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In the Forum: Melquiades Amplifier
In the Thread: 6 Channel Version of Super Melquiades

Post Subject: The Milq upperbass crossover.Posted by Romy the Cat on: 12/8/2014

anthony wrote:
Romy, I appreciate that this is an old thread now and that you may not remember everything from your time developing these amplifiers, but I have a (hopefully) simple question about the upperbass crossover in the schematic above. All other channels have crossovers that are rather straight forward: bass is a low pass RC filter; Fundamentals is a RCL bandpass filter; MF is RL high pass filter; HF is a third order T Section high pass filter; but the Upperbass Channel as I read it is a RC low pass filter only (bandpass is required) within the first stage bias. Are you relying on the coupling cap (0.022uF) to act as your high pass filter for Upperbass?

Yes, Anthony, the upperbass crossover is bandpass. The filters that is integrated with bias is low pass with voltage divider (effectively a resistor) and cap to ground. This filter squeeze the range from 500Hz and above. Generally using this filter the upperbass that I have (Fane Studio 8M in 36" Tratrix) and in context presents of Fundamental Channel is now a good idea as Fane will drive HF too much over this very shallow filter. However, it would be the care of passive filters and the inductance of Fane would compromise the filter. My filter is line-level filter and even if I use a series indictor (I would not use it as I like subtraction filters that I use all over Milq) then the indictor will not "see" the speaker coil. Ideally I would like to see in there slightly sharper crossover at upper knee. I did experiment in there a second order and it was too not bad. However, on the long run I felt that the slower filter would be more suitable. I think if we were talking about rock-n-roll-type crap then probably I would stick to second order. Anyhow, as you said, the coupling cap is high pass, unloading the unwanted LF from the horn. It is controversial if a second order would be better choice for this high pass. I can argue both sides. In context of my relatively large room I do not think it is practically critical.

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