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Old 2nd November 2011, 12:09 AM   #31
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by Defiant View Post
Back to the gyrator, it or any CCS load really only makes sense when the absolute maximum gain is needed from the single stage(which is seldom if ever the case) AND it is being fed into a very high impedance load, preferably DC coupled to the grid of another small signal tube.

A cascoded current source is pretty handy for driving a low impedance load via the mu follower output. Can be configured as a gyrator too. Worked nicely for me here: Unholy Alliance Phono Amp

Sheldon
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Old 12th November 2011, 04:27 PM   #32
mogliaa is offline mogliaa  United Kingdom
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I have adjusted now the cascoded gyrator from previous post to my supply levels and also simulated the 45 output valve circuit (fixed bias) with a 220k resistor and an equivalent capacitance of about 50pF.

The optimal operating point for minimum distortion at full drive (anode voltage to around 100Vpp) is Va=260V and Ia=7mA based on my previous tests on a breadboard driver setup.

The gyrator 1 (left circuit) is Wavebourn's and the gyrator 2 (right) is the mosfet version that many are using as well.

If I connect the output of the gyrator 2 from the mosfet source, the setup is now a mu-follower which I read is better for output valve drivers. You can see in the simulations that the frequency response is improved if you connect the output capacitor in the mosfet source and not in the 6J5 anode.

I'm planning to build both version so I can test and listen to differences.
Would you recommend mu-follower? Any changes before I etch a couple of PCBs?

Also, have seen others bypassing the LEDs with a good capacitor. I have a couple of 33uF PIO which could use. They don't impact clearly on the frequency response due to the low dynamic resistance of the LED arrays, however I bet they do contribute to the sound. Any recommendations based on your experience?

Thanks for the help....
Ale
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Old 12th November 2011, 05:07 PM   #33
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by mogliaa View Post
If I connect the output of the gyrator 2 from the mosfet source, the setup is now a mu-follower which I read is better for output valve drivers. You can see in the simulations that the frequency response is improved if you connect the output capacitor in the mosfet source and not in the 6J5 anode.
No disadvantage to the mu follower, but much lower output impedance.

Sheldon
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Old 12th November 2011, 05:13 PM   #34
mogliaa is offline mogliaa  United Kingdom
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Hi Sheldon,
Are you referring to the mu-follower as the one with lower output impedance?
Thanks, Ale

PS: I'm keen to replicate your DHT RIAA preamp. May be my next project!
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Old 12th November 2011, 05:14 PM   #35
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Quote:
Originally Posted by Sheldon View Post
No disadvantage to the mu follower, but much lower output impedance.
+better PSRR, +less of parts that means lower cost and higher reliability.

On currents higher than 10 mA I prefer version number 2 (source follower configuration), on lower currents I prefer version 1 (P-type configuration).
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Old 12th November 2011, 05:24 PM   #36
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by mogliaa View Post
Hi Sheldon,
Are you referring to the mu-follower as the one with lower output impedance?
Thanks, Ale

PS: I'm keen to replicate your DHT RIAA preamp. May be my next project!
Yes. And to the PS: It's a nice little pre.

Sheldon
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Old 12th November 2011, 05:29 PM   #37
mogliaa is offline mogliaa  United Kingdom
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Quote:
Originally Posted by Wavebourn View Post
+better PSRR, +less of parts that means lower cost and higher reliability.

On currents higher than 10 mA I prefer version number 2 (source follower configuration), on lower currents I prefer version 1 (P-type configuration).
Hi Anatoly,
You have been away for some time! Rod has kindly helped me out with your gyrator. Now I got the basics for SMD soldering for the bsp225 MOSFET.

Any particular reason why you prefer version 1 on lower currents?
Thanks
Ale
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Old 12th November 2011, 05:37 PM   #38
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Quote:
Originally Posted by mogliaa View Post
Any particular reason why you prefer version 1 on lower currents?
Properties of devices I can get in physical reality.

I myself don't like to solder SMD devices... But that BSP225 are quite good, in terms of voltage and capacitances. And I have a reel of them.
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Old 12th November 2011, 05:48 PM   #39
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I like version 2 and have used it on a number of occasions...

To me, its simplicity and effectiveness wins through....
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Old 12th November 2011, 05:57 PM   #40
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Originally Posted by Alastair E View Post
I like version 2 and have used it on a number of occasions...

To me, its simplicity and effectiveness wins through....
Which devices do you use for currents around 5 mA?
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