How to calculate RIAA correctly?

[Onvinyl]

thanks for all the replies!

e.g. I try to understand the network of la boheme:
http://www.klaus-boening.de/html/sch....html#MKIIInew

As a reference, one might use
http://www.kabusa.com/riaa.htm
So, R1 is the output impedance of the preceding stage, which with RL=4.7K should be around 4.5K.
According to the reference, R1 should be around 7.3K with the chosen values. Seems I don't know what happens in a balanced design...

Rüdiger

[Jocko Homo]

AES preprint # 1424, Nov. '78.

Deals with active de-emphasis circuits, inverting and non-inverting;

Active inverting pre-emphasis;

Passive pre-emphasis.

Jocko

[SY]

IIRC, Lipshitz (or someone following him) wrote up passive and active RIAA calculations in Audio Amateur. This would have been in the late '70s or early '80s. He took into account the "secret" pole and the interaction between the RCs that determined the time constants.

As a side note, anyone building their own RIAA stage ought to spend an afternoon and $50 or so to build a buffered precision inverse RIAA network. At some point, you have to turn the calculations into real ciscuits, and trimming is a good thing to be able to do.

[Jocko Homo]

That assumes that their inverse network is correct.

The high-tech method that I am able to employ involves generating the exact RIAA curve in software on my FFT, and comparing it to the UUT.

Jocko

[SY]

Getting an inverse correct is a lot easier- you don't care much about noise or sonics, just freq response. There are some excellent published designs (I used one from AA), and building one up with 0.5% or better tolerance components (I used 0.1% for mine) and input and output buffers will get you something pretty nice without having to trim.

Not every hobbyist has your software That's a slick way to go, but not one I can implement without sending you my preamp to tweak.

[ALW]

Walt Jung's Op-amp Applications book shows a method for doing reponse deviations in SPICE, by comparing sim results to an ideal Laplace transform.

Probably similar to what Jocko is doing with real circuits.

I'll dig out the ref later.

Andy.

[Jocko Homo]

Why not? I'm only in in for the money.

(Gratutious image of Mothers of Invention album left off.....for now at least.)

Anyway, noise and sonics are not the problem. Pole-zero interaction is there even in passive networks, and it if you saw how much a small change makes, you would understand why ALW and I have the upper hand.

The other problem is getting a source that has good frequency stability and resolution. And way of really measuring it. I imagine a good sound card and FFT program would be a step in the right direction.

Hey.......I know......I could make a pre-emp box......and sell it for $$$.

Only no one tell PerAnders, he may try to beat me to it.

Jocko

[ALW]

Walt Jung "SPICE Technique Compares Frequency Responses", EDN, November 25, 1993, pp.188 and 190.

Section 6.20 of the latest Op-Amp Applications book has the Laplace transform listing.

Andy.

[SY]

Jocko, that's the real problem with passives- normally, just changing a tube will throw off the EQ unless the network is buffered, which isn't great design. So will tube aging. Feedback EQ has passive beat all to hell for stability, which, of course, is why I use passive.

[Jocko Homo]

Some of us use JFETs. Nice and quiet, no aging problem. Passive is easier to tune, and does not have to worry about open loop gain to interact with, or worse, degrade and really interact with.

And then you get into the whole amount of feedback vs. frequncy thing with active EQ.

No, thanks. I'll stick to passive.

Jocko