Vacuform - Vacuum tube diode SVF

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BARD
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Vacuform - Vacuum tube diode SVF

Post by BARD » Sat Dec 15, 2018 6:22 pm

Hi
I'm currently working on something fancy - it's 12dB state variable filter with two EAA91 vacuum tube diodes as a dynamic resistance element.

11 mar 2019: I have updated DIY version layout:
Image

(This is how old prototype looks like [quick and dirty decal]):
Image

I have tried to keep it in soft saturation all the time, running 6N3P triode @ 55V anode voltage. It can be clean sounding at very low input levels, but "clean" is not what you have tubes for :sb: On the other side high signal levels tame resonance so it doesn't escape into harsh sound territories easily.
Overload LED shows approximately when input signal starts to stifle resonance. Soft saturation begins way earlier.
Resonance is currently voltage controlled with vactrol - I considered using pentode VCA for fast responses, but that would be like additional 95mA for little more functionality.

Entire path is discrete at the moment, but I plan to implement VC-attenuverters in non-DIY version for inputs that will have op-amps.
The three audio inputs have attenuverters with silent zone - Making them voltage controlled would add much more possibilities (ring modulation / VCA, LPG/BPG/HPG etc).


Current draw is ~300mA @ 12V and ~20mA @ -12V now (Current draw for DIY version is to be measured soon). I'm thinking about making optional switch for omitting onboard inverter and supplying tubes with +5V directly from bus.

Sound demos - classic transistor oscillators running into it, with some patches having additional tube VCA:
https://soundcloud.com/bardsynth/vacuform-early-demo

It even tracks about two octaves :cloud: Gonna do some more tests next weekend.
Would you put it in a rack?
Let me know what you think about it and what also you would see in it. I'm open to suggestions!

update may 29 2019

Interest list:

Basic version (PCB + tubes set) (95USD)
fitzgreyve
Prunesquallor
Moog$FooL$
LED-man
anto32
artilect99
Eric The Red
uuav
Euro pcb + panel + tubes set (125USD)
Drillionaire
oberkorn
psykon
furanku x2
Ayab x2
Addam
Swyndger
designator
paperCUT
frozenkore
numan7 (second kit)
limpmeat
acgenerator
artilect99
paperCUT (possibly upgrade to full kit)
Full Euro kit (155USD)
nimmen (whick kit?)
luchog(Euro kit / builded)
degeneratedsines
mOBiTh
numan7 (first kit)
Rex Coil 7 (first kit)
electricanada
Stides
jonny_w
Rexxx
Synthsense x2
nimmen
xthrasherx
d.simon
jaidee
ArboriaAuralist
kennymester
yoggyone
metasonix
sceledra
keninverse
windspirit

Assembled Eurorack module (270USD)
Yes Powder
modullos

Leave me PM if you would like to have more custom option!
Last edited by BARD on Wed May 29, 2019 4:29 am, edited 8 times in total.

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Revok
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Post by Revok » Sat Dec 15, 2018 6:28 pm

Sounds awesome.

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Post by Eric the Red » Sat Dec 15, 2018 11:37 pm

Yes, I would put this in a rack!
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Post by Jarno » Sun Dec 16, 2018 12:14 pm

Looks and sounds fantastic, nice job!

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Moog$FooL$
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Post by Moog$FooL$ » Sun Dec 16, 2018 12:53 pm

i have tons of used & new diode tubes....... wish i had the design chops to use them like this.

nice work. :tu:
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Post by Schlumpfhut » Sun Dec 16, 2018 1:02 pm

Excellent demo for a great idea. Any chance having this in 5U?

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Post by windspirit » Sun Dec 16, 2018 3:47 pm

This thing sounds amazing, great job.

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Post by lisa » Sun Dec 16, 2018 3:53 pm

Sounds splendid, very yummy!
My first modular track where I used drum modules! There's also a ton of FM cross modulation from the Instruō Cš-L in there and the Metasonix R56 is a big part of the sound. :star:



We also just did a live performance. Just eurorack, a mixer and two nitwits. :hyper: http://tiny.cc/8ndspz

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Post by SlightlyNasty » Sun Dec 16, 2018 5:29 pm

My god, that low end!
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BARD
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Post by BARD » Sun Dec 16, 2018 7:52 pm

Yay, that's overwhelmingly positive response :love:
Schlumpfhut wrote:Any chance having this in 5U?
Having tubes in 5U is great idea and I think is totally doable in 2U/2MU width. I planned to do small series in Eurorack format, but making single modules for 5U also would be fun :hmm: Let's see what interest is.
Moog$FooL$ wrote:i have tons of used & new diode tubes....... wish i had the design chops to use them like this.
I have bought big bag of EAA91s two years ago without having idea what to do with them. They came in handy for sure 8-) If your diodes are indirectly heated then it will be possible to use them just like ordinary semiconductor diodes... in most cases.

