Hi all,
I’m looking for some advice. I’m building some portable speakers for friends based on cheap class-d amps. I’ve designed a simple preamp with a tl074 so they also work with a mic. This is where I ran into trouble.
It turns out the negative supply for the amplifiers is directly connected to the negative signal input. The battery I’m using is the negative rail for my preamp and the amplifier. I'm using the tl074 as an inverting amplifier and a buffer and made a virtual signal ground. This means that when I connect the signal ground for the preamp to the negative input for the amplifier, I’m creating a short-circuit between the negative rail and the signal ground. The preamp bias is then thrown out of whack and it stops working properly. (I hope I explained this well enough for people to understand)
I’m sure I’m not the first running into this problem, but I’m also not certain where to look for a solution. Can anyone here help me with this issue? To me, it seems like I need to isolate the two stages or something, but I could be very wrong. Any tips, further reading or suggestions would be greatly appreciated!
Telecaster
I’m looking for some advice. I’m building some portable speakers for friends based on cheap class-d amps. I’ve designed a simple preamp with a tl074 so they also work with a mic. This is where I ran into trouble.
It turns out the negative supply for the amplifiers is directly connected to the negative signal input. The battery I’m using is the negative rail for my preamp and the amplifier. I'm using the tl074 as an inverting amplifier and a buffer and made a virtual signal ground. This means that when I connect the signal ground for the preamp to the negative input for the amplifier, I’m creating a short-circuit between the negative rail and the signal ground. The preamp bias is then thrown out of whack and it stops working properly. (I hope I explained this well enough for people to understand)
I’m sure I’m not the first running into this problem, but I’m also not certain where to look for a solution. Can anyone here help me with this issue? To me, it seems like I need to isolate the two stages or something, but I could be very wrong. Any tips, further reading or suggestions would be greatly appreciated!
Telecaster
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Is your amplifier using a single rail?
If so use a TC7660 as a negative voltage generator, that will solve you problem.
Basically if there is 9volt +ve DC as one rail, (Battery supply), you can easily achieve a 9v -ve supply from only a few components.
Whatever the +ve rail is, this IC will produce a balanced -ve rail.
If so use a TC7660 as a negative voltage generator, that will solve you problem.
Basically if there is 9volt +ve DC as one rail, (Battery supply), you can easily achieve a 9v -ve supply from only a few components.
Whatever the +ve rail is, this IC will produce a balanced -ve rail.
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Thanks for your reply! That's a great chip to know about.
In this case, however, I'd rather keep it simple and not make the circuit more complicated unless absolutely necessary. I'm kind of new to this and I'm still learning at every step. Using an extra component only makes this more likely to fail, in my limited experience.
For me, the question is still open: how do I 'decouple' the negative rail of the amp from the virtual ground of the preamp.
In this case, however, I'd rather keep it simple and not make the circuit more complicated unless absolutely necessary. I'm kind of new to this and I'm still learning at every step. Using an extra component only makes this more likely to fail, in my limited experience.
For me, the question is still open: how do I 'decouple' the negative rail of the amp from the virtual ground of the preamp.