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2nd March 2006, 01:33 PM  #11 
diyAudio Member
Join Date: Aug 2002
Location: Germany

...the plot
edit: bad pic, well, the range is 30dB at 1Hz till +77 dB at 20kHz. It rather should be at 0dB Rüdiger 
2nd March 2006, 01:47 PM  #12 
diyAudio Member

Did you check the "resources tab" at the Beige Bag web site ?
www.beigebag.com The formula is given in that article about the RIAA correction. Application might be slightly different in that GUI but you get the idea.
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2nd March 2006, 02:04 PM  #13 
diyAudio Member
Join Date: Aug 2002
Location: Germany

Hi,
The formula itself seems to be ok, my problem is the actual implementation. I'm sure, the beigebagspice software is good, but I shall get it working with ltspice, Rüdiger 
2nd March 2006, 06:08 PM  #14 
diyAudio Member
Join Date: Nov 2002
Location: Netherlands

Hi Rudiger,
In plain pspice text as a sub circuit this works for me: .SUBCKT I_RIAA IN OUT PARAMS: tau_1=3180u tau_2=318u tau_3=75u +tau_4=3.18u * E1 OUT 0 LAPLACE {V(IN)}={(1+tau_1*S)*(1+tau_3*S) +/((1+tau_2*S)*(1+tau_4*S))} R1 OUT 0 1meg * .ENDS For a normal invers RIAA make tau_4=0 and for a corrected RIAA incorporating the 3.16 us time constant, make tau_4=3.18u Maybe that works in your pspice? Cheers 
2nd March 2006, 06:44 PM  #15  
diyAudio Member
Join Date: Nov 2002
Location: Netherlands

Quote:
E_RIAA out 0 LAPLACE +{1117*V(in)}={(1+0.00318*S)*(1+0.000075*S)/(1+0.000318*S)} Btw. Why that factor "1117"? 

2nd March 2006, 06:51 PM  #16  
diyAudio Member
Join Date: Aug 2002
Location: Germany

Quote:
there is no next line. however, the expression computes without error warning, but shows strange behaviour. This is not related to the gain modifier (1117*) I give up for today, Rüdiger 

2nd March 2006, 07:14 PM  #17 
diyAudio Member
Join Date: Nov 2002
Location: Netherlands

This is what I get with the sub circuit mentioned.

2nd March 2006, 07:38 PM  #18 
diyAudio Member

In beigebag and multisim there is a transfer function utility  just multiply and apply the constants:

2nd March 2006, 10:09 PM  #19 
diyAudio Member
Join Date: Nov 2002
Location: Netherlands

Hi,
That sub circuit should work in any standard pspice compliant simulator. Since we are most time interested in the gain at 1 kHz I have modified the model so it gives 0 dB gain at 1 kHz: .SUBCKT I_RIAA IN OUT PARAMS: tau_1=3180u tau_2=318u +tau_3=75u tau_4=3.18u CORR=9.897 E1 OUT 0 LAPLACE {V(IN)}={(1+tau_1*S)*(1+tau_3*S) +/((1+tau_2*S)*(1+tau_4*S)*CORR)} R1 OUT 0 1meg .ENDS Cheers 
2nd March 2006, 10:57 PM  #20 
diyAudio Member
Join Date: Jun 2004
Location: Richmond CA

Here's an LTSpice example of Laplace for inverse RIAA. This inverse RIAA includes the "Neumann" 3.18us or 50kHz lead in addition to the usual 50/2122Hz lags and 500Hz lead. The laplace works well in LTSpice only for AC analysis, for transient analysis you should use an RC network. Of course you need the RC network or a test record for frequency response verification if you built something.
The example uses the "El Cheapo" feedback network with an ideal 1pole opamp, results are similar to OPA637 model. I have built and tested frequency response of both tube and solidstate phono preamps modeled in LTSpice, agreement between simulation and measurement from 100Hz and 10kHz normalized at 1kHz is usually within 0.2dB, 0.7 to 1dB from 20Hz to 20kHz. I doubt it is possible to verify frequency response this closely with a test record and phono cartridge, if you have done this please let me know. The E source with the Laplace formula used adds 19.9dB gain at 1kHz, so for 5mV on the preamp input the AC source (V3 in this example) should be 505.8uV. The example circuit for Laplace: 
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