9V discrete VC LP filter?

[Isaiah]

Hi all,

I'm going nuts trying to think of a good discrete filter that will run on 9V.

I tried a basic transistor buffer like an EHX LPB (actually 2 in series, gain adjusted so the 1st didn't overdrive the 2nd).
On each stage I added another transistor as a VC element between the LPB's Collector and a 0.1uF to +V.
I kind of hoped it would be a little like a VC EHX Hog's Foot.
Anyway, it was rubbish! Didn't work at all like I expected. Let's forget about that!



Starting again -
I'd like something pretty simple and discrete that will run on 9V battery.
It's for a multi-effect thing I'm working on (for guitar, bass, synth etc).


I've been looking at the VCFs here -
http://www5b.biglobe.ne.jp/~houshu/synth/
Some of the designs are really interesting.

http://www5b.biglobe.ne.jp/~houshu/synth/VcfTp0211.gif
Could this circuit work on 9V do you think?
I figure I could lose the op-amp block at the bottom of the ladder which sets the maximum filter frequency.
But how would I tackle the op-amps while remaining discrete (and simple!)?


http://www5b.biglobe.ne.jp/~houshu/synth/Vcf0111.gif
Could anybody suggest any articles or schematics that could help me take a diode/cap arrangement like the link above
and implement it in a circuit, please?

I guess the closest thing would be the Steiner VCF...
I don't like the sound of that so much though.


My head is aching...
Thanks in advance for any help!

Alex

[aron]

I think you are heading towards an old analog synthesizer direction. I wonder if the old Oberheim filter circuits or Moog circuits are adaptable. I think they were discrete.

[Isaiah]

Sorry, yes, I didn't mention - I am after a synth VCF.

But I figured since I'm after something running on 9V, I would ask here

I've seen Slacker's adaption of the Steinder Synthacon VCF, but I don't like the sound of it.
Also, as good as Tim Escobdeo's Idiot Wah is (2 in series sounds ace!) that's not what I'm after either.


I'm unsure whether a Moog transistor ladder, diode ladder or 'single-sided' versions of either of those would work
on just 9V - Do you know, Aron? Perhaps Paul Perry might...

Perhaps you could suggest something to school me in using diodes and filters
as VC resistors (that is what the transistors act as, isn't it?), please. I'd appreciate that if you could.

If I knew for sure that the classic Moog VCF could run on just 9V, or even +/-9V, I'd built it in a second.
Even a cut-down version would be great (2-pole instead of 4, for example).

Thanks for your help, Aron.

Alex

[R.G.]

It won't run on 9V, but it will run on 18, or +18/-9, both of which you can get from a 9V battery and a single charge pump doubler/inverter chip.

[aron]

R.G. brought up a great point. Where would you find this info!

http://geofex.com/circuits/circuit_sweepings.htm

[slacker]

I've seen Slacker's adaption of the Steinder Synthacon VCF, but I don't like the sound of it.

seriously though I have to admit after playing around with some other filters it's a bit lacking. I think it probably needs to run at a higher voltage so you can get more quack out of it, I think it runs out of headroom at 9 volts.
Does your filter have to be discrete? If not and you want something simple then Tim Escobedo's Q&D VCFs sound good and are voltage controlled.
Or something like Juergen Haible's wasp filter clone or a tweaked MXR envelope filter are good.
A DIY Moog filter stompbox would be cool though 

[Paul Perry (Frostwave)]

The circuits in the LM13700 data sheet will run on 9v.
I made a useful 9v envelope follower using one with a simple op amp & diode rectifier feeding the resistor to the control input.
Note the circuits are shown for +-15V rails, so you have to dick around a bit.

[dano12]

If you are in to super simple, Tim's Quick & Dirty VCF might fit the bill.

http://www.geocities.com/tpe123/folkurban/fuzz/snippets.html

I've built several versions of this and it performs very nicely given the part count. I drive it with an 8-step sequencer based on a 4017.

[Isaiah]

RG - Thanks, it's nice to know it will run on 18V or +/-9V. I don't mind using two 9V batteries. Have you tried this yourself?


Slacker - I wasn't putting you down in any way, I hope it didn't appear that way! I think it's great you adapted the design for stompbox use,
but it's the actually sound of the filter itself I don't like, not your adaptation.


Dano - Thanks for the suggestion, but I don't really like the sound of those sort of filters. It might become obvious - I'm picky about filters haha. But I appreciate your input.


Paul - I'm undecided on the OTA-based filter sound - I don't know if I like it or not haha.
They seem pretty common in old Japanese synths - they have that
squelchier sound (thought the Roland TB-303 was pretty squelchy and that was a transistor ladder IIRC, maybe diode).
I looked at the Electronics for Music website and in one of the PDFs (3500, I think) there's a load of transistorised OTA-based filters.

On the Electro Music forum, someone pointed me towards this - Discrete Op-amp


If the Moog transistor ladder will definitely run on two 9V batteries, that's almost certainly what I'll build.

