DIY Plate Amp

**JonP** · 22 February 2009, 02:27 Sunday

Well, the plate amps have active crossover filters, not as simple as the passive ones at that site. With all the parts costs of the transformer and everything else, it's hard to beat the price of a off the shelf amp, but it's possible. Price out everything you need first to see what a pair of chipamps will cost you...

If you find a cheap old stereo amp, you might be able to get by with the passive, but you probably want 4th order rather than 2nd order, and as you add parts to do it you lose even more gain. You might end up needing a preamp just to make it work, then you might as well have built/bought your own active filter circuit.

It would also be better to have a highpass to roll the bass off the speakers, as well as the lowpass to roll the highs off the sub... now we're talking a dual active crossover filter. (look at the Sallen-Key link in that link you posted. Try not to let your eyes roll up in your head at the math...) :W

Look at Marchand's site, the XM1 crossover for an example of a small active dual crossover. You can buy one built, or get a bare board for pretty cheap.
Marchand XM1 It will need an external power supply

Another way to go, if you want something built already, is the Reckhorn F1, a self contained unit that does adjustable highpass and lowpass. Not quite as good as the XM1, but has it's own supply, is more easily adjusted, etc. It's about $50 shipped.
Reckhorn F1

You might also look at Rod Elliot's site for possible filter/crossover circuits, with possible boards to buy... you only really need a single lowpass, but having both is better. Maybe there's a cheaper, single filter there.

And finally, another way to go would be finding a cheap home theater amp in your budget, which would have internal high and lowpass filters for the sub and sattilites.

Hopefully all this will be encouraging rather than discouraging... you might spend a bit more than you expected, but you can end up with a even nicer than plate amp solution for a bit more than the basics.

**evilskillit** · 22 February 2009, 03:55 Sunday

Nah not discouraging, as always thanks for the help and input. Rod Eliott has alot of really great designs, I have already bought some boards from him and am cursing the oversized tip of my soldering iron right now as I try to put together my Class A headphone amplifier.

The Reckhorn F-1 is pretty interesting and could probably fit into my budget. Considering half of the fun of having 2 subs is being able to cross them over a bit higher and run stereo its somewhat of a let down that the thing downmixes the subs to mono but for $60 what do you expect.

But yeah basically a DIY circuit for something like the reckhorn is what I was hoping for, Rod has alot of great crossover designs but they're all statically adjusted by changing alot of different resistors, I'm surprised nobody has a DIY solution that does what the reckhorn does. Also the highpass would be handy but not totally needed in my opinion, my small bookshelves naturally cut off high enough that it shouldn't bee too hard to match subs to them using only the lowpass filter. I could find out I'm wrong tho.

**brent_s** · 22 February 2009, 14:26 Sunday

DIY electonic xovers have been attempted. Someone a few years back went so far as to have a number of circuit boards made so that the buyer only had to order the parts and plug (solder) them in. Problem is, it's still rather complex to assemble and there's no product support if the thing doesn't work after your finished stuffing the board. Added together with the lack of OEM type volume discount on piece parts, it's simply more cost effective to buy something like the Reckhorn or eD's eQ.2 or even a pro oriented Behringer/Ashley than to roll your own.

The P-E SA240 is currently on sale for $115. Except for wanting to run stereo subs, there's no reason to use two plate amps. The 240 with 240@4 ohms, would have more than enough power for your subs even if they're 4 ohm and need to be wired in series to show a safe load. It would also leave you with room to grow if you decide to upgrade to more capable drivers down the road.

-Brent

**evilskillit** · 22 February 2009, 14:41 Sunday

Hrm, you've a valid point. If I do that I'll have to build a new enclosure to fith both of them because I have already built separate enclosures to use them as bass bins

. I guess I could get the reckhorn b1. It seems really neat, its a bit pricy but if I can pull together then spare cash to buy it I could use it far into the future if I ever get around to buying an ep2500 and some serious subs or IB setup.

**A9X** · 22 February 2009, 20:40 Sunday

Buy a Behringer CX2310 to use as the xover and a secondhand AVR that has > 4 channels and analogue line level in to use as the poweramps.

