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 Forum index » DIY Hardware and Software » Jürgen Haible designs
Variable Slope Filter / Phaser
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interested?
yes
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no
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Total Votes : 42

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davebr



Joined: Jun 09, 2007
Posts: 181
Location: portland, or

PostPosted: Mon Aug 03, 2009 7:52 pm    Post subject: Re: Variable Slope Filter / Phaser
Subject description: Panel Design
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numbertalk wrote:
I was looking at your mods:
http://www.modularsynthesis.com/jhaible/varislope/DJB%20Varislope%20enhancements.pdf
And had a question about adding the 3 inputs with buffer - I have a CGS DC Mixer board I'm going to use for this. It has a 1K output resistor - I notice for your mod you have no output resistor - the output of the TL074 goes straight into the IN pad of the PCB - would I want to exclude the 1K resistor here and use a jumper instead?

The 1K resistor is there to protect the output of the op amp, especially with plugs and jacks since the tip will short to ground when connecting. There isn't any need for it in a direct connected circuit so I would replace the 1K with a jumper.

Quote:
Also, are those 100K Audio taper pots for the input attenuators?

I do not use audio taper pots for input attenuators. First with linear potentiometers, I can kind of estimate the input levels. For example, to not overload the mixer, I can't sum three 10 volt pk-pk signals. However, I can probably have them all at a third and get it pretty close. Also, with 100K potentiometers and 100K input resistance for the op amp, you have somewhat of a semi-log control anyway. 50% is at about the 1:00 position. Go to http://www.mindspring.com/~clist/PotGraph.html and graph 100K for each and you can see the response.

Quote:
And for the output buffer, I'm assuming I could use a TL072 here fine and that you used a TL074 for the extra op-amps for the other mods you did, right?

Correct.

Dave
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numbertalk



Joined: May 05, 2008
Posts: 980
Location: Austin, TX
Audio files: 5

PostPosted: Mon Aug 03, 2009 8:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the help and information Dave!

JH, I'm assuming all the pots in the schematic (except the one for the input level which you have labeled as audio taper but I plan to use an input mixer to allow more inputs anyway) are linear taper, right?
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davebr



Joined: Jun 09, 2007
Posts: 181
Location: portland, or

PostPosted: Thu Aug 06, 2009 9:01 pm    Post subject: Variable Slope Filter / Phaser
Subject description: FrontPanelExpress
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I got my FPE panel today. It's really nice. However, the spacing from the top edge to the potentiometers across the top is exactly 0.5". I forgot when I used this dimension for my YuSynth FFB that I used smaller potentiometers. It fits, but is closer than I would like. I went ahead and adjusted the FPE file on my site by moving the controls 0.050" down from the top. Thought I'd mention it in case someone is using that file.

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

http://modularsynthesis.com/jhaible/varislope/varislope.htm

Dave

Last edited by davebr on Fri Aug 07, 2009 4:00 pm; edited 1 time in total
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Thu Aug 06, 2009 11:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

numbertalk wrote:
Thanks for the help and information Dave!

JH, I'm assuming all the pots in the schematic (except the one for the input level which you have labeled as audio taper but I plan to use an input mixer to allow more inputs anyway) are linear taper, right?


Yes.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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davebr



Joined: Jun 09, 2007
Posts: 181
Location: portland, or

PostPosted: Sat Aug 08, 2009 4:05 pm    Post subject: Variable Slope Filter / Phaser
Subject description: Switch wiring
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I got enough of my module wired to operate and calibrate it. Here's some tips I had to figure out.

The switch wiring isn't very clear on the schematics although it was documented in a previous posting.

Open=Bandpass, Closed=Allpass
Open=Dirty, Closed=Clean

Also, R62 isn't listed in the adjustment procedure. It is the 1V/Oct calibration.

Dave
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JoeMorris



Joined: Apr 26, 2009
Posts: 160
Location: Brighton

PostPosted: Mon Aug 10, 2009 4:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Im currently looking into building a custom keyboard synth for a nice long term project... I was thinking of using the Living VCOs and this filter project as part of this keyboard... good idea or not?
Also, would it be worth me populating the whole board or just going for the cut down filter-only version?