Failing that, I quite like the look of these -

http://www5b.biglobe.ne.jp/~houshu/synth/PhTrR2.gif
I realise it's an All-pass filter, not Low-pass. How could it be converted to a Low-pass response?
I'm sure 2, 3 or 4 of those in series would sound pretty sweet (it'd be no ladder filter, but it might be good).

http://www5b.biglobe.ne.jp/~houshu/synth/Vcf99081.gif
Similar to the Moog transistor ladder, I'm sure it'd sound different though, but retain that heavy filter sound that I think non-ladder filters
seem to lack IMHO.
Those op-amp buffers offer 6, 12, 18 and 24dB (1, 2, 3 and 4-pole respectively) filter outputs, I could omit most of those.
http://www5b.biglobe.ne.jp/~houshu/synth/VcfTp0211.gif
Looks like a variation of the one I just linked to. Again, I could omit the 6db output buffer.

Thanks to all who have helped so far!

[Mark Hammer]

Having been a witness to the development of Sam Hoshuyama's "lunchbox synth" while he was visiting here in 2002 (shown below), I can vouch that he made it his mission to develop a totally CMOS system that would run off a single-ended 9v supply.  The assorted schematics at his site show a +15v supply and occasionally +/-15v, but I imagine much of it can be adapted to run off a single-ended 9v supply.  And yes, it really worked and sounded pretty darn good.....and those are wires you see in the containers, not soba noodles.   This is an example of what can happen when a talented industrious guy finds himself thousands of miles away from his wife and daughter for 6 months.  As distracting obsessions go, it gets my vote.

[Isaiah]

Awesome!
He seems like a cool guy - he's got some very interesting designs.
I love the fact that he designed a whole modular around CMOS components - kind of the opposite of what I'm trying to do haha!

http://guitarfool.com/modules/DiodeVCF.html
A diode ladder filter looks like a much smaller headache than a transistor ladder.
No resistor chain biasing the transistors etc.
The differential amp used in the link above is actually an OTA, but I'm sure it could be replaced
by a transistorised op-amp. Same goes for the Resonance/feedback OTA (I have no use for VC Resonance).
It's shown as working on +/-12V, so I guess it would be fine running on two 9V batteries.

[Mark Hammer]

The diode ladder one you link to is one of Tom Gamble's modules.  A number of years ago, before he went all digital and revenue-generation on us, Tom G had a more elaborate EFM site and included a number of both tested and untested analog designs.  One of them was, if I'm not mistaken, a 9v based diode ladder.  I have that schematic at home.  I'll see if I can dig it up.  Again, not sure if it is tested or not.

[Isaiah]

That would great! Thanks, Mark!

[slacker]

Slacker - I wasn't putting you down in any way, I hope it didn't appear that way! I think it's great you adapted the design for stompbox use,
but it's the actually sound of the filter itself I don't like, not your adaptation.

Don't worry I didn't take it like that.

There's some more interesting filter ideas here
http://www.uni-bonn.de/~uzs159/

[g.]

i've build a stand alone version of the Wacky zany weird filter
A.K.A. Weird Sound Generator or WSG

http://www.musicfromouterspace.com/analogsynth/YOUR_FIRST_SYNTH/YOUR_FIRST_SYNTH.html

works good on 9v

[Isaiah]

Any luck finding that circuit please, Mark?
Thanks.


The filter in this schematic looks interesting -
http://experimentalistsanonymous.com/diy/Schematics/OOP%20Japanese%20Electronics%20Book/gtr-synth.gif

Could certainly be made entirely discrete.
But the link i posted in this thread a while ago about stated that the discrete op-amp circuit needs 12V.
Do you think it could run on 9V? or could this filter run on 18V?
Has anyone built this filter before? I'm not really sure what it would sound like - not quite a diode ladder...

Thanks,
Alex

[Mark Hammer]

Any luck finding that circuit please, Mark?
Thanks. Alex

One's luck in finding is always increased by one's effort in looking, and that in turn is helped by remembering to look.   We've got company coming and have been engaged in some last-minute remodelling.  I got sidetracked.

[slacker]

The filter in this schematic looks interesting -
http://experimentalistsanonymous.com/diy/Schematics/OOP%20Japanese%20Electronics%20Book/gtr-synth.gif

Could certainly be made entirely discrete.

Yeah that's a cool schematic, I've been thinking of building the filter part for a while. It's a variation of the Synthacon VCF with the transistor pair replaced with an opmap. There's some more versions here.

[Mark Hammer]

Any luck finding that circuit please, Mark?

Found it!  I'll post it tomorrow near lunchtime.  Unfortunately I don't have the URL for my Photobucket account at home and will have to wait until I'm at work.  But I do have it and it is a +9v single-ended circuit.  Whether it works is another thing.  Tom Gamble used to post a lot of untested things and once in a while they didn't work.

[widdly]

There is a diode ladder LPF running of 5v here...

http://www.elby-designs.com/pixie/pixie-vcf3.pdf

There is also a state-variable wasp one for 5v here...

http://www.elby-designs.com/pixie/pixie-vcf2.pdf