Understanding Tube Based Overdrive Pedals

[joelorigo]

I have been looking up a bunch of overdrive pedal that have a tube (or tubes). Could someone help me understand what is going on under the hood? It seems that some are tube only, while other ones have FETs or LEDs. Do the FETs and LEDs distort the signal and then the tube amplifies it. Adds more distortion? If they don’t have these parts then the tubes are doing all the distorting? Some have “starved plate” while others have lots of voltage?

i am wondering because I have an old Bandmaster head that in my home/garage I really only have the volume at 2-3, maybe higher for a little bit, but it is still totally clean at that volume. I have plenty of overdrive pedals, but I was wondering if a tube based one would be a cool “2nd, dirtier channel,” or 2nd and 3rd depending on the pedal.

 

[zgrav]

the goal with a tube amp is to have something -- a solid state amp or another tube -- overdrive another tube. The distortion comes from the overdriven tube. Some circuits provide less power to the tube than it could use to run clean to reduce the headroom and make it clip/distort more easily.

 

[Chuck D. Bones]

You'll have to try it and decide for yourself. Before you plunk down a pile of money on a tube pedal, consider that a clean boost overdriving the first stage of your tube amp will provide plenty of tasty tube distortion at any volume. In other words, you don't need tubes in a pedal if you have tubes in your amp. An Integral Preamp will drive the shit outta any amp and provide an extra set of tone controls. Just sayin'.

 

[HamishR]

I started out playing using only whatever overdrive came in my amp. Then as I got fussier/more frustrated I began using non-MV amps so needed an external source for dirt, especially if I wanted to use delay, so I could put the dirt before the delay in an amp with no FX loop. So I tried things like the Matchless Hotbox which is basically a Vox Top-boost preamp in a pedal. The greatest version of this concept (IMO) is the Badcat Two-tone, which sounds absolutely amazing and a lot like an overdriven tube preamp - because that's what it is. It uses two 12ax7s at full plate voltages.

Over time I discovered that I could get a sound so close to that of the Badcat Two-tone with a SS pedal that I couldn't tell them apart I started using the SS pedal. Smaller, runs off 9V like my delay and just easier - no tubes to wear out.

Now you can buy overdrives with tubes which don't use full plate voltages, or use diodes to clip. That's a good idea - if it sounds better. But I haven't found anything which sounds better than my regular SS pedals. But that decision is up to you. And my favourite sounds come from a great OD pedal driving a tube amp. So you're getting both silicon and tube distortion. AS Chuck implies, that's when it all starts to happen.

 

[joelorigo]

You'll have to try it and decide for yourself. Before you plunk down a pile of money on a tube pedal, consider that a clean boost overdriving the first stage of your tube amp will provide plenty of tasty tube distortion at any volume. In other words, you don't need tubes in a pedal if you have tubes in your amp. An Integral Preamp will drive the shit outta any amp and provide an extra set of tone controls. Just sayin'.

What is an Integral Preamp compared to something like a pedal that strictly sends more level like a MXR Micro Amp, Wampler DB+, TC Spark, etc. and boosters that have some EQ function like the BOSS FA-1, DOD 410, etc.?

 

[joelorigo]

I started out playing using only whatever overdrive came in my amp. Then as I got fussier/more frustrated I began using non-MV amps so needed an external source for dirt, especially if I wanted to use delay, so I could put the dirt before the delay in an amp with no FX loop. So I tried things like the Matchless Hotbox which is basically a Vox Top-boost preamp in a pedal. The greatest version of this concept (IMO) is the Badcat Two-tone, which sounds absolutely amazing and a lot like an overdriven tube preamp - because that's what it is. It uses two 12ax7s at full plate voltages.

Over time I discovered that I could get a sound so close to that of the Badcat Two-tone with a SS pedal that I couldn't tell them apart I started using the SS pedal. Smaller, runs off 9V like my delay and just easier - no tubes to wear out.

That's the whole point of my inquiry, I have spent time trying out different combinations of boosts and ODs and have gotten some great sounds. I am just wondering what a pedal with tubes doing the overdriving, like the one above, or the Effectrode Tube Drive, or another, would sound like.

Now you can buy overdrives with tubes which don't use full plate voltages, or use diodes to clip. That's a good idea - if it sounds better. But I haven't found anything which sounds better than my regular SS pedals. But that decision is up to you. And my favourite sounds come from a great OD pedal driving a tube amp. So you're getting both silicon and tube distortion. AS Chuck implies, that's when it all starts to happen.

What is the technical effect of not having full plate voltages?

