Impedance Question?

Not all preamps that have equal output impedance specs, say 600 ohms, have the same impedance across the frequency band, and often much higher at the lower (bass) frequencies. The result would be a loss of mid/low bass with those having this condition when paired with an amp having low input impedance. 

To mate a preamp with a 10K input impedance amp one would need to know the output impedance of the preamp across the frequency range. 

OK so I got an email back from Rolf at SL and he suggest staying 100-300ohm.

Cary says that on the SLP-98 in the manual 800 but on the item page it says 440. LOL

It is so confusing isn't it?! I'm currently looking at room measurement mics so I can stop going completely by 'feel'.

Good luck! I use a dared mc7-p preamp (class a tube) with my class d monos and it sounds beautiful. I think it only has an output impedance of 100 ohms and there is certainly no roll off in the bass zone.

OK so I got an email back from Rolf at SL and he suggest staying 100-300ohm.

I would agree with this recommendation. Many say the general rule is 10:1, Amp input impedance:preamp output impedance.

However, in many cases this is not enough. Many manufacturers, like Audio Research, recommend a 20:1 or 30:1 minimum ratio.
The main reason is because most stated preamp output impedance is not a ruler flat measurement, but rises quite a bit in the lower bass regions.

For example, my ARC Ref 5 preamp has an output impedance rating of 600 ohms (balanced). ARC, the preamp manufacturer, recommends an amp load of a minimum 20K input impedance (33:1 ratio).
The reason being that measurements show the output impedance of the Ref 5 rises to 1447 ohms at 20 HZ.

This is common with many tube preamps, the stated output impedance can more than double in the lowest octave.

Another example is the Cary SLP-98 that you mention. The spec sheet states a 800 ohms output impedance.
According to Stereophile measurements, " The output impedance in the midrange and treble was usefully low, at 370 ohms, but this rose at 20Hz to 6.8k ohms, due to the limited size of the output coupling capacitors."


In a nutshell, your manufacturers recommendation of a preamp with an output impedance of 100-300 is a good one for an amp with a 10K input impedance. This will eliminate most tube preamps, but not all.

Cheers,
John

OK thank you guys!! So I was discussing with Dan ModWright about his 2 preamps and he said either of his would work LS36.5 110ohm and the LS100 300ohm.
Do you guys agree and feel that those pre’s will match up with 10k input on SL RG1?