Power Amp - set to full constantly ?

[Simon Lewis]

This amp has an input sensitivity of 0.775V. When the front panel controls are set fully clockwise, you need only this voltage to deliver full output power and to be at the point of clipping.

 

I can't find your exact mixer model, but others in the MG series have a nominal output level of +4dBu, so we can assume that when the LEDs hit "0" the mixer is putting out 1.23V - far more than is need to cause the amp to clip. The maximum desk output before amp clipping would need to be 4 dB below "0" on the bargraph.

[voodoo1967]

2 x 4 ohm loudspeakers in series = 8 ohms.

2 x 4 ohm loudspeakers in parallel = 2 ohms.

 

Are you sure they're actually series wired (this is a bit fiddly to do) and not just linked together using speakon connectors with an 'in' and 'out' on the first loudspeaker, as this is actually parallel wired.

 

Jason

 

The amp has 2 outputs (channels A and B) the vocals were on channel A and everything else on channel B , on both channels there are 2 speakers and these are 'daisy chained' (I know thats not the technical term) ie channel A to speaker1 input and then 'speakon' cable to the other speaker (does that make it parallel or series ? - I thought it meant series )

[David A]

This amp has an input sensitivity of 0.775V. When the front panel controls are set fully clockwise, you need only this voltage to deliver full output power and to be at the point of clipping.

 

I can't find your exact mixer model, but others in the MG series have a nominal output level of +4dBu, so we can assume that when the LEDs hit "0" the mixer is putting out 1.23V - far more than is need to cause the amp to clip. The maximum desk output before amp clipping would need to be 4 dB below "0" on the bargraph.

 

And if you run your mixer 4db below "0" you instantly increase the noise in the system

[voodoo1967]

This amp has an input sensitivity of 0.775V. When the front panel controls are set fully clockwise, you need only this voltage to deliver full output power and to be at the point of clipping.

 

I can't find your exact mixer model, but others in the MG series have a nominal output level of +4dBu, so we can assume that when the LEDs hit "0" the mixer is putting out 1.23V - far more than is need to cause the amp to clip. The maximum desk output before amp clipping would need to be 4 dB below "0" on the bargraph.

 

Just called my mate they have a yamaha MG206-C mixer

[boswell]

Just called my mate they have a yamaha MG206-C mixer

That model is +4dbu nominal and goes to +20dbu before clipping !!

[Simon Lewis]

...and stops someone coming along, winding up the amp further and either destroying your sound balance, or your speaker components.

 

I have come across installations where the designer has calculated the correct gain structure, and had the necessary attenuation (couple of resistors) soldered inside the XLR plugged into the amp.

 

The designer gets correct gain structure that isn't going to be trashed the moment he signs off the system; the user sees the amp front panel controls turned fully clockwise and just knows that he's got 'maximum' power ;-)

[dboomer]

Even large power amps rarely require more than +8 to drive them to full output. Most mixers will deliver +20 to +24 before they clip. So if your amp is left wide open you would be wasting 12 to 16 dB of headroom and decreasing your SN by the same amount.

 

If you are concerned about the potential for unwanted fingers moving your setting you could install fixed pads in-line.

 

Now if there are other components in the line (EQs, limiters, DSP, etc) you will need to gain set for each stage in the signal flow

 

The formula is:

 

AMPLIFIER ATTENUATION(db) = AMPLIFIER SENSITIVITY(dbu) - Max out preceding stage(dbu)

 

Choosing a gain structure often involves making a compromise between best signal to noise ratio and reasonable working range to avoid distortion. In other words ... you may want to include some "slop factor" to allow for some mixing indiscretions.

[voodoo1967]

Thanks for all these replies , so to sum up :-

 

1. It shouldn't really matter (that much) if the AMP (T-amp 2400) is set to max, ie full clockwise right.

 

2. If they have 2 x 4 ohm speakers (connected together - daisy chanined ie in parallel) on channel A, and then that will equate to 2ohms - which it seems the T-amp2400 doesnt like - and that will potentially cause a problem (clipping ?) , Q any ideas how they can get around this 2ohm issue (as you can tell I'm not up on my ohms knowledge) , could they for example , change the setup so that they connect the 8ohm instruments speaker to a 4 ohm vocal speaker on each channel , apart from the cross over - this would severley limit their ability to direct the vocals and instruments to seperate speakers (I gues they are stuck - other than changing the 2 4ohm vocal speakers - and getting 8ohm ones instead - at least that way the T-amp shouldnt complain (help...)

