another Valvecaster question

[rangermaster]

Hello

There are already a lot of questions been asked about the valvecaster tube driver on how to modify it. But after searching for two days i still haven't found what i'm looking for.

I'm building this for a friend and he plays on a les paul. So humbuckers.

The first one i build for him sounded really good but he wants it to be less muddy and have it really transparant sounding. Maybe you have some advice on which values to use best ?

also when he uses his WAH pedal it totally destroys the sound of the wah sweep. is there a simple way to modify it so it will handle a wah better? maybe like they did with those fuzz faces (10K input resistor) ?

I'm using the layout in attachment but without the tone cap.


tnx for the help!

[FiveseveN]

have it really transparant sounding

Take the metal bits out of the tube, then you can see right through it. Rub the labels off with acetone for maximum transparency!

If you want some high-pass action make the input cap smaller, of course. Start with an order or two of magnitude lower and use your and your friend's ears to determine the desired cutoff.

his WAH pedal it totally destroys the sound of the wah sweep

What does that mean? Maybe he would prefer the wah after the 'caster?

[GibsonGM]

A 12AU7 running on starved plate (very low voltage) probably isn't going to be 'transparent', lol.  You could increase the supply voltage (while holding the heater at 9-12V of course).    There is just only so far a signal can swing in a tube without high voltage before distorting (VERY low headroom).
One could try lowering the value of C1, maybe to 22n...see if that does anything, I suspect the HB's are hitting it with low freq's.

Don't know why the wah is having trouble...the Zin of the VC should be high enough to not cause issues (hmm). Feel free to pop the traditional 10k in there, see what you get! 

There are a zillion mods to the VC, try searching the net. You might find a variation that is just right

[antonis]

I presume you refer on the following diagram:



In the absence of C4 (10nF) cap, C4/VR2 LPF turns into a C3/(VR2,VR3, R3) HPF, of 1/2πC3(VR2//VR3 + R3) corner frequency..
(VR3 & R3 can be ignored only for VR2 very low value settings..)
You see that, even for VR2 setting at 90%, corner frequency is only 16Hz..

I'd let C4 be there and tweak C2/R4 and C1/R1 HPFs values..
(starting from 1/10 of C1 & C2 values..)

edit: Faster than me guys already responded..

[rangermaster]

thanks for the replies

i forgot to mention i use a 12AT7 tube and it runs on 12volts.

[rangermaster]

I presume you refer on the following diagram:



In the absence of C4 (10nF) cap, C4/VR2 LPF turns into a C3/(VR2,VR3, R3) HPF, of 1/2πC3(VR2//VR3 + R3) corner frequency..
(VR3 & R3 can be ignored only for VR2 very low value settings..)
You see that, even for VR2 setting at 90%, corner frequency is only 16Hz..

I'd let C4 be there and tweak C2/R4 and C1/R1 HPFs values..
(starting from 1/10 of C1 & C2 values..)

edit: Faster than me guys already responded..

ok thanks for the help. I will replace C4 with the stock value and wire it to ground(because of no tone pot). i'll try experimenting with C1 and C2 values first

[FiveseveN]

I will replace C4 with the stock value and wire it to ground

What's that going to achieve?!

@antonis' post oddly assumes "without the tone cap" means it was replaced with a short, not left open i.e. removing the LPF ("tone" control).
Can you please provide a schematic of what you actually built before we venture into further speculation?

[antonis]

I will replace C4 with the stock value and wire it to ground(because of no tone pot).

Without Tone pot (or any other series resistance), you'll result into a 318Hz LPF.. 
(muddy as hell..)
If you don't want to use Tone control, delete BOTH C4 and VR2..

P.S.
As FiveseveN correctly noticed, "in the absence of" for a series item is synonym with "shorted"..

[rangermaster]

I will replace C4 with the stock value and wire it to ground(because of no tone pot).

Without Tone pot (or any other series resistance), you'll result into a 318Hz LPF.. 
(muddy as hell..)
If you don't want to use Tone control, delete BOTH C4 and VR2..

ok so C3(1uf) directly to lug of volume pot i understand.

[GibsonGM]

12AT7's suck, to be honest    I think you might like it better with a 12AU7...

[rangermaster]

12AT7's suck, to be honest    I think you might like it better with a 12AU7...

i'll try a 12 au7 again after i modified it 

[GibsonGM]

I think it will be improved by the changes/proper tube.  I play a les paul and don't have any real complaints about the VC, for what it is.   

To make it an actual clean booster (mostly clean), you'd have to get into the world of the "Real McTube", running on higher voltages using back to back transformers.  A different thing altogether.

