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Post by puffin on Nov 3, 2018 9:30:05 GMT
Has anyone gone from a two channel amp to a bridge mode? A lot of NAD amps have this facility built in. I modified a pair of Cambridge two channel amps some years ago to bridge mode as a project. I have recently been using them to good effect on the LF of my EAR Primary Drive speakers. There seems to be some divergence as to how much more power is available as a result of bridging, some say 4X into half the load, some disagree. What it does do is increase the current output and this seems to control things better. Of course it may not simply be that alone and a multitude of other factors come into play.
When I first posted (on another forum) that I was intending to modify the amps in this way I was told that the amps would self destruct as the heat sinking was far too flimsy to cope with the mod. Several years on they are still working and only run luke warm even when pushed pretty hard. It is a fairly simple mod and others might find an old amp or two you have laying around could be given a new/different lease of life.
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seanm
Rank: Trio
Posts: 169 
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Post by seanm on Nov 3, 2018 9:42:13 GMT
Hi Puffin,
Thank you for your post. Which CA amps did you modify?
Cheers
Sean
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Post by puffin on Nov 3, 2018 9:48:37 GMT
2 P500s.
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Post by MartinT on Nov 3, 2018 9:59:58 GMT
As I understand it, bridging will almost double the voltage swing but will not increase the current capability. I'm happy to be corrected, we need colin14 to verify. The other key thing to remember is that the 'negative' speaker terminal is no longer at ground so don't try connecting grounding boxes and the like to them. |
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seanm
Rank: Trio
Posts: 169
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Post by seanm on Nov 3, 2018 12:15:07 GMT
Thanks.... back home in blighty, I have a pair of P500s bi-amped in a bedroom system.
Cheers
Sean
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Post by puffin on Nov 3, 2018 17:35:13 GMT
As I understand it, bridging will almost double the voltage swing but will not increase the current capability. I'm happy to be corrected, we need colin14 to verify. The other key thing to remember is that the 'negative' speaker terminal is no longer at ground so don't try connecting grounding boxes and the like to them. Hi Martin, my speakers are connected to both POS terminals of both the L&R channels, the NEG chsnnels are not used. |
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Post by MartinT on Nov 3, 2018 18:18:13 GMT
No, I meant the 'negative' or black terminal at the speakers.
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Post by puffin on Nov 3, 2018 18:25:07 GMT
One of the POS terminals acts as a NEG, there is a push-pull as usual. In effect there is a NEG, is that what you mean?
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Post by MartinT on Nov 3, 2018 18:28:09 GMT
What I mean is that the +ve terminal at the amp that connects to the -ve (Black) terminal at the speaker is not at ground potential, so you must be careful not to connect anything 'earthy' to it like a grounding box.
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Post by puffin on Nov 3, 2018 18:38:53 GMT
Ah yes, I see what I you mean now. Are these the boxes designed by Wizards that contain ferrite dust or some other "dark" matter?
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Post by MartinT on Nov 3, 2018 19:02:44 GMT
Them's the ones! The danger is having one grounding wire connect to a speaker's -ve terminal and another connecting to something at true ground. Molten amp results!
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Post by puffin on Nov 3, 2018 19:10:16 GMT
Yes got it. I must say I am intrigued by what I have read of Mike's experiences with the RTZ grounding box. I would never discount anything until I had heard it. However the price is quite a lot out of my league.
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Post by MartinT on Nov 3, 2018 22:33:43 GMT
Then see my review of the SGS Grounding Box which is very reasonably priced and has had a startling effect on my system's sound quality. |
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Post by ChrisB on Nov 4, 2018 8:04:36 GMT
In relation to your original question, Rob, I recall reading that the number of available watts is multiplied by four, but both the current and the damping factor will be reduced by half.
I also remember that the full fourfold increase in watts is rarely available in practice due to power supply limitations.
And that exhausts my entire knowledge of the subject! (And it's probably wrong anyway!)
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Post by dsjr on Nov 4, 2018 10:01:07 GMT
My geriatric Crowns had a bridging option and later versions even put a switch on the rear to most easily enable this. I have here my stereo D-60 which is 35 - 40WPC at 8 ohms and 64WPC into 4 ohms (back then, a 6 ohm load was regarded as fairly low impedance I remember). Bridging to twin D-60's gives at least 80W each into 8 ohms but the 4 ohm drive goes to pieces, along with the high damping factor these amps have always exhibited. I inherited these as a bridged pair and have used them for years that way, but noticed that the equally geriatric inherited Spendors tended to have their character 'exaggerated' by the bridged amps and it wasn't always good... I came by an age-related stereo wired D-150 which has the same Watts output (80WPC+ into 8 ohms and 4 ohm drive current limited deliberately, so not sure) and the high damping factor tightly drawn dry 'sound' of this amp suits the old boxes very much better if I want to hear less of the speakers and more of the music and this makes up my very vintage main stereo, which I can't really call 'HiFi' as I don't feel it is really by any modern standard.
I believe big Naim amps use bridging or at least did a few years ago in the top two or so models, although I'd have personally thought this not the best way to increase their capabilities.
I've never done this, but later Crown studio (at least) amps offered DUAL MONO/parallel internal wiring to increase the current output rather than the voltage. No idea at all, but these days with speakers being 4 to 6 ohms more routinely, this may be a preferred option.
Sorry I can't help further. Bridging totally alters what the amps are doing and your speakers may like or not like the change. It's certainly very audible, good or not...
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Post by ChrisB on Nov 4, 2018 11:29:10 GMT
Useful thoughts, I'm sure, from someone who-dunnit. Thanks Dave.
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Post by puffin on Nov 4, 2018 13:59:42 GMT
ChrisB, what you say makes perfect sense to me. DSJR, an interesting read of your experiences with bridged amps. They are working for me.
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Post by puffin on Nov 4, 2018 14:03:22 GMT
Then see my review of the SGS Grounding Box which is very reasonably priced and has had a startling effect on my system's sound quality. I had a look at that thread after reading about the RTZ. Is it just one connection IN and one OUT? Where do you connect it to? It looks like 2 4MM banana sockets? |
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Post by MartinT on Nov 4, 2018 15:03:54 GMT
There is one terminal post. I use a spade and 4mm cable (two). There is no concept of in or out for grounding boxes.
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Post by dsjr on Nov 4, 2018 15:37:02 GMT
In a way, my geriatric bridged amps work too, it's just in my case, the speakers 'character' seemed exaggerated slightly although I lived with and very much enjoyed the sound for years with no complaint. It obviously depends on the speakers and amps used I reckon.
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