Should unplugged active EQ/Comp pass same signal when powered off?

[poppaflavor]

Aaargh. I know this is such a dumb question. Are active EQs and compressors (solid state, presumably op amp, not tube) supposed to pass the same signal when the are powered off as when they are powered on?

It's happened to me twice. Once with a used XTA graphic EQ bought from Sam Ash a few weeks ago, and now again with a brand new EQ/compressor from a reputable company.

The devices pass full signal when powered off.

I'll describe the new EQ/comp here since I have that in hand and am seriously fretting about the situation. I reached out to tech support at the EQ company but haven't heard back yet.

So here goes... I tried the new EQ with a two track mix, but no matter what I dialed I got no effect on the audio. Input, output gain maxed out or set to minimum? No effect. HPF, LPF at severe settings? No effect. Compressing on EQ bands? No effect. Finally out of frustration I turned it off and it was still playing the same level and sound as when on(!). Which frankly freaked me out.

So I used REW to assess signals through it.

When the EQ was turned off I got the same exact REW frequency response through the new EQ as I did through a loopback test (FR 18i8 DAC -> ADC).

Also, the same exact frequency response and level when the EQ is on whether bypassed, EQ in but set flat, any combination of dial settings, etc. It just passes the same signal no matter what.

I recorded the two track through the EQ powered on and then again with it powered off. Played them at the same time and flipped the phase on one track. They nulled quote a bit, down to about -35 dBfs residual signal.

So, obviously the unit is jacked up because it doesn't do anything. But also, should an active sold state EQ/Comp pass signal when powered off? If not, what would allow this? A short circuit?

 

[Evertide]

Read the manual

 

[Harvey Birdman]

Hi there, this will depend on whether it uses switch bypass, relay bypass or electronic switching.

If it uses a relay bypass then it will depend on how the relay is powered.

If the relay is wired so that there is no voltage applied to the coil when it's in bypass mode (contacts NC, normally closed) then the signal will flow from the input to the output even when the unit is not connected to the power.

When you have it powered on is there any indicator, LED, lamp or display that lets you know that it's in Bypass mode or the EQ is active?

 

[Harvey Birdman]

"Finally out of frustration I turned it off and it was still playing the same level and sound as when on(!). Which frankly freaked me out."

The fact that exactly the same thing happened with 2 different pieces of outboard gear tends to indicate there may be a problem with the way you have them patched.

If it were me, I would plug a CD player or some other device that can output program directly into the input of the EQ/comp and then patch the output of the EQ/comp directly into the input of your mixer and see what happens.

Hope this helps.

 

[poppaflavor]

Thank you very much, that explanation about the relay really helps.

Yes, there are LED lights that turn on when I activate the bypass buttons. There are two bypass LEDs, one for each channel. It's a two channel dual mono EQ with no stereo link between channels. When the bypass is disengaged (EQ in) the bypass LEDs turn off. There is also a power on LED for the EQ.

 

[Brian Roth]

More than a few audio devices (not usually inexpensive ones) include a "hardwire" bypass relay to directly connect input to output when power from the gizmo is removed.

Bri

 

[Khron]

Thank you very much, that explanation about the relay really helps.

Yes, there are LED lights that turn on when I activate the bypass buttons. There are two bypass LEDs, one for each channel. It's a two channel dual mono EQ with no stereo link between channels. When the bypass is disengaged (EQ in) the bypass LEDs turn off. There is also a power on LED for the EQ.

Photos of the units?

 

[poppaflavor]

"Finally out of frustration I turned it off and it was still playing the same level and sound as when on(!). Which frankly freaked me out."

The fact that exactly the same thing happened with 2 different pieces of outboard gear tends to indicate there may be a problem with the way you have them patched.

If it were me, I would plug a CD player or some other device that can output program directly into the input of the EQ/comp and then patch the output of the EQ/comp directly into the input of your mixer and see what happens.

Hope this helps.

Thank you for the reply and suggestion. I should have clarified the following. The first device (used XTA GEQ off Reverb store) from a few weeks ago was dead on arrival. It wouldn't even power on. But it would pass signal even though it wouldn't power on.

Perhaps I shouldn't have conflated that instance with this current one. With the current new EQ/comp it will power on, all LEDs (for EQ band bypass or channel bypass or Q sharpness) turn on and off appropriately. But no functions work at all. None of the gain of EQ knobs have any effect on audio or REW signals.

I use this routing quite frequently and even retested it with an Aphex 204 in the midst of my testing of the non-functional new EQ. It works fine with other devices, just like it usually does.

I actually did consider this early on in the testing. So I double and triple checked the interface routing in it's software to make sure I am not sending the Outs directly back to the Ins or to the monitors.

My routing is fairly simple. For audio I use Ableton Live DAW and put an "external audio effect" plug-in on a stereo track that routes the audio out of channels 3&4 of the DAC in my FR 18i8 (I avoid going out of Ch 1&2 as Ableton reserves those for monitors that the DAW master track is routed to). Then from the EQ (or other external device) I come back into the 18i8 ADC on Ch 1&2 and back into the DAW "external audio effect" plug in and route that stereo track to the master.