Cheers
Joe
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Mon Aug 10, 2009 9:52 am    Post subject: Reply with quote  Mark this post and the followings unread

JoeMorris wrote:
Im currently looking into building a custom keyboard synth for a nice long term project... I was thinking of using the Living VCOs and this filter project as part of this keyboard... good idea or not?
Also, would it be worth me populating the whole board or just going for the cut down filter-only version?

Cheers
Joe


I haven't checked if the tracking and stability of the Living VCOs is good enough for polyphonic applications or not. It may well be, but I haven't personally tried it.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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JoeMorris



Joined: Apr 26, 2009
Posts: 160
Location: Brighton

PostPosted: Mon Aug 10, 2009 10:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh, I only meant a minimoogesque monophonic keyboard synth - i think that's quite enough of a project for me at this stage, I cant imagine making a DIY poly - just yet anyway!

So am I right in thinking that i should only populate the board as suggested in the 36db filter thread? I'm a bit funny about not using the board to its full capacity, always seems like a waste, but then if the phaser part wont be any use then there'd be no point.

So would this filter on its own make for a good filter section on a monophonic lead synth?

Cheers,
Joe
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Mon Aug 10, 2009 10:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah, I see. Yes, why not. No need for the onboard LFO if you have other modulation sources.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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numbertalk



Joined: May 05, 2008
Posts: 980
Location: Austin, TX
Audio files: 5

PostPosted: Mon Aug 10, 2009 1:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Dave,

I was hoping you wouldn't mind explaining in a little more detail your output buffer driver mod - what's the benefit? So you're bypassing all the components between MIX and OUT on the schematic, right? You don't use the OUT pad at all - just take out straight from MIX pad? So no need to link out with jumpers or install any of these components using this mod, right?

Thanks,
Paul
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davebr



Joined: Jun 09, 2007
Posts: 181
Location: portland, or

PostPosted: Mon Aug 10, 2009 9:39 pm    Post subject: Variable Slope Filter / Phaser
Subject description: Modifications
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numbertalk wrote:
Hi Dave,

I was hoping you wouldn't mind explaining in a little more detail your output buffer driver mod - what's the benefit? So you're bypassing all the components between MIX and OUT on the schematic, right? You don't use the OUT pad at all - just take out straight from MIX pad? So no need to link out with jumpers or install any of these components using this mod, right?

Thanks,
Paul


First, I borrowed the modifications from Scott Juskiw, but I can tell you why I was interested.

I started designing a panel, and came to the conclusion I had more knobs and controls than would fit in a 2U MOTM-style panel. Panel space is important to me, but I decided this module had enough cool features that I would go up to a 3U panel. I really like multiple inputs on my modules so wanted to add at least one to two more inputs. I could have just added additional inputs into U1B but hate floating that many resistors and wires plus I like to not do too many modifications to a PCB. That took one op amp.

I wanted a reversing attenuator - that took a second op amp.

I wanted a bi-Led indicator for the LFO. I'd rather drive it with a current source, so that took a third op amp. That left a fourth unused op amp.

I'm sure the output buffer is perfectly fine, but since I had a spare op amp I decided to replace the emitter follower. Rather than run the Mix signal back onto the Varislope PCB I will connect it to my enhancement PCB. That leaves two pins unused on the 8 pin connector - Mix and Out. I replaced R45 with a jumper to have an extra ground pin. That way I can use one ground pin for the Feedback control and the second ground pin for a twisted pair input from my enhancement PCB.

I added a jumper from LFO Out to R47 so the Out pin becomes LFO out. That way I can use the 8 pin connector to interconnect to my enhancement PCB with three wires (In, Gnd, LFO Out).

I'm not sure there is any significant benefit of the op amp output buffer. I did add an inverting stage to the input, so I'd rather have an inverting stage on the output to keep the phase relationship the same. I also prefer a nice low Z output, short circuit protection, and DC coupling (no need for the coupling capacitor) and had the spare op amp.

