Audio input

Gene Heskett gene.heskett at verizon.net
Sat Dec 16 03:03:10 UTC 2006


On Friday 15 December 2006 17:05, Mikkel L. Ellertson wrote:
>George Arseneault wrote:
>> At the risk of sounding dumb:
>>
>> How old is the phono-player?
>>
>> The reason I'm asking is because some of the older
>> players have a different style of pre-amplifier and
>> require a special input. (long time since I dealt with
>> this... I think it was called a "ceramic input")
>> Without the right input on your amplifier it would
>> sound very faint or possibly not be audible at all.
>
>I thought the ceramic input actually gave a higher level input the
>the magnetic ones. In any case, the phono pre-amp also has to
>compensate for the response curve of the magnetic cartridge. This is
>why amps (used to?) have a phono input besides the aux unput - the
>levels and response curve is different between a phone-player and a
>tape deck.
>
>Mikkel

Yes, the magnetic cartridges are very hard put to generate more than a few 
millivolts of output, and they are not amplitude sensitive, but velocity 
sensitive.  Low frequencies from the vinyl result in very slow effective 
velocities and low output.  This translates to a need for a gain 
characteristic in the preamps that fairly well matches a 6 db increase in 
needed gain per octave below about 5khz.  Above that, the recording and 
pickup coil inductances compensate enough to get by, generally speaking.

Ceramic or 'crystal' cartridges are generally amplitude sensitive, but 
they also have a capacitance effect in series with the generator symbol, 
so they need very high load impedances to preserve the bass response, 2.7 
to 10 megs being the typical input load for those.  You can get an idea 
of that problem by actually measureing the capacitance of the device.

One well versed in this now elderly art could write at least 10 pages in a 
manual describing how to get the best results for the money spent on 
either of these devices.  And then there was the Weathers capacitative 
pickup, but since it wasn't stereo, good as it was (and it was damned 
good in 1959), it went away.  So todays epitome of fine cartridges pretty 
well describes the Shure V15 series, even radio shack sold them at one 
time.

Audibly cleaner than anything else, and hundreds of times easier on the 
recordings than any other cartridge then, or probably even now.  It will 
need a good arm and a stable turntable as its optimum tracking pressure 
is 1.5 grams, which includes about .8 grams used for a carbon fiber brush 
that cleans the dust out of the grooves in front of the needle.  I put a 
pair of them in at a radio station back in '80, and it took our most ham 
handed DJ 6 months to wreck the first needle.  In that 6 months we saved 
the cost of the needle several times over just in the 45's we didn't have 
to replace because of cue burns on the leadin track or general 
deterioration of the sound the older Stanton 500 catridges did as they 
plowed their way around the record with needle pressures in the 6 to 8 
gram range.  Needle life was 2-3 weeks with those.

>-- 
>
>  Do not meddle in the affairs of dragons,
>for thou art crunchy and taste good with Ketchup!

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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Copyright 2006 by Maurice Eugene Heskett, all rights reserved.




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