Impedance Question?

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?

Well, I'd say you should trust the manufacturers more than us. But putting together what they both said, I'd say they seem like they'd work. Proof is in listening, of course

jmcgrogan2 has the best answer +1

Our tube preamps don't have an output coupling cap- so they can drive 600 ohms let along 10,000 ohms with ease. The output impedance is the same at 5Hz as it is at 1KHz or 30KHz.

Generally speaking though, most tube preamps are likely not to play bass right driving 10K, simply because of the output coupling cap being too small.

That said, I have a Dared MC7P (there’s a dash in there somewhere..) and it played nicely with a Crown amp that had in input impedance of 10k and currently plays well with ICEpower monoblocks. The Dared apparently has a low input impedance.

It’s all so freaking variable!