I did add a few more jumpers to the Varislope PCB that are documented on my web page. I turned the AC 5 pin connector to a +/- 15 volt connector to power my enhancement PCB. Since then I decided to use a MUUB-4 for the enhancements. That has a separate 4 pin MOTM-style power connector so I can either make a daisy chain power cable, or a simple interconnect cable to the AC 5 pin connector (which is now DC power).

I also modified the U1B for unity gain, and added a gain control on U2A so I can adjust the overall module for unity gain. I like a 10 volt pk-pk input with a predictable 10 volt pk-pk output. I know that having three summed inputs can over drive the input, but with linear controls I can just set the levels so they add to 10 and get it pretty close. Again, these changes are now documented on my web page.

I've yet to build the MUUB-4 so there might be a few issues to deal with. I'll probably not get to it until the weekend and will keep my web page up to date.

I do like the wave feature and the S&H is quite nice. I've yet to wire up the Mix and Feedback controls so haven't played with that yet.

Dave

Last edited by davebr on Tue Aug 11, 2009 12:35 pm; edited 1 time in total
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numbertalk



Joined: May 05, 2008
Posts: 980
Location: Austin, TX
Audio files: 5

PostPosted: Tue Aug 11, 2009 5:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for all the info Dave! Very much appreciated and very helpful.
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JoeMorris



Joined: Apr 26, 2009
Posts: 160
Location: Brighton

PostPosted: Thu Aug 13, 2009 2:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Forgive me the silly question but are 50ppm resistors ok for things like this project or not?
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Thu Aug 13, 2009 2:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

JoeMorris wrote:
Forgive me the silly question but are 50ppm resistors ok for things like this project or not?


50ppm/K temperature? Sure - quite good, actually!

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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JoeMorris



Joined: Apr 26, 2009
Posts: 160
Location: Brighton

PostPosted: Thu Aug 13, 2009 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK, cool. They were really cheap so I thought they might be too ropy for a nice squelchy filter.
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JoeMorris



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Posts: 160
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PostPosted: Thu Aug 13, 2009 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ive decide to build the whole thing for my keyboard synth, I like the look of that LFO and I'm going to chain this filter up with a multimode filter too so I can have the option of it operating as a phaser after that filter anyway. Woo. I like the idea of some built in effects anyhow.
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davebr



Joined: Jun 09, 2007
Posts: 181
Location: portland, or

PostPosted: Thu Aug 13, 2009 9:06 pm    Post subject: Variable Slope Filter / Phaser
Subject description: Completed module
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I completed the front panel wiring tonight on my module. Wow - what a lot of wires. This one took a lot of patience and breaks to complete. I'll be verifying it and updating my web page over the next few days.

Photos at http://modularsynthesis.com/jhaible/varislope/varislope.htm

Dave
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TekniK



Joined: Aug 10, 2008
Posts: 1062

PostPosted: Fri Aug 14, 2009 2:55 am    Post subject: Re: Variable Slope Filter / Phaser
Subject description: Completed module
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davebr wrote:
I completed the front panel wiring tonight on my module. Wow - what a lot of wires. This one took a lot of patience and breaks to complete. I'll be verifying it and updating my web page over the next few days.

Photos at http://modularsynthesis.com/jhaible/varislope/varislope.htm

Dave


nice,i think this is your most expensive module (with all those pots)?

Can we expect some cool demo's to dave?
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davebr



Joined: Jun 09, 2007
Posts: 181
Location: portland, or

PostPosted: Fri Aug 14, 2009 5:52 pm    Post subject: Re: Variable Slope Filter / Phaser
Subject description: Completed module
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TekniK wrote:
nice,i think this is your most expensive module (with all those pots)?


Actually not. My CVS module was as complex and more. I have 16 pots on it but also the LCD, MIDI, and a bunch more jacks. http://modularsynthesis.com/cvs/cvs.htm

I'm now using BI Technology pots. They are very affordable but hard to find. The only distributor that sells them that I can find is Rapid for £1.65. Shipping to the US was prohibitive so I ended up buying a lot directly from the manufacturer. The price was very good so I no longer worry about how many pots a panel has as long as they are all 100K! The minimum lot size was 240.

