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 Forum index » DIY Hardware and Software
LM331 freq to volt chip??
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loss1234



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PostPosted: Thu Mar 13, 2008 9:22 am    Post subject: LM331 freq to volt chip?? Reply with quote  Mark this post and the followings unread

lm331?


anybody made a successful circuit with this? jameco has em in stock and there is a forrest mims schematic for converting frequency into volts..thought it might be worth trying out if this chip is any good.

thanks

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factus10



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PostPosted: Thu Mar 13, 2008 11:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Forrest's schematic is from a working model.
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loss1234



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PostPosted: Thu Mar 13, 2008 11:23 am    Post subject: Reply with quote  Mark this post and the followings unread

has anyone tried it? i guess what i meant about Mims schematic is i wonder if its a good application for CV/music uses.

thanks

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Danno Gee Ray



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PostPosted: Thu Mar 13, 2008 3:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is the schematic linkable / postable?
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caress



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PostPosted: Thu Mar 13, 2008 3:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

the same chip is used in the 4ms atoner pedal. weird fuzzy sort-of-pitch-shifter...

http://www.4mspedals.com/atoner.php

you can also drop in a KA331 as well.
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loss1234



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PostPosted: Thu Mar 13, 2008 4:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

i thought they used the 4151?

same thing i guess

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caress



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PostPosted: Thu Mar 13, 2008 10:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

oh yeah 4151... same thing.
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loss1234



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PostPosted: Sat Apr 05, 2008 11:33 am    Post subject: Reply with quote  Mark this post and the followings unread

well i tried building the foresst mims f/v converter and it basically doesnt work. i can slightly hear it changing the pitch on my vco when i feed it a line level musical track, but its not strong enough to fully change the pitch. maybe i need a level shifter on the input or output? or an amp?

could i use a transistor amp?

the mims design has an audio transformer on the input...but i could only get this working WITHOUT the transformer. questions-its a 1k, 8 ohm transformer. it has 3 in wires, and 2 outs. i figured coming in i would give one in gnd, and one in the hot signal and then out the 2 outs, one would be gnd and one would be hot signal. IS THIS HOW YOU USE AN AUDIO TRANSFORMER???

thanks--i will keep you posted

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EdisonRex
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PostPosted: Sat Apr 05, 2008 12:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

The transformer is very likely to be balanced.

Otherwise it wouldn't be there.

Makes sense, reject as much noise as you can and you won't end up sending the CV equivalent of 60Hz (or 120, or 180).

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Tim Servo



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PostPosted: Sat Apr 05, 2008 1:03 pm    Post subject: LM331 freq to volt chip?? Reply with quote  Mark this post and the followings unread

Hey Loss,

Yes, there may be problems with the levels involved, but keep in mind that most commercial F-V chips are meant to work with very simple signals (sine or square) and won't work with complex signals like a guitar. I'm pretty sure the applications for these chips are things like deriving motor speed from simple encoders, so they're looking for a signal that is simple and doesn't change freq that quickly (exactly what we don't get from a musical input). If you're feeding a F-V chip a mixed musical track, there's no way it will give a meaningful output. Pitch (Frequency) to voltage conversion is a very tricky business, so while some of these chips are fun to play with, don't expect a properly tracking, top quality conversion from a simple circuit.

Tim (doesn't always track properly either) Servo
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loss1234



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PostPosted: Sat Apr 05, 2008 2:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the wisdom from both of you


maybe i will try build that F to V circuit from Polyphony instead.

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loss1234



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PostPosted: Sat Apr 05, 2008 3:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

i checked out the jensen article on transformers but i am still confused about how to apply it. if there are three input wires, (middle being black) can i just duplicate the signal to both outer wires?? or i guess i might try using a TRS cable and hooking up all three that way,

thanks

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loss1234



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PostPosted: Sat Apr 05, 2008 4:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

I GOT IT WORKING WITH A GUITAR!!!

MORE LATER

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Blue Hell
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PostPosted: Sat Apr 05, 2008 5:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool
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loss1234



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PostPosted: Sat Apr 05, 2008 5:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

a few things.

it seems to work better with the schematic from lm 331 datasheet than the forrest mims schematic. not sure why but....

anyway, the schematic in the data sheet works well with no transformer with line level signals (especially if they are distorted to the point of smoothing the edges) and i am now running the audio through a plug in that gets "sine" distortion....works very well with HIGHER notes on the guitar neck or LOUD microphone stuff.


this might work better with a noise gate pre.

i would be interested in other peoples experiences with f to v chips.


its hardly precise but it makes for very cool effects.


thanks

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Blue Hell
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PostPosted: Sat Apr 05, 2008 5:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

loss1234 wrote:
its hardly precise but it makes for very cool effects.


In general for f->v to work you'll want a clean signal, and a noise gate is not a bad idea at all. You might want to try some low pass or bandpass filtering before the converter.

But indeed when it gets confused it's fun as well, as it goes wild sometimes and it listens at other times, the fun part for me is on the edge of recognition Very Happy

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loss1234



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PostPosted: Sat Apr 05, 2008 9:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

just a question
if i were to put the output of my freq to v converter into a mixer, what would i hear? would i still hear the guitar? or nothing? i just want to make sure i have it set up properly.
thanks

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EdisonRex
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PostPosted: Sun Apr 06, 2008 5:38 am    Post subject: Reply with quote  Mark this post and the followings unread

The output of a frequency to voltage converter is, well, hopefully, control voltage, which is DC, which won't sound like much. You might try listening in on the signal at the input side of the LM331, for what it's worth.

I'd have thought that Jan's advice should be best practice with these things.

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loss1234



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PostPosted: Sun Apr 06, 2008 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

i seem to be getting some bleed on the outs of actual audio (the input bleeding through)

i will try jans advice of filtering

thanks

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Rolbista



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PostPosted: Wed Jun 25, 2014 7:08 am    Post subject: Filter Reply with quote  Mark this post and the followings unread

Do you think that this chip would be good enough for tracking pitch of a keyboard (with a pretty steady singnal processed with a comparator) so that VCF's cutoff follows note played?
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JovianPyx



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PostPosted: Sun Jun 29, 2014 1:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

A lot of really good information about what this IC does and how it works internally is available in the datasheet. Here is one such datasheet. The specification itself for linearity looks very good. However, there are, like anything else, conditions that the circuit must meet in order to attain this linearity. One thing I saw was that for a F to V converter, the device expects a pulse train. This tells me that if you want to use random waveshape signals, you will need to convert them to glitch-free pulse trains before applying them to the circuit input. I'd also suggest that the amplitude of this pulse train be large and within the input specs of the device. Other issues to look at are going to be tracking speed and range. It is often the case the F to V converters are slower and lower frequencies.

Additionally, this device will output a voltage that is linear with respect to Hz, not octaves. Therefore, if you expect to use this in an expo type modular, you will need an additional chunk of circuit at the V output of the IC to convert the CV to expo.

In the end, the best way to tell whether this will work for your particular application is to get an IC and build.

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prgdeltablues



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PostPosted: Tue Jul 01, 2014 2:30 am    Post subject: Reply with quote  Mark this post and the followings unread

I've built an F- to-V circuit, using a different chip - LM2917. See my post:

http://electro-music.com/forum/topic-55362.html

As I noted, tracking isn't too bad, but the main problem is that the output drops down to 0 when the input signal stops, or drops below the threshold. You can gate the end of your signal of course, but that's quite abrupt, and when a new note starts, it has to climb up in pitch....The only way I can see to get round that would be to add in a delay, so the output of the chip was muted until it reached its proper level.

Peter
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