YUSYNTH EMS-diode ladder filter

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

Hi Yves:
I was aware of the input level and I did the test with the input at mark 4,
also I measured with my PC oscilloscope the point at the input starts to
overdrive, and it was at mark 4 indeed.
Now I tryed lowering the input level and the unestability goes away with
the input below mark 2. The output level is low, but the filter sounds great.
The self oscillation still dissapearing at 9KHz.
Thanks a lot for your help.

kkissinger · Posted: Mon Jan 17, 2011 3:41 pm Post subject: Another diode ladder filter!

negativspace · Joined: Dec 25, 2010 Posts: 17 Location: Manhattan, Kansas

Interesting that you settled on the value you did, Kevin. I build one of these a couple of weeks ago, and I ended up using a 120k resistor in that spot to achieve the same resonance behavior you describe.

bc547c

Hello, sorry for reposting this old post;
i have already built one of these filter, after classic 220K mod for resonance but I have a big problem:
- when I turn the cutoff pot to the max range I listen a "hole" in filtering; this hole become present about to the end of the range of the pot.
What's the problem? Bad matched diode? I don't use a polyester cap but red cap type with tolerance of 4%...
I use a CA3096, Harris CA3046 and TL074, the cutoff pot is good (Alpha 10K lin).
I try different pot ma the problem still remain.

I post a demo of the problem:
Than you

Untitled2.mp3

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Download (listen)

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Untitled2.mp3

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Snaper · Joined: Feb 28, 2014 Posts: 217 Location: Hungary

wackelpeter · Posted: Fri Jan 02, 2015 12:25 pm Post subject:

Hello @all and first of all a happy new year everyone.

after finishing my stripboard Version of the steiner parker filter succesfully i thought to give another try to the Diode ladder filter. i've tried to build it before in another Version that was flying around in the WWW which was designed by Marian Urekar but failed... and then lost touch with it going deeper into it...

well know i've build it on stripboard with +12V and -9V supply the discrete Version with one ca3046 and it wouldn't work...
the Sound i'am getting is very thin and quiet and even vc wouldn't work really...

by the time i've stumbled across some scanned pages of the original schematics (supposedly scanned by Ives himself as the water stamp suggests) there i saw some different values written onto it...
are These reference voltages that must be measured at this specific Points? and if this is the case with Signal applied to the filter or any CV (OV) or pot turned in that or this direction?
For example at the emitter of the Transistor Q24 in the original which is pin 10 and 13 of the ca3046 stands -0.5 which i think means -0,5 Volts...
i measure there -2,99 up to -3,14 Volts depending on the frequency pot turn...
There are also slightly or totally different voltages present at some of the other Points which are indexed with an value...

here's what i measured at the Points of the ca3046 with an +/-5V Triangle Signal...
pin1 Input Signal going from +0,8 to +2,8 V (centered around ca. 1,7 Volt)
2 Input Signal going from +1,2 to +3,2 V
3&14 0V
4 +8,3V (very slight Signal Content just about some mV with negative Peak only)
5 +8V
6 +2V
7 +3,3 to +3,4 V
8 +12V
9 -2,1 to -2,4 depending on freq pot and A2 trimmer
10&13 -3V

Nothing gets hot or is smoking away...
checked all traces and resoldered suspect looking solderpoints all resistors seem to be correct and also all trannies where inserted the right direction...
flat side in front of you and the from left c,b,e

anyone with an idea what i have possibly made wrong? just to mention i swapped the CA3046 already... but only have those 2 left at the Moment...

Edith says: i can test the CA3046 with my Rene Schmitz/Ken Stone VCA where i used them instead of normal trannies... will check that soon...

P.P.S. Ca3046 seem to be well intact... my VCA works properly with them...

wackelpeter · Posted: Sat Jan 03, 2015 6:04 am Post subject:

Today i've managed to "rebuilt" the filter w/o Resonance using Circuit Simulator V1.6d (won't provide a download link as i can't remember where i got this from and wouldn't guide you to a unsafe download site)
the Programm requires Java btw.

anyway the circuit is here and in theory it works... most of the values drawn into the scanned schematics seem to be the same with just a few slight differences...

so maybe someone can guide me now a bit and by checking and comparing theoretical values with the ones in my build i can fix the error...

first i see the Output at pin5 of my ca3046 the collector of the differential pair should be negative (or for simplicity the same as on pin 1 but with negative Peak)
Is this correct?

