[Oublie]

Hi guys n' gals,

Simple enough question but if you have a pair of stereo amps how does the bridged mono on some of them work does it just feed a mono signal i.e. left or right simultaneously to each amp and combine the output or is it something more complex any schematics out there and can a normal stereo amp be converted to a bridged mono unit.

thanks.

 

[error401]

Normally only one input is used. One amplifier is used to amplify it directly, while the other amplifier amplifies an inverted version of the same signal. Instead of one speaker lead tied to 0V and the signal swinging around it, both leads are driven with opposite signals.

If you build an inverter circuit you can use a regular stereo amp this way.

 

[Oublie]

cool, Ill have a look for an inverter circuit. I'm assuming the invertion works prior to amplification.

 

[NelsonVandal]

You can use an opamp to invert the signal. There are also some simple one-transistor preamps. Another option is to use a transformer.

One problem with inverting (pre)amps is a lowish input impedance, and depending on the output impedance of your CDP (or whatever you're using), you might need a buffer in front of the inverting preamp.

 

[nikongod]

You could also do the fancy thing and call 2 signals of equal amplitude with perfectly inverted phase "balanced". If your source/preamp dosnt have a balanced output, there are (as mentioned above) a few ways to get one. I personally prefer transformers to opamp phase splitters, but who's counting?

Be forewarned, not every power amp will deal well with having its outputs bridged. A great many newer amps are coming with the outputs already bridged! Trying to "rebridge" (for lack of a better word) these can cause some "interesting" and bad problems.

 

[Oublie]

The reason I asked was i was thinking of building 2 dual mono chip amps and bridging them for more power. I.e a bridged mono amp for each channel. So i'm thinking it may be possible to just feed a single rca input into both mono's simultaneously and join the outputs or would i still need to invert the signal and take the output from the + of one mono and - of the other? btw the plan was to have a seperate trafo and seperat power circuit for each of the 4 amps. this will be used with a stax energizer.

 

[dcheming]

Quote:

Originally Posted by Oublie /img/forum/go_quote.gif The reason I asked was i was thinking of building 2 dual mono chip amps and bridging them for more power. I.e a bridged mono amp for each channel. So i'm thinking it may be possible to just feed a single rca input into both mono's simultaneously and join the outputs or would i still need to invert the signal and take the output from the + of one mono and - of the other? btw the plan was to have a seperate trafo and seperat power circuit for each of the 4 amps. this will be used with a stax energizer.

Just make sure the mono chip amps aren't already bridged or you'll have problems as nikongod said.

 

[nikongod]

Quote:

Originally Posted by Oublie /img/forum/go_quote.gif So i'm thinking it may be possible to just feed a single rca input into both mono's simultaneously and join the outputs or would i still need to invert the signal and take the output from the + of one mono and - of the other?

you need to split the signal somewhere
drv-134 is probably the least expensive thing that is designed to do it. It also has a pretty low output impedance which fits well with the trend to put a buffer between the volume control and the amplifier IC.
Quote:

btw the plan was to have a seperate trafo and seperat power circuit for each of the 4 amps. this will be used with a stax energizer.

you will get better PSR by running both amps of the channel off of 1 PS.

As another thing you may want to think about: do you *need* to use a bridged gainclone? using these amplifier chips at too low of a power level causes distortions (check the data-sheets....) You may wind up better off running a single chip HARD than letting 2 chips loaf along.

 

[Oublie]

Thanks for the info Nikon,

Ill look into it. For me this is the next step up from a couple of cmoy i built so i have a lot to learn. I think may i would be wise to just build the one dual mono chip amp for now and upgrade if necessary.