"Funky MF (Multimode Filter)" - LM13700 Multimode Envelope Filter

[flo]

I works by using an OTA which is a voltage controlled current source.
Operational Transconductance Amplifier:
http://en.wikipedia.org/wiki/Operational_transconductance_amplifier

Just like with a LED/LDR combo or other means, the OTA provides a way to change the cutoff frequency of the filter usually wiring it as a voltage controlled resistor.

Check also the datasheet of the LM13700 OTA chip.

[frequencycentral]

I thought I would take up the challenge of creating a layout for this effect.  Would someone kindly double check this?  I am not sure I am going to build it, but thought since people were asking for a layout that I would create one.

Here it is:
http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=38445

If there are any corrections or errors please let me know.

Cheers,

Steve

That's a very impressive piece of work Steve - I couldn't do what you've done there.

Thanks and respect. I'll check it over in detail over the weekend.

I hope you guys don't mind this, but I'd like to ask a few questions about how this thing works. From what I can tell, like in the meatball, this has one section that uses an opamp to convert volume into voltage. Then that voltage is put into one part of the lm13700. There seems to be two filter stages, which, I think I read somewhere, increases the "talky" sound of the wah. Where does the parametric filter come from? I will admit I have no idea how the lm13700 works, so maybe there's something there that I'm missing. Any explanation would be awesome.  Thanks.

Worth reading: "The Technology of Auto-Wahs / Envelope-Controlled Filters" at http://www.geofex.com/

.....and http://en.wikipedia.org/wiki/Voltage-controlled_filter

I think I've read both of those, so let me be a little more specific. How does this filter work without using LEDs? The one in the GEOFEX article uses LEDs and the Meatball that I built uses LEDs. The FSH-1 and this project don't, and I've been curious about the difference. Also, is this one more controlled in sound? I know the meatball, with certain settings, can have some strange sounds. Then again, that probably depends on the detector, not the filter. Anyway, thanks again, and I'll take another look at those articles.

Aah, ok! The LM13700 belongs to a family of chips known as OTAs, or Operational Transconductance Amplifiers (along with LM13600, CA3080, CA3094, and some others): http://en.wikipedia.org/wiki/Operational_transconductance_amplifier

So - imagine an opamp with the Meatball's LED/LDR combination built in to it. That's not actually how it works, but probably the easiest way to think about it. Or imagine a compressor with a side chain.

The OTA's Iabc (pins 1 and 16 on the 13700, as it is a dual OTA) input accepts a current which defines the output. So where other circuits use a LED/LDR or a FET as a voltage controlled resistor, an OTA circuit uses a voltage applied via a resistor to the Iabc input to do the same job. Probably not the most technical explanation, but that's how I rationalise it - Mark Hammer will no doubt be along shortly with a more detailed/informed explanation!

Your second question - 'is this one more in controlled in sound?' - you're probably right in saying that it depends on the detector part of the circuit. OTAs are used a lot in synth VCFs/VCAs, and can be very controlled, as there is no detector in those circuits.



EDIT: thanks flo - we were typing at the same time. I posted anyway.

[orangetones]

UPDATE:

I have moved the pads around in the top left corner of the board so that they are all in a single line now.  This doesn't change any other part of the board, so the layout really hasn't changed at all, just the lining up of those pads.  I have uploaded the new file here and deleted the other one from my gallery.

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=38490

Cheers and thanks for the compliment Rick.  I just hope I haven't committed any major routing errors or unconventional routing practices.

Steve

[frequencycentral]

UPDATE:

I have moved the pads around in the top left corner of the board so that they are all in a single line now.  This doesn't change any other part of the board, so the layout really hasn't changed at all, just the lining up of those pads.  I have uploaded the new file here and deleted the other one from my gallery.

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=38490

Cheers and thanks for the compliment Rick.  I just hope I haven't committed any major routing errors or unconventional routing practices.

Steve

I've spotted one thing to be aware of:
 
LM324 - pin 4 +ve, pin 11 ground.
LM13700 - pin 6 ground, pin 11 +ve.

.....so it needs bearing in mind that LM324 pin 1 should be connected to the 1n4148. In prctice, this doesnt change anything else, as the LM324 pinouts are so symetrical. Worth indicating which is pin 1 on each chip though.

