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RIAA, Questions only please

I have closed the previous thread on RIAA and concluded that very few indeed understand the curves or the purpose. Here is my closing statement from that thread. For those who want to understand and have valid well stated questions I am happy to answer. 

Not wanting to leave the party without a clear and accurate statement I will say the following:

The answer to the question concerning noise reduction is that the simple filter that RIAA decided upon was to raise the high frequencies gradually by about 12 dB starting below 500 Hz, being up 3 dB at the 500 Hz pole. The circuit then cancells the pole with a zero at 2,200 Hz and there is then 3 dB of boosting left as one goes to 20 Khz. It is all done very gently with just two resistors and two capacitors.

By reversing this process on playback we get to enjoy 12 dB less noise above 500 Hz.

The RIAA part of things is the same for all cartridges. However we are accustomed to seeing RIAA combined with the 6 dB/octave compensation for a velocity cartridge. That takes off 12 dB, and along with two things that happen at the very ends of the response, brings the total EQ for a velocity cartridge to 40 dB. Next time you look at an RIAA curve ask yourself why there is that flat bench between 500 and 2,200 Hz.

An amplitude cartridge needs only the RIAA EQ of 12 dB. Which also speaks to the fact that the majority of the spectrum of a record is cut at constant amplitude. When you put a sewing needle in a paper cup and play the record you are getting amplitude playback not velocity.

I study these things because they interest me. Anyone can look up the parts values to make an RIAA filter or inverse RIAA. What interests me is that some manufacturers still get it wrong.

ramtubes
ramtubes's avatar
ramtubes OP
451 posts
 
At this rate I doubt this post will last long. We are already off topic. 

Sorry if you miss the old post. Several members posted such long and confucing replies I could hardly get through them myself. 

I have nothing to gain here. Im not going to win a prize if I am correct. I chose this topic because vinyl is on a comeback, our local club is about 50% vinyl, we have phono preamp "shootouts" which take a great deal of time and effort to set up. We want to know first if we are listening to a preamp with more than a few dB of RIAA error, so I check for that as I am matching levels.

Wouldn't it be nice to know what RIAA is? Is there anyone here who would like to have a go at explaining RIAA to me. I am all ears.

I had a nice half hour conversation with Peter Ledermann of Soundsmith today. We agreed this is a difficult concept to grasp.
ct0517's avatar
ct0517
1,798 posts
 
^^^
Roger
I contacted Peter myself by email, this week,  for clarification on his SG cartridge and unique preamp. I did this because there was incorrect info posted on your other thread about his product. He confirmed some things for me. I was going to publish corrections but your thread was deleted .....not locked. Locked would have allowed viewing without input.  
ramtubes's avatar
ramtubes OP
451 posts
 
sorry I didnt know about Locking. However, in my opinion the original thread was an embarassment to all. To take a simple technical question/concept and bury it, as it had been, with opinion, off topic commentary and an argument between myself and Ralph that was going nowhere deserved to be burried. Each post was more disheartening than the previous.

Do you recall what the incorrect info concerned? Of course his preamp is unique, it employs RIAA plus amplitude EQ not RIAA plus velocity EQ.


ct0517's avatar
ct0517
1,798 posts
 
I am not sure if locking of a thread is even an option. If Tammy Audiogon Support sees this maybe she can confirm either way.

Roger - the posters comments were along the lines of connecting the SG Cart up to his own personal preamp, first using the phono input, and then if I recall using the AUX input; with no mention of Peter's preamp. This is an incorrect setup. As I understand, Peter's unique preamp goes hand in hand with the SG Cart, cannot be separated. Based on my limited knowledge of them, his SG Cart and Preamp appear to be - "real thinking/ design out of the box". 
  
As far as how it is eq'ed, maybe you can get Peter to provide his input here since you have talked with him already, so we can have sharing and learning by all of us. That would add a lot of value for me. On a thread like this I am looking to learn. FWIW - I find the available online documentation for RIAA inconsistent, confusing, misleading, incorrect data .. no wonder, imo, it is difficult to grasp when we have experts like yourself contradicting words and terms we have read online..... trying to fill in the blanks. 
 
A definition of terms for important Words would help to fill in some blanks.   

Like for example - Constant Velocity, Constant Amplitude

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@ct0517 What is the title of the original Thread? 
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