DIY Filter Question...

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DIY Filter Question...

Postby MetroSonus » Sat Nov 10, 2012 7:53 pm

Ok nerds.. since we were talking about (or at least I was for a moment), what do the triangles mean in this diagram? I assume a diode?

Would it be possible to build a working filter from this diagram?
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Re: DIY Filter Question...

Postby ElectricPuppy » Sat Nov 10, 2012 11:44 pm

MetroSonus wrote:Ok nerds.. since we were talking about (or at least I was for a moment), what do the triangles mean in this diagram? I assume a diode?

Would it be possible to build a working filter from this diagram?

Yes, if you have a CEM3320, you could make a working filter from this diagram. :lol:

The little triangle on the left is a exponential converter, the delta-A triangles are probably current-controlled amps, the "B" triangles are gain amps. The topology of this filter isn't unusual, what was unusual at the time was that they put it all into a single chip.

I've seen this filter before as discrete components, not sure if I can find the schematic again, let me look...

Yeah, here it is. The trick with this is that you have to come up with a lot of matched transistors.
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Last edited by ElectricPuppy on Sat Nov 10, 2012 11:48 pm, edited 1 time in total.
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Re: DIY Filter Question...

Postby MetroSonus » Sat Nov 10, 2012 11:47 pm

Yea if you got it, lemme see :) I figured it was a stand in for some proprietary component. Maybe the triangle just shows direction of the signal flow..
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Re: DIY Filter Question...

Postby ElectricPuppy » Sat Nov 10, 2012 11:48 pm

Schematic added, see above.
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Re: DIY Filter Question...

Postby MetroSonus » Sun Nov 11, 2012 12:01 am

Thanks.. What's a matched transistor? A quick search doesn't explain much
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Re: DIY Filter Question...

Postby ElectricPuppy » Sun Nov 11, 2012 12:07 am

Transistors, even those of the same type, can have different beta (a characteristic of transistors). Matching means that you grab a pile of them, and test them against each other, with the goal of finding all the ones that have beta as close to each other as possible.
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Re: DIY Filter Question...

Postby ElectricPuppy » Sun Nov 11, 2012 12:09 am

Are you interested in this style of filter specifically, or just any VCF? I tried building that specific filter in the schematic above, but didn't have luck; I might try it again someday. The filter I *did* build and is in my DIY modular is a Moog ladder. More matched transistors. :lol: But it actually works.
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Re: DIY Filter Question...

Postby MetroSonus » Sun Nov 11, 2012 12:24 am

I like the cem in particular, but ill try any thing for fun or learning. I found a real simple vcf online id like to try. It had a good YouTube tutorial too.

why do you think it didn't work?
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Re: DIY Filter Question...

Postby midinut » Sun Nov 11, 2012 1:19 am

I suddenly feel way out-geeked by the company in this room. :freak:
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Re: DIY Filter Question...

Postby gregwar » Sun Nov 11, 2012 4:21 am

since we're on the topic i've been researching diy quite a bit the last few weeks. its been part of the electrical engineering and computer science in the mit open course warez.

i may start a blog on the education process called the self-education of gregwar and want to develop music/theory educational tools but thats a ways off at the moment.

i've built a few simple guitar pedals and a simple but loud as hell bass amp, can read basic schematics and such. i did take physics in my undergrad but i'm not exactly a wizard my major was political science lol.

i've got a good idea what scope, crimps and a better quality soldering iron to get and want to start with a rack of blacet research frac modules.

do you guys have any advice ?
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Re: DIY Filter Question...

Postby ElectricPuppy » Sun Nov 11, 2012 4:44 am

Midinut: Welcome to the treehouse! We geek freely here. :lol:

Metro: I'm not sure why it didn't work. It's entirely possible that it was a mistake on my part, because I was attempting to breadboard the circuit and that can get kinda complicated with keeping track of where all the connections are. Looking at the schematic, I don't see anything obviously wrong, BUT I'm not well-versed enough to be able to make a full analysis of it to try to verify it just by reading it. I'm still interested in trying to build it, though.

