View Full Version : Preamp inverted L-R channel output? (Yamaha C-70+)


sydsfloyd67
02-16-2006, 09:47 PM
I understand that those few preamps that have an "inverted' pair of outputs in addition to the normal set can be used to bridge any two amplifiers (first item below).

I had not heard the following claim from Yamaha -that using the invert outputs, and reversing one speakers phase, can afford some benefit to the amplifier's power supply. Does this make sense to any of you technically minded guys? -sf

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"The PRE OUT NORMAL & PREOUT INVERT terminals are a versatile feature of the C-70.

- When using a separate power amplifier for each channel, the alternate hookup permits the use of ordinary stereo amplifiers (without the "BTL" feature) to be operated monaurally, a unique feature of the C-70.

- The bass response of many power amplifiers is limited by power supply capacity. When a strong bass note enters the amplifier's left and right channels simultaneously, the fact that the two signals are in phase means that the total demands for power may exceed the capacity of the supply. The C-70's unique PRE OUT INVERT jacks can be used to solve this problem. The left and right channels of the power amp are operated out of phase, greatly reducing the demands of low frequency signals on the power supply. This can dramatically improve bass reproduction on many power amps.
Note that it is necessary to reverse connections to one speaker to preserve proper phase.
___________________________

bully
02-16-2006, 09:50 PM
My Yamaha C-80 will invert phase to allow bridging. I have bridged the two PCR800s for 900 watts per channel into 4 ohms. Yikes.

sydsfloyd67
02-16-2006, 09:53 PM
B., yes but what do you make of that second claim regarding running a single amp with each channel in opposite phase (and each speaker) to reduce the demand on the power supply (somehow?)? -sf

txsviking
02-17-2006, 08:29 PM
Just to bump this, as I am interested in the invert function too.

I'll start a new thread tomorrow with another question relating to this. :scratch2:
But not to hijack this one. :)
Terry

phidauex
02-17-2006, 08:40 PM
Mmm... That is a dubious claim, at best. However, it may have some truth to it, especially when using amplifiers that have wimpy power supplies...

Imagine a big powerful bass transient that demands a lot of current. Since both channels are swinging the same direction, they are pulling power from the same power supply rail. If they exceed its ability to supply current, it will begin to collapse as the capacitor tries to supply enough current. The result would be wimpy bass, because the amplifier's power supply can't keep up with the demands of the amp.

Inverting the phase of one channel means that on that transient, one amp channel is pulling from the negative rail, and one is pulling from the positive rail, each supplied with its own rectifiers and capacitors, so you are lessening the strain on each rail, restoring low end performance. Inverting the speaker connection phase at the same time preserves the phase of the actual speaker cones.

Now... This would be a moot point on amplifiers with properly designed power supplies, or dual power supplies. However, it sounds like an interesting idea for cheaper amps that don't have as high capacity power supplies.

Note: I'm no amplifier designer, and I'm only modest a repairing them, so my explanation could be BS! Its just my best guess, given my limited understanding of the situation.

I suggest you give it a try, and tell us if you notice anything! If you don't, try again with a cheaper amp! :)

peace,
sam

yamahammer
02-17-2006, 08:46 PM
i have a c-70 preamp and m-80 amp and wouldn't ever dream of just the thought of toasting either of them for the sake of a experiment like that

phidauex
02-18-2006, 12:20 AM
i have a c-70 preamp and m-80 amp and wouldn't ever dream of just the thought of toasting either of them for the sake of a experiment like that

?? Are you referring to my experiment? Or the bridging experiment? I wouldn't recommend bridging any amplifier not meant to handle it, but the other experiment, the invert one side, and invert its speaker outputs, couldn't hurt a flea. It might not do anything, but its certainly not going to hurt anything either. :)

peace,
sam

phidauex
02-18-2006, 12:24 AM
If you've got a good amp, and you've got the headroom, both in output power, and power supply capacity, then the experiment won't do you any good, it would only help a wimpy supply.

peace,
sam

sydsfloyd67
02-18-2006, 10:07 AM
If you've got a good amp, and you've got the headroom, both in output power, and power supply capacity, then the experiment won't do you any good, it would only help a wimpy supply.peace, sam

I'd say that's the answer. The claim seems pretty dubious to me as well. -sf

txsviking
02-18-2006, 05:32 PM
Can the Invert feature be used in a Bi Amp system?
Like 2 M-70's and AR-9's ( Without the jumpers ).

As it is now, ( Not using the invert ) the M-70 on the 4 woofer's will
dim the lights above normal volumes. AR-9's are power hungry. :yes:
Terry

phidauex
02-18-2006, 05:46 PM
This 'invert trick' won't lower the total power usage, just the power usage per rail at a given moment. If its dimming lights, you should get it onto its own circuit!

peace,
sam

bully
02-18-2006, 06:51 PM
I should look for my C-80 manual, I think it says the same thing.
Driving the big amps I have I don't worry too much of maxing them out. My head would implode before we clipped those bad boys.
What I like to do is bridge a pair of amps. I did that with my pair of Soundcraftsmen PCR800 for some huge MOSFET output. The M-80 is more than robust enough to be bridged--I would love a second M-80.

the-real-mandak
02-19-2006, 11:47 AM
bully:

Who would not?
In my case a M-85 :)

bully
02-19-2006, 11:51 AM
:banana: :D

sydsfloyd67
02-20-2006, 01:37 PM
Two PM860s, now on the way. :banana:

bully
02-20-2006, 01:49 PM
FaR oUt! They should sound great with the C-70! Hope your speakers are up to some serious tickling :thmbsp:

sydsfloyd67
02-20-2006, 03:20 PM
B., I'm with you in terms of high power mosfet in terms of the nature of the sound at very modest volumes. Now I'm ready to find out what "extreme" can do at normal levels. :huge: -sf