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Old 20th February 2010, 12:14 AM   #891
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Default Joachim

Dear colleague,

You are like me, always busy and I bet you're also designing in your dreams don't you!?

Nevertheless, I admire your work and like your new design.
Keep up the good work.

Tjuus,

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Old 20th February 2010, 12:44 AM   #892
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Thank you very much. That is ecouraging.
Tomorrow i will post some balanced RIAA´s based on the Discreet INA.
I design with my subconciesness. When you do something very intense the brain works in the backround but who am i talking too ?
What really fascinates me is that this is a never ending story.
It opened up a new world for me and i am really enyoying it.
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Old 20th February 2010, 02:58 AM   #893
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Default Saturday afternoon project

I thought about a little project i can make on saturday afternoon with parts i have.
It´s the INA with Balanced Shunt-Passive RIAA all in one go Unbalanced Out.
I can spare the capacitive RIAA that way. For the output chip i will try the LT1468 instead
of the OPA134.
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Old 20th February 2010, 09:28 AM   #894
brianco is offline brianco  Ireland
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OT
Have you seen Jan's site re. intuitive decision making etc?

http://www.linearaudio.nl/musings-1.htm

I suspect that the trick is to learn to trust intuition .
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Old 20th February 2010, 12:06 PM   #895
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Yes, that phenomenon is interesting.
Tabletennis is a good example too.
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Old 21st February 2010, 10:05 PM   #896
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My project was successful. I was a bit nervous but also exited because this is the first balanced RIAA i build. I had designed some on paper and did the 75usec part balanced but not AIO ( all in one).
It worked right away.
Some elaboration is posible and leads to better performance.
I am posting the circuit to that i listen momentarily.
It has a servo added. The DC offset was around 50mV without servo. No problem in a system where a cap follows. If you want to go "naked" use the servo. It performs better too because it creates a virtual ground which isolates the transimpedance RIAA from ground current polution.
See the 3.3kOhm resistor from output to - supply. It makes the LT1648 biased into class A. I found this better then wihout.
The next step whould be a balnced in - balanced out RIAA and the new Burr-Brown BI-BO chips are perfect for that. I ordered some and will test the circuit.
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Old 21st February 2010, 10:14 PM   #897
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Here are the circuits.
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Old 23rd February 2010, 11:09 PM   #898
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I am listening for a while now to the Low Z INA and i am very happy. The only thing i did not try is the buffering of the feedback resistors to lower noise. The Low Z version will not profit much from that because the cartridge is in parallel noisewise. So noise impedance goes down from 3.55 Ohm to 2.62 Ohm. An improvement of only around 0.1nV/qHz.
I felt that the commercial linestage i am using limited the result so i designed a no compromise linestage. It has quite amasing Data. I optimised for transient response so
frequency response is down only -3dB at 25Mhz, limmited by an output Zobel.
It is a transimpedance class-A design with fast buffer in the feedback loop.
Two of my engineer friends that saw the circuit thought that i whould never get it stable but it is totally stable now. Noise and distortion are nill too and i build a special balance and volume control that works in shunt mode with a Charcroft Z foil resistor.
I went to great pains that crosstalk is very low up to high frequencies.
The calculation of the gain and control structure took the the best of two weeks.
I also made sure that common mode distortions are avoided because i decided on series feedback. I am currently back engineering what i did and then will post the circuit.
Now moving into balanced i need a Balanced-In , Unbalnced - Out converter.
There are very good integrated solutions from Burr-Brown for example but i have a lot of Opamps around and like to roll my own.
I will use the Superbal topology that has the advantage that input impedance on hot and cold are equal for both differential and common mode.
i found this idea in D.Selfs book "Self on Audio".
I am looking forward to read his new book. He promissed a lot of new discoveries.
We are living in exiting times for audio.
Attached Files
File Type: pdf Superbal Balanced In- Unbalanced Out.TSC - TINA.pdf (37.7 KB, 90 views)
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Old 25th February 2010, 12:11 AM   #899
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Today a friend came by and we listened to the Low Z INA. He thought that the sound was very good but somehow a bit to intense for him. Just for fun a substituted the mix of NE5534 and OP27 with 4 OPA134. They work in this circuit without stability problems.
My friend found the sound warmer and more spacious. He said that the sound got "0.5m wider". Strange isn´t it that he could give that exact value. I myself do not think that OPs
have a "sound". It matters very much how you use them so just swapping OPs does compare aplles to oranges. Later in the evening i listened alone and found the sound less precise and tight. For my taste the NE5534 works wonderfull in transimpedance mode.I think it is also known to be able to drive a tough load whereas the OP134 is less robust. See the catalog data and Samuel Groners survay. It´s still a goody, even today.
The OPA134 may have had some trouble with current delivery and in other test i made
it gave a very attractive but somehow distorted treble. D.Self is not a fan of that OP eather beacuse it has higher distortion as the NE5534 and cost quite a bit more.
Anyway, my INA will leave the house soon and play in a system of another hifi buddy.
I will build him a compleet preamp with remote control and line buffer stage.
Now is the time to build an INA for myself. I will build a fully balanced version that has both High Z and Low Z input. See my diagrams with my component choices. As resistors i will use the good old Dale RS55 0.1% antimagnetic. The PSU caps are from Frolyt, an innovative east german maker. For RIAA i use LCR styroflex and Röderstein MKP1837. They are compact and come in 1% tolerance. I tried the Röderstein as coupling caps in front of my poweramp and can not hear any loss of detail at all.
Maybe i get old.
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Old 25th February 2010, 02:13 AM   #900
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Quote:
Originally Posted by Joachim Gerhard View Post
I will use the Superbal topology that has the advantage that input impedance on hot and cold are equal for both differential and common mode.
i found this idea in D.Selfs book "Self on Audio".
I am looking forward to read his new book. He promissed a lot of new discoveries.
We are living in exiting times for audio.
What is the rational behind this? The common mode and differential source impedance of a cartridge (connected in true differential mode) are quite different. I would think you want to maximize the ratio of differential to common mode gain at the output (in the ideal case no common mode gain). You might want the commom mode impedances equal for cancellation, but I see no reason to make them equal to the differential impedance.
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Last edited by scott wurcer; 25th February 2010 at 02:20 AM.
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