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 Forum index » DIY Hardware and Software
LM13600
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crazeydazey



Joined: Feb 15, 2007
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PostPosted: Fri Apr 20, 2012 3:33 am    Post subject: LM13600 Reply with quote  Mark this post and the followings unread

Hi,

I've just bought myself a few LM13600s to play around with and was gonna try some of the VCFs straight off the data sheet.

Before I ruin any chips by messing just wanted to know if I am only using 1 amp do I need to put any pins of the other to ground and any other pins that don't seem to be used, or do I just leave em??

Cheers

Daz

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bod



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PostPosted: Fri Apr 20, 2012 6:58 am    Post subject: Reply with quote  Mark this post and the followings unread

for prototyping it wont hurt to leave them unconnected on the bread board, but if you were making a finished module and one half wasnt used then it would be better to ground the inputs.
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crazeydazey



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PostPosted: Fri Apr 20, 2012 7:28 am    Post subject: Reply with quote  Mark this post and the followings unread

brilliant thanks bod..

I think if it comes to creating a final module, I'll have a use for both..

on the datasheet there is a low pass and a high pass.. I was thinking of messing with both of these and I've also been studying the MS20 and Korg Delta VCF so I'm getting other ideas to check in there too.. might not get anything out of it, but it will be fun messing

cheers

daz

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JovianPyx



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PostPosted: Fri Apr 20, 2012 9:55 am    Post subject: Reply with quote  Mark this post and the followings unread

A note of caution: LM13600 and LM13700 are certain to die if the Iabc current maximum is exceeded. It's important to know that the Iabc current is referenced to the negative rail, not to ground. Iabc absolute max is 2 mA. Exceeding this current is probably the most common cause for burnout. Otherwise, they are pretty robust. If you are using a resistor to set the Iabc current, make sure you calculate the current using the voltage supplied to the resistor to the negative rail. For example, using a +/-15 volt supply, the resistor is commonly connected to +15. This means the voltage used will be 30 volts. In this case, the resistor should be no smaller than 15K ohms.
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Dave Kendall



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PostPosted: Sat Apr 21, 2012 2:45 am    Post subject: Reply with quote  Mark this post and the followings unread

The EFM VCV6C is an interesting filter, using a diode ladder with an LM13600 in the circuit. It has a non-linear resonance behaviour, where resonance falls off as the freq is swept down. It can scream nicely too Smile
The forum notes show some mods, like changing the DC blocking cap in the resonance path to give different tonal effects.
It would also be worth adding CV and audio summing mixers on the inputs.

Docs here;
http://www.modular.fonik.de/files/EFMforum/orgEFMfiles/vcf+6c.pdf
http://www.modular.fonik.de/files/EFMforum/VCF%206C%20forum.pdf

cheers,
Dave

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crazeydazey



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PostPosted: Sat Apr 21, 2012 4:04 am    Post subject: Reply with quote  Mark this post and the followings unread

brilliant thanks Dave, I'll have a play with that Smile

and thanks JovianPyx for the note of caution.. I'm a total noob at designing my own stuff and knowing what does what so I may have killed it..

Although saying that (bear with me here.. as I said I a noob so what I'm about to say me be total garbage Smile)

I was looking at lots of VCF circuits that use the LM13600 and noticed they all the expo tranny bit on the Iabc (look at me sounding like I know what I'm talking about.. it's probably all wrong), so I was just going to pinch that so hopefully I may not kill em.. but knowing me.. I'm sure I'll manage to set it on fire somehow and that will be before I even add any voltage to it Very Happy

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JovianPyx



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PostPosted: Sat Apr 21, 2012 7:06 am    Post subject: Reply with quote  Mark this post and the followings unread

When a transistor current source is used to drive the Iabc pin, things are a bit more complex, it's no longer a simple resistor that is used to set the current - it's that transistor. Hopefully, the designer has calculated the way his current source works and knows that it cannot exceed 2 mA by design. Using a current source from one known to work LM13600 schematic to drive an LM13600 in another schematic is probably going to be OK, especially if both circuits use the same power supply voltages.
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crazeydazey



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PostPosted: Mon Apr 30, 2012 6:51 am    Post subject: Reply with quote  Mark this post and the followings unread

I have breadboarded the Triangular/Squarewave VCO (fig 19) from here

and it sounds pretty cool.

