PV 231EQ - Phantom power?

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Petesouthpaw
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PV 231EQ - Phantom power?

Post by Petesouthpaw » Fri Mar 10, 2023 12:30 pm

Hi folks!

I'm hoping someone can answer this quandry for me...

I've been using the above 231EQ for many years as an input EQ on my dynamic Kick and Snare mics. The unit simply sits in the chain before the interface to tame some of the harsher frequencies. The chain is as follows:

Mic - XLR - PV231 - XLR - Focusrite Octopre interface.

The system works well for me but I recently bought a new condenser snare mic and connected it as usual (routed through the PV as above) but there is nothing coming through. I assumed that, as the 231 had balanced in/outs, it would just carry the phantom power through from my interface to the mic. Have i missed something? Every other component has been checked such as the new mic in another input separate from the PV 231, the XLRs have been swapped out, dynamic mics have been checked etc.

The problem seems to simply be that the 231 doesn't carry phantom power through its circuitry. Am I correct and, if so, is there a technical reason for this? I can do a workaround but just felt a bit stumped - hence my appearance on here!

Thank you in advance!
Pete

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dak
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Re: PV 231EQ - Phantom power?

Post by dak » Fri Mar 10, 2023 5:40 pm

There is no sensible way to "carry through phantom power" without also carrying other parts of the signal and/or seriously deteriorating signal quality. There is essentially no device doing anything of consequence that will pass phantom power: if something provides phantom power on its inputs, it will generally generate it itself. The closest to "passing" phantom power I can think of are adapters for providing "plugin power" to electret microphones and converting the unbalanced electret microphone signal to a balanced signal. Those take phantom power from their balanced output in order to get the low voltage required on their unbalanced input.

Balanced outputs of self-powered devices tend to be impervious to phantom power but don't utilize it. Apart from microphones running on phantom power, active DI boxes can often be powered in that manner (the before mentioned plugin power adapters can be thought of as sort of a DI). But devices with mandatory external power will as a rule just ignore the presence of phantom power on one of their outputs. Whether they provide phantom power on their inputs is generally a separate thing.

The PV231EQ doesn't; at least that's what I read into its user manual.

Cagey
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Re: PV 231EQ - Phantom power?

Post by Cagey » Sat Mar 11, 2023 6:29 am

Ignore the useless nonsense like the rest of us...



A single channel phantom power unit for $20 might solve your problem along with preamp ***if needed- he said it worked without one.

https://www.amazon.com/1-Channel-Microp ... B07FFC4NF1

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Last edited by Cagey on Sun Mar 12, 2023 7:36 am, edited 3 times in total.

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dak
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Re: PV 231EQ - Phantom power?

Post by dak » Sat Mar 11, 2023 8:18 am

There's also the possibility of putting a mod in: as this is a powered device, it is likely to have something like 12V inside, and a number of phantom-powered devices will actually work with 12V. The main disadvantage of 12V compared to 48V is that the resistors are considerably smaller and will put a significant load on the signal. I've done a switchable supply in viewtopic.php?f=21&t=53636 which might also work here (no idea what the internal voltages of the 231EQ are).

Petesouthpaw
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Re: PV 231EQ - Phantom power?

Post by Petesouthpaw » Sat Mar 11, 2023 8:52 am

Thanks chaps!

That all makes perfect sense. I've just installed a small DI box into the chain between the mic and the EQ - works great and as intended! Appreciate the time (and patience) that you've taken to help me out with the technical explanation.

All the best,
Pete

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Re: PV 231EQ - Phantom power?

Post by Dookie » Sun Mar 12, 2023 7:32 am

First if you have been using this setup for years and have been happy with the sound then the final choice of the signal chain is up to you. Regardless of phantom powered microphones or not being used. Here is just something just to think about.

Modern power amps are designed to see a load at their outputs. In general, modern amps are designed to work within 2 to 16 ohms within a voltage range to give X amount of useable wattage.

