Tube Filter Board
  • Hei!

    Ok now that shruti filter boards cover a wide panel of filtering styles… And now that I’ve spent a whole night playing with a shruti through tubes…

    I wonder if something is possible combining the shruti architecture, and for example eric barbour’s tube filter design…

    I guess it would require a rework of the powering part of the board too…?

    And of course, a specific, dreamy, unique, steampunk case…

    Anyone has, like me, sparkling eyes, and waves of dreams, with punk unicorns riding them? Or is it that I haven’t got enough sleep?

  • Where valves would help is with their natural compression characteristics when signal gets too loud. They also can amplify a lot in one go, but that’s only really of benefit if you’re designing a power amplifier.

    Other than that I don’t know how much better it would be. You would need to leave it on for maximum reliability? :)

  • Do you mean something like this?

  • Like this

    since he (metasonix) made a eurorack module, I guess there is something that can be done with a 12V power supply… no need high voltage psu.

  • I think the lower voltage tube circuits are starved plate designs, which some consider to be a substandard use of tubes..
    Plus tube circuits are not very DIY friendly.. Being cumbersome, and generally using high voltages. I don’t think it would offer any advantages that you wouldn’t also get from just about any other filter being put through a tube overdrive type box/pedal?

  • They’re also fragile, produce lots of heat and have a short life. They’re good for amplifiers and distortion though. Transistors clip quite sharply.

  • They’re quite cool for this, too:

    a|x

  • I was really into tubes for a while. It was fueled by tube guitar amps and a Univalve. I wish I hadn’t sold that :-\

    Anyway, I had a shitload of NOS tubes and some OOS tubes. I have a 1930s tube tester somewhere around here. I bought some old used Mullards and stuff. Tubes can be a lot of fun.

    Nothing beats the glass and the glow and the heat. And they do sound different. There’s no question about it. The Univalve quickly proves that there are subtle but real differences among different tubes, even among different brands/manufacturers of the same tube.

    I have heard rumors that the US Navy keeps a supply of tubes and tube gear around because they’re supposed to withstand a nuclear electromagnetic pulse.

    I don’t know about you, but I want to my Shruthis to work after the nuclear electromagnetic pulse.

  • @toneburst – That’s cool! Did you make that?

  • >I don’t know about you, but I want to my Shruthis to work after the nuclear electromagnetic pulse.

    Not much will work, the CPU will be fried, the transistors dead, the regulators and voltage inverter fried.

  • @Titus Raindrops no, that’s just a photo I found on the net. I do have a nixie clock that’s similar to that though. I bought it as a gift for my girlfriend years ago. I planned to buy a kit, but time was short, and I spotted one on eBay ready-made, for less than the cost of the kit, so I went for that.

    a|x

  • What? This calls for a complete 1950s-era Soviet nuclear EMP-proof redesign. Ask the people in Khazakstan.

  • The Shruthi-1950:

  • It would be possible to incorporate a tube VCA into a Shruthi using soviet submini tubes that only draw as much current as an LED-have a look at Ken Stone's design here: http://cgs.synth.net/modules/cgs65_vca.html and datasheet for the 1J24B here: http://www.techtir.ie/blogs/watty/miniature_valves_2

    Only thing would be getting a plate supply-an inverter would handle that (I believe Metasonix do that with their Euro modules)
  • Yeap, I was thinking about tube vcf and vca. but maybe only vca could be enough to “tube” the sound, and would be easier.

    I was also thinking of lpg in shruti, since the sound my borg filter makes as lpg. But that’s another topic.

  • [erased – wrong thread]

  • The problem with tubes, submini tubes included is :

    - they dissipate a lot of heat, and consume a lot of current (for the heater) : not good for the power supply, and moreover not good for components around. If you’re going to design a vcf using tubes, you’re going to use a dedicated enclosure. There’s no way the shruthi can handle such heat in its standard enclosure, even though there would probably be just as enough room as needed for the tubes.

    - they require high voltage.

    You can overcome the high voltage thing using a “nixie switch mode power supply”, which is pretty easy to design and work with. It only requires a ne555, a high voltage mosfet, a fast switching diode and a small inductor (as well as a bunch of resistors and high voltage capacitors obviously). It’s enough to provide something like 2W at 200v, which is largely enough for signal processing, and even for power amplification.

    The heater issue can be dealt with a “beefy” 12v power supply (like the ones used for external hard drives) if you use pairs of (almost identical) tubes which heaters are wired in series. If you only use one single tube, a single 7806 might be enough, otherwise you’re probably going to need another SMPS system or a radiator (and a fan maybe).

    Or, you can use a dedicated power transformer, providing directly the high voltage and the heater voltage… which is far from being light ;)

    As submini tubes, i would recommend the 6n33bs and 6n16bs, maybe the 6n17bs also as double triodes (the tech tir web page only mentions pentodes, although double triodes are very useful). There aren’t much informations on the 6n33b, but they are really high gain (like… really) with a very high impedance, so it’s pretty easy to use them with an high voltage SMPS.

    Actually, i’ve designed a submini tube amplifier for my guitar. It’s loaded with 0.35W (!!!) of full tube power ; and the shruthi sounds lovely plugged into it.

    You can find details here (sorry it’s written in french)

  • another thing with tubes is, as Eric Barbour keeps mentioning, that they don’t work very linear. however, i’ve played the Shruthi through metasonix filter and vca (TM2 and TM5) and, like everything you send through those boxes, sounds great.

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