I briefly measured the LM3886 x 3 parallel board this morning. THD vs freq for one, two in parallel and three in parallel are measured.
Load of 4 Ohm was also tested. When using one 3886, the on-chip protection activates periodically when doing low frequency (~ < 500 Hz) test. No such protection operation happens for the same output level for higher frequencies (>1kHz). The problem goes away when using 3886s in parallel.
Posted 15th August 2011 at 05:14 AM bypanson_hk Updated 15th August 2011 at 05:58 AM bypanson_hk
The DC offset of the three 3886 are interrelated. Hence, adjusting them all 0.0 mV is tough if not impossible. I now made them all 8.9 mV to achieve DC balance. Next will adjust the AC gain. DC offset may need readjust again. This is a game for $ (cost foe DC servo) vs time.
Posted 12th August 2011 at 08:14 AM bypanson_hk Updated 12th August 2011 at 08:28 AM bypanson_hk
Here is assembled LM3886 x 3 (inverting) board. I think you may see similar/identical board before. Who is the original? Copycats are everywhere. The kit comes with a Solen like film cap. Most likely a fake one. The measured data is not too bad though. The three LM3886 are samples from NS. Original!
The kit provides 0.2R 5% instead of 1% for paralleling the three 3886. Gain setting is by 200k and 10 k 1% metal film. Three 50 k trim pot are provided for DC offset adjustment. I do not solder the three 0.2R first in order to see the gain of the three 3886s.
One of the 3886 DC offset can't be adjusted to 0.0 mV. It has ~25 mV. The other two can be turned to 0.0 mV. This may cause a problem among them. Let see.
I can resist the low price from TaoBao. An LME49810 300W amp kit (w/o heatsink) is just RMB 200.00, ~$32.00. Similar "identical" kit is available from ebay for similar to higher price. So, it is time to buy some and evaluate. I just ordered such an amp kit and one 3886 x 3 amp kit.