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. :blush:
 
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 [email protected] 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.
 
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
 
peranders,

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

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 :sing: (and some do until today: vdHul, Supex / Koetsu, Ortofon). I do not say anthing about clearaudio without my lawyer being present. :shutup:

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.
 
Bernhard: Better include the capacitance of the phono cable in your calculations. The electrical resonance of an MC can be quite highQ, but luckily with a low-impedance (low-inductance) design, the frequency is very high and frequently can be ignored. With a high-voltage high inductance design, the frequency starts to come down into potentially risky territory, and you may want to do something about it.

In general, high-inductance designs are a mess electrically, which is one reason why I prefer to have nothing to do with them (although I do acknowledge that they are useful if you have a phono stage that, err, needs help).

I also prefer phono stages that have reach up to the MHz region, and I usually use a cap at the input of my phono stages to take care of CB'ers and other RF perils of modern society. Personally, I don't like the sonics of micas, and so I use copper-foil styrol or polypropylene.

I've been meaning to do some research and write an article on cartridge loading for our website, as I regard most of what I have read on the subject as ill-informed, and a partial solution at best. My problem is that I am practically always up to my ears in design and development, so while the article has been in the back of my mind for some while, I haven't been able to find the time to put anything down on paper yet.

regards, jonathan carr

PS. When you mentioned Clearaudio, did you have anything around 12~13kHz in mind? (grin)
 
Jonathan,

Cable capacitance, of course, i forgot to mention it, it is in || to the input cap.

Caps:
Copper foil styrenes, you make my eyes green of envy. :sigh: would like to know where to get them; Siemens/Epcos ceased to make those fancy orange-potted KS styrenes a while ago. They cease to make about anything they once were famous for. And next they cease to be if i look at the stock exchange news.

Singleplate silver mica, they are something super special .... shall i send you a sample to try them out? I may have a couple of 200pF left. Maybe in exchange for some copper foil styrenes? :angel: ... :)

Methinks, the lead2element contact is one of the things that makes or breaks sonics of caps and resistors. Many micas are weak in that. Most foil caps are very weak in that. Tin foils and MKVs are gorgeous in that. BTW, there is a group purchase going on in the Electronics & Parts board and there are Epcos MKVs orders not yet closed. So if you are looking for 1st class coupling caps, 1µF/700V, for your personal need only as Epcos revoked them, maybe you try them?

Clearaudio: if i say something negative and detailed in public, e.g. about business manners, processing of warranty claims, I probably would get sued by Peter Suchy.
So i say something positive: he can be glad he has such a great guy as US distributor. A guy obviously making customers happy. And i admit i once listened to a system having a medium-superexpensive clearaudio cartridge as source and this system (was it the Prädikat?) really pleased me and :sing: made me throroughly float in the music.

Cartridges: there was one Lyra cartridge you recommended once for being special, i do not remember which one, was it the Parnassus? And i would like to know more about your Helikon Mono, what advantages does it have to stereo cartridges playing mono records? I need a cartridge with a spherical 25µm stylus for pre1956 vinyl and another one with a spherical 60µm stylus for shellac records. And i am undecided which to choose, Ortofon SPU, Andreoli custom-made or yours. Ortofon problem is that they consider spherical as inferior .. hence QC is not as tight and rumours tell they do not use crystal-oriented diamonds like used of expensive MCs. So i would expect their spherical styli to wear fast.
 
dice45 said:
Singleplate silver mica, they are something super special ....

Altough I'm not a real component freak, mica is above everything else (I have this feeling).

Mica, solid rock, material from nature with very good properties.

Silver, the best conductor there is. Inbeatable combination!

It's a shame though that they are big and come in small values. I like the shape of them too.
 

fdegrove

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
MC LOAD

Hi fellows,

All politics aside:

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.

Per,

If you don't need the cap to rid the headamp/xformer of severe RFI injection then I wouldn't use it.
In real life the added capacitance of the phonocable will already introduce some HF filtering forming an RC filter with the input stage's resistive load.
In MC designs the cartridge's frequency response generally tends to present a tilt at higher frequencies.
The need for a resistive low ohmish load is usually variable from MC to MC and often spoken of in combination with a transistor (fet or bipolar,etc.) design it is fed into anyway.
The function of that resistor is to put a brake on the cantilever/coil interface electrically as to provide better control of it's movement and flatten it's frequency response.
(Consider it a way to control back EMF from the coil field).
Other than providing this and manufacturers a means of providing the customer with a fancy frequency graph it does alter the perceived and measured response of the cartridge.
I think you can well imagine that bleeding off the already very low output of these MC's into a small resistive load will only make for more output loss.
Most manufacturers recommendations on loading their particular model are a good starting point but by no means restrictive.
They are what they say:a recommended load.
By no means have they got any idea what is going to be the RCL load of the customer's next stage.
Experimenting with restive loads is certainly one way to tweak the system's freq. response and probably a matter of personal taste as well.
What is often overlooked is that the prepreamp is fed into a load optimized for MM cartridges:i.e.: 47K + some C (100pF to 220pF).
Now that will roll-off that precious MC cartridge's high freq. response for sure.
That's the first component to hit the bin when I know the customer is not going to switch back and forth between MM and MC.
If,however RFI is a problem then I will try to keep it out at the input of the prepreamp since that is going to be amplified all the way up to speaker level.
Gate stoppers or grid stoppers are usually quite effective here.
Naturally the quality of that small shunting cap is going to be important but I would keep my copperfoil (and I even prefer silver foil) styrenes for my RIAA correction network.
From optimising phono stages I can tell you with absolute certainty that in almost all situations I prefer a highish impedance (for tubes) say 47 to 100K into low capacitance (most already present some Miller effect anyway) then the low resistive high capacitance road.
This allows me to have a flat response from that MC well into the 100KHz range.
No need to compensate with another RC constant pole here for any roll-off at high freq.
(I'm calling that the Neumann pole).

Surely I could go on and on whith this but I'm sure you get the picture by now?;)

Cheers,
 

fdegrove

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
MC

Fellows,

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.

It doesn't really matter what anyone claims here.

What is more important IMHO is the phase relation of that bandwidth.
One could argue ad infinitum about the pro's and con's of wide bandwidth amps or preamps.

Also from what I am to understand from these posts:

Wouldn't it be a good idea to explain the following:

-What a cartridge is and what it is expected to do.

-How it does what it does.

-What materials are often involved and what they do.

-The differences between transducers such as MM MC MI et all.

-The mechanical and electromechanical principles involved in the process.

-Self resonances of materials,damping and how it influences the end result.

The list could be endless.

Hell,I don't blame anyone for not understanding the basics here,I was born in the transistor area and other than my grandparents' tubed radio set,I had never seen anything like it either.

Making your own cartridge would be the ultimate DIY challenge IMO,and if anyone could design a half decent arm along the way....

Just kidding.;)
 
Re: MC LOAD

fdegrove said:

The function of that resistor is to put a brake on the cantilever/coil interface electrically as to provide better control of it's movement and flatten it's frequency response.
(Consider it a way to control back EMF from the coil field).

This immediately makes me wonder if it would perhaps be better
to have this resistor as close to the coils as possible, perhaps
even at the cartridge contacts? In that case we would have to
use a higher input impedance in the phono amp, which could
cause other problems because of cable capacitance etc. One
could consider splitting the input impedance into two equal
parallel resistors, one at the cartridge or in the turntable and
one in the phono amp.

Would this make sense, or are the effects of the cable at such
high frequencies that it doesn't matter at what end we have
the "damping" resistor?
 

fdegrove

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
MC LOAD

Fellows,

This immediately makes me wonder if it would perhaps be better

Yes,this has been done before, as indeed it seemed the more logical thing to do.

Granted it is not a very elegant solution,and it kind of makes you wonder why the manufacturer doesn't build the R's in the coils in the first place?
The answer is in the previous post I made.

However,a good compromise seems to load the cartridge at the lead out wires on the tonearm.
Doing as such would give more resistive than capacitive loading without compromising too much of the looks and weight of the cartridge as when you would put these resistors at the cartridge pins.;)

Good thinking Christer!:)