MFOS Wave Former

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dummyplugconspiracy
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MFOS Wave Former

Post by dummyplugconspiracy »

Hi -

I am about to embark on this build and I was reading up on it. The MFOS site has a link to expanded info on the VCO and sequencer parts of the project. Though the Wave Former page doesn't mention any component adjustments for +/-15V power, when you check out the VCO page, there are these notes:

+/-15V Users Take Note
While helping diyer Doug Slocum improve the tracking on his MFOS VCOs I found a few things +/-15V users should change.

Change R46 to 1.54K metal film (1.5K carbon will be ok too). This sets the bias for the comparator since it changes at +/-15V. This corrects the whole rest of the waveform chain's amplitude.
Change R10 to 150K and R65 to 43K this will give you a better range on the coarse freq control. Use metal film.
Change R28 to 1.5M metal film. Changes the starting current of the expo convertor to 1uA.
Use OP275 for U1. Its performance is superior to other op amps.
Make sure and use a 100K multi-turn for the high frequency adjust.

There are no such notes for the sequencer section.

So my question is this . . . are the components I got in my Soundtronics parts kit sensitive to these notes? Or should I make the substitutions? I know the MFOS info can be dated and sometimes you have already made the necessary improvements on your boards and parts. In this case, do I need to make those changes? Or just stick with the stuff in your kit?

THANKS!
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Paul Cooper
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Re: MFOS Wave Former

Post by Paul Cooper »

dummyplugconspiracy wrote: Fri Nov 11, 2022 10:10 pm So my question is this . . . are the components I got in my Soundtronics parts kit sensitive to these notes? Or should I make the substitutions? I know the MFOS info can be dated and sometimes you have already made the necessary improvements on your boards and parts. In this case, do I need to make those changes? Or just stick with the stuff in your kit?
No, the kit only contains components listed in the MFOS parts list and any kludges.

You should be guided by the MFOS website on substitutions for 15V operation. Our boards are genuine MFOS boards, they are not manufactured by Soundtronics or modified by us in any way. Our kits are for building modules inline with the MFOS website and as 12V is also our go-to voltage, we rarely investigate operation on higher voltages due to time constraints.
dummyplugconspiracy wrote: Fri Nov 11, 2022 10:10 pm There are no such notes for the sequencer section.
Builders often change default values to suit operating on different voltage such as 15V by fault finding. You will be on your own on this one as it falls outside of our scope of support. However, the first consideration would be to check that any components directly powered by the line voltage are suitably rated rather than pop them by an over-voltage. A quick look at the sequencer schematic looks like it should be fine at 15V with some tweaking, for example changing R63 to 120k.
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Re: MFOS Wave Former

Post by dummyplugconspiracy »

OK thanks. I will read that sequencer page in a little more detail, but that substitution you mentioned isn’t something I would’ve figured out on my own. I guess I’m not quite at that level yet. Is there anything else you recommend on that build to adapt it to 15 V? I haven’t found any other resource for that yet, but I suppose I could open a thread over on the MFOS page and see if anybody has done one for 15 V. I definitely don’t want to take chances with a build this complicated. Thanks!
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Re: MFOS Wave Former

Post by Paul Cooper »

dummyplugconspiracy wrote: Sat Nov 12, 2022 8:28 pm Is there anything else you recommend on that build to adapt it to 15 V?
Not looked and as I am not the designer of the module, the time taken to research this is time I do not have. If not already covered by the designer or by another user, then you will have to resolve a supply voltage change yourself. Often it is nothing more than changing values to correct ranging but sometimes it is biasing. As previously mentioned, the components can take 15V so build it, try it and then fault find if it doesn't work. In this particular case, it is likely to work anyway on 15V and the resistor change I quoted is simply for correction of the ranging.
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Re: MFOS Wave Former

Post by dummyplugconspiracy »

Hi -

Two things:

Just so you're aware, the wave former parts kit ships with far more diodes and resistors than the build calls for. I'm guessing it's the full diode and resistor list from the full build of the vco and the sequencer, but you only need less than 1/3 of them for the partially populated wave former project. Not complaining. Just letting you know.

Also, I didn't notice when I asked about it earlier that the resistor substitution for 15V on the vco includes some slightly exotic resisted values I don't have in the giant mixed resistor kit I bought. Is it one of those situations where you can just get close enough? Or do I really have to order these specific values? I'm referring to 1.54k and 43k. I'll order them if I have to but I wanted your advice first.

Thanks!
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Re: MFOS Wave Former

Post by dummyplugconspiracy »

Hi -

I wasn't having much luck finding a 43k or a 1.54k resistor to order without having to buy a million of them. So I hope what I've done here is ok. I remember on a past MFOS build I was instructed to gang multiple resistors across two solder points to achieve unusual resistance counts. So I assumed this was safe to do here too. As long as they're all sharing those two points on either side of the resistor position, I don't see a problem with it. Resistance values are simple addition, right?

To get a 1.54k I stacked these values:
1R
39R
1.5k

To get 43k I stacked these:
33k
10k

I tried to take a picture but it was kind of hard. I haven't fired it up yet. Is this going to work?
Thanks!
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harpooneer
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Re: MFOS Wave Former

Post by harpooneer »

Resistance values are a simple addition when in series - the photos look like you might have them in parallel.
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Re: MFOS Wave Former

Post by dummyplugconspiracy »

You’re right. And I just did some additional research that contradicted my earlier research. So I gather my way won’t have the desired results. I have to put them in series instead. But if I do that …. Then it will work bad intended?
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Re: MFOS Wave Former

Post by dummyplugconspiracy »

Sorry … I meant work AS intended.
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Re: MFOS Wave Former

Post by harpooneer »

Yes, series should be fine
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Re: MFOS Wave Former

Post by dummyplugconspiracy »

Super. I just created a little loop instead of a stack. Thanks!
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Re: MFOS Wave Former

Post by Paul Cooper »

Paul Cooper wrote: Mon Nov 14, 2022 9:08 am Just so you're aware, the wave former parts kit ships with far more diodes and resistors than the build calls for. I'm guessing it's the full diode and resistor list from the full build of the vco and the sequencer, but you only need less than 1/3 of them for the partially populated wave former project. Not complaining. Just letting you know.
You should only receive 4 diodes as per the BOM, if you have more than this then they are freebies ;)
Paul Cooper wrote: Mon Nov 14, 2022 9:08 am I'm referring to 1.54k and 43k.
43k is an everyday standard resistor, juts make sure you buy resistor kits that are E24 series as most MFOS designs use values from this series. 1.54k is not standard but equally cannot be that important if a 1k5 carbon resistor will do as these have a tolerance of 5%. Just use a 1k5 metal film resistor.
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Re: MFOS Wave Former

Post by dummyplugconspiracy »

Agreed that 43k isn’t really exotic. I just didn’t have one. But in any case, I’m going to try my chained together solution and see how it goes for now. Thanks!
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