Vintage Mic Transformer for MC step-up - gain-phase and impedance measurements

[Cqwet Dbdfte]

phasemation.com make MC transformers with a centertaps, and promote balanced MC signalling. I dare not ask what they want for their piece of kit.

I just measured the RB300 tone arm to "ground" (tonearm center post) , open. Cart case to "ground", open.
Left channel cold is tied to shield on RCA. I suspect the connection is done on the "wire board" inside the tone arm post.
The one channel with higher noise is now fixed, by repositioning the transformers. Likely source of EMI, line amp 60Hz magnetics. Noise is now down 65dB from 90dBspl peak listening level on both channels, i.e. 15dB above room background noise.

Some dude quipped that center-tapped MC transformers are "impossible" to get right, but the phaseme-guys seem to have confidence selling it.
The concept is correct. I suppose a connecting the shield to a center-tapped resistor could also work, just to get equal potential to shield on the pair.
The resistance could likely be much higher than the load resistance, thus not loading down the signal.

Twisted shielded pair with shield grounded at only one end is old school, https://www.hollandlink.eu/VandenHul-Wiring Diagrams.pdf.

 

[volker]

The MIDI connector is not the same as the tonearm connector. I’ve never seen the tonearm connector used for any other purpose. XLR was used for audio in Europe and the US from the 1960’s on.

There are different variants for five pins, yours might be the first one in second row from what I've seen on phono devices.

 

[Gold]

Here are the aforementioned connectors. The top one in the first photo is the MIDI connector. The next one down is the tonearm connector. The third one down is the Tuchel Amphenol ( it’s six pin)and the last one is the big Tuchel.

The only five pin amphenol I could find is attached to the lathe. That’s the next photo.

 

[Cqwet Dbdfte]

Nice collection!
The common consumer audio 5-pin DIN (15mm dia.) used 45°, 180° etc. The 60°, 240° etc, not so common.
The second down does not look like a typical 12mm diameter tone arm connector?

http://www.elektron-bbs.de/elektronik/kabel/audio/din.htm...has DIN wiring connection standards, including mikes of different signal types. The "symmetrisch" (balanced) two microphone connector would also be applicable to an MC cart. Shield is only connected at one end.

 

[Gold]

Nice collection!
The common consumer audio 5-pin DIN (15mm dia.) used 45°, 180° etc. The 60°, 240° etc, not so common.
The second down does not look like a typical 12mm diameter tone arm connector?
View attachment 118434
http://www.elektron-bbs.de/elektronik/kabel/audio/din.htm...has DIN wiring connection standards, including mikes of different signal types. The "symmetrisch" (balanced) two microphone connector would also be applicable to an MC cart. Shield is only connected at one end.

The connectors I call tonearm connectors fit two tonearms I have. The Ortofon RM309 and the Stax UA70

 

[Cqwet Dbdfte]

I do not know what 5cm/sec, represents as value of max lateral peak typically used.

Using the 5cm/sec track my MC preamp outputs ~2.6Vrms, noise is at around 2.5mV, and a loud Elvis record peaked out at 8.80V rms.
I thought it sounded kinda loud;-)
The ~ 315Hz tracking ability tracks works up to 80um then skips on the 90, and 100, and max output is 14.15Vrms at the 80um.
I'm guessing this level would be rarely used?
This level would indicate a 79.5dB dynamic range.
All the 120Hz artifacts are gone, noise is dominated by random very low frequency noise.
My 120V line cords are now all the shielded variety. Can't hurt.

 

[Gold]

I do not know what 5cm/sec, represents as value of max lateral peak typically used.

Using the 5cm/sec track my MC preamp outputs ~2.6Vrms, noise is at around 2.5mV, and a loud Elvis record peaked out at 8.80V rms.
I thought it sounded kinda loud;-)
The ~ 315Hz tracking ability tracks works up to 80um then skips on the 90, and 100, and max output is 14.15Vrms at the 80um.
I'm guessing this level would be rarely used?
This level would indicate a 79.5dB dynamic range.
All the 120Hz artifacts are gone, noise is dominated by random very low frequency noise.
My 120V line cords are now all the shielded variety. Can't hurt.

Your SNR is about 50dB. 2.6V is your reference level and 2.5mV is the noise floor. You have a high clip point at +36dBu but you have to take into account that 20K is 20dB above 1K. Just because you are not clipping at 1K doesn’t mean you aren’t clipping at 15K.

 

[JohnRoberts]

Your SNR is about 50dB. 2.6V is your reference level and 2.5mV is the noise floor. You have a high clip point at +36dBu but you have to take into account that 20K is 20dB above 1K. Just because you are not clipping at 1K doesn’t mean you aren’t clipping at 15K.

Yup... RIAA EQ varies +/- 20dB relative to 1 Khz.... It also looks like a LPF rolling off at roughly 2kHz.

JR

 

[Gold]

2.6V is about +10.5dBu. Since 5cm/sec is 3dB lower than 7cm/sec, you have about 11.5dB more gain in your system than I have in mine.

 

[Cqwet Dbdfte]

Log(2600/1.5)*20=64.77

 

[Cqwet Dbdfte]

Using my old Fluke 8050A (new NiMH batteries!) normalized to 0dB with the 5cm/sec/1kHz level track, noise measures -59dB on a 600 Ohm scale, needle up, and -61dB with shorted input.
The Ortofon test record now tracks on the 100um without skipping, setting anti-skating to default did the trick on the RB300 arm. Max level on 100um test track about +15.5dB, did not check on the scope yet.
The loud Elvis 12" 45rpm record maxes out at +10.84dB with the slow Fluke 8050A.
All my other DMM's are useless at 20KHz.
As to clipping at 15kHz I cannot yet say, no references to this yet, but program content dominates under 1kHz an especially under 200Hz, the rest are harmonics and not much compared to 1kHz, survives. I'd like to find a spectral peak hold survey of max program content to find reasonable clipping limits for the non-feedback input stage. The second stage is of filtered by the passive RIAA network and would receive 40dB lower voltage than the input stage, and any harmonics 3h, 5h, 7h would be effectively attenuated by the RIAA filter.