Bridged versus stereo

[Haselsh1]

A week ago I thought I would experiment with my power amplifiers. I use a Rotel RC850 preamp with two bridged monoblocked power amps but thought I would ‘stereo’ one of the power amps, reconnect everything, and give it a go. The result was very interesting indeed with a much warmer, softer and more musical sound. The overall impression was of a much better sound but there was as usual something not quite right.

I bridged the amplifiers again and put them back into the circuit to see what the difference was. Immediately there was a massive stereo image with cavernous depth that was completely missing from the stereo power amp alone. I was using Younger Brother’s ‘A Flock of Bleeps’ as the test record which is so well known for its stereo effects and this was blatantly obvious with the bridged amps. The sound was less musical but equally more dynamic and powerful with much more slam and guts so for me, the bridged and monoblocked RB850’s are definitely staying.

Source is a Marantz CD 6005 and loudspeakers are KEF Q500’s which I am still amazed by.

[Barry]

I'm not surprised Shaun.

Not only will the bridging double the available power and hence help improve the dynamics, but being monoblocks the only circuitry the two now share is the mains supply so cross talk is reduced, improving the stereo image.

Well done for experimenting and thanks for reporting your findings.

Good one!

[loo]

with that set up you could also try bi-amping , I don't know if it will be better than mono blocks but if your
up for experimenting it could be worth a try , it will give each speaker its own amp channel :)
Paul

[Barry]

Yes, you could experiment between passive 'horizontal' bi-amping and passive 'vertical' bi-amping.

[loo]

Indeed Barry, and vertically arranged would retain the channel separation that you pointed to with monoblocks
good call;)
Paul

[Macca]

Could be one of those situations where the improved clarity from the bridging shows up another component so it is more musical but less awesome with just one power amp when what you should have with the bridged set up is more awesome and more musical. Maybe the Pre amp or the Cd player is the issue?

[DSJR]

I can only say that in my case, bridged is definitely better than one stereo amp (Crown/Amcron D-60's bridged into Spendor BC2's), but in my case, the amps don't like 4 ohm loading (may not be a problem with modern designs). I need to compare the bridged 60's with a stock stereo D-150A, which has roughly the same output in standard two channel form (the D-60's are around 40WPC into 8 ohms stereo and around 75 - 80W bridged into 8 ohms, with limiting coming in to low impedances)

There's also an option occasionally for double-mono operation. I don't know how it's configured, but the Wattage doesn't necessarily increase, although current output is doubled.

Hope I'm not totally talking out my backside on this and that an engineer member can explain the above properly.

[Ali Tait]

A bridged amp is less capable of driving low impedances, so it can change the frequency response of the speaker it's driving. This could be a good thing too of course.

[The Barbarian]

I used to use a pair of A&R Cambs 'SA200' in bridged mono

[DSJR]

They were pretty mean in stereo as well I remember :)

[Barry]

I can only say that in my case, bridged is definitely better than one stereo amp (Crown/Amcron D-60's bridged into Spendor BC2's), but in my case, the amps don't like 4 ohm loading (may not be a problem with modern designs). I need to compare the bridged 60's with a stock stereo D-150A, which has roughly the same output in standard two channel form (the D-60's are around 40WPC into 8 ohms stereo and around 75 - 80W bridged into 8 ohms, with limiting coming in to low impedances)

There's also an option occasionally for double-mono operation. I don't know how it's configured, but the Wattage doesn't necessarily increase, although current output is doubled.

Hope I'm not totally talking out my backside on this and that an engineer member can explain the above properly.

Depends on how the amp is bridged. Connecting the outputs in series will double the output voltage swing, connecting the outputs in parallel will double the current.

Quad supplied a note on how to impliment either of those options with their 405 amplifier. I have their engineer's service manual; I will scan the relevent section if anyone is interested.

[337alant]

I have two Rotel RB860 amps in the loft which I used to use in my main system I actually preferred them Bi amped one stereo for the tweeters and one for Bass mids
In bridged mode there was more raw power but no finesse, I found them much more natural and musical in bi amped mode

Good amps the rotels for the money they were a bargain

Alan

[The Barbarian]

They were pretty mean in stereo as well I remember :)

Yes with the 'A60AP' as the Pre..

[Haselsh1]

Could be one of those situations where the improved clarity from the bridging shows up another component so it is more musical but less awesome with just one power amp when what you should have with the bridged set up is more awesome and more musical. Maybe the Pre amp or the Cd player is the issue?

Martin, the preamp is definitely an issue here as I also have a Fidelity Audio Pre-120 with which I have been box swapping and the differences are amazing. The Rotel has an amazing amount of bass detail and tone, the Pre-120 is fat and overblown. The Pre-120 has a gorgeous midrange and superbly delicate treble whereas the Rotel has a peaky treble with an average midrange. Then I changed my interconnects and that fat, overblown bass disappeared, the midrange gained a few ounces of extra detail and everything was back in order. So at the moment here it is; Marantz CD 6005 CD Player/Thorens TD160 MkII/Linn LVV/Ortofon OM40. Fidelity Audio Pre-120 preamp into Rotel RB850 bridged monoblocks into KEF Q500 loudspeakers. Interconnects are Atlas Equator and loudspeaker cables are some cheap Maplin stuff biwired.

[Macca]

That is good to hear. There is usually always a solution to these things even if we have to find it by trial and error. Also shows that when a system gets past a certain point the fine tuning actually becomes quite critical.
I'd rather it wasn't the case but it so often is.