[mozz]

There are some 12v tubes meant for car audio that run on lower voltages called space charge tubes.
6GM8 -- Twin Triode with 6.3V on filaments and plates (Data PDF)
12AC6 -- Remote Cutoff Pentode (Data PDF)
12AD6 -- Pentagrid Converter (Data PDF)
12AE6 -- Dual Diode & Medium-Mu Triode (Data PDF)
12AE7 -- Medium-Mu Triode & Lo-Mu Triode (Data PDF)
12AF6 -- Remote-Cutoff Pentode (Data PDF)
12AG6 -- Pentagrid Converter (Data PDF)
12AJ6 -- Dual Diode & Hi-Mu Triode (Data PDF)
12AL8 -- Medium-Mu Triode & Power Tetrode (Data PDF)
12BL6 -- Remote-Cutoff Pentode (Data PDF)
12CN5 -- Remote-Cutoff Pentode (Data PDF)
12CX6 -- Remote-Cutoff Pentode (Data PDF)
12CY6 -- Remote-Cutoff Pentode
12DE8 -- Diode & Remote-Cutoff Pentode (Data PDF)
12DK5 -- RF Pentode
12DK7 -- Dual Diode & Power Tetrode (Data PDF)
12DL8 -- Dual Diode & Power Tetrode (sep. cathodes) (PDF)
12DS7 -- Dual Diode & Power Tetrode (Data PDF)
12DU7 -- Dual Diode & Power Tetrode (Data PDF)
12DV7 -- Dual Diode & Power Tetrode (Data PDF)
12DV8 -- Dual Diode & Power Tetrode (sep. cathodes) (Data PDF)
12DW8 -- Diode & Dissimilar Dual Triode (Data PDF)
12DY8 -- Medium-Mu Triode/Remote-Cutoff Tetrode (PDF)
12DZ6 -- Remote-Cutoff Pentode (With Curves) (Data PDF)
12EA6 -- Remote-Cutoff Pentode (Data PDF)
12EC8 -- Med.-Mu Triode/Semiremote Cutoff Pentode (9 pin) (PDF)
12EG6 -- Dual-Control Heptode (Pentagrid Amplifier) (Data PDF)
12EK6 -- Remote-Cutoff Pentode (Data PDF)
12EL6 -- Dual Diode & Hi-Mu Triode (Data PDF)
12EM6 -- Diode & Power Tetrode (Data PDF)
12EZ6 -- RF Pentode (Data PDF)
12F8 -- Dual Diode & Remote-Cutoff Pentode (Data PDF)
12FA6 -- Pentagrid Converter (Data PDF)
12FK6 -- Dual Diode & Lo-Mu Triode (With Char. Curves) (Data PDF)
12FM6 -- Dual Diode & Medium-Mu Triode (Data PDF)
12FR8 -- Pentode & Triode & Diode (Data PDF)
12FT6 -- Dual Diode & Triode (Data PDF)
12FX8 -- Medium-Mu Triode & Pentagrid Converter (Data PDF)
12GA6 -- Pentagrid Converter (Data PDF)
12F8 -- Dual Diode & Remote-Cutoff Pentode (Data PDF)
12G8 -- Dual Triode
12J8 -- Dual Diode & Power Tetrode (Data PDF)
12K5 -- Power Tetrode (Data PDF)
12U7 -- Dual Medium-Mu Triode (9 pin) (Data PDF)
8056 -- High-Frequency Triode (Nuvistor) (Data PDF in German)

[GibsonGM]

Many of those have promise, tho can be a little costly.  The 12G8 ~~ 12AT7 which I don't like the overdriven sound of but that may just be me 

12U7 is much like 12AU7, price is competetive with 12AX7...some have also done preamps with the 6GM8.

[momo]

I have 3 Nuvistors...

1 General Electric  SV188-5
2 RCA- B-437, H-25

[mozz]

Don't know about using nuvistors in a preamp/whatever, they are mostly a RF/tuner tube and i have sold some to fund other projects so there is a small market for certain types as they are of course no longer made.

Many of those have promise, tho can be a little costly.  The 12G8 ~~ 12AT7 which I don't like the overdriven sound of but that may just be me 

12U7 is much like 12AU7, price is competetive with 12AX7...some have also done preamps with the 6GM8.

Well, I rarely buy tubes, oddball tubes anyway. If I need 6v6s JJ's or el34's or 6550 i have to buy them. Sort of inherited and collected a few thousand tubes (+6000) over the last 20 years so using oddball tv tubes is sort of a hobby.

As to 12AT7, yeah they aren't known to sound good for some reason. People plug them in where a 12ax7 circuit is set up when they should have their own value plate and cathode resistors. 12AT7 and 6DJ8 are on my project list for a cascode circuit, which I have a few starting schematics, just haven't had the time to breadboard it yet.

[GibsonGM]

That sounds like an interesting project, Mozz, I'd look forward to hearing how it turns out!  I have many car radio tubes, but really nothing I can do with them...oscillator tubes and so on, not very useful for amps!  I suppose I could light up the heaters and make a display or something, ha ha...

[momo]

They had Nuvistors in the original AKG C12a mic. It was part of the sound, there must be something to do with these!...anyhow.

[GibsonGM]

You can probably find some useable schematics to build a project from!

[andy-h-h]

I think the earlier version of the Valve Caster actually had smaller input and output caps.  I've found some 12AU7s can run completely clean on the VC, some seem to always be a little dirty.