DUAL Valvecaster - the real deal

[Jule553648]

I built dual valvecaster according to the lower schematic. It is basically two valvecasters stacked togheter.



Except i used only one tonestack. The switch is for choosing to choose only one tube or both.

But the thing is:

The normal valvecaster has very big volume amplification factor. It is like a big boost to drive your amp.


So when you stack two of them togheter, the first tube drives the second tube into quite high distortion even with both of the gain knobs all the way down (les paul).

So i dont get all the sounds out. On one tube only it is nice chrunch, on both is ready for solos or rock.


BUT,

When I turn both gain knobs more than  12 o'clock, the annoying compression occurs and it sounds like crap.


WHAT I WOULD LIKE TO DO:

To lower the gain of the second tube or something like that (still i want normal valvecaster on first tube), to archieve two stage overdrive. This is impossible now, because the signal from the first tube is too big.

any suggestions?

[merlinb]

Replace R4a with a gain pot?

[fatfoohy]

I would take the signal from the first valvecaster, have that going into one outside leg on a 1M pot, have the other outside leg tied to ground, and the connect the wiper (center leg) to pin 2 of the second section and call it done

[merlinb]

I would take the signal from the first valvecaster, have that going into one outside leg on a 1M pot, have the other outside leg tied to ground, and the connect the wiper (center leg) to pin 2 of the second section and call it done

That job is already performed by VR3, so a quick option would be to feed the 3rd triode from that pot, instead of directly from the 2nd triode. Ala:

[markie83]

kind of an old thread but what about runnin the 2 valve casters in parallel instead of series......BIG boost low distortion and one poor 12ax7 in my amp 

[Zoot]

Hello, no issue here, just my rendition of the dual valvecaster before boxing it.
Of the mods I haven't added much. A little filter for the noise (Reg7812+ Cap 100uF), which works, and "cleaning" or decreasing gain on the first circuit with a 12k resistor before the gain pot. For this, with my son we tried 12K-resistors before both gain pots, in none, and to him on the first stage only sounded better. He is the guitarist... and the excuse for my building addiction...
These are 12AU7 tubes, an old Gold Lion I got from the preamp of a Luxman HiFi (A-384 I just repaired), and an old Sylvania I bought for EUR20.
Hope you like it!
Zoot

[Zoot]

Hello,
Now that I boxed the project above I have a question.
Connecting the pin 5 of the tubes directly with the +12V keeps them "on" all the time.
Is there a way I turn the tubes on with the switches, or should they be on all the time?
Thanks!
Zoot

[Gattoconglistivali]

I built dual valvecaster according to the lower schematic. It is basically two valvecasters stacked togheter.



Except i used only one tonestack. The switch is for choosing to choose only one tube or both.

But the thing is:

The normal valvecaster has very big volume amplification factor. It is like a big boost to drive your amp.


So when you stack two of them togheter, the first tube drives the second tube into quite high distortion even with both of the gain knobs all the way down (les paul).

So i dont get all the sounds out. On one tube only it is nice chrunch, on both is ready for solos or rock.


BUT,

When I turn both gain knobs more than  12 o'clock, the annoying compression occurs and it sounds like crap.


WHAT I WOULD LIKE TO DO:

To lower the gain of the second tube or something like that (still i want normal valvecaster on first tube), to archieve two stage overdrive. This is impossible now, because the signal from the first tube is too big.

any suggestions?

Hi, here's my suggestion
https://www.diystompboxes.com/smfforum/index.php?topic=126685.0

but I'm very unsatisfied with my tone control, it only controls treble. Adapt the tone stack from the Big Muff might be a good idea.

Adding gain to a Valve Caster is always going to sound bad, because of it's flat frequency response, which is best for clean tone.

If you found the overdrive sound muddy, it's already too late to cut the low end to get your sound right.

The point is: don't clip the bass signals, only clip the mid, or higher. That's why an amp's clean and drive sound always have to be made into separated channels, they can't share frequency response.

I'll be developing a gain control only effective to mid range, just like some classic distortion pedals in my next project

[kaycee]

Hello,
Now that I boxed the project above I have a question.
Connecting the pin 5 of the tubes directly with the +12V keeps them "on" all the time.
Is there a way I turn the tubes on with the switches, or should they be on all the time?
Thanks!
Zoot

I expect that if you added power switching to the bypass, then you would get a pop and delay in the circuit coming in. I add a separate power switch to valve projects to turn the power off while they just sit on the pedal board not being used, to save the valve.

[GibsonGM]

Hello,
Now that I boxed the project above I have a question.
Connecting the pin 5 of the tubes directly with the +12V keeps them "on" all the time.
Is there a way I turn the tubes on with the switches, or should they be on all the time?
Thanks!
Zoot

I expect that if you added power switching to the bypass, then you would get a pop and delay in the circuit coming in. I add a separate power switch to valve projects to turn the power off while they just sit on the pedal board not being used, to save the valve.

Yes. Re. tube longevity, I wouldn't worry about leaving them on 'for the gig', but it seems wasteful to just let them idle and idle and idle...won't hurt 'em tho, generally speaking.  If you aren't using it in the set, it surely won't hurt to shut it off for an hour...  An actual power switch is a great idea. 

[anotherjim]

It was found that tubes were more reliable if never switched off! Same as filament light bulbs, they almost always blow when you switch them on.

[amptramp]

If you are concerned about excessive compression, add cathode resistors to the cathodes that go to ground in the existing design.  This prevents you from pulling grid current because the second and fourth stages are not biased by anything else and you may get blocking / gulp distortion at higher signal levels.  There is some contact potential bias from the grid intercepting electrons coming off the cathode but you might need several megohms for this, although it is a low B+ circuit, so you can get away with minimal bias.  You won't need much in the way of cathode resistors - 1 K might do it but experimentation is encouraged.  This could be the answer for getting rid of muddy response in the presence of low frequencies.

[PRR]

...tubes were more reliable if never switched off!...

And not stomped-on/around.

Tubes are cheap for their goodness. Don't be clever and "save" them.

[Zoot]

Clear guys, and thank you very much.
The sound is fine, my son likes it.
The wall-plug the pedals are connected has a switch, which gets turned off from time to time.
So I will do... nothing... when it gets turned off, ok, when it doesn't, ok too.
In any case, thanks for your reactivity.
Awesome.
Cheers,
Zoot