DIY Passive Line Mixer?

[frederic]

Rackmount enclosures:

http://www.budind.com/chassis.shtml

http://www.budind.com/view.php?part=ch-rm



Mouser and Digikey sell Bud Industries products BTW.

 

[FALKEN]

thanks, man!

I think I must be crazy for trying this.

but my current situation is making me crazy so I guess that's what happens.

 

[FALKEN]

do they make pots that 'click' into center position (like for a pan) ? what would that be called?

 

[mshilarious]

do they make pots that 'click' into center position (like for a pan) ? what would that be called?

Yes, look for something with a "center detent".

 

[FALKEN]

what do you call the kind of switch you find on a les paul? they are asking me what kind of mounting (through hole?) and switch function (DPDT?)? I need mono and stereo versions. also, what current rating should I be looking at for a passive circuit?

 

[mshilarious]

what do you call the kind of switch you find on a les paul? they are asking me what kind of mounting (through hole?) and switch function (DPDT?)? I need mono and stereo versions. also, what current rating should I be looking at for a passive circuit?

A Les Paul has a SPDT on-on switch. Switches and pots are usually described as chassis mount or PCB-mount (through-hole or SMT). A stereo switch would need to be DP. Current ratings for line-level stuff is nominal--25V into 10K ohms should be conservative, that's 2.5mA and .06W. Most of the chassis mount stuff you will find, like the pots used on a guitar for example, have much higher ratings.

 

[FALKEN]

A Les Paul has a SPDT on-on switch. Switches and pots are usually described as chassis mount or PCB-mount (through-hole or SMT). A stereo switch would need to be DP. Current ratings for line-level stuff is nominal--25V into 10K ohms should be conservative, that's 2.5mA and .06W. Most of the chassis mount stuff you will find, like the pots used on a guitar for example, have much higher ratings.

hmm..chassis mount does not seem to be an option. they are showing me: panel mount, quick connect, screw, surface mount, through hole, vertical mount.

here is a pic of what I am trying to do. The little grey circles are supposed to be les paul type switches. the black knobs are going to be boss-type, and the white ones are fender type volume knobs. this is going to be a real guitar player's console! made to fit into a 4-space rack. but I'm having trouble finding the 5-position switch for the bus selector. I might end up having to do mono busses with a 3 position les paul switch. what kind is the up/middle/down and what kind is just up/down?

 

[mshilarious]

hmm..chassis mount does not seem to be an option. they are showing me: panel mount, quick connect, screw, surface mount, through hole, vertical mount.

Panel mount.

but I'm having trouble finding the 5-position switch for the bus selector. I might end up having to do mono busses with a 3 position les paul switch. what kind is the up/middle/down and what kind is just up/down?

You need a dual 5-way rotary switch? Hmmm, how about this:

http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=6769&Row=109815&Site=US

This is gonna be an expensive box with all these guitar-type controls ya know

 

[FALKEN]

You need a dual 5-way rotary switch? Hmmm, how about this:

http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=6769&Row=109815&Site=US

This is gonna be an expensive box with all these guitar-type controls ya know

that's it! I don't know how u found that. I guess cuz I am a newbie I don't know all the names for everything.

yeah it will be expensive, but cheaper than a mackie 8-bus. I think it will cost me about $500. I recently bought a vintech 1272 and I have not been so in love with a piece of gear in a very long time. I am hoping that if I make this thing passive and use that for makeup that the sound will be very good.

 

[mshilarious]

that's it! I don't know how u found that. I guess cuz I am a newbie I don't know all the names for everything.

It really helps to have the Digikey catalog, sometimes it's easier to flip pages and look at pictures than do a search on their site. I like to use both

 

[FALKEN]

A Les Paul has a SPDT on-on switch. Switches and pots are usually described as chassis mount or PCB-mount (through-hole or SMT). A stereo switch would need to be DP. Current ratings for line-level stuff is nominal--25V into 10K ohms should be conservative, that's 2.5mA and .06W. Most of the chassis mount stuff you will find, like the pots used on a guitar for example, have much higher ratings.

I am still confused by this, because I told you a les paul switch, which wasn't true. only because a les paul has a center position. I am looking for one that is just up/down. is this still the same one?

 

[frederic]

Falkan,

If I may interject and offer some advice.

Instead of building the whole thing, and potentially being disappointed, why not just buy one of each part the first round, solder up one channel, one buss, and one selector switch (which obviously can only select one buss), and test it out for a few days to a week, with your gear. Play with the levels by swapping what you plug into it, and listen what comes out on the other end.

I happen to completely agree with Ethan about passive mixers, dispite my trying to help you the best I can.

I'd rather see you spend $30, and be disappointed instead of $500, and go "crap, I just wasted all this money and time".

And if it works to your satisfaction, then at least you know you have a sound design to work with, and the extra shipping involved in ordering parts in two batches, is a small price to pay to offset the risks.

 

[mshilarious]

I am still confused by this, because I told you a les paul switch, which wasn't true. only because a les paul has a center position. I am looking for one that is just up/down. is this still the same one?

I misspoke earlier about the LP switch, that is really 3 throw (SP3T) on-on-on, I believe.

Anyway, an SPDT on-on switch will work fine, just leave one side not connected. On-off switches aren't as common. Switchcraft probably has an identical-looking switch that is double throw, but I don't know a supplier offhand.

 

[FALKEN]

Falkan,

If I may interject and offer some advice.

Instead of building the whole thing, and potentially being disappointed, why not just buy one of each part the first round, solder up one channel, one buss, and one selector switch (which obviously can only select one buss), and test it out for a few days to a week, with your gear. Play with the levels by swapping what you plug into it, and listen what comes out on the other end.

I happen to completely agree with Ethan about passive mixers, dispite my trying to help you the best I can.

I'd rather see you spend $30, and be disappointed instead of $500, and go "crap, I just wasted all this money and time".

And if it works to your satisfaction, then at least you know you have a sound design to work with, and the extra shipping involved in ordering parts in two batches, is a small price to pay to offset the risks.

mshilarious, thanks for the help.

frederic,

thanks for watching out for me.

I was thinking that if the passive mixer blows, I can always add an IC at each bus output.

Funny thing, I posted this thread trying to build a passive mixer, and you guys convinced me to build an acive mixer. so I went over to prodigy pro to get some more advice on active mixers, and they convinced me to build a passive one. specifically, this design. The guys over there seem to think that with this design the largest overall volume swing you are gonna get is .4db, which is tolerable.

I have a feeling that the busses might complicate it to the point of needing opamps in the design. but the guys over at prodigy-pro don't feel like helping me out. they have left my thread hanging for a few days, even after I made a diagram and everything.

so I haven't ordered any parts for the reason you stated.

I WAS thinking that if it doesn't work I can at least mute 8 of the channels and send everything to the main bus and then I would have a 16 channel mixer identical to that diagram, which must work no??

anywayz what is running audio through a pot and a resistor going to show me that you couldn't describe here?


so yeah, I guess I'm starting to get discouraged. doesn't matter though. They're launching a rocket today around 1:00, about 100 miles from here that is carrying 24 pounds of plutonium. Pluto, bitches. I'll probably be dead this afternoon anyway.

 

[mshilarious]

Funny thing, I posted this thread trying to build a passive mixer, and you guys convinced me to build an acive mixer. so I went over to prodigy pro to get some more advice on active mixers, and they convinced me to build a passive one. specifically, this design. The guys over there seem to think that with this design the largest overall volume swing you are gonna get is .4db, which is tolerable.

That's because of the shunt resistors. The tradeoff is the mixer loss, @ 46dB I think that is 20 dB worse than NYDave's other design. I don't know if that is overall better or worse, given the smaller resistor values, but NYDave is a mixer genius, and they are both his designs. I think I would trade back some of that, for example a 1K shunt resistor on a 16 channel board gives you a max swing of 1.5dB (again that would be in an extreme situation), but you get back 9dB of signal. Or a 470 gives you swing of 0.6dB and +5dB of signal.

but the guys over at prodigy-pro don't feel like helping me out. they have left my thread hanging for a few days, even after I made a diagram and everything.

For some reason that board has quieted down a lot. I think they made a mistake in splitting off the Drawing Board, because individual threads get a lot less attention now. I rarely go there anymore.

 

[FALKEN]

That's because of the shunt resistors.

That's what I was trying to ask them about!

mind explaining what is a shunt resistor?

 

[mshilarious]

That's what I was trying to ask them about!

mind explaining what is a shunt resistor?

It's just another voltage divider, in this case one that gives up lots of signal. Since it is dumping so much, the variable loss to the rest of the network is less significant.

With respect to the simplified diagram below, let's set output impedance of the input devices at 1K, and input impedance of the output device at 10K.

First let's ignore the shunt resistor. With the faders in the middle (let's pretend they are linear), each channel will lose 6 dB to the fader, and then (if I haven't screwed anything up, which is likely) 8.9 dB across the mix resistor to the mix network in parallel to the output (10K against ~12.7K||10K, or 5.6K).

Now if we move one channel fader all the way up or down, that changes to a 9.5dB loss (10K against 10K||10K). Not a big difference, but this is only a two channel mixer, it gets worse with more channels.

However, with the shunt resistor, the change in the mix network resistance makes little difference:

middle fader: 10K vs 12.7K||1K||10K (848K) = -22.1dB
one fader cut: 10K vs 10K||1K||10K (833K) = -22.3dB

So your difference is a smaller 0.2dB, but it cost you 13dB in level.

 

[FALKEN]

sweet. sounds like an even deal to me.

is it the same as a regular resistor or do I have to search for a "shunt" resistor on digikey?

I would probably want one at the output of each bus, no?

 

[mshilarious]

sweet. sounds like an even deal to me.

is it the same as a regular resistor or do I have to search for a "shunt" resistor on digikey?

Regular resistor. "Shunt" is just its job in the circuit.

I would probably want one at the output of each bus, no?

Yes, although that probably impacts the value . . . maybe not a big deal, I'm not sure offhand.

 

[FALKEN]

Regular resistor. "Shunt" is just its job in the circuit.



Yes, although that probably impacts the value . . . maybe not a big deal, I'm not sure offhand.

i did the math...2 channels u would want a 204 ohm resistor and 16 channels you would want 234 ohm...not that much. I wonder do you want the output volume pot to replace the shunt.