Some time back I decided I wanted a set of mini monitor type speakers ,Having previously heard a vintage set of Goodmans Maxims ,and being very impressed ,I liked the way in particular they handled vocals ,something about the proximity of the tweeter and mid/bass lent itself to good imaging. So I decided to get a couple of sets of Fostex Pm03d's.
One pair, the two left had speakers,without the amp module ,I used in an install job driven by a seperate integrated amp ,very impressive results,the other pair with the stereo digital amplifier modules built in I used myself .Initially I tried just one channel per speaker,then I bi-wired the cross over and added the second channel in a passive bi-amp scheme. I really wasnt impressed with the class d amplifiers ,appart from at very low volumes ,pushing anything more than a couple of watts through the class d amps yielded distortion of several % ,its not the kind of distortion you get from a driven class a/b amp either ,very tiring on the listening g(ear),despite these amp modules being rated at 2x15 watts.
So I removed the class d amp modules ,and fitted four banana plug sockets,split the crossover,removed the attenuator resistor from the high pass x-over section.
Now it was time to try some proper amplification, I had a nice old Leak delta 30 ,which deserved to be made use of ,and a home baked stereo EL84 triode connected 2x1.5 watt headphone amp ,which was made from a pair of tiny output transformers from a dansette record player suplemented with a proper powersupply .I decided just to stay with the passive filters high and low pass, post amplification .I did add some caps in the cables from my pre-amp ,one on the low, set for -3db @20hz and one set for -3db@ 200hz feeding the tweeter amp .Low end on the Pm03d's starts to tail off sharply from about 110hz,so Looking for a way to re-purpose an old kef 103ab single speaker I had ,found an old powered sub, took the amplifier module out ,and mounted it in the back of the kef 103 cab ,disconnecting the tweeter ,and leaving the passive filtering in place .
Im really happy with the hybrid tri amp set up, only passive passive filtering on the Hi/Mid section ,and active filters on the sub module .The fact that neither of the amps looks into a crossover seems to improve matters in terms of load ,regarding the hi/mid amplifiers ,while reducing signal path compared to a fully active x-over set up ,removal of the attenuator on the hi pass section means the 10-1 power ratio between mid-hi works out well also .
Id be very interested to hear from anyone else who might have tried this approach ,any questions very welcome also ,
Cheers and Merry Christmas to all Group Diy'ers.
One pair, the two left had speakers,without the amp module ,I used in an install job driven by a seperate integrated amp ,very impressive results,the other pair with the stereo digital amplifier modules built in I used myself .Initially I tried just one channel per speaker,then I bi-wired the cross over and added the second channel in a passive bi-amp scheme. I really wasnt impressed with the class d amplifiers ,appart from at very low volumes ,pushing anything more than a couple of watts through the class d amps yielded distortion of several % ,its not the kind of distortion you get from a driven class a/b amp either ,very tiring on the listening g(ear),despite these amp modules being rated at 2x15 watts.
So I removed the class d amp modules ,and fitted four banana plug sockets,split the crossover,removed the attenuator resistor from the high pass x-over section.
Now it was time to try some proper amplification, I had a nice old Leak delta 30 ,which deserved to be made use of ,and a home baked stereo EL84 triode connected 2x1.5 watt headphone amp ,which was made from a pair of tiny output transformers from a dansette record player suplemented with a proper powersupply .I decided just to stay with the passive filters high and low pass, post amplification .I did add some caps in the cables from my pre-amp ,one on the low, set for -3db @20hz and one set for -3db@ 200hz feeding the tweeter amp .Low end on the Pm03d's starts to tail off sharply from about 110hz,so Looking for a way to re-purpose an old kef 103ab single speaker I had ,found an old powered sub, took the amplifier module out ,and mounted it in the back of the kef 103 cab ,disconnecting the tweeter ,and leaving the passive filtering in place .
Im really happy with the hybrid tri amp set up, only passive passive filtering on the Hi/Mid section ,and active filters on the sub module .The fact that neither of the amps looks into a crossover seems to improve matters in terms of load ,regarding the hi/mid amplifiers ,while reducing signal path compared to a fully active x-over set up ,removal of the attenuator on the hi pass section means the 10-1 power ratio between mid-hi works out well also .
Id be very interested to hear from anyone else who might have tried this approach ,any questions very welcome also ,
Cheers and Merry Christmas to all Group Diy'ers.
