Variable Slope Filter / Phaser

Useemu · Joined: Jun 06, 2009 Posts: 42 Location: Germany

How can i adjust the V/Octave response? What should i measure?

JoeMorris · Joined: Apr 26, 2009 Posts: 161 Location: Brighton

Push it into self-oscillation and check it with a tuner?

jhaible · Posted: Mon Feb 14, 2011 12:46 am Post subject:

Useemu · Joined: Jun 06, 2009 Posts: 42 Location: Germany

Well yes i know that, but i need a good tracking in filter mode. I have several filters (not only JH Design) and i want to track them as good as possible.

Adjusting in this or that osc-mode is not sufficient i think. I can do that, but i need to know which one equals the filter mode.

BTW. Jürgen: I did the HPF changes you suggested (hardwired) and it works. One more reason to have the LPF and HPF Section with equal tracking to become a good BPF.

Any more thoughts?

jhaible · Posted: Mon Feb 14, 2011 2:50 am Post subject:

Useemu · Joined: Jun 06, 2009 Posts: 42 Location: Germany

Useemu · Joined: Jun 06, 2009 Posts: 42 Location: Germany

oozitron · Joined: Apr 02, 2007 Posts: 38 Location: USA

I need help Rolling Eyes

Big time...

I have my filter/phaser built and mostly wired up, but when I sweep the Cutoff knob the effect is barely noticable. Adding some Resonance helps, but the filtering is very weak, and only happens during the first (lowest) 10% of the knob range (0 ~ 1.5 volts)

If I increase the Resonance into self-modulation, turning it farther causes the self-modulation pitch to go down (about an octave by the time the Res knob is all the way CW)

I am taking my output directly from the FILTER output pad near the power supply components. Power is coming from a Blacet PS.

I have all the pole switches open. The Cutoff pot outputs 0 ~ 15 volts as you sweep it. All chips are getting their -15 and +15 volts. I was able to set the six trimpots so that the 'setup' voltages are -7.5 volts.

This is driving me nuts! My Living VCOs are desparate to send their waves into the filter... can someone give me some things to try? I have a voltmeter but no scope.

Drew

Useemu · Joined: Jun 06, 2009 Posts: 42 Location: Germany

JoeMorris · Joined: Apr 26, 2009 Posts: 161 Location: Brighton

my filter has been in storage for a bit while I built a proper case for my synth, which is now done and looking and sounding amazing in no small part due to my living vcos and living filter.

Unfortunately, an issue that had been around and then went has now reared its head again - the variable LFO S&H doesn't work - it just gives out a very quiet square wave. I'm guessing that maybe the noise source is playing up..?

Also the slope CV in doesn't seem to do anything. any hints?

JoeMorris · Joined: Apr 26, 2009 Posts: 161 Location: Brighton

noone wanna help poor little old me?
Crying or Very sad

where should I be looking on the schematic for noise generation?

jordroid · Joined: Jan 17, 2010 Posts: 193 Location: ithaca, new york

It looks like Q11 is your "noise" transistor, and trim pot R137 is for adjusting the noise amplitude. If you have a scope you should see noise at the output of U18, and the amplitude should vary while adjusting R137.

With back biased transistor noise, like this one, it is sometimes useful to try a few different transistors for Q11 until satisfactory noise is observed. I would of course first try adjusting R137, but if you get no luck you could try a socket here so you can easily audition PNP transistors.

I've really got to build one of these, all the clips i've heard of it are amazing!

regards,

jordan Smile

:edit: oh yeah, if the manual pot for variable slope R52 works, but the slope CV input does not, there is not much it could be, something is just miswired around the jack or attenuator R53, or something is weird with R54.

If neither the manual slope pot or slope CV input works then it could be something else, but it shouldn't be too hard to find, let us know if you need more assistance.

JoeMorris · Joined: Apr 26, 2009 Posts: 161 Location: Brighton

thanks

ill let you know how i get on.

you should build one definitely, they sound beautiful.
(as do all of jh's designs)

jordroid · Joined: Jan 17, 2010 Posts: 193 Location: ithaca, new york

Well, i've breadboarded this filter and indeed it is glorious sounding. Since it's on a breadboard it's easy to configure each stage for low pass, all pass or high pass, and i've found a pretty deadly band pass sound by configuring the first stage as high pass and the remaining five stages as low pass, with the slope fairly shallow and resonance high, it's quite nice! Six high pass stages sounds great as well.

