Variable Slope Filter / Phaser

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

hmm got the oscillators sorted but still not cracked this filter lfo....

c19 is 470nf, i replaced it with a new one too...
rate pot is fine...

ive tried to trace this to work out what is going on and ive swapped all the chips round but no joy in getting this thing to run slower!

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

swapped out q9 and q10, seems to work now....

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

...and again, sounds brilliant, especially with the living vcos.

This is my first foray into modulars, and it's a revelation. All my other synths sound like toys. I can see this being a dangerous development.

TekniK · Joined: Aug 10, 2008 Posts: 1059

dingebre · Posted: Mon Mar 01, 2010 10:56 pm Post subject:

I'm gearing up to build one or two for a Frac Rack system. So, here's my close to order FPD panel file for your consideration. It does not have mounting holes for the PCB yet. I like to use a pair of standoffs and mount the PCB vertically if i can. Anyway, this panel includes all the controls except a bypass switch. I figure I can unplug it if I don't want it. It also includes JH's Mix/Filter switch which is not on the schematics. It takes the mix pot out of the loop. JH used a Push/Pull type pot. I'm going to use a DPDT switch.

I've test fitted Alpha 12 mm pots, Swichcraft "tiny" jacks, and the small SPST switches and I think it is good to go. Bigger pots will probably not work especially on the top row.

This should translate well to a Euro size with little or no modifications. other than panel width and mounting holes.

Please let me know if I have missed something. I'll probably order the panel in a couple of weeks.

The name is in Bulgarian as are all my custom designs (long story) and reads, "JH Variable Slope Filter".

EDIT *****************************8

I made some small changes to the panel and added some mounting holes
on the right side. Also, note that the pot holes are 0.2813 inches which works great for the 12mm alpha pots.

I don't think the switches on the bottom are ideal, but i like to put labels on top and so this configuration worked best for me.

David

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dingebre · Posted: Mon Apr 05, 2010 6:12 pm Post subject:

Just finished the PCB. JH, I think you only missed one or two standard values of resistor between 220 ohms and 10 Meg Smile

I've never seen so many different values of resistors on one PCB... Thank heaven Mouser packages their resistors separately and labels them.

David

jhaible · Posted: Tue Apr 06, 2010 12:09 am Post subject:

TekniK · Joined: Aug 10, 2008 Posts: 1059

i have to wire this one + another one to built

jhaible · Posted: Thu Apr 08, 2010 12:27 am Post subject:

TekniK · Joined: Aug 10, 2008 Posts: 1059

dcreatorx · Joined: Jun 02, 2009 Posts: 17 Location: Barcelona

Hello, my varislope is already built, but now I need a panel. Can somebody say where to get one or give another solution ?

Thank you all !

guitarfool · Posted: Tue May 11, 2010 5:55 pm Post subject:

Okay, I finally got my Variable Slope Filter/Phaser done. I did a full-up panel with all the options (except a Wave CV input, but I'm going to add that in), and I'm glad I did. The LFO section is really amazing - worth building this just for that.

Here's a crappy audio file using only JH modules, with the Vari-Slope LFO controlling. A drone from a Living VCO is the input, with the "LFO Wave" set somewhere between "S&H" and "Square". Varislop output goes straight into the mixer. The LFO output also feeds a Tau Phaser set just below self-resonance, whose output goes through a String Filter. That's the drum sound that comes in after the start. Halfway through I hit the "Color" switch on the Tau to change the drum pitch a bit. No other modules or effects were used!

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

OK, let me see if I get this straight...

If you build the Variable Slope Filter version (no modulation or phaser), you would be able to switch from 6dB up to 36dB in increments of 6dB...correct?

And if so, it should be pretty easy to switch between those with a 6P rotary switch.

Would it be easy to build it with the LFO and the Filter only? Always need more LFOs...just thinking.

jhaible · Posted: Thu May 13, 2010 9:02 pm Post subject:

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

Thanks for the reply. I was thinking of a couple different uses for this project and one of them would purposefully be more limited, thus the rotary switch idea.

