Film-Tech Forum ARCHIVE: How to mono an amplified stereo signal

This is topic How to mono an amplified stereo signal in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Richard May (Member # 2627) on 08-26-2007, 01:20 PM:

This is actually for music outside of a building. I have 2 speakers that are fairly far apart. How can I mono the left and right amplified signals to these speakers to eliminate the stereo effect. I'm using an amplified tuner with left and right outputs. There are no controls to mono the signal internally.

Posted by Steve Guttag (Member # 268) on 08-26-2007, 01:32 PM:

It is odd that there is no "mono" button on the tuner as that often is a way to improve the quality of a weak signal.

Anyway...there are several way to mono up a signal. You can try to use a simple "Y" cable but since the tuner's outputs are bound to be low impedence, it is possible that it won't want to see the "other channel's" low impedence output. The way around that is to use resistors. Odds are that anything over 1K will work (I'd start with 4.7K).

Alternately, you can go the active route and use a summing amplifier available from many different sources like RDL.

Steve

Posted by John Hawkinson (Member # 1135) on 08-26-2007, 04:42 PM:

See Rane's technote, Why Not Wye?. It provides some simple schematics.

--jhawk

Posted by Bruce Hansen (Member # 281) on 08-27-2007, 11:41 AM:

DO NOT ever connect two speaker outputs together. They WILL blow each other up. You may be able to sum the two speaker outs with 8 ohm (or 10 ohm) resitors. This will cut the output level a little though. Use power resistors that are about the same power as the output of the amp.

Posted by Larry Zuverink (Member # 1483) on 08-27-2007, 01:26 PM:

Richard,
I'v used Speco(not the platter guys)TSM-30's for years. They work great. You can get them online for less than $15.00

Posted by Steve Guttag (Member # 268) on 08-28-2007, 06:12 AM:

Wait a minute...I might have missed a key element in this problem that Bruce hit upon...are you saying that you do not have access to the tuner signals directly as they come off the tuner stage and only the amplified outputs? If so, Bruce is dead on in that a resistive/inductive solution is your best bet. The problem with pure resistive is that you will affect the damping factor significantly and will likely have exaggerated bass as a result.

Steve

Posted by Larry Zuverink (Member # 1483) on 08-28-2007, 06:57 AM:

Steve, I also missed that it was speaker level. The TSM-30 is for line level.

Posted by Louis Bornwasser (Member # 3063) on 08-28-2007, 02:03 PM:

At one time you could buy a 3 winding transformer. 2 primaries for the amp outputs and one secondary to feed mono to any number of speakers. Don't know if this is still made, but 2 individual transformers may work also. Louis

Posted by Phil Hill (Member # 371) on 08-28-2007, 03:44 PM:

The TSM-30 is speaker level.

Posted by Larry Zuverink (Member # 1483) on 09-04-2007, 12:24 PM:

Your right Phil, I get more confused every day. [Smile]