[time-nuts] COMPLETELY off topic - but I know you'll read itanyway.
Don Johnson
True-Cal at swbell.net
Sun Oct 12 00:04:58 UTC 2008
Jim,
Ahh audio, my first love and almost 50-years of experience. You already have replies with the right answers but here is my 2-cents..
>I've dug out the manual and even though the specifications say it can do 4
>ohms in bridged mode, there is another statement that says it doesn't
>recommend it.
The recommendation is due to current limiting in the amplifier. The amplifier output impedance is doubled from the typical 4-ohm per channel to 8-ohm when bridged. If you loaded the bridged output with 4-ohm (both 8-ohm speakers in parallel), it would require double the current through each output stage in addition to 2x the draw from the power supply. Current limiting, probably in the power supply, would result at a much lower peak voltage from each channel. The result is less power (earlier clipping/distortion) with this lower than design point load.
>"The A channel handles the positive voltage and the B channel becomes the
>negative, thus doubling the output voltage swing."
This is a very odd way to state what's happening in the bridged mode. You gatta love manuals written by the marketing department. Not totally wrong but only accurate during complex instances in time when the positive half of the output is indeed handled by ch-A and the negative by ch-B. In another instance however, this will be reversed. A more accurate description is what someone else has already stated as a push-pull arrangement of the out-of-phase driven channels. The bridge mode switch couples one of the input channels to both output stages but also inserts an additional op-amp stage (phase inverter) in only one of the channels. Now as the input signal goes positive, the "hot" terminal of ch-A will be driven positive while the "hot" terminal of ch-B will be driven negative equally. All this reverses as the input signal goes negative.
The clincher for you to NOT operate in bridge mode is that you have TWO speakers of the correct impedance to match each channel separately. Just drive both input channels with a Y adapter from your mono source and you will have the best arrangement. If there is ever a time that you want to only drive one of the 8-ohm speakers, now you would want to bridge the amp and connect the one speaker accordingly.
Regards...
Don
----- Original Message -----
From: Jim Palfreyman
To: Discussion of precise time and frequency measurement
Sent: Saturday, October 11, 2008 7:48 AM
Subject: Re: [time-nuts] COMPLETELY off topic - but I know you'll read itanyway.
Thanks folks for your quick replies.
I've dug out the manual and even though the specifications say it can do 4
ohms in bridged mode, there is another statement that says it doesn't
recommend it.
Here is what it says about bridged mode:
"The A channel handles the positive voltage and the B channel becomes the
negative, thus doubling the output voltage swing."
Needless to say, Poul's comment regarding running them as two separate
channels because if one fails I'll have another as a spare is the clincher
for me. Being from an IT background - backup is all important.
Thanks folks!
2008/10/11 Javier Herrero <jherrero at hvsistemas.es>
> If 500W are specified for a 4 ohm load, you will only obtain 250W for
> each channel over a 8 ohm speaker. In bridged mode, it is not true that
> basically one channel drives the upper part of the sine and the other
> the lower: they operate in push-pull, supplying each side of the speaker
> with opposite phases so you will obtain the double peak-to-peak voltage
> value over the load than in the single ended configuration. Double
> voltage would mean four-times power, so the amplifier surely is not
> rated for the same load in bridged mode than in single-ended two-channel
> mode. If minimum load for each channel is 4 ohm in single-ended mode,
> usually it is 8 ohm for two channels in bridged mode.
>
> So if you have 8 ohm speakers... use it in single ended mode (better
> reliability also, as Poul-Henning pointed), and you will get 250W per
> channel. In brigde mode, you could only put the two speakers in parallel
> if the amplifier is rated for 4 ohm loads in bridged mode.
>
> Regards,
>
> Javier
>
> Jim Palfreyman escribió:
> > OK I have an interesting but simple problem that has nothing to do with
> > time. But I'm sure someone on this list will know. And besides I can't be
> > stuffed finding another list with such a good S/N ratio.
> >
> > In my spare time I play in a band.
> >
> > I have a 1000W amplifier that can be either two 500W stereo channels or a
> > single 1000W mono running in "bridged" mode. (Basically one channel
> > amplifies the upper part of the sine curve and the other the lower.)
> >
> > The amp can drive speakers down to 4 ohms.
> >
> > I have two 8 ohm speakers.
> >
> > The source is mono.
> >
> > Do I run each 8 ohm speaker on its own 500W channel?
> >
> > or
> >
> > Do I run in bridged mode and put the two speakers in parallel onto the
> 1000W
> > amplifier?
> >
> > Any takers?
> >
> > Regards,
> >
> > Jim
> > _______________________________________________
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>
> --
> ------------------------------------------------------------------------
> Javier Herrero EMAIL: jherrero at hvsistemas.com
> HV Sistemas S.L. PHONE: +34 949 336 806
> Los Charcones, 17A FAX: +34 949 336 792
> 19170 El Casar - Guadalajara - Spain WEB: http://www.hvsistemas.com
>
>
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