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Old 1st February 2012, 01:17 AM   #5031
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Default WOW Mr G.

Quote:
Originally Posted by Joachim Gerhard View Post
Here is a simple idea. The output would be differential of cause so we can not simply sum it for unbalanced. It would cancel. For unbalanced we need a high CMR INA like the Thats 1200. The Fets at the input should be cascoded. This shows only the principle.
Cute !

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Old 1st February 2012, 01:21 AM   #5032
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Yes, it is very simple. I do not know if it would work exactly like this and we have to check offset issues but it is a start.
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Old 1st February 2012, 01:37 AM   #5033
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Default Current mirror

I ones did something like this before with the front as is but the output with onlt T11 and T14 and not a RIAA but a simple preamp.

I must look for it, I have it somewhere lying around.

I love current mirrors too


The output had CCS on each transistor leg (emitter ).


Offset was not a problem due to a cap !


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Old 1st February 2012, 12:25 PM   #5034
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I solved the problem with the balanced input and Samplers Mirror-Buffer. It is again so stupid simple that i had to smile. The minus pole of the cartridge simple goes into the sources. The differential INA at the output is now obsolete.
The node between the sources can even have a DC shift against ground because there will not flow current into cartridge. The gates of the Fet isolate that current, so this node can be trimmed for minimum distortion. With the resistor values given ( 5 and 2 Ohm ) and the N-Channels running on 7mA each plus the P-Channels running on 8mA each the offset null and the distortion null fall aprox. in one place.
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Old 1st February 2012, 12:26 PM   #5035
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I would of cause cascode the Fets. That can be arranged as a driven cascode too.
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Old 1st February 2012, 12:56 PM   #5036
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Here is the input gain cell.
Attached Files
File Type: pdf Starless Balanced Input Gain Cell.TSC - TINA.pdf (6.6 KB, 115 views)
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Old 1st February 2012, 01:01 PM   #5037
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Old 1st February 2012, 01:04 PM   #5038
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Quote:
Originally Posted by Joachim Gerhard View Post
The node between the sources can even have a DC shift against ground because there will not flow current into cartridge. The gates of the Fet isolate that current...
If the node between the FET sources is not at ground potential, how do you prevent current flow through R12?
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Old 1st February 2012, 01:06 PM   #5039
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Thumbs up Perfect !

I have to admit it's a different animal !
There is something about it that I don't quite seem to understand, but I'll be back !
I like it.



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Last edited by Audiofanatic; 1st February 2012 at 01:08 PM.
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Old 1st February 2012, 01:16 PM   #5040
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Jacques, you are right. R12 should be high impedance or the source node trimmed.
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