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Old 28th July 2004, 01:26 AM   #1
bowdown is offline bowdown  Australia
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Default Bridging problem

Hi everyone i built a 2ch stereo leach super amp which work absolutely fine (the amp has been running for over 6 months). i wanted to get more power so i went out and bought a bridging kit from a place called altronics in Australia, anyway i built the circuit it works fine when i put it on the scope to test it, then i put it on the amp and put both outputs on the scope and they both work fine( one is inverted the other is non inverted), without any load it looks fine on the scope,but when i attach an 8ohm dummy load the amp goes into oscillation(really really bad oscillation) even at low power and the power output is the same as one channel @8 ohms( approx 450wrms) it should be almost double of what im getting into 4ohms(approx 650wrms) per channel so bridged it should be approx 1200-1300wrms @ 8ohm but im getting only 450wrms. I have checked all wiring and cannot find what i have done wrong.I have built plenty of circuits which all work perfectly.If i bypass the bridging circuit the amp works perfect.Is there someting i might be missing??Please help.Thanx in advance.

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Bowdown
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Old 28th July 2004, 09:09 AM   #2
djk is offline djk
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The B+ for both channels must be hooked together as must the B-, no mono blocks.

Use this method of bridging.

http://sound.westhost.com/project20.htm
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Old 28th July 2004, 01:05 PM   #3
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Quote:
Originally posted by djk
The B+ for both channels must be hooked together as must the B-, no mono blocks.

Use this method of bridging.

http://sound.westhost.com/project20.htm

Doesn't that method input the distortion of the upper stage into the lower stage?



Carlos
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Old 28th July 2004, 07:41 PM   #4
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Hi Carlos,


Most definitely - YES.

It can sound awful too if the loudspeaker has a complex crossover network and the drivers are highly resonant.


Cheers ............ Graham.
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Old 29th July 2004, 12:55 AM   #5
djk is offline djk
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Do you guys want something that works, or not?
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Old 29th July 2004, 02:15 AM   #6
K-amps is offline K-amps  United States
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Quote:
Originally posted by djk
The B+ for both channels must be hooked together as must the B-, no mono blocks.

Use this method of bridging.

http://sound.westhost.com/project20.htm

Thats the method Nelson used in the Adcom 555. PS: I have bridged Mono-blocks and it seemed to work fine. So sometimes it works even in Mono-block configuration but prolly more risky as far as oscillations go. The only thing I did was tie the two grounds together with a 4 gauge harness. Other than that, it was just one resistor and some cabling.
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Old 29th July 2004, 07:07 AM   #7
bowdown is offline bowdown  Australia
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Thanx guys but i got bigger problems than that now that bridging kit i bought has destroyed the output stage on both channels and also about 65% of all the transistors on both channels . Man this sux i dont think im game enough to try and bridge the amp again once i have fixed it....might just have to use the power i got...
Thanx again... hope i can bring it back to life asap... miss my music..

Regards
Bowdown
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Old 29th July 2004, 08:34 AM   #8
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Very sorry to hear that Bowdown.

My choice is to NOT bridge, but to drive both channels the same and use each amplifier to separately drive a pair of loudspeakers or a double voice coil driver.

Yes the NFB loop arranged bridging circuit will 'work', but has anyone ever compared it with optimised single working?

Its crap.

Cheers ........ Graham.
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