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Building a sound mixer within my guitar amp with line IN & mic input

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dazz:

--- Quote from: Zero999 on June 03, 2019, 01:55:16 pm ---
--- Quote from: dazz on June 03, 2019, 12:09:15 pm ---I'm reading about 3 op amp instrumentation amplifiers now and I'm a bit confused. Apparently it's a differential op amp with both inputs buffered through 2 low noise op amps. But that would have a very high input impedance, didn't I need low impedance at the inputs
--- End quote ---
Yes, that's correct, it will have a high impedance input. The good thing about it is it doesn't require adding any resistors in series with the microphone, which increase noise. The impedance can easilly be reduced by adding resistors in parallel with the microphone.

--- End quote ---

Of course  :palm:


--- Quote from: Bassman59 on June 03, 2019, 04:17:37 pm ---
--- Quote from: dazz on June 02, 2019, 08:56:24 pm ---Those INA163 go for 12€ on ebay
--- End quote ---

They're easily less than half that through a proper distributor. eBay? Why bother.

Also consider THAT 1510 or 1512.

--- End quote ---

Because after shipping fees to Spain it's actually pricier in digikey or mouser last  time I checked.
I'm making a parts list for  the preamp that Yansi suggested, but I'm pretty sure that I have everything I need except for the pnp transistors.

How about this INA217? The plan right now is to build both, the one with instrumental opamps and Yensi's design

Audioguru:
An instrumentation amplifier has all the resistors needed perfectly matched for excellent common mode rejection. They have a high input resistance because they are used to measure high impedance heart and brain waves. A differential circuit needs the resistors matched which is either with very expensive resistors or with a trimpot or two for you to fiddle with.

Zero999:

--- Quote from: dazz on June 03, 2019, 09:28:19 pm ---
--- Quote from: Zero999 on June 03, 2019, 01:55:16 pm ---
--- Quote from: dazz on June 03, 2019, 12:09:15 pm ---I'm reading about 3 op amp instrumentation amplifiers now and I'm a bit confused. Apparently it's a differential op amp with both inputs buffered through 2 low noise op amps. But that would have a very high input impedance, didn't I need low impedance at the inputs
--- End quote ---
Yes, that's correct, it will have a high impedance input. The good thing about it is it doesn't require adding any resistors in series with the microphone, which increase noise. The impedance can easilly be reduced by adding resistors in parallel with the microphone.

--- End quote ---

Of course  :palm:


--- Quote from: Bassman59 on June 03, 2019, 04:17:37 pm ---
--- Quote from: dazz on June 02, 2019, 08:56:24 pm ---Those INA163 go for 12€ on ebay
--- End quote ---

They're easily less than half that through a proper distributor. eBay? Why bother.

Also consider THAT 1510 or 1512.

--- End quote ---

Because after shipping fees to Spain it's actually pricier in digikey or mouser last  time I checked.
I'm making a parts list for  the preamp that Yansi suggested, but I'm pretty sure that I have everything I need except for the pnp transistors.

How about this INA217? The plan right now is to build both, the one with instrumental opamps and Yensi's design

--- End quote ---
The INA217 looks perfectly fine to me.

It's possible you wouldn't be able to tell the difference in sound between the two designs, especially if you didn't know which one was in the circuit, assuming you set the gains the same. This isn't because there won't be any difference in performance, just that it could be imperceivable.

dazz:
Thanks again guys. I'll order the parts I need to build those preamps, and while they arrive I'll see if I can get this one working with a TL082. Not sure how to set the gain in that one though



Then I can compare their performance

Yansi:
Look for single opamp differential amplifier at google. Gain way to easy! In this circuitabout 316. And you are supposed to trim the bottom feedback path to exact resistor ratio as the upper one for best rejection. However wit the input impedance imbalance it is pointless anyway.

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