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Post by Eric the Red » Mon Dec 17, 2018 12:39 pm

I think I would prefer 5U as opposed to Euro for this. I think if you just build it to be compatible with +/- 15 volts, most 5U Builders would be ok with flying wires for the build. Most of the stuff that we build seems to be this way.

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Post by maltemark » Mon Dec 17, 2018 1:00 pm

Beefy!

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Post by MARK27 » Mon Dec 17, 2018 2:29 pm

If you offered a black panel option, I would buy it in a heart beat.

:hihi:

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Post by MARK27 » Mon Dec 17, 2018 2:36 pm

The other option you might consider is a way to power the +5V independently, like Trogotronic does with their tube VCA.

Just a thought.

The unit sounds beautiful.

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Post by Reality Checkpoint » Mon Dec 17, 2018 3:27 pm

SlightlyNasty wrote:My god, that low end!
I would quite like this in an LW/SN format!

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Post by mOBiTh » Mon Dec 17, 2018 6:10 pm

i would love one!

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Post by fitzgreyve » Tue Dec 18, 2018 4:45 am

Brilliant - would love a PCB

Yes, useful to have the option to power the valve heaters from an independant source.
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Post by Prunesquallor » Tue Dec 18, 2018 5:10 am

Reality Checkpoint wrote:I would quite like this in an LW/SN format!
+1

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Post by BARD » Tue Dec 18, 2018 5:38 am

Talking about 5U / 4U (even 3U for the stubborn!) DIY version there are two options:
- PCB parallel to panel, tubes protruding from panel, skiff
- PCB perpendicular to panel, tubes inside, ~9cm deep
Both options would have tube sockets mounted on PCB, saving eventual impedance / hum problems + wiring. Both options are the same PCB :roll:
Unfortunalety I don't have option for making low volume bent panels at reasonable price (especially multiple types), so PCB + tubes / sockets / parts in eventual kit only.

The boards would have combo power connectors, +-15V or +-12V operation, external filament supply (connect to internal bus or external power jack), pots and jacks on wires, all THT parts. About 8x10cm of blue, two-sided PCB, cool and nice 8-)

It also would have:
-Low pass, band pass, high pass inputs (optional attenuators soldered offboard)
-Two cutoff frequency control inputs
-Resonance control input
-Cutoff, resonance and output level pots
-Mounting holes
-Onboard +50V charge pump

We'll see what comes out of it :razz:

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Post by Moog$FooL$ » Tue Dec 18, 2018 11:47 am

i think i would be into a basic diy version...... one where i could do my own pnl.
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Post by J3RK » Tue Dec 18, 2018 11:56 am

Wow, that sounds REALLY nice!
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Post by mome rath » Tue Dec 18, 2018 12:13 pm

looks and sounds great! Really like your front panel design/knob selection
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Post by frozenkore » Tue Dec 18, 2018 12:36 pm

BARD wrote:(even 3U for the stubborn!)
This sounds great! I'd totally be in for some 3U action!
Cheers!
Brian

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Post by luchog » Tue Dec 18, 2018 12:52 pm

I would definitely like to have this in Euro. Either as a finished module, or a DIY kit.

One thing about tube mounting, it's far better to have tubes protruding from the panel like in the OP, because even run conservatively, those things can build up a lot of heat. Keeping them out simplifies cooling (which is why Metasonix and Trogotronics keep theirs protruding). Plus, it just looks cooler.

One change to the layout I'd make is to move the jack and pot that are currently above the tubes to beside or underneath them. Keeping it on top makes it more likely someone is going to touch the tubes and, like I noted, they get hot.

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Post by BARD » Tue Dec 18, 2018 4:46 pm

luchog wrote: One change to the layout I'd make is to move the jack and pot that are currently above the tubes to beside or underneath them. Keeping it on top makes it more likely someone is going to touch the tubes and, like I noted, they get hot.
That's valuable notice, but those tubes actually don't get very hot @ 5V filament voltage... I have tried to keep them as far as possible to the rest of layout components. Patching and tweaking is comfortable by Eurorack standards :hihi: Hovewer, I'll keep them on top in DIY version since that will make mouting / arrangement easier. I guess there will be builders who will run tubes at nominal filament voltages (only visual improvement at these cathode currents :roll: ).

How about Skinburntronic approach?
Image :hihi:

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