Vibracaster - or "How to turn your Valvecaster into a Tremolo"

[MikeH]

Looks awesome!  I'm going to make a little add-on board and make this a switchable mod.  Looks cool.  Does it behave the same @ 12v vs 9v?

[frequencycentral]

Looks awesome!  I'm going to make a little add-on board and make this a switchable mod.  Looks cool.  Does it behave the same @ 12v vs 9v?

I breadboarded the oscillator at 9 volts, It seems to work the same at 12 volts. Tubes circuits definately work better at higher voltages!

[Salvatore]

Yeah, I'm planning to make the 5672 VCA too - you should translate the whole thing for me - the only Dutch I know is "Let Op! Drempels!"

Well, at least you know some relevant Dutch, "watch out ! Thresholds".
If you want I could translate the interesting bits, that would not be to much work.
But I could not start until at least a week from now, bit busy at the moment with a new band.

[jacobyjd]

I may have missed it above, but I know most are running their Valvecasters at 12v (or higher)--would 12v be too much for running this add-on?

heh, never mind   Too fast for me! 

[Jimmy-H]

Build this one Jimmy, the Bipolar Disorder is a lot more pain for not much more gain. The BD took ages to iron out problems with, LFO bleed and thump, the Vibracaster just worked well first time. Also, the parts count for the Vibracaster is just tiny in comparison with the BD.

OK Rick, I'll keep that in mind.
By the way, I just listened to your recording of the pedal, sounds great!
Keep up doin' the good work 

[nokaster]

"Let Op! Drempels!"

being belgian... this was a very funny read!
weird which phrases end up as the only one someone knows in a certain language!

[frequencycentral]

Here's a schematic for the Vibracaster with pinouts and heater circuit if you want to use a 6111 submini tube instead of a 12AU7:

[Fl!P]

Well done!

But, uh... Excuse me for asking, but can I get some sound clips?

[Renegadrian]

http://www.myspace.com/doctoranalogue 

[Fl!P]

http://www.myspace.com/doctoranalogue 

Thanks!

[comfortably_numb]

I'd like to take the opportunity to point out that the 12AU7 heaters can be run in parallel at 6.3 volts as well, and so any of these circuits can be safely used at 9V with the heaters in parallel following frequencycentral's voltage drop technique.  The 12U7 data sheet does not specify a parallel heater voltage, but as there is a center tap (pin 9) I imagine it would function similarly.

[Renegadrian]

yeah, I remember it was discussed in the main valvecaster topic...the way you can use pin 9  and what it's for...

[frequencycentral]

I'd like to take the opportunity to point out that the 12AU7 heaters can be run in parallel at 6.3 volts as well, and so any of these circuits can be safely used at 9V with the heaters in parallel following frequencycentral's voltage drop technique.  The 12U7 data sheet does not specify a parallel heater voltage, but as there is a center tap (pin 9) I imagine it would function similarly.

Might need a recalculation for the series resistor value @ 9 volts though. 

[Renegadrian]

Hey Rick, I have some BC 548, both B and C - would they fit? Or should I stick to the 547s you used???
Also, why did you use a 100k LIN and not LOG for VOLUME? And why a 100k for the GAIN, instead of the 50K of the original?

[frequencycentral]

Hey Rick, I have some BC 548, both B and C - would they fit? Or should I stick to the 547s you used???
Also, why did you use a 100k LIN and not LOG for VOLUME? And why a 100k for the GAIN, instead of the 50K of the original?

Just comparing the BC547C with the BC548C on their datasheets, they appear to have the same gain, the 'B' version has too little gain though, and probably wouldn't be suitable. You should socket the transistors though, just in case they don't work for some reason.

Volume - I'm going to build mine with a trimpot or resistor voltage divider (to achieve unity between the bypassed and effected signals) instead of a Volume control - you don't usually see tremolos with volume controls. As to 'why Lin and not Log', I've built a lot of synth stuff, where Lin in used for signals and Log for control voltages. Different pot manufacturers label their pots differently too, an 0MEG Lin is 'A', an Alpha Lin is 'B' - very confusing.

Gain - having a 100K instead of a 50K allows more resistance between the cathode and ground, and therefore more clean headroom. Again, I'm building mine without a gain control, I'll use a 100K resistor instead - you don't ususally see tremolos with gain controls either. I will also be using 100K resistors for both the plate resistors, again aiming for a clean sound.

So mine will just have two pots - 'Speed' and 'Depth'.

I've also made a few improvements to the design - just tweaks here and there - and one of the resistor values I posted was wrong (doh! - the first 4K7 at the emitter of the second transistor should be 47K), so hold off from building it for a day or two, to give me time to update the schematic.

[Renegadrian]

Well, I usually use sockets, so no problems...I'll try those BC548C

You wrote that with the depth pot at zero you have a standard valvy, right?
So I want to build it with all the pots then...
I'd have a standard valvy and a tremolo at the twist of that pot?
The way you'd do it it would use valvy part just to clean boost the sound...

Wait for the updates then!!! Thx for your useful explaination!!! 

[frequencycentral]

Here's the latest update, it's the version I'll be building. It's the 6111 submini version with no gain control and no volume control. I'm building mine as a tremolo only - no boost/overdrive - just unity gain between the bypassed and effected signals. Tremolos don't usually have gain/volume controls.

The tweaks are circled in red. (though somehow it seems to have changed to purple in Photobucket)

A. I've changed the gain pot for a 100K resistor - for hardwired clean headroom.

B. I've changed the 100K plate resistor for a 220K - to achieve unity gain between the bypassed and effected signals.

C. I've added a 1N4148 to negate a bit of LFO bleed I found.

D. This was 4K7 on the original schematic. It was a mistake! Oops! It should be 47K.

I'm still having problems adding a rate LED - it flashes nicely but it causes audible ticking - I've tried a few solutions (including Jack Orman ones) with no luck. I guess a rate LED isn't essential - but I won't let it beat me - so I will post the solution when I find it.

[frequencycentral]

..........and here, finally, is the way to add the LFO rate LED without causing any popping.

[Renegadrian]

so it should be that way? What is that 100k res at the base? Also, will this circuit work as a stand-alone (without the tube part) or it needs something to boost the sound???

[frequencycentral]

so it should be that way? What is that 100k res at the base? Also, will this circuit work as a stand-alone (without the tube part) or it needs something to boost the sound???

Sorry - I don't understand the question.............

EDIT: Aah - got it! No way Adriano - that arrangement would tick like a Swiss cuckoo clock at midnight! The LED circuit uses an EXTRA transistor. Like this: