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Tube VCF on Dutch synth forum
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j.baars



Joined: Jan 11, 2008
Posts: 16
Location: netherland

PostPosted: Sat Sep 20, 2008 11:38 am    Post subject: Reply with quote  Mark this post and the followings unread

the resistor at 15 volts should be 350 0hms, use a 1 watt type .
the diode thingie is to keep the filament (heather) voltage aproxx. 0,7 volts.
I did use the antiparallel confg to make sure the filament is not burned when the powersupply is
accidently inverted when experimenting.
bye,
jeroen baars
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Luka



Joined: Jun 29, 2007
Posts: 1003
Location: Melb.

PostPosted: Thu Oct 30, 2008 6:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

mr baars

was the mosfet chosen for it's particular attributed or can i substitute with another fet like mpf102. just wondering if you used that as you had it on stock or if it is crucial for the design


well im going to try this today, hopefully it works, ill post my results

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j.baars



Joined: Jan 11, 2008
Posts: 16
Location: netherland

PostPosted: Fri Oct 31, 2008 3:22 am    Post subject: Reply with quote  Mark this post and the followings unread

the fet is used as a variable resistor, you can use almost every substitute you can find.
even a npn transistor will do the job. ( with more distortion )

you can find another tube filter design here; http://www.synthforum.nl/forums/showthread.php?t=96176&page=4&highlight=diy+modulair

bye,
jeroen
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Luka



Joined: Jun 29, 2007
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Location: Melb.

PostPosted: Fri Oct 31, 2008 4:12 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks jeroen
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problemchild
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crashlander42



Joined: Oct 21, 2006
Posts: 292
Location: Orlando, FL (US)

PostPosted: Sun Nov 23, 2008 11:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

I breadboarded the tube VCA and am pleased with it's sound. It almost sounds filterish. It has a neat woosh. I added a mod to it that acts almost like an amount pot, but also changes the timber. It's actually Frequency Central's "HiGain" mod for his pentadriver with a 100k pot instead of a 68k resistor.

Really, this seems to act more like a PWM than a VCA, but it does the trick. Even with the original design.

Anyway. Here's a video. http://www.youtube.com/watch?v=3SxKiEdGgxo

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Luka



Joined: Jun 29, 2007
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Location: Melb.

PostPosted: Mon Nov 24, 2008 12:22 am    Post subject: Reply with quote  Mark this post and the followings unread

did you put resistors on your freq pot to restrict the voltage?
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frequencycentral



Joined: May 25, 2008
Posts: 186
Location: UK

PostPosted: Mon Nov 24, 2008 10:48 am    Post subject: Reply with quote  Mark this post and the followings unread

crashlander42 wrote:
I breadboarded the tube VCA and am pleased with it's sound. It almost sounds filterish. It has a neat woosh. I added a mod to it that acts almost like an amount pot, but also changes the timber. It's actually Frequency Central's "HiGain" mod for his pentadriver with a 100k pot instead of a 68k resistor.

Really, this seems to act more like a PWM than a VCA, but it does the trick. Even with the original design.

Anyway. Here's a video. http://www.youtube.com/watch?v=3SxKiEdGgxo


That sounds most excellent! Seeing as how you mentioned it, here's the Pentadriver MkII with the high gain mod. It's posted elsewhere on the net ( I mostly hang out at the DIY Stompbox forum http://www.diystompboxes.com/smfforum/forums.html?topic=71381.0), but now it's here too.....

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

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LektroiD



Joined: Aug 23, 2008
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PostPosted: Wed Jan 07, 2009 12:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm quite interested in this, I wonder how easy or hard it will be to transfer to stripboard? Since I don't have an etching kit.
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janvanvolt



Joined: Nov 24, 2005
Posts: 285
Location: Mainz, Germany

PostPosted: Mon Feb 23, 2009 8:00 am    Post subject: Reply with quote  Mark this post and the followings unread

HELP!

I am still having issues with my two built tubes.
They still do not work (as expected).

I am using this here: http://www.casia.org/modular/SF/tubevcf.jpg
(which the grounding of course) BUT:

a) if i turn input counterclockwise, i still have an input signal.
b) Resonance also does not work as expected.

I simply didn't get the "tube" sound at all, more or less a "passing" signal.

