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
16,009 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.

gthirteen OP
354 posts
 

Erik-

 

Thanks.  I'm literally, multimeter illiterate. 
"Volts AC" is what I needed.

 

Thank you!!

erik_squires
16,009 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.

holmz's avatar
holmz
2,328 posts
 

for those more electronically endowed, how would I measure as Erik suggested- what’s the pretty picture look like?

~V

Or a squiggle over or under a horizontal line.

Usually AC is denoted by a small v and DC by a capital V.
By my meter has volts DC as =V when the bottom part of the = is dashed.

avanti1960
1,452 posts
 

if the a21+ is new, it will sound extremely smooth at 450 hours or so like mine did, so that could be an option.  

you can set an amps gain with a test tone and measure the voltage at  the terminals without speakers attached.  the problem is that tube amps require the load of a speaker or you could damage the amp.  

just play pink noise bands above and below the crossover of the woofer and adjust gain so they sound close.  use tracks 47 to 56 on this disk or download

https://sheffieldlab.com/item.php?item_id=52

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