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What does an impedance-matching issue "sound" like?

I recently added a 2nd Luxman MQ-88uSE to my 2 channel system, bridged to mono so I am running a Luxman to each of my 6ohm Volti Rivals.

The SE version of this Luxman amp only has single speaker taps which output 25Wpc to 6 ohms, and 20Wpc to 4 ohms and 8 ohms (from the manual). I used a jumper between each of the "positive" taps so I am not sure what the bridged output is to the 6 ohm Rivals.

Now what I am hearing is definitely more power and presence in the sound, better bass, as well as improved separation. BUT occasionally I am hearing what sounds like a bit of breakup deep in the mix of some songs. Like the whole channel isn’t breaking up, but suddenly a rhythm guitar part sounds noisy like it’s being played through an AM radio or something. On some songs, the entire mix may sound reduced in scale and less dynamic.

I am not sure if my ears are playing tricks on me, or if I’m crazy, or if there could be something happening in the pairing of these amps and speakers that is bad for the equipment and sound. I realize this is a complicated issue because one amp is brand new and the other is broken in, and they are both tube amps., So chasing down the culprit could get messy.

Is it possible there are impedance issues at play here? What would that sound like?



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Showing 2 responses by ieales

ieales's avatar
ieales
1,201 posts
 
I've never been a fan of anything paralleled or bridged. IMO, the sonics always suffer.

Looking at the mq88 schematic, there is a complex output filter and a multitude of pots for bias, gain and balance. It is possible that the particular combination of all the parts moves the channel symmetry enough at certain frequencies to cause an imbalance. Tube non-linearities/sub-par tube could also contribute.

Transformers like to see the load for which they are designed. The best advice here is to Bi-Amp. Doing so could help to isolate a problem in one particular channel.

After reading the Stereophile article and viewing the measurements, well... let's just leave it at that.
ieales's avatar
ieales
1,201 posts
 
For BiAmping, you really should have crossover, otherwise the amps see an infinite impedance out of band.

A simple 6db HP crossover can be effected with a single capacitor for the upper and a LP for the low with a choke.

It would be better to use slopes similar to the in-built crossover.

For a quick cheap & cheerful XO, pick up a dbx 223 or similar. It's 4th order or 24db/octave. 
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