Question re: Bridging Amps

Early B.

Does bridging an amplifier affect its sound quality in any way?

Thanks.

hoosier21

Yes, sometimes better, sometimes not.

reeltrouble1

I had some NAD amps that sounded nice bridged mono.

Gee now who sold me those??:D

Why it was Hoosier!!:eek:

RT1

Early B.

hoosier21 wrote:

Yes, sometimes better, sometimes not.

Hell, so does this mean we gotta go through a trial and error process? Damn. That could get expensive and frustrating.

OK, the reason I ask this question is because I heard that bridging an amp affects SQ. I don't recall where I heard it or why it does, so I figured I should ask the experts on this forum to gain more clarity.

I've only bridged one amp -- an ATI 1502, and it didn't sound as good as I expected it to.

unc2701

Yes and no. Always some positives because you've got more power and that's always a good thing. Always some negatives because if the two channels are less than perfectly matched, it'll screw up the signal.

The idea that bridging results in worse SQ is largely a myth stemming from the higher THD spec that you usually see. In fact, many of the super-high power monoblock amps that you see (>500 WPC) are beefed up versions of bridged stereo amps. The bryston 7b, for example, is just a bridged 4b.

Early B.

unc2701 wrote:

Yes and no. Always some positives because you've got more power and that's always a good thing. Always some negatives because if the two channels are less than perfectly matched, it'll screw up the signal.

What do you mean by two channels being less than perfectly matched? Why would both cahnnels NOT be identical within the same chasis of a two channel amp, for instance?

Thanks.

RuSsMaN

Solid state amps have a bias adjustment similar to tube amps. Not all output transistors spec exactly equal.

I'm not 100% on this, but I BELIEVE when you bridge a sand amp, you send one side into push, the other pull - and they don't always have exactly the same force - ie the push is greater than pull (or vice versa).

Can you bi-amp instead? I've always preferred biamping over bridging.

Cheers,
Russ

faster100

I bridged an older rotel 980 amp and it sounded compressed to me.. true mono blocks of course work best... I think bridging some amps press the limits and the sound qaulity isnt there..

unc2701

RuSsMaN wrote:

Solid state amps have a bias adjustment similar to tube amps. Not all output transistors spec exactly equal.

I'm not 100% on this, but I BELIEVE when you bridge a sand amp, you send one side into push, the other pull - and they don't always have exactly the same force - ie the push is greater than pull (or vice versa).

Yep- that's exactly the problem. Manufactures put a lot of effort maching transistors within a channel, but not so much across channels. Anyhow, you can bridge any common ground amp, even if it doesn't have a switch, as long as you've got balanced input- you just tie the negatives (well- they should already be tied...), use a y splitter to send the same signal to both channels and flip the pos&negative on one of the balanced cables.

madmax

Look at it this way:

Class A uses the same transistor to do both the + and - half of the signal. (best SQ)

Class AB uses two seperate transistors, one for the + half of the signal, one for the - half of the signal. It is critical to have the changeover point exactly right, otherwise you end up with what is called crossover distortion. This is where the + and - meeting point is either overlapped or has a space. To sound good the + and - changeover point must be the same.

Class AB in a bridged configuration gets the - swing from the combination of the + and - of one channel and the + swing from the combination of the + and - swing from the other channel. (On a side note this is generally a problem for SDA owners because the final - signals from the two pairs of amp circuits are not necessarily equal to each other, therefore not common ground). In summary, with the bridged amp not only do the crossover points of each amp channel have to be matched correctly, so does the combination crossover points of left side and right side have to match exactly. Not an easy thing to guarantee and over time and temperature can vary anyway.

madmax