Cadet Scaler Alternative builds discussion

Forum DIY
#1

So, after some discussion with @rempesm and others about the alternative builds of the Scaler, we decided it needs a topic to discuss the options.

I have layed out the ALT B schematic with the values as described in the Alt B BOM.
(newest version from Github)
This might shed some light on the question if this version scales from 0-1v to -5+5v

As far as I can tell, the voltage reference is used (R30 and R31 have specific values) to pull down the voltage to get bipolarity. U4 is placed (but for some reason C5 and C9 are not)

Scaler Alternate B schematic
Scaler Alternate B schematic2657Ă—1704 65.7 KB

Notes:
R4, R18, R6 and R20 are not mentioned in the ALT B BOM .
I set these values to 100k, as used in the ALT A BOM and schematic.
C5 and C9 are DNP, but U4 is still used?

#2

R1/R4 are a voltage divider, so they can be used to scale down voltage ranges.
On a typical LZX cadet they’re often there, as 499R/100K, so inputs lose 0.5% of their voltage swing. In theory you might think you’d be better off without populating R4, to get 100% of your input voltage at the op-amp + input and not lose a tiny bit to ground, but then the op-amp input would be Not Connected when nothing is plugged in to the socket, which could cause unpredictable voltage fluctuations on the op-amp output. So it’s usually populated, as a trade-off to ensure empty sockets give 0V output on the buffer op-amp in this case.
I’d populate it with 100K (or greater) just as you’ve done.
C5 and C9 obviously should be populated for good practice, if you’re populating U4. But it’s only a TL072 so not all that bad.
Basically I agree with everything you’ve said and done :slight_smile:
Interestingly, as a consequence of this in a down-scaling scaler alternative that populates the R1/R4 (etc) voltage divider with significantly different voltages the impedance of the module will be different too. But I think that is only really important if you’re patching in to it with passive multiples.

#3

I’m going to build this one (just waiting on a few parts) and will confirm if it works. I have the other permutations (1V->5V, 5V->1V, +/-5V->1V) built so far.

#4

What BOM did you use for these versions?
Basic Schematic = ±5v to 1v
Alternate A = 5x gain
Alternative B (schematic above) =? 0-1v to ±5v ?

#5

For +/-5V to 1V, I used the BOM you posted here: https://drive.google.com/drive/u/0/folders/0B_gD4TorwvAdSzJzaG5Id0hOUm8

For 1V to 5V, I used LZX’s BOM: https://github.com/lzxindustries/documentation/blob/master/Cadet%20V%20Scaler/Cadet%20V%20Scaler%20BOM%205V%20to%201V.csv

And yes, for 1V to +/-5V, I used the schematic above. Should be able to finish building this and confirm by next week when parts show up.

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#6

@reverselandfill I built your schematic above this evening and it checks out fine on the scope. Thanks for puzzling that out!

@Z0NK0UT, would it be possible to update LZX’s BOM here to be relabeled as 0-1V to +/-5V instead of the other way around. The only errors are that R4, R18, R6, and R20 should be 100k resistors and C5 and C9 should be 100nf caps.

The +/-5V to 0-1V BOM here is correct on the scope as well and could be added to the site to cover most conversions folks would be after.

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#7

Still not clear for me if in the case 0-1 to ±5, C5 and C9 should be placed or not. I previously referred on this by Luix:

#8

I’m about to build 2 of these (one to get in and one to get out of audio eurorack) and I’m wondering what the advantage of converting to 0-1v over +/-1v is. For instance if I send a bibolar lfo swinging +/- 5V to 0-1v scaler does that mean the LFO will now swing above and below .5v or will the negative portion be cut? Similarly, if I send a unipolar 0-5v envelope into a +/- 5V to 0-1v scaler I assume the output is not a constant .5v rising to 1v upon trigger right? Am I missing something simple?

And vice versa, if I am sending a cadet vco out to audio land to a filter or divider or whatever “expecting” a bipolar voltage is there an advantage to only sending 0-1v out as opposed to +/-1v to +/-5v?

I know there are workarounds using offsets, just curious how these work exactly.

#9

For instance if I send a bibolar lfo swinging +/- 5V to 0-1v scaler does that mean the LFO will now swing above and below .5v or will the negative portion be cut?

if you send a +/-5V LFO to the +/-5V to 0-1V scaler, the entire LFO will fall within the range of 0-1V. essentially it divides the signal by five and adds a 0.5V offset to bring the whole thing within the positive range. if you send that same +/-5V LFO to the +/-5V to +/-1V scaler, the negative portion of the signal will show up as black, effectively adding black spaces between the positive segments of your LFO.

if I am sending a cadet vco out to audio land to a filter or divider or whatever “expecting” a bipolar voltage is there an advantage to only sending 0-1v out as opposed to +/-1v to +/-5v?

this really depends on your use case. if you’re trying to use video oscillators in the audio realm (or as bipolar modulation sources) then definitely stick with the 0-1V to +/-5V. send those same 0-1V signals to the +/-1V to +/-5V Cadet and you’ll have oscillators with a DC offset - since video oscillators only range from 0-1V, you’ll never get any negative portions of the signal. i guess if you want to use them as envelopes or absolutely need unipolar modulation then this would be the way to go - otherwise i’d stick with the 0-1V to +/-5V configuration.

i built myself one of each Cadet V Scaler but in practice i mostly find myself using the +/-5V to 0-1V and 0-1V to +/-5V pair.

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#10

Thanks, this is exactly what I was looking for! I’ll stick with +/-5V to 0-1V and 0-1v to +/- 5v (it’s much easier for me to apply offsets once I’m back out of lzx if I need to for slower unipolar modulation, or to attenuate a bipolar signal down to less than +/- 1v without offsetting to send into lzx). I suppose what I’m lacking or need will become more apparent once I get something up and running. :man_dancing:

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