But these seem awesomely flexible and powerful...so I ordered 2. Hopefully you got my email.

dingebre · Posted: Fri May 14, 2010 11:51 pm Post subject: FLAMES!!!!!

I hate to display my ignorance, but this was too good not to share.

I was finally able to make time to start calibrating the filter. I finished it a week or more ago but had not plugged it in.

I'm holding the module in my lap, plug in the power... and FLAMES!!!! The rate pot was actually on fire! It "popped" and a tiny jet of flame was coming out of the pot. I just stared at it. It was so out of context, it took me a full 5 or 10 seconds to realize I might start my pants on fire!

I've exploded electrolytic caps, wired things backwards and seen the magic smoke, but not an honest to goodness flame. This is a whole new level of "DUH!" for me.

The pot was mis-wired. I had ground to the wiper so when I rotated the pot, it shorted out to -v.

I will not confirm that I wired the replacement pot the same way and fried it, too before I realized what I had done Smile

David

(The module is fine, just smells a bit like a campfire.)

jhaible · Posted: Sat May 15, 2010 1:10 am Post subject: Re: FLAMES!!!!!

jhaible · Posted: Sat May 15, 2010 1:19 am Post subject:

dingebre · Posted: Sat May 15, 2010 9:32 am Post subject: Re: FLAMES!!!!!

MR-808 · Joined: Sep 30, 2010 Posts: 28 Location: Portland, OR

jhaible · Posted: Mon Oct 25, 2010 12:27 am Post subject:

Sure, you can disconnect the path from the previous stage to the OTA input, while leaving the capacitor connected to the previous stage, thus forming a HPF function. Just like this old Emu patent, and the SSM2040 data sheet, show. And with the voltage controlled pole spread circuitry on that board, you get a Variable Slope HPF.

The reason why I had not implemented this on the board right from the start is simple: I have contributed a Variable Slope HPF, using this technology, to become a MOTM module. But that was many years ago, and I haven't seen it seeing the light of day, so yes: it's a good thing to modify the circuit like this.

Just a little hint: Instead of packing another six DG switches somewhere on the solder side (?), build a second board and hard-wire it to HPF function. Omit the DG's altogether, wire the caps to the previous stage, and omit the 100k resistors from previous stage to OTA inputs. You may even omit the whole LFO stuff on that HPF board. Then, connect two of the filter boards in series (speaking of signal path), and enjoy a varible slope HPF - LPF configuration. You may find an unused opamp on the HPF board to make a CV inverter, and route some Voltage Controled Bandwidth function for the resulting BPF filter. (I think Buchla or Serge had something like that, but certainly not in 12-pole configuration, and probably not Variable Slope, either.)

How about that?

JH.

numbernone · Joined: Aug 16, 2006 Posts: 477 Location: new york city

After scraping up enough 13700s that were lying around, I did final assembly, and hooked the filter up to my test supply.

This brings me to the strangest problem I have ever encountered which is preventing any further troubleshooting/enjoyment.

On power up the -V rail enters the circuit at -15v. Ground connection is noce throughout. However the +V rail is pulled down to near 0 at the supply. Power down, power up same deal. Unhook supply and rail returns to 15v, test with other modules...fine. Rehook to filter, +V rail takes a dive again.

No smoke, no spark, no heat, no nothing.

What the hell am I missing here??

thanks.

jhaible · Posted: Sun Jan 23, 2011 8:58 am Post subject:

numbernone · Joined: Aug 16, 2006 Posts: 477 Location: new york city

Getting there now, seems I had not read the docs in quite sometime. I assume my use of physical switches AND the DG419s was causing some problems? With the DGs pulled, I am getting some action happening, seems it will need some serious trimming, as it is not at all acting as I would expect. Self oscillation only at high frequencies, switches have no effect. LFO is AWESOME!!

More questions later if I cant arrive solo.