Increasing Plate Voltage

[kurtlives]

Been working on designing and tweaking a two 12AU7 pre-amp for the past few weeks. I have spent a lot of time on it and it sounds really really good now, I am seriously liking the tones I am getting from it. I have spent a lot of time altering vales of caps and resistors to get things just right, choosing the right value and material of coupling cap, adding/removing and tweaking little filters. Even spent time tonight trying to figure out what kind of resistor material I like best for plate resistors.

I quite like playing with low voltage designs...Right now the B+ is 30V. Ill say it again, I am really happy with the sound.

All those comments of "its not a real tube design" and "starved plates BOO!" etc etc have been coming to my head throughout the process of design/tweaking. I am thinking of increasing the plate voltage.... I am not sure how much I want to increase it though (maybe I wont increase it even?)


So what will happen if I increase the B+ from say 30V DC to 80V DC or even 150V DC? I would think the tone to open up a bit and the output would increase.


The thing is I have spent a lot of time getting things just right at 30V DC. I don't really want to experiment on the breadboard while there is 160V DC so basically I would have to gamble and just build the unit with 160V DC. I am worried I will have a big tone change and all my hard work and tweaking will be for nothing.

Any insight or comments into the matter?

Thanks...

[Ripthorn]

You could always put together another unit, and if it doesn't sound right at higher voltages, you have a backup .  I know that that is not the most enticing of ideas, but I think it is better than blasting yourself on the breadboard.  Actually, you could charge pump up to about 100V on the breadboard and see if you like it, I would think that would not be too deadly since frequencycentral did that with his murder one amp.

[kurtlives]

Ya I guess I could do that....

String out 30 electro caps and diodes is kinda a pain though.

[newfish]

If it sounds right, then it *is* right.

Simple...

[Ripthorn]

Ya I guess I could do that....

String out 30 electro caps and diodes is kinda a pain though.

I know, but I guess it all depends on just how interested you are in knowing what a different voltage will sound like.  I breadboarded my tube project and am feeding a regulated 24V, but when I build it all up, I plan on having a switch to go from 24V to 100V (assuming the current parts sound good with 100V)

[drewl]

if it ain't broke don't fix it!

A while back I found some weird Bogen tube preamp type thing that had a nice HV transformer I used to make a marshall type tube preamp. With B+ voltages around 250v it sounds incredible, so there is something to say about good high plate voltages.

[DougH]

It sounds like you are finished to me.

[kurtlives]

It sounds like you are finished to me.

Ya but I just keep wondering about it ya know....



Can alone possible describe what may happen to the tone as the voltage increases?

[frequencycentral]

I think you can get to a point with a design where you are basically happy with what the circuit is doing - but you wonder what it will do if.............

I've been there a few times - for example I ran my Vintage Vibe at 80 volts just to see what it sounded like, it wasn't really any different so I stuck at 12 volts. I could have done some more work on it to make it into a Vibe/Phase, but I can see me wanting to use Vibe and Phase simultaneously, so that's another project.

Looks to me as if you are there right now. If you really like it how it is now then stick with it and call it finished. You can always build something similar incorporating the changes you're thinking of making at a later date - and a few other additions that will occur to you in the intervening period as you expand your knowledge. You've got 50+ pedals, so why not a second 12AU7 preamp?

As for the charge pump, you can get up to 80 volts with 12 caps and 12 diodes. I'm thinking of building a little charge pump box with multiple voltage outs just for breadboarding. Flexible and really small, like this one:

[kurtlives]

I think you can get to a point with a design where you are basically happy with what the circuit is doing - but you wonder what it will do if.............

I've been there a few times - for example I ran my Vintage Vibe at 80 volts just to see what it sounded like, it wasn't really any different so I stuck at 12 volts. I could have done some more work on it to make it into a Vibe/Phase, but I can see me wanting to use Vibe and Phase simultaneously, so that's another project.

Looks to me as if you are there right now. If you really like it how it is now then stick with it and call it finished. You can always build something similar incorporating the changes you're thinking of making at a later date - and a few other additions that will occur to you in the intervening period as you expand your knowledge. You've got 50+ pedals, so why not a second 12AU7 preamp?

As for the charge pump, you can get up to 80 volts with 12 caps and 12 diodes. I'm thinking of building a little charge pump box with multiple voltage outs just for breadboarding. Flexible and really small, like this one:

That's what I am thinking... I am going to build this second pre-amp that's for sure. Its just a matter of how to finish it now. I shouldn't feel like I should increase the plate voltage, the pre-amp sounds good right now plus I got 5 other amps I built with high 400V+ in them.

I found a mini breadboard with the charge pump on it this morining prior to going off to school. I think I bread boarded that little pump circuit after you showed off you "Murder One". I only have 4 stages now and I overload the MAX1044 to 11.7V DC. This got me 40V DC. Ill do some more experimenting later, more stages.

Nice charge pump setup there, that should make things easier.

[DougH]

Everything changes with higher voltage. You will need higher plate resistors and etc to get it to bias right. I can't describe how the sound will change because I haven't built a high voltage preamp pedal (just preamps for my amps). But there is nothing wrong with low voltage, as you know. I love my 30v pentode driver. I ran it into the fx return of my 100W amp the other night- just the PD and the power amp. What a sound!

[frequencycentral]

Nice charge pump setup there, that should make things easier.

Thanks, I've done a layout for my next one - even more compact:



I might give it it's own thread - could be useful to some folks.