Problems/advice with PM351 (could apply to all IEM systems)

[stoken6]

I played a gig last night at a "pub-with-live-music" venue. The venue had house PA: QSC K10s and Ksubs for FOH, plus Citronic wedges (15in I think). Allen Heath MixWizard desk (16channel, 4 aux sends, not sure of the model).

 

I have a Rolls PM351, and so I chatted to the onsite sound engineer, saying I could give him a DI of my keyboards, and I wanted a monitor feed sent back to me on a jack. No problem, he replied.

 

He gave me a monitor send on an XLR! Presumably all signals from desk to stage went via an XLR snake. I had anticipated this, and had brought an adapter. Here's where things went a tiny bit wrong:

 

1. The Rolls expects a line-level monitor signal. The signal I actually received from the desk was very weak, as if mic-level. (I assume the A&H desk sends a line-level pre-fade aux? I glanced at the desk and saw the aux master sends at 9 o-clock)

 

2. I then switched to using the Rolls mic input for the monitor signal (I wasn't singing on this gig). So I didn't use my XLR/Jack adapter. Two problems - firstly that seemed to overload the Rolls mic input, as I got a little distortion on the signal. Secondly, and more bizarrely, the monitor signal seemed out-of-phase with the keys signal I was sending into the Rolls. So I would turn up the Instrument channel, and then the Mic channel (foldback from the desk), and the keys would drop out of my monitor mix!

 

So I'm going to invest in a polarity reversal adapter and possibly an in-line XLR attenuator.

 

I'm grateful for any advice here: is it reasonable to ask an in-house engineer for a line-level monitor mix? ("Can you turn Aux Send 4 up to 3 o'clock please?") Why was I getting phase reversal between a DI'd keyboard output and the same signal sent back via a pre-fade send? What do I need in my "weird problems" toolkit?

 

Thanks,

 

Cheers, Mike.

[WesG]

Aux mixes are normally +4dBu -- pro audio line level -- which is *much hotter* than a home-stereo "line level" mix (-10dBv). I don't know which the Rolls is expecting.

 

But the aux send knob usually has about 22dB of sweep on it.

 

Asking the guy for enough level would have been the right choice. Using the mic input - not so much.

 

As for phase, that's weird. Sometimes a board will invert phase, not really a big deal in most cases, but obviously was in this one. Could even have been something to do with using the mic input. Some boards also have a per-channel phase inverter. Little button at the top of the strip. It may have been on for the keys channel by accident. Before using an adapter, ask the sound man if he can try flipping your phase. If he can't, pull out the adapter.

 

If you're using a belt-clip, the smartest adapter to use is probably a 6' cable with the signal pins flipped.

 

Something else you should have in your toolkit - a way to get a TRS snake return in your IEM mixer.

 

Wes

[Hoochie]

My bet is the mic cord had a flip in it

because it was soldered wrong.

It happens. Since you were monitoring yourself

directly too you noticed it.

 

I would have a direct box and a mic cable that

I brought to do this. Keeps your options open.

Keep some XLR/TRS adapters and some

female XLR flippers handy.

 

Most all DI's are for taking an instrument feed

and turning it in to a mic signal.

You can do the opposite. Your just impedance

matching. They work both ways.

 

I keep a little "Oh S**t" bag with all kinds

of adapters and stuff. Comes in real handy.

 

John

[Kenny Ingram]

First of all, I always just tell the sound guy not to bother putting any keys in my mix when using the PM351. 99% of the time I'm getting a mono signal aux send (which is fine), but I don't want my keys in mono. And I don't want two signals of my keys either. So no keys in the aux mix, and I just dial in however much I want using the "Instrument Level" on the PM351.

 

Next, if it's not at an appropriate level (i.e. they're not close to the same volume when on the same knob positions - around 10 o' clock), then I just ask for more general level. If I have to say, crank the aux level ("Line" knob), chances are I'm going to experience a LOT of hum, which is really distracting. It's just easier to ask for more in general, and usually they'll just turn up each instrument in your mix the same level.

[stoken6]

Asking the guy for enough level would have been the right choice. Using the mic input - not so much.

I agree - and Kenny made the same point below.

 

Some boards also have a per-channel phase inverter. Little button at the top of the strip.

No phase invert buttons on the mixer, unfortunately - I did check.

 

Something else you should have in your toolkit - a way to get a TRS snake return in your IEM mixer.

You mean a XLRF -> TS adapter? That's now on the shopping list!

 

My bet is the mic cord had a flip in it

because it was soldered wrong.

I think you must be right. I was wondering whether there might be a different wiring standard between Rolls (US) and A&H (European), but a bit of research tell me that's a pile of crap.

 

Most all DI's are for taking an instrument feed

and turning it in to a mic signal. You can do the opposite. Your just impedance

matching. They work both ways.

Well... see a DI turns a line-level signal (could be hi-Z) to a mic-level signal (low-Z), but can also drop the signal level. Doing the opposite would require a gain stage - it would be a mic preamp. I'll get one if I need one, but it's more hassle to wire up.

