Mono sum box with stereo link outs.

[cedd]

I've had a good look around, but can't find what I need. Have had a go at building my own, but it's less than perfect. 

For my Aviom rack, I need to be able to sum stereo inputs from keyboards, stereo click tracks etc. I don't want to use a pair of the Aviom channels to do this using their stereo link feature - I need all the channels I can get and mono inputs isn't a problem. I still want the stereo outputs to go to my front of house desk, but I need mono for the Aviom. Ideally analogue split before it hits the desk, rather than having to use up a bus to do this like I'm currently doing. 

The absolute perfect box has dual xlr/jack inputs, then a mono summed xlr output, and a pair of stereo xlr outputs, which remain stereo and isolated. I'd ideally like 4 of these units, in some sort of rackmount enclosure.

My own solution was to use one of the 8 channel behringer ms8000 mic splitters (which has a link function, but this doesn't leave the stereo outputs isolated from each other, they mono up). Instead I took a pair of the split outputs and summed them through a resistive summing network, keeping the other pair of outputs as the stereo link outs. This works, but there's crosstalk on the stereo outputs, so my stereo image is squashed. 

 

Any suggestions appreciated!

[Stuart91]

Klark Teknik DN200?

Not cheap but seems to do what you want. The link through outputs are jack rather than XLR however. 

 

The other possibility would be to speak to Orchid Electronics about getting something custom made. 

[themadhippy]

Quote

I need to be able to sum stereo inputs from keyboards,

Had a weird one doing that sevral years back were the middle keys on the keyboard disappeared,ended up having to keep it stereo .Cant recall the keyboard make ,but the artist certainly wouldn't have been using anything cheap.

[paulears]

Pretty common, sadly. The stereo is sort of pseudo stereo. I've had two Roland's and a Korg that responded badly to being manually mono'd, or using their mono output. They seem to like messing with phase to widen and thicken things like the strings and piano - so in mono, the things closer to dead centre cancel out! It's a real pain.

[sunray]

I've been here before and always thought it was to do with picking off the balanced outputs  of a keyboard to an unbalanced input, in my case it was purely to feed to a PA and stereo wasn't required. Yes it definitely had a phase cancelling effect, even when plugged into 2 mono unbalanced inputs. I know I tried a phase reversal on one channel but it didn't provide a cure.

 

Fortunately I had a had some time to play, IIRC I ran the stereo through isolating transformers then did some resistor/capacitor mixing. I know I took pics at the time, I'll try to have a rummage but likely not to be till Monday.

[kgallen]

I have a sort of similar requirement I've yet to solve related to summing stereo inputs into a hearing loop and whilst maintaining the stereo pass-through.

Digging around I looked at products like the following. Like me, I don't think they fully match what you need, so I'm interested what products others might suggest to solve your problem!

I quite liked this for the "lack of big knobs for folk to fiddle with": https://www.thomann.de/gb/the_tracks_ds_2418.htm (Manual: https://images.static-thomann.de/pics/atg/atgdata/document/manual/c_244501_r2_en_online.pdf) (Behringer have the DS2800 which has "knobs"!).

(*) This has been useful in a number of scenarios on occassion: https://www.thomann.de/gb/behringer_mx882_v2.htm

For the MX882 you need to find the "proper" manual (not the QSG) which gives the signal routing diagrams so you can see if the routes you need are available. I'll have a google... Oh here we go: https://static.bhphotovideo.com/lit_files/91711.pdf

Inputs are jack and phono but does have stereo and mono out: https://www.img-stageline.com/products/mixers/analogue-mixers/ulm-164-sw/

 

(*) ETA:

Looking at this again for my application, possibly this could be done with the MX882 using the Channel inputs for all sources, panned L (main inputs not used), set into MIX mode with LINK=OFF then using Main Out L for the mixed mono send and using channel outs as feed throughs. The stereo inputs would have separate (rather than ganged) knobs, but I think this would work ok looking at the signal block diagram.

For you, you could do 2 stereo keyboards through one MX882. Steer one keyboard (input channels 1&2 panned R) to Main Out R and the other (input channels 3&4 panned L) to Main Out L with channel outputs 1&2 and 3&4 as your feedthroughs to the desk. Yea there is a chance there will be a little crosstalk I guess...

Edited April 30, 2023 by kgallen

[DavePallant]

Thomann do stereo combiners which look like they are transformer decoupled.

https://www.thomann.de/gb/millenium_sml_21.htm

You would need four of them to go with your 8 channel splitter so it does get a little expensive.

Dave

[cedd]

Thank you everyone

Have emailed orchid for a price on such a beast, and also am now in possession of a circuit diagram to build something suitable. 

Those Thomann combiners look useful things to have a couple of in my tool box, so might pick up a pair anyway. 

Thanks

Chris 

[cedd]

Hi all

Just wrapping this one up. 

Orchid came back saying it should be possible to build one, but I never heard back from them with a price. 

However I've just discovered the Palmer PAN 04A DI box, which looks to do exactly what I need. Haven't bought any yet as I'm short if funds, but once I can afford some I'll be buying. 

Thanks for all the input.