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In the Forum: Horn-Loaded Speakers
In the Thread: Jessie Dazzle Project
Post Subject: Crossover balancing act; Act IIIPosted by Romy the Cat on: 1/25/2010


I was trying to evaluate the gain of my amplification in respect to larger room and again was thinking about your case. I think something that you do it not correct. You are complaining that you have not enough gain in upperbass, but I think you have not properly set gain reference point in your playback. You need always have gain reference point, which most likely will be the channel with lowest sensitivity. Let see how it done in Milq. It is milliamp or not - it is irrelevant, we are taking about gain now.

The bass channel is chosen as a reference gain channel, marked as “A”, and everything is measured in respect to it gain. In the Milq you see it running wide-open. The 30K resistor in the input crossover and the green resistor of bias do not form a voltage divider as they are refers to different sores and the shunting resistor is 1Meg   

The upperbass channels make as “B” sits behind voltage divider (30K and 12.1K to ground). I do not remember but I think it doe 3dB. Pay attention that the upperbass runs from ½ of the tube, so proximally 1-2 db also is lost to the running 3C33C with a half-plate.

The gain of Fundamentals Chanel “D” is heavily killed by attenuator in secondary.

 The midrange “E” runs in my case full open at line level.

In your case you run your bass channels from a separate amp and the horn channels from Lamm ML2, right?  Lamm has a LOT of gain, much more then Milq, I think it is 26dB. It has 26dB gain and will out 17V into 8R at 1000Hz. This is a LOT; you most likely have a preamp that has 5-15dB gain – so look at the voltage that your playback can swing.  For instance your Vitavox S2 driver in my room and from 8-9 feet needs 250-500mV to sound at comfortable level.  With 1V it will scream very loud. If you remember at the time I used Lamm ML2 and drove my S2 from it I has 14dB voltage divider and used 4R ML2 tap. So, if you run your S2 from wide-open ML2 then it would not be a surprise the you have no other channels match it.

What you need to go it to find how much gain you need. I do know what preamp you use but as a rule- connect it to the less sensitive horn channel – let pretend that it will be your upperbass. Run the channels at it max out and to see how loud it gets. You need to be able to play very loud with your volume control set at 60-70% of the full gain. After you find this configuration then begin to roll off your MF and HF channels until they match your upperbass. I do feel that you will attenuate your S2 quite aggressively. You might even put some 16R LPAD before S2 and to use it for messmates, determining how much you need to attenuate it (do not use it for listening as the LPAD inductance will kill HF). So connect your wide open upperbass and your MF behind the LPAD. Then run a 20-20000Hz sweep and adjust the LPAD until your upperbass will have the same out as your MF. Then measured the LPAD’s impedance to one and another side and you will have your resistors for your voltage divider.  Replace the LPAD’s with none-inactive fixed restores of 1W-5W and your will be all set.

Jessie, I do think that you run your MF too hot. Where is the volume control setting in your preamp when you run your playback too loud? I presume that it at 20-30% of the full scale….

Romy the Cat

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