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Moving-Magnet Head Amp - without RIAA
Moving-Magnet Head Amp - without RIAA
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Old 21st January 2019, 08:55 PM   #61
billshurv is offline billshurv  United Kingdom
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Moving-Magnet Head Amp - without RIAA
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Originally Posted by Bonsai View Post
I think you would have to look at the exact measurement set-up to decide where the mid-range dip came from. Tone arm resonance? Head shell resonance? Was the response measured using a reference disc? If so, was the EQ ok etc etc.

This is half the fun which is why families of readings from the same person with the same disk are my preference for lookoing for patterns. Pink noise appears to vary horribly, so any measurements with those need to be taken with a pinch of salt.


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The HF resonance within reason is easy to understand (cart L, cable C, input amp C.


The peak and steep roll of yes, but the dip you often see from 2kHzish upwards isn't easily modelled. Something causes it but what?


Of course if you are using digital correction you can just dial in a low Q peak to compensate if your record is accurate.
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Old 22nd January 2019, 03:05 AM   #62
scott wurcer is offline scott wurcer  United States
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Originally Posted by Bonsai View Post
I think you would have to look at the exact measurement set-up to decide where the mid-range dip came from. Tone arm resonance? Head shell resonance?
This is what I see and it seems to at least roughly match some other results. This is a log sweep at constant velocity, flat pre-amp, no equalization (500Hz to 50kHz (48 actually)), and has been fairly repeatable with several setups. The groove modulation prevents this from going <500Hz. I don't see this being explained by tone arm or headshell resonance.
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Old 22nd January 2019, 06:15 AM   #63
rsdio is offline rsdio  United States
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Originally Posted by scott wurcer View Post
I measured it (IIRC I posted it here) with a CBS labs unequalized constant velocity 500-50kHz sweep and flat pre-amp. [...] It might help if we had more measurements on completely magnetics free cart systems.
So, this disk was cut without RIAA EQ? Very interesting.

I was going to ask whether that makes the bass frequencies too strong to track, but I see that the test tone starts at 500 Hz, which is basically where the bass part of the RIAA EQ stops.

As for the high end, there's no tracking issue, just S/N. So, not having the RIAA boost during cutting probably makes it easier to measure the playback system response without too many variables to account for.

Is this CBS Labs disk available for sale somewhere?
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Old 22nd January 2019, 11:41 AM   #64
scott wurcer is offline scott wurcer  United States
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So, this disk was cut without RIAA EQ? Very interesting.
CBS Labs STR 120, unfortunately good luck finding one now. They were a stock item in the Audio Amateur store until the 80's.

One side is left/right/lateral/vertical at three groove diameters at -8dB re 3.54cm/sec @1kHz. The text says that this sets the minimum groove curvature of 18 microns at the innermost track to 20kHz. There are also constant amplitude 10-500Hz tracks. The track is 48 seconds long at 24 sec per decade.

IME these LP's were produced under laboratory conditions and most or all were optically verified. My impression is they did whatever they needed to the signal path in the lathe to get the desired results, something we have not been able to do. BTW the slight discontinuity at around 31.5s is an artifact I can't recall if it was a dimple in in the surface of this track or something else. The equipment used to do the sweeps were at this time mechanical devices and I have found a couple of range switching artifacts that might not show up when using tracking filters and chain drive chart recorders.
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Last edited by scott wurcer; 22nd January 2019 at 11:48 AM.
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Old 22nd January 2019, 11:47 AM   #65
Hans Polak is online now Hans Polak  Netherlands
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Originally Posted by scott wurcer View Post
This is what I see and it seems to at least roughly match some other results. This is a log sweep at constant velocity, flat pre-amp, no equalization (500Hz to 50kHz (48 actually)), and has been fairly repeatable with several setups. The groove modulation prevents this from going <500Hz. I don't see this being explained by tone arm or headshell resonance.
Hi Scott,

At what level is roughly the noise level while playing a blank groove when projected in your recording image ?


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Old 22nd January 2019, 12:04 PM   #66
scott wurcer is offline scott wurcer  United States
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Hi Scott,

At what level is roughly the noise level while playing a blank groove when projected in your recording image ?
The spot noise was about 10dB over lifted stylus at high frequencies. The software decimates the actual samples and shows the peak which exaggerates the visual appearance of impulsive noise.
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Old 22nd January 2019, 02:39 PM   #67
Bonsai is offline Bonsai  Europe
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Originally Posted by scott wurcer View Post
I measured it (IIRC I posted it here) with a CBS labs unequalized constant velocity 500-50kHz sweep and flat pre-amp. Some day I'll bring it over to Kevin's and try it with his strain gauge carts and fancy schmancy styli. It might help if we had more measurements on completely magnetics free cart systems.
What cartridge were you using Scott?
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Old 22nd January 2019, 03:11 PM   #68
scott wurcer is offline scott wurcer  United States
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What cartridge were you using Scott?
Just a Grado, BTW this is mostly a help out/intellectual exercise for me at this point. I have no interest in $$$ carts and TT's.
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Old 22nd January 2019, 06:34 PM   #69
Bonsai is offline Bonsai  Europe
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Originally Posted by scott wurcer View Post
This is what I see and it seems to at least roughly match some other results. This is a log sweep at constant velocity, flat pre-amp, no equalization (500Hz to 50kHz (48 actually)), and has been fairly repeatable with several setups. The groove modulation prevents this from going <500Hz. I don't see this being explained by tone arm or headshell resonance.
I wonder if youd get a different result with only one channel connected and the other open circuit. Are the channels slightly coupling magnetically in the cart causing cancellation which is then followed further up in frequency with resonance?

No interest $$$ carts from my side either. My customers can afford that stuff. Im with the Ortofon Red and @billshurves stylus trick. Listening to Ella on the LS50s with a sub bass right now. Wonderful stuff.
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Old 22nd January 2019, 08:09 PM   #70
scott wurcer is offline scott wurcer  United States
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Originally Posted by Bonsai View Post
I wonder if youd get a different result with only one channel connected and the other open circuit. Are the channels slightly coupling magnetically in the cart causing cancellation which is then followed further up in frequency with resonance?
We've been over this stuff, none of these experiments do much of anything.
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