Sanwu 2.1 S ub-woofer Pre-amp Module w/ Sub Frequency, Sub Gain and Master Gain controls
Overview: A promising unit that suffers from two issues that significantly decreases its real-world usability.
The pre-amp is compact module measuring 1.25" x 3.25" using SMT technology. The wave soldering seems fine. The manual component solder was mostly fine except for a canted pot (easily fixed with a soldering iron). My unit came with the connectors and 6" tails as shown on the auction site. It also came with the silver knobs pictured (although that was not shown or mentioned in the offer). Power is via a standard 5.5 DC jack.
In addition to sub gain and sub LP frequency controls, the module supports a master gain control that can provide 4 X voltage gain to the L-R audio output and the sub-output signal already increased by the sub gain control. This is a nice feature for the chip amps with lower gain where many headphone outputs cannot drive the amps to full output. And since the op-amps operate at the module's supply voltage, there is plenty of headroom for additional sub gain above the L-R gain. On a 19 V laptop "brick" the module output 8 V p-p before clipping set in.
Testing:
I have not reverese engineered the module as of yet so I can only estimate some parameters.
First, the module seems to suffer from the two issues that plagued the PE sub-woofer pre-amp analyzed here. That is: (1) The highest LP corner frequency (Fc) seems to be around 100 Hz. More importantly, as the LP frequency is lowered, the sub-woofer gain also decreases. By 50% rotation of the frequency control, the Fc seems to be in the vicinity of 30 Hz, and, with maximum sub gain, the sub-woofer output signal is now lower than the L-R output. This makes the module useful range extremely narrow.
I'd have to have a personal need before I would reverse engineer and attempt to fix this board.
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