I am trying to design a compressor using a triode instead of an opto-coupler (such as the T4B modules). What sparked the idea was reading Eric Barbour's article on Ken Stone's page where Eric used a triode as a voltage-controlled dynamic resistance instead of the Vactec VTL5c4).
Audio Synthesis via Vacuum Tubes
Audio Synthesis via Vacuum Tubes
What are you trying to achieve? Do you know about vari-mu type compressors yet? Are you thinking that this idea will outperform a tube vari-mu compressor?
Maybe he wants to experiment, i´d encourage it rather than question it
Concerning the original post yes you can, I´ve also thought about it and is a possible DIY project further down the road for me.
I would like to build a compressor from the parts I have available. Most of these parts are based around tube designs. When you said Vari-mu what came to mind was Manley's Vari-mu Compressor + what I read about vari-mu valves on Merlin's page "valve-wizard".
You're reading negativity into my reply that isn't there. You're assuming he wants to experiment; I think it's smarter to ask what level of performance is sought and if the poster knows what the current performance bar is for existing designs.
Yo guys, let's squash the beef -- I'm going to need both your guys' help to accomplish this.
Yes, quality matters..
But so does using the parts I have available..
so discussing *Both* options is a HUGE benefit to Me + others that will read this post in the future.
Yes, quality matters..
But so does using the parts I have available..
so discussing *Both* options is a HUGE benefit to Me + others that will read this post in the future.
What can you guys tell me about using Vari-Mu cakes for Dynamics -- do you have a schematic I could simulate or we could discuss?
I can gladly take the driver's seat here & just ask questions of you two --
Or you can go off in your own tangent of what YOU would do if you were in my shoes.
I have available a plethora of tube-parts. We can even build the final Push-Pull stage around my ell80 -- a dual output pentode designed for pp applications in 1-tube.
The output will be a Balanced 600-ohm Line-Level signal for studio use. Probably through a utc-A25 plate-to-line Transformer. *(the utc-A25 might be a interstge transformer -- but I still want to incorporate them in the build).
*We can work the Utc-A25's in to the "multiple OT options" as seen in the Shadow Hills Mastering Compressor.
I'm still deciding if the unit will be just a Compressor or a channel strip w/ a Pre + Simple Tube-Eq. If so the Input will have both Line-Level + balanced Mic inputs *as well as a nice DI.
But let's focus on how the unit will recognize the peak transients first -- handling + discussing the Vari-Mu comlreau option VS. using the Triode as a Variable Resistance Module as seen on the Link I attached in the Topic Description.
I can gladly take the driver's seat here & just ask questions of you two --
Or you can go off in your own tangent of what YOU would do if you were in my shoes.
I have available a plethora of tube-parts. We can even build the final Push-Pull stage around my ell80 -- a dual output pentode designed for pp applications in 1-tube.
The output will be a Balanced 600-ohm Line-Level signal for studio use. Probably through a utc-A25 plate-to-line Transformer. *(the utc-A25 might be a interstge transformer -- but I still want to incorporate them in the build).
*We can work the Utc-A25's in to the "multiple OT options" as seen in the Shadow Hills Mastering Compressor.
I'm still deciding if the unit will be just a Compressor or a channel strip w/ a Pre + Simple Tube-Eq. If so the Input will have both Line-Level + balanced Mic inputs *as well as a nice DI.
But let's focus on how the unit will recognize the peak transients first -- handling + discussing the Vari-Mu comlreau option VS. using the Triode as a Variable Resistance Module as seen on the Link I attached in the Topic Description.
To be blunt I think what you are trying to achieve and the parameters you have placed on it are a fool's errand. Designing a studio quality compressor is a huge undertaking, and your wanting to use parts in hand tells me you are more likely cost driven than anything else, and probably not aware of how expensive DIY really is. A new design DIY studio quality compressor will not be cheap in cost or time or motivation to see through.
I recommend you look at building the 12AU7 compressor designed by forum member PRR (retired?). It's the only studio quality low cost compressor I have ever heard of.
Perhaps the single biggest design challenge in using a valve as a variable resistor is that changing the resistance changes the dc operating conditions and it needs to be biased to some quiescent current in order to act as a variable resistor. This means the control voltage appears in the output signal. In a synth with relatively slow moving control voltages this is not a problem and can be reduced by using a low value coupling capacitor.
In a compressor, where you probably want a fast attack time and good low frequency response, this is a problem and manifests itself as a thump in the output. Vari-mu compressors have exactly the same problem. The classic solution is to run a balanced pair of tubes so the thump cancels in their output. That is why most vari-mu compressors have a 'balance' control to minimise thump.
Cheers
Ian
In a compressor, where you probably want a fast attack time and good low frequency response, this is a problem and manifests itself as a thump in the output. Vari-mu compressors have exactly the same problem. The classic solution is to run a balanced pair of tubes so the thump cancels in their output. That is why most vari-mu compressors have a 'balance' control to minimise thump.
