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

Showing 5 responses by erik_squires

erik_squires
16,592 posts
 

PS - 5 V AC corresponds to about 3 Watts at 8 Ohms.  A very low level well within the capability of both amplifiers, but high enough that you can get a solid reading from a meter.

erik_squires
16,592 posts
 

OP: Not sure what you mean, it seems simple enough.

First, find test tones from somewhere in the 50-60 Hz range. Attach a multimeter to one of the tube amp’s outputs. Set the multimeter to read volts AC. Adjust the preamp until the output reads 5V exactly.

Switch to the SS amp and try to adjust the amp’s level settings there to the same.

erik_squires
16,592 posts
 

@russ69 - Assuming passive biamping, meaning the original crossover is still in place, SPL matching is done in the speaker's crossover.

Did I misunderstand the OP's problem?

erik_squires
16,592 posts
 

OP:

I gave you the solution! :)  Find a 60 Hz tone, play it and measure the amplifier's output.  The only problem you might have is if your tube amp is has the higher gain. 

Multimeters perform best at 50-60 Hz.

erik_squires
16,592 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.

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