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Old 24th September 2002, 08:59 AM   #1
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Default MC load, normal input characteristics

HI!

I was wondering about a normal load for a couple of MC pickups, low level, normal level and high level.

The resistance is usually low, 100 ohm or slightly more but what about the cap? Does it matter really? What does the expertise say? In MM amps it's very important to have the right capacitance because of the resonance at 10-20 kHz.

Sorry, I just became aware of the similar thread in this forum.
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Old 24th September 2002, 02:33 PM   #2
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If it is low enough, why would you want to put a cap there?

Jocko
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Old 24th September 2002, 02:40 PM   #3
artnyos is offline artnyos  United States
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Default Cap

To provide low impedance load at ultrasonic frequencies for damping and to filter RF.
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Old 24th September 2002, 02:43 PM   #4
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Default Filter RF

Isn't that what gate resistors are for?

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Old 24th September 2002, 03:03 PM   #5
dice45 is offline dice45  Germany
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peranders,

i have to second Jocko's and Art's point from the tryout side: no input cap for MC cartridges. Even for a HO-MC with about 1mV for 0dB@1kHz fed into the MM input, you are better on sonically if you take the cap out. Unless it is one of those fancy singleplate micas with riveted legs out of my special part bin. Sorry, yet another mica won't do in || to phono input.
Must be a sonically proven one.

For MC loads, see the other thread you found.
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Old 24th September 2002, 03:28 PM   #6
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Default I don't want to have to 'splain this again...

2SK147 noise figure graph, all zipped up so that is readable.

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Old 24th September 2002, 03:38 PM   #7
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I built an MC phono amp based on INA103. First built it with 23.5k resistors and small value caps on input to ground. Removed the caps and didn't work no more Amp was oscillating due to cartridge inductance?? I don't remember what the deal was, but put the cap back in and it worked fine again. Based on Scott Dorsey's article in Positive Feedback years ago. He stole most of it from AD guide book (riaa network) and BB data sheets

Ron
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Old 25th September 2002, 09:29 AM   #8
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MM's has an electrical resonance which this C eliminates. You will get a rather sharp peek at 10-20 kHz which in some cases don't sound good.

My question was if MC's of some sort have this electrical resonance (probely not?) worth noticing and therefore do something about?

Are there any facts (not opinions) in this matter?
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Old 25th September 2002, 08:32 PM   #9
dice45 is offline dice45  Germany
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peranders,

had a lengthy post for you that went down the tube called browser crash.

In short: the MC has a low voice coil inductivity in the µH range which forms an LC low pass with a ridiculously high roll-off frequency. The cap does not hurt or not much, in measurement terms.
The MM has a high stator coil inductivity, in the H range. This alone yields to a roll-off in the audible range but overlays with the stylus/vinyl resonance located at about 55 to 60 kHz. So, by the cap it is easy to adjust the MM freq.response to be deadflat.

Not so with MC cartridges, here the designer has to take means to compensate the stylus/vinyl resonance.
No cartridge resonance counteracting.
Jonathan Carr, if you happen to read this, correct me if i am wrong here.

Back in the late 70ies to mid 80ies, when MC became really popular, most MC freq-responses were rising from 10-12 kHz or even below. Not many cartridge manufacturers managed to make MC cartridges with a flat freq.response. The proverbial MC treble boost was usual (and pain to my sonic taste).

But a few well-designed and also well-voiced MCs delivered pure sonic beauty (and some do until today: vdHul, Supex / Koetsu, Ortofon). I do not say anthing about clearaudio without my lawyer being present.

transducer,

if your amp oscillates or performs other stunts, this is a reason to leave the cap in.
But this cap is a coupling cap: it couples HF to ground. It has sonic flaws as all coupling caps have, only that, being a shunt coupling cap, it acts subtractive and not additive like series coupling caps. I have made the observation that sonic flaws of coupling caps hurt the more the lower the signal level is. A cap doing ok on line level will be most probably unusable for MM or MC level. You need caps with best and proven sonics here. I bragged about my singleplate micas not without reason.
Micas selected for sonics, good KP and good *potted* KS are fine, NP0/COG ceramics also should do a good job.

Another thing. Provided the phono preamp makes it to the MHz range, you might hear time constants located below 1MHz.
Allen Wright claims a phono preamp has make it to the MHz range, i do not. He says that in such amps HF roll-offs or rises are audible, so do i. Not necessarily eveyone hears it but i have met a couple of people who do. So i guess i am not only fooling myself, saying so.
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Old 25th September 2002, 09:51 PM   #10
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dice45, thank you for your long answer. What should I write at Google to get this type of answer

Anyone who has more or other opinions?
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