It makes me want to try out Jurgen's suggestion of building two of them for a VC bandwidth band pass filter, one could have quite the monster filter box with two of these ( with the LP, AP, HP option ) in a mu-tron bi-phase series/parallel type arrangement. It would be a little bit expensive and knob heavy, but sure to impress Smile

I used what i had on hand for FETs and PNPs, which was MPF102s and 2N3906s, and 100pf caps for the filter stages, it seems to be working fine, it certainly sounds good. I did have to mess with R103 to get it to sweep nicely, but not drastically.

thanks for the great project Jurgen,

jordan

The Bad Producer · Joined: Mar 08, 2009 Posts: 282 Location: The Manhole

Absolutely amazing module!

I just finished my first filter (took a while!) and noticed that you have to have the depth control turned down to calibrate, otherwise the voltages wander around...

Also, I put an 072 where the noise 071 goes, (I always do that... sigh) so that didn't work until I burnt my finger and realised my mistake!

Here is my panel design, I've not built the final panel, so I just have a prototype with a paper sticker until I get a proper one made...

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Charlie

emdot_ambient · Joined: Nov 22, 2009 Posts: 667 Location: Frederick, MD

Nice!

I've got two of these in my backlog...had considered building one as only a variable slope LPF only, leaving off the phaser parts (for a special stand alone synth I had dreamed of making, as the design called for up to 36dB LPF and this is the only filter I've seen that can go that high, and it happens to also have the variable slope thing). But it kind of seems like a waste since the other functions are there.

Anyway, can't wait to see yours actually finished! (Or mine for that matter)

SubG (deactivated) · Joined: Oct 09, 2009 Posts: 70

that panel looks realy good!

The Bad Producer · Joined: Mar 08, 2009 Posts: 282 Location: The Manhole

Thanks guys, I want to hold off on getting it done properly until I can get a good source of anodized aluminium, the stuff I get tends to scratch too easily at the moment...

I've got a couple more to build, and would be tempted to make one just as the LPF, maybe build it up to that level and see how they compare in usefulness...

But first I want to get on with the SOST!

norman phay · Posted: Wed Jan 09, 2013 6:05 pm Post subject:

I just got one of these things up and running - I need to calibrate it but have just had a good play w it. 2 messups were - I forgot to hook up the gnd connection on a bunch of the depth pots, and I managed to blob together the filt and dry pins on the 8-way connector.

It's very impressive! Beefy sounding, and able to go to some wuite extreme effects I found. I can see myself using this a lot, as a filter as well as as a phaser. If you have one of these on your bench or in your to-do pile, I recommend you get it finished up, it's another great and musical circuit from our deceased comrade.

The Bad Producer · Joined: Mar 08, 2009 Posts: 282 Location: The Manhole

Okay, this may sound like an odd request! I've built a couple of these before, but now building another and can't seem to find any reference to how to wire up the mix/filter switch???

I have actually pulled out an old module to have a look, and I could copy that, but where did I find the info to wire that one up?

Am I going mad?

Shocked

sduck · Posted: Thu Apr 11, 2013 6:42 pm Post subject:

The Peasant · Posted: Thu Apr 11, 2013 7:29 pm Post subject:

I looked at the documentation from when I buiilt mine, and apparently the switch just goes in the line between the "dry" output and the "mix" potentiomenter to completely cut off the dry signal. From a post from JH on page two of this thread:

Mix / Filter - In "Filter" position the "Mix" potentiometer is disconnected for 100% filter signal without any crosstalk from the dry signal (important for powefull 36dB/Oct LPF effect).

If anyone wants I can scan the schematic where I hand-drew in the switch.

Take care,
Doug

sduck · Posted: Thu Apr 11, 2013 8:09 pm Post subject:

That makes sense - so you just put a switch in the Dry line between the pcb and the CCW side of the mix pot? Should it switch to ground or will just an open circuit work?

The Peasant · Posted: Thu Apr 11, 2013 8:17 pm Post subject:

The Peasant · Posted: Thu Apr 11, 2013 8:26 pm Post subject:

Oh, and if you meant connecting the end of the wet/dry potentiometer to ground, that would convert it to an output level control. I suppose you could do that if you wanted to.

Take care,
Doug