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Old 19th October 2012, 08:20 PM   #361
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There is, MiiB told you. You can make the mirror unbalanced so that more current flows into the output. Higher emitter resistors on the input side and lower resistors on the output side.
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Old 22nd October 2012, 03:15 PM   #362
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Quote:
Originally Posted by MiiB View Post
you could shield the current output by a jfet cascode... that will have substantial higer impedance than the mirrors

funney you want to save something so insignificant, and compromise in other vital areas... make the circuit using cheap parts to eval it...
if good and stable then you can go down the exotic route....

But I must say it again... in this kind of riaa the components matter a lot less.... and teflon caps are for many reasons vastly inferior to other industrial types of caps....
I have been away a couple days, so I answer with delay to your comments.

1) Could you please post a sketch of your idea of shielding the Servo? I am sorry I don't understand exactly what you meant and I want to make sure I get your idea right as I am sensing it is a sensible idea.

2) For the RIAA caps, could you tell me what capacitors are you recommending and say they sound better than AuraT capacitor? I will get those and try them out. However as far as impact of the RIAA capacitors my findings are different from yours. I found the RIAA capacitors toimpact significantly the sound also, and I am talking on the paradise, the ELCAP makes a huge difference. I just ran 2 different type of capacitors, same vale, and even my wife jumped out of the counter asking me what I changed.
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Old 22nd October 2012, 03:17 PM   #363
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Quote:
Originally Posted by Joachim Gerhard View Post
There is, MiiB told you. You can make the mirror unbalanced so that more current flows into the output. Higher emitter resistors on the input side and lower resistors on the output side.
This is a wonderful idea.
Having more output current helps driving RIAA at high frequency.
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Old 22nd October 2012, 05:44 PM   #364
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Yes, that should work. I was away some days too.
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Old 23rd October 2012, 05:52 PM   #365
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Quote:
Originally Posted by Joachim Gerhard View Post
Yes, that should work. I was away some days too.
observation: if you unbalance the mirror, how can it still work since the base current of the two halves connected together will be different?
I mean it works, but I tried that yesterday on the modified paradise and there are issue for the servo to try to zero out the voltage.
so I am trying to find the cause and a possible fix to that.

EDIT: Simulation wise it works, but There is something that doesn't pen out in my head for some reason when trying to unbalance the mirror.
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Old 23rd October 2012, 07:00 PM   #366
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More gain also gets you more offset.
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Old 23rd October 2012, 07:18 PM   #367
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More gain also gets you more offset.
True, but I only had 3dB more.
What I want to try to audition is less BJTs in parallel just to understand if I can get a more "enjoyable" sound out of it.
It is already pretty nice, but in my set up and with my type of music, IMHO it still needs tweaking to get it to my liking.

I want to see if halving the BJTs, although paying in terms of more noise, can have an overall improvement or not.
Also I want to revisit Supply Voltage and current bias and perhaps input device.
I want to, in other words get familiar with this structure and see if BJTs can get to sound as colourful as JFETs, maybe not, maybe yes...I want to try...
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Old 19th March 2013, 04:01 PM   #368
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Thanks to Joachim, we are back with this thread.

Here is the initial draft proposed by Master J and also a proposition for the Servo controller.

The idea is to utilize the super FET IF3602 and explore possibility of a fully balance phono stage.

I was wondering if anybody can point me out as far as getting LTSpice Model for the OPA1632 so that I can start simulating.
Attached Images
File Type: jpg MasterpieceFirstDraft.jpg (3.2 KB, 158 views)
Attached Files
File Type: pdf retro_schematic.pdf (34.6 KB, 40 views)
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Old 19th March 2013, 05:11 PM   #369
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I will publish the starting values of the RIIA soon.
The high frequency cap is a bit odd. I usually trim with Vishey teflon trimmer.
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Old 19th March 2013, 05:24 PM   #370
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Quote:
Originally Posted by Joachim Gerhard View Post
I will publish the starting values of the RIIA soon.
The high frequency cap is a bit odd. I usually trim with Vishey teflon trimmer.
What I usually do and correct me if this is wrong, I do the other way around i.e. I get standard cap and trim resistor if it can help.
Sometime, like in Paradise, you need no matter what a custom cap.
I would like to avoid using a custom cap.
What if in this approach we split high freq cut after first stage and then the other two time constants as shunt feedback?

soes this sound stupid?

I know that by doing this there is a loss with the passive low pass filter at the input.
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