So I'm pretty confident that it's not a routing issue.

 

[poppaflavor]

More than a few audio devices (not usually inexpensive ones) include a "hardwire" bypass relay to directly connect input to output when power from the gizmo is removed.

Bri

Thanks, I didn't know that. This device isn't super high end but isn't inexpensive. (~$1800).

So I'm gathering from the responses that passing signal when off isn't unheard of and can be explained.

But that still leaves me with a completely non-functional unit. It's so surprising that I'm still sitting here second guessing myself. It's just so much easier to think I'm doing something wrong than that s reportable company shipped me a brand new nonfunctioning device. I never would have imagined a new device can be dead on arrival with no function. I still can't believe it and am kinda gaslighting myself. So I plan to repeat testing again tomorrow for the third time just to be certain in my conclusions.

It's not a complicated scenario though. I should be able to plug it it, route from and to my DAW and twiddle knobs to get an effect as I have done with dozens of other gears for the past few years. But the device does nothing.

 

[poppaflavor]

Read the manual

I did. Please read my description? This scenario is most certainly not covered in the manual.

 

[Harvey Birdman]

"So I'm pretty confident that it's not a routing issue."

OK... if your certain it patched correctly then then I think you may have a faulty unit. It appears that the unit is permanently in Bypass mode regardless of what the front panel indicates.

If it does use a relay to switch between active and bypass and the coil of that relay was open circuit, then it would be permanently in bypass mode.

What is the brand and model number of this device?

 

[poppaflavor]

Photos of the units?

I hesitate a bit to post photos yet because I haven't heard back from their tech support and I didn't want to impugn the company's reputation in the (increasingly slim) chance I'm just missing something basic.

I'll post the pictures and identify the device tomorrow after I've given them some more time to reply. I think the text support is in UK (I'm in the US), so I want to let them get into their workday and get a chance to reply to me.

I'm usually trying the function of a used (sometimes vintage) or new piece of gear every week or two, so this process is pretty familiar to me. For this reason I'm pretty sure the new EQ is just a bad unit. But I want to be sure before making the company's name public here.

I hope you might understand that reasoning.

 

[poppaflavor]

"So I'm pretty confident that it's not a routing issue."

OK... if your certain it patched correctly then then I think you may have a faulty unit. It appears that the unit is permanently in Bypass mode regardless of what the front panel indicates.

If it does use a relay to switch between active and bypass and the coil of that relay was open circuit, then it would be permanently in bypass mode.

What is the brand and model number of this device?

Thanks that makes perfect sense. Please see my post immediately above this? I note that I'll post the brand and model tomorrow, but feel I should give the company's tech team a chance to reply before posting their name and device. Hopefully that is understandable. Not trying to hide anything, but want to be fair to the company.

 

[Harvey Birdman]

Thanks that makes perfect sense. Please see my post immediately above this? I note that I'll post the brand and model tomorrow, but feel I should give the company's tech team a chance to reply before posting their name and device. Hopefully that is understandable. Not trying to hide anything, but want to be fair to the company.

Ok, no problem.

Cheers

 

[NoisyIndividual]

Having a hard bypass in the event of a power failure is very desirable in a live situation, where you just lose the compression, not the whole bass guitar/vocal etc.

I would say it is more often found in older, higher end devices than cheap modern ones, but it is/was certainly quite common.

 

[gyraf]

On the other hand, a bypass-when-unpowered relay would require power to be "in" - and as it's electromagnetic'ly activated, I prefer to keep this from not happening near my audio transformers.

So I wire bypass relays so they bypass when powered (and any magnetic interference thus dosen't matter), not the other way around

/Jakob E.

 

[Estomagado]

On the other hand, a bypass-when-unpowered relay would require power to be "in" - and as it's electromagnetic'ly activated, I prefer to keep this from not happening near my audio transformers.

So I wire bypass relays so they bypass when powered (and any magnetic interference thus dosen't matter), not the other way around.

I quite agree with you, audio transformers tend to be fairly picky about EM interference from nearby coils.

BUT... that means if the power line feeding the gear fails, the audio is muted. I'm sure in a studio this would be a very minor concern, easily detected. In a live situation, it would be a slightly bigger concern.

 

[warpie]

On the other hand, a bypass-when-unpowered relay would require power to be "in" - and as it's electromagnetic'ly activated, I prefer to keep this from not happening near my audio transformers.

So I wire bypass relays so they bypass when powered (and any magnetic interference thus dosen't matter), not the other way around

/Jakob E.

I'm not sure what you mean here. That an activate relay would cause EMI?

 

[RuudNL]

Personally I prefer a 'power safe bypass', in the form of a relay that connects the output directly to the input when there is no mains voltage. Certainly in a life situation, it is better to have no compression or no EQ, instead of no signal at all when the mains power gets interrupted...

 

[JohnRoberts]

Back in the 70s I designed a well respected studio efx SKU (Loft 440/450 delay line/Flanger). I used a relay to effect a hardwire bypass.

The vast majority of my value designs while at Peavey did not support hard bypass relays.

JR