Edit:
just disconnected C13 and C14 to see what is going in the circuit and to have the same reference in my Demonstration...

unfortunately i found out that my postitive power rail goes down to 10V... a few days where i checked everything there where 11,79V... hmm maybe the module itself or the Regulator is causing htis or i have meanwhile added to much load on my psu or accidentally created a short when stuffing modules in and out... sssshhhh... have to chek and correct that first...

emsvcf1.txt

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file with ems vcf schematic... can be imported into circuit simulator

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emsvcf1.txt

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wackelpeter · Posted: Sat Jan 03, 2015 1:27 pm Post subject:

okay did some Progress in my check...

following my Simulation there wasn't enough voltage at pin 13 and 10 of the CA3046 ... swapped the on leg of the trimmer A2 from GND to +12V and voila i can hear my filter... well it sounds rude at the Moment but i think that is whilst feeding +/-5V Signal in the tl074 ... will have to add the attentuator and Change maybe some resistors for Level compression... but is cutting off manually and by cv...

regarding that leg of the trimmer A2 going to GND in the schematics... i think when i look at the scanned original schematics it's also between +12V and -9V... correct? can see the lines but not really if theres a junction respectively a Point on the ground trace or if it's simply crossing it... there the scan lacks a bit of contrast...

first of all i'm happy to get some small step Forward.... resonance is also working partially... not self oscillating now but i've seen some pages ago where to look for that...

but for today i need a break and rest a while... Very Happy

wackelpeter · Posted: Mon Feb 16, 2015 1:32 pm Post subject:

edit: solved

Snaper · Joined: Feb 28, 2014 Posts: 217 Location: Hungary

Hi Guys,

Finished this beauty last year, because of problems, did the resonance resistor mod, mentioned here earlier, now resonance is OK, but the filter is still odd.

If I remember correctly, left the completed module in my "unfinished" box, but now, I have a panel for it, so I have solve the other mystery, a problem with the Frequency pot itself.

Actually, it works weirdly :S

Measure it, I have -9 and +12 on it, the output of it is good, but still behave badly.
Sounds like the whole frequency control section messed up, because if I use CV to control the freq. the problem is the same.

I can't explain it, haven't experienced anything like this before.
I've recorded a short sample, where you can see, what I'm talking about :

https://www.dropbox.com/s/lg3y72wwtli9nw2/Recorded%20Sample%2001.wav?dl=0

This is a simple saw wave, into the filter, modulated with a short adsr from an FCUK system X ADSER.

As you can hear, the filter simply can't react to the CV. There are weird noises and stuff like this.
Like some kind of switching sound?

Actually, If I turn on the resonance pot a bit, it solve the problem, but if I adjust the Freq, it will ruin everything again.

I'm sure this is not a unique feature of this, I think I've ruined something, but have no idea what...

Its the tranny version...

LFLab · Posted: Tue Oct 10, 2017 4:21 am Post subject:

I did my own layout for this filter, the discrete version, and also added a VCA on the board (also from Yves' site, but the simplified version as can be found on the Kassutronics site).
It worked right away but does not oscillate (yet). Also, applying control voltage doesn't seem to do anything.
Will tweak the trimpot for range first, but short of trying out different FETs, what are the parameters for a FET that works well in this circuit? Idss range and such? In FET based phasers, where the JFET is used as a resistance, you need to match them to make sure they are all the same, but since there is only a single one in this circuit.. Can one adjust bias to suit this to a certain fet or perhaps select a FET with a certain Idss/ Vgs(off)?

Will try a different value for R41 as well.

dummyplugconspiracy · Joined: Mar 23, 2023 Posts: 1 Location: USA

Hi -

First time on this forum. I was sent over by Paul at soundtronics UK. I built the YuSynth EMS filter and had a similar problem to a user a few years back. Not sure whether this is even still monitored, but I need help if anyone is still out there! My resonance control has no effect unless controlled by CV. It seems to work roughly correctly when I apply CV test voltage and I can achieve self-oscillation. I already did the R41 resistor mod to change to 220K. That confirmed that self oscillation was possible, but didn't fix the resonance knob issue. Paul at soundtronics has recommended swapping out Q12 and I am tempted to flip the 3046 chip to see if I got a reverse version - is that generally safe to try? Or will it damage it if it was correct all along? What else can I try here? Should I start shopping for other 3046 chips and 3819 transistors until I find ones that work? HELP!