rene schmitz 4069 VCO

crazeydazey · Posted: Wed Apr 25, 2012 8:40 am Post subject: rene schmitz 4069 VCO

Hi all,

I'm half way through knocking this up on pref board and had to stop because I'm missing a few resistors Sad

although I do have 5% (I was gonna do it all in 1% resistors)

so I then got thinking, maybe there a quite a few resistors on here that don't really need to be 1%.. but I'm not clever enough to work out which ones myself.

could someone please tell me which resistors ideally should be 1% and which could be 5%

many thanks

daz

JingleJoe · Posted: Wed Apr 25, 2012 9:29 am Post subject:

Schematics would be helpful Razz

try meassuring a few resistors with your multimeter, you may find some 5% which are within 1% tolerance.
In a random selection of five 10% resistors I can usually find one within 2% of the stated value.

crazeydazey · Posted: Wed Apr 25, 2012 10:29 am Post subject:

sorry mate, just thought it was one of those circuits that everyone had looked at at some point..

it's - this one..

slacker · Posted: Wed Apr 25, 2012 1:47 pm Post subject:

I think the only ones that need to be 1% are the 100k and 10ks connected to the CV Ins, and they only matter if you want accurate V/octave tracking on both the inputs.
Like Jingle Joe said you could just match those resistors by measuring a bunch from your 5% ones. What you want is resistors that are the same value if they're a bit higher or lower than 100k doesn't really matter because you can adjust for that with v/oct trimmer.

crazeydazey · Posted: Thu Apr 26, 2012 8:23 am Post subject:

thanks for that guys, I've managed to find some 5% ones that are pretty close Smile

next question... I don't know if it matters or not, but it doesn't actually say what type of capacitors I need to use.. I know some circuits I've built clearly state (these ones need to be polyester, these ceramic.. tbh, I don't really know the difference I'm not that clever with electronics, I just know what I need to and copy other peoples circuits.. it gets me by Smile

)

so can you recommend a type or can I just go with polyester?? I have a few of those kicking around - I think)

cheers again

daz

elmegil · Posted: Thu Apr 26, 2012 10:20 am Post subject:

Had a recent conversation about caps that was similar (polystyrene rather than polyester) and this reference turned out to be a good one to explain the differences among capacitor types:

http://my.execpc.com/~endlr/

Ian Fritz was saying that most circuits that call out poly* caps can do well with C0G / NP0 (different names for the same thing) high quality ceramic caps instead, and VCO's in particular.

If you have the polyesters around and not the ceramics (common non-polarized usually circular...) I don't see why you couldn't use them--but I'm not a whole lot more experienced than you are so take my words with salt Smile

. I built this circuit using aluminum electrolytics for the polarized caps and standard (not the C0G) ceramics for the non-polarized ones and it worked fine.

crazeydazey · Posted: Fri Apr 27, 2012 1:23 am Post subject:

thanks for the reply elmegil.. I think I may have some ceramics kicking around too, but they may only be cheap nasty ones I got on ebay from china (about a million for £1 Smile

), so I tend to only use this on breadboards..

I may just buy some new ceramics (not sure what NPO and COG are, tried searching on ebay for these and go no items returned).. I'm a bit of a shopaholic and love buying new components.. a bit sad really, I guess I can see why women like doing it with shoes and handbags Smile

Paradigm X · Joined: Feb 15, 2011 Posts: 254 Location: Null and void

its np [zero] and c [zero] g not NPO and COG btw, prob why you cant find Smile

Rapid UK have a load of them.

For example.

elmegil · Posted: Fri Apr 27, 2012 5:14 am Post subject:

Sorry about that I just looked at my breadboard and not the circuit diagram again.

I have 10uF polarized caps across the power leads out of habit, but not any in the circuit proper.

Benjamin AM · Joined: Nov 04, 2010 Posts: 48 Location: Boise

I've been trying to convert this circuit into single power rail version. My expo converter is more true to the ARP version: normal Tempco to ground at summing node rather than the NTC, PNP's collector to ground. I've been struggling to get the oscillator to move at reasonable speed(it's to fast) unless I use a negative reference at the summing node. A larger capacitor distorts the signal, so that's out. Any suggestions? Should I just use a charge pump.
Does a 1V/oct single rail sawtooth core VCO already exist? No reason to reinvent the wheel on this one.