[NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

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Jason Brock
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Post by Jason Brock »

So I searched through this thread but I'm still unclear regarding this: does the VCFS self-oscillate when you max out the Q control? Or does it need something else patched in to do so?
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woodster
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Post by woodster »

It needs self patching, output back to input to go into self oscillation. Doesn't need something else I don't think.
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Post by lohacker »

Jason Brock wrote:So I searched through this thread but I'm still unclear regarding this: does the VCFS self-oscillate when you max out the Q control? Or does it need something else patched in to do so?
It doesn't self oscillate, you need to feed the phase inverted band out to one of its inputs to make it happen.
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Post by nikvudu »

Did you ever solve this problem? Mine is pretty quiet too: for a sawtooth input of -5V - +5V, here are the best-case specs (I adjusted freq, slope, and Q to maximize amplitude in each case):
Lowpass: -4V to +3V
Bandpass: -3.7V to +2V
Highpass: -6.5V to 6V

Does this seem right? Compared to my other filters it is just perceptually very quiet in most settings.

In the lowpass case, this setting is from maximum slope and maximum Q.

In the bandpass case, this setting is from minimum slope and maximum Q. With higher slope, the output is much more symmetrical, but much more attenuated.

In the highpass case, this setting is much higher amplitude because it's picking out the fundamental frequency so strongly. Uses maximum slope and maximum Q.

tommy.york wrote:Question: my VCFS is very quiet, like 500mv p-p. Everything works though. Where would y'all recommend starting to troubleshoot?

Edit: Intellijel Polaris with same signal looks like it's about 5v p-p.

I'm guessing resistor value and might go check that out.

Edit: nm, I recently swapped in a film 470p (and not the correct 470n) capacitor because I'd originally built it with a ceramic capacitor and not film because of size issues. I think I may have even mistakenly put in 470p ceramic in the first place. Pretty sure this was the problem.

:deadbanana:

Until the new capacitor gets here, I'm using a 220n mylar film capacitor. Seems to work well. Does anyone with more of an EE background than me want to explain what C10 is doing here and why I got the results that I did with 470pf / 220nf?
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Post by ldezem »

lohacker wrote: Fri Jun 07, 2019 2:12 pm
Jason Brock wrote:So I searched through this thread but I'm still unclear regarding this: does the VCFS self-oscillate when you max out the Q control? Or does it need something else patched in to do so?
It doesn't self oscillate, you need to feed the phase inverted band out to one of its inputs to make it happen.
Thank you for this tip! Patched the band-pass output to an inverter and back to the device: This produces a strong tone, which seems to track well and makes for umbfy kicks.
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robertlo wrote: Fri Sep 07, 2018 5:11 pm I have a VCFS that I built from a Thonk kit, and everything works wonderfully except one thing: in low-pass mode, once I get down lower than about 10 o'clock on the frequency knob, the low frequencies are not present. In other words if I go lower than about 10 o'clock, the sound dissolves into silence.

The problem is only in low-pass mode; I can get normal low frequencies in both high-pass and band-pass modes.

Does anyone here have any thoughts as to why this might be? I've double- and triple-checked all connections, all components, and just can't seem to figure it out.

I'll mention one thing in case it helps. During the build, I accidentally installed the transistors the wrong way, then replaced the transistors entirely (and positioned them correctly) just to be safe. Might that have caused another component to fail and be causing this issue?

Would hugely appreciate any help at all -- thanks!
Hi, digging this one back up (and quoting myself!) because I was never able to get this figured out and it pains me greatly to not be able to use this module.

Any ideas? Aside from the low-pass situation I mentioned, the Q and Slope controls are verrrrry subtle, I think more so than other demos of the module I've heard.

Are there reference voltages anywhere that I could check to help trace down the problem?

Thanks again for any help.
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Re: Re:

Post by ldezem »

robertlo wrote: Fri Sep 07, 2018 5:11 pm Hi, digging this one back up (and quoting myself!) because I was never able to get this figured out and it pains me greatly to not be able to use this module.

Any ideas? Aside from the low-pass situation I mentioned, the Q and Slope controls are verrrrry subtle, I think more so than other demos of the module I've heard.

Are there reference voltages anywhere that I could check to help trace down the problem?

