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Help hooking up a Equalizer.

Radio Face

Active Member
Nov 2, 2017
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Could someone give me a quick how to on hooking up an EQ to a CB for receive purposes. One from an old stereo. Also, what is involved in wiring one into the transmit? Thanks for the help in advance.
 

If you're running from the EXT speaker jack probably just 3.5mm to dual RCA adapter cable is all you'd need.
 
It's useless for that purpose because of most key frequencies are out of CB audio bandwidth.
So you are saying it would not help me to fine tune the sound for my hearing? How about cut out some of the high tone.. like a high cut filter?
 
An eq on the output jack of your radio works great... Cutting off the highend hiss sounds fantastic... I use a 4 band parametric eq. It does help if you have a good sounding speakers as well
How about connecting one to the transmit. Does that work also?
 
In light of what you're asking.

There are different Mic ELEMENTS that can make your efforts harder to complete.

The typical Cobra 29 / 25 Uniden Grant XL or PC-122 or the Cobra 148 - use DYNAMIC elements, its a simple speaker on a cord - you talk, the diaphragm vibrates, the magnetic coil picks up this vibration and changes it to a signal - the radio takes care of the rest - it's extremely amplified - but that is due to the very very small signal you are putting into the radio.

Another type is Electret, uses a small trickle power of current and voltage - but it has an amplifier in the cartridge to make it stronger. They use a diaphragm called a membrane - that one side is exposed to the outside while the membrane then rests in a cavity where another plate is used that sees the vibration as a change of capacitance. A voltage is present on the membrane and the plate - and so it exerts a field and changes when vibrated. An FET amplifier built in to the Electret, sees this change and amplifies this as a signal.
  • Dynamics use coils - so it's inductive, Electrets use Capacitance.
The FET - changes it to an audio signal (AC-Audio) to about 1 volt less in voltage than the DC power it uses. The trick in making this a workable signal is thru the IMPEDANCE - the amount of effort the signal has to overcome in ohmic effort from 0 to XX volts - and the amount of current behind it to force that power - in amps, only in uA onto mA of draw into a known load of ohmic measurement. The Line Level reference is to demonstrate a "strength" of signal - into known ohmic loads.

upload_2021-1-13_21-53-54.png

  • It's not that you can't - it is that you will encounter problems if you don't know how to properly transfer the audio from one source (your Mic) thru your EQ, then into your Radio - without knowing how to properly drive and terminate the signal so your system seems a balanced = equal impedance - condition.
To begin a journey of learning more...try here...
https://en.wikipedia.org/wiki/Line_level

The effort to change the DC power thru the element - into AC - is this Impedance and Drive Level Power. (Strength of signal)

Dynamic elements have very little capacity to push power.

Electrets can use a known voltage across a known resistance - to generate this signal as a difference. So in theory and practice, they can take a higher voltage and low-power current to obtain a higher outputs drive level. They convert the signal by blocking the DC component of the power, and allow the changing power levels of both voltage and current - by using a blocking cap to transfer the signal from one sourcing to another - this is where the Impedance and the effort (Strength) comes into play.

So when it comes to EQ's, your Mic - if it's Dynamic, may not push the drive level very well, maybe as a public address system - using an EQ that can work with Dynamic or Magnetic Cartridges will work fine, they will amplify the power level to obtain what they call Line Level inputs, an industry standard.

So as you are thinking about the EQ, remember your EQ - needs to have a "standard" input and output - to interface with your project.

So if you use an old Radio Shack Equalizer - it's used in a Tape Monitor Loop for Home stereos - a little different Line-Level signal is needed.
 
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In light of what you're asking.

There are different Mic ELEMENTS that can make your efforts harder to complete.

The typical Cobra 29 / 25 Uniden Grant XL or PC-122 or the Cobra 148 - use DYNAMIC elements, its a simple speaker on a cord - you talk, the diaphragm vibrates, the magnetic coil picks up this vibration and changes it to a signal - the radio takes care of the rest - it's extremely amplified - but that is due to the very very small signal you are putting into the radio.

Another type is Electret, uses a small trickle power of current and voltage - but it has an amplifier in the cartridge to make it stronger. They use a diaphragm called a membrane - that one side is exposed to the outside while the membrane then rests in a cavity where another plate is used that sees the vibration as a change of capacitance. A voltage is present on the membrane and the plate - and so it exerts a field and changes when vibrated. An FET amplifier built in to the Electret, sees this change and amplifies this as a signal.
  • Dynamics use coils - so it's inductive, Electrets use Capacitance.
The FET - changes it to an audio signal (AC-Audio) to about 1 volt less in voltage than the DC power it uses. The trick in making this a workable signal is thru the IMPEDANCE - the amount of effort the signal has to overcome in ohmic effort from 0 to XX volts - and the amount of current behind it to force that power - in amps, only in uA onto mA of draw into a known load of ohmic measurement. The Line Level reference is to demonstrate a "strength" of signal - into known ohmic loads.


  • It's not that you can't - it is that you will encounter problems if you don't know how to properly transfer the audio from one source (your Mic) thru your EQ, then into your Radio - without knowing how to properly drive and terminate the signal so your system seems a balanced = equal impedance - condition.
To begin a journey of learning more...try here...
https://en.wikipedia.org/wiki/Line_level

The effort to change the DC power thru the element - into AC - is this Impedance and Drive Level Power. (Strength of signal)

Dynamic elements have very little capacity to push power.

