I've learned there's two anti-RIAA filters you put at the input of
preamp to be simulated: the laplace on and and RC passive one.
All my sims with RIAA premps have the passive filter at the input,
where I feed the AC signal through.
According to one of my colleagues at DIYaaudio, "Laplace is the most
accurate but can only be used in the .AC mode.
For the .Tran mode you will have to use the RC model.
As you mentioned on the use of Square Waves: you can tell quite a lot
about even an audio circuit's performance, by looking at its square
wave response. Tilt in the flat tops or ringing on the edges tells
you that something is amiss with the low frequency or high frequency
response, respectively. It's a quick-and-dirty way to judge the
broadband response.
That's what ignited my curiosity, and the recent tests with square
waves and a scope in an actual built preamp on the thread by one of
our pals.
I did try some of the SW settings that you suggested, and for now
found different responses according to the opamp being used. Now I
need someone to translate those results into actual distortions or
limits, and if possible play with the variables.
On power amps, SW testing helped trim the parallel small caps on the
feedback, which later showed as distortion changes in THD sims.
This is the passive Jung filter I use on all my RIAA sims.
(Lipshitz_and_Jung_1980)_RUS.png
Carlos
On Sun, Mar 30, 2025 at 1:21?AM Andy I via groups.io
<AI.egrps+io@...> wrote:
RIAA is intended for audio applications. Why in the world would you even think of square wave input?
Actually, you can tell quite a lot about even an audio circuit's performance, by looking at its square wave response. Tilt in the flat tops or ringing on the edges tells you that something is amiss with the low frequency or high frequency response, respectively. It's a quick-and-dirty way to judge the broadband response.
That is, of course, assuming that you include an accurate inverse RIAA network. Without that, it would be meaningless and pointless.
Andy
