Active Crossover Kit for DIY Speaker Builders
The Simple and Flexible Active Sub Kit
with Prebuilt Regulated Power Supply
$47 (USA shipping included)
Introductory Price; Subwoofer not included ;^)
Basic Idea:
If you have an old stereo amp laying around, you can use it with this kit to build a bridged or unbridged powered sub amp that is highly tunable to your needs. This kit was designed to be cost-competitive with, yet more flexible than any of the active sub amps currently offered to the DIY sub builder (that I am aware of). It was also designed to be usefull for those with the bare-minimum equipment.
You need at least: Main integrated amp and main speakers (sats).
A Subwoofer
An amp for your sub. Any amp will
work (old reciever, etc.)
My active filter will get a signal from the pre-out, sub-out, or headphones-out of your main amp. It will then cut out the high freq's (as well as other functions), and then pass this signal to the amp you will use to power your sub.
Stage of Project / Ordering info (4/13/00)
The $47 is for a mono circuit (but you can hook as many subs to it as you want). Add $26 for a stereo version. If you need even more, contact me for a lower price. I am now shipping kits. Today, I have seven more pre-packaged and ready to go. The price covers shipping costs plus the recently added phase and volume control.
I recently signed up for a PayPal (3rd party) account, which obviates the need for me having to worry about personal checks or you having to worry about money orders. You can sign up with PAYPAL to pay me by credit card using this link: https://secure.paypal.com/, and type my email address (JohnPomann@yahoo.com) as the referral. You might get $5 for signing up, and I might get a $5 referral bonus (not sure - their promotions have changed a few times now). Alternatively, please e-mail me to get my address if you want to pay by MO. In either case, be sure to send me your address.
Background:
After listening to the desires of many sub-builders, I finally settled on a design for a 'universal' active subwoofer filter kit. In addition to having a very low cost, it features the popular functions most people want. These functions are all individually selectable / bypassable. A PCB is provided to solder the kit onto. Sockets are provided to change jumper settings and R values to program the filter.
Here's what it can do:
1) A sub lowpass to mate to the sats with a Fc range of 28 - 134 Hz, selectable in steps smaller than 1/3 octave. The slope of this lowpass filter can be varied between 1st, 2nd, 3rd and 4th order by changing the resistor socket settings.
2) A 2cd order highpass useful for variable bass boost, or as a rumble filter. The center freq of this filter can be adjusted from 12 to 45Hz in steps smaller than 1/3 octave. Boost is continuously adjustable from less than 1 dB up to about 8 dB.
3) An additional output for bridging a stereo amp to use with a mono sub.
4) Volume Control and Phase Shift Control (recently added).
5) There is no active highpass for your sats. If you dont have a pre-amp, then you could not use this anyways. Consider a passive highpass for your sats, or just leave them "full-range." If you DO have a pre-amp, then you should consider adding an active highpass to the sats. There is enough room left over on the PCB to add this later if you want (I dont support this yet, but I could give you the parts if you want). Alternatively, you might consider the higher-grade kit on my main page which does cover this.
Please see an independantly-developed active sub kit very similar to this created by Phil Abbate of PhilsAudio: http://philsaudio.stryke.com/apprenti1.htm. It lacks the variable bass boost and bridging, but is otherwise very similar.
Difficulty Level: Moderate
You will need to know how to solder. I upgraded the difficulty to 'moderate' because mounting and soldering all the components will take some time and care. To give the greatest number of people access to the kit, a detailed PCB stuffing guide is included to show where every part should be placed on the board. Furthermore, a high-mag photo of the finished board is provided. A pre-built fully regulated power supply is included. A table in the docs shows the jumper settings required for the most popular functions.
Advantages of this Kit Over Pre-Fab Active Sub Amps
1) Cost. This is clearly true if you have an old stereo amp laying around anyway. Since many people are 'upgrading' to home theater, there are tones of perfectly good stereo amps starting to collect dust in attics across the U.S. - just ask a friend or visit a garage sale. Alternatively, you can buy a new and rather powerful "plain stereo amp" for about $100 nowadays.
