passive voltage attenuation and mono/stereo ouput switch?

[neilwight]

just finishing off drawings for a custom build analog summing box.
its all pretty straightforward, 6 stereo channels, flexible routing with rotary switches etc etc however ive a couple of points im scratching my head on.

i am contemplating adding some form of voltage attenuation on the main output.
my initial thought was to just add a double tracked potentiometer across the hot feed to the L and R XLR outputs, especially given that this system is passive and has no power. has anyone got any better ideas regarding how to accomodate this. it may be that i just leave off completely however i feel it may be a nice addition if i can get a solution that wont degrade the audio signal. there will be no requirement to gain signal, just attenuate.
any thoughts regarding pot size? it will be running line levels at +4dbu.

second point is that i thought about adding a mono/stereo output switch as an option.
my initial though had been to add a 6 pole 2 way rotary to the output feed, in one position the feed would basically just pass through to the main outputs, in the second they would be joined to one (summed) and then passed to L and R outputs.
again any thoughts about this, im finding inexpensive 6 pole rotary switches hard to locate here in the UK. i guess i could use 4 pole and just use the + and - wires for each output, ground being effectively the same anways however again, any thoughts on this would be much appreciated.

using a 6 pole would be more correct but would it make any practical difference, especially since it will only be just for auditioning then switched back.
i guess i could incorporate some form of M/S option that would allow narrowing of stereo image right down to mono however i feel a straight switch may be best.

 

[NewYorkDave]

It'd be a lot easier to answer your questions if you'd post your drawings.

 

[neilwight]

yeah, i sort of figured that once id posted. problem is they are on a notepad, in pencil, scrawled over and with my own symbols for things (ie dots and letters) lol.

its nothing very fancy in design, in its simplest its 6 stereo inputs on balanced XLR with rotary switches on each to turn off (poles not connected to anything) or send to main output where the all just add together. theres some more options relating to output options on channels for strapping hardware across but for these questions this part can be ignored.

if you basically think of it as a set of xlr inputs all joining together and then going to a pair of stereo XLR outputs you will have it.

hopefully that helps enough to get some advice/opinions.

 

[Kev]

A 64-step relay attenuator

add 5 volts and your choice of local or remote, controller board

and for the more complex control options and user save presets etc

:green:

see Mikkel's site
... some additions, changes and options like an active section for meter drive cue send ... dim/cut/mono stuff
as a DIY Factory project

 

[neilwight]

thanks for the replies kev,

i had looked at a simpler stepped attenuator using a series of resistors and while it seemed a nice addition i wasnt sure if it was overkill. to get nice control its been my experience that you need alot of stages (as in your example).

im just going over to mikkel's site to have a look however with these things they can grow arms and legs very quickly.

its also been my experience that the more thats added to these the more sonic degradation or character change is imparted. if you look at say the dangerous 2 buss, its very simple and highly regarded accordingly.

im using this as a mastering console primarily but felt that the addition of being able to use it purely for analog summing was a relatively simple procedure.

its was after this that i though that perhaps voltage attenuator may prove handy though definately not necessary and the mono/stereo switch option was just for luxury. i was just sounding out loud to see if it stood out as being immediately incorrect or anyone had worked out simple solutions previously.

 

[Kev]

That picture is a stereo balanced 64 step attenuator

... its also been my experience that the more thats added to these the more sonic degradation or character change is imparted.

for most of these features no more components are in the signal path
these features are just specific attenuation levels and and left right tricks

Bringing the signal up to the desk and back to the amps with an inacurate pot could be more damaging

 

[PRR]

> problem is they are on a notepad, in pencil, scrawled over

Why is that a problem?

Almost any framework for visualization, no matter how unconventional, is better than prose description.

 

[neilwight]

kev, agreed.

im seriously leaning to leaving volume attenuation off completely though a simpler design of what you have shown would be the way forward. it wouldnt need to take off more than 6-10db. it would be there mainly to protect inputs on my AD however with summing this should be controlled via DAW and with outboard i could just control via them instead which may prove preferable.

prr, ive done some ropey drawings that ill try to stick up later on.