2. speakers
  3. 152682-120167

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?



128x128jsqt
jsqt's avatar
jsqt OP
117 posts
 
With the amp presumably now optimized for a 3 ohm load perhaps it isn’t happy driving such high impedances in the mid-range and lower treble. Or perhaps the tubes or something else in the amp isn’t well matched between the two channels, and the two channels are trying to put out slightly different signals and are therefore fighting each other to some degree as a result of having their outputs connected together.

This is more than likely contributing to the issue since one amp has about 300 hours on it (and the tubes) and the other new one has about 15. 

audiorusty
270 posts
 
I certainly do not have the electronics background that everyone else has on this thread but I find it interesting that the issues seem to be only in certain instruments and certain recordings to paraphrase. Is it possible that the problem could be in the recording itself? When you come across a track with an issue, does it repeat with subsequent listenings or is it totally random?
georgehifi's avatar
georgehifi
10,312 posts
 
jsqt OP


I believe Eli on diyaudio is quite clued up, from pass posts I’ve read, combining the feedback of both channels becomes an issue beside other things, here is what he says about paralleling tube amps.
"Very few amps work well, with simple paralleling. Unfortunately, heat and distortion are the typical result."

Cheers George

jsqt's avatar
jsqt OP
117 posts
 
Again I have to come back to the fact that while there is a lot of discussion about what should and shouldn't be done bridging or paralleling tube amps in general, I have specific instructions directly from Luxman on how to do this, and the Luxman distributor specifically approached me with this idea.

So while there may be many amps - even most amps - that this is not recommended for, I have specific instructions from Luxman for this amplifier, so I'm not clear how the overall configuration could be an issue. Nonetheless, this thread does bring up some interesting questions.

georgehifi's avatar
georgehifi
10,312 posts
 
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.
Read this above that you posted then this below from Eli. I see a similarity.
"Very few amps work well, with simple paralleling. Unfortunately, heat and distortion are the typical result."

As well I would have thought 2 separate channel negative feedback’s suddenly linked together via the transformer secondary tap could also be a problem, and maybe a source of this distortion.

I could see if there was no global feedback as in some amps, then paralleling could work.
But Luxman tube amps all use global feedback from the circuits of their’s I’ve seen.
This is one that would be almost the same as yours, with the feedback highlighted. https://ibb.co/pRpGtPQ

Just found the 88 circuit https://ibb.co/RhG8hJj

Cheers George
More to discover