I then tried pinching an expo circuit from EMFs 4600 series here

and thought I'd be somewhere near, change a few resistors etc and fannys my auntie.. OOOHH noo how wrong was I??

it did nothing at all Sad, took my expo off and tested again VCO still worked didn't blow anything.

I checked and double checked the 2 trannys and a handfull of resistors where all connected properly and all looked good, so how can a simple circuit that looks like it's used everywhere not work at all for me ?? Sad

I might draw up the full circuit I had and see if anyone can see a problem .. it would be cool to think I'd made my own VCO (well really pinched too halfs and stuck them together.. but please let me have a little moment of glory.. it's a start Smile)

cheers

daz

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JovianPyx



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PostPosted: Mon Apr 30, 2012 7:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Remove the current source from the Iabc pin and replace it with a resistor that is greater than or equal to 15K (assuming +/- 15 volt PSU). If the VCO still doesn't work, the problem is in the VCO, not in the expo converter. Miswire, wrong value somewhere, bad solder, something like that.
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crazeydazey



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PostPosted: Mon Apr 30, 2012 7:27 am    Post subject: Reply with quote  Mark this post and the followings unread

no I've tried that and with a resistor the VCO works fine
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JovianPyx



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PostPosted: Mon Apr 30, 2012 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Argh... Ok, well, it's definately narrowed down to the expo converter, but sadly, I don't know enough about them to help...

At least you know where the problem is.

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crazeydazey



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PostPosted: Mon Apr 30, 2012 7:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Smile cheers for your help though..

is there any way I can make a really simple expo, connect it up to my midi-cv, play a c1, and I should be able to measure voltage (assuming that 1v per oct, I should get 2v out of the midi-cv), so I then need to know what I should be expecting in at Iabc, (well I don't but I'm sure with a bit of maths I could)

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crazeydazey



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PostPosted: Mon Apr 30, 2012 7:36 am    Post subject: Reply with quote  Mark this post and the followings unread

sorry take that back A2 is 2 volts.. I assumed it started at C DOH!!
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crazeydazey



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PostPosted: Tue May 01, 2012 11:34 am    Post subject: Reply with quote  Mark this post and the followings unread

I've finally got round to doing a schematic of what I've done..

as said before the VCO is taken from the LM13600 data sheet (wel I didn't say that, but's it's excatly the same as nuts and volts article just with different values) and the expo is one I've seen all over the place (mainly EFM).

the VCO works by its self, with a higher val on R4 (not wanting to blow the LM13600 - thanks JovianPyx for the warning Smile)

when I connect the expo.. nothing at all...

I'm sure the circuit is fine, maybe the values of the resitors and caps are not right, but I'm not clever enough to do the maths..

anyone??

cheers

daz


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JovianPyx



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PostPosted: Tue May 01, 2012 12:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've searched with google and got a lot of hits, but nothing simple until I saw a post by Blue Hell here on e-m that pointed here:

http://hem.bredband.net/bersyn/VCA/lm13600%20vca%201.htm

Note that this is a VCA, but you can see the expo current source that drives the Iabc pin of an LM13600. This same current source should work with your VCO. It seemed that every expo current source for an LM13600 I've seen has this opamp arrangement added to the two transistors - I'm assuming it's required, but as I said before - I really don't know how they work because I don't use expo myself.

Anyway, have a look, maybe that's all you need is to add an opamp as shown.

An unfortunate note about EFM - there are many schematics that can be found all over the web for EFM stuff. Some work, and unfortunately, some do not. Tom has had a history of putting stuff on different sites and it's known that some of the schematics and documentation have errors. Not all of those sites have been maintained, so not all of the corrections that he and others have made have been taken up by all of the sites that had/have his designs. I personally have helped at least one person with an EFM schematic that had blatant "ain't gonna work" errors. In that case, it was an ADSR.

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Last edited by JovianPyx on Wed May 02, 2012 4:51 am; edited 1 time in total
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crazeydazey



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PostPosted: Wed May 02, 2012 2:54 am    Post subject: Reply with quote  Mark this post and the followings unread

excellent.. again cheers Smile

I'm gonna build that too... this sort of thing is exactly what I want.. I'm not very good with electronics and I'm not very good with maths and I want to build a decent synth as easily and cheaply as possible..

daz

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