Tube vs Solid State

OK, good luck Lalit.  Regarding the McIntosh possibilities you mentioned, be sure to keep the following potential impedance compatibility issues in mind:

The MEN220 has an input impedance of 10K, balanced or unbalanced, which will result in deep bass rolloff and possibly other sonic issues when driven by many tube preamps.  Most ARC line stages and preamps, for example, have a minimum recommended load impedance of 20K.

The MC601 and MC301 have input impedances of 22K, balanced or unbalanced.  So if they are driven by a single output stage (per channel) within a preamp or line stage that output stage will see a load impedance of 11K, which again will be too low for good results with many tube preamps.  And most preamps and line stages that provide two output connectors per channel drive both connectors from the same output stage.

Fortunately the MC601 and MC301 have the same gains, and both are very powerful, so biamping them without an electronic crossover seems like a reasonable approach.

Best regards,
-- Al
 

You’re welcome! A minor correction to my previous post: The width of my room is 13.5 feet, not 12 feet.  Length is 22 feet as previously stated.

Best regards,
-- Al

That’s an interesting point, Lalit. The sensitivity of our ears to deep bass frequencies, relative to their sensitivity to higher frequencies, will of course be less at relatively low volume levels than at higher volume levels, per the Fletcher-Munson effect.

Which leads me to wonder about the gains your amps provide when used in bridged mode vs. when used in a vertical biamp configuration. The gain of the amp is spec’d at 26 db, a typical number for a power amp, which I presume applies to the stereo mode that would be used when biamping. But I would suspect that their gain in bridged mode, which does not appear to be specified, may very well be (and probably is) 6 db higher. And if so, unless you took special measures to accurately compensate for the reduced gain when you tried vertical biamping the result might have been that you were listening at a somewhat lower volume in that mode, which might account for your perception of less weighty deep bass.

Don’t know about you guys, my room is 15’D x 30’W and 60db’s is plenty loud.

Although it’s not particularly relevant, I’ll mention that my room is 12W x 22D, opening to another room in the rear. My listening is mostly to classical music, and in many cases to recordings having very wide dynamic range. Average SPLs at my 11 or 12 foot listening distance are typically in the mid-70s or thereabouts, but I have at least a few orchestral recordings that were engineered with minimal or no compression, and produce SPLs that can vary between around 50 db and brief peaks of 105 db on the same recording!

Best regards,
-- Al

Thanks for chiming in, Ralph.

Regarding the earlier discussion of the LS36.5’s output impedance, after researching a little further I see that its outputs are transformer coupled, rather than capacitor coupled. And as previously stated its output impedance is nominally specified as 110 ohms. So it should have no trouble driving relatively low impedances, including the 7.5K impedance it would have been driving when Lalit tried using the amps in a vertical biamp configuration.

Given that, I have no idea why he would have found the vertical biamp configuration to result in a less weighty deep bass compared to running the amps in bridged mode.

Regards,
-- Al

George, while that would be a good suggestion in many applications, if my speculation about the LS36.5's output impedance at low frequencies is correct the 10K input impedance of the Schiit is likely to be a problem.  Also, it only provides unbalanced ins and outs, and balanced connections to whatever amps Lalit ends up with may be preferable.  He is apparently using balanced connections now.

Regards,
-- Al
 

"My suggestion is that you consider trying your existing amps in a passive vertical biamp configuration...."

Al, thank you for your feedback. I have already tried this, while I gain bit of better separation in mid’s and high’s, the bottom falls out a bit. The low bass frequencies are not a weighty as they are when I run the amp in bridge mode.

Secondly, the LS36.5 is configured with dual balanced outputs in parallel to accommodate bi-amping or a sub with balanced inputs.

If both of the "dual balanced outputs in parallel" are driven from the same output stage within the line stage, as seems very likely, the lack of bass weight in the vertical biamp configuration could very possibly be due to the impedance compatibility concern that I cited earlier. You may want to discuss that with Dan.

If he confirms that both of the output connectors provided for each channel are driven by the same output stage, and if he indicates that the output impedance of the line stage rises significantly at deep bass frequencies (as is very common with tube line stages and preamps), you may want to consider inserting some sort of a buffer stage between the line stage and the amps, that would provide high input impedance and low output impedance, and re-trying the vertical biamp configuration.

Regards,
-- Al

Not only are your speakers vicious (and tube-unfriendly) loads, as George points out above, but in the bridged mode you are using your amps will "see" speaker impedances equal to half of the already very low values he cited.  Which can't be good for the sonics of the amps, even though I note that you indicated in this 2015 thread that Dan Wright had "optimized these amps for bridged mode," whatever that may mean.  

Also, as others have alluded to there are a great many ways in which using solid state and tube amps in a biamp configuration can do more sonic harm than good.  And even more so when the speaker is inherently not tube friendly in terms of either its impedance characteristics or its power requirements.

My suggestion is that you consider trying your existing amps in a passive vertical biamp configuration, with each amp operating in stereo mode rather than bridged mode.   Your speakers have low impedances in much of the bass region, and the 250 watt/4 ohm rating of your amp in stereo mode could very conceivably be adequate, especially given that each channel of the amp would only be supplying current and power in part of the frequency range when used in that configuration.

The one caveat that occurs to me related to that configuration is that I'm not sure about impedance compatibility with your line stage.  In that configuration the line stage's output for each channel would be driving the inputs of two amplifier channels, and would therefore see a load impedance equal to half of the input impedance of each amp channel.  The input impedance of the amp is spec'd at "15K at 50Hz; 23K at 1Khz."  The LS36.5 has a specified output impedance of 110 ohms, which would seem compatible with a load impedance of 15/2 = 7.5K, but as with many tube preamps the 110 ohm figure might be considerably higher at deep bass frequencies.  That would be a question for Dan.

Also, assuming you are using balanced interconnections between the line stage and the amps you would need an XLR splitter, such as these.

In your older thread that I referenced earlier, BTW, I had advocated against a vertical biamp solution, but that was under completely different circumstances prior to your purchase of the Modwright amps.

Good luck.  Regards,
-- Al