**evilskillit** · 23 February 2009, 01:06 Monday

Wow the Behringer is a pretty good deal. I didn't know you could buy something like that for so few dollars. I'll have to keep it in mind if I ever decide to try bi-amping a set of two way speakers or something. However for pure subwoofer control the reckhorn b1 seems to have better control with the stereo variable high pass and low pass filters on the same lines plus the variable frequency variable gain parametric eq. I mean its not nearly as advanced as some things out there but for sub control for $99 it seems pretty complete.

On the other hand, I could get that Behringer and try bi-amping my recession buster kit as I have not put the thing together yet, heh.

**JonP** · 27 February 2009, 03:36 Friday

Originally posted by evilskillit

The Reckhorn F-1 is pretty interesting and could probably fit into my budget. Considering half of the fun of having 2 subs is being able to cross them over a bit higher and run stereo its somewhat of a let down that the thing downmixes the subs to mono but for $60 what do you expect.

But yeah basically a DIY circuit for something like the reckhorn is what I was hoping for, Rod has alot of great crossover designs but they're all statically adjusted by changing alot of different resistors, I'm surprised nobody has a DIY solution that does what the reckhorn does. Also the highpass would be handy but not totally needed in my opinion, my small bookshelves naturally cut off high enough that it shouldn't bee too hard to match subs to them using only the lowpass filter. I could find out I'm wrong tho.

Well, since you're not adverse to the soldering iron... I'm sometime soon planning on publishing some mods for the F-1. Interestingly enough, there are two paths for the A and B mono sub filters and outputs. If you could remove the summing and re route the L and R, they could be a single stereo pair, instead of the current summed mono pair.

I have come up with a fairly simple way with some cuts and a jumper, so you can have it switchable for stereo or mono. You could want either, depending on what you do with your system, and being able to switch it adds a lot of utility. I'm also planning on playing with the filter values, to make better sloped filters, (they start flattening out above 100hz) and possibly raise the crossover point higher, but haven't gotten far on that yet. If you're interested, send me a PM and I'll let you see what I've got so far.

If you get one, you should look for a thread on, uh, another forum that has the REW/BFD threads... where Bob Ellis did a nice investigation and listed some important improvement mods. I'll post my mods around when I get them properly nailed down and pics taken, etc...

**evilskillit** · 27 February 2009, 13:08 Friday

Thanks, I'll make sure to send you a PM here in a bit because I am definitely interested.
Howevever I thought everyone might be amused by what I am about to say. The subwoofer I'm bulding is a sortof absolute bottom barrel budget sub, thus far it has literally been assembled out of trash laying around my house with the exception of the enclosure it's self.

The drivers are Goldwood gw-1244 that I bought a couple of years ago to try to ressurrect a pair of old galaxy foor speakers with rotten woofers. Well that went miserably, they sounded bad. So I put them in the attic and forgot about them. Well it occoured to me I might be able to make subs with them so I went and got the drivers out, bought some damaged MDF from the home depot so my total cost so far was under $20. Now I need to power at least one of these guys, right? I went back into the attic and found an old Aiwa home theater in a box subwoofer that one of my room mates left a few years ago when he moved out. I thought maybe I could use the amp out of this thing?

So I opened it up and man what a piece of junk that speaker and cabinet were, but the amp actually wasn't half bad looking. So I took it out, and adapted it to drive one of the subs I built and you know what, it works pretty well. Has adjustable phase 0/180, adjustable gain, 3 low pass filter options, 60/100/150. And it seems to make more than enough power considering the goldwoods are way over excursion by 50 watts so this thing will drive one of them as hard as I need it to be driven.

So I have a fully functional sub that is, with room gain fairly flat to 30hz at about 105db for less than $20 out of pocket.

Now obviously I need a better amp and better sonic control that what I've got, eventually I'd like to get a stand alone power amplifier and something like the reckhorn, but in the mean time I'm just :rofl: at what I've managed to do with basically "junk"

**ThomasW** · 27 February 2009, 13:24 Friday

The Behringer CX2310 is quite good, particularly considering it's very modest price. Not quite as sonically transparent in the high frequencies as the much $pendier units from Marchand, but this isn't noticeable unless one has expensive playback electronics

Note that the CX2310 doesn't roll-off the bottom of the low frequency passband even when a sub is used. If you want to filter out all the subwoofer bass from the woofers that takes the CX3400

DIY Plate Amp

DIY Plate Amp

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