Tubes on top and Class D on the bottom

I am curious about an experiment involving tubes for the tweeter midrange and Class D Bel Canto M300s) on the woofers of my Von Schweikert VR-4JRs. After reading about the little Miniwatt N3, which is an integrated amp, can I use it for level matching? I would be feeding a signal from a Modwright SWL 9.0 tubes pre-amp to both amps. Or, would I blow everything up in the process, like Mister Wizard?
Not a good idea.

First, you won't be able to match the gains with the volume control on the N3 because, I'm pretty certain, the gain of the M300 is greater than the gain of the N3 when the N3's volume control is set at max.

Second and more importantly, if you could match the gains, keep in mind that that would mean that when a given voltage level is fed into the amps, it would produce a voltage at the output of each amp that is the same as the voltage at the output of the other amp. Therefore, if you attempted to utilize any significant fraction of the M300's power capability, you would undoubtedly drive the output of the N3 way beyond its clipping point.

In other words, in a passively bi-amp'd arrangement that uses different model amps for the bottom and for the top, the voltage swing capability of the lower powered amp will typically limit how of the higher powered amp's capability can be utilized. If you go beyond that point, the mid/hi drivers of the speaker will receive a severely distorted signal.

Best regards,
-- Al
I say go for it! I did the same w/ my VR4-JRs, using a VAC tube amp on top and a Digital Amplifier Co. Cherry amp for the bass. If the gains are close enough, it works great. Tried a monster Carver SS amp on the bass but it was dramatically outperformed by the Cherry. (Tip - it can help to evaluate each amp, either the bass amp or the M/T amp, by disconnecting the other amp - for example listening to only the bass cabinets w/ no M/T is very revealing!)

Turns out the Cherry sounded so good full-range (along w/ heat/ tube life considerations) I sold the VAC and now run a Cherry JR full range.
Al-thanks for the info. It seems the only safe way is to buy a separate tube power amp for the top and use a PVC on one or the other to level match. Correct?

Mfsoa, I have heard that tubes on top and SS on the bottom is a good match. I want to take full advantage of the bass which will go down to 20 Hz in my room and SS can do that.

Its not that I am unhappy with the BC amps, just interested in experimenting for fun. Thanks to both of you.
Mfsoa, you may not be realizing that the question concerned pairing an amplifier rated at 300 watts (into the 4 ohm impedance which the speaker has at low frequencies) with an amplifier rated at 3.5 watts.

Please see my earlier post regarding the implications that would have. Essentially, it would convert the 300W amplifier into little more than a 7W amplifier (7 rather than 3.5 due to the fact that the woofer section's nominal impedance is 4 ohms, while the impedance of the mid/hi section is nominally 8 ohms).
It seems the only safe way is to buy a separate tube power amp for the top and use a PVC on one or the other to level match. Correct?
Tom, using a pvc is certainly a way that it could be done. A fixed resistive attenuator having the right values might also be readily available off-the-shelf, or else could probably be obtained customized to your requirements.

But given my earlier point that the fraction of the M300's power capability that could be utilized would be limited by the voltage swing capability of the lower powered amp, I think it would only make sense to choose a tube amp with a fairly hefty power rating. In that case you may very well be able to find an amp which, besides being a suitable choice sonically, would also be a close enough gain match to not require any special matching provision.

Best regards,
-- Al
I was wanting to do the same thing with my 4jr's and I emailed a few people on this site and got great advice and sold the m-300's and bought a Moscode 401hr which was exactly what the doctor ordered. It's also fun because you change the sound easily with tube changes. This is one fantastic amp with the 4jr's. Sorry I couldn't answer your question but I thought you might want to look into this.

Good luck
Thanks for all the information. Still experimenting....
FWIW there are tube amps that go full power to 2Hz...

20Hz response with zero squarewave tilt is thus possible. So I would not use the 'response to 20Hz' issue as an argument against tubes, just say'n...
Atmasphere, thanks for your reply. I am thinking that tube amps that go below 20 Hz with authority are expensive. At what price range do they start?

IMO, you can certainly do it, at the expense of musical involvement.

The sound will never be cohesive with different amps on top and bottom.

It can be fun with each amp working in it's "best range", but it won't be cohesive or ultimately satisfying.
this reminds me of a dirty joke involving a pre-op. no wait, that was boobes on top and...
Tgrisham, I think it all depends on the power output. Now for an amp that simply goes below 20Hz... well, most of them do. But to play 20Hz properly you usually need to go lower than that. There are many tube amps that go to 10Hz. The thing that really helps a tube amp to play bass though is simply to make sure the load at low frequencies is not difficult to drive. That makes all the difference in the world.
Thanks to all....I continue to learn. I will post my final decision, when it happens. Any and all info is appreciated.