, this could be the ticket. All sims I've done so far are dominated by 2nd harmonic, with the 3rd down 10-20 db, and the rest much lower.
This one is promising!

I will be waiting
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Old 4th April 2012, 07:43 AM   #74
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The Goldmine part turns out to be an HUF75329G, with much less gate capacitance than the other two devices I mentioned previously (~1000pF vs 1500 or more). It's rated for 55 V, so will be perfect for a Pass-ish single-ended amp. Goldmine is sold out of these devices, unfortunately, though those curious enough might be able to find the same thing elsewhere, or something similar or better in Fairchild's current lineup of devices.

I wouldn't obesess about it though, as just about any mosfet capable of dissipating the required power and voltage would work.
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Old 4th April 2012, 09:57 AM   #75
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Wrench, lower device has to be enhancememt mode,correct. It would de nice to try LU or RO85 down low. Right now, i am thinking of 2sk2013 pre version. Love following the thread, btw.
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Old 4th April 2012, 10:54 AM   #76
juma is offline juma  Germany
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Quote:
Originally Posted by Skorpio View Post
... power follower driving duty...
To drive a small PF (5-10W, 24V PS, see post #65) I'd use a Mu follower variant:
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Old 12th April 2012, 08:41 AM   #77
Skorpio is offline Skorpio  Denmark
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Originally Posted by juma View Post
To drive a small PF (5-10W, 24V PS, see post #65) I'd use a Mu follower variant:
If this fakes a SIT or a triode, I guess my ZEN4 is already a fake SIT amplifier?

And when I get around to upgrade it with the Semisouth FET, will it still be?

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Old 12th April 2012, 12:10 PM   #78
tp147 is offline tp147  Germany
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Originally Posted by juma View Post
To drive a small PF (5-10W, 24V PS, see post #65) I'd use a Mu follower variant:
Hi Juma,

I'm just collecting parts to build your nice pre amp for my F3.
For tweaking my Naim gear I have a nice PSU which provides +/-15 V powered by two 15-0-15 V centertapped r core transformers. Regulation is alternatively ALW Superregs with AD797 or Teddy Pardo Regs.
While the Naim pre is also a SE amp, the symmetrical PS is a nice step forward.

I guess it would also be nice to drive your pre amp with a symmetrical PS. What has to be changed in your circuit and which regulation would you prefer?

thanks in advance

Thorsten
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Old 13th April 2012, 01:54 PM   #79
juma is offline juma  Germany
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Originally Posted by tp147 View Post
....
I guess it would also be nice to drive your pre amp with a symmetrical PS. What has to be changed in your circuit and which regulation would you prefer?

thanks in advance

Thorsten
I don't see the advantage in using the symmetrical PSU. Circuit would lose its elegance, and coupling cap(s) would still be present.
It can be redesigned but it wouldn't be better...

The circuit has high PSRR and I didn't notice the improvement by changing the PS from LM317 to shunt reg...
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Old 13th April 2012, 05:20 PM   #80
tp147 is offline tp147  Germany
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Thanks Juma,

only, because I've such a DIY PS on stock...

A little bit funny, but I'll build this little pre on small boards exactly as big as the Naim gain stages in my NAC 72 and I'll use it as a drop in replacement.

cheers

Thorsten
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