 

[Chuck D. Bones]

What is an Integral Preamp compared to something like a pedal that strictly sends more level like a MXR Micro Amp, Wampler DB+, TC Spark, etc. and boosters that have some EQ function like the BOSS FA-1, DOD 410, etc.?

The Integral has higher output than the others you mention. Having some EQ before the tube amp lets you control the muddiness, brightness, etc.

A Tube-based pedal with high voltage on the plates will have a bigger clean range, more signal swing and can hit your tube amp harder if you want. Lower plate voltage gives you more distortion and compression and in the extreme case, will not be able to play clean. Pedals with high plate voltage and low plate voltage will sound very different. I think it comes down to where do you want to make the distortion, in the pedal, amp or both?

 

[HamishR]

This is a such a huge grey area where you will get a ton of different opinions, and not many of these opinions will be based in anything like fact. I honestly don't know a fraction of what Chuck does but I have tried a ton of different things to get the sound I like.

For me I have established that I don't care how the dirt/distortion/overdrive is achieved as long as it sounds good. So I am happy with Jfets, Mosfets, germanium or silicon BJT transistors creating the waveform clipping, or a tube, or an opamp being clipped with diodes - I have achieved great results with all of them. None is "better" than the other, it all comes down to (a) what sound you want, and (b) how they are used. Right now I am enjoying a couple of pedals which use the classic opamp with diode clipping arrangement, as long as they are pushing a tube amp. What I want may be (probably definitely is!) different from what anybody else wants. You just have to try a bunch of stuff.

FWIW: When I was using the Bad Cat Two-tone I had a Marshall DSL50 head for a while which had an FX loop. If I plugged the Two-tone directly into the FX return it meant that I was effectively using the Two-tone as the preamp as I was completely bypassing the amp's preamp. So it was very much as if I had a Bad Cat/Marshall hybrid amp. It sounded great! Thicker than the Marshall's preamp but not as dirty.

 

[giovanni]

Echoing what others have said: it all boils down to your preference and the tone you are looking for, with an eye on how a new pedal/preamp will interact with the rest of your gear. The guys from That Pedal Show have made some videos about tube preamps (high plate voltage) that might be interesting to watch to get some inspiration.

 

[Chuck D. Bones]

All true. I have a tube-based pedal that a friend of mine built for me. In clean mode it is crystal clear. The detail is breathtaking. In overdrive mode, there aren't enough "o's" in smooth. Plates run about 140V. It draws an amp at 9VDC. I thought my tube amps sounded good on their own. This pedal takes it to a new level.

 

[joelorigo]

So in summary, yes, some tube pedals use only the tubes to distort. Some use other other LEDs or diodes. Some use a combination.

Some use high voltage some use starved voltage.

I might like a tube based pedal. I might not. Sound right?

 

[giovanni]

Yep. Only you can answer that question!

 

[joelorigo]

That means I might have to buy the $429 Effectrode Tube Drive I've been GAS-ing about to really know!!!

 

[HamishR]

Yup.

I may be wrong, but I suspect that where tube-based ODs excel is in the clean and only slightly dirty area. Once you get into mega dirt you may as well be using diodes. As you may have guessed by now using tubes is no guarantee of good sound. It's the design, not just the nuts and bolts, which determine quality.

 

[joelorigo]

Well I bought one off of reverb so I’ll let you all know what I think after a while! Thanks for the talk.

 

[Chuck D. Bones]

Maybe you will do us a favor and trace the circuit?
Pretty please.

 

[fig]

All true. I have a tube-based pedal that a friend of mine built for me. In clean mode it is crystal clear. The detail is breathtaking. In overdrive mode, there aren't enough "o's" in smooth. Plates run about 140V. It draws an amp at 9VDC. I thought my tube amps sounded good on their own. This pedal takes it to a new level.

that sales pitch...er description worked it's magic. man I am so easy.

pics? soundclip? schematic?

 

[joelorigo]

Maybe you will do us a favor and trace the circuit?
Pretty please.

I’ve never done that and don’t know where to begin or what to do but ok.

 

[Chuck D. Bones]

We don't want you to break anything. Detailed photos of both sides of the board are a good start. We need to be able to see the traces and read component values. I figure the circuit is pretty straightforward and if we can see most of it, we can guess the rest.

 

[Chuck D. Bones]

that sales pitch...er description worked it's magic. man I am so easy.

pics? soundclip? schematic?

I'll ask the designer if he wants to share the schematic. I can tell you that it's based on / inspired by the Dumble #124 Preamp. Here's a pic of the front. Behind the tweed lurks a pair of Russian sub-mini dual triodes. It's an ambitious project that turned out extremely well.