Stereo To Mono?!! (1 Viewer)

[Mark Amayao]

Is it possible to convert a stereo signal to mono via some device or accessory? .....

e.g.

cd player stereo output -> mono accessory -> mono to amp stero inputs w/ "Y" connection.

Thanks guys!

 

[Chu Gai]

Yes, like the cables found here.

 

[David_Rivshin]

Not to correct Chu (I'd never dare to do such a thing ), but all I see there are Y splitters... Please correct me if I've missed some device on that page which would be better...

Technically a Y splitter is not the correct solution. That will connect both the left and right outputs of your device together, causing them to drive each other. If they play almost the same signal then perhaps its not a problem, if they play very different signals you'll likely get output which isn't blended between them very well. Not to mention it's not particularly nice to the electronics (although I doubt any permanent damage will result, someone else would be better to comment on that).

Basically using a Y splitter (or combiner in this case) to sum a stereo signal has the same problems as using one to sum a signal from multiple devices, or as a replacement for a switchbox. Y splitters are for just that: splitting a single signal into 2 (or more) identical signals. IOW 1 in -> 2 out, not 2 in -> 1 out.


In any event, the "correct" solution is to use a mixer. You can either get one off the shelf (cheapest is perhaps $50), or you can build one. For your purpose a simple 2-input 0-gain summing amplifier would be fine. You can find schematics for such devices by doing a general search online. I'm sure books on basic analog electronics would have info too, it's a fairly classic circuit.

Hope this helps
-- Dave

 

[Chu Gai]

I've seen a few approaches to this but frankly haven't tried any. David's approach is one, the Y-splitter approach is another, a variant of the Y-splitter include the presence of resistors, and perhaps a very workable approach is to use software and create a mono disk off your computer. I must say it must be one heck of a device you want to put this through.

Absolutely you should correct me. For $2 or less it's worth a shot specially when you can return the thing.

 

[Wayne A. Pflughaupt]

You can either get one off the shelf (cheapest is perhaps $50), or you can build one.

Wow – I know I don’t have the best equipment, but I sure wouldn’t put a $50 anything in my signal path!

Not to mention – any mixer short of a full-blown digital console (and especially a $50 one) is going to combine the two channels with the pan control – which is nothing more than a potentiometer. Which is functionally the same as the in-line 10k resistors.

Regards,
Wayne A. Pflughaupt

 

[Mark Amayao]

I have a client that wants a Niles ZR8630 ..... unfortuantely when he approached me he had already wired his home.

different zones using either stereo or mono speakers inceiling.

he didnt factor in stereo outputs of sources ... therefore installed just single speakers not stereo input speakers.

I was wondering about accessories mainly because he would need an adaptor for all 8 sources! lol .......

sorry i shouldve elaborated on the application.

thanks guys

 

[Chu Gai]

well that sounds like someone who flunked 8-track audio. heck i'd work a way to put the extra speakers in.

 

[David_Rivshin]

Disclaimer: I'm a software engineer, not an analog engineer, so I only know enough about such things to be dangerous. I don't claim to be an expert (publicly )

You all do have a point. If you take a summing amplifier and take out the op-amp you basically have a Y splitter (combiner) with a resister on each input. I've seen some caps to ground also used to remove DC (if memory serves) but I don't think that'd be necessary in this case. Since I don't believe that a 0-gain op-amp would do anything for this circuit other than provide a buffer to the next stage, I think you'd be safe leaving it out. This will also remove the need for batteries or a some other power source.

The only downside I can think of is that the impedance seen by the next device might be not quite right, but careful choice of the resistors value should make it all come out in the end.

Some quick notes:
LO/RO = L/R output
LI/RI = L/R input
R1 = impedance of LO/RO
R2 = resisters in combiner

 straight through: 
 LO (R1) --------> LI 
 RO (R1) --------> RI

impedance seen by LI and RI is "R1"

 with combiner/splitter: 
 LO (R1) ---> R2 - /---> LI 
 |-----| 
 RO (R1) ---> R2 -/ ---> RI

impedance seen by LI and RI is:
2 * ((R2 + R1)/2) = R2 + R1
impedance seen by LO and RO is:
R1 + R2 + R2 + R1 = 2 * (R2 + R1)
which is probably why the signal from LO doesn't push into RO; the path to LI is much easier than the path to RO.

