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Old 31st October 2011, 04:49 PM   #2981
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The Buffalo Bill Linestage prototype works. Now i am building the cabinet.
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Old 31st October 2011, 08:38 PM   #2982
RCruz is offline RCruz  Switzerland
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I am very tempted to do it but need some more info so I can fine tune it in the end.

How is the 2187uS determined in your schematic ?

As you do not use a Riaa input resistor, I guess this value should be determined by 1st stage output impedance // R15 = 412k x C7. In this case C7 should be 5.3nF.

To determine the 750uS pole 412k x C8 so C8 would need to be 1.8nF.

To determine the 318uS pole using C7 = 5.3nF we would need R16 to be 59.9kohm.

Does it make sence to you or am I missing something.... Why did you not include an input resistor in the Riaa circuit ?
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Old 31st October 2011, 09:11 PM   #2983
MiiB is offline MiiB  Denmark
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Quote:
Originally Posted by RCruz View Post
I am very tempted to do it but need some more info so I can fine tune it in the end.

How is the 2187uS determined in your schematic ?

As you do not use a Riaa input resistor, I guess this value should be determined by 1st stage output impedance // R15 = 412k x C7. In this case C7 should be 5.3nF.

To determine the 750uS pole 412k x C8 so C8 would need to be 1.8nF.

To determine the 318uS pole using C7 = 5.3nF we would need R16 to be 59.9kohm.

Does it make sence to you or am I missing something.... Why did you not include an input resistor in the Riaa circuit ?
It's current output so riaa is formed by changeing signal levels to ground, think the output mirrors ensure a rather highish output impedance, I have simulated this circuit and treated output impedance as beeing ideal, this gives a riaa curve with less than 0,25 dB difference.....From the theoretical. Calculated with LaPlace tranformation and timeconstants.
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Old 31st October 2011, 09:42 PM   #2984
RCruz is offline RCruz  Switzerland
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Ok... in that case, the usual methods to calc Riaa values do not aply .... How do you do it ?
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Old 31st October 2011, 10:05 PM   #2985
sampler is offline sampler  Lithuania
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Ok... in that case, the usual methods to calc Riaa values do not aply .... How do you do it ?
Hi RCruz,
Floating input transconductance circuit does not work, I checked it in my circuit as simulators are somehow flaky about floating things. But I think I was wrong about grounded sources, it should work, at least it sim'med ok.
Output impedance of current sources are frequency and power supply dependable, so when calculating by hand the math is quite strong with this one.
Why you don't want to try transimpedance arrangement ? The only down side is that you have to be extra careful with input offset and don't fool around with live circuit when cart is connected, or you could fry it (as MiiB has pointed).
Anyhow, how much gain do you need ? I think I can sim something for you.
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Old 31st October 2011, 10:20 PM   #2986
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Ok... in that case, the usual methods to calc Riaa values do not aply .... How do you do it ?
See post 2962.

"If you want to use 10n for C7 I arrive at R15 218k7, R16 31k8 and C8 3n43. "

These can be scaled accordingly for different gain.

The values apply for infinite output impedance at that point.
If the impedance is lower only R15 has to be adjusted.
Formulas may follow tomorrow if you need them.
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Old 31st October 2011, 11:46 PM   #2987
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Here are the theoretical values for a transimpedance RIAA. This values assume an infinite output impedance of the current source ( mirror ) and an infinite input impedance of the buffer. It is true. Only R1 has to be adjusted.
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Old 31st October 2011, 11:54 PM   #2988
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Sampler, grounded source was my first idea. If it works, fine, we have another option.
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Old 31st October 2011, 11:58 PM   #2989
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Gain at 1kHz is approximate : Output impedance of the mirror in parallel to R1 / ( 1/10 R2 ).
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Old 1st November 2011, 12:46 AM   #2990
sampler is offline sampler  Lithuania
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Yes Joachim, you were right, it works just fine. Here is output impedance plots of current mirrors with -+18V supply and 374 Ohm emitter resistors. I think it's really worth using helper transistors, as with higher output impedance you get better frequency response, for the same theoretical riaa values. So adding 500k to the ground already gives you almost straight impedance line to the 25k Hz and perfect riaa compliance.
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