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Trim knob; The final mystery.


1001gear

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I attend a weekly amateur jam; good enough PA/Monitoring. It's run wutcha brung and the sound is audible (.). The one big minus: input distortion. People just plug in their acoustics with too much bottom, plug their bass into a channel reserved for mics, or just get up and start yelling. Fix it you say? Nobody cares or worse, hears. So,

questions; Is overloading channel ins destructive? And since some singers actually seem to prefer distorted sound, is there an effect that will reproduce it?

 

Just curious. I have no intention of paying to correct this problem..

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I attend a weekly amateur jam; good enough PA/Monitoring. It's run wutcha brung and the sound is audible (.). The one big minus: input distortion.

 

Assuming it's an analog mixer of some kind... go to the very top row of knobs - you're looking for something labeled "gain" or "trim" or "input level" - there's probably a red LED up there flashing like crazy (or staying constantly lit) - turn down the knob until the red light goes out or just flashes very occasionally.

 

Assuming they're plugging into the right type of inputs, that should solve your problem.

 

People just plug in their acoustics with too much bottom,

 

You can't control how people decide to set their EQ on their own instrument. A knowledgeable soundperson could compensate for that using EQ (and especially the high pass filter) on the board, but if you don't have a soundperson... :idk:

 

plug their bass into a channel reserved for mics,

 

If there's someone to run the board, they can deal with all of that. That's all part of the gig.

 

How big is the board - how many input channels? Is there a direct box (or several) available for bassists and acoustic guitarists to plug into? If there's something there specifically for them, and the board has enough channels to leave that all set up, then there should be no reason for them to mess with the mic channels.

 

or just get up and start yelling. Fix it you say? Nobody cares or worse, hears. So,

questions; Is overloading channel ins destructive?

 

Well, there's overloading... and then there's the audio equivalent of trying to drive a semi truck through a mouse hole - you're not likely to break anything on the board by yelling into a mic connected to a board with the mic preamp cranked, but it's not likely to sound all that great - it depends on the board. The overdrive you hear on John Lennon's guitar on Revolution was just him running direct into two cascaded, overdriven tube mixing board preamps. But if someone does something really dumb, such as trying to plug the speaker level output from their amp directly into an input on the board, yeah, you can release the magic smoke and fry the board, and the board just won't work without magic smoke. Try to keep the magic smoke contained within the board at all times. :cop:;)

 

And since some singers actually seem to prefer distorted sound, is there an effect that will reproduce it?

 

Just curious. I have no intention of paying to correct this problem..

 

Heck, there's all kinds of ways to get distorted vocals. I could probably spend a couple days writing about it - in fact, that's probably a really good idea for an article.. :idea::) Short answer? Vocal processors (floor mounted), rackmount effects processors (used with aux sends or as channel inserts), guitar pedals used as insert effects with the board (sometimes even with actual attention paid to impedance and level matching, sometimes with those concepts gloriously and brazenly tossed aside... :lol: ) overdriving (preferably cascaded, which gives more gain stages and better overall control of the final output level) board channels or outboard mic preamps, overloaded tube mics and (mis)using "lofi" microphones, running a high impedance mic for the vocalist into a cranked guitar amp and miking that up, as well as intentionally impedance mismatching microphones and messing up gain stage settings throughout the signal path... oh, and bullhorns can be fun too.

 

And I didn't even mention tape saturation or plugins once! ;)

 

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Yow! Thanks for the insight.

The board is a fairly new 16 channel Yamaha with a couple monitor busses and individual compressors lol. Too hot mic.; I can run up and grab the trim - once I find the channel. They are never labeled. The hosts just host. They know zip about sound or "A MIX" nor do they care besides you can hear everybody and it doesn't feedback. Thank god everybody objects to feedback. biggrin.gif there's no sound checks for anything let alone individual acts.

I do what I can but it boils down to I'm just a casual participeon. So this rant

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This explains how trim is set. http://tcttest.iawti.org/sound-tech-training/lesson-2-trimgainlevel-controls/

 

Allot of people don't know the differences between what a trim control and channel volume actually do differently.

 

This ultra simple schematic may help.

 

If you follow IN 1, the first thing you come to is a 50K pot. This pot works the same as a guitars volume control and will adjust between full signal when full up and either a fixed attenuated level or a complete ground so no signal passes it. Think of it as the guitar's volume knob which attenuates the pickup signal before it feeds down the cable to the amp. You dial this to get the input signal level to nominal levels as explained in the link above. This is a set and forget adjustment.

 

The second pot P4, feeds the preamp and actually changes how hard the preamp works. Think of this as a guitar amps input volume. You'd use this for matching levels between all the mics feeding the board. The channel strip will also have tone controls and effects loops, much like a guitar amp does.

 

The master volume again is just like a guitar amp. It adjusts the feed to the power amp to set the overall maximum volume level.

 

 

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All three of these need to be set to avoid one stage overdriving another. To be safe you want the master volume set higher then channel volume and channel volume higher then Trim/input volume. Distortion occurs when the trim is set too high and feeding a signal too hot for the preamp, or cranking the preamp up and overdriving the power amp.

 

Distortion can also occur if the sum of all channels feeding the power amp is too great, power amp is insufficient to drive the cabs or the speakers unable to handle the power amps wattage. What you normally do is set the PA to a nominal level with maximum clean volume and minimum feedback then have the bands match they're levels to the PA. How well that winds up working is a matter of how experience of the performers are running that system.

 

As you found out, many simply haven't got a clue and have no desire to learn. You should advise them they should have a pro at least set they're trims and then mark the settings. Then if they stick to using the same channels at least that will be one less bottleneck in their way to getting decent sound.

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