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futiboho 12th October 2004 08:50 AM

best place for volume control in 3-amp system
I would appreciate to learn where is the best place to put the volume control in a 3-amp system (or what are the alternative options and cost/benefits), namely (i) at the input of the active cross over, or (ii) at its output, or (iii) at the input of each of the 3 amps. What I have considered so far is that option (i) is easier but will result in more noise from the XO+cables, option (ii) requires 3 stereo pots on one knob which is more difficult/costly and option (iii) seems to have lowest XO/cable/RF noise but has the challenge of how one can drive 3 pots in synchrony when they are in 3 different cabinets... My idea for option 3 is to run the pots via a joint remote control. Is that a good idea? :confused:

wintermute 12th October 2004 01:04 PM

I may be talking rubbish here (not having done it myself), but thinking about it, I'd say you would want one master control before the active xover, and then separate vloume controls on each amp for trimming (ie getting the levels right).


AndrewT 12th October 2004 01:09 PM

Hi, option 1 is the conventional solution. The noise ouput from each narrow band filter is less than an equivalent wide band preamp. The gain in the poweramp will be between 26db and 36db and will not amplify the noise excessively. You should find the noise performance acceptable and it avoids all the other problems that you have identified.
Option 2 is where you put the balancing presets to equalise the gain & sensitivity of the amp/speaker combo.
I have no experience of option 3 but think it might be very complicated to keep the tracking between 6 channels of output in step(stereo 3 way). But if someone has an elegant but simple solution, then lets hear it.

futiboho 12th October 2004 01:16 PM

Thanks. It is conventional to have a master pot at the XO input, as far as I know, but my effort was to make it more maniac, if justified. Every pot distorts the signal and therefore I wish to avoid too many things on the signal path, particularly as the XO (THEL 30.2) has trimers at the output, to adjust for differenced of the amp gaind and/or the drivers' sensitivity. In their manual, however THEL do not discuss the volume control options cost/benefits.

As the subwoofer section of the XO does not have an output trim I have placed 2 pots (10k) at the XO input and at the subwoofer amp. To my astonishment, when the first pot (XO) is at zero level, I still can hear the music and make it louder via the amp pot???
What is that mistery ???:bigeyes:

mhelin 12th October 2004 02:24 PM

With digital crossovers you don't want to have a master volume control before A/D stage! You have no options except how to implement the volume control for each power amp input conveniently. Digital controller like DS1669 is one option. VCA or OTA another. Also a step attenuator (if you happend to find an unexpensive dual or quad rotary switch).

futiboho 13th October 2004 10:41 AM

If I go for option (iii), i.e. a pot at the input of each of the 3 amps, is it possible to rotate these MOTOR-attached pots (e.g. Panasonik conductive plastic) in synchrony via a common remote control? Are the motors going to operate at same speed???

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