Some questions about filter/crossover design
« on: September 30, 2018, 08:09:57 AM »
Sup GDIY,

I thought I'd start a new thread for this project to keep the previous one on track.

Anyway, one evening I got bored and coiled a simple transformer as well as rolled a few capacitors. Then I took apart a small mixer build I had made from leftover components and put together a crossover.

Here's some testing I was making earlier (it was originally for a synth)



Here's the initial schematic for the crossover (ignore the component values, the prototype uses DIY caps)



Some components (I have some off-the-shelf caps too but I'm afraid they're either too small or too big.. the protype uses a preamp)



Here's the case with internals



And a close-up of one of the modules.. (edit : I might make a proper PCB if I get around to it.. cardboard isn't quite professional yet very retro)



As of now it looks something like this :



Here's a front shot (I accidentally painted the freq curves the wrong way around) :



Now, I have a few questions... I don't have a cap tester, or amps to do passive tests with, as well as having a go at calculators for cap values which brings into mind a few questions... is it generally speaking better to use inductors? Or multiple smaller caps to get close to the exact values? The high band is a stereo 1st order and the low is a mono cascaded 2nd order filter (I have some modules to up the HPF 2nd order or put them in series with tweeters)

The idea isn't to tweak the xover every once in a while to match the input signal hot enough to keep it running.. I may try with some other caps (I've been looking at Amp Ohm, Audyn and Nichicon) as it's very quiet atm.

Thanks in advance,

-ef

EDIT : one idea was to make the filter network active..

EDIT 2 : another question is whether it's a good idea to keep the 2nd and higher order filter resistor values the same with a single pot?

EDIT 3 : almost everything has been done so far by ear and intuition.. although I might make a calculation or two to make sure I'm on the right track every once in a while. Some of the modules have a nice thump to them.. others sound very gritty. My guess is that the caps last a year or so, because they're essentially tin foil, paper/cardboard, felt/fabric, stearine/parafin and oil. I made a few from aluminium and copper sulphate, sealed with hot glue.

EDIT 4 : I'll revise the schematic once I get around to it..
« Last Edit: September 30, 2018, 11:16:38 AM by efinque »


Re: Some questions about filter/crossover design
« Reply #1 on: October 01, 2018, 04:27:36 PM »
Interesting experiment with the home made caps ,
I think I understand what your trying to do ,
you have speakers with passive crossovers already ,you simply want to reduce the amount of low bass fed to the mid high amp  and at the same time reduce the highs being fed to the speakers handling the bass .
Its do-able and it will help you not to fry as many tweeters in your rig
Probably what you could do is ,buy or make a few simple passive filters and fit them into male to female rca connetors ,split the mixer outs into four, 2 left ,2 right ,one pair with HPF ,the other pair of adapters LPF . Just for illustration purposes  check the link ,if you find the right components for the job you could fit it all inside a metal tube like this ,nice and simple .  Basic rca male female plugs could be used along with some scrap metal  pipe to house it .The other bonus is  you can save your original enclosure /op amp and power supply for your next project. If you already have a volume control on your poweramps you wont need the volume  after the filter so you can save the pot for something else too .


https://www.ebay.ie/itm/2-Harrison-Labs-FMOD-200hz-Low-Pass-Crossovers-Subwoofer-Speaker-Subs/162605923075

boji

Re: Some questions about filter/crossover design
« Reply #2 on: October 01, 2018, 09:56:56 PM »
Damn, rollin your own C's.   That's hardcore DIY.

Re: Some questions about filter/crossover design
« Reply #3 on: October 02, 2018, 06:51:55 AM »
Damn, rollin your own C's.   That's hardcore DIY.

Thanks.

Performance-wise they're not the best I think, and the build quality isn't quite there either. Plus getting a closely "matched" pair for stereo use without proper tools requires some precision.

I just upped the HF band 2nd order, haven't tested it yet though.

EDIT : also fixed the grounding

EDIT 2 : I put a Nichicon cap in the 2nd pole of the LPF to see if it helps because it distorted the sound somewhat.. the HF 2nd pole uses some poly caps, nice and crisp. I haven't auditioned the LF band yet..
« Last Edit: October 03, 2018, 07:46:11 AM by efinque »

Re: Some questions about filter/crossover design
« Reply #4 on: October 03, 2018, 09:08:16 AM »
Here's the revised schematic as I promised..



It's missing a few values because of the DIY caps and the potentiometer values may seem strange since I made it from stuff I found while going through boxes and drawers, ie. happened to have at hand..

