RIAA Stuff

This collection of documents involve accurate phonograph reproduction according to the RIAA curve.

1993: SPICE Technique Compares Frequency Responses‘ appeared as an EDN Design Idea, November 25, 1993, pp. 188, 190. This article illustrates how to enable a software-based frequency response comparison using SPICE, between an ideal RIAA deemphasis curve and a modeled reproducing amplifier.

1980: ‘Topology Considerations for RIAA Phono Preamplifiers‘ AES Preprint # 1719, was presented at the Fall 1980 AES convention. The networks featured can be used in either active or passively equalized preamps.

1980: A High Accuracy Inverse RIAA Network‘ by Stanley Lipshitz and Walt Jung, appeared in The Audio Amateur, Issue 1/1980, pp. 22-24.


 

4 thoughts on “RIAA Stuff”

  1. I am building the passive RIAA preamp from Op Amp Applications, Fig 6-17. It uses 2 AD745 op amps with an optional servo. I am wondering if a BUF 634 could be used on the first stage or if it would add too much noise there.

    Thanks

    Mike W

    1. Hi Mike, thnx for the query. What you propose sounds logical and worthwhile to me. I am assuming you mean to insert the buffer after the first stage, before the RIAA network. This would be topologically like 6-15, with a AD745 for U1, and the BUF634 buffering it as U2, correct? The overall difference would be that there is no RIAA feedback network around U1, i.e., U1/U2 operate as fixed gain stage with R4/R3 connected after the buffer (as in 6-17).

      This should work quite well, I’d think. With the extra drive of the buffer, you could in theory also lower the component values of the network a bit. But, that is up to you to decide on the merits vs. the hassle of chasing potentially weird R-C values.

      The presence or absence of the buffer after U1 will not impact noise. Look on it as adding a beefier output stage within the U1 op amp.

      Can you still get AD745s? A good choice for this application, but I had thought they’d gone UN-obtanium some time ago.

      Good luck with it!

      Walt Jung

  2. I am very grateful for your rapid response. I’ve been using your designs and advice since your first articles in TAA.

    I got the AD745s ($4) and some OP37s ($4), along with the BUF634s ($4) and some BUF03s ($6) – all about 2 years ago on eBay. The first 3 appear quite genuine; the BUF03s are rumored to be sketchy and don’t look the same as the 6 I have left from the old days. I’ll have to do an A-B in the old Corey Greenburg “Buffered Passive” preamp I have lying around somewhere.

    I may use the BUF03s vice the BUF634s; the second are amazingly detailed but the first are somehow more “analog”.

  3. Sounds good Mike. I’ve moved your comments here to RIAA Stuff, which is more suited. Thanks for your kind comments.

    If you wish to alter the RIAA values, do so as to maintain the same Ratios. That is, multiply all Cs by a common factor, and divide Rs by that same factor. For example, if C1 goes to 1uF, the factor is 3.3.

    Check list for the network used:

    R1C1 = 2937 microseconds
    R1C2 = 1007.2 microseconds
    R2C1 = 236.79 microseconds
    R2C2 = 81.21 microseconds
    (See AES preprint 1719 here)

    If you do use a buffer twixt U1 and the network, then the stage 1 gain set Rs (R4 and R3) can be lowered.

    Walt Jung

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