Simple tube vca issue with pin 6 no output.

[J M Fahey]

But one of my friend on Facebook built it from that verroboard layout and it works fine...

Why do you ask for solutions to your problems, make us WASTE time and then despise advice?

I´m OUT.

[Norke]

Why do you ask for solutions to your problems, make us WASTE time and then despise advice?

I´m OUT.

I'm sorry if i despise you, was really not my goal, i really appreciate your help, it's just that i'm trying to understand how the hell my friend over the internet got his to work. I was asking you some other schematic that would be better for a tube distortion vca similar to this but better designed and you refered me to a solid state instead Really sorry about that, i'm really just trying to make this work or something similar with a better design but i like to keep the tube 12ax7...

[Norke]

Let's talk about the 'tube sound' for a moment. Tubes - as in this circuit, single-ended triodes - color the sound by ever so slightly distorting the pure wave form of the signal in an asymmetrical fashion. This gives the 'hollow' or 'reedy' sound from exaggerated (mostly 2nd) harmonics. They do this simply by passing signal. No special control circuitry needed. More signal, more color. The relationship between adjustment and effect is direct and completely intuitive. This, to me, is the primary function of triodes in a tube circuit. After all, if I wanted clean gain I'd use transistors

I suggest you build a tube pre-amplifier circuit - potentially even simpler than the VCA you're attempting to build - which has the sole function of coloring the sound by adding some 2nd-harmonic distortion. This way you can focus on the desired result of getting the tube sound as a function of the circuit and not simply as a byproduct. Divide and conquer, as it were.

The VCA circuit function is to envelope-modulate the signal, not incompatible with coloring the sound, but not really related in any functional way. Hope this helps.

Yeah i kinda new it all of this, you worded it better than i can, i'm french actualy...
Could you suggest another circuit that you think is good? please? Using 12ax7

[Norke]

Yes i did it but no one here seems to confirm the image i posted about that coupling cap emplacement on the schematic.
I thought it was weird too seing such a big dc voltage at theopamp input mixed with the signal lol
Yes i already have that L-1 tube module actualy but it uses a russian mini tube and i'm not sure how to translate his shematic using a 12ax7

[eschertron]

Yeah i kinda new it all of this, you worded it better than i can, i'm french actualy...
Could you suggest another circuit that you think is good? please? Using 12ax7

There are a lot of basic musical instrument-oriented tube circuits, many of which are identical to design standards and popularized by Fender. Compare schematics found here and see how similar they are at the input of the amp.
https://music-electronics-forum.com/...l=1#post161286

For a specific example, look at the input stage of this amp. The values for input grid leak (1M), grid stop (68k), anode (100k), cathode resistor (1.5k) and cathode bypass capacitor (22uF) are the same values that Moses brought down from the mountain. Pretty much guaranteed to work in any device, regardless of B+ voltage. Use a coupling capacitor between the anode of the input, and a second stage identical to the first, and you'll have a classic tube preamp. Tone shaping, gain control, etc., can be similarly 'copied' from existing designs with the caveat that your selection of low voltage will require some tweaking/experimenting to find values that work best for you. I started working with tube circuits a few years ago and learned the theory as I experimented and heard the reality of the sound. Start with simple circuits and few components.
http://web.archive.org/web/200710160...der/fchamp.gif

There may be schematics of existing designs on the web, so sorry, I am not aware of them.

[ric]

There are a lot of basic musical instrument-oriented tube circuits, many of which are identical to design standards and popularized by Fender. Compare schematics found here and see how similar they are at the input of the amp.
https://music-electronics-forum.com/...l=1#post161286

For a specific example, look at the input stage of this amp. The values for input grid leak (1M), grid stop (68k), anode (100k), cathode resistor (1.5k) and cathode bypass capacitor (22uF) are the same values that Moses brought down from the mountain. Pretty much guaranteed to work in any device, regardless of B+ voltage. Use a coupling capacitor between the anode of the input, and a second stage identical to the first, and you'll have a classic tube preamp. Tone shaping, gain control, etc., can be similarly 'copied' from existing designs with the caveat that your selection of low voltage will require some tweaking/experimenting to find values that work best for you. I started working with tube circuits a few years ago and learned the theory as I experimented and heard the reality of the sound. Start with simple circuits and few components.
http://web.archive.org/web/200710160...der/fchamp.gif

There may be schematics of existing designs on the web, so sorry, I am not aware of them.

Norke, you might try googling "Matchless Hotbox schematic". It's a stand-alone tube preamp. High voltage, but it might be a starting point for what you're looking for.

[Norke]

Thanks to everybody, it now works but only with the added 100n between the pin 6 of the tube and the opamp 071 input pin3.
It's weird that it didnt work while connected exactly the same but using the 072 (having the pinout changed of course)

[Norke]

Norke, you might try googling "Matchless Hotbox schematic". It's a stand-alone tube preamp. High voltage, but it might be a starting point for what you're looking for.

Ok thanks i'll look at it but i might electrocute myself with that...

[Norke]

There are a lot of basic musical instrument-oriented tube circuits, many of which are identical to design standards and popularized by Fender. Compare schematics found here and see how similar they are at the input of the amp.
https://music-electronics-forum.com/...l=1#post161286

For a specific example, look at the input stage of this amp. The values for input grid leak (1M), grid stop (68k), anode (100k), cathode resistor (1.5k) and cathode bypass capacitor (22uF) are the same values that Moses brought down from the mountain. Pretty much guaranteed to work in any device, regardless of B+ voltage. Use a coupling capacitor between the anode of the input, and a second stage identical to the first, and you'll have a classic tube preamp. Tone shaping, gain control, etc., can be similarly 'copied' from existing designs with the caveat that your selection of low voltage will require some tweaking/experimenting to find values that work best for you. I started working with tube circuits a few years ago and learned the theory as I experimented and heard the reality of the sound. Start with simple circuits and few components.
http://web.archive.org/web/200710160...der/fchamp.gif

There may be schematics of existing designs on the web, so sorry, I am not aware of them.

Whoa that's a lot of ressources! Thanks! But they are all high voltages right? I can use theses with +12 and -12 volts easily?

[eschertron]

Whoa that's a lot of ressources! Thanks! But they are all high voltages right? I can use theses with +12 and -12 volts easily?

You can try

[Jazz P Bass]

"but no one here seems to confirm the image i posted about that coupling cap emplacement on the schematic."

Maybe it's me, but the 'image' is just an icon with no image behind it.

[Norke]

"but no one here seems to confirm the image i posted about that coupling cap emplacement on the schematic."

Maybe it's me, but the 'image' is just an icon with no image behind it.

Oh... that's why ... lol thanks here it is hosted on this forum:

[ric]

Ok thanks i'll look at it but i might electrocute myself with that...

Sorry, my mistake. Thought you where looking for tube preamp designs.

[doombass]

Oh... that's why ... lol thanks here it is hosted on this forum:

[ATTACH=CONFIG]54358[/ATTACH]

Move the end of the cap from R7 to pin 6 of the tube. That means you create a junction at the cap, R7 and op amp input (schematically keep the junction and switch places of the lead at pin 6 with the cap at R7, look at C4 in the L1-schematic in post #15 for reference). That way the cap blocks the DC feeding the tube plate from reaching the op amp input. You will only want the AC portion of the circuit reaching the op amp input.

[Norke]

Sorry, my mistake. Thought you where looking for tube preamp designs.

Yes but not at high voltages, i'm still pretty new to this..