Gregwar: I guess it depends on what understanding you're trying to obtain. I've been puttering with electronics since I was 9, completely self-taught. But with that comes many holes in my knowledge. :lol: If you want to just learn how to build kits, then you're already on the right track. If you want to know how they WORK, that's more involved, and I think you'll want to start with a grounding on the basics. Try to find some books on basic electronics and read up. The book that comes to mind was great for me, but I'm not sure it's appropriate for a newb, "The Art of Electronics". I've refered to it alot. You might also check in at the Electro-Music forums, lots of DIY folks over there, and I think there's a number of threads or links to resources for electronics beginners.

And, for what it's worth, if you have questions, I can try to answer them. :wave:
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Re: DIY Filter Question...

Postby ElectricPuppy » Sun Nov 11, 2012 4:49 am

Dammit, you guys are rasing my DIY GAS. :lol:
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Re: DIY Filter Question...

Postby gregwar » Sun Nov 11, 2012 7:42 am

so far one of the most confusing things is ordering parts from mouser or whatevs. here's a medium short module parts list from ken stone's slope detector for example: http://www.cgs.synth.net/modules/cgs62_sd.html

Capacitors:
100nF (0.1uF) 6
C low 100nF See text 1
10uF 25V 2
100uF 25V 1

Resistors:
10R 1
1k 3
1k8 3
2k2 2
10k 5
47k 3
100k 3
1M 2
RLED pick to suit LEDs 3

Semi's:
1N4148 1
BC547 1
BC557 3
TL072 1
LED 3

Misc:
1M Lin pot 1
Ferrite Bead (or 10R resistor) 2
0.156 4 pin connector 1
CGS62 VER1.2 PCB 1

how do i convert something like this parts list into an actual order ? is it just that websites like mouser are difficult to figure out ?
:confuse:
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Re: DIY Filter Question...

Postby MetroSonus » Sun Nov 11, 2012 12:50 pm

At least in not the only one! I went looking yesterday and remembered why I never go there.

I don't think they certainly make it easy to browse.
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Re: DIY Filter Question...

Postby ElectricPuppy » Sun Nov 11, 2012 5:41 pm

OK, so lets pick a capacitor, like 100uF.

I'm sure you'll find hundreds of different 100uF caps at Mouser. At least he specified the voltage, so that immediately narrows down the range. But the next big cap characteristic isn't specified, namely the type. Caps come in all types, like ceramic, electrolytic, tantalum, polystyrene, etc. The reason that there are so many types is to deal with the other characteristics: Resistance, inductance (yes, caps have these in trace amounts and it can sometimes be important), temperature rating, size, lead configuration, and 'natch, price. What you pick depends on what really important in the context of how the caps is used in the circuit.

Since I don't have the schematic in front of me, I'll toss some random thoughts out about this cap:

100uF tells me that this is LIKELY being used as a power rail bypass cap. In that case, an electrolytic cap will do. Electrolytics can provide large capacitance values (like 100uF) in small packages. Way back when, a capacitor of that value would have been one of those largish silver cans you see in old radios. Today, though, a 100uF cap out to be the size of a pencil eraser.

The next important thing, since you already have a PCB that it need to go in, is to pick one with the correct lead configuation. For electrolytics, that's gonna be either radial or axial. Axials have one lead poling out of each end of the cap cylinder. Radials have BOTH leads poking out of the same end. Look at the PCB where the cap has to go; If the holes are only about 2-3 mm apart, then you want a radial. If the holes are instead about 10 mm or so appart, then you want an axial. Sometimes the PCB maker will silkscreen an outline of the cap where it goes; If it's a circle with the two holes in the circle, then a radial goes there. If it's a rectangle with the holes outside of it (usually), then it's an axial.

The BOM specifies 25V, so be sure it's at least 25V. The voltage specifies how high a voltage the cap can handle before blowing up (literally). If you pick a higher-voltage cap, you'll be fine but you trade in size for that; Higher-voltage caps are bigger.

The next thing I would usually pick for is temperature, but since this is just a DIY project, you don't need to worry about that; Just about any temp-rated cap will work for you.

Finally, price and availability, and VOILA! You've picked a cap. :thu:

Shoot, I forgot something: These days, surface-mount components are becoming more common than through-lead components. Fortunately, most DIY stuff is still through-lead, (as in, "the component lead goes THROUGH the board") so you should be able to eliminate all the SMT (surface-mount tech) components in Mouser's catalog. You dont' want to try to solder those things anyway, they're a pain.

Resistors:

Same kind of deal: Lots of charateristics not being specified in the BOM, but GENERALLY speaking, you'll be safe with 1/4 watt resistors if the BOM doesn't explicitly call for something heavier. Nearly all through-lead 1/4W resistors are axial.

If you don't already have the PCB, I recommend getting that FIRST and then figuring out what components you need for it, because the hole placement will dictate size and lead configuration for the parts you pick.
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Re: DIY Filter Question...

Postby gregwar » Sun Nov 11, 2012 10:11 pm

wow ep thanks for the advices

one other noobular question if i may, how do you attach the pcbs to the aluminium panels ? this has always been a mystery to me
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Re: DIY Filter Question...

Postby Plink Floyd » Sun Nov 11, 2012 10:24 pm

Hey, you guys are having a geek thread without me! You waited till I was outside ON PURPOSE!!

:mad:

I know you've been in good paws listening to teh Pupster, though. I've worked with so-called 'engineers' who didn't get it like he does. He's a smart doggie.

Mouser & Digikey are wonderful. Usta be you had to have a bunch of bulky 1000 page catalogs from RCA, NTE, Fairchild, Newark ect., and get new ones every year or two.

We know that before going to Radio Shack or Fry's Electronics or Guitar Center, we have to do our homework beforehand because we can't expect any intelligent help once we're there. But @ MouserKey we can do our homework right there because they link all the doodads to their respective datasheets. I already knew that any widget that has a name starting with "1N" is a diode, but beyond that, who knows what kind a 1N4148 is? The sheet knows all and tells more than most need to know. Physical size, mounting scheme, current rating, piv, switching speed and much more.

The sheets can also tell you if a cheaper part may be substituted, or a more robust one can be had for the same dosh.

TL072? pfft. Everyone knows the JFET-input operational amplifiers in the TL07x series are similar to the TL08x series, with low input bias and offset currents and fast slew rate. The low harmonic distortion and low noise make the TL07x series ideally suited for high-fidelity and audio preamplifier applications. Each amplifier features JFET inputs (for high input impedance) coupled with bipolar output stages integrated on a single monolithic chip.

Or did I?
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Re: DIY Filter Question...

Postby MetroSonus » Sun Nov 11, 2012 10:57 pm

gregwar wrote:wow ep thanks for the advices

one other noobular question if i may, how do you attach the pcbs to the aluminium panels ? this has always been a mystery to me



I once had the same question! Either with standoffs directly behind the panel or with brackets at a 90 angle. If you DIY it'll probably be either of those unless you have access to a sheet metal brake or you can have it dine, you can bend a tab or bracket right on the panel.
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Re: DIY Filter Question...

Postby gregwar » Mon Nov 12, 2012 1:58 am

i really like the serge shop panel format with its own housing, power, etc with 2 rows of modules each and banana jack patch points. i've been considering designing the panels and getting them etched from shaeffer

what about making your own panels ? the price for cnc machines varies wildly and is a hobby in and of itself lol. i've seen them cheaper second hand and i'm handy with grinders, dremel tools, welding, etc. i think it would be cool to be able to offer them to other diy tinkerers

what do you guys think about making pcbs ? is it impractical ? i've seen people building simple modules with bread boards from the roland system 100m. i've also seen cnc'ed cooper panels. is there a big advantage to going with teh 'green" pcbs ordered online ?

is it possible to make the 'green' pcbs ?
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Re: DIY Filter Question...

Postby Plink Floyd » Mon Nov 12, 2012 5:26 am

The easiest way to mount circuit boards to front panels is to use panel mount jacks, pots & switches:

Image

Image

Image

But panel mount parts are usually a bit more expensive, and it's more challenging to come up with a good pbc layout.

Does anyone know a way to print ink jet graphics onto a plastic sheet which then can be glued to our front panels? Then we could hide these on the front. (If you want to know how to set them in with a vise, ask me later.)
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