Tube boost + overdrive running off a 9 volt battery

[rankot]

I will try to make this kind of power supply for my Valvecaster: I plan to use 9V supply, then to make 2x 6V for heater using two of 78L06 (very cheap and providing just enough power for one half of heater), and I will push 9V to 40V using MC34063A charge pump. Any thoughts about this idea?

[PaulBass]

I've used all types of voltages but you really hear its full potential when you're at 36v and above. at 50v the sound is killer

[suncrush]

"Full potential". I get it!!!

[rankot]

I've used all types of voltages but you really hear its full potential when you're at 36v and above. at 50v the sound is killer

For bass or guitar use?

[vigilante397]

I've used all types of voltages but you really hear its full potential when you're at 36v and above. at 50v the sound is killer

Keeping the heaters regulated much lower though, of course. Running a higher plate voltage will always get your more of that typical valve sound, otherwise our amps would run off 9V supplies. The whole idea behind the creation of the pedal (in my humble opinion) was not to make the best sounding tube preamp in the world, but to make something that sounds pretty darn good with what is generally considered an absurdly low plate voltage.

[thomasha]

Using a SMPS to boost the 9v is a good idea, with very nice results in mini amplifiers.

I used a 555 to boost the voltage to 250v in a preamp using the ef184 tube.
The thing with smps is that they're very sensible to layout and components. A cheap inductor will introduce some switching noise.

But there are a lot of different configurations. With the icl7660s you can build a charge pump that would easily deliver 50v without the inductor.

At lower voltages adding a transistor to the plates also works as an improved anode resistor.

[rankot]

I don't like 7660, it has very low working frequency. Inductors are not a big issue - they are small for currents needed for tubes. What do you think about using two 78L06 for powering heaters in parallel?

[bluebunny]

I don't like 7660, it has very low working frequency.

With the icl7660s . . .

The 7660S has the high-speed boost option.

[iainpunk]

Bump

Hi guys, im new here.
I am building a hybrid amp of which the preamp is based on the valvecaster, modded and upgraded to within an inch of its life. On certain guitars it kinda farts out a bit when the gain is up, i suspect its an overload of mids hitting the tubes. The bass cut pot prevents this (cuts everything below 750hz by -3db/octave), but it also cuts out the bottom end, which makes it sound thin. Now for my question, how can i reintroduce the bass in my signal??

[vigilante397]

Bump

Hi guys, im new here.
I am building a hybrid amp of which the preamp is based on the valvecaster, modded and upgraded to within an inch of its life. On certain guitars it kinda farts out a bit when the gain is up, i suspect its an overload of mids hitting the tubes. The bass cut pot prevents this (cuts everything below 750hz by -3db/octave), but it also cuts out the bottom end, which makes it sound thin. Now for my question, how can i reintroduce the bass in my signal??

Welcome to the forum

Your question is a tricky one: "I'm taking all the bass out of my signal, how do I put it back?"

The Valvecaster is a pretty dark-voiced pedal, the fartiness you're hearing has nothing to do with what the tube is taking in, it's all going to be on the output. The 12AU7 has a pretty wide frequency response. I would recommend looking at a different tone stack for the Valvecaster stage and see if you can get the tone you're looking for. Good luck!

[iainpunk]

Bump

Hi guys, im new here.
I am building a hybrid amp of which the preamp is based on the valvecaster, modded and upgraded to within an inch of its life. On certain guitars it kinda farts out a bit when the gain is up, i suspect its an overload of mids hitting the tubes. The bass cut pot prevents this (cuts everything below 750hz by -3db/octave), but it also cuts out the bottom end, which makes it sound thin. Now for my question, how can i reintroduce the bass in my signal??

Welcome to the forum

Your question is a tricky one: "I'm taking all the bass out of my signal, how do I put it back?"

The Valvecaster is a pretty dark-voiced pedal, the fartiness you're hearing has nothing to do with what the tube is taking in, it's all going to be on the output. The 12AU7 has a pretty wide frequency response. I would recommend looking at a different tone stack for the Valvecaster stage and see if you can get the tone you're looking for. Good luck!

Hey, i found the problems solution, the farting out was due to an abundance of low mids, so i  changed the caps and resistors i had going on in between the stages, this cuts out the farty mids a lot. Still a mid-rich sound, but not so over done and farty like it was. (If you look at a fender or marshall preamp frequency response, they both cut out a lot of mids, mine does less so). At first i wanted to keep the elaborate tone circuit i had going on in between the stages, but after minimizing and redoing everything, it sounded great. Il post a schematic for the preamp when i find a way to make them on my phone. (Any suggestions?)

