old amp inputs

[greggfarnham]

My son has an ancient amp (mid 70's) that he wishes to connect an old CD player to. The amp has inputs labelled; tuner, mic, xtal, mag, tape. But I'm unsure which is the right one to put the CD into. Please give us the benefits of your experience and advise.

 

[Dozuki]

Tuner or Tape would be fine. not sure what xtal or mag are, but definatley not the mic input as this should have a preamp built into it.

-D.

 

[karma]

my old tube amp has mag its for phono

 

[Centauri]

mag & xtal are turntable inputs for magnetic or crystal pickups. These have EQ for vynal discs and are not suitable for CD.

As mentioned, tuner or tape inputs will be fine.

Cheers

 

[greggfarnham]

Thanks, I thought tape would be fine but didn't want to bust anything!
He's now all go with the tape input and we'll NEVER hear the end of it!

 

[planet10]

mag & xtal are turntable inputs for magnetic or crystal pickups. These have EQ for vynal discs and are not suitable for CD.

xtal should have little or no EQ and about the same gain as an aux in, so it would do in a pinch.

dave

 

[sreten]

the Xtal input will have the right voltage sensisitivity, ~ 1V,
but the high input impedance (1Mohm ?) will compromise
noise levels when used with CD.

sreten.

 

[Ouroboros]

the Xtal input will have the right voltage sensisitivity, ~ 1V,
but the high input impedance (1Mohm ?) will compromise
noise levels when used with CD.

sreten.

Although this will be true for the input if nothing is connected to it, the low output impedance of the CD player will swamp the high-Z input so it shouldn't affect the noise.

I have my doubts though whether an input designed to take an old crystal or ceramic pick-up cartridge will cope with perhaps 2V rms from a CD player.

 

[sreten]

Although this will be true for the input if nothing is connected to it, the low output impedance of the CD player will swamp the high-Z input so it shouldn't affect the noise.

I have my doubts though whether an input designed to take an old crystal or ceramic pick-up cartridge will cope with perhaps 2V rms from a CD player.

Whilst true in terms of source resistance noise, the actual circuit
will not be optimised for low noise with this source resistance.

The xtal input is more likely to be able to cope
with 2Vrms than the tuner or tape inputs.

sreten.

 

[sreten]

Although this will be true for the input if nothing is connected to it, the low output impedance of the CD player will swamp the high-Z input so it shouldn't affect the noise.

I have my doubts though whether an input designed to take an old crystal or ceramic pick-up cartridge will cope with perhaps 2V rms from a CD player.

Whilst true in terms of source resistance noise, the actual circiut
will not be optimsed for low noise with this source resistance.

The xtal input is more likely to be able to cope
with 2Vrms than the tuner or tape inputs.

sreten.

 

[Centauri]

xtal should have little or no EQ and about the same gain as an aux in, so it would do in a pinch.

It is still a phono input, and therefore should still have the usual psuedo RIAA eq applied, even though the gain would be ok.

Cheers

 

[Ouroboros]

No, old crystal and ceramic cartridges usually worked into a high-impedance input, and didn't use any RIAA network. The basic design of the cartridge had (roughly) the right characteristic to correct for the RIAA curve when loaded by >1Meg.

 

[sreten]

No, old crystal and ceramic cartridges usually worked into a high-impedance input, and didn't use any RIAA network. The basic design of the cartridge had (roughly) the right characteristic to correct for the RIAA curve when loaded by >1Meg.

Correct. Output is dependent on stylus displacement not velocity.

sreten.

 

[Centauri]

Mmmmm, interesting.... An old Mullard circuit I have shows the same EQ used for both magnetic and Crystal inputs, with the crystal input loaded with 100k.

Could be that the response of the xtal input could vary with the amp manufacturer and designed input impedance.

Cheers

 

[Ouroboros]

This is where it gets a bit complicated. If the crystal/ceramic cartridge feeds a very high input impedance, then the output is essentially a function of stylus displacement as Sreten has said and has a self-correction for the RIAA pre-emphasis.
If you load it with a conventional 47K then the output will be velocity sensitive (roughly, but then these are only rough cartridges!). The output from the cartridge will then need RIAA equalisation.

So a rough rule of thumb is: Load greater than 1Meg, no eq needed; load less than 100k needs RIAA equalisation.

(I'm old enough to remember trying this on the old Decca Deram and Sonotone 9TAHC cartridges!)