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Help with unpowered sub
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Old 22nd June 2011, 06:21 PM   #1
Randallm is offline Randallm  United States
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Default Help with unpowered sub

I'm trying to get my 14 year old daughter interested in building a sound system. All she cares about is pounding base (this does not bode well for me).

I've seen 2.1 chip amp boards on ebay for $30. Each stereo channel is 18w, and the .1 is 2 chips for 36w. I want to build a couple of 2-way speakers, and a sub.

Conceptually, can I just mount a Dayton Audio SD270A-88 10" DVC Subwoofer in a box and run the .1 leads to it? I've only built a couple of pairs of speakers, and I've become accustomed to seeing powered subwoofers. I don't even know how to search for unpowered subwoofer designs (given 5 minutes of effort).

We're looking cheap, and not too powerful (turn that racket down!!!!)
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Old 22nd June 2011, 06:41 PM   #2
richie00boy is offline richie00boy  United Kingdom
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Well that would actually be a powered sub.

It is not clear if the board has a low-pass filter for the sub. For the price buy it and if it needs a filter you can probably add something in. Don't know how they do it for the price.

A 4 ohm load might be a struggle for that amp though.
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Last edited by richie00boy; 22nd June 2011 at 06:43 PM.
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Old 22nd June 2011, 06:51 PM   #3
Randallm is offline Randallm  United States
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Isn't that price amazing? I wonder if they're seconds that failed Quality Control. I meant to post an 8 ohm speaker.

I know the sub is 'powered' from the board, but it's not powered from a separate plate amp ON the sub. I'm just trying to validate my belief that this configuration just replaces the plate amp on the sub with the chip amp on the board. (and solicit other relavant observations - e.g., I wondered if 4 ohm would be easier or harder to drive)
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Old 22nd June 2011, 07:00 PM   #4
Cokewithlime is offline Cokewithlime  Canada
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I haven't had experience with that particular board but Lepai (another Chinese manufacturer) has a pretty good rep in the DIY community here's a link to a Lepai version of the 2.1 board you are looking at.
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Old 22nd June 2011, 07:32 PM   #5
sofaspud is offline sofaspud  United States
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Quote:
Isn't that price amazing?
And the kit is <$17 including shipping! Don't know about the QC questions, nor would I call the TDA2030 a great chip, but it's good enough at this great price. Yes you can connect the amp right to your passive speakers; it seems likely the board contains a LP filter for the sub. The 4-ohm connection of the SD270A-88 ought to be fine. For all things subwoofer I'd recommend a look at Brian's Subwoofer DIY Page.
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Old 22nd June 2011, 07:32 PM   #6
richie00boy is offline richie00boy  United Kingdom
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I think the one randall linked to looked better, at least the impedance rating and power claims are real.
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Old 22nd June 2011, 07:49 PM   #7
Dr_EM is offline Dr_EM  United Kingdom
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As far as I can tell this board has 3 inputs. You'll need to sum your stereo signal and low-pass filter it off-board to feed it to the '.1' input. The inputs and outputs visible on the board don't really follow this theory though so it's a bit of a mystery. I'd email for a schematic.

Also, it does state that 2 chips are used BTL, and hence for that '.1' output you can use an 8Ohm speaker minumum (effective 4Ohm load on each chip).
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Old 22nd June 2011, 08:06 PM   #8
sofaspud is offline sofaspud  United States
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Hmmm... I thought that was the LGR input beside the pot at the lower right in the photo, with the terminal block outputs at the opposite end behind the caps. The speaker impedance is good advice. That Dayton DVC may not be the best choice here.
What I mean is I'm taking it that the summing is done on the board by the DIPs, and the pots are just volume control for each channel. I'd try to get a schematic in any case.
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Last edited by sofaspud; 22nd June 2011 at 08:36 PM.
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