Just my $0.02, but there is absolutely no logical reason for a modern power amp to have less than a 47K Ohm input impedance. A lower input impedance makes it very difficult to mate a preamp (particularly from a different manufacturer) to drive the power amp properly, presuming the ratio of 10:1 is used. This is particularly true in the OP's specific situation of biamping.
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Erik and George are of course correct that impedance compatibility needs to be carefully considered in this situation, given that preamp-to-power amp impedance incompatibilities tend to arise most often when tube-based preamps are used in conjunction with solid state power amps, and given that in this case the preamp would be driving two power amps. However, given the following statement in this thread I think there is a good chance that the Rhumba 1.2 Extreme would be suitable in that respect: BackertLabs 8-17-2018 The 75 ohm figure is most likely based on a mid-range frequency such as 1 kHz, and is probably a good deal higher at 20 Hz, but this statement nevertheless appears to suggest that the match stands a very good chance of being suitable. Regarding the LS27, the 8008 MkII is spec’d as having an input impedance of 46K single-ended and 70K balanced (which probably means 35K per leg), and while various versions of the Palladium have low single-ended input impedances (for versions which provide single-ended inputs), their balanced input impedances are in the vicinity of 44K (which probably means 22K per leg). The ARC LS27, like most ARC line stages and preamps, has a recommended minimum load impedance of 20K, although it is not clear if that applies to the single-ended outputs, or to the balanced outputs, or to each leg of the balanced outputs. 70K in parallel with 44K is 27K, while 35K in parallel with 22K is 13.5K. So it is possible that the LS27 would be a suitable match if you were to drive both amps with its balanced outputs, via XLR splitter cables, and depending on how ARC’s 20K minimum load recommendation is defined. And the match might also be within reason (although not ideal) if you were to drive the 8008 MkII with the LS27’s single-ended outputs while driving the Palladium with the LS27’s balanced outputs (the resulting load impedance in that situation on one of the two signals in the balanced signal pair probably being 46K in parallel with 22K, which is 14.9K). Good luck. Regards, -- Al |
One tube pre-amp designer who does so for both the consumer and pro markets is Tim de Paravicini. His EAR-Yoshino pre-amps are designed to drive a 600 ohm load, the standard in recording studios. The EAR 868L has four pair of stereo outputs---2 pair unbalanced on RCA jacks, 2 pair balanced (via transformers) on XLRs. |
lilrock
Eric is right one amp is 15k the other is 46k you have a combined impedance of 11kohm that the preamp will see, forget about tube preamps, unless they are less than 1kohm output or less and very important maintain that <1kohm from 20hz to 20khz. I would play it safe and get a solid state pre they are usually around 100ohm or less, they will have no problem with this 11kohm loading. If your hooked on tube, then get a Schitt Freya, at least with this you'll have the option of tube, solid state or even passive. Cheers George |
