DIY active x-over for 2.1 application

peter_m

Member
2007-05-14 7:33 am
Hi everyone,

I am looking for an active crossover, like the ones you find in the average HT amp. With a variable frequency from 40 to 200hz. I need it to have both high-pass and low-pass outputs. This way I can re-use existing amps I have lying around for a 2.1 project.

Any chance of you guys seeing an inexpensive DIY design floating out there?

Peter
 

peter_m

Member
2007-05-14 7:33 am
pedroskova said:
You could pick and choose from Linkwitz. Everything is there, just add psu.

Looks like what I am looking for... Ready made PCB are for cheaters!

Ok, what I want is this: http://www.linkwitzlab.com/filters.htm#3 I got the spreadsheet to calculate the R and C values. Now what about the OP amps? What are the IC modes numbers that I need? It doesn't specify anywhere. In a different forum someone mentioned the "NE5532".

Also does it require a special power supply or anything relatively clean will do?

Peter
 
Daveis said:


Aren't there issues with some of the modern fast opamps and board layout?

For instance, you couldn't just wire perf board or bread board could you?

I haven't tried it yet(but I will be). With perf board, there is no reason why it can't be done since you can place the components as close or closer than with a pcb. I want to try a breadboard just for convenience sake, with 0.1uf decoupling caps right next to the +/-ve pins...don't know if this is too much to ask for the other components.



Also does it require a special power supply or anything relatively clean will do?

search the electronics discounters for regulated +/- 12-15 VDC psu's. I've seen a couple for ~$15USD that have more than enough capacity, but I don't have an URL handy at the moment.
 

peter_m

Member
2007-05-14 7:33 am

F1 FAN

Member
2006-06-21 3:39 am
Polypropylene caps are the recommended type and 15 uf is way too large for placement on a PCB. Cap values are usually in the .022uf -1.0 uf range.It might be advantagous to use bigger caps (.47-1.0uf)for lower frequency crossover points (say under 200hz )as this will allow the use of smaller value resistors.Apparently the smaller resistor values produce less noise.Also good op amp choices are the OPA2134,OPA2604 and the excellent LM4562.
 

peter_m

Member
2007-05-14 7:33 am
F1 FAN,

Thanks for your input. Yes 15 nF is what I meant... Ok, so I should try to aim for a C value that allows for the smallest R values.

As for the OP amps, can you help me narrow it down? Also will the increase of price be justified by a noticeable increase of sound quality? How much better then the NE5532 ?

Also, are the different OP amps directly interchangeable without having to adjust anything?

Peter
 

F1 FAN

Member
2006-06-21 3:39 am
peter_m said:
F1 FAN,

Thanks for your input.
Your welcome
As for the OP amps, can you help me narrow it down? Also will the increase of price be justified by a noticeable increase of sound quality? How much better then the NE5532 ?
Honestly Im' not sure how much of an improvement an OPA2134 will be over the old NE5532 ,but the OPA2134 is a much more modern device that Burr Brown designed for audio.I use these in my active crossover and they sound very good.The price difference between these two should be insignificant.The 5532 might cost $1-$2 and Digi Key sells the OPA 2134 for $3.32 ea.
Also, are the different OP amps directly interchangeable without having to adjust anything?
Yes most dual op amps can be interchanged without other changes to the circuit being neccessary.

I would recommend ordering a Digi Key catalog.http://www.digikey.com/ They have a Canadian depot.
 
Originally posted by peter_m
Looks like what I am looking for... Ready made PCB are for cheaters!

LOL, I admire your DIY spirit Pete! Here is what I used to make an active filter circuit. It was a summed L+R low pass which I installed in the chassis of my subwoofer amp. A simple toggle switch (on the back) allowed the filter to be defeated for full range duty. The circuit ended up being the size of my thumb with a small external 3VA transformer for power(+/-6 volts). The board is called vector board and requires cutting the tracks to suit with a knife or small drill bit (~0.100"). Inserting the drill tip into a hole and giving it a quick twist is all it takes to divide a track.

Since I didn't need a chassis to house it, the cost came to about $25CDN. If you could scrounge an old chassis and transformer I'd guess you could do your 2.1 project on one pcb for about the same cost. As others have pointed out the power supply is the key to keeping costs down. Regarding opamps, I tried LM358's and Burr Brown devices in the same circuit and heard no difference.

http://rocky.digikey.com/WebLib/Vector/Web Photos/New Photos/8022.jpg
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=V2018-ND

Kevin