On the other hand, the Apex Jr. active sub amp as well as others certainly provide a lot of value for the money. Not as flexible as my kit, but a real bargain none-the-less (and hey - it's preassembled). Anyway, you might want to check out their web page.
2) Amp flexibility. Hand-pick the amp you want to drive your sub(s). 50 watts, 5000 watts; unbridged, bridged. You decide.
2) Lowpass flexibility. I dont know of any reasonably-priced sub amp that offers 1st through 4th order lowpass filters. If you have vented sats (4th order rolloff), and want to match these to your sub, this feature might be of interest to you. Furthermore, this lowpass can work in conjunction with the 2cd order variable sub filters found on many home theater amps for even greater flexibility. The max lowpas freq is 134Hz for 4th order filters and 188Hz for 1st and 2cd order filters when using the standard R's I supply. If you need to go higher, then let me know and I will add a few more R values to your kit.
3) Bass boost / rumble filter flexibility. You can control both the freq of the boost and the amount of boost independently. This gives you great flexibility in your sub design. In many cases, you can lower the F3 of your sub by 1/2 to 1 octave (at the expense of increased power consumption, and decreased transient response). You can play with this filter to find the trade-off that suits you best.
If you set the filter to the lowest freq (12 Hz), and smallest boost (<1dB), it will act as a rumble filter. Raise the filter freq from there to get rid of as much rumble as you desire. Finally, you can choose to bypass this function.
Why is the cost so low?
Because these filter functions deal with only low-frequencies, mylar caps may be used instead of polypro's. Furthermore, this circuit places very few demands on the op amps. NE5532's are excellent for this application. Because the circuit is small and simple, a PCB is provided to solder the kit onto (no bread-board). I feel these components fit this application very well. I dont believe that costlier components would be 'hearable' an an AB test. However, I'm open to debating / hearing your thoughts on this question. Anyway, if you want upgrades, I have them.
This is a stereo-summing or 'mono' kit. However, you can use it to drive as many subs as you want. I could have built a bare-bones stereo version for about the same price, but it would not have all these features. If you want true stereo subs, you can buy another identical kit minus the power supply for an extra $26. For those of you who need no power supply, the first kit will cost $35, with each additional being $26 (shipping included).
As usual, I dont expect to get rich off of this (I think the price speaks for itself). This is a hobby of mine. It takes quite a bit of time to design the docs, layouts, photos, etc., not to mention counting all the sorting all the components in each kit. When I drive by the post office, and the line looks really long, I'll probably wait till tomorrow to mail you your kit.
Here's the Photo:
This is easier to build that it might appear because the docs have such a great stuffing guide. The left-most pot is volume control. The right pot is boost level control. The phase control pot is not shown (panel-mount). R's plug into the sockets to program the freq's and slopes of your filters. There are also sockets for RCA In and RCA Out, so your can switch your RCA Out from unbridging to bridging and back.
Here is what you MUST have to build the project (some Radio Shack part #'s provided):
1) Soldering Iron (I like the fine, flat tips)
2) Wire strippers (RS#64-2129, $2.99)
3) Small spring-loaded diagonal cutters
4) Small spring-loaded pliers with small 'teeth'
5) Solid Copper hook-up wire (RS#278-1221, $4.49, 22AWG red, black, green
90 ft total); You might instead consider 24 gauge to plug into the sockets
more easily.
6) Stereo headphone plug or RCA cable to get a signal from your amp or preamp;
another to send to signal to the woofer amp.
Optional Items:
7) RS#274-852 2 RCA gold-plated connectors ($2?) Get 2 packs of 2 if you
want to use RCA jacks for both ins and outs.
8) RS#62-5003 Radio Shack Getting Started in Electronics, by Forest Mimms,
especially if you are new to soldering (read the section on "How to Solder").