 

First of all, I always just tell the sound guy not to bother putting any keys in my mix when using the PM351.

As it happens I did have my own send, but often I have to share with someone. It's never been a problem, I just add the tiniest bit of myself to the basic monitor mix.

 

Next time we're at that venue, I'll be armed with a polarity flipper, a XLR-TS adapter and I'll ask for a hotter foldback signal.

 

Thanks all,

 

Cheers, Mike.

[MorayM]

If you're running your keys in stereo it could be creating some weird phase issues with the way the desk sums to mono for the monitor feed?

[stoken6]

If you're running your keys in stereo it could be creating some weird phase issues with the way the desk sums to mono for the monitor feed?

 

Hmmm... possibly? The Rolls takes a stereo feed from my keys, and I gave FoH a DI of the right channel only. So I was hearing the "direct" signal (keys->Rolls->earbuds) in stereo, together with a mono feed of the R channel sent to the desk and sent back with other instruments (in mono) to the Rolls monitor channel.

 

I don't think there's any "differential" processing in that chain (R-L, pin-2 minus pin-3 or anything). I think Hoochie's guess is the right one: somewhere in the chain from my Rolls DI, via the snake, to the desk input channel, out of the aux send, back through the snake, and into the Rolls, there's a polarity reverse going on.

 

Cheers, Mike.

[EscapeRocks]

Here's how I incorporate my Rolls PM351.

 

I run my keys in stereo.

I use a Radial Pro D2 DI box.

 

hookup is such:

 

Keys L+R to DI box

DI box L+R XLR out to FOH

DI box L+R THRU to PM351 1/4" instrument input via TRS Y cable (2 female TS to male TRS) Jumper on PM351 set accordingly.

 

Microphone XLR to MIC IN on PM351

Microphone XLR THRU to FOH

 

Monitor mix from FOH or Monitor desk to PM351 via XLR to 1/4" TRS.

 

 

I do NOT use the PM351 to send keys to anything.

 

FOH sends me the rest of the band (drums, guitar, bass, other vocals). We adjust the relative levels of those.

 

FOH does NOT send me keys or my vocals.

 

Easy setup.

 

I have total control over band, my vocals, and my keys in my ears.

 

I have not encountered the issue described in the original post at any venue. Instead of running a monitor feed to a wedge I get a monitor feed to my Rolls PM351.

[WesG]

No board I have ever seen outputs a mic-level signal. There is no point. What device would it interface with? Trying to use a DI backwards in this situation is a non-starter. Get more level.

 

You mean a XLRF -> TS adapter? That's now on the shopping list!

 

No. Some snakes have female TRS aux returns. A TRS male to XLR male adapter will give you XLR. A cable is safer than a solid adapter, in case the TRS jacks are really close together.

 

XLR to TS, or balanced TRS to TS adapters are losers IMO unless the adapter is large and costs more than $40 -- this would be because it has a transformer inside it. There is no use-case I can think of with the Rolls where you would need one.

 

Wes

[hardware]

Snake Return adapters are definitely great advice.

 

I had similar problems not because I want to hear myself, but others and at the levels I need.

Had a custom 100ft. Snake made for the sole purpose of ample I/Os and level checked returns for IEMs.

 

700 bucks but a sound investment.

24 x 12.

This makes IEM users happy (2 of us) and the dual wedge whiners happy (3 of them).

 

Plus anyone else who wants to grab a spare wireless mic.

[stoken6]

You mean a XLRF -> TS adapter? That's now on the shopping list!

 

No. Some snakes have female TRS aux returns. A TRS male to XLR male adapter will give you XLR. A cable is safer than a solid adapter, in case the TRS jacks are really close together.

 

XLR to TS, or balanced TRS to TS adapters are losers IMO unless the adapter is large and costs more than $40 -- this would be because it has a transformer inside it. There is no use-case I can think of with the Rolls where you would need one.

Wes

 

Got you if the snake has a TRS return, I would need some way of picking up the "hot" side (if balanced), or one of the channels (if stereo). I'm good there already.

 

I've seen snakes where the returns are on XLR male, and some where they wire conventional snake channels to the returns, so it ends up on an XLR female. Need to cope with both!

 

Cheers, Mike.

[WesG]

1/4" TRS jacks in the pro-audio world are balanced connectors, they are basically never used for a stereo signal except when feeding headphones. Sending a stereo unbalanced signal over a snake would be a recipe for disaster. I can't imagine any sound man doing it (it would also require special/custom cables at the mixing desk).

 

TRS can also be used for unbalanced channel inserts, but that doesn't apply here.

 

You should not try to pick up the "hot" side of a balanced signal. Use both phases. Otherwise, you will not have the benefit of common-mode noise rejection and you lose 6dB of signal right off the bat. Your Rolls has a balanced (XLR) input. Just use a TRS male to XLR male adapter or cable.

 

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