Slajeune: Ruby Tube Preamp

[The Tone God]

Slajeune: I have posted a tube preamp schematic for the Ruby Tube. Give it a shot to see how you like it. Tweaking is always possible.

Ruby Tube Schematic

Andrew

[bobbletrox]

Would that schem work as a tube boost/overdrive if the output went to a guitar amp rather than the 386?

[Peter Snowberg]

Very cool!

I've done the pot in the plate thing before.... but it was always at high voltage so the range was nothing like what you have there. Wow... 1K to 251K.... That's VERY cool!

One suggestion to try... You might want to swap the fixed 100K resistors in the bias generator with a 100K pot. Lots of tuneabality.

Take care,
-Peter

[The Tone God]

Would that schem work as a tube boost/overdrive if the output went to a guitar amp rather than the 386?

I suppose it could. I didn't have any 386s lying around so I just throwing it into a test amp using it like a preamp. There is a large output change between the min and max settings as the final volume of the Ruby Tuby was intended to be adjustable by the master volume control to the 386.

You could raise the gain control limiting resistor to say 10K to prevent the output from dropping as much. You might also want to tack on a boaster section to the end to provide more and adjustable output.(i.e. Mini-tubes, LPB-1, Mosfet, opamp, etc.)

I've done the pot in the plate thing before.... but it was always at high voltage so the range was nothing like what you have there. Wow... 1K to 251K.... That's VERY cool!

Thanks. I wanted to get rid of the opamp front end. The lowest setting provided a good clean setting that was hard to overdrive with pickups.

One suggestion to try... You might want to swap the fixed 100K resistors in the bias generator with a 100K pot.  Lots of tuneabality.

I think I played with that before but didn't get back to it since I was busy trying to get a good gain range. I'll go play with it again to see what happens with the new settings.

Just a note; Vcc is 12volts.

Andrew

[aron]

I've done the pot in the plate thing before.... but it was always at high voltage so the range was nothing like what you have there. Wow... 1K to 251K.... That's VERY cool!

Me too. I shudder to think about how dangerous that was.  :shock:

I've since gone to adjusting the cathode resistor instead.

Very cool!

[Ansil]

thank you lol i was tryign to remmeber the vcc of the original threayd..

[puretube]

don`t you get loud scratchy noises when turning that plate-resistor pot?

[Peter Snowberg]

don`t you get loud scratchy noises when turning that plate-resistor pot?

This is the vintage version of the infamous "crackle-OK" gain pot of ZVex fame.

Take care,
-Peter

[bobbletrox]

I've gotta admit, what I find interesting about the Ruby Tuby isn't really the 386 part...it's more the possibilty of using the super-simple tube section in a pedal.  There seems to be quite a few tube overdrives out there of varying degrees of complexity and voltage requirements...which is daunting since I've never used tubes before.

The closest thing I've seen to a simple tube circuit with a familiar power source is the Ruby Tuby...and a simple tube circuit for a pedal would be a great starting point for us tube-noobs!  There probably isn't any advantage from using tubes in a boost, or passive eq type pedal...but at least it'd make a good learning experience.

[Lonehdrider]

Yeah its one I intend to learn as a toob noob as well, the thought of putting myself into a main's project at this point is ahem, shocking to say the least. I didn't even like the bite I got years ago testing to see if the ground switch was right between old fender amps and the pa mike let alone something with way way more voltage. Maybe a dumb question, but I know working one handing with one in the pocket is the safest way, but are like insulated rubber glove(s) any help at all? My hair is kinky enough without adding to it... (Black Irish, guess thats why I play the blues hehe). Now if I can just get Nurse Quacky to Quack (to late to try it, got the power LED lit though, but its that pesky LFO lite I want to see thats the hard part, third time I've tried the circuit, always seemed to ground out something or rather, this time a perf with no soldering pads and it looks way better than my last attemps, sorry for the OT, just excited to try it out and see if its another back to the drawing board, or doing the funky chicken (or duck or whatever it is)....

Regards,

Lone


Regards,

Lone

[slajeune]

Hi Andrew,

WOW thanks for the schematic.  I didn't have time to test it but I definately will try it.  If I can get rid of the opamp, it might be a good idea!

BTW, I posted the latest schematic on geocities. (http://www.geocities.com/slajeunesse/ruby_tuby.html).  I am happy with the sound that I am getting, but, if I can simplify the design even more (thanks to your help!) it would be even better!

Thanks,
Stephane.

[slajeune]

Hi Andrew,

I have a some questions about your design:

- In my schematic, the cathode is connectly directly to ground (0V) where yours is connected at 6V, what is the purpose of that?!?!  This is the major difference between your design and the one in the Ruby Tuby.
- Any good links / reference to basic tube design?  I am always looking for good information on the subject.  I have something else planned but I need more basic (or advanced) tube info.

Thanks!
Stephane.

[bobbletrox]

You could raise the gain control limiting resistor to say 10K to prevent the output from dropping as much.

Is that the 1k resistor before the gain pot that you're talking about?

[bobbletrox]

Is this kinda what the schem for a self contained Ruby Pre would look like?

Ruby Boost/Pre Schematic

...although the 78L12 could be disregarded because it's for the benifit of the 386 isn't it?  I'm not sure whether the second 1000uF cap would be needed either if that were the case.  :?

Anyway, sorry for taking over your thread!

