I'm still on the hunt for the schematic... would it help if I try to draw the part of the schematic? Power lines and bigger lines that are not smd?
A G+M GM-1050-CD is included in this data sheet:
file:///C:/Users/Alan/AppData/Local/Temp/Compact-S_Data_sheet.pdf
I presume your model is similar, but without the CD playing facility?
file:///C:/Users/Alan/AppData/Local/Temp/Compact-S_Data_sheet.pdf
I presume your model is similar, but without the CD playing facility?
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Full specs here, including details of output connections:
https://www.gm-elektronik.swiss/wp-content/uploads/ds_Compact-S_02_en.pdf
Sadly, no schematic!
https://www.gm-elektronik.swiss/wp-content/uploads/ds_Compact-S_02_en.pdf
Sadly, no schematic!
Most likely all you have to do is connect your low impedance loudspeaker between two of the transformer output leads.
With two output transistors the power out should be between 50 to 100 watts. At 100 volts out the impedance at full power would be 100 to 200 ohms. Going between the half power output and the full power output should be lower impedance.
The impedance for each output is 100 squared/load resistance. Note the turns ratio will be the square root of the power change.
If the power rail is 39 volts and you want 100 VRMS then the step up ratio for full power is going to be around 141/37 allowing for some transistor loss.
I see from the specifications it is rated at 150 watts and 67 ohms output impedance. I do not see what the output level controls do.
That puts the primary impedance closer to 4 ohms. But as it is push pull you can't connect a loudspeaker at that point.
So if you know the rated power level for each output level step you can calculate all of the turns ratios. Then see if there are two ratios that differ By 40% and use that set.
I suspect with one 100 V output set to maximum and another 1 step down, going between the 100V terminals for each will be about the right impedance.
With two output transistors the power out should be between 50 to 100 watts. At 100 volts out the impedance at full power would be 100 to 200 ohms. Going between the half power output and the full power output should be lower impedance.
The impedance for each output is 100 squared/load resistance. Note the turns ratio will be the square root of the power change.
If the power rail is 39 volts and you want 100 VRMS then the step up ratio for full power is going to be around 141/37 allowing for some transistor loss.
I see from the specifications it is rated at 150 watts and 67 ohms output impedance. I do not see what the output level controls do.
That puts the primary impedance closer to 4 ohms. But as it is push pull you can't connect a loudspeaker at that point.
So if you know the rated power level for each output level step you can calculate all of the turns ratios. Then see if there are two ratios that differ By 40% and use that set.
I suspect with one 100 V output set to maximum and another 1 step down, going between the 100V terminals for each will be about the right impedance.
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Yep, my model is gm 1050... it`s the same... I was looking at this, but sadly no schematic is there...
There are secondary voltages writen on modulation pcb: 0v 4o nc (but wire is still connected anyway) 50v 50v 70v 70v 100v 100v...
Each pot has 10 steps
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It works 🙂
I need to make aux cable for further testing because fm reception is bad where I live....
Will report...
Short answer: I think you can´t. Sorry.
* one way to make high impedance/70V/100V PA amps is to make a conventional one, symmetrical supplies, etc. which CAN straight drive a regular (4/8/6 ohm) speaker ,and add a 4-8-16 ohm to 70-100V transformer, often an autotransformer because it saves weight and cost and is simpler to wind.
In that case, removing the transformer and straight connecting to speaker is easy and all that´s required.
* BUT, there is another style of high voltage power amps, which is designed for regular Mains use but can be used on battery power, for various reasons, main one being (in a warehouse-supermarket-train station-hospital) *emergency* use: if mains power is lost (accident-fire-hurricane) you still NEED a working way to communicate with public and staff, give warnings and instructions, etc. or simply you are using it outdoors or on the backof a trucks, no mains available.
There is a "niche" kind of such amps, they *typically* work out of 36V something supplies, which can be replaced by 3 x 12V car batteries in series, providing full power and all functions, many accept 24V (truck batteries) , somewhat reduced power but still LOUD, very usable.
