Sanwu Sub-Woofer Pre-Amp Module - Test Results

[Millstonemike]

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.

[donradick]

Thanks Mike!

Appreciate your expertise and sharing.
One of these days, the CN shops will finally get the basic design correct, then we'll have some fun.

[Millstonemike]

Thanks Mike!

Appreciate your expertise and sharing.
One of these days, the CN shops will finally get the basic design correct, then we'll have some fun.

Thanks.

As a side note, this module could provide a nice L-R line level boost (sub channel not used) for those applications where some line level gain is needed.

[a4eaudio]

...This makes the module useful range extremely narrow.

Interestingly, if I was to use this module it would be for a Voxel build paired with Quarks. I figured the Subwoofer would need to be crossed at 100-120Hz. If 100Hz was a good crossover point with the Quarks, the extremely narrow useful range just happens to be what I need. Am I interpreting your post right?

[Millstonemike]

Interestingly, if I was to use this module it would be for a Voxel build paired with Quarks. I figured the Subwoofer would need to be crossed at 100-120Hz. If 100Hz was a good crossover point with the Quarks, the extremely narrow useful range just happens to be what I need. Am I interpreting your post right?

Yes, you are. The only caution is that ~100 Hz Fc is an estimate. But at the price you'll find it for, I would go for it. And there'll be the several week order delay via the "slow boat" from China.

And it will provide a good ability to boost the sub signal above a boosted L-R signal as long as the freq. pot is at/very near full clockwise rotation.

Please let us know your outcome ...

[RexDog]

Yes, you are. The only caution is that ~100 Hz Fc is an estimate. But at the price you'll find it for, I would go for it. And there'll be the several week order delay via the "slow boat" from China.

And it will provide a good ability to boost the sub signal above a boosted L-R signal as long as the freq. pot is at/very near full clockwise rotation.

Please let us know your outcome ...

That sounds pretty consistent with my experience with this little preamp.

[Wushuliu]

I think finding a TPA-based 2.1 (for cheap) that works well will be tricky, but in other news there is now a cased Nobsound mono TPA amp you can buy for only $25 (not incl. PS). So 100w mono that can do 2ohms per the TPA3116 specs. Available in 'full frequency' for speakers or 'low frequency' for subs. Plug and play. Incredible.

[IBM5150]

Thanks for the review Mike.
What is the effect of the middle sub gain knob? Is there any high pass XO for the mains or are they run full-range?

[Millstonemike]

Thanks for the review Mike.
What is the effect of the middle sub gain knob? Is there any high pass XO for the mains or are they run full-range?

The middle knob adds gain to the sub. The "volume adjust" applies gain to both the L-R channel and the sub channel (adds to the sub gain). So yu cab level adjust between the and L-R speakers using the middle pot. Then control overall volume.

There isn;t any HP on the L-R.