Iain

[iainpunk]

The schematic after some simpifying the tone stack (im to lazy and frustrated with the program to make a "before" schematic). There were no tube symbols, i hope these squares are sufficient.



I left out the heater, but its supply is the same 12v supply as the rest.

Iain

[PRR]

"Classic" guitar input uses 12AX7 at 300V. Will take over 0.5V peak from guitar without rude noises.

ValveCaster 12AU7 at 12V, input overload may be 0.15V even 0.1V. Will overload on signals that an old Fender will pass clean.

The today-answer is to turn-down the guitar, turn-up after the ValveCaster.

But that gets you closer to Universal Hiss.

[iainpunk]

"Classic" guitar input uses 12AX7 at 300V. Will take over 0.5V peak from guitar without rude noises.

ValveCaster 12AU7 at 12V, input overload may be 0.15V even 0.1V. Will overload on signals that an old Fender will pass clean.

The today-answer is to turn-down the guitar, turn-up after the ValveCaster.

But that gets you closer to Universal Hiss.

Or, you lower the gain of the first stage and put a gain control (volume pot) in between stages (instead of the awful bias control) and make the second stage higher gain, so the gain control lets you turn it clean or dirty.

[ETMoody3]

Adding to an old thread here...

6947 tube works in this circuit as well. 

You can also use an LM2596 or other high frequency buck converter for the heaters *without noise* and without converting a lot of power into heat. 

[FantomXR]

Hey people,

I have build a Valvecaster and it works great so far.
I have changed the Gain-Control to what @DryRoasted posted here https://www.diystompboxes.com/smfforum/index.php?topic=63479.msg518438#msg518438
R2 and R3 are both at 100k to decrease the gain. Input-Cap is at 47nF. I tried lower values, but this cuts the signal too much in my opinion. The VC runs at 12V.

When the gain-pot is turned down completely I still have some kind of overdrive in the lower frequencies especially when playing chords. It's not really noticeable when playing single-notes. Why is that?

When I use the original gain-pot-wiring (connected to pin3 instead of pin7) I don't have that behavior. It's clean. But on the other side I have a lot of noise / crackling when turning the gain-pot which is not the case with the wiring from DryRoasted :-D

Could I just ground both pins and add an amplifying stage in front? Does that give the same results?


Thanks,
Chris

[Gattoconglistivali]

...When the gain-pot is turned down completely I still have some kind of overdrive in the lower frequencies especially when playing chords. It's not really noticeable when playing single-notes. Why is that?

Because this modification sounds less cleaner than original. Low frequency signals usually contain more energy, in another words, low string/fret is louder than  high string/fret. So when the pickup outputs higher signals like lower string /fret or multiple strings, it saturate while single notes could stay clean.

...When I use the original gain-pot-wiring (connected to pin3 instead of pin7) I don't have that behavior. It's clean.

First we have to make clear that gain is one thing, clipping voltage is another, together they create distortion. Only when they are independent to each other and the latter fixed, you can say distortion is related to gain. For instance : diode hard clipping circuits.
So in the Valvecaster design, turning down the gain is increasing the cathode resistance, by this way, we take away voltage from the tube, make it easier to saturate, or you can say lower the clipping voltage.

Noises  when turning pot... I'm not sure what caused the difference,but if you have a good pot,it's likely going to be quiet anyway.

Could I just ground both pins and add an amplifying stage in front? Does that give the same results?

Yep, you'll need to deal with a lot of low frequency though

[iainpunk]

wow, weird to read my own post from 4 years ago, fun fact, i just took the tube circuit off of the breadboard last December...

Noises  when turning pot... I'm not sure what caused the difference,but if you have a good pot,it's likely going to be quiet anyway.

that's changing the bias, that always crackles, look at the ''crackle owkay'' knob in ZVex pedals, they change both gain and bias, so it crackles.

the overdrive in the low end when the gain is set low can be an effect of the altered bias, it gets biased lower (current, higher voltage) and closer to the rail voltage/cutoff point this makes hitting that threshold easier. if you change the plate resistor to accommodate for that, it might gate out when the gain/bias is set higher.

i generally don't like the gain/bias control on the original design, instead, i place an input attenuator in front of the first gain stage to set its gain, and just let the tubes do their thing without changing the bias at all.

another trick i like on low voltage tubes is adding a single transistor buffer after the gain stage to deal with the high output impedance:

this is what i build with a friend of mine,
the one on my breadboard had a big muff tonestack in the feedback loop of the first gain stage and some cross-over distortion diodes in-between the stages, for some subtle ''dirty gate'', to enhance grit and lower the hiss.

you can use a gain stage in front of the tube, as long as you want more gain that it already has, and turn it in to a fuzz!

cheers