Electronics > Beginners
Building a sound mixer within my guitar amp with line IN & mic input
dazz:
--- Quote from: Yansi on June 02, 2019, 09:21:59 pm ---Instead of simulating stuff, where it tells you nothing more that the simulation is worth, try breadboard it.
--- End quote ---
You're right, Yansi. OK... let's see... where's the Spice model for the breadboard? :-DD Just kidding, I know you're right.
I noticed the difference in input impedance and was trying to fix it changing resistor values. But again, I was relying on the god damn simulation and something told me that wasn't the proper way to go about it.
Oh, I see what you mean by EMI protection now. It's those 1nF cap & R10 between the inputs, a lot like what X caps do at the input of a power supply, right?
As for R9, I put it there after reading this: https://www.eeweb.com/extreme-circuits/balanced-microphone-preamplifier
It's supposed to prevent oscillations with no input load
Thanks for the schematic and everything else!
Zero999:
--- Quote from: Yansi on June 02, 2019, 09:21:59 pm ---Jeez. Why 12GBP part for something that can be solved with a couple of discretes?
--- End quote ---
Fair point, the INA163 and AD8429 are a bit overkill, but it depends on what the goal is. If it's speed, i.e. just getting it done as quickly, as possible, with predictable results, it's the best way. If you want low cost, then discrete devices are cheaper and are more educational, so I agree, is probably best for the original poster.
Anyway what do you think of the NJM2122? I was thinking it would work well in a three op-amp instrumentation amplifier configuration, with it providing most of the gain and the third op-amp, a cheaper one.
--- Quote ---Your differential mic amp is useless. Instead of simulating stuff, where it tells you nothing more that the simulation is worth, try breadboard it.
--- End quote ---
LTspice can simulate noise, but I've not played with it much.
--- Quote from: dazz on June 02, 2019, 09:45:30 pm ---As for R9, I put it there after reading this: https://www.eeweb.com/extreme-circuits/balanced-microphone-preamplifier
It's supposed to prevent oscillations with no input load
Thanks for the schematic and everything else!
--- End quote ---
Thsat's a sensible enough circuit. No offence, but it'll better than what you've posted so far.
R3 in that circuit is required because the NE5534 is not stable with noise gains under three. When the input is disconnected, the noise gain is reduced, as R1 and R2 are no longer in the circuit. R3 reduces the noise gain, to prevent oscillation. It's not required if you're using an op-amp which is unity gain stable, such as the NE5532, TL072 etc.
See the following thread for more information.
https://www.eevblog.com/forum/beginners/op-amp-spec-noise-gain-configuration/msg2401983/#msg2401983
schmitt trigger:
Yansi:
Would general purpose PNP transistors work here?
dazz:
--- Quote from: Zero999 on June 02, 2019, 10:11:36 pm ---
--- Quote from: Yansi on June 02, 2019, 09:21:59 pm ---Jeez. Why 12GBP part for something that can be solved with a couple of discretes?
--- End quote ---
Fair point, the INA163 and AD8429 are a bit overkill, but it depends on what the goal is. If it's speed, i.e. just getting it done as quickly, as possible, with predictable results, it's the best way. If you want low cost, then discrete devices are cheaper and are more educational, so I agree, is probably best for the original poster.
Anyway what do you think of the NJM2122? I was thinking it would work well in a three op-amp instrumentation amplifier configuration, with it providing most of the gain and the third op-amp, a cheaper one.
--- Quote ---Your differential mic amp is useless. Instead of simulating stuff, where it tells you nothing more that the simulation is worth, try breadboard it.
--- End quote ---
LTspice can simulate noise, but I've not played with it much.
--- Quote from: dazz on June 02, 2019, 09:45:30 pm ---As for R9, I put it there after reading this: https://www.eeweb.com/extreme-circuits/balanced-microphone-preamplifier
It's supposed to prevent oscillations with no input load
Thanks for the schematic and everything else!
--- End quote ---
Thsat's a sensible enough circuit. No offence, but it'll better than what you've posted so far.
R3 in that circuit is required because the NE5534 is not stable with noise gains under three. When the input is disconnected, the noise gain is reduced, as R1 and R2 are no longer in the circuit. R3 reduces the noise gain, to prevent oscillation. It's not required if you're using an op-amp which is unity gain stable, such as the NE5532, TL072 etc.
See the following thread for more information.
https://www.eevblog.com/forum/beginners/op-amp-spec-noise-gain-configuration/msg2401983/#msg2401983
--- End quote ---
No offense taken, of course. Really appreciate your help guys, even (or specially) if it involves telling me to stop doing stupid things.
I'm obviously a clueless hack, but hopefully I'll learn a thing or two in the process of building this thing
Yansi:
--- Quote from: Zero999 on June 02, 2019, 10:11:36 pm ---
--- Quote from: Yansi on June 02, 2019, 09:21:59 pm ---Jeez. Why 12GBP part for something that can be solved with a couple of discretes?
--- End quote ---
--- Quote ---Your differential mic amp is useless. Instead of simulating stuff, where it tells you nothing more that the simulation is worth, try breadboard it.
--- End quote ---
LTspice can simulate noise, but I've not played with it much.
--- End quote ---
I thought more of a practicality standpoint. Noise-wise it will be horrible no doubt, but the input impedance imbalance is a real issue in practical application. With such imbalance, you can't even design a sensible EMI protection around it that will not screw the CMRR even more.
H.
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