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Old 2nd July 2011, 02:41 PM   #2321
RCruz is offline RCruz  Switzerland
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Can it be powered using Salas shunt ?

I have good experience with this regulator and know it is very good.
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Old 2nd July 2011, 02:52 PM   #2322
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I do not understand 100%. A folded cascode could be an alternative. It could have more gain as an advantage. Disadvantages are that 16.5V has to develop over the collector resistors of the input BJT cascodes for maximum dynamic range and the current of the input stage plus the current of the folded cascodes have to flow in that resistor. Contrast that to my mirror. It looses only 3 x Vbe plus the loss in the emitter resistors. Letīs assume they are 150 Ohm and 28mA flows in the input stage ( 4 plus 4 2SK170BL , 2SJ74BL ). That amounts to 6.15V and only 28mA is flowing in both legs of the mirror.
Ricardo, here is a first attempt on dimensioning the circuit.
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File Type: pdf MPP Summer 2011 FET AIOG 1.0.TSC - TINA.pdf (15.6 KB, 115 views)
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Old 2nd July 2011, 02:56 PM   #2323
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Ricardo, why not a Salas Shunt ? The only problem can be oscillation.
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Old 2nd July 2011, 03:05 PM   #2324
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Quote:
Originally Posted by Joachim Gerhard View Post
So Jan you could do the layout and Michael do the simulation ? Then we would have something like the official MPP DIY version. A PSU has to be developed too. I could make a suggestion . Another option would be to use the Jung - Didden regulator that Pilgham Audio makes. Ricardo i will fill in some values but they have to be checked. Especially the servo is not that easy because it will influence the deeper frequency range of the RIAA. The input stage has some thermal drift. After adjusting the 10 Ohm pot i get around plus - minus 1V over the RIAA. If we make the Servo too quick it will influence the RIAA more then necessary, if we make it too slow we end up with a drifting offset. Earlier i solved that with a cap in front of the buffer but then Vds of the input Fets floats around. With the servo we can adjust the 10 Ohm pot for minimal distortion and still get less then 1mV offset.
Joachim,

A nice servo trick is to connect both the sense and force connections of the servo to the same point, the output. It's like the servo nulls it's own input and there is no impact on the rest of the circuit.
I've used it a few times and even if it looks funny it works great!
I'll put a small diagram together for later.

Edit: attached

jan
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File Type: pdf self-servo.PDF (5.7 KB, 89 views)
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Last edited by jan.didden; 2nd July 2011 at 03:23 PM.
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Old 2nd July 2011, 03:06 PM   #2325
Salas is offline Salas  Greece
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Quote:
Originally Posted by Joachim Gerhard View Post
I do not understand 100%. A folded cascode could be an alternative. It could have more gain as an advantage. Disadvantages are that 16.5V has to develop over the collector resistors of the input BJT cascodes for maximum dynamic range and the current of the input stage plus the current of the folded cascodes have to flow in that resistor. Contrast that to my mirror. It looses only 3 x Vbe plus the loss in the emitter resistors. Letīs assume they are 150 Ohm and 28mA flows in the input stage ( 4 plus 4 2SK170BL , 2SJ74BL ). That amounts to 6.15V and only 28mA is flowing in both legs of the mirror.
Because there is a drop to be developed over a resistor if to go folded, sizing that resistor for given psus and not much Vds to avoid Ig, its either enough loading value and reduced current or small loading value and more current. When going telescopic cascode with mirror CCS you can afford Id near Idss with no resistor sizing compromises, you can allow more standing current to drive the passive part of the filter load. I asked to understand if you thought of that and preferred the telescopic, since enough PSRR can be had by the mirrors already. Or for some other reason.
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Old 2nd July 2011, 03:08 PM   #2326
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I have seen that in a norvegian phonostage of the 90th. Go ahead. That can be interesting.
My desire was the fix Vds of the input Fets.
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Old 2nd July 2011, 03:14 PM   #2327
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by Joachim Gerhard View Post
Ricardo, why not a Salas Shunt ? The only problem can be oscillation.
Oscilation ? why is that ?
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Old 2nd July 2011, 03:16 PM   #2328
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Salas, instead of the resistor for the folded cascode a constant current source could be used. That drives up the gain even more. I build circuits like that that worked. I do not know why but i fell more comfortable with my current mirror solution. It would be nice if you could draw a circuit that illustrates your point. I am more of a visual type you know.
Instead of my current mirror one could use a mirror with cacodes. That is different from the
cascoded mirror or the enhanced Wilson i use. In fact there are nearly infinite possibilities to make a precision mirror.
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Old 2nd July 2011, 03:18 PM   #2329
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Ricardo, i had that problem with the Salas on one of my current mirrored stages but i did not find the time to look more deeply into that problem. Everything got really hot and the sound was a bit sharp. I am sure this can be solved easy.
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Old 2nd July 2011, 03:20 PM   #2330
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Self-servo attached. What this does is to servo out the offset at the output (at your terminal VF2) without injecting anything upstream.
Maybe you or anyone else can add that to the simulation to verify. The servo RC should be the usual 1megohm and 1uF; the resitor going back to VF2 should be tried out; depends on the Zout of your circuit.

jan didden
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File Type: pdf self-servo.PDF (5.7 KB, 73 views)
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