Thanks again for any help.
I have a DIY'd module here on my table and I have similar experiences. I've understood that the Slope / Q controls are very subtle by design. My experience is that their effect on a sound is most notable when the potentiometer is around 11-12'clock (not when it is cranked all the way). This is by design which I've grown to like as it invites experimentation: Combinations of knob-tweaks yield more notable results then turning all knobs to the max. I think the module is subtle. Concerning the LOW output: I run a simple test with sine wave from Disting mk4 (attenuated by the VCFS mixer). With my headphones the sound goes silent at 9'clock, but this can be and issue with the headphones which don't cover very low frequencies (I can hear a square wave verrrrry faintly at 8'clock). I've used the LOW output as a lowpass gate of sorts and I really enjoy this feature.
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by transistorresistor »

Just received a Thonk kit with some discrepencies I cant sort.

bags of resistors labeled:
330R- R1, R7, R8
22k- R3, R4, R5, R6, R7, R8

Bom says:
330R- R1, R7, R8
22K- R13, R15, R34, R35, RM1, RM2

Havent traced this closely, but looks like R7 and R8 are input level, so can understand that adjustment.

Can anyone explain the difference in the 22k on the bom vs. the sticker on the bag?
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by Kosmikos »

Yes I noticed the same issue, but it all made sense in the end as these resistors aren’t anywhere else anyway.
I think I just ignored the decimal difference and followed the prints on the PCB. I can send you a picture of my build if you are in doubt, my VCFS works really well.
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by transistorresistor »

Kosmikos wrote: Thu Jun 02, 2022 3:51 pm Yes I noticed the same issue, but it all made sense in the end as these resistors aren’t anywhere else anyway.
I think I just ignored the decimal difference and followed the prints on the PCB. I can send you a picture of my build if you are in doubt, my VCFS works really well.
thanks for the feedback, got it sorted. Really wonderful sounding filter, quite surprised this one isnt discussed more frequently on the forum.
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by robertlo »

Kosmikos wrote: Thu Jun 02, 2022 3:51 pm Yes I noticed the same issue, but it all made sense in the end as these resistors aren’t anywhere else anyway.
I think I just ignored the decimal difference and followed the prints on the PCB. I can send you a picture of my build if you are in doubt, my VCFS works really well.
I'd love to take you up on this, if you could possibly post some photos! Still can't get mine quite right and it would be great to have something to compare to. Thanks so much!
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by Kosmikos »

transistorresistor wrote: Fri Jun 03, 2022 12:46 pm
Kosmikos wrote: Thu Jun 02, 2022 3:51 pm Yes I noticed the same issue, but it all made sense in the end as these resistors aren’t anywhere else anyway.
I think I just ignored the decimal difference and followed the prints on the PCB. I can send you a picture of my build if you are in doubt, my VCFS works really well.
thanks for the feedback, got it sorted. Really wonderful sounding filter, quite surprised this one isnt discussed more frequently on the forum.
Glad you got it sorted.
Agreed, I love the fact that it gives a really gradual/low pole slope at its min, but then can still sounds like a 4 pole and anything in between at the turn of a knob, and being able to CV the slope brings a total new dimension to the filtering.
robertlo wrote: Fri Jun 03, 2022 12:49 pm
Kosmikos wrote: Thu Jun 02, 2022 3:51 pm Yes I noticed the same issue, but it all made sense in the end as these resistors aren’t anywhere else anyway.
I think I just ignored the decimal difference and followed the prints on the PCB. I can send you a picture of my build if you are in doubt, my VCFS works really well.
I'd love to take you up on this, if you could possibly post some photos! Still can't get mine quite right and it would be great to have something to compare to. Thanks so much!
Here’s a picture of my build of the Thonk kit, with the differences talked above. If you click on the picture you should be able to get a good enough resolution and tell the resistor colour bands if needed:
85C6469C-7E89-437E-ADF9-3DB5EDFDF74C.jpeg
Kosmikos’ tracks on Soundcloud: https://soundcloud.com/user-254876270
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Peake
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by Peake »

I would like to purchase one variable slop generator pls
.
variable slop.jpg
variable slop.jpg (5.16 KiB) Viewed 356 times
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by robertlo »

Kosmikos wrote: Fri Jun 03, 2022 1:08 pm Here’s a picture of my build of the Thonk kit, with the differences talked above. If you click on the picture you should be able to get a good enough resolution and tell the resistor colour bands if needed:
85C6469C-7E89-437E-ADF9-3DB5EDFDF74C.jpeg
Many thanks, this is perfect!
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by Kosmikos »

Peake wrote: Fri Jun 03, 2022 1:13 pm I would like to purchase one variable slop generator pls
.
variable slop.jpg
Wrong thread, variable slope filter here, but here you go, it looks like you can buy it here:
https://randomsource.net/serge_eurorack?mod=RS_DSG_E

I don’t get the attached picture, am I missing a good joke? :hmm:
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by B0bcat »

Kosmikos wrote: Fri Jun 03, 2022 1:56 pm am I missing a good joke?
yes
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by Kosmikos »

.
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Re: [NEW] Serge Variable SLOPE Filter VCFS for Euro by R*S

Post by Peake »

:chug:
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