So, I was wandering through my friend's scrap warehouse and saw these two units that had just came in so I grabbed them figuring they may have some useful components.
It appears that they were used for audio/visual projects or institutional P.A. systems as they have some interesting features such as a 28 Volt DC aux output and 70V/25V speaker outputs. There are two 2N3773 transistors on the heat sinks. I powered them up and tested the DC outputs and they were a bit higher than advertised, but both units read the same 32 Volts. I hooked up a music source and plugged a speaker in and they worked.
My level of audio knowledge is mediocre, so I stopped there until I can understand the following statement "the balanced outputs for 70.7 volts and 25 volts are for speakers designed for constant voltage lines. Each speaker must have a line matching transformer and the speakers muct be connectted in parallel."
The output impedences are listed as follows 70.7V = 83.3 ohms, 25 Volts = 10.4 ohms
Anywho, I am planning to work up to building a 30-50 Watt guitar combo amp sometime in the future (2x10 or 2x12) and wondered if this unit could be upgraded to potentially accomplish the task at some point. I assume they could drive two 8 ohm speakers as is, but the internal circuitry is perhaps not "high fidelity" At the very least the transfomers, chassis, and/or heat sinks could be repurposed I suppose. I was planning on using a high end chip amp for my main power for my first guitar amp, but these might come in handy for a later project.
Any thoughts?
It appears that they were used for audio/visual projects or institutional P.A. systems as they have some interesting features such as a 28 Volt DC aux output and 70V/25V speaker outputs. There are two 2N3773 transistors on the heat sinks. I powered them up and tested the DC outputs and they were a bit higher than advertised, but both units read the same 32 Volts. I hooked up a music source and plugged a speaker in and they worked.
My level of audio knowledge is mediocre, so I stopped there until I can understand the following statement "the balanced outputs for 70.7 volts and 25 volts are for speakers designed for constant voltage lines. Each speaker must have a line matching transformer and the speakers muct be connectted in parallel."
The output impedences are listed as follows 70.7V = 83.3 ohms, 25 Volts = 10.4 ohms
Anywho, I am planning to work up to building a 30-50 Watt guitar combo amp sometime in the future (2x10 or 2x12) and wondered if this unit could be upgraded to potentially accomplish the task at some point. I assume they could drive two 8 ohm speakers as is, but the internal circuitry is perhaps not "high fidelity" At the very least the transfomers, chassis, and/or heat sinks could be repurposed I suppose. I was planning on using a high end chip amp for my main power for my first guitar amp, but these might come in handy for a later project.
Any thoughts?
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So, as of yet I am unable to find the schematic for the amp. My first thought is to take one of them and strip out all of the internal circuitry/transistor out and just mount a 3886 circuit onto the heat sink and use it that way... I may save the other one to replace the circuitry with better transistors and a pre-amp circuit when I'm confident to take on such an endeavor.
Very good amplifier but a "one trick pony", it was designed for "institution" use (school church warehouse train station) .
And very different from conventional amps.
Not practical to disassemble or rebuild nor to reuse its parts so best is to use it as-is.
User manual says you can connect 10.4 ohms worth of speakers to one 25 V winding, meaning from common to one of the 25V taps, pick one.
Feeding it 60W RMS.
I suggest you build a 16 ohm cabinet: 2 x 8 Ohm speakers in series, which is easy.
Amp will work fine and put out some 40W RMS, not bad at all, and connect it from common to one 25V tap.
And very different from conventional amps.
Not practical to disassemble or rebuild nor to reuse its parts so best is to use it as-is.
User manual says you can connect 10.4 ohms worth of speakers to one 25 V winding, meaning from common to one of the 25V taps, pick one.
Feeding it 60W RMS.
I suggest you build a 16 ohm cabinet: 2 x 8 Ohm speakers in series, which is easy.
Amp will work fine and put out some 40W RMS, not bad at all, and connect it from common to one 25V tap.
