Hello Guys,
I own an old Realistic SP-150 speaker (2W @ 8 Ohms). It's the same model that was used in the Nasa Control Room for Apollo mission communications.
What I would like is:
- transform this passive speaker to an active speaker with a small mono amplifier and WITH a balanced XLR Input.
I tried to find some electronics boards, but I can't find a small board (or drawing) with a small amp, ideally 12V input or less and this famous balanced XLR input. I don't want an over powerful amplifier like 60W or more. Just the right one for this speaker.
Do you have any idea where or how I can find it ?
I can do PCB and soldering or buy a fully finished product.
Best regards,
Marc
I own an old Realistic SP-150 speaker (2W @ 8 Ohms). It's the same model that was used in the Nasa Control Room for Apollo mission communications.
What I would like is:
- transform this passive speaker to an active speaker with a small mono amplifier and WITH a balanced XLR Input.
I tried to find some electronics boards, but I can't find a small board (or drawing) with a small amp, ideally 12V input or less and this famous balanced XLR input. I don't want an over powerful amplifier like 60W or more. Just the right one for this speaker.
Do you have any idea where or how I can find it ?
I can do PCB and soldering or buy a fully finished product.
Best regards,
Marc
You can use any OPamp: lm386, lm1815, tda2030...
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQz1scefBpi9TZMQXtfuvBZ8ePXuSnvCZ6YuQ&usqp=CAU
https://sound-au.com/articles/balanced-io.htm
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQz1scefBpi9TZMQXtfuvBZ8ePXuSnvCZ6YuQ&usqp=CAU
https://sound-au.com/articles/balanced-io.htm
I would probably use the TDA2002 or 2003, designed for 12V operation, about 2 watts in 8 ohms. Those little amp boards, and the bridged version which will give 5+ watts are all over the place for cheap as complete kits. Don‘t go to the 2030 or 1875 if all you have is a 12 volt single supply. Adding the balanced input is easy with an op amp, 6 resistors and 3 caps but if you want an easy peasy one component solution use the Triad TY141P or 142P transformers. They sound better than they have a right to and the low end is really limited by primary inductance. From a 600 ohm or less source they go down much lower than the rated 200 Hz. And that doesn’t matter at all with a little 4” speaker. Not bad at all for a $6 transformer.
If you buy one of the little PCBs as a finished unit or kit you do run a risk of getting fake TDA2003’s. Every one I’ve ever bought had the old SGS logo and was from a surplus house and every single one I tried worked. I still use them for things - not all of them audio-soecific. I’d trust one at $5 from Jameco before one for 5 cents from aliexpress. The cheap ones may work, but then again they may not.
Modern offerings replacing these old things are all class D. But you can buy them anywhere - Parts express, many Aliexpress vendors (who likely still have the old 2003 boards). Any class D board running on 12 volts is going to be only 10 watts in 8 ohms, running full bridge mode. Dont believe anything they tell you about higher power because without an output transformer thats not possible. Need a balanced input with one of the little class D boards? Simple - just add the transformer I suggested at the input. Works with anything and you don’t have to worry about a noisy cheap class D board generating power supply hash on a separate op-amp board for the balanced input.
If you buy one of the little PCBs as a finished unit or kit you do run a risk of getting fake TDA2003’s. Every one I’ve ever bought had the old SGS logo and was from a surplus house and every single one I tried worked. I still use them for things - not all of them audio-soecific. I’d trust one at $5 from Jameco before one for 5 cents from aliexpress. The cheap ones may work, but then again they may not.
Modern offerings replacing these old things are all class D. But you can buy them anywhere - Parts express, many Aliexpress vendors (who likely still have the old 2003 boards). Any class D board running on 12 volts is going to be only 10 watts in 8 ohms, running full bridge mode. Dont believe anything they tell you about higher power because without an output transformer thats not possible. Need a balanced input with one of the little class D boards? Simple - just add the transformer I suggested at the input. Works with anything and you don’t have to worry about a noisy cheap class D board generating power supply hash on a separate op-amp board for the balanced input.