But to have high power with such reduced supply voltages, they typically use "tube type" push pull circuits, with an output transformer where center tap goes to +V, and collectors go to primary winding ends.
There you NEED the output transformer.
To confirm this, turn amp ON and measure voltage from each collector (metallic case) to ground.
If you get those 37V on both, it´s the kind I´m describing.
If so, you can remove the power amp and OT and replace it with a Class D bridged output amplifier, fed from existing +37V
Pity you showed "everything" EXCEPT the vital Output transformer, the most important part here.
Oh well.
* one way to make high impedance/70V/100V PA amps is to make a conventional one, symmetrical supplies, etc. which CAN straight drive a regular (4/8/6 ohm) speaker ,and add a 4-8-16 ohm to 70-100V transformer, often an autotransformer because it saves weight and cost and is simpler to wind.
In that case, removing the transformer and straight connecting to speaker is easy and all that´s required.
* BUT, there is another style of high voltage power amps, which is designed for regular Mains use but can be used on battery power, for various reasons, main one being (in a warehouse-supermarket-train station-hospital) *emergency* use: if mains power is lost (accident-fire-hurricane) you still NEED a working way to communicate with public and staff, give warnings and instructions, etc. or simply you are using it outdoors or on the backof a trucks, no mains available.
There is a "niche" kind of such amps, they *typically* work out of 36V something supplies, which can be replaced by 3 x 12V car batteries in series, providing full power and all functions, many accept 24V (truck batteries) , somewhat reduced power but still LOUD, very usable.
But to have high power with such reduced supply voltages, they typically use "tube type" push pull circuits, with an output transformer where center tap goes to +V, and collectors go to primary winding ends.
There you NEED the output transformer.
To confirm this, turn amp ON and measure voltage from each collector (metallic case) to ground.
If you get those 37V on both, it´s the kind I´m describing.
If so, you can remove the power amp and OT and replace it with a Class D bridged output amplifier, fed from existing +37V
Pity you showed "everything" EXCEPT the vital Output transformer, the most important part here.
Oh well.
I had just made it work 🙂 Connected speaker to first secondary 0v and 4o mark on pcb... they are also two thickest wires of secondaries... it works like a charm on 6ohm speaker.
There is nothing to see on that transformer... its a toroid with no label. secondaries can be seen on modulation pcb.
It`s the type with 24v power option...
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I think the legends actually say '0V and 4Ω'!
The lower legs of the ohms symbol are obscured by the blob of solder?
It`s done, I added rca connections for aux and it plays superb.
Heavy bass, clear sound and it`s loud. I tryed rock, heavy rock, techno, pop, bass tests...
No buzz, no static noises, no mains hum...
I had connected it to pair of my 6ohm Pioneer CS-770 speakers in parallel to 3ohm.
Declared 50w.... I don`t think so. It`s pushing my Pioneers really good with no audible distortion at all.
Heavy bass, clear sound and it`s loud. I tryed rock, heavy rock, techno, pop, bass tests...
No buzz, no static noises, no mains hum...
I had connected it to pair of my 6ohm Pioneer CS-770 speakers in parallel to 3ohm.
Declared 50w.... I don`t think so. It`s pushing my Pioneers really good with no audible distortion at all.
Amplifier has protection circuit (that will not cut the speakers with my modification, but will still turn the light on) and it has fan, that didn`t turn on in 4 hours of listeting to music 🙂
Hi, I know this is a bit of an older thread but I'm asking similar question..…
I picked up a Yamaha XH150 which you guessed it is an high impedance amplifier, and I'm looking to see if you can mod it to an low impedance amplifier?
I've attached the service manual that also has schematics.
Any help will be greatly appreciated?
Thank you!
I picked up a Yamaha XH150 which you guessed it is an high impedance amplifier, and I'm looking to see if you can mod it to an low impedance amplifier?
I've attached the service manual that also has schematics.
Any help will be greatly appreciated?
Thank you!