This is the layout of the input section of a PA amplifier I have. The Positive input is grounded to pin #3 of the balanced input connector. I'd like to change it to a single ended input because I don't have anything balanced and don't plan to. Is that something thats easily possible?
Yes, ground the negative input, but to the audio ground on the pcb (not to the chassis) to minimize hum.
It's an inverting amplifier. The easiest thing to do is connect your RCA signal to the negative phase of the XLR, the RCA "ground" goes to your circuit common. Leave the positive XLR input open.
The circuit has a slight amount of gain, you might be able to simply connect your RCA input to where the output of that circuit went.
Yeah, drawn "upside down", good call Ray.
The circuit has a slight amount of gain, you might be able to simply connect your RCA input to where the output of that circuit went.
Yeah, drawn "upside down", good call Ray.
The gain is another issue I need to address because I first hooked up the RCA with + to pin 2 and - to pins 1&3 and it worked but I needed to turn the volume pot all the way up and still wasn't very loud.
So I can try connecting RCA + to pin 3 and RCA - to pin 1? Nothing to pin 2 Wouldn't I need to ground the non inverting input?
That stage can provide more gain. Increasing the value of the 18K will do that, not sure how much you need. Depending on teh op amp, you might have to replace it with a "better" one, like an NE5532 (dual) or NE5534 (single). There are faster ones, but that may get you into trouble or simply not buy you anything.
Messing with this, you need an oscilloscope to make sure it doesn't oscillate.
Messing with this, you need an oscilloscope to make sure it doesn't oscillate.
The ground symbol on my sketch is audio ground I'm using DIY layout creator and theres not many symbols to choose from.
It's a bit odd because normally the 18K would be 10K as well. That gives equal gain from both phases.
I would look at a circuit for single ended that has gain. This one is close and could be modified easily. I'm working, so I don't have a lot of time to look at it.
I would look at a circuit for single ended that has gain. This one is close and could be modified easily. I'm working, so I don't have a lot of time to look at it.
I appreciate your time, I started messing with it a bit and changed some of the 10K resistors to 2.7K.
For unbalanced connections:
pin #1 chassis ground (already connected internally)
pin #2 positive input
pin #3 negative input (jumper to the internal audio ground, but often pin #3 is jumpered to pin #1 instead)
Never leave any XLR pin unconnected.
Umm, in most cases you can just connect the RCA connector directly, tip to XLR pin 2 and shell to XLR pin 3 - this often works fine and provides some common mode noise rejection. The usual guidance would also be to connect XLR pins 1 & 3 together but this is a great way to create a ground loop. (In this case connect pin 3 to the audio GND on PCB and ignore pin 1.
Raising gain requires modifying the input amplifier. There are several alternatives. Simplest would be to jumper the inverting input to GND, change the 10K (Rin) to 4.99K. On the non-inverting side change Rin from 10K to 1K and apply the input to the non-inverting input. This will give you 6dB more gain and eliminate the 6dB of attenuation on the non-inverting input. (Now <1dB)
I use balanced (over XLR cables) in two systems here at home.
Raising gain requires modifying the input amplifier. There are several alternatives. Simplest would be to jumper the inverting input to GND, change the 10K (Rin) to 4.99K. On the non-inverting side change Rin from 10K to 1K and apply the input to the non-inverting input. This will give you 6dB more gain and eliminate the 6dB of attenuation on the non-inverting input. (Now <1dB)
I use balanced (over XLR cables) in two systems here at home.
This is an important point, the positive input is presently being attenuated by half, which may be the source of his gain problem.
Yes, exactly. He wanted to add an RCA jack I think. An XLR to RCA adapter would be my first suggestion, but without enough gain in the input stage, that isn't enough.
Personally, I would simply convert the balanced input circuit to a straight single ended gain stage. Set up the required gain and you're done. Of course, if the amp is good enough you might want to use an NE553x depending on if it is stereo or mono. Depends mostly on where the quality of the rest of the amplifier falls. Higher gain will require a bit higher bandwidth depending on how much more gain you are going for.
Personally, I would simply convert the balanced input circuit to a straight single ended gain stage. Set up the required gain and you're done. Of course, if the amp is good enough you might want to use an NE553x depending on if it is stereo or mono. Depends mostly on where the quality of the rest of the amplifier falls. Higher gain will require a bit higher bandwidth depending on how much more gain you are going for.
Losing all the 10k resistors will reduce noise, so replace the section with a simple opamp unity-gain follower for single-ended input. The original circuit lacks any RF filtering so you really need to add that, maybe 1k into 2.2nF-to-ground?
The original circuit is a low-pass filter, suggesting its for a sub-woofer? Well that's assuming the caps are 47nF and not 47pF ?
The original circuit is a low-pass filter, suggesting its for a sub-woofer? Well that's assuming the caps are 47nF and not 47pF ?