Tube OD?

[karbomusic]

Sorry if I'm being a little lazy here. I did a couple searches but that ends up being two hours of sifting to get close to the answer I want. Just looking to tackle a tube based overdrive project that can run in a pedal @12-18VDC. I'm comfortable with circuits that raise the voltage for the tubes etc. I'm mostly interested in something with a schematic + potential verfied PCB layout so that I can breadboard it first, experiment, then etch and experiment more. I can do my own PCB layout if needed but if the perfect project is already here, I can start with one that exists, then mod and do my own later.

Doesn't have to be incredibly feature-ridden. Maybe something with a tone control, drive and output level that I can get some decent dirt yet clean up well would suffice (I'm a heavy guitar knob user). Ideas?

[Luke51411]

THcustoms has a few.

[karbomusic]

That I can source parts build and breadboard on my own? I haven't checked them out but not looking for a prefabbed kit but rather a DIY thread of something that has gained popularity or similar. Sorry if my PCB comment was confusing, that was a side statement in case such was here and I was missing it. I saw some in some threads but they are so long, I get lost on which schemo or layout is the actual working one. I can do my on PCB if needed, that was just a best case ask. However, if they have the schemos and part list, I can use that as a potential source so thanks.

[Luke51411]

Thomas is good people, he's active on madbean. He sells just pcbs and the schematic is there as well, I think he has a couple different versions of a tube driver and even has suggestions for how to build it low, medium, and higher gain. http://diy.thcustom.com

[Transmogrifox]

The McTube is a good starting point and easy to build from commonly available parts:
www.dogstar.dantimax.dk/tubestuf/mctube2.pdf

Pretty easy to expand upon this by adding a standard BMP style tonestack, or the typical Fender 3-band stack, etc.  Lots of mods and ideas based on this circuit floating around the webs, so looking for McTube will narrow your search a lot more to real Tube OD's and variants of McTube.

[GibsonGM]

Either the McTube, which does have a mains connection that you need to get right and do safely,  or one of the low-voltage tube designs would be my suggestion.  No need for reinventing 100 year old tech!

Get over to the Valve Wizard's site, read about the basic triode gain stage!  All it seems you're really shooting for, for OD, is that, in a nutshell.   Then you can tailor bypass caps, coupling caps for tone shaping, and use partial bypass for gain.   McTube is in this category.

[karbomusic]

Thanks guys!

I'm not neck deep in it yet but once I get some free time I wanted to get one of these on the bench to begin experimenting with. I'll review all the suggestions and pre-order some quantity of parts that I don't already have so I'll have plenty of options. This is something that will eventually wind up on my pedal board for gigs etc. Thanks again and I'll update this thread once I get started.

[J0K3RX]

Might check out Bajaman's (Steve Bartlett) real tube overdrive... the thing sounds great and has an awesome layout as well!





All his stuff is pretty damn cool actaully...

http://s197.photobucket.com/user/bajaman002/library/?sort=3&page=1

[GibsonGM]

^ That IS damn cool!!!     Might be right up Karbo's alley.

[karbomusic]

Yea that is cool. I'll definitely check that puppy out and some of the others!

[FuzzFanatic71]

Have you considered the Matsumin Valvecaster? Not really all that difficult and can be built right on the back of the valve socket. No need to worry about a PCB. Not very dirty in stock form, but you can add a switch with some clipping diodes and it sounds great. I used a three way on-off-on toggle switch with some NOS silicon diodes on one side and some NOS germanium diodes on the other side. Stock no clipping in the centre. Sounds very nice if you like vintage style dirty tones. It has become an always on pedal for my board. There is a 150+ page thread on the subject on this site if you're at all interested.

[tubelectron]

Well, I have never built low-plate voltage overdrive pedals (starving-plate, etc...) because the few commercial models that I tested were not convincing : Overlord, Tube Driver BK Butler, Maxon and Ibanez Tone-King... So I didn't go further, but I should.

Here are the 3 models that I have : a Westbury W-20 The Tube, and 2 DIY ones. All of them uses diode clipper and high plate voltage...

With only one or two triode stages, you can't obtain a satisfactory overdrive tone and decay : you need additional amplification. That's what I discovered during my tests.















A+!