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janvanvolt



Joined: Nov 24, 2005
Posts: 285
Location: Mainz, Germany

PostPosted: Sun Mar 01, 2009 7:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

*sigh*

nobody able to help me ?

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Luka



Joined: Jun 29, 2007
Posts: 1003
Location: Melb.

PostPosted: Sun Mar 01, 2009 7:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

i got a couple dud 5672s in my batch
had you tried replacing them?

also are you sure your tube is orientated correctly?
it is really confusing with j.baars schems as he numbers them with a different orientation to the datasheets. you have to pay attention to the dot not the numbers. i think he said in this thread that he copied the numbering format from an old schematic but it is something to be aware of.

i havent made the filter but i have made the vca. i have a modded version with an input mixer, negative bias on the grid and output amping. the output amp can move the distortion more towards opamp distortion and not purely tube but i like the outcome. once i have properly tested it i will post the design.

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problemchild
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janvanvolt



Joined: Nov 24, 2005
Posts: 285
Location: Mainz, Germany

PostPosted: Wed Mar 04, 2009 7:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Luka,

a) the red dot is (hopefully) correct, it will be on the "upper" direction.
b) i have built two pcb's from this forum post, both are acting same strangely.
c) i can try to get other 5672 tubes...

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crashlander42



Joined: Oct 21, 2006
Posts: 292
Location: Orlando, FL (US)

PostPosted: Wed Mar 04, 2009 8:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

I build the VCF from the schematic and was never happy with how it sounded. It doesn't really seem to filter, just passes sound thru. There is resonance though. It's weird. I should probably breadboard it and play with it.
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Luka



Joined: Jun 29, 2007
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Location: Melb.

PostPosted: Thu Mar 05, 2009 3:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

ill give the vcf circuit a go on my breadboard next week jan
ill let you know how i go.

i know that my vca didnt work first time when i used the initial layout but i think that was due to a bad etch and perhaps a bad tube. once i studied the circuit i decided i wanted to change it anyway.

One thing i was told by eric from metasonix in respect to the tube designs is that they need a negative bias on the grid. This circuit doesnt include that. He suggested -0.4v for the 5672. I have implement this into my vca design. I might try it when i breadboard the vcf and see if it makes a difference.

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problemchild
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janvanvolt



Joined: Nov 24, 2005
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Location: Mainz, Germany

PostPosted: Fri Mar 20, 2009 6:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Too bad that my VCF still doesn't work Sad do you have an update on the breadboard design ?
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Ayab



Joined: Oct 27, 2015
Posts: 96
Location: London, UK

PostPosted: Sun May 28, 2017 5:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
quick questions

some of my friends are running on 12v supplies. will this be possilble for this module?


I realised that the schematic is for 12V Embarassed

Going to give it an etch Laughing
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Ayab



Joined: Oct 27, 2015
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Location: London, UK

PostPosted: Fri May 04, 2018 4:17 am    Post subject: Reply with quote  Mark this post and the followings unread

I want to etch a mean sucker vcf but I don't understand part of the schematic I have outlined in pink on the schematic (pictured under the layout below):

Specifically:

1. What does "Rx" mean? (alternately a fixed resistor?)
2. What is the dotted line between 'Rx or 1m Lin' that leads to 'input'. How do I connect this in a circuit?
3. What do the two slashes on either side of 'Rx 220k' after 'input' mean?

The pcb by Etaion (see green layout below for ease of reference) seems to match the schematic other than the 350r resistor which is for +15V and I will run it on +12V with a 275r resistor. If anyone can see any other differences please let me know.

Thanks very much.


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Ayab



Joined: Oct 27, 2015
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Location: London, UK

PostPosted: Thu May 10, 2018 5:21 am    Post subject: Reply with quote  Mark this post and the followings unread

I realise that this probably means either 1m lin potentiometer or R 220K but can someone please confirm.
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Blue Hell
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Joined: Apr 03, 2004
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PostPosted: Thu May 10, 2018 6:13 am    Post subject: Reply with quote  Mark this post and the followings unread

That is my interpretation too, select one of both options.
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Ayab



Joined: Oct 27, 2015
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PostPosted: Thu May 10, 2018 7:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Jan

As you think so I will use 1m linear pot instead of 220k

Appreciate your help and will let you know how it works out
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