Electrets can use a known voltage across a known resistance - to generate this signal as a difference. So in theory and practice, they can take a higher voltage and low-power current to obtain a higher outputs drive level. They convert the signal by blocking the DC component of the power, and allow the changing power levels of both voltage and current - by using a blocking cap to transfer the signal from one sourcing to another - this is where the Impedance and the effort (Strength) comes into play.

So when it comes to EQ's, your Mic - if it's Dynamic, may not push the drive level very well, maybe as a public address system - using an EQ that can work with Dynamic or Magnetic Cartridges will work fine, they will amplify the power level to obtain what they call Line Level inputs, an industry standard.

So as you are thinking about the EQ, remember your EQ - needs to have a "standard" input and output - to interface with your project.

So if you use an old Radio Shack Equalizer - it's used in a Tape Monitor Loop for Home stereos - a little different Line-Level signal is needed.
Thank you for the explanation. It sounds a little more complicated that I thought It might be. RF
 
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It's easier to start simple, then expand as you see fit.

Hooking up an equalizer from your home stereo, well, you can do it, but you will encounter problems.

Mostly the issues will be of problems it will need - with shielding and termination of the signal - most techs use terminating resistors to help with the signal level - just parse, trim, turn down the output of one, to better meet the next piece of equipment in the line -follow down the chain - to get to the radio - which will need and have it's own share of reduction to obtain that which you want.

You don't have to run "speakers" - you can use the PHONO input of the Stereo, to obtain an Tape Monitor output, that can be interfaced to your radio - but if you want EQ - that is the LAST of the steps - in the tape monitor loop - before your radio, but this piece of equipment is also going to be the one that is the most touchy, you'll have to "terminate" the output and balance it properly.

If it was MONO - thats one thing, but you have two inputs and two outputs and a lot of open loop antennas called unused inputs and outputs all along the way.

Those will have to be terminated, either by a resistor - or a direct short, which you'll have to know some aspects of how they insert their signal - some have "live input" that simply is buffered thru a capacitor into the high gain circuit then branched off to the various filters to EQ that signal - summed together then put thru a buffer amp to simply drive to the next stage - not amplification or reduction just equalization....
  • No, Were not discussing Speaker output, for that is a low-impedance high-drive level that will damage equipment if you try to use it without knowing how to interface it.
  • Best to use the "headphone" and Tape Monitor options - keep your speaker outputs off - save the Stereo's outputs for another time.
Others AMPLIFY only the output result of the EQ process of the filtering - which makes the outputs more unbalanced and susceptible to feedback looping and squeals.

So termination is easy, you just make up a simple divider and resistor network to take in both inputs to CENTER - both SHIELDS are TIED (Bonded) together - and between the two CENTER outputs - each one gets a resistor - to sum together, then that output point, is another resistor ACROSS that point to SHIELD - the difficulty is in how much resistance to use.
 
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An eq on the output jack of your radio works great... Cutting off the highend hiss sounds fantastic... I use a 4 band parametric eq. It does help if you have a good sounding speakers as well
I have a old Realistic parametric eq. Could you give me a little more information on how to make it work on the cb receive? I am kinda green at this. Thanks
 
Is this in any way comparable to the mods that Drail is doing ?


He likely changed out some filters to add more bandwidth which is different than adding a EQ inline going into the mic jack.

The EQ in line with your microphone lets you make adjustments with the audio going into the radio but it doesn't change the way the audio goes through the radio (which he changed in that 955). The UR6QW can still make a difference in your tone, audio levels, compression, etc. but you'll always be limited by the circuit in the radio.

When guys start to talk about hi fi in AM radios like a Cobra 29 they'll start talking about direct injection or the mouth mouth mauldulator, etc.

Here's a CBer talking about 3 ways of feeding audio into the radio. -
 
This can easily go beyond the scope of this thread, but the above vid shows the differences not just between the types of injection- but their limitations of the mic amp if you go thru the route thru the mic jack...

The typical Mic amp built into the radio, uses an op amp, or transistor to amplify the low-level signal...

So you're running into some constraints...mostly the built in limitations the amp; the gain and frequency response, is already set and pushes against the audio arriving to it...

There are similarities, and differences...

InputOffset_4558Chip.jpg
The above op amp approach, as well as most typical AM-only Radios that use the Audio Amp of several watts - pushed into a transformer to make Phase Modulation then clipped to form the drive the Driver and Final use, follow some simple established protocols...
  • I say "Clipped" because of the purpose and function the diode does, of preventing
  • the reverse bias or negative peaks from damaging the equipment this signal is being sent to.
upload_2021-1-21_20-41-18.png

Another aspect not addressed, but depends on the application of what you have to work with...

And that is the DISCRETE form of amplification...

upload_2021-1-21_20-28-40.png

Anther type of amplification is also discrete, not often seen anymore but quite useable...Even some simple Power Mic's you can find at local truck stops do this method of a varying degree...
MICROPHO.JPG
The PC-122 use the above...not as much constraint in it's fidelity, only some filtering is done, but much of the effect the above circuit provides is in Compression...

PB_122AU.GIF

I'm sure you may have seen these different types floating about the net...

So really, to obtain any form of EQ, you can use the built-in mic amp of your radio to a certain degree.

You won't sound like Tom Jones (well, maybe) but Barry White - is a little more Baritone than most radios can process, let alone even reproduce in their receiver - faithfully.
 

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