Amplifier for 4 piezo mics to 4 mono speakers

AnalogKid said:

Not quite.

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OK, wrong component. But do I at least understand that the relay contacts and the 4PST relay coil that you mentioned are part of the same component? Just trying to understand the overarching logic of the circuit design.

pin board simple (no extras = minimal components) -- microphone , amplifiers with volume control, speaker -- circuit (just a "one channel" of your project) see how it works then advance

(((o))) said:

But do I at least understand that the relay contacts and the 4PST relay coil that you mentioned are part of the same component?

Click to expand...

Yes.
https://en.wikipedia.org/wiki/Relay

Read the sections on Basic Design and Operation, and Pole and Throw. For your application you need 4 poles and either single or double throws. You need single throws, but double throws might be more available.

ak

ci139 said:

pin board simple (no extras = minimal components) -- microphone , amplifiers with volume control, speaker -- circuit (just a "one channel" of your project) see how it works then advance

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Yeah, sounds like a good plan!

AnalogKid said:

Yes.

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Great, thank you! I have read the article you suggested and am reviewing the section on relays in the Make:Electronics book. I'll see what parts I have around and try to work something up. I'm sure I'll have more questions!

Another quick question for you. It looks like most of the simple amp circuits I am coming across already have a volume control. Since I want the volume between the preamp and the 4 gang global volume pot, what should I do about the amp volume? Can I just replace the variable resistor with a low-value resistor in the amp circuit? Or leave it out altogether?

Some power amplifier circuits use the volume control to bias the input at 0V and some power amplifier ICs have the resistor to ground built in.
So check the schematic of the power amplifier to see if you must add a resistor to ground if you remove the input volume control.

audioguru said:

some power amplifier ICs have the resistor to ground built in

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the lm386 has also on chip gain control : **broken link removed**

ci139 said:

the lm386 has also on chip gain control : **broken link removed**

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If the gain is less than about 9 times then the LM386 oscillates at a high frequency because it is de-compensated so that when its gain is high then high audio frequencies are not attenuated.
It is odd that the Japanese company shows BANG-muting by shorting pin 7 to ground. It isn't a little POP, it is an explosion that also occurs when that kind of muting is turned off. I would be better to ramp the voltage at pin 7 down then ramp it back up.

audioguru said:

gain is less than about 9 times then the LM386 oscillates

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like that ? - i mean - i cannot set up the high frequency osc. cir. you hint exists
. . .
in attempt to find one i came across of this ??? http://www.rexresearch.com/flanagan/flanagan2.html
. . .
back to stability -- has a hint of simply ac shorting the pins 1 & 5 . . . (busy) . . .

-

it looks we have your signal !!!

did some experiments /!\ what it's worth :

Why does your simulated LM386 circuit have so many parts? The bass boost circuit in the datasheet reduces the gain of mid and high frequencies to a little more than 9 times with one resistor and one capacitor.

it's because im an IT dude and perhaps analog DC amp.s hobbyist not an audio guy

OK, thank you! I will check to see if I need a resistor to ground if I remove the input volume control. Is there a particular simple amp circuit that might work well with this project?

ignore #30 because of #32
you need to set master vol before channel volumes (just to save power)
but you may need separate channel volumes before master 1 to range your instrument-mic. combinations to "fit"/match the master vol input

my only advanced mic. experiment was with a bunch of electro-dynamic speakers in parallel as a microphone to lm387 this to coAUX.INP to internal equallizer to MAX bass MIN treble (e.g. ? trough a linear-ramp low pass filter) then likely to a second coAUX to do normal specrum adjust . . .
. . . after 3x amp-s and 2x filters it was reasonable (near ok) but not good as professional quality

if you want to get a good quality sound look around www for simple/cheap but good quality equipment or find sponsors
e.g. there might be some simple setup that meets your needs -- but more likely you have to invest 10x more time to development experimenting with this stuff than you now think it takes

(=)(!")"(&%)#&%) i forgot why i started this reply in a first place
is the power limiting - - there should be - - as the burnt fuse are troublesome to find - - the most simple one is current limiting - - might be and input or output amplitude limiting / chip PCB temperature shutdown e.c. e.c.

How much amplifier power do you want? If the microphone can hear the speaker then a sound goes around and around causing howling and squealing acoustical feedback. Keep the mics and speakers far apart, turn the speakers away from the mics and turn down the amplifier power to eliminate feedback.
An LM386 amplifier IC has an input resistor to ground and produces 0.45W into an 8 ohm speaker when powered from 9V. About as loud as a cheap clock radio.

AnalogKid said:

ak

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So in my spare time I think I have come up with a serviceable block diagram. Before I move ahead with prototyping it, I wanted to ask about possibly simplifying my plan.

Your suggestion calls for mics>mutes>preamps>individual volume controls>etc. Part of the complication of this circuit was the requirement that each mic feed its own speaker, unless something was plugged into the switching jack.

What if I instead combine the 4 mics into a stereo signal? I believe this would require a much simpler layout. I have read that you can feed 4 piezos into a single preamp without much signal degradation. If this is true, and if it would work moving the individual volume controls before the preamp, then I believe this would work:

4 piezos>4 mute buttons>4 individual volume controls>preamp>global volume control>SPDT relay>amp>stereo pair
Then the switching jack would be connected to the SPDT relay coil

Even if I need 4 preamps, it still seems like this would be a less involved circuit, as only one amp and no mixer is required.

I have attached a couple drawings below. Could you please let me know if the diagram for my original idea looks like it's on the right track, and also whether my simplification seems workable?

Thank you!

perhaps there's some help on the google's colored picture book https://www.google.com/search?q=simple+line+amplifier+audio+mixing+circuit&tbm=isch

not a must but one possible option ↑from↑ https://circuitscheme.com/audio-mixer-vu-meter.html