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Old 24th September 2012, 10:34 PM   #21
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Quote:
Originally Posted by Joachim Gerhard View Post
Why are the 2SJ74 connected to the cascodes with the sources ?
ok that is probably a glitch on the schematic. both J74 and K170 are connected to the cascode through their drains.
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Old 24th September 2012, 10:40 PM   #22
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Quote:
Originally Posted by Joachim Gerhard View Post
I have to study that complex circuit in detail but i also have to prepare for a show in Venthoven this weekend. I will jump in when i find the time.
thanks, looking forward to hearing back from you.
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Old 25th September 2012, 08:29 AM   #23
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this is getting very complex... Why did you use two circuits in series ? Is is a split riaa ?
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Old 25th September 2012, 09:07 AM   #24
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Quote:
Originally Posted by RCruz View Post
this is getting very complex... Why did you use two circuits in series ? Is is a split riaa ?

Split indeed. The servo alone is looking bulkier than my entire phono pre
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Old 25th September 2012, 03:15 PM   #25
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Quote:
Originally Posted by RCruz View Post
this is getting very complex... Why did you use two circuits in series ? Is is a split riaa ?
Thanks for your post.
I used two circuit in series to be able to split RIAA, having more control on the precision and split the "burden" on each stage and I wanted to operate each stage at lower gain
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Old 25th September 2012, 03:18 PM   #26
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Originally Posted by analog_sa View Post
Split indeed. The servo alone is looking bulkier than my entire phono pre
ahahah that made my day! ahahaha!!

Anyway yeah the servo is a little bulky, but remember you are trying to correct the differential signal so you need the inverting stage to be able to do it.
alternatively you can

1) use coupling caps (which is not the best soluition IMHO)
2) use two single sevos.


This phono is not going to be a simple little kit but it is hopefully going, with the help of Mr. Joachim and other experienced people on the forum here, to be a very fine balance design.
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Old 25th September 2012, 04:23 PM   #27
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Quote:
Originally Posted by Stefanoo View Post
Thanks for your post.
I used two circuit in series to be able to split RIAA, having more control on the precision and split the "burden" on each stage and I wanted to operate each stage at lower gain
This way you add a lot more parts in the signal path... do you believe that is a good idea ?

What are the benefits of doing the 50hz -500hz shelving in the first stage and than the low pass filter on the second besides beeing more acurate in the shelving itself ?
PS:
I can not read the schematic values... would you care to post a PNG pic file with more resolution ?
I would like to play with your values... just for learning purposes
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Last edited by RCruz; 25th September 2012 at 04:34 PM.
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Old 25th September 2012, 04:34 PM   #28
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Thanks for your objection.
The reason is:

1) more control and more accuracy on the shape of the RIAA
2) each gainstage operates at a lower gain which gives you benefits in terms of both harmonic distortion and frequency response
3) No use of Big electrolytic capacitor on the signal path (whether in series or parallel)

Let me know your thoughts.
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Old 25th September 2012, 04:51 PM   #29
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So to avoid the big EL you want to use lower gain.... That is a very good reason.

I never used a split riaa because using one more amplifying stage I would invert signal (because I use SE single transistor amplifiers).

Thank you for your input Stefanoo.... can you post a finer pic ?
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Old 25th September 2012, 04:52 PM   #30
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For everybody's enjoyment, here is a balance version of the paradise wrapped up for you with values and everything.
The relative RIAA's accuracy is attached as well.
I lowered the "bootstrap"'s cap values as it still yealds to a very precise shape
As it can be seen it doesn't use Standard values for the RIAA and getting custom made values for this is going to be pretty hard only with a group by they probably can be had at a good price.

Now I or anybody here with some skill can obviously build this.
What I have objected with this, is the use of high value electrolytic capacitors.
In my experience anytime such a part is introduced whether on coupling or on feedback or on shaping pole to compensate thermal they have constituted a deterrant effect on sound quality.
The effect on the sound is something I can clearly remember for as bad as it sounds compared to different approach.
This is the only objection I have with this topology.
In order to overcome that, I feel you need two gain stage unless we can come up with some alternative to it.

the servo works differentially so you can't simplify it unless you decide to use coupling cap but I guarantee you it is not going to sound as good.
Other aspect regarding the servo is that differential voltage is going to be perfectly zeroed out, but my concern is that absolute offset my wonder around and maybe another fix there might be needed.

If we can come out with a simple -one gain differential stage approach- I am obviously in favor of that over the 2 stage just to make this clear: I am not in favor of unnecessary complexity.
However, custom caps will be needed for this approach.

My intent here is to bring all the know-how of this forum to build the best of the best or like Joachim wants to call it: the MasterPiece.
Attached Images
File Type: jpg Balance Paradise.JPG (148.0 KB, 479 views)
File Type: jpg RIAA Accuracy.JPG (67.8 KB, 465 views)
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