mono as primary

[jefec]

any potential damage from using stereo sources though my Fisher 500? Also, ideas about using two speakers? Thanks.

 

[mashaffer]

Just be sure to use a resistive summing network so that the left and right signal channels don't "see" the low Z of the other channel. I am doing that with an iPod into my Sparton console right now. For mono I prefer a single speaker (other than sub if desired).

mike

 

[Scuzzer]

I don't understand the use of resistor networks for line level summing when you only want a single mono signal. Can someone point me to a technical link that describes the benefits?

I routinely use my mp3 player for mono duty. Sometimes I use the internal Rockbox mono setting other times I just plug it into a Y connector. Both of them sound exactly the same to me.

 

[wilberforce]

I don't understand the use of resistor networks for line level summing when you only want a single mono signal. Can someone point me to a technical link that describes the benefits?

I routinely use my mp3 player for mono duty. Sometimes I use the internal Rockbox mono setting other times I just plug it into a Y connector. Both of them sound exactly the same to me.

see this:
http://www.rane.com/note109.html

This is what I bought for my Zenith console radio:
http://www.edcorusa.com/Products/ShowProduct.aspx?ID=21

 

[Scuzzer]

see this:
http://www.rane.com/note109.html

That link says this:

"Life is wonderful and then you stub your toe. The corner of the dresser lurking in the night of this Note has to do with applications where you want to sum two outputs together and you want to continue to use each of these outputs separately. If all you want to do is sum two outputs together and use only the summed results (the usual application), skip this section."

I'm assuming then that all the stuff before that quote was for people who wanted to take a stereo line level signal and use both the left and right channels while summing to mono for a sub.

 

[wilberforce]

the way I read it they're saying skip what follows--the paragraph that talks about using three signals together (original L and R, plus the summed signal) and avoiding crosstalk. And although the example is about summing stereo to mono for a sub, the stuff about impedance applies to any time you combine stereo to one channel. in short, a "Y" adapter is for splitting signals, not combining them. you could damage your equipment.

 

[Scuzzer]

you could damage your equipment.

That's why I asked for a technical explanation but none was forthcoming. Every tube era preamp I've worked on simply joined the left and right signals together to make mono, no resistors (or anything else) differentiated stereo playback from mono playback. I'm trying to find information that would tell me why it's wrong to do it that way. All I've stumbled across so far is how to sum a channel to mono for sub use.

 

[becketma]

With two 8 ohm speakers you can sum them for 16 ohms and use the 16 ohm tap. Similar to summing two 8 ohm resistors for 16 ohms.

Bob

 

[Scuzzer]

I think I finally found a quote that makes sense of the conflicting information I've read. Here it is:

"As far as summing, it depends on the type of output device
you are dealing with. Transformer or capacitor coupled
devices could be summed with no problem, anything active
should be summed through resistors. I don't see any
physical harm being caused in any case."

So for pro audio ultra low output impedance active stuff, you need summing resistors. For old tube amps, high output impedance units and other cap coupled devices they aren't needed. This squares with what I've experienced since I've only played with the second category of equipment.