Which economy active crossover to build?

[kimbo]

I will shortly be building an economy (I'm trying to avoid the word 'cheap'!) active crossover for a two-way system. (I’m on a very tight budget but already have a pair of good amps) I am trying to decide which kit to purchase. Marchand, HEL, Silicon Chip or something else out there. I’m very interested in any members experiences with any of these or anything else.

The Marchand XM1 has been mentioned a few times on these posts and has reasonable figures for noise and distortion. It is also quite reasonably priced at US$25 for board and parts (2 required for stereo)
http://www.marchandelec.com/xm1.html
Harmonic distortion at 1KHz: less than 0.01%
Signal to Noise ratio: better than 110dB

HEL (High Efficiency Loudspeakers) market a stereo kit for US $86 which includes the power supply.
https://secure11.websitecomplete.com...t.asp?dept=531
http://www.highefficiencyloudspeaker...cDiagrams.html
They have responded to my email regarding figures that the distortion etc are too low for them to measure (?) and assuring me that extremely low noise and distortion are critical to their design.

The third option is the project from “Silicon Chip”Jan 2003. A kit is not available, however the cost of the board is AU$30 and parts would be under $50 or $60
http://www.siliconchip.com.au/cms/A_30278/article.html
Total harmonic distortion Typically .003% at 1V RMS
Signal to noise ratio -94dB unweighted (22Hz to 22kHz) with respect to 1V RMS

[planet10]

Check out the MOX group buy as well...

And if 1st order (or droopy 2nd order) is suitable a PLLXO is really cheap...

http://www.t-linespeakers.org/tech/f...ssiveHLxo.html

dave

[richie00boy]

Check out fellow Aussie Rod Elliott (ESP) site for a good project including PCB.

[kimbo]

thanks for the info Richie00boy and planet 10.

Although having no active components appeals to me I am drawn by the steeper slopes that an active design can provide, so PLLXO is out.

I had a look at Rod Elliott's site and it's pretty interesting. I had a close look at the circuit on it for the 2way and then had a closer look at the circuits on the HEL and Silicon Chip sites and realised that the three are almost identical. Don't know why I was suprised! Anyway two differences are that SC and RE use an extra op amp for an output buffer. Possibly a bit unnecessary - I'd prefer a lower number of amps in the signal path if possible.

Another difference is that as the SC version is 3way, and even if I only use two channels, there are more op amp stages (TL074 )used for each mid and LP section (six each!). I would need to add a link to bypass them.

The Marchand also has a number of LF353 op amp stages (six for two channels) but the circuit is quite different to the other three (HEL, SC and RE) and does not have an output buffer.

I am starting to lean towards either the HEL option - single board, no output buffer (5 NE5532 op amp stages per channel), incorporating the power supply or a pair of Marchand XM1's.

If the links in the original post don't work, try these.....
http://www.highefficiencyloudspeakers.com/

and this one for Rod Elliott.....
http://sound.westhost.com/projects.htm

[planet10]

Originally posted by kimbo
The Marchand also has a number of LF353 op amp stages (six for two channels) but the circuit is quite different to the other three (HEL, SC and RE) and does not have an output buffer.

The Marchand is a state variable filter (i've still not grokked how those work despite reading many references)

dave

[tiroth]

The HEL kit seems reasonably priced as far as such things go. I do think the extra buffer is a good idea if you are using the pots and driving lines...if the amps end up in the same box, then no worries.

I've also experienced nothing but good things from Rod Elliot. It's a bonus that you and he are both in Australia.

If you are interested in checking out MOX, there is a group buy open for the next week. The topology is very similar to the HEL...it offers a few more features, but it would be harder to setup than a complete kit.
http://www.diyaudio.com/forums/showt...ost&forumid=46

[kimbo]

The MOX looks very interesting...... took me a while to wade through the original thread, it's pretty long. However as I don't require any EQ I think you are right in that it is probably a bit of overkill and would take a bit more to set up.

The Marchand circuit is beyond my meager circuit knowledge.....I can see how the output of the chain of op-amp stages is fed back to the inverting input at the begining but the analysis is to difficult for me to grasp. I'll see if I can find some "state variable filters for dummies" site to satify my curiosity. Never-the-less the performance appears good.

I've also had a rethink on the desirability of an output buffer stage. Even though the interconnects will be pretty short and wont present a problem, the two power amps I'll be feeding are quite different, so perhaps a buffer is needed to avoid any changes in the response caused by the different power amp input impedances. Is this correct?

[Bill Fitzpatrick]

Buffers are your friends.

[catapult]

I get lost trying to trace state-variable filter circuits as well. My 3rd-grade-level understanding of the basic concept is pretty easy though. The idea is you can derive the highpass signal by subtracting the lowpass signal from the full-range signal. That's good for adjustable XOs because it always keeps the highpass and lowpass synchronized as you change Fc.

[Davey]

Yep, they're convenient because a four-gang pot can accomplish an adjustable frequency capability. However, state-variable filters have a couple of problems. The "derived" nature means you can't have slightly different high/low pass crossover frequencies and they also won't support asymetrical (different sloped high/low pass) operation. For the most part neither of those would be a concern, but for those DIYer's that really want to optimize their designs a Sallen-Key topology would be better.

Cheers,

Davey.