Trapping MCs

[Salas]

After having measured a moving coil cartridge and there is an embedded HF resonance, like in many of them, I just thought why not implementing a parallel tank resonance trap in the phono unit? The whole game is judged in having a well behaving coil at the needed frequency and dBu level. It can be calculated in between stages of the phono, or on its output, given that it will be driving a known level input Z all the time. It can be optionally defeated by a sorting switch as well. That would open up sonically very many cartridges!
It takes a full range pink noise track on a test record and an FFT. I would not trust any manufacturer measurements. Also just paralleling a cap on the input load resistor, makes a mess earlier before the resonance peak. Half measure. Only a properly tuned trap will do. Parametric EQ in other words. In loudspeakers when some ringing is gone they really sing. Cartridges are transducers too. I would expect such performance gains. Does anybody know who can make correct mini inductors with good distortion cores preferably 0dBu or +6dBu on special value order?

Me I got lucky, because I measured the input of the Dynavector DV6/Z and it averages 0.35H in between channels. Just the value that I was looking for! Sorted the output to avoid hum injection, and made a 12.5 kHz Q=2 trap for the measured resonance of Ortofon Virtus and 50K line stage input Z termination. He, he! Revelation! Add $$$. Right on the money!
Lucky me, the Dyna did not saturate at 200mV AC RMS that I put it to work!

THE POISON



THE REMEDY

[Salas]

Found one nice set of measurements for the Lyra Dorian cartridge on the TNT site. Has the peak thing too. They almost never present measurements in cartridge reviews now days. This one is a good example for the MC peaking thing, and a proper review.
There is a concise description of the last octave (10k-20k) resonance common in many MC cartridges.
If you are equipped with a calibrated FFT running PC (ARTA is OK) and a tone test disc, I highly recommend the method I used. The audio quality gain is HUGE. The RLC can be easily implemented in a DIY phono stage that the terminations are known. Its easy to calculate an anti resonance trap. I guess that transformer manufacturers can wind a mini core coil with appropriate inductance circa 15kHz on special order. OK it takes a little work and common circuit sense. But it pays off.

Lyra Dorian Measurements & Review (TNT)

[Werner]

The Rega Ios has a trap for their Apheta cartridge:

http://www.rega.co.uk/html/Ios%20pho...0amplifier.htm

Thanks for the praise on the Dorian review. Still, I don't quite endorse
compensating for these peaks. Vinyl is such a lossy medium with respect to treble (treble limiting in the cutter, stamper wear, LP wear, tracing losses, ...) that when all is said and done, a cartridge with a truly flat response nets a total (system) response with drooping treble.

But then I listen on fairly neutral speakers, not modern treble-hyped junk.

[Salas]

Hello Werner

I appreciate your view since you have extensive experience in many vinyl replay systems and you know more about the average needs of the medium.
In a DIY situation things are very flexible though. I have in mind to incorporate a 3 way switch. One way could be full compensation, second way half amplitude compensation, third way = defeat.
Since the speakers are a very real factor as you mentioned, plus the vinyl pressings differ a lot, some flexibility is adequate I guess.
My rather limited experience is that most systems using MC cartridges sound thin in the end for most of the records. I remember a Supex a Benz and a Koetsu that were not exaggerating this feeling.
I understand that in DIY the net target can be easily met for very certain circuits and cartridges or speakers. It is impossible to exactly cater for every unknown commercial system's tone out there so I guess that most cartridge manufacturers use some over boost just in case.

[nicoch58]

OT

Supex ? you know the 901 ?

[Salas]

Yes. Mother of Koetsu. Very sweet.

[nicoch58]

dl 160 at 47k from vinyl engine

[Werner]

Don't know who made that measurement, but
he sure needs to learn a bit about signal theory
and FFT before attempting things like these.

In short: pretty useless.

[Salas]

Ditto. I will measure it for you soon nicoch46.

[nicoch58]

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