GC Transformer Considerations for 4 ohm spk

[toque_101]

Hi Everyone,

Going to be assembling my LM3875 BrianGT kit soon and was wondering which transformer to go for. I currently have 8 ohm (~88db efficiency) speakers but will probably be moving to 4 ohm (89db efficiency) speakers eventually.

Currently I am running my lm3886 gc on 500va, 17.5 volt secondaries with no problems into my current 8 ohm speakers.

So, the transformer I was going to get is dual 18V, 300VA plitron. But, does the lm3875 require a higher supply in order to drive a lower impedance speaker? I was thinking of going to 20 or 22 volt secondaries instead? Any comments?

-steve

[jeff mai]

Originally posted by toque_101
So, the transformer I was going to get is dual 18V, 300VA plitron. But, does the lm3875 require a higher supply in order to drive a lower impedance speaker? I was thinking of going to 20 or 22 volt secondaries instead? Any comments?

No - it's just the opposite, in fact. The LM3875 does better with lower rail voltages into 4 ohms. It has to dissipate less heat this way. The ideal situation, however, is to use your LM3886 amp on the four ohm speakers. It was designed to run at 4 ohms.

Read the National Semiconductor datasheets for these chips. It tells you all about this. Also, there is a lot of material you could find by searching this forum. This issue has come up literally dozens of times.

[Leolabs]

True,lower supply rail safer for lower load

[toque_101]

Thanks for the responses guys!