Re: [ARSCLIST] RIAA EQ software

[Scott Phillips <scottp@xxxxxxxxxxxxxxxxxxx>]

Yes, it is a moving coil type I was using. As best I understand it, the
generality Richard has here for a moving magnet type is about what I
read as a starting point as well. His other point is well taken as well.
I used the impedance bridge to get an idea of the combination of
cartridge and cables used, since cables of practical length have a
meaningful effect on what load characteristics need to be. Since I built
the preamp sans RIAA, I had easy leeway to have an input impedance
better than 100k... not typical for a phono preamp. Again, I'm no
expert. Perhaps Bob or someone else has a better or more practical
approach to loading. I started looking at this as an interesting
intellectual exercise instead of a professional one, but I see it is
both, and in an area I have never before troubled myself to investigate.
After puttering around some more and using my test record and a consumer
grade preamp with RIAA EQ in it, the results were not quite the same. It
made more sense when I looked at the preamp input characteristics vs.
the needed values of the R/C I needed to add to flatten out the
response.

Scott  

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:ARSCLIST@xxxxxxx] On Behalf Of Richard L. Hess
Sent: Tuesday, August 26, 2008 3:49 PM
To: ARSCLIST@xxxxxxxxxxxxxxxx
Subject: Re: [ARSCLIST] RIAA EQ software

At 04:12 PM 2008-08-26, you wrote:

>Capacitor in the bridge - now that's getting fancy.  I should have 
>thought that resistance, alone, was the issue.  I wonder if my 
>"flat" transfer would have gone better had I used a y-cable between 
>the phono and the ADC, with the other end going into the normal 
>phono preamp?
>This way, I could hear the record play, for confidence, from the 
>preamp without having to listen to the non-de-emphasized version 
>playing, shrilly, into the ADC, and the (ideal) input Z of the 
>preamp would be summed with the (lower) input Z of the ADC (I was 
>using) to make a nigher-to-perfect load, as seen by the cartridge.

Hi, Andrew,

You don't want to double-terminate the cartridge. I use moving magnet 
cartridges as I don't do transfers for a living. It looks as if Scott 
used a moving coil with those values. I forget the exact range of 
values for a moving magnet cartridge, but the resistance should be 47 
K ohms and the capacitance is around 100-200 pF. Cable is often 20-40 
pF per foot.

Specific numbers would require more research, but moving magnet 
cartridges (like most Shures and Stantons) are very sensitive to 
loading. One of the comments was that the A-D was 10 K which is way 
too low for a moving magnet cartridge.

Cheers,

Richard


Richard L. Hess                   email: richard@xxxxxxxxxxxxxxx
Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
Detailed contact information:
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.