What's So Bad...About BRIDGING?

CDLehner

CDLehner

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So...I've always heard, and the prices seem to bear it out; that bridging is "bad". For example...(and this is when the idea was laid out to me; early in my audiophile-dom)

Why not buy (2) Parasound A23s, for ~$2k and are said to deliver "400wpc"; as opposed to an A21, for ~$2500...and "only" 250wpc? (or, for that matter, JC1s; which are ~$9k for the pair...and deliver the same "400wpc".

Now...I've put all of the power figures in quotations, because I realize...you cannot get blood from a stone. Obviously...the A21, and especially JC1; have a larger power supply, deliver more current...and therefore, will have more to MUCH more headroom, and handle a true "400wpc" load easier.

And not that, it alone...is not insignificant; but is that it? Did I just ask and answer, my own question?

Because I'm wondering it, for "real"; about a pair of Bryston 2.5B3s. I see Joe already posted, the review...that also caught my eye. Actually, I was reading about the Rogue ST-100...which garnered "10 LPs"; but JS kept mentioning, the 2.5B3.

In that review; JS...who IMO, is notoriously tough on kit...gave the little Bryston, 9.5 LPs, and compared it to the Pass XA-30.8!

Here's my "concern"...and where I'm looking for some answers, from you EE types...lol; I've also always heard "with BIG power, can come BIG problems"...sonic-wise. I'm not even going to try and venture an uninformed opinion here; but I guess maybe, it has something to do with the amount of negative feedback needed...to control, BIG power...and the impact that has on sound?

And here's where I have a specific concern, about the 2.5B3. In his review...one of the things JS notes is "the 2.5B3 has only one pair of output transistors per channel, reducing parts count, simplifying the circuit, and potentially offering the purest sound possible from the “Cubed” circuit topology."

That kinda sounds like, it plays into the answer about BIG power/BIG problems a bit; and so I'm wondering...do I run the risk, of negating that "purity of circuit", by Bridging a pair??
 
I will offer my Objective view on this before giving my subjective opinion and BTW an indepth answer on this would eat up Mikes bandwidth . :)

Firstly your speaker is listed as 86db/w/m , i would recommend at the very min 200watts/ch for best results without clipping, this will of course eliminate your Small amp position, well unless you are not affected by clipped signals. In past practical testing has shown, that speakers with avg sensitivity ( yours is below avg) and played at a nominal din of 86db will clip a 200 watt amplifier on music with good crest factors. Since most philes tend to under power their systems to begin with, IMO, most end up choosing clipping characteristics as oppose to sonic characteristics....

https://pmc-speakers.com/products/consumer/twenty5/twenty523

Bob Cordell's experiment ... The Peak Power Demands of Well-recorded Music


"This demonstration was a real "Wow" for the attendees. The Rickie Lee Jones (RLJ) cut was played at realistic, but certainly not unpleasant, levels in the relatively small hotel exhibit room on speakers with an estimated sensitivity of about 89 dB. The average power typically read 1-2 Watts, while the power on peaks often topped 250 Watts (the power display monitored only one channel, so these numbers should be interpreted as Watts per channel). On this cut, most peaks occurred with an aggressive "thwack" to a snare drum positioned dead center.

While it is true that the RLJ track has an unusually large dynamic range, this data still suggests that many listeners may be clipping their amplifiers more often than they think. This may especially be the case for those with tube amplifiers who are not using extraordinarily efficient speakers. The amount of clipping, and the way in which amplifiers handle clipping, may account for more of the perceived differences in amplifier sound than we realize. As an aside, it would be nice if all amplifiers had accurate and fast clipping indicators. It might be a real eye-opener. If your amplifier is clipping, have you left the realm of high fidelity? "





http://www.cordellaudio.com/he2007/show_report.shtml

Output stage:

The output stage and more specifically the amount of output transistors to use is very dependent on design goals criteria, a low wattage 8 ohm ( 10-30 watter) only amp can be done with 1pr or 2pr , not so on a high powered amp or one design to drive into low -Z loads as represented by many large multi -driver speakers today. The output transistors are really slaves to the driver circuit, think of them as current devices when slaved in multi pr's , so things like SOA, Beta droop, et al becomes important and very dependent on output device type , etc.

Never heard a 1 or 2 pr sound better than a 4/6/8/16 pr amp just because of outputs used, then there's output impedance and stability. Considering your speakers you are going to need at the very least 100watts/ch , which would require a min of 2 prs for stability, at 200 watts pr ch at least 4 prs and if mosfets , much more, because of them favoring more class-A bias than a BJT type output transistor.

More important than the output stage is PSU, on amps where the output is marginal , most tend to undersized the psu for safety, there's plenty involve in power amps, more than just the output stage quantity..


Subjective Opinion,

You are going to have to listen , many online experts are just that, Online self proclaimed, i would suggest you choose the most powerful amp you can afford ( the higher voltage controls the bass better too ) and listen, whats good for Mr Audiophile , might not mean good for you , i cant tell you how many times i have heard this will "wow" them systems and found them barely more than Meh and dont get frustrated if you have to go thru a few amps to get what you want, after all it's "your" hi-fi system ... ...



Regards ...
 
Hi Folks,

Remember also that when you bridge an amplifier it 'see's' 1/2 of the impedance it does in stereo - so 4 ohms becomes 2 ohms which means the amplifier has to deliver that much more current to the load.

james
 
Not considering the extra power --- I've found that some amps sound better in bridged mode and some not so much. But thats an objective thing. You really need to listen to it both ways to see if its something that works for you.
 
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