I'll do some more checking.

[orangetones]

Pin 1 on each IC is noted by the square pad.

[captntasty]

Fantastic layout - I'm always amazed how you guys come up with these layouts.  Thank you, thank you, thank you!

[frequencycentral]

Pin 1 on each IC is noted by the square pad.

Oh yeah - nice! Didn't spot that!

[Radamus]

Thanks for clarifying. I figured it had something to do with that. I'll take a look at the OTA wikipedia page. Does this use less current than an LED/LDR combo It would seem like it would as LEDs can use a lot. Is there any differences with using simply a voltage controlled OTA rather than the LDR? I thought the behavior of the LDR allowed the sound to be so rounded, as in it takes a little while for the resistance to fall back down again, even thought the LED is off.

[orangetones]

I really should modify my IC graphic that I use though to add the pin one marker or the little scooped u shap at the top end of the IC.  When I am back in town I will adjust and update the file.

I haven't had the chance to print this out and trace over it to check yet either.  I usually print the schematic and the layout and go to town with the highlighter.  Although that is also the same thing I do when designing the layout.  I open the scemo up in photoshop and higlight the connections and parts as I connect them.

The layout was done using Inkscape and a home made library of parts.  It works for me until I learn Eagle or I get too frustrated with it.

Cheers,

Steve

[orangetones]

Anyone built this from my layout yet?  I haven't had time yet, but thought someone might have...  I have been busy with a Dub Machine and a Boss Slow Gear.  Fun stuff.

[Slade]

Thanks for this wonderful project, Rick, and thanks for your beautiful layout, Mr. Little.
I've just bought some LM13700 (LM13600 is really difficult to find at my country) and I'll give a try to your layout soon.

Greetings!

[captntasty]

I just finished assembling and populating and no funk.  It passes signal but it's just plain uneffected signal - the overall volume is also  decreased.  It also sucked a 9v that I was using just for testing before boxing up.  I had it plugged in for maybe ten minutes and it went down to 8.3v from 10v.  I'll post voltages after the Super Bowl....  I know they are screwy.

edit: I used a lm13600d - would this make a difference?

[frequencycentral]

I just finished assembling and populating and no funk.  It passes signal but it's just plain uneffected signal - the overall volume is also  decreased.  It also sucked a 9v that I was using just for testing before boxing up.  I had it plugged in for maybe ten minutes and it went down to 8.3v from 10v.  I'll post voltages after the Super Bowl....  I know they are screwy.

edit: I used a lm13600d - would this make a difference?

OK, post your voltages, I'll take mine and post them too. Did you use orangetones' layout? I'll check that too. Is the LM324 in the right way around? It would be worth fiddling with the trimmer, and the Range pot, as at some settings the filter could be alway open, and would sound clean. Also, triple check all you off-board wiring - there's a lot of it right? I haven't tried mine with a battery, I run mine from a 12 volt PS. I'm concerned that you have volume loss, as the volume control provides quite a bit of boost from unity if turned fully clockwise. Not sure about the 13600d - I'll look it up - but it should be the same.

[captntasty]

OK, I tacked a power jack and powered from an adaptor...

Here we go:

V=8.83v

LM324
1 7.58
2 0.20
3 0.20
4 8.83
5 6.52
6 6.85
7 6.85
8 4.43
9 4.42
10 4.37
11 0.00
12 4.37
13 4.41
14 4.41

LM13600d

1 1.31
2 0.00
3 4.41
4 4.41
5 0.76
6 0.00
7 0.76
8 0.00
9 0.00
10 0.76
11 8.83
12 0.76
13 4.41
14 4.41
15 0.00
16 1.31

TL072
1 4.41
2 4.41
3 4.20
4 0.00
5 4.41
6 8.05
7 8.05
8 8.83

I haven't checked in comparison to the schematic yet - I'm doing that during the 3rd quarter.

