Adding microphone to line input

[stuee]

Hi.
I have a jukebox with this amp installed
**broken link removed**

i also have pair of wireless microphones that use one base receiver and 1 channel mono out.
Info in picture.

The setup is basically the computer running the jukebox software, this is line out to the amp, the amp is set at 3/4 volume and volume controlled by the pc.
I need to somehow get the microphones working with the amp but there is no mic input.
I was hoping i could put some type of potentiometer inline then join them to the pc line input.
Would this work, if not would anyone have any solutions. No suggestions to get a new amp as this one is perfectly fine and almost new.

thanks
Stu

 

[flat5]

I believe you need a preamp.
Your mic setup provides >25mv
Your amp wants 775mv for full output.

 

[stuee]

Thanks flat5.
Would this 12v circuit suit, could i add a potentiometer somewhere to control the volume?
**broken link removed**


Also would you know if there is some way i can run the sub from both the speak outputs with a filter and volume control?

Cheers

 

[audioguru]

The spec's for the (Chinese?) receiver has many errors. Its sensitivity is 600W?
It does not say its minimum load impedance so it might not be able to drive the low input impedance of the transistors mic preamp.
An audio opamp preamp will be a simpler circuit with fewer parts and better performance. It will have a high input impedance that any receiver can drive.

An good audio opamp preamp circuit (without a transistor) is on that sound.westhost website. But it might produce an Australian accent.

 

[flat5]

Lots of ways to go.

You might buy a fancy soundcard for the PC. The all have mic inputs. External with USB output.

The preamps you pointed to are overkill, as preamps, I think.
A simple opamp circuit powered by 9 volts will do. An external plug in power supply (wall wort) to power it.

The wireless mic receiver already has mic level controls, does it not. The amp has level controls too, I would think.

A small 2 or 4 input mic mixer would give you future flexibility.

Since you are going to send this to a 1000 watt amp (!) A mixer with a parametric and graphic equalizer might be a good idea.
1000 watts of feedback is a scary proposition.

I assume the output of the wireless mic reciever is unbalanced. Two 'wire'. Hot and shield.

If you want to build a preamp I think this page might be useful.

https://www.willegal.net/preamp/preamp.htm

Well those are my thoughts at 4:42 in the morning. zzzzzzzzzz

 

[audioguru]

Another mic preamp with a very low input impedance that the wireless mic receiver might not be able to drive. Use an audio opamp preamp instead that has a high input impedance.

I also shudder when I think of 1000W of acoustical feedback howling breaking all the windows. How will the feedback be prevented? The mic in one city and the amplified speakers in another city?

 

[flat5]

OK, op amp is best if you don't know what is driving the preamp.
Truth is, I got tired of looking for simple unbalanced mic preamps.
I thought it would be simple to find a basic op amp preamp.

EQ can be very useful to protect from room hi Q resonances I found in my limited experience.

Edit: **broken link removed**
But don't use a 741 op amp. It's just is not a good product by today's standards.

**broken link removed**

 

[audioguru]

The 741 opamp circuit is inverting so it has a very low input resistance. You want a high input resistance so the opamp circuit should be non-inverting.
A 741 opamp is 46 or 47 years old and has too much hiss noise for a preamp. Also it works poorly above 9kHz but audio goes up to 20kHz so more than one octave of high audio sounds is missing.

Here is a preamp using a low noise audio opamp in a non-inverting circuit with a high enough input resistance. It works perfectly with very low distortion up to 100kHz, remove R1 that powers an electret mic:

 

[flat5]

Yes! That should solve his gain problem. Part of the battle.
I think he should look for a used small mixer board.

 

[4pyros]

Yes go with a small mixer, Radio Shack used to have a 3 channel one for around $30.

 

[eTech]

Hi

Buy a sound card with Mic inputs, that way you can control them from the PC like the Jukebox software.

Or...You can buy a small mixer with mic inputs and USB interface, connect it to the PC, then connect the power amp to the mixer output.

eT

 

[audioguru]

He does not need a mixer since he is switching only one of the mics to the input of the preamp at a time.

 

[4pyros]

He does not need a mixer since he is switching only one of the mics to the input of the preamp at a time.

The mixer would take the place of the preamp, and some day they may want to hook up more, they always do.

 

[audioguru]

He listens to one mic at a time with a switch so a mixer is not needed.

 

[4pyros]

I need to somehow get the microphones working with the amp but there is no mic input.
I was hoping i could put some type of potentiometer inline then join them to the pc line input.

Sounds like more than one to me. That are some how mixed at the receiver.

i also have pair of wireless microphones that use one base receiver and 1 channel mono out.

 

[audioguru]

Sorry, I thought this is the thread where a guy uses a few mics to listen to rattles in a car and he switches each mic one at a time to hear which one picks up the loudest sound.

Each wireless mic must have its own transmitting/receiving frequency if more than one is used at a time which maybe he does not have.
A series resistor from the PC line out and another series resistor from the mic preamp output can join together at the amplifier input for a simple audio mixer.

 

[eTech]

Hi AG
The instructions read that both microphones have different color indicators on the receiver. So it probably does have two receivers.

Stuee
Can both mics be used simulaniously? Are there separate outputs on the receiver for each mic? Or a single "mono" one?
How do you intend to use the mics with the system? Is it for DJ'ing or Karoake?

eT

 

[stuee]

Hi, thanks everyone for your inputs, I have decided and purchased a simple 2 channel mixer and mounted it, it works great with the microphone simply.
Just to answer one question. both microphones are on the 1 receiver and 1 channel mono output.

I now do have another question.
I have 18: sub in a almost 1m x 1m box. Is there a kind of crossover with the filter (adjustable would be handy) that i can use from the left / right amp output to my sub.

Thanks
Stuart

 

[4pyros]

There are some here but most are meant to be mounted in the sub woofer.
https://www.ebay.com/bhp/subwoofer-crossover

 

[audioguru]

I have 18: sub in a almost 1m x 1m box. Is there a kind of crossover with the filter (adjustable would be handy) that i can use from the left / right amp output to my sub.

You have a problem if you have a stereo amplifier but only one sub speaker. The sub needs to have its own mono amplifier because you cannot connect the left speaker and the right speaker outputs together to get mono for the sub.

You have another problem because you do not have a low level signal to feed the amplifier for the sub, then your stereo speakers will also play (and maybe get damaged) the very low and powerful sub frequencies. The stereo amplifier usually has highpass filters at its inputs.

I put together a crossover circuit that feeds the inputs of your three power amplifiers: