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-   -   bridging ucd amps (http://www.diyaudio.com/forums/class-d/80854-bridging-ucd-amps.html)

mazurek 4th June 2006 02:52 PM

bridging ucd amps
 
First, I'm not knowledgable enough to know search terms or a good starting place, so reply with them if this question is too obvious.

I want to build a four channel ucd 180 amplifier, where two of these channels can optionally be bridged together. How does one bridge two of these modules?

The problem context is that I have bookshelves on top of a bass bin with a 12" driver, and I would like to move to an integrated floorstander with 2x10" drivers. So in the meantime, I would like to use two bridged ucd-180's to run the 12" subwoofer, and once I get the other speakers built, I would have each ucd-180 run each 10".

Thanks,
Lee

mazurek 4th June 2006 07:24 PM

Can I just invert the input on one of the modules? Then connect the two grounds between the modules, and use the inverted amps+ terminal as the new negative terminal?

When I'm inverting the amp input, would I just connect the positive to inverting input, and rca shield to positive and ground?

guyv 5th June 2006 03:54 AM

Search the posts by Bruno Putzeys. While he might not cover the basics I recall he provided some tips into UcD bridging.

ghemink 5th June 2006 03:58 AM

Quote:

Originally posted by mazurek
Can I just invert the input on one of the modules? Then connect the two grounds between the modules, and use the inverted amps+ terminal as the new negative terminal?

When I'm inverting the amp input, would I just connect the positive to inverting input, and rca shield to positive and ground?


Somewhere in some of the threads there is some info on bridging them. In fact I plan to try it as well. The way you describe it should be OK. One more thing that was mentioned was that when bridging, you may want to synchronize the oscillation frequency of both modules, this seems to be possible by adding a small capacitor of 47nF or so between the two + output terminals of both modules. I think Bruno mentioned somewhere that 47nF was enough.

Best regards

Gertjan

guyv 5th June 2006 04:08 AM

Also remember that you will get twice the voltage but that the bridged amp will "see" a load that seems half the actual impedance. So if your 12" woofers are 8 ohms it is good but if they are 4 ohms you might get less benefit from bridging. No benefit for amps that don't go under 4 ohms but since the UcD has high current capability it might help.

If your 12" is 4 ohms I would try a single UcD180 first since it will give you a full 180w of power.

mazurek 5th June 2006 04:08 AM

EDIT - you guys replied while I was making my ascii art

Thanks, I get this from Bruno

"Wire the differential inputs in opposite phase and connect 47nF from one output to the other (=in parallel with the load)."

I guess I'll just connect one out of phase.

Just checking though, after its out of phase, the connections go from this to this right? (| signifying wire, _ signifying jumper)

Code:

|  |  |  |
|  |  |  |
+  -  -  +

|          |
|  _____  |
+  -  -  +


mazurek 5th June 2006 04:17 AM

I'm using a 12" Dayton RS HF, it is 4 ohms.

I simulated using WinISD, with a linkwitz transform and first order highpass which combine to get me an F3 of 25Hz, it needs exactly 180 VA according to the simulation. I suppose I could live with the UCD 180, but I know they get to be current limited as the driver dips in impedence down to 3ohms.

Are you saying that the built in current limit on the UCD modules will prevent me from gaining any benefit from bridging? Alternative solution is just to live with zero headroom margin, which is probably ok.

guyv 5th June 2006 04:32 AM

The power you get is RxIxI. When R is 3 you need I to be square root of 60 to get 180W or about 7.75 amps, well within the capability of one UcD180.

On the other hand when bridged the amp is still limited to 10 amp so your only benefit is to get twice the voltage to drive high impedance loads. In your case the load will look like 1.5 ohms so 1.5x10x10 (10 amp peak current) gives you only 150w of power for the 3 ohm region of your driver and that's pushing the UcD180 to the limit.

Conclusion: it is detrimental to bridge for a 3 ohm load, and even for a 4 ohm load your single UcD180 will have more headroom.

Guy

guyv 5th June 2006 04:36 AM

In theory you could parallel the UcD180 instead of bridging them but:
1. I don't know if this is feasible
2. 20 amps might fry your 12" driver?

Guy

ghemink 5th June 2006 07:12 AM

Quote:

Originally posted by guyv
In theory you could parallel the UcD180 instead of bridging them but:
1. I don't know if this is feasible
2. 20 amps might fry your 12" driver?

Guy


Using two UcDs in parrallel does not sound like a good idea to me. If the gain is a little bit different, they will start "fighting" with eachother. The output resistance of the UcD is very low, so one of the modules will supply a lot of current while the other will suck it away, if you know what I mean :-)

Gertjan


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