[captntasty]

I've been over all the external voltage connections and they seem alright.  I'm not sure about the internal connections of the IC's and what they should be so I'll need some help there.  I also went over the layout and schematic with a highlighter and everything seems to be in the right place.  The effect does seem to change the frequency response of the signal - it cuts high frequencies.  One thing I did as a temporary measure because I did not have a SP3T switch is to use 3 SPST switches with the common pole daisy-chained and each mode independently switchable.  There is no difference when switches are thrown other than no signal is passed when they are all off.  I plan on ordering a SP3T switch soon...

[frequencycentral]

OK, here's my voltages. I measured them with all the pots (including the trimmer) at halfway - 12 o'clock. The mode was set to HP. Nothing plugged into the input or output. My PS reads 11.99 volts. I've had to retrace my steps a little, as my build is on perf, and the opamps are in different places to the orangetones' PCB - not that it matters. I'm pretty sure I got it right. Also, just to be sure, I just tested it at 9 volts and it runs just the same as at the 12 volts I usually run it at. As I took my measurements at 12v and yours are at 9v, you'll have to factor mine down by 25% - sorry that's a hassle. I suggest you set all the pots (including the trimmer) at halfway - 12 o'clock , and take your readings again, as how the knobs are set will affect the voltages. Then you'll be comparing like with like. Post them again and we'll analyse them.

LM13700

1 - 1.025
2 - 0.002
3 - 5.98
4 - 5.98
5 - 7.13
6 - 0.00
7 - 7.13
8 - 5.93
9 - 6.01
10 - 7.19
11 - 11.99
12 - 7.19
13 - 5.99
14 - 5.99
15 - 5.99
16 - 1.025

TL062

1 - 5.99
2 - 5.99
3 - 5.97
4 - 0.00
5 - 5.78
6 - 5.96
7 - 5.95
8 - 11.99

LM324

1 - 0.001
2 - 0.009
3 - 0.003
4 - 11.99
5 - 0.197
6 - 0.655
7 - 0.655
8 - 5.96
9 - 6.00
10 - 5.99
11 - 0.00
12 - 5.99
13 - 6.00
14 - 5.99

[captntasty]

I switched to a 12v adapter.  Here are the voltages in comparison:

V=12.14v


LM13700

1 - 1.025        1.33
2 - 0.002        0.02
3 - 5.98          6.07
4 - 5.98          6.07
5 - 7.13          0.77   *
6 - 0.00          0.00
7 - 7.13          0.77   *
8 - 5.93          0.00   *
9 - 6.01          0.00   *
10 - 7.19        0.80   *
11 - 11.99      12.14
12 - 7.19        0.80   *
13 - 5.99        6.07
14 - 5.99        6.07
15 - 5.99        0.69   *
16 - 1.025      1.32

TL062

1 - 5.99         6.07
2 - 5.99         6.07
3 - 5.97         5.78
4 - 0.00         0.00
5 - 5.78         6.01
6 - 5.96         6.07
7 - 5.95         6.07
8 - 11.99       12.14

LM324

1 - 0.001        10.95   *
2 - 0.009        0.30
3 - 0.003        0.30
4 - 11.99        12.14
5 - 0.197        9.42     *
6 - 0.655        9.73     *
7 - 0.655        9.73     *
8 - 5.96          6.07
9 - 6.00          6.07
10 - 5.99        6.01
11 - 0.00        0.00
12 - 5.99        6.01
13 - 6.00        6.08
14 - 5.99        6.10

I'll check the board for bridges across traces.  I don't really know what to make of the differences.
I have a question about the orientation of the diode - is it band side out to the 2M2 and Attack pot or the other way around.  I have it band side out to the 2M2.

[frequencycentral]

I have a question about the orientation of the diode - is it band side out to the 2M2 and Attack pot or the other way around.  I have it band side out to the 2M2.

Yup your diode is correct. It's late here - but I have a day off tomorrow (snow day - yay!!) so I'll give it some thought and see if I can work out why. Are you sure the PCB itself has no errors?

[orangetones]

Pin one of the LM324 seems oddly high.  Bad diode? Solder bridge?  The other areas of concern I haven't considered yet. That one just jumped out at me.

[captntasty]

Yeah, that's what I thought - replaced the diode, tried a different 324 and also a TL074 - no dice.  Reflowed all the solder pads, scraped in between all the close together pads - still.  I don't get it?