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Old 2nd January 2006, 05:01 PM   #1
Giaime is offline Giaime  Italy
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Default Giaime's last nightmare - aka RIAA faceoff

Hello friends!

It's time to decide something about the RIAA stage in my preamplifier. I've already prototiped one of the circuits below, the Audio Innovations one and I'm quite satisfied.

Btw B+ is at 220V regulated.

Here is a little confrontation about RIAA and phono stages:

Click the image to open in full size.

The respective circuits are those:
Click the image to open in full size.
Audio Innovations one - blue line

Click the image to open in full size.
Kevin R. Kennedy's phonostage - black line

Click the image to open in full size.
Thoersten's phonostage - red line

(image attached below)
A phonostage, from Construire Hi-Fi (by kind permission of Andrea Bassanelli, Blu Press) - yellow line

So what do you think? What's the best RIAA curve, what's the best circuit?
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Old 2nd January 2006, 05:17 PM   #2
poobah is offline poobah  United States
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Giame,

Why don't you include the actual RIAA curve in your graph???

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Old 2nd January 2006, 05:20 PM   #3
Giaime is offline Giaime  Italy
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Ehm.... the problem is that I don't know how to do it

I made the graph by copying the simulation results from Multisim, and paste one on top of the other.

If it would be possible I'd have done it

Maybe if I transport everything to Excel... but how?

(even aside from that, shame on me )
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Old 2nd January 2006, 05:34 PM   #4
poobah is offline poobah  United States
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Here, this shows the poles and zeros, also has links to excel...


http://www.euronet.nl/~mgw/backgroun...kground_1.html


Goto Page 2 and you will see a passive circuit that you can simulate... you may have to add some perfect gain to adjust the overall dB

Kepp in mind the difference between "Classic" RIAA and "new IEC" RIAA. The difference, like what you have posted, is mostly about RUMBLE filtering
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Old 2nd January 2006, 05:44 PM   #5
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Thorsten has an ECC83 phono?
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Old 2nd January 2006, 06:16 PM   #6
Giaime is offline Giaime  Italy
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Here's the results of the simulation of the circuit in figure 2.3 in page 2, poobah:

Click the image to open in full size.
It doesn't look like a RIAA


Quote:
Originally posted by analog_sa
Thorsten has an ECC83 phono?
dc phono
isn't it this phono pre (on the bottom of the first page)? Wait, does Thoersten nick = Kuei or am I wrong?
The circuit I've simulated would be the adaption for using ECC83 even in the second stage, as SY and others suggested me in this thread Plate choke on a line stage?
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Old 2nd January 2006, 06:26 PM   #7
poobah is offline poobah  United States
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Giame,

The first pole (lowpass 50 Hz) and the first zero (high pass 500 Hz) look good. The second pole (low pass 2212 Hz) looks bad because of loading from the first stage. You need a buffer between the 2 stages ( Perfect Buffer; Zin = infinity, Gain = 1, Zout = 0).

Remember this is not a real circuit... just a way to make the curve.

Use figure 2.2 and insert a perfect amplifier with gain = 1 between section 1 and 2...

Also see page 1 there is an excel spreadsheet with the RIAA..

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Old 2nd January 2006, 07:11 PM   #8
Giaime is offline Giaime  Italy
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Thank you poobah, I'm a bad student

How do I implement a perfect amp? I've tried an opamp with the output tied to the - input, but nothing, even a voltage-controlled voltage source, nothing, I tried a voltage controlled current source (transconductance 0.3mMho to get the proper gain) and the result is strange...
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Old 2nd January 2006, 07:17 PM   #9
poobah is offline poobah  United States
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Yes... any op-amp should do well... output to negative input.

You curve is looking correct now... now add some gain to the end to match to the other curves in your first post.

Does your simulator have perfect gain functions? Or do you use only real parts?
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Old 2nd January 2006, 07:20 PM   #10
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Giaime,

If you use a 'X7 section in the 2nd gain block, instead of a 6922 section, you have to deal with very limited drive capability. The seminal RCA circuit has the problem too.

Is your phono section going to be part of a full function preamp, where the poor drive capability of the 'X7 is of minimal concern?
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