Bridging

[craftsmansky]

Can the a 300 or any of the basx series be bridged mono

[garbulky]

nope. However, the XPA-2 gen 1 and gen 2 (not gen 3) can be bridged for 8 ohm loads only.

[leonski]

The question THAN becomes:

Is bridging worth the sonic consequences?

[craftsmansky]

what are the consequences? distortion? heat?

[KeithL]

Bridging is an interesting subject.

First of all, bridging isn't necessarily bad (a "bridged amplifier" is effectively the same as "a fully differential amplifier").

However, there are several considerations......

1)

A fully differential amplifier is designed to run in bridged mode...

Whereas normal amplifier channels are NOT designed to run that way.

This can lead to stability issues.

(That's a tactful way of saying that some amplifier channels can be bridged and run just fine; but a few may become unstable or oscillate; it just depends on the design details.)

2)

In a bridge configuration, each side sees half of the load...

So, if you connect an 8 Ohm load to a bridged amp, each side sees a 4 Ohm load.

This changes the efficiency and power calculations.

(For equal efficiency, if an amplifier is designed to run into lower impedance loads, it  uses lower rail voltages.)

So, all else being equal, an amplifier designed to be run in bridged mode will use lower supply rails.

(And, if an amp is intended to be able to power a 4 Ohm load in bridged/differential mode, then each side must be able to power a 2 Ohm load individually.)

3)

In order to run an amplifier in bridged mode you must have a source of both a non-inverted and an inverted signal.

With a balanced input, this is as simple as connecting the input to one channel directly, while flipping the two signal lines to the other channel's input.

With an unbalanced input, you need a small piece of extra circuitry to generate the inverted signal - or you need to rearrange a couple of wires inside the amplifier.

(This is simple, but it is active circuitry, so either it has to be included in the amp, or you have to add a separate "black box" to do it.)

4)

For good performance both amplifier channels need to be pretty closely matched.

In short.... a given amplifier can be optimized for either bridged or non-bridged mode....

In a given situation, if you run a "normal amplifier" in bridged mode, it will run a bit hotter, but the distortion may actually end up being slightly higher or slightly lower.

Feb 12, 2019 11:29:04 GMT -5 craftsmansky said:

what are the consequences? distortion? heat?

[leonski]

Feb 12, 2019 12:12:29 GMT -5 KeithL said:

Bridging is an interesting subject.

First of all, bridging isn't necessarily bad (a "bridged amplifier" is effectively the same as "a fully differential amplifier").

However, there are several considerations......

1)

A fully differential amplifier is designed to run in bridged mode...

Whereas normal amplifier channels are NOT designed to run that way.

This can lead to stability issues.

(That's a tactful way of saying that some amplifier channels can be bridged and run just fine; but a few may become unstable or oscillate; it just depends on the design details.)

2)

In a bridge configuration, each side sees half of the load...

So, if you connect an 8 Ohm load to a bridged amp, each side sees a 4 Ohm load.

This changes the efficiency and power calculations.

(For equal efficiency, if an amplifier is designed to run into lower impedance loads, it  uses lower rail voltages.)

So, all else being equal, an amplifier designed to be run in bridged mode will use lower supply rails.

(And, if an amp is intended to be able to power a 4 Ohm load in bridged/differential mode, then each side must be able to power a 2 Ohm load individually.)

3)

In order to run an amplifier in bridged mode you must have a source of both a non-inverted and an inverted signal.

With a balanced input, this is as simple as connecting the input to one channel directly, while flipping the two signal lines to the other channel's input.

With an unbalanced input, you need a small piece of extra circuitry to generate the inverted signal - or you need to rearrange a couple of wires inside the amplifier.

(This is simple, but it is active circuitry, so either it has to be included in the amp, or you have to add a separate "black box" to do it.)

4)

For good performance both amplifier channels need to be pretty closely matched.

In short.... a given amplifier can be optimized for either bridged or non-bridged mode....

In a given situation, if you run a "normal amplifier" in bridged mode, it will run a bit hotter, but the distortion may actually end up being slightly higher or slightly lower.

Feb 12, 2019 11:29:04 GMT -5 craftsmansky said:

what are the consequences? distortion? heat?

Keith gives a bunch of technical stuff ALL of which is true.
Still remains that many persons report audible problems with bridged amps.       Besides?   What are you going to gain?    3db or so?  
The A300 is at the budget end of the spectrum and for all it does well, I'd not expect the highest matching of components which would work against bridging.

Save up, perhaps, if you really think you need more power.