Cheers
Ian
Re the original question: I think if you used a vari-mu triode you would end up reinventing the vari-mu compressor, and if you used an ordinary triode it just wouldn't work very well. Audio tubes are designed for linearity, that means they try to minimise variations in mu, gm and Rp with current, so they don't work too well as VCAs or voltage controlled resistors. The 12AU7 is pretty nonlinear by audio standards.
If you are still interested, take a look at the tremolo circuit of the Vox AC30. Note the weird little RC filter for killing control voltage feedthrough.
If you are still interested, take a look at the tremolo circuit of the Vox AC30. Note the weird little RC filter for killing control voltage feedthrough.
If you're into relatively uncharted water (AFAIK), here's a 1952 article on triode operation without anode supply, and some concepts and circuits include a limiter which you might find interesting. I've never tried, just recall it as curious. The valve is still active, BTW.
http://www.radiomuseum.org/forumdata/users/6435/powerless/page_a.png
http://www.radiomuseum.org/forumdata/users/6435/powerless/page_b.png
http://www.radiomuseum.org/forumdata/users/6435/powerless/page_a.png
http://www.radiomuseum.org/forumdata/users/6435/powerless/page_b.png
The only parameter that is relatively constant in most small signal triodes is mu. Both gm and rp vary over a wide range with operating current. A vari-mu compressor does not work by varying mu; it works by varying the stage gain which it achieves by varying gm which it achieves by altering the grid bias voltage. I guess vari-gm did not sound so good to the marketing men of the day or maybe they were just trying to deliberately obscure the way it actually works.
Cheers
Ian
Well I'm gonna build something, one of the two -- whether it's the DISA limiting compressor on Gyraf's site that Manley huh
What about making a cheap opto cell with auto resistors from Radio Shack like throwing something together really quick and easy with parts that are available but I don't have to purchase online I eat I can have it done today for testing (the opto-cell that is)
What can I make w/ Cadmium-Sulfide Photocells + some LEDs? *Yes Money is an issue -- but still Quality trumps spending additional money. The whole point of me saying I wanted to use the parts I already had available was because I have so many parts -- I need to start using them. Period. Well I'm down to try different ways of achieving our goal here -- which is in-fact having an Audio Compressor/Limiter based on vacuum tubes. I am not a purist so semiconductors are wekocme (specially in regulation of the supply). All-in-all I just want to get this project done + ready to test so I can be used in the studio asap. So again. I'm up to anyone's ideas + imagination.
I will do some reading today on the Vari-Mu design + study the DISA schematic I posted above. I will also try my handout on making a cheap Photo-resistor (like T4B) w/ the photocells I mentioned ^above^.
*if the prototype could have multiple takes on the Photo-Resistance that also be cool. For example. The option to go from:
1) T4B
2) homemade unit made from radioshack photocells + LEDs
3) Vari-Mu way (I still do not understand this method -- If someone can explain or link an article of how it works that be awesome -- I did some reading on Manley's page but that is it).
4) using the Grid of a tube as a Variable Resistance as in the Eric Barbour schematic I posted above from Ken Stone's Synth Page.
*I'm not afraid of having lots of options on the prototype
I will do some reading today on the Vari-Mu design + study the DISA schematic I posted above. I will also try my handout on making a cheap Photo-resistor (like T4B) w/ the photocells I mentioned ^above^.
*if the prototype could have multiple takes on the Photo-Resistance that also be cool. For example. The option to go from:
1) T4B
2) homemade unit made from radioshack photocells + LEDs
3) Vari-Mu way (I still do not understand this method -- If someone can explain or link an article of how it works that be awesome -- I did some reading on Manley's page but that is it).
4) using the Grid of a tube as a Variable Resistance as in the Eric Barbour schematic I posted above from Ken Stone's Synth Page.
*I'm not afraid of having lots of options on the prototype
Check on the price of the 6386 tubes before going down this road.....over $100USD each.
There are some TV tubes with similar properties, but I haven't found anything that works as good as the 6386.
Tubelab those puppies are expensive... Check this thread out on 6ba6's as substitutes + what PRR says. Great point bringing that up -- & I thought my money would be going into the Iron! ..well let's try + get this puppy drawn-out! In excited to prototype this once a schematic finally comes together :'D
http://groupdiy.com/index.php?topic=2711.0
http://groupdiy.com/index.php?topic=2711.0
I tried the 6BA6 and it can be used. I think I could get 60 db or so of gain range out of a 6386, and maybe 35 or 40 out of a 6ba6. If I remember right the 6AS6 is another possibility. You can use either G1 or G3 for gain control. There is a TV tuber triode that worked good, but I can't remember the number and all my notes and stuff it packed away due to a recent move.
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