The same is true for a microphone/preamp setup. I don't know what you are using for a microphone but a standard SM58 has an output impedance of 150 ohms. You'll find a microphone preamp on a desk might be "around" 1500 to 3000 ohms or so. The two will work together. In a way the Microphone becomes like a speaker giving a load to a power amp. The desk sees the right input impedance so the two can work together. The Input impedance of the EQ is 50,000 ohms. The Microphone and the Equalizer may not be ideally matched as far as their input and output impedance.

Another part of this is the voltage. A power amp puts out Voltage. This voltage will interact with the load from a speaker, so it produces wattage to do the work. To find the wattage a power amp puts out you would use, voltage squared divided by impedance. *In simple terms*. When a microphone is plugged into an equalizer there is a fixed voltage reproduced. The voltage between the microphone and equalizer is fixed. You can turn the "Level" up or down on the eq but this is a preamp inside the eq after the input. This may or may not be ideal. When a microphone is plugged into a mixer the preamp is variable so the gain/voltage can be increased or decreased as needed. Yes, when you come out of the Equalizer and go into a microphone preamp you can adjust the gain of the microphone/equalizer combination but the "sound" that that combination coming in may not be ideal. It may sound thin or muddy and the Signal to Noise as the voltage the equalizer makes with the load may not be correct for what is needed. The 2 may just sound "different".

Although you may have done this before there is something you can try. Take 2 channels of your Focusrite Octopre interface and set them up so they are the same with the sound coming in. Take one of the Non phantom powered microphones you have been using or a microphone like a SM58. Go out the SM58 and go straight into the Focusrite Octopre interface on one channel. Then on another channel go out the SM58 and into the Equalizer, out the Equalizer and into Focusrite Octopre interface. Make sure the Equalizer is set to Bypass on all settings so the level in/out of it is the same and you match the levels as close as possible using the Focusite preamps of the 2 channels. Give each a listen carefully when you talk into them. Do they sound the same? Does one have more Hiss or noise? The idea is to see what the eq does to the sound in the chain, even when everything else is bypassed on it.

It maybe they sound close enough to each other that you are happy with the results. Or you may find the eq is adding or taking away in a way that you may have not noticed before. Adding a phantom powered preamp is a good idea before the eq as it may change some the input/output impedance combination in a way that is useful to you or not. Hard to say until you put the signal chain together and see as a whole how the entire chain interacts.

The eq in general is a Line Level device. A microphone is expecting to see a preamp level device. How this input/output impedance match effects the sound is something you can test and make a decision on if it is the best thing for you to do or not.
All the above is a very basic explanation that I wanted to make you aware of. Only you can determine what is best for you. You may find picking up a small 2 channel Stereo mixer with phantom power put before the eq may give you a better match. Just pan one microphone to the left and go left out from the mixer to one eq channel, the other microphone pan to the right and go into the other channel of the eq.

Does your Focusrite Octopre interface have inserts per channel? Can you go out the Focusrite insert, through the eq and back in? Which Focusrite Octopre interface do you use? I seem to remember 2 or 3 models, but I haven't looked at them in a while.

Again, all the above is general information and what you are using for microphones does come into play, but I thought I'd share and if nothing else give you something to think about.

Doug

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dak
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Re: PV 231EQ - Phantom power?

Post by dak » Sun Mar 12, 2023 11:21 am

"Sharing" is the word. Knowledge is not a competition but something to increase by sharing. And there are a lot here that are glad to share, not because it makes them look good but because it helps. That's what makes this a place worth visiting.

Petesouthpaw
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Re: PV 231EQ - Phantom power?

Post by Petesouthpaw » Mon Mar 13, 2023 6:57 am

And this is the reason I don't interact online...

I ask a simple question and the thread turns into a ridiculous bitching match. I got my answer, found a solution that works and was happy. I returned here to close my original post only to find it had descended into the usual online bull***t of opinionated mud-slinging, self-obsessed posturing and pointless abuse.

My first return to online forums in over ten years has, once again, left a very bitter taste in my mouth. I will not return.

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