2. amps-preamps
  3. 182257-2603

Bi-Amping: How can I determine relative output?

Long Story Short:  I have a 50w/channel pair of tube monos, and a 300w stereo solid state amp playing through a set of JBL 4367s. two way monitors.

The tubes are on the horn tweeter and the solid state is on the 15" woofer, crossover is apparently 700hz.

Doing absolutely nothing, some music sounds completely "normal" and some music sounds artificially bass heavy.

The solid state amp has gain adjustments for each channel.

I have a Fluke 115 multimeter, and access to plenty of test tones, but nothing to read SPL.

Is there a way to measure output at the speaker terminals such that I could dial the woofer amp down to "match" the tube amps?

If so, would this be more or less constant as the preamp driving the amps changes  volume, or would it only "match" (to the extent that it actually matches at all) at one volume level?

 

 

 

gthirteen
erik_squires
16,285 posts
 

Amplifiers are voltage amplifiers, and provide a fixed amount of gain (voltage out x voltage in).  There is a convention of 23 or 26 dB, but best to measure it. 

You can use an average multi-meter if you can find a 60 Hz test done.  At this frequency multimeters are spot-on. 

So, play a 60 Hz signal through both amps at the same time and set them so they output the same on the amps.

You don't have to go very loud.  A 5V signal is plenty to tell.

hiend2's avatar
hiend2
443 posts
 

Input sensitivities might be a little off so maybe as you turn up the volume one amp may give more power compared to the other

Buy a test tone CD and a sound level meter

Those old simpson sound level meters are good and cheap these days.

Good luck

 

holmz's avatar
holmz
2,328 posts
 

You might be better off just using the tube amp, or using 1 good amp.

carlsbad's avatar
carlsbad
1,551 posts
 

I like what Erik described above but in the end, you'll have to go with your ears.  My thought is that the songs that sound normal have room for more bass in them.  They might even sound better with the more bass to many or most people.  I would use a bass heavy song and turn it down until it sounds right.  Done.

gthirteen OP
355 posts
 

SS Amp has a right and left gain controls.  Using the Fluke, is it possible to measure at the speaker outputs (if so what would I be measuring) in order to get the right/left levels the same?  
 

A little background- the tube amps are plenty for normal use, and sound great.  I’ve been having an itch to run the JBLs at ridiculous levels, so I bought a Parasound A21+ to play with. It sounds great and the combo allows for wall shaking sound, but isn’t as smooth as when using the tube monos. 
 

I noted the gain controls on the A21+, and set out to try a biamped setup.  Given that the speaker is a two way with a pretty low crossover, I though that it may be possible to get decent sound.  With zero adjustment, it sounds much better than I expected.  Currently using the line level pass through on the Parasound, however I have a spare set of the IC I’m using and plan to try connecting to the 2nd output of my line stage.

if there were some way to get both sides adjusted as to some actual metric, not by ear or according to SPL, I’d love to start from that point, and tweak if necessary.

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