[ramdram]

Ref #23

 

Summing up:

 

1). You can but try the gain control at different settings and do the listening test. Not every venue will have the same "sonic" quality so you would be best to sort this in your sound check. I believe the saying is mix with your ears.

 

2). Sorry, could not quite grasp what you mean.

[David A]

To sum up it absolutely matters about the settings on the amps, if you had read any article on gain structure by any manufacturer , Yamaha, Rane etc or the article I posted at the beginning of this thread you would have seen it is crucial that every stage of a system is set correctly.

The fact that many people get it wrong should not mean that you have to.

[voodoo1967]

Ref #23

2). Sorry, could not quite grasp what you mean.

 

They have 2 channels from the amp , channel A has 2 x 4ohm speakers (for vocals) and channel B 2 x 8 ohm speakers (for instruments). It seems that by having 2 x 4ohm speakers - this gives them 2 ohms , which the amp will have a problem with. They did it this way so thay can seperate the vocals from the instruments.

 

If they decided instead to put on each channel 1 x8 and 1 x 4 ohm speaker - coudl they do this - and what would the ohm be ? , and secondly obviously if they did this - they would have no way of separating the vocals from the instruments.

 

A concurrent post has been automatically merged from this point on.

 

To sum up it absolutely matters about the settings on the amps, if you had read any article on gain structure by any manufacturer , Yamaha, Rane etc or the article I posted at the beginning of this thread you would have seen it is crucial that every stage of a system is set correctly.

The fact that many people get it wrong should not mean that you have to.

Hi David,

 

I read that articles (a few times) - I obviously need to read it a few more times....but to be honest it seemed very long winded (for my simple mind) - my mates band effectively do it all themselves, they usually have about 90 minutes to unpack the van, setup the PA and all the kit - sound check and then leave the room until the wedding / corporate guests have done their speaches etc - then they play for 2 hours - pack up and go home again - I'll read that article again later - thanks for all your advice.

[boswell]

If they decided instead to put on each channel 1 x8 and 1 x 4 ohm speaker - coudl they do this - and what would the ohm be ?

2R667

[David A]

OK here is a simpler version

http://www.yamaha.com/yamahavgn/CDA/Conten...D227500,00.html

[ramdram]

REF #25

 

David A, notwithstanding the info on gain structure, surely the acid test is going to be the overall volume (as in cubic units) of the venue where voodoo and ensemble are working, and, where the speakers are positioned?

 

If he has, according to the gen on the amp, 1200W per channel to play with, then to arrange his sound desk so that the faders are parked on the zero level position, on the desk channels, the gain controls to the amp would have to be set accordingly.

 

If he was playing in a venue the size of the Albert Hall (merely to set the scene for a comparison) as opposed to the back room of a pub say, once the gain structure has been set throughout the program chain, then the only way of reducing the actual output sound level in the venue is to adjust the gain controls on his amp?

 

And, on top of that, there may be the added "complication of the big brother sound level mic" sitting across the mains supply...so the input to the amp would have to be turned down regardless.

 

That is my take on the thread thus far, so if that is not quite right please jump in and do the correction thing.

 

 

 

Ref voodoo's comment on the spkr arrangement; from the way I read it you are keeping the vocals to one amp channel and the instruments to the other. This implies, to me at least, that to balance the vocals v instruments the band are using the amp gain controls as a very crude mixer anyway.

 

This would imply further that the "sound" of the mix (to the audience) would differ depending on where individual members of the audience were positioned in the venue.

 

Now, unless I am grossly mistaken, would it not be "better" to do the mixing on the...mixer? If the do requires the use of the kit for amplifying the vocal from the microphone, then only the mic channel(s) need be open.

 

On the subject of overall spkr impedance/loading you will have to do the sums according to the published calculations:

 

http://www.bcae1.com/spkrmlti.htm

 

Ignore the guff about cars, the equations are the same and there is a even an online calculator to do the sums.

 

Briefly the parallel equation amounts to product over sum which for an 8ohm and a 4ohm spkr in parallel the overall is 2.67ohms.

 

The gen on your amp says you can go down to 4ohms, so a load of only 2.67 ohms is going to allow too much current to be drawn. This means the amp is not going to be happy, and any protection circuits will operate, eventually, to protect the amp.

 

May I suggest you google up as much gen as poss on setting up your kit...you may find there are perhaps better ways of arranging things than hitherto. If you encounter any probs then you can always come back to the forum.

 

HTH

 

I believe the numerical answers above are correct but again anyone feel free to correct the sums...or any of it, ** laughs out loud **.

[themadhippy]

Nothing wrong with one pa for the vocals and 1 for the instruments,especially if your a dead tribute band.