I have some off-the-shelf 100uF/25V Lelon caps as well as 100nF ones and a few spare 100uF/50V Nichicons too but since it seems to work there's no reason to change them. The lows aren't as saturated as before after switching to the Nichicon in the LF 2nd pole (edit : could it be due to the individual pole cutoff bands not overlapping?)

EDIT : I also confiscated a wall wart SMPS from an old WLAN router to power the thing so no more fooling around with an adjustable one..

EDIT 2 : of course I have no scientific data to back up my observations as every test is conducted differently. I could play tones 10Hz, 100Hz, 1kHz and so forth and measure the output in millivolts too.. unfortunately if someone is on to try one I can't measure the 1st order caps. A common filter theory states that the following cap should be 1/10th of the previous, I highly doubt mine are..

EDIT 3 : oh, C3..4 are 6,3V
« Last Edit: October 03, 2018, 12:32:44 PM by efinque »

Re: Some questions about filter/crossover design
« Reply #5 on: October 05, 2018, 12:33:51 PM »
I was thinking whether it would benefit from a compressor.. I made a prototype just today (edit : at first I was thinking a varistor or something but found a simple circuit to test..)

« Last Edit: October 05, 2018, 12:43:33 PM by efinque »

Re: Some questions about filter/crossover design
« Reply #6 on: October 05, 2018, 06:46:03 PM »
You could try epoxy dipping your caps to prevent the foils oxidising .
I can see your making the most from what you can scavenge ,and the giant scrap heap generated by electronic waste is a treasure waiting to be found . I prefer reusing components to new anyday ,cause the resources of the earth are finite and war is the only option to extract new stuff.

Re: Some questions about filter/crossover design
« Reply #7 on: October 05, 2018, 06:51:27 PM »
You could try epoxy dipping your caps to prevent the foils oxidising .

Yes, but I think the oil and parafin does that to some extent too.

Quote
I can see your making the most from what you can scavenge ,and the giant scrap heap generated by electronic waste is a treasure waiting to be found . I prefer reusing components to new anyday ,cause the resources of the earth are finite and war is the only option to extract new stuff.

For one-offs yes, but if and when you need spares they can be hard to find.

EDIT : added an L-shaped copper heatsink to the MOSFET, I had some left from making jewels. The design is from ESP, fig 1. I changed a few components where I had no matching ones. The 1Meg resistor is probably too large in the CV input.
« Last Edit: October 05, 2018, 07:50:10 PM by efinque »

Re: Some questions about filter/crossover design
« Reply #8 on: October 05, 2018, 08:27:26 PM »
Make the best you can with what you have my friend, and be proud of it .Your learning of electronics need not be impeded by lack of components only lack of imagination and ingenuity.

Re: Some questions about filter/crossover design
« Reply #9 on: October 06, 2018, 10:02:34 AM »
Here's a pic of the updated version with the compressor in the LF



EDIT : I was also thinking a clip LED for the comp/limiter

EDIT 2 : if anyone is interested I substituted R2 with a 10K trimmer, R4 with 4k7, C2 and C3 with 100uF/25V and VR1 with a 10K trimmer. Q1 is a IRF520 MOSFET. I've been doing tests with 12V and it didn't melt so I guess it's all good.

EDIT 3 : I'll post a revised schematic with the compressor in it too once I get it sorted..
« Last Edit: October 06, 2018, 04:10:21 PM by efinque »


Re: Some questions about filter/crossover design
« Reply #10 on: October 08, 2018, 04:02:06 PM »
Did some testing with an optocompressor too (using a photoresistor and a LED meter)... it reacts nicely (sort of like a gate) but introduces a fair amount of distortion.
« Last Edit: October 08, 2018, 06:09:25 PM by efinque »

Re: Some questions about filter/crossover design
« Reply #11 on: October 09, 2018, 01:19:53 PM »
Here's the revised schematic..



It's missing stuff like the input connectors for the preamp etc and some of the values are a bit off but I hope you get the idea.

EDIT : fixed a few things like component numbering and C8 was the wrong way around ..
« Last Edit: October 09, 2018, 11:16:44 PM by efinque »

Re: Some questions about filter/crossover design
« Reply #12 on: October 11, 2018, 07:55:42 PM »
Fitted the thing rack ears.. it's still missing the cover though.

Re: Some questions about filter/crossover design
« Reply #13 on: October 12, 2018, 07:09:45 AM »
Here's another build pic with the rack ears and the case finished..



 

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