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Mixer - Schematic

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Jbliss:
Finally got around to implementing all the changes and fix ups
Let me know what you think !!

Thanks All
JBliss

nick_d:
Looking pretty sweet :)

I have some concerns about the GNDREF. What is the part number of the amp that generates GNDREF? Op-amps generally don't like their outputs to be capacitively loaded, though it does depend on the part (a 7805 for example is an amp which doesn't mind driving a capacitive load). I would omit the capacitors on GNDREF. Perhaps you can get away with say 1nF to VEE only, if you're actually concerned about noise on the reference.

Then I would make sure that GNDREF is used only internally to the circuit and no significant power is taken from it. Particularly the supply bypassing of all the op-amps currently uses a split bypass with GNDREF in the middle, change this to a single bypass from VCC to VEE.

The XLR connectors should use the VEE not the GNDREF on pin 1. That pin really isn't used for anything except for getting the two amplifiers to some kind of a ballpark similar potential. The relative potential does not really matter provided it is within the voltage rating of the capacitors that are in series with the output (I would use 100V there). If the receiving equipment is single supply it will be connected to the VEE which will be exactly what you want.

Check what the GND pin is used for on the output amplifiers, if the audio is referenced to this then the current connection to GNDREF is correct, otherwise it may need adjusting.

Is there a particular reason to use separate single op-amps everywhere, or is it simply that you wanted to finalize the circuit before counting up packages? Looks like you can do it with 2 quad op-amps. If you're worried about noise and cross-talk, don't be, since the audio frequencies are not really that prone to noise.

cheers, Nick

Jbliss:

--- Quote from: nick_d on December 22, 2018, 02:22:10 pm ---Looking pretty sweet :)

I have some concerns about the GNDREF. What is the part number of the amp that generates GNDREF? Op-amps generally don't like their outputs to be capacitively loaded, though it does depend on the part (a 7805 for example is an amp which doesn't mind driving a capacitive load). I would omit the capacitors on GNDREF. Perhaps you can get away with say 1nF to VEE only, if you're actually concerned about noise on the reference.

Then I would make sure that GNDREF is used only internally to the circuit and no significant power is taken from it. Particularly the supply bypassing of all the op-amps currently uses a split bypass with GNDREF in the middle, change this to a single bypass from VCC to VEE.

The XLR connectors should use the VEE not the GNDREF on pin 1. That pin really isn't used for anything except for getting the two amplifiers to some kind of a ballpark similar potential. The relative potential does not really matter provided it is within the voltage rating of the capacitors that are in series with the output (I would use 100V there). If the receiving equipment is single supply it will be connected to the VEE which will be exactly what you want.

Check what the GND pin is used for on the output amplifiers, if the audio is referenced to this then the current connection to GNDREF is correct, otherwise it may need adjusting.

Is there a particular reason to use separate single op-amps everywhere, or is it simply that you wanted to finalize the circuit before counting up packages? Looks like you can do it with 2 quad op-amps. If you're worried about noise and cross-talk, don't be, since the audio frequencies are not really that prone to noise.

cheers, Nick

--- End quote ---


Hi Nick_d

Thanks Once agin!

1. So the Part generating the split rails is BUF634, there is some info in its data sheet regarding is use in this configuration attached below. I was also concerned about the capacitors on the output and was going to leave the footprints there for safety.

2. Will Change Bypassing of Opamps to single bypass.

3. Ahhh Excellent. I was wondering about that !

4. Ok so the DRV 134 I believe is just using the GND pin as a audio ref I have attached some info from the data sheet below.

5. Exactly, wanted to finalise circuit and see what parts I had in stock here and what is readily available!

Cheers
JBliss

Jbliss:
Updated Schematic

Jbliss:
back after a short break anyone had a chance to look at the latest schematic ?
Cheers

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