[slajeune]

Hi Bobbletrox,

it looks good from my point of view.  I would keep the 78L12 for the following reason, you regulate the voltage going to the heaters.  This is a good thing.  Also, the 1000uf caps filters the DC comming in, therefore, it reduces hum.  You can try to remove them, but, you might induce some hum.

It is important to note that for the 78L12 to work, it needs >2 volts higher than the target voltage.  Therefore, the 78L12 needs >= 14volts input DC to regulate the voltage to 12V.  My 12V wallwart was outputing 14.4V, therefore I am using it.  Make sure that your wallwart can supply at least 500ma (300ma is needed for the heaters alone).

The only thing not shown on your diagram (and mine and Tone God's one) is the heater connection.  Pin 4 of the tube is connected to VCC and pin 5 is connected to ground.  Pin 9 is left unconnected.

Also, if this is the first time you use a tube, please note the following: pin connections are always shown looking at the pins from the bottom of the tube with the gap between pin 1 and 9 facing down.

Hope this helps!  Keep us posted on the outcome of the preamp!

Cheers,
Stepahne.

[Peter Snowberg]

Hi Bobbletrox,

One omission, one addition, and one reposition for you.

First, your schematic needs an additional 1M resistor between the 1st tube grid and the Vbias generator. Second, when you use a BIG cap on the "downstream" side of the regulator you should also install a diode (1N4001) between the in and out pins with the anode connected to the regulator output. Better regulators build this diode in, but the 78xx series does not have it. The diode protects the regulator when you cut the power by stopping the voltage at the output from being higher than the input, which can cause damage.

The regulator output cap really doesn't have to be large at all and because of the increased ESR & ESL of the larger cap, you're actually much better off moving both the big caps to the input side and then using a very small cap on the regulator output. 0.1uF is actually just fine on the output. The purpose of that cap it to stabilize the regulator and not to provide any power storage. I typically use anything around 1uF in that position but results will be the same from 0.1uF to 10uF so there is a big margin. If this cap is small, you don't need the protection diode across the regulator.

Keep us posted on your success!

Take care,
-Peter

edited to repair an anode/cathode flip-flop. Whoops.

[The Tone God]

Ok there are several replies so let go through them.

don`t you get loud scratchy noises when turning that plate-resistor pot?

Not really. I was using a new pot so there wasn't any noticeable cracking. If there is some I think I could work around it. It should be observed that some pot manufactures attach the shaft/bushing/casing to the wiper or wiper ends.

I've since gone to adjusting the cathode resistor instead.

I agree that in a high voltage situation I would not put a user accessable control on the plate. In that situation I would do the cathode control too but this low voltage so I figure why not indulge myself in something I wouldn't normally be able to do.

I also find that under starved conditions cathode adjustments results is slightly less symetrical behavour through out it's range especially with a high plate resistor. I suppose you could componsate with the bias network attached to the grid but thats bodging IMHO. The cathode cap makes the cathode control alittle anonying too.

In my schematic, the cathode is connectly directly to ground (0V) where yours is connected at 6V, what is the purpose of that?!?! This is the major difference between your design and the one in the Ruby Tuby.

The cathode is still connected to ground in this circuit but I added a cathode cap. I personally like the sound of cathode caps in plate starved situations. I assume you are talking about the grid resistor being tacked to 1/2 V+. I biased the grid higher to get more output from the triode section but it won't really add any more gain/distortion.

Any good links / reference to basic tube design? I am always looking for good information on the subject. I have something else planned but I need more basic (or advanced) tube info.

Check out Aron's Tubes for Dummies section. Also follow the links he gives in that to the likes of Geofex Debug page and Akien. Most of my tube information comes from these funny looking pre-organized piles of paper called books.

Is that the 1k resistor before the gain pot that you're talking about?

Yep. When in doubt play with the pot till you find the lowest range you want it to go, messure the pot, and put a resistor in with that value. I let it go down to 1K because it makes it tough to distort the tube at the level so it gives a nice clean sound. The lack of output would be made up in the Ruby Tuby by the 386. You could tack on a boaster section after to do the samething.

You do need the 12v for filmants. You didn't forget those did you ? Using the 12v for both the B+ and filmants makes the circuit simpler.

The 1000uF cap on the end of the regulator is overkill now. That value was originally suggested because there may have been noise issues with the power supply. That seems have been cleared up now so its not really needed. I typically use 1000uF cap with a 0.33uF or 0.47uF tant on the input and another tant or maybe up to 10uF electro on the output.

I do think this is a pretty simple and low voltage (read: safe) circuit that can be played with to get an idea of how the different parts of the circuit work for a tube so experiment away and have fun.

Andrew

[bobbletrox]

Thanks for the tips Stepahne, Peter, & Andrew.  I revised the schematic according your suggestions, although I left the two 1000uF caps and went with the protection diode option for simplicity's sake.  Unfortunatly I can't afford to start this project straight away but I'll try to figure out a PCB layout and wiring diagram for it in the meantime.  I reckon it'll be a pretty cool pedal if it all fits inside a BB sized enclosure with the tube standing vertically through the top!  Btw, I hear 12AX7LP Sovteks are supposed to be good for DC.

Thanks again guys  

Revised Ruby Preamp/Boost

[Peter Snowberg]

:oops: Whoops! Sorry, I should have said ANODE to output.

:!: You'll want to reverse that protection diode. Anode to output and cathode to input.

Sorry about that!

Take care,
-Peter

[bobbletrox]

Fixed  :wink: