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Old 26th January 2008, 04:12 AM   #1
jn2630 is offline jn2630  United States
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Default Ceramic or Magnetic with new preamp?

I have just built a phono preamp. It has two settings, Magnetic and Ceramic. The ceramic channel has a flat equalizer, gain 5. And the Magnetic has the RIAA equalizer.

I have a problem though, when using the Magnetic setting, the high notes produce static. Low notes produce static. Mids sound great.

On the ceramic setting, its clear, but no RIAA equalizer.

I don't know if I have a ceramic cartridge or magnetic cartridge, but if my cartridge is ceramic, will it produce the described results, or is there something wrong with the circuit? Thank you.
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Old 26th January 2008, 09:57 AM   #2
Bobken is offline Bobken  United Kingdom
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Hi,

Ceramic cartridges generally date back to very many years ago, and as far as I am aware haven't been made for a long time as their performance was superceded greatly with the advent of better subsequent technology.
Doubtless, someone will correct this view if there are any modern ceramic cartridges, as I am not aware of every cartridge which has ever been made.

Therefore I assume that unless you have a very old cartridge, yours will be a magnetic.

I am not certain what you mean by "static" but presume that this is some kind of distortion, although using a magnetic cartridge with an input designed for Ceramic cartridges should sound very poor, as there is no RIAA correction. So, these 'symptoms' are a bit of a puzzle.

IIRC, ceramic cartridges gave a higher output than magnetics by quite a large factor (but I would need to check back to be certain as it was well over 40yrs ago when I last used one) and assuming this is so, the ceramic input will presumably be less sensitive on your preamp. Accordingly, I am guessing that the output level of your cartridge may well be too high for the input sensitivity of your magnetic input, and you are suffering from overload distortion. This would be reduced or eliminated with a less-sensitive ceramic input, although the overall balance of sound will be very poor.

The way to check this for certain (and maybe permanently eliminate it) would be to reduce the cartridge's output with a suitable attenuator (perhaps an 'L' pad) to see what this does to the sound. Alternatively, the input sensitivity of the magnetic input might be reduced if you wish to use this particular cartridge.

If you can find a record with a passage which is recorded at a very low level, possibly a very quiet part in some orchestral music, and if this sounds better, it is almost certainly an overload problem which you have here.

Edit. I just noticed that you mention the ceramic input's gain is merely '5', so this will be a much less sensitive input than that for a magnetic, as I suspected.

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Old 26th January 2008, 12:41 PM   #3
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I think Bob is correct. The ceramic cartridge was similar to the crystal cartridge, if memory serves. The crystal cartidge had a high output and didn't need RIAA correction if it was connected to an input impedance of around 1 Meg. It was pretty crude and has indeed been superseded long ago by better magnetic cartridges,
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Old 26th January 2008, 05:49 PM   #4
oshifis is offline oshifis  Hungary
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You can test your cart with a multimeter in 20 kohm range with a 10 kohm resistor connected in series. If you measure infinite, it is a ceramic, if you measure around 10 kohm, it is a magnetic type. The series resistor is necessary for protecting the delicate internal wire of the magnetic cartridge.
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Old 26th January 2008, 06:07 PM   #5
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If you have a component turntable rather than a changer I would almost guarantee that you have a magnetic cartridge. Ceramic cartridges replaced crystal cartridges around 1960 and were the standard for economical phono reproduction for the next 25 years. They were mostly installed on changers that were part of a console or all-in-one system. Interestingly, some of the better ones were capable of remarkably good reproduction, considering their cost. In many ways their piezoelectric function is similar to an electrostat. They have a very high output impedance and expect to see 1M ohm or higher loads. When loaded by the relatively low input impedance of a magnetic phono amp much of their high output goes away, but there is still probably enough to overload the amp. With that kind of load the bass disappears more than the treble, since the device is similar to a small capacitor, so the RIAA curve actually restores a bit more natural sound.

A magnetic cartridge connected to a ceramic input usually sounds very weak and sounds like the bass is all the way down and the treble is all the way up. It is not listenable at all. There are some ceramic phono inputs that function in a different manner and will cause a magnetic cartridge to sound very muddy but I don't understand why as I have not examined the circuit of one of this type.

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Old 26th January 2008, 06:09 PM   #6
EC8010 is offline EC8010  United Kingdom
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Some ceramic cartridges were actually intended to be used into magnetic inputs. The Connoisseur SCU1, for instance.
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Old 26th January 2008, 06:21 PM   #7
jn2630 is offline jn2630  United States
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My turntable was acually part of an all in one system from the early 90's. I took it apart and made a new base for it. I think theres a good posibility of have a ceramic cartridge. I will try to get my hands on a mag turntable, see if it changes.
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