Oakley Sound also will sell them. I have bought a few 1M from them.

Dave
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davebr



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PostPosted: Fri Aug 14, 2009 9:39 pm    Post subject: Re: Variable Slope Filter / Phaser
Subject description: Completed module
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davebr wrote:
I'll be verifying it and updating my web page over the next few days.

I managed to get some time tonight to verify the module. I had a couple of front panel wiring errors but got everything operational and calibrated.

I did have one issue. My LED circuit loaded the LFO Out circuit and clipped the waveform as it can only source current. Even without my LED circuit I would want more drive capability. I went ahead and added an op amp buffer on my MUUB-4 board and then drove the LED circuit and LFO Out jack from it.

I was hoping to do my enhancements in four op amps but it took five. There might have been a simpler way but my module was built and it was easier to piggyback an op amp on the MUUB. I've updated the schematics and documentation on my web site. http://modularsynthesis.com/jhaible/varislope/varislope.htm

Dave
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numbertalk



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PostPosted: Mon Aug 17, 2009 6:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi JH,

Just started stuffing my board and noticed there aren't spots for ferrite beads or even 22R resistors for those of us building this as a module to be powered by our synth power supply. Just wondering why you decided to leave those out for this board and if there are any implications with not having them?

Thanks.
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Tue Aug 18, 2009 1:24 am    Post subject: Reply with quote  Mark this post and the followings unread

numbertalk wrote:
Hi JH,

Just started stuffing my board and noticed there aren't spots for ferrite beads or even 22R resistors for those of us building this as a module to be powered by our synth power supply. Just wondering why you decided to leave those out for this board and if there are any implications with not having them?

Thanks.


Return question: Do you need them?

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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numbertalk



Joined: May 05, 2008
Posts: 980
Location: Austin, TX
Audio files: 5

PostPosted: Tue Aug 18, 2009 5:40 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Return question: Do you need them?


Ah, but see, this is also my question Smile There are 2 electrolytic caps and 2 22R resistors or ferrite beads (one for each rail obviously) for power supply filtering on all of my other modules. While I do absolutely trust that if you didn't put space for the beads or resistors on this board that this module doesn't need them, I'm just wondering what is different about this module and am curious as to why it doesn't require ferrite beads on the power rails. The beads and caps form an RC low pass circuit on each rail to filter out any HF noise coming or going from or to the power supply, right? Just to make sure I'm being clear, I'm not at all questioning your decision to not include them here - I would just like to learn more about these kinds of things as I build circuits Smile

Thanks.
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Tue Aug 18, 2009 5:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, ferrite beads are a good thing, certainly!
If you have them on your module, it becomes "harder" against high frequency interference coming in from the power supply lines. That's why I put them onto the Living VCOs boards, to make them "hard" agains any unvoluntary "soft sync" effects.

When do you need them on an audio processing module? I say: if you get any audible noise on your module, coming from the PSU or from other modules. I think it's unlikely that you do. *If* you do, it may be recommended to add them (somewhere on the solder side of the PCB, maybe). But as it's unlikely, I didn't reserve board space for them.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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numbertalk



Joined: May 05, 2008
Posts: 980
Location: Austin, TX
Audio files: 5

PostPosted: Tue Aug 18, 2009 6:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah, ok. Thanks for the clarification!

jhaible wrote:
Well, ferrite beads are a good thing, certainly!
If you have them on your module, it becomes "harder" against high frequency interference coming in from the power supply lines. That's why I put them onto the Living VCOs boards, to make them "hard" agains any unvoluntary "soft sync" effects.

When do you need them on an audio processing module? I say: if you get any audible noise on your module, coming from the PSU or from other modules. I think it's unlikely that you do. *If* you do, it may be recommended to add them (somewhere on the solder side of the PCB, maybe). But as it's unlikely, I didn't reserve board space for them.

JH.
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