Testing with test-records of RIAA amp.
Hi I have a question to all about testing the hole phono circuit and how to do that properly.
What do I want to measure:
Rumble level of the TT.
Linearity of the RIAA amp.
THD of the RIAA amp.
Performance of the cartridge with a sweep.
THD of the cartridge.
With a MLS program like Arta I can test the RIAA pre-stage with a divider for the test signal to get the right input level. The divider can also contain a passive RIAA curve so we get a flat frequency response.
The problem is then I can't calibrate the passive divider but with carefully measured low tolerance components we can assume influence on THD and linearity is marginal.
That would be the most simple way to get results for the amplification part IMO.
To test a cartridge is a other challenge. How does it work with a test record and witch test record is use-full for testing I know Shure had some. But it has to have more information on it then only for cartridge alignment.
Who can help?
No one ever did use a test record?
Be aware that some test records are RIAA and some are a simpler curve with bass turnover (bass boost below 500) but constant velocity above 500. Most of the quality test records were by Shure and RCA.
In the end you will be testing your system, but you will also be testing the quality of the test record. None of them are perfect.
The results, well, if you believe that High Fidelity is realised by low THD and flat frequency response that LP is HiFi, maybe best not to measure.
Me, I like the way LP sounds...
The HifiNews testrecord is very good to get an idea what you can measure with the help of a computer, but I used it to get the best setup of the cartridge and that can be done by comparing left and right channel distortion at different settings. Still I was surprised by the low measured quality. Even the pressing has noise, pops and crackles. Tones are not constant and things like that.
But for a hobby it's a nice job to play around with.:)
The CBS STR-100 was the classic and IMO best test record. There may have been a later 101 or something. There have been a dozen or so other records that are useful, but the biggest thing you learn using these is how poor a recording medium an LP really is. Constant frequencies are neither constant amplitude nor constant frequency, not to mention the pops and local disturbances. Test records usually have some warp just like any other record. Yes, LPs sound good, but not because of their perfection.
IMO you should test your system from the input, using an inverse RIAA network, and leave it at that. It will likely be far more accurate. A test record will mainly tell you about high frequency tracking and the CBS liner notes make it clear that under the best conditions the high frequency tracks will have limited life. When you could still get them, they weren't cheap! Music and the price of your stylus will tell you most of what you need to know.
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