Denon or any amplifiers in Bridge mode

[raffajaffa]

Hi

Curiosity ? Somewhere in my recent reading re the Denon amplifier circuits I read that these should only be used with speakers of 8 ohm or more?
Can anyone explain why.?
I must confess I cannot understand the " seemingly generic circuit" of the Denon amplifiers which have a genuine bridged mode switch which seems to route the input signal along a central circuit and create additional power plus additional wiring .The circuit would appear redundant when in stereo mode. ????
Does this guidance re 8ohm or more apply to all amplifiers that can be bridged.

 

[ubergeeknz]

The specs indicate 4 ohm is fine for stereo operation.

Bridge mode will be inverting the signal for one channel so the stereo amplifier becomes a mono bridge mode amplifier. Pretty standard.

In bridge mode, each amplifier "sees" only half of the load impedance. So if they are rated for 4 ohm apiece, in bridge mode you wouldn't go below 8 ohms.

 

[mchambin]

Yes.
Loudspeaker Vpeak is doubled when bridging.
Using the same speaker, the power in the speaker is quadrupled, while for each of the two amps, the power is doubled.
This is a way to get more power, at the risk of frying the amps.

 

[Douglas Blake]

Hi
Curiosity ? Somewhere in my recent reading re the Denon amplifier circuits I read that these should only be used with speakers of 8 ohm or more?
Can anyone explain why.?

It's probably a current limitation of the amplifier. Running less than 8ohms might overheat it.

I must confess I cannot understand the " seemingly generic circuit" of the Denon amplifiers which have a genuine bridged mode switch which seems to route the input signal along a central circuit and create additional power plus additional wiring .The circuit would appear redundant when in stereo mode. ????
Does this guidance re 8ohm or more apply to all amplifiers that can be bridged.

The manual you attached is for a Rotel amp.

When you bridge an amplifier you are driving it's two channels out of phase. This effectively doubles the voltage to the speakers but it does not double the current limits of the amplifiers, so often you do run into this limitation.

 

[raffajaffa]

Ah Thanks for explanatations. I now mostly understand.

It is also very interesting because I suspect the amplifier I aquired was indeed used in bridging mode at least for a short while.
Prior to purchase I had previously looked up the history of this Denon series of amplificaton (They all seem to have a similair circuit in their values and layout for the amplifier) Their is a regular failure of overheating of chip 2sc2910 (Or 2sc2911 in this circuit)

I wonder if this is connected ?.
Soon will hope to have a look at why one channel has died on the amplifier albeit whilst driving speakers loud. NOTE I have myself not used it in bridge mode. .

I may even consider soldering (or gluing) that selection switch into permanant stereo. or better still BYpass the switch altogether.

The loudspeakers are ok even though one had a 17.9V DC fed for a few seconds . (Fuse did not blow?)

 

[Douglas Blake]

Ah Thanks for explanatations. I now mostly understand.

It is also very interesting because I suspect the amplifier I aquired was indeed used in bridging mode at least for a short while.
Prior to purchase I had previously looked up the history of this Denon series of amplificaton (They all seem to have a similair circuit in their values and layout for the amplifier) Their is a regular failure of overheating of chip 2sc2910 (Or 2sc2911 in this circuit)

I wonder if this is connected ?.
Soon will hope to have a look at why one channel has died on the amplifier albeit whilst driving speakers loud. NOTE I have myself not used it in bridge mode. .

I may even consider soldering (or gluing) that selection switch into permanant stereo. or better still BYpass the switch altogether.

The loudspeakers are ok even though one had a 17.9V DC fed for a few seconds . (Fuse did not blow?)

First ... are you sure you have the correct schematic? The one you attached to your first message was for a Rotel amplier. These things are usually very specific to a particular make and model.

If you are getting a DC offset on one of the outputs, you probably have a blown output or driver transistor.

 

[raffajaffa]

thanks for pointing out the error

First ... are you sure you have the correct schematic? The one you attached to your first message was for a Rotel amplier. These things are usually very specific to a particular make and model.

If you are getting a DC offset on one of the outputs, you probably have a blown output or driver transistor.

OOOOps Sorry Dunno why I keep calling it a Denon but I did have one for a very short while recently.



IT IS definite Rotel as per schematic. ( I am on strong tablets at this moment)



Yes I believe it will be s transistor thats blown as I was listening when it gave up the ghost so to speak.Currently have my right hand bandaged so testing is an option in a few days. Also realizd from comments that It has Vishay .6w on the rails to the first 4 transistors. Interesting to see if that may be a problem? Hope not, even in those postitions they improved the sound. (10 per channel at the moment)

 

[raffajaffa]

If you are getting a DC offset on one of the outputs, you probably have a blown output or driver transistor.[/QUOTE]


At last Got the bandages off and checked the DC backwards from speaker terminals and it traces back to that 2sc2911. ( Yep previously they were 2910s tin earlier models) had kept overheating (Assumed) So bought matched pair with 2sa1209 .


Another curiosity as I was checking around as some of the resistors were 2% metal films and not the 1% specified ? Also found One of the 100k resistors R814 to be 75K I assume this had been changed as it was a different type metal film. . Bit weird. After resoldering a lot of the underside of the board which had plenty of flux visible I rechecked faulty DEC offset at 12,78V

Transistrors from Littlediode on their way.