If I've gotten anything wrong in there someone please correct me. As I said I'm nothing even approaching an electrical engineer, so I have no formal training in such matters.

PS. does anyone know how to get the

 tag to not make everything come out double spaced? wreaks havok with ASCII art...

 

[David_Rivshin]

Oh, I almost forgot to talk about this part:

Wow – I know I don’t have the best equipment, but I sure wouldn’t put a $50 anything in my signal path!

Not to mention – any mixer short of a full-blown digital console (and especially a $50 one) is going to combine the two channels with the pan control – which is nothing more than a potentiometer. Which is functionally the same as the in-line 10k resistors.

I certainly wouldn't use any kind of digital mixer for a simple analog application such as mixing two mono signals

I was thinking more along the lines of a Behringer MX602A, or even the new UB502 which would be perfect for minor mixing applications.

I know you're well familiar with Behringer products, Wayne, but for the benefit of anyone else who might be interested, here's the URL for the UB502:
http://www.behringer.com/02_products...UB502&lang=eng
With a schematic here:
http://www.behringer-download.de/UB-...PECS_Rev_B.pdf
(look at page 3)
By my reading the signal would go through:

1. main in left (channel 2 and channel 4)
2. an input level pot (can be set full-up to remove it)
3. an op-amp
4. a balance level pot (can be set full-left to remove it)
5. a summing amplifier circuit
6. an output level pot (can be set full-up to remove it)
7. an op-amp
8. main out left

So in total 3 pots (which you should hopefully be able to set to 0 Ohm and directly connect the contacts), 2 buffering op-amps, and one summing amplifier (resistors and op-amp(s))

Not perfect, but not all-in-all horrible either. Especially for a distributed audio application. I also believe that Behringer uses decent op-amps, even in these lower-end products. Although it might be fun to see about replacing them with some Burr-Browns for the discerning listener

(I hope all of this was of some interest to someone... other than myself )

 

[Wayne A. Pflughaupt]

main in left (channel 2 and channel 4)
an input level pot (can be set full-up to remove it)
an op-amp
a balance level pot (can be set full-left to remove it)
a summing amplifier circuit
an output level pot (can be set full-up to remove it)
an op-amp
main out left

That is a lot of added circuitry for a simple function. Not to mention from a bottom-of-the-line product from a company generally not regarded for its superior sonics to begin with.

But like you said, it should be fine for a distributed application. However, if you had to do more than one component the price could really add up in a hurry!

I mentioned before the in-line resistors we used in pro installations – I had forgotten that we often used an outboard passive summing network for this application – a little black box not much bigger than a box of safety matches. I think that’s the route I’d go for this application: Small and unobtrusive, effective and cheap. Now, if I could just remember who made the thing...

Regards,
Wayne A. Pflughaupt

 

[David_Rivshin]

I mentioned before the in-line resistors we used in pro installations – I had forgotten that we often used an outboard passive summing network for this application – a little black box not much bigger than a box of safety matches. I think that’s the route I’d go for this application: Small and unobtrusive, effective and cheap. Now, if I could just remember who made the thing...

Do you remember if it had any form of power supply, battery or external? I'm assuming since you mentioned it was passive that it did not, but if it did I would guess it's just a summing amplifier. If not I'd guess it's exactly what we're talking about: the same thing without an op-amp

In any event I believe the cost of the box and connectors would far outweigh the cost of anything inside the box. Unless, of course, you want for the granddaddy of all op-amps: the AD797 (see: http://www.analog.com/productSelection/pdf/AD797_d.pdf) at $8 a pop, about 4 times the cost of a high quality Burr-Brown (say an OPA134, see: http://focus.ti.com/lit/ds/symlink/opa134.pdf). I'd hazard to guess you could build a 4 channel mono passive summing network for around $10 in materials and time, or an active one for $20 plus the cost of batteries.

Someday I may just finish the mixer I was going to build before I got that super-cheap RadioShack box... I wonder if I still have the schematics I drew up for that... I think the raw parts for that cost more than the UB502, although it was going to be 4 stereo channels instead of 2