Has any got a schematic for the FSM600? Or has anyone added a "mono" button?

I need to add a mono button to mine. It's now got a new lease of life at a social club I'm involved in. Most of the tracks that are played are from the 50's to the 70's and no problem whatsoever. Some though are in the vintage stereo where, for instance, the left channel has the vocals and guitar and the right channel has the drums and bass. So hence needing a mono button for the few that are like it.

BTW, I'm not gonna run the system in mono for the rest of the time (so don't suggest it!) and the button will go in place of the 12V lamp BNC connector. It's currently on my workbench as the club is still shut (CV19) and during my furlough time I've managed to get to my workbench... first time properly in six years, and it's having the first service I've done on it in the 20 odd years I've owned it. And only one crackly pot needed to be changed!

You could knock up a little external box to sum stereo signals to mono, either between source and mixer or post mixer to processing? 9V battery would run it fine for ages and shouldn't clip unless you like to smash the mixer output!

Few opamps and a switch. I expect there are products out there for similar.

I'd probably try and keep the toggle unit outside of the mixer, for ease of life and preserving resale value and normal operation when wanted etc. Unless you are not bothered by such things?

@snowflake: Can't really say... yet, until it changes from a working mans club to a proper social club by allowing female members! I saw what happened, and how quickly, to The Brunswick Club and don't wanna go down that route. But it's a small club with only about 150 members and about to go through a re-birth and ad campaign.

I'm not fussed about the mixer! It served me well for several years after buying it in 1999 for £200... it was paid for in it's first gig! I'm not going to use it again but the club will, and do.

I did think about an external box but thought there must be an easier way with just a switch and a resistor or two. I could sit here and work it out from the pcb, but thought I'd ask just in case.

If you have a tiny bit of spare headroom you could build a passive combiner by taking two male xlrs and connecting them pin to pin and then taking two female xlrs and joining all pin ones together, then using some 1k resistors join pin 2 of the females together, join pin 3 of the females together and join those to the males. This will give you 2k between each pin 2 and the same for pin 3 thereby mixing the outputs without shorting out the outputs

Maybe I should retype that...

Yeah that's a route also. Put it into a box with a suitable switch (DPDT?) and you could mix signals passively. Especially if you wanted to play all evening in one setting. I expect switching live would probably be ok. I like op-amps and do tend to forget about the simpler options.

Another route could be converting the source material to true mono, depending where playback is and how many tracks are in question?

Form the Rane Aplication note 109 "Why Not Wye":

Balanced Summing Box - https://www.ranecommercial.com/legacy/note109.html

I was going to suggest that. 

I never knew about the Brunswick Club until after it closed. A few people talked about crowdfunding to keep it as a club but the estate agents didn't seem interested in selling it - I think they were set on converting it into office space and then flats.

I did think about changing the source material but... when I'm playing in there I normally get supplied with several pints of Bass, (as in, sounds like 'sass', not 'base'). This means that I completely forget which tracks it was that had the problem, and certainly wouldn't be able to write them down... let alone actually write!

snowflake wrote: I never knew about the Brunswick Club until after it closed. A few people talked about crowdfunding to keep it as a club but the estate agents didn't seem interested in selling it - I think they were set on converting it into office space and then flats.

Money was the one of the main factors, but as soon as 'certain political factions' found out it was male members only, the writing was on the wall. You can (even in 2020) still have a male members only club... just don't try and do any advertising. It won't work and WILL back-fire!

The club is somewhere I've been a member of since I was 18, my Dad was a member from 18 years old (and Chairman at one point) and my Grandad was a member for 50 years from 1939 til his death in 1989. The place is in my blood and, at last, the concensus of members is that it needs to change to carry on for many years to come. For several years many members kept their (cheap) membership just waiting for the place to fold so they could get their equal share of the proceeds of sale. That ain't gonna happen.