8 x Bo Hansen Di + summing to Stereo pair.
« on: January 31, 2012, 09:33:12 AM »
Hello guys! How things going?

Im working with a band that plays some backing track thru 8 analog lines, (4xstereo) and we need to feed the PA mixer with those separated channels, but in some ocasions, we have had issues in some festivals, where some channels were out of phase on monitor mixer, and sometimes you couldnt hear the bass at all, sometimes we could hear the kick drum, well, a mess. so on those 8 DIs we would like to have a summ of those 8 channels into a stereo, that will be our monitor signal. just to make things easier, specially when we are playing in festivals without sound check, and new monitor engineer every night...
So, for PA mixer 4 stereo channels and monitor mixer stereo signal from the summ of the 4x stereo.

I was thinking that i could build 8x Bo hansen Dis and for the summ, get the signal from each "amplifier out" and summ it with 10k ohm resistors on to 2xXLR connector. the makeup gain will be made with the monitor mixer mic pres.

My doubt is, will i hurt the signal going into the PA mixer from the DIs outputs with this parallel summing?

Thank you!
Pedro



Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #1 on: January 31, 2012, 10:36:36 AM »
I think the DIs are un-nescessary, you can just sum the 8 channels  to 2 and hand the sound guy a stereo line level from the output or mic(ish) level (summing without make up gain). The purpose of the Di is to knock instruments down to mic level, so if you did that then you'd have to amplify those back up to line level only to have to loose gain in summing and then add more gain again for the summing, it's a step you don't really need to take.

Jean Clochet

    Currently taking a break to smell roses and the coffee
  • Posts: 387
Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #2 on: January 31, 2012, 10:51:09 AM »
Are the 8 signals that you want to sum coming from the 8 DI's or from 8 mic amps that the DI's feed?

The 8 signals that you want to sum, do you mean 4 channels feeding left and 4 channels feeding right?

Combining signals passively means a loss.  So, if you're combining the signals from the DI's then you'll need another 12dB from the pair of summing mic amps in addition to the loss that the DI has already incurred.  Also, the resistance/impedance that the make-up mic amp is expecting to see is somewhere around what a typical mic impedance would be.  Your 10K resistors will present too high a source impedance.

So, assuming you're summing straight from the DI's and we're talking about 4 stereo pairs... shooting from  the hip:

I'd use an 800 ohm resistor for each polarity of the DI's balanced output.  IOW, each DI presents roughly a 1K6 output impedance.   With 4 channels, the total source presented to the make-up amp is about 400 ohms and we have about a 12dB loss through the combining network.  Also the load looking backwards to each DI is in line with what it is expecting to see.

400 ohms might be a bit too high of a source for the make-up mic amp so shunting another 400R resistor across the final output will bring it down to 200 ohms.  Right in line with what the mic amp wants to see. 
However, this 400R shunt will result in another 6dB loss -  for a total network loss of 18dB.  Use your judgement as too whether this is an OK additional amount of gain to have to make up.

Juggle around with something like that and you should be fine.
And if I misunderstood what you're doing, just ignore this  ;)






John Roberts:  I am generally not enthusiastic about the project with or without trimpots...

Holger

Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #3 on: January 31, 2012, 11:42:00 AM »
Are you looking for the functionality this device provides?

http://smproaudio.com/index.php/en/products/diboxes/di8e

(Duck and cover, i know this is a DIY forum...)

Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #4 on: January 31, 2012, 12:06:10 PM »
I make this draw to make it easier to understand what i need.
I need to provide the 4x stereo to FOH and a summ of the 4xStereo into a stereo signal to the monitor desk...
The Di's also need to sound great...
What do you guys think of this?

Thanks!

Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #5 on: January 31, 2012, 12:15:16 PM »
That makes a lot more sense now. Should sound really good too.

Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #6 on: January 31, 2012, 02:52:39 PM »
The reason i want to do the summing if because makes life easier for the monitor engineer once normally is a guy from the PA company that never worked with the band, the FOH engineer is from our crew and he needs the channels separately...

Will the summing of the amplififer outputs affect the signal that goes into the XLR output? or will it be fine once is buffered?
Thanks for your help
Pedro

Edward

Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #7 on: January 31, 2012, 05:11:24 PM »
I was reading about Bo Hansen DI boxes and stumbled into this thread.

Why not have your FOH engineer mix the eight channels the way they are supposed to be mixed, then return that as a stereo mix to the monitor engineer?

Just a though.

Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #8 on: January 31, 2012, 05:35:41 PM »
I was reading about Bo Hansen DI boxes and stumbled into this thread.

Why not have your FOH engineer mix the eight channels the way they are supposed to be mixed, then return that as a stereo mix to the monitor engineer?

Just a though.

That's extra lines for them to setup and in a festival situation there usually isn't time to set that kind of stuff up I'd assume

Edward

Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #9 on: January 31, 2012, 05:49:51 PM »
That's just two extra return channels going to stage, plus a stereo group / aux on the FOH console. Doesn't really take long to set up.

It is more a question if that method works for the artist, and FOH engineer, i think.

Just a suggestion thou.



 


Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #10 on: February 01, 2012, 07:45:24 AM »
Hi Edward!
Thanks for the input, although like benlindell said, sometimes we have a very limited time for line-check, 15 minutes to check 34 channels, sometimes is almost not enough, so the setup should be the most plug'n'play that we can possible.
Thanks guys!
Pedro

MatthisD

Re: 8 x Bo Hansen Di + summing to Stereo pair.
« Reply #11 on: February 01, 2012, 02:05:19 PM »
Hello Pedro, this is the best solution I can think of, the 325 line amp with a transformer with two or three outputs as shown in Bo's page below. The line outputs from each channel would then go to a balanced summing stage followed by a makeup amp to feed the monitors.

http://www.hansenaudio.se/API%20325%20DI%20mod..jpg

If I understand it right you need four separate stereo DI boxes rather than one 8-in-one unit, so then you would need four +/-16v PSUs to power the four pairs of line amps and the passive mixer would have 4 left and 4 right channels. You could build each stereo DI and its power supply in a microphone PSU sized enclosure.

You could make a pair of external power supplies, so the two instruments/musicians closest to each other would power their DI box off the same PSU, that would be a bit more economical depending on the choice of power transformer and enclosure.
One thing I don't know is how the instrument will sound after being padded down to mic level and then re-amp'd with the PA mic input. Surely any PA would have line-ins so you could have two line outs from the DI instead. 

Its a nice puzzle you have for yourself
Matt


 

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