Interesting norwegian RIAA amp

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#4
analog_sa said:
The riaa network appears to be fed by the current mirrors (transconductance amp). Is it possible to calculate the driving impedance with sufficient accuracy?
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It's not kind of taste of driving RIAA networks but I think that the output impedance is rather "resistive" in the audio band, therefore the gain wil be predictable.

It's also not my kind of taste to have parameters that give varying results. The gain (I suspect) will differ between different amps because the transistor parameters will variate.
 
#5
Peranders

I was not worried about the gain but rather about RIAA accuracy. Don't you need to know very accurately the driving impedance in this configuration? There doesn't seem to be a resistor between the transconductance amps and the 'passive' RIAA.



cheers

peter
 
#6
analog_sa said:
Peranders

I was not worried about the gain but rather about RIAA accuracy. Don't you need to know very accurately the driving impedance in this configuration? There doesn't seem to be a resistor between the transconductance amps and the 'passive' RIAA.
Click to expand...

The "resistor" is the output impedance and the gain will variate but, not the much the RIAA curve looks, just a little maybe.
 
#7
It's obvious the output impedance is the 'resistor'. But how do you calculate its value without knowing the current gain of the transistors? That's why normally there is a resistor with value a lot higher than the preceding stage output impedance. Is this circuit supposed to be tuned to the selection of active devices?

peter
 
#9
Andiha homepage

peranders said:
When I've taken a closer look I believe that the DC-gain is (R23/R17)/2, quite predictable.
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If I was to judge by the formulas at Andiha Homepage Andiha Audio
I would say he probably knows what he is doing.

This page for example, makes me 😉 DIZZY 😉 just by a quick glance:

The Complete Amplifier

And this is what he is talking about
a typical voltage feedback operational amplifier
 

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