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Old 8th September 2011, 07:21 PM   #2661
MiiB is offline MiiB  Denmark
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sorry it had noting to do with the ajustable circuit.. but the resistors over the mirrors to give a predictable impedance for the current gain Riaa circuit..
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Old 8th September 2011, 07:24 PM   #2662
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As i said, i have not tried this out. Is is possible for you to simulate it ?
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Old 8th September 2011, 07:38 PM   #2663
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The circuit diagram in post 2658 has a mistake at the output and it should read "rumble".
Thanks AS.
This should work ......
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File Type: pdf JG EQ control.TSC - TINA.pdf (14.3 KB, 73 views)
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Old 8th September 2011, 08:27 PM   #2664
MiiB is offline MiiB  Denmark
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Quote:
Originally Posted by Joachim Gerhard View Post
As i said, i have not tried this out. Is is possible for you to simulate it ?
sure....can you send med the circuit....then i can model it...and evaluate the riaa correction via LaPlace...
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Old 8th September 2011, 10:17 PM   #2665
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This is the circuit i am interested in, with and without additional helper transistors or differential feedback resistors on various "levels".
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File Type: pdf Starless and Bible Black MC RIAA Proto MIIB.pdf (11.9 KB, 161 views)

Last edited by Joachim Gerhard; 8th September 2011 at 10:25 PM.
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Old 10th September 2011, 07:43 AM   #2666
MiiB is offline MiiB  Denmark
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If i take the circuit as it is...Then

Gain is app 65 dB at 1 KHz.
The Riaa curve Fits perfectly will app 0.2 dB low-end lift.
Distortion is not super low at app -50dB for the second order, but only second and third order exists. 3.order app a hundred times lower...
Juggling a little with the offset....It's low (app 2 mV/out) when the circuit is floating.. but at -1.5V with fixed rails..hmm
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Old 10th September 2011, 09:32 AM   #2667
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This effect with second harmonic is interesting. Should sound like tubes ?
Distortion could be brought down a bit by lowering the gain to 60dB maybe. I am happy that my RIAA values worked out so well. I simply used Baxadall´s formula and interpolated the output impedance of the mirror. How did the buffer perform with the floating supply ? Was the output current limited in any way as Calvin predicted ?
The DC offset could be trimmed away in the fixed rail version by using the trim components like in the output buffer maybe. That is a little bit more noisy with the 5 Ohm resistor in series. I could life with that. Thank you Michael that you put serious work into this.
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Old 10th September 2011, 10:21 AM   #2668
MiiB is offline MiiB  Denmark
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The supply for the buffer also needs a tie in the center..but it could be that in real life it can be floating...think often the simulator goes basurka (Viking like) when something is floating,, where in real-life it'll find a balance..

Gain can be lowered 5-8 dB by scaling the Riaa

If the trimmer in the buffer is 15 ohm.. its possible to trim the offset...so it in the uV range..but thermally I don't know how it'll drift. Don't fancy a servo...and to be honest would A cap in the output do any damage....?? apart from the fact that DC-coupling would be nice..

Think your realistic experiments will reveal this if thermal drift is a problem..

I think the distortion specter is super nice....only second order...and the rest is super super low...even if distortion was 10 times higher is would still be nice...I believe distribution matters much much more than level.

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+03 2.306e-01 1.000e+00 179.98° 0.00°
2 2.000e+03 1.082e-04 4.695e-04 -90.05° -270.03°
3 3.000e+03 2.606e-09 1.130e-08 -170.18° -350.16°
4 4.000e+03 2.327e-11 1.009e-10 69.02° -110.96°
5 5.000e+03 2.104e-11 9.123e-11 176.24° -3.74°
6 6.000e+03 1.155e-11 5.008e-11 -169.19° -349.17°
7 7.000e+03 6.884e-12 2.985e-11 -79.82° -259.80°
8 8.000e+03 1.891e-11 8.202e-11 -15.56° -195.54°
9 9.000e+03 1.334e-11 5.786e-11 2.59° -177.39°
Total Harmonic Distortion: 0.046946%
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Old 10th September 2011, 10:25 AM   #2669
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What can be done is put the cap BEFORE the buffer. Then it can be a very low value.
The buffet itself has to be proven to be thermally stable. It´s time to build something.
I do that today.
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Old 10th September 2011, 10:50 AM   #2670
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I you put a cap there... the trimmer can be 10 ohm.. to get balance...the buffer adds a little offset, that must be trimmed away....what about the super-fast BJT buffer...??
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