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Old 28th September 2012, 03:18 PM   #131
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Buzz,
I think that this thread is Stefano's and his original post was of a design that was his. He was attempting if I say this right to build his ultimate circuit implementation for a two-section RIAA stage and this was his baby. He is just letting those who want to to contribute to that level of design or just to watch the build. He said this was not going to be a group project in the first post. If you want to build it you are on your own for a board or anything else. If he gets this right and is nice enough he may give us the artwork to go make our own boards and try and build one ourselves.
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Old 28th September 2012, 03:28 PM   #132
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What? He has clearly stated that it is an open project and has asked for help. I was simply pointing out that reducing complexity might help him achieve his final goal. More simply stated, strip it down to basic structure and work back up. It was just a suggestion, that he decided not to heed. No harm done. Just a suggestion.
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Old 28th September 2012, 04:02 PM   #133
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Quote:
Originally Posted by buzzforb View Post
What? He has clearly stated that it is an open project and has asked for help. I was simply pointing out that reducing complexity might help him achieve his final goal. More simply stated, strip it down to basic structure and work back up. It was just a suggestion, that he decided not to heed. No harm done. Just a suggestion.
Yes, you two are both right. I would like to achieve the best and I am sharing my solutions to those who are experts to improve it and work it out.
If everything works fine, the details to build it will be here on these pages.

Starting from a simpler circuit to work the way up if the circuit MasterPiece-R5 can't be worked out due to some reason, could be a possibility.

I am going to change simulation back to 2 servos to see if the approach works (I remember that even two servos with this arrangement could possibly not work)

I will post back shortly I have other tasks I need to work out first here at work
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Old 28th September 2012, 08:53 PM   #134
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Ok, here it is finally.
It was a lot of work, more than what I thought it was going to be to get both combination of gain and DC offset right.
The way the schematic was drawn in Rev.5 wouldn't allow not even 2 separate servos to work properly unless the differential feedback was re-stored.

With this approach instead (a little bit of symmetric differential feeback and common mode feedback as well to allow common reference for both halves), at least theoretically, the offset is guaranteed both absolute and relative with only minor loss of gain (went down to 60dB but it can be eventually brought up by either tweaking the network again or by paralleling more FET).

Please feel free to comment.



I will probably test this tonight hopefully and I will let you all know if it works in practice as well and I am confident we can knock the servo down to a single one and hopefully people here will start cheaping in a bit more .
Attached Files
File Type: pdf MasterPiece-R6.pdf (40.5 KB, 65 views)
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Old 28th September 2012, 11:40 PM   #135
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Ok, now it gets interesting. Good luck.
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Old 29th September 2012, 01:37 AM   #136
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Originally Posted by Joachim Gerhard View Post
Ok, now it gets interesting. Good luck.
Tonight and tomorrow I am making the paradise to start listening to it...also because I have been out of a phono stage for quite some time now ...also by having it I will have a reference to listen to.
The only variant to it will probably be that instead of bjts I will use jfets not sure yet.
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Old 29th September 2012, 09:25 AM   #137
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If you decide to use jfets in your paradise, will you be droping the big EL caps ?

Is it possible to use just half of Masterpiece 6 as a unbalanced amp ?

What is your reasoning behind using R68 R79 as 22ohms... do you need more current there ? (Or is it because the buffer is working at +-35v here) ?
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Old 29th September 2012, 01:42 PM   #138
MiiB is online now MiiB  Denmark
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I have built the paradise using Jfets and without the big caps... grainy and muddy compared to the Bipolar's, they have a warmer tone, but lacks the crisp and dynamic, so dull an warmer is what you get.

Sorry I don't understand the current mirror around the current source, it's a dead short, no need for that in the way you have designed this, only reason it works is the current running to and from the ground. your Jfets are running on IDSS.. In simulation that would sort of OK'ish as they are all the same...REaL-life..??

Last edited by MiiB; 29th September 2012 at 01:45 PM.
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Old 29th September 2012, 02:03 PM   #139
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Strip it down, as i suggested. There is plenty to learn with simpler circuits.
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Old 29th September 2012, 02:07 PM   #140
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Quote:
Originally Posted by MiiB View Post
I have built the paradise using Jfets and without the big caps... grainy and muddy compared to the Bipolar's, they have a warmer tone, but lacks the crisp and dynamic, so dull an warmer is what you get.
Thank you for your input MiiB

PS: Remenber my PM ?
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