Hello,
I had bought G+M GM-1050 100v line amp with built in digital FM tuner. I can even get usb player module for it.
It was a bargain for 30EUR, I was buying it for the the casing, but now I`m thinking... This thing looks quality, it`s Swiss made.
Is there any way to modify this for low impedance speakers without transformer? 4 or 8 ohm...
This is my first time looking into 100v line amp.
I get no continuity from speaker terminals towards amplifier board... even with amplifier turned on.
I can`t find schematics, will post pictures to get an idea...
Pictures will be there in 10 minutes, I need to get home first...
Thank you
I had bought G+M GM-1050 100v line amp with built in digital FM tuner. I can even get usb player module for it.
It was a bargain for 30EUR, I was buying it for the the casing, but now I`m thinking... This thing looks quality, it`s Swiss made.
Is there any way to modify this for low impedance speakers without transformer? 4 or 8 ohm...
This is my first time looking into 100v line amp.
I get no continuity from speaker terminals towards amplifier board... even with amplifier turned on.
I can`t find schematics, will post pictures to get an idea...
Pictures will be there in 10 minutes, I need to get home first...
Thank you
I`m trying to upload the photos, but website is not cooperating... loading...
I can`t find any schematic, but I am looking for it...
It has 2 MJ11016 transistors, it has 4 speaker outputs and level control pcb with 4 pots for 4 outputs... it has 7 wires coming from the toroid and it says "MODULATION TRANSFORMER" under the solder points of those wires...
there is another small transformer on this pcb, there is another small transformer on amplifier board and 1 on control board.
I had amplifier board removed, but didn`t took the photos
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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Progress!
Modulation transformer has primary connected to amplifier board, I had disconnected it and after quick check with multimeter and o-scope I was comfortable with connecting old speaker to it... there is sound, but it`s not loud and it is distorted... connection points come from transistors, there are ceramic resistors in series, had tryed to bypass those, but no change in sound... had tryed to connect one wire for the speaker to gnd (modulation transformer middle tap was connected there) and sure I get much louder sound, but there is alot of distortion and mains buzz when volume it turned to zero....
Will post pictures of amplifier board and will mark what is where to get an idea...
Modulation transformer has primary connected to amplifier board, I had disconnected it and after quick check with multimeter and o-scope I was comfortable with connecting old speaker to it... there is sound, but it`s not loud and it is distorted... connection points come from transistors, there are ceramic resistors in series, had tryed to bypass those, but no change in sound... had tryed to connect one wire for the speaker to gnd (modulation transformer middle tap was connected there) and sure I get much louder sound, but there is alot of distortion and mains buzz when volume it turned to zero....
Will post pictures of amplifier board and will mark what is where to get an idea...
If i take a look of this schematic from web transitor outputs are joined after resistors, this got me thinking should I join them and connect positive speaker wire there? and negative to gnd... however both transistors are the same mj11016...
I start to think, with 2 identical transistors, that the amp really needs the transformer, like a tube-amp. Maybe you could add anothe secondary winding to it for low impedance output.
It has only positive power supply, 39v
I marked transformers with ellipse
Resistors with rectangles, bigger rectangle on the right is gnd, center tap
And transformer connection points with rectangles.
There is empty space on the pcb for 2 another output transformers (150w version).
On the other side there is alot of smd... it has alot of interconnections with other boards and dc power switch, so this is not only amplifier board, it also supplies power to other boards.
I marked transformers with ellipse
Resistors with rectangles, bigger rectangle on the right is gnd, center tap
And transformer connection points with rectangles.
There is empty space on the pcb for 2 another output transformers (150w version).
On the other side there is alot of smd... it has alot of interconnections with other boards and dc power switch, so this is not only amplifier board, it also supplies power to other boards.
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Like a tube amp with only a positive supply. If you can remove the toroid and measure it we could say more.
Yes, will do that. Is the primary measurements enough? I must desolder secondaries.
if you know the rated power of that 100v PA amp, then you can determine its impedance and therefore you can get a suitable transformer to couple to an 8 ohm speaker if this is what you want...
if you know the +- rails to that amp, we can estimate power to 8 ohms...
then everything becomes just turns ratio...
if you know the +- rails to that amp, we can estimate power to 8 ohms...
then everything becomes just turns ratio...
It's 50w. Yes I want 4ohm or 8ohm... more likely 4, that way I can connect 2 8ohm speakers in parallel.
50 watt into 8 ohms is 20 vac, therefore a 100 volt line is 100/20 turns ratio of 5....the 100 volt line therefore represents an impedance of 25 x 8 or 200 ohms, that is the impedance of the output traffo in that PA amp...
but i wonder why you can not feed the 8 ohm speaker directly to the output and forgo of the 100 volt output traffo...i believe that is just possible...for all we know it might even be possible that an auto traffo with that turns ratio was used in that amp to raise the voltage to feed 100v lines...
but i wonder why you can not feed the 8 ohm speaker directly to the output and forgo of the 100 volt output traffo...i believe that is just possible...for all we know it might even be possible that an auto traffo with that turns ratio was used in that amp to raise the voltage to feed 100v lines...
The dc resistance is not important, you need to remove it and connect for safety some 24 v ac to the 100 v secondary and then measure the primary
With speaker disconnected I get +-27vac on outputs, with 6ohm speaker connected voltage colapses to +3v -6v
we need to know the circuit used, otherwise we will just be speculating...
any way you can still use the amp as is just add an external output traffo with a turns ratio of 5 and you should be ok...
any way you can still use the amp as is just add an external output traffo with a turns ratio of 5 and you should be ok...