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Old 6th September 2011, 02:52 AM   #1
Lo_Tse is offline Lo_Tse  Canada
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Join Date: Dec 2006
Default Bridging parallel LM4780

Hi, Peter

I am thinking of building a "BPA200" kind of amp via bridging 2 LM4780 chips and planning to get 2 of your LM4780 amp kits to do that. Since your kit can be set up in parallel mode (for one LM4780), all I have to do is using something to bridge 2 of them (correct me if I am wrong). After spending quite a lot of time searching this forum, I cannot seems to find any detailed information on this plan of mine.

By chance, I came across a post of yours mentioning that you have run bridged amps based on LM4780 using an Edcor transformer as the bridging tool. It is so much simper than using a BLD such as the DRV135/135. My question is would you have any info posted somewhere on how to construct this "BPA200" type amp? Partcularly, I have read that the DC offsets between chips can be a hassle to tackle. Also, being a Newbie, I need pointers on how to set up the PSU for the bridged amp. By the way, can one use SMPS instead of a linear PSU since SMPS's usually are regulated and have soft-started mechanism built-in.

Lastly, regarding the use of the Edcor transformer (WSM10K/10K) for bridging. Does it mean that the input impedance of the amp will then be 10K? If it is, is it a bit on the low side for a power amp? I plan to use this amp with my passive preamp which is a transformer-based volume control whose output impedance is 5-600 ohms, would it work? There is a WSM15K/15K transformer which also has a 1:1 turn ratio, can I use it instead to boast up the input impedance a bit? Also, there is another transformer in this series that has a turn ration of 1:1.2, can it be used to obtained a 20% gain (in voltage I presume).

Sorry for asking so many questions. Hope you can shed some light on my queries. Thank you so much in advance.

Lo-Tse
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