Everythin you ever wanted to know about installing an equalizer
To insert an equalizer or similar in-line processing device, one needs to insert it somewhere in the circuit path. You must break the circuit, send the signal out to the device, and then return it into the circuit exactly where it left it.
This is generally done with a tape monitor loop circuit, which is activated by a “Tape Monitor” switch/button located on the front panel. This is more than just a tape input and output jack.
I have yet seen an AVR with a “Tape Monitor” switch. Your only hope then is if your AVR has preamp out jacks and access to a power amp in, whether it be jacks in the receiver, or an external power amp.
Please note that some units, like my two-channel NAD 1600 (from 1990) have an “External Processor Loop (EPL) button that does exactly the same thing as a tape monitor loop.
The next few paragraphs deal with using a tape monitor circuit on a stereo receiver. The one possibility for AVR’s are covered a few paragraphs down.
In the good old days of analog two-channel stereo, adding an equalizer was as simple as pie. You simply located the tape monitor output on the back panel, ran an interconnect from there to the eq’s input, and then ran another interconnect from the eq’s output back to the tape monitor’s input on the receiver. You turn on the eq, push the “Tape Monitor” button on the receiver in, and, viola! Your eq is now in the circuit!
Or, to put in a more visual sense
• Amplifier/receiver tape output to equalizer input
• Equalizer output to Amplifier/receiver tape input
• Press “Tape Monitor” button on the Amplifier/receiver and you’re in business/
Likewise, to take the eq out of the circuit, you just pushed the “Tape Monitor” switch again to restore the internal signal path.
Essentially, what the “tape monitor” button does can be described in two steps.
1) When the “tape monitor” button is in its “out” position, the signal is fed internally from the “tape out” jacks to the “tape in” jacks.
2) When you push it in, that internal out/in connection severed, the signal goes out the “tape monitor out” jacks, through the external device, and then back into the “tape monitor in” jacks.
This is why pushing the “tape monitor” button in when nothing is connected to the “tape monitor” in and out jacks, the signal will disappear. It’s going out but never returning.
Now, if one is talking about one of the current AVR's, simply having tape out and tape in jacks on the back panel does not guarantee that it will create the needed "monitor loop" configuration. Again, I have yet seen an AVR with a tape monitor switch.
While many AVR’s might have “tape out” jacks on the back to allow you to send an analog two-channel signal out to an external device, it’s generally a one-way trip.
Likewise, they might have a “tape input” on the back to allow you to play tapes (or any high-level input) through your system, but odds are it must be selected via the input selector, which makes it worthless for the purpose of inserting an eq into the circuit.
The key is to scour the front panel for a "tape loop" or "tape monitor" button. Without that, these two sets of jacks simply allow a signal to be sent out to a tape deck but that tape deck's input must be selected as another input, not the out/in loop, as many have discovered.
So, if you do indeed have the needed "tape monitor loop" then you're good to go but be aware that it will only affect two channels, most likely the front two.
One way to verify you do have what's needed is to take one stereo interconnect and connect the tape output to the tape input in question. Switch the receiver to FM, CD or some other source besides tape, and press the tape monitor switch. It should sound exactly the same. If you lose the signal, there's a problem.
Likewise, not being able to find the "tape monitor" button/switch on the front panel is a problem also.
But, not all hope is lost. In some cases, you can use an eq between the preamp stage and power amp, assuming the receiver offers these I/O options. Some receivers have outputs but no power inputs. In that case, you'll need to feed an external power amp. There’s a downside here in that you might pick up a bit more moise than you would if you had used the tape monitor loop, but sometime you have no choice. Using this option, you’ll need a separate equalizer channel for each channel you want to eq. For a 6.1 channel system (I’ll ignore the sub here), you’ll need six channels of equalizers, or three stereo eq’s to eq all channels.
Remember, when you boost a frequency, you put more demand on the amps in that range and since they don’t increase the amplifiers power at all, all this means is that you’ll run out of headroom sooner. They are best used in a cutting the signal as opposed to boosting it.
