I've gone active

beano

Member
2015-05-30 1:15 pm
So I've gone through with a plan to actively bi-amp my speakers. It's now opened a whole new can of worms lol.

Here is what I've got set up:
Source:
project TT with ortofon om10 (4mv output)

Pre/phonoamp:
Yaqin MS-12B (phono input sens =5mv output=0.7v gain=43db)

crossover:
DBX223xs

Tweeter+mid Amp:
Musical paradise mp-301 (input sens=0.5v output=7.48v for 7watts into 8 ohms therefore gain=23.5db)

Woofer Amps:
Two audiosource amp100 as monoblocs (input sens=0.775v output =34.64v for 150watts into 8 ohms. therefore gain= 33db)

Speakers:
DIY endorphine p17's (Endorphine from Kingston Kitchen
I have the bass amps hooked directly to the woofer and the mid+tweet amp hooked up with a passive x-over between the tweet/mid

I'm new to these calculations, Do my gains look correct?

The part that leaves me scratching my head is how to use these numbers to correctly set the crossovers (dbx223xs) gains (input and output) correctly. As well as the volume knobs on the amps. Everything I've read about it seems to refer to PA gear. They all mention using the amps/mixers clipping indicators to find the optimum setting. This is a problem as none of my gear has any such indicators. They also talk about turning the amps on without speakers connected which again presents a problem for my tube amp. Is there a way to do it just by the numbers?

I've got A LOT to learn but I love it. Any help/advice/opinions would be greatly appreciated.
 
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beano

Member
2015-05-30 1:15 pm
Yes I have a minidsp measurement mic and REW. I have used this to match the actual spl/volume between the bass and treble but I can do it with multiple combinations of crossover gains/pre amp volume seetting/poweramp settings.

I'm worried about (and don't quite fully understand) the gain structure/clipping/headroom/dynamics.
 
well, some of the dbs axtive crossover used biquad opamps. And yes, switching out opamps for even $5 ones makes a big improvement, along with bypassing the horrible electrolytic caps in the signal path.

And yes, without eq, it is tough unless you cross near the baffle step or use some hf lift circuits if you are using compression driver / horns.

But use high end compression drivers and woofs with shorting rings, you can have a really good setup.
 

wintermute

Administrator
Paid Member
2003-08-03 11:43 am
Sydney
The key thing is the relative sensitivity of your drivers. If you run a preamp you should have a master volume control. The crossovers I would imagine have some form of level adjustment.

You do your relative adjustment with the level adjusters in the crossover. Run the driver with lowest sensitivity with no attenuation, attenuate the other until you get balance (note that since your amps appear to have different gain you need to factor that in as well, your bass amp has more gain so the first comment about driver sensitivity may be taken care of by that). In an ideal world it would (I think) be best to adjust the gain of the amps to suit the levels of the drivers, rather than adjusting for levels in the crossover.

Run both amps wide open (ie on max volume, remember your preamp is the master volume control) If they have a direct input bypassing the pre (assuming they are integrated) then use that.

With respect to the gain structure, I believe Ideally you set the gain on your amps such that they are just below clipping with a 2V input signal (into your preamp), however this is the one thing I have not done in my similar active setup. If you haven't read it, read Michael Mardis' exelent article on gain structure! http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html .

Tony.
 
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