[GibsonGM]

Well, I'd have to say it depends what you want to get out of your tube circuit, doesn't it, Bruno? 
If you want to push your amplifier harder ("overdrive"), then even 1 stage will do that.  If the amp is expecting .7V and you feed it 4V, you've accomplished quite a lot.

If you want to hear actual tube distortion with more quality than "bzzzzz", of course we need more than 2 stages...

If you're feeding a tube amp, you're really just adding another stage or 2.    If a clean transistor amp, it's not the same, and then you really may need the additional stages and to KEEP the transistor amp from clipping...

[karbomusic]

Hmm.. Some good points. I was hoping to get away from diodes as clippers in this build. A combo of both pushing the tube(s) in the pedal and/or pushing the input of the amp.

[tubelectron]

If you want to hear actual tube distortion with more quality than "bzzzzz", of course we need more than 2 stages...

Yes, that's it.

I meant : a standalone overdrive pedal need more than 2 stages to give you a good overdrive tone and decay by itself, otherwise you need additional amplification or diode clipping integrated in the pedal.

Well if you think about using a tube stompbox to push another tube amp in the overdrive tone, it is doable of course, but I am not sure that it would be really more interesting than a much simpler single 2N3904 clean booster stompbox for pushing the tube amp into overdrive.

Hmm.. Some good points. I was hoping to get away from diodes as clippers in this build. A combo of both pushing the tube(s) in the pedal and/or pushing the input of the amp.

But if you think that a simple 1 or 2 stage-cascading tube stompbox will be suitable for pushing a transistor amp into a tubey-like overdrive, you may be disappointed...

A+!

[karbomusic]

But if you think that a simple 1 or 2 stage-cascading tube stompbox will be suitable for pushing a transistor amp into a tubey-like overdrive, you may be disappointed...

I don't use transistor amps on stage. This would go onto my pedalboard feeding my Boogie DC5 and would like a non-diode OD with tube(s) with potentially some breakup from the tubes as well as driving the input of the amp.

[Groovenut]

If you are wanting to keep it to just one 12AX7 and get good overdrive, I would suggest using an opamp as the input amplifier stage, then run into the first tube stage. Bias the first tube stage much like the second stage of a JCM800 but with a cathode bypass cap so there is plenty of signal to overdrive the next stage. Follow the first tube stage with a coupling cap and 2:1 voltage divider (possible with a treble peaker) then into the second tube stage. IMO you will want to center bias this tube gain stage to act more like the clipping diodes you're leaving out. From there another voltage divider into an opamp buffer stage to either a tonestack or level control.

I have done this to produce very convincing tube overdrive to full on distortion but it all depends on how you bias the tube stages. I like to run 250V to the plate resistors and setup the opamps to run on a single rail 30V with a bias voltage of 15V.

[tubelectron]

If you are wanting to keep it to just one 12AX7 and get good overdrive, I would suggest using an opamp as the input amplifier stage, then run into the first tube stage........

Yes, I would do it as you describe it, Groovenut. That's the only way to go if you want to use a single double-triode tube without a diode clipper, IMHO.

A+!

[J0K3RX]

OK, maybe this is up your alley, maybe not.. Actually this is something that I am working on now along with about 19 other things to satisfy my ADHD, which it does not do...

Dunno if you have ever heard of Mueller or Muller Amplification but Marc Mueller makes some wicked high gain amps, this is one of his older designs but hardly out dated

Look at the schematic on page 2, notice the OD section in front. Now, scroll down to the very last page and have a look at the back side of the amp and you will see the tube screamer like "Gain/Tone/Volume" controls on the right side. Now scroll back up and look at that schematic again... 
http://www.jogis-roehrenbude.de/Leserbriefe/Marc-Alexander-Mueller-Classic/Bauanleitung_Mueller_Classic_A4.pdf

How to power it you may ask? Do a search for GTFO here on this forum and there in your answer will be...

So there is your schematic and of course, you can pretty much guess that it works... Now all you need is a layout.. hmmm? Part count not including the PSU is not far over 20 pieces. Use a small piece of turret board

[J0K3RX]

How does it sound?

6505 reamped
https://dl.dropboxusercontent.com/u/11178619/Mueller/6505%20reamp.MP3

Tube OD - 6505 reamped 
https://dl.dropboxusercontent.com/u/11178619/Mueller/TubeOD%2B6505_Reamp.MP3
TubeOD settings - Drive 9o'clock/Tone 2o'clock/Level 2o'clock