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[Patrick Tracy]

Obviously the RIAA LP playback curve will be there, but how well is it implemented?

I compared the two I could get to easily, the one in my home receiver (Onkyo TX-DS474) and a Realistic 42-2101A I picked up at a flea market. Input level was not changed for these two measurements. The receiver's signal was taken from its tape output. No smoothing was used.

The Realistic 42-2101A:




Two things are clear. The Realistic has more gain, and its LF rolls off at a higher frequency. You can also see a bit of 60Hz/120Hz getting into the Onkyo's signal. From about 150Hz up the Realistic slopes gently down relative to the Onkyo.

Perhaps at some point I can measure in/out voltages to get actual gain figures, and maybe measure the THD.

I'm curious how other phono preamplifiers compare, from DJ mixers to audiophile gear.

[John Roberts {JR}]

To make a EQ quality comparison, you need to normalize the gain of both at 1kHz.

The poles and zeros for RIAA eq are 3180 uSec, 318uSec and 75 usec, From looking at those plots the Onkyo looks closer to proper RIAA, than the realistic, that's not that realistic.

RIAA does not define transfer function below 20 Hz and above 20 kHz (was 30 Hz and 15kHz originally). Later IEC proposed adding another pole at 7950 uSec, but RIAA ignored them too.

I wouldn't lose too much sleep over this. cartridge loading can make noticeable differences in top octave.

JR

[Ivan Beaver]

I don't know a lot about the details of the RIAA curve-but could possibly the difference be between a ceramic and a magnetic cartridge intended usage.

It has been a few decades-but I seem to remember different settings on some receivers which had a different "sound".

[Patrick Tracy]

I don't know a lot about the details of the RIAA curve-but could possibly the difference be between a ceramic and a magnetic cartridge intended usage.

It has been a few decades-but I seem to remember different settings on some receivers which had a different "sound".

I think by the time the Realistic preamp was made pretty much all cartridges, aside from those for kids' turntables, were magnetic.

[Ivan Beaver]

I think by the time the Realistic preamp was made pretty much all cartridges, aside from those for kids' turntables, were magnetic.

I had some turntables that were "medium grade" and were  ceramic.  They were still being sold as individual "separates" untll the late 70s (or later) I believe.

Agreed all the "real" ones were magnetic.

[John Roberts {JR}]

I'll bet dollars to donuts that the rat shack pre is using crappy lousy tolerance cheap capacitors in the EQ playback network. The Onkyo is probably using only slightly better parts.

They look like they are designed for the same spec, just don't expect precision components from a $2 BOM.   

JR

[Bob Leonard]

What's the goal here??

[Patrick Tracy]

What's the goal here??

It's the Basement. There doesn't have to be a goal. But if anybody feels like posting something for comparison it would certainly be interesting to me. For example, are there substantial differences between basic home audio stuff, esoteric stuff, DJ stuff...? The loading issue clouds things a bit, but I think it's still useful information.

[John Roberts {JR}]

It's the Basement. There doesn't have to be a goal. But if anybody feels like posting something for comparison it would certainly be interesting to me. For example, are there substantial differences between basic home audio stuff, esoteric stuff, DJ stuff...? The loading issue clouds things a bit, but I think it's still useful information.

Yawn,,,,  I used to design high end (IMO) phono preamp (kits) back in the '70s-'80s. A good preamp would follow the RIAA spec to within a small fraction of a dB. Another subtle point if you want to properly terminate the preamp input, the source impedance of a typical MM cart was around 1-1.5k with some inductance.

After decades of designing preamps I came to the conclusion that customer behavior wrt to proper capacitance termination (for the specific cartridge), made a larger difference than my 1% resistors and 2% caps in the EQ network.

A cheap preamp OTOH can vary, and it was not that unusual to cheat a phono input in a pinch with tone controls maxed full boost on the bass end, and full cut on the treble. RIAA EQ varies about +/-20dB wrt 1khz gain. 

JR

[Kevin Graf]

One of JR's pre-amps.

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