What do you think about these RIAA parts value ?

Hi

I recently got a phono stage I plan to upgrade. I checked the RIAA values of the parts and they seems to be far away from ideal values.
When doing RIAA calculation, to determine R!, should I take the value of R1 (270K) in parallel with R3 (347K) ?

I looked at many RIAA circuits and it seems most of them don't respect the ideal values for correct RIAA.

Any opinion how to correct the parts value of this phono stage ?

Thanks
 

Attachments

  • Tokyo Sound RIAA.jpeg
    Tokyo Sound RIAA.jpeg
    511.4 KB · Views: 176

rayma

Member
2011-04-29 8:37 pm
When doing RIAA calculation, to determine R!, should I take the value of R1 (270K) in parallel with R3 (347K) ?

Yes, that's right, use the Thevenin equivalent value. This circuit does lose 5dB of gain.
It would be better to have R3 before R1 to avoid that attenuation.
Or instead, make R1 smaller and R3 larger, so the parallel combination
is the same but the loss is smaller. Gate resistors may be useful, too.

http://www.mh-audio.nl/calculateRIAA.asp

Use this inverse RIAA network for testing.

http://www.hagtech.com/pdf/riaa.pdf
 
Last edited:
legarem said:
I looked at many RIAA circuits and it seems most of them don't respect the ideal values for correct RIAA.
Two reasons for that:
1. some people don't know how to calculate values, and can't be bothered to find out - there are plenty of resources on the web for this;
2. some people don't wish to calculate values, but instead 'tune by ear' thus ensuring that they get the RIAA curve wrong.
 

rayma

Member
2011-04-29 8:37 pm
I paralleled R1 (270000) with R3 (1M) so R1 become 2125984. Am I finally right or wrong when I take R3 in my calculation ?

Yes, that's necessary to get a correct value for the RIAA components.
Also, the output impedance of the first stage should first be added to R1,
before paralleling it with R3.
The input capacitance of the second stage should be added to the value of C2 as well.
 
Last edited: