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Bridging an amplifier

I recently watched a YouTube video, a few years old, that featured Flemming Rasmussen, the highly regarded founder and engineer for Gryphon (now retired I believe). Flemming was speaking of his class A monoblock amplifiers in the Antileon Evo, Colloseum and Mephisto. Flemming was expressing his disdain for Monoblocks that are actually 2 internally bridged amplifiers, (such as DNA 500,Clayton M300s and also class A Luxman that can be used as Monoblocks in the BTL mode (bridged tied load), calling these types of Monoblocks inferior and not true Monoblocks. He claims dedicated Monoblocks where all push pull transistors are paralleled, are vastly superior to summing the two channels via bridging (antiphase summing). I’d love to know if most audiophiles and engineers agree with Flemming. I have owned and found both the DNA Monoblocks and Clayton M300 Monoblocks to sound excellent, and a friend uses two M-800A Luxman class A amplifiers in bridged tied load mode (BTL switch) with great clarity and power. Thank you for your thoughts!
audiobrian
cal3713's avatar
cal3713
1,421 posts
 
@almarg As always, thanks so much for your teaching. Now I finally understand why the first watt f4 manual is written the way it is. 

"As a stereo amplifier with single-ended inputs and outputs, it will deliver up to 25 watts into 8 ohms with a damping factor of 40. It will do 50 watts into 4 ohms, and as a mono-block amplifier with parallel inputs and outputs, it will do about 100 watts into 2 ohms. As a mono-block amplifier with balanced inputs and outputs the power output rating is 100 watts into 8 ohms at 1%."

I've built one and am in the process of building a second and couldn't figure out why Nelson kept changing the impedance in his description...
georgehifi's avatar
georgehifi
10,312 posts
 
audiobrian
Flemming was expressing his disdain for Monoblocks that are actually 2 internally bridged amplifiers

Flemming is right, and these are these are the reasons for not bridging amps.


  I’ve said it before in other threads here it is again

"Nice amp, if you want to hear them at their best, don’t bridge "if there’s no need to", as all you’ll gain is watts, everything else takes a hit when you bridge amps.

Pro’s=
More watts.

Con’s=
Worse damping factor
Higher output impedance (has relevance to damping factor)
Lower stability (especially into low impedance’s)
Current ability is reduced (especially into low impedance’s)
Higher distortion.

And if you have two of them better to run them in stereo mode and vertically bi-amped, instead of bridging (mono’ing).
http://www.av2day.com/wp-content/uploads/2014/05/biamp2.jpg"

Cheers George
mijostyn's avatar
mijostyn
8,570 posts
 
First of all Rasmussen is not an engineer. I believe his degree is in graphic arts. He is a very rich old audiophile who had nothing else do do with his money. Wonderful, any way great audio equipment comes to life is fine by me.
Although I am ace with a soldering iron my knowledge of electronic engineering is basic at best. I only know what I hear. With the exception of the Benchmark AHB2 I have not heard a bridged amp sound as powerful as a dedicated mono amp of similar power. The Benchmark is an enigma. This is on ESLs , planars and subwoofers. 
audiobrian OP
186 posts
 
Hi George:

Thank you again for your ‘input’.  I’m just wondering why designers/engineers from Constellation, Naim, Clayton, McCormack and other fine manufacturers, who obviously are aware of these compromises, choose to use balanced bridged designs in their reference products. Do you believe their decision is based partly on cost, generating maximal wattage without the robust power supplies and output stages needed to generate 200 wpc in a non bridged, high current, class A design?  Interesting...thanks again!
georgehifi's avatar
georgehifi
10,312 posts
 
It's all out there to search, Al has also given some good info on it as well, above. If all you need is watt's then bridging is the way to go. 

Cheers George
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