Multi channel amp power questions

[CraigV]

I know this is going to be a general question and maybe not easy to answer, but I’ll give it a shot. I have a B&K Sonata Video 5 amplifier. Since I’m no longer using it to power a center channel speaker, I un hooked the cable from my BD55 to the pre amp, and from the pre amp to the amp. There are level controls for each of the channels. I turned up the controls for the 4 channels in use, and turned down the one for the center.

My question is, in dialing down the control for the unused channel, will the power be diverted to the other four? Also, when I open up the amp, there are similar potentiometers on top of each of the channel banks. Any idea what these might control?

Or, do I need to contact B&K?

Thanks

 

[Seth=L]

I know this is going to be a general question and maybe not easy to answer, but I’ll give it a shot. I have a B&K Sonata Video 5 amplifier. Since I’m no longer using it to power a center channel speaker, I un hooked the cable from my BD55 to the pre amp, and from the pre amp to the amp. There are level controls for each of the channels. I turned up the controls for the 4 channels in use, and turned down the one for the center.

My question is, in dialing down the control for the unused channel, will the power be diverted to the other four? Also, when I open up the amp, there are similar potentiometers on top of each of the channel banks. Any idea what these might control?

Or, do I need to contact B&K?

Thanks

Have pictures of this baby?

The level adjustments for each channel are simply gain controls. Since the channel won't be used it will make no difference on the amplifier's overall output if the gain is set to maximum or minimum. If that channel is not receiving input it will not consume any power from the power supply. The power supply (transformer and capacitor bank mostly) delivers power to the channels that need it. It's unlikely you will notice a power output difference between using 4 speaker or 5, but in theory each of the four channels has more potential output assuming the power supply is being used to it's maximum current capability.

Those other potentiometers are likely bias controls, I would not make any adjustments to them.

 

[PENG]

If the B&K uses one power supply transformer for all 5 channels then Seth is generally correct, part (only to some extent) of the power no longer needed by the center channel will become available for the remaining 4 channels. This however, assumes that the amplifier is power supply limited and not amplifier limited. If it is amplifier limited then any gain will be minimal. Without much more detailed information it is only possible to give you an 'approximate' answer. Since there is nothing to lose, you should go ahead and phone B&K about it. Please tell us what they say.

 

[Seth=L]

If it is amplifier limited then any gain will be minimal.

What does this mean?

 

[PENG]

What does this mean?

I mean if the specified output is first limited by the amp section, then the power supply.

Let me use an exaggerated example:

Amplifier A: 130WX2 but 45WX7 (a Yamaha?)
Amplifier B: 70WX7 but 100WX2 (a HK ?)

I would then call Amp A power supply limited and Amp B amplifier limited. This is all relative as like anything else there are always the in between scenarios.

 

[CraigV]

I just got off the phone with B&K, and it’s pretty much as Seth=L said - it doesn’t divert more power to the other channels, but more power can be at hand when those channels need it.

He also said the pots inside are indeed bias controls. What do they do?

 

[Votrax]

I just got off the phone with B&K, and it’s pretty much as Seth=L said - it doesn’t divert more power to the other channels, but more power can be at hand when those channels need it.

He also said the pots inside are indeed bias controls. What do they do?

In a push-pull amplifier the transistors require a small bias current to prevent switch over distortion. All transistors require a minimum voltage to turn on. For example a MJE4343 transistor has a "base-emitter on voltage" of 3.9VDC. You would adjust the base voltage with the bias pot to a voltage slightly higher than 3.9VDC so a small current is flowing through the transistor. Without this bias current the transistors wouldn't turn on until the audio signal was +/-3.9V.

Example of switch over distortion: