Starved Tube Distortion

[RipGlitter]

"Normally, a 12AX7 tube is run with 100-200V on the tubes plate terminals for clean amplification, lowering the plate voltage to 30V starves the tube of the regular flow of electrons and causes the tube to readily distort. Tube distortion produces pleasant sounding even harmonics, contrast that with the scratchy odd-harmonic distortion (often called crunch) that comes from transistor/diode distortion circuits. Tube distortion tends to make more of a howling electronic sound that is commonly heard in late 1960s / early 1970s rock-n-roll recordings. A good example of the tube distortion sound is Eric Clapton with Cream playing "Sunshine of Your Love". Producing tube distortion in a starved tube circuit instead of an overdriven tube guitar amp has the advantage of making good tone at much lower volume levels."


Is this really true? Are old Marshall amps "starved"?

[zaphod_phil]

No, none of them are. Nor really any of the well-known tube amps. They just overdrive their tubes with very large signal levels, in the region of 100V to 200V peak-to-peak. Starved tubes are mainly used as a means of getting tubes to distort more readily in low voltage circuits, with lower signal levels, such as pedals. But not all tubes sound good in starved mode, if any at all do. In my experience a lot of the starved tube tones I've heard have sounded more like transistor fuzz pedals than overdriven tubes. Higher voltage operation tends to give better definition. IMHO that article could be pretty misleading.

[RipGlitter]

Thanks Phill, Theres just so much confusing info on the internets.

[rjgtr]

I agree with phil.

Unfortunately, the result of low B+ is a sound with a lack of low end, punch and mushy highs. Most of the more recent tube distortion pedals use a real power supply and put 180+ V on the tubes. They sound a lot better than old style starved type, but still require a tube amp for a really good tone.

The trick of "good sounding" preamp tube distortion is first deciding what you want the end result to be.

If you're looking for an 80's hair metal sound then using higher values for cathode resistors will get you the raw cutting distortion of the era. If you're looking for something closer to power tube distortion then a lower value cathode resistor seems to round things out. It's all a balancing act. To get reasonable distortion from 12ax7s you need at least 2 tubes to get enough stages to balance the drive evenly.

[pylet2000]

Not necessarily, the SIB Varidrive is a single 12AX7 preamp pedal that sounds incredible with a good tube amp behind it, and covers a wide range of tones. I should probably trace the circuit and put a schematic together, it's pretty awesome...

On the other hand, I have a Budda Phatman that doesn't even come close tonally, and it's a 2-12AX7 design. I rarely use it unless I want a very specific tone. I'm sure this has to do with the specific EQ of the pedal, and I've often thought about modding it's tone stack.

[zaphod_phil]

I may be somewhat biased, but I think I can safely say that the P1 eXtreme, with it's single 12AX7 preamp, gives excellent clean and distortion tones. It's not a low-voltage or starved-tube design though. And it sounds even better with a 12BZ7 tube in it running at 350V. You just need to know how much to attenuate the signal between stages, how to EQ along the signal path and how hot/cold to bias them. I'm sure you could put the same P1eX preamp into a pedal format.

[rjgtr]

Not necessarily, the SIB Varidrive is a single 12AX7 preamp pedal that sounds incredible with a good tube amp behind it, ... it's pretty awesome...

Is it a starved voltage design?

If it is, maybe what you're hearing is a good SS Distortion colored by the tube slightly. Otherwise, it just may be well voiced. I've heard good reports about the Tonebone series, too. And don't forget Mesa's pedal - a lot of people liked it.

I didn't say that all tube pedals sound bad to me - just the starved plate variety in general.

[zaphod_phil]

IIRC the Mesa pedals use high voltages, and aren't really starved tube designs. However they have far too much SS c**p inside for my liking. No idea about the ToneBone pedals...

[rjgtr]

IIRC the Mesa pedals use high voltages, and aren't really starved tube designs. However they have far too much SS c**p inside for my liking. No idea about the ToneBone pedals...

Agreed on the Mesa pedals. It's funny how close it sounds to the DualRect preamp shoved in a box. The Tonebone is a probably a buffered design on input and output, which the Marshall JCM900 line also was! But so far I'm hearing good things about it. But all pedals have drawbacks.

I personally think part of the feel of an amp is that it is all connected to the same power supply. While many of these pedals can be fun and sound pretty good, there's usually a difference in feel from an amp. Most of the guys getting great sounds from tube based pedals are actually pushing the front end of a tube amp and not so much using the pedal for the distortion.

[RipGlitter]

Eddie Van Halen "starved" his amps with a variac to get the famous and highly sought after "brown sound". So I thought there might be somthing worth learning about starved voltage designs.

[kd]

I was thinking about putting one of these together. Anyone built one?

http://www.dogstar.dantimax.dk/tubestuf/mctintro.htm

Ken

[zaphod_phil]

Eddie Van Halen "starved" his amps with a variac to get the famous and highly sought after "brown sound". So I thought there might be somthing worth learning about starved voltage designs.

That's not quite true. He just lowered his amps' rail voltages to get them to break up sooner. However, they weren't actually running in starved mode.

I was thinking about putting one of these together. Anyone built one? http://www.dogstar.dantimax.dk/tubestuf/mctintro.htm

With the stock resistor values, these sound just like a transistor fuzz box. Although the rail voltage is quite high the stock resistor values put the tubes into starved mode. However, they can be tweaked to sound real good. Good starting values to try are:
R4 = R6 = 100k
R6 = anything from 1.5k to 820 ohms
R7 = 820 ohms
C7 = C8 = 2.2uF

[RipGlitter]

I would like to build a complete "tweaker" amp.

Seperate adjustable power supply transformers for each tube stage.

All adjustable componets in the amp with the turn of a pot.

Then when you dial all that mess in to a killer tone, you could design a "fixed circuit" to these values.

yeah, that would be sweet.

[kd]

Thanks Phil, I'll try those modes when I get around to building it. I'd be really disappointed if sounded like of transistor fuzz box.

Ken

[pylet2000]

Not necessarily, the SIB Varidrive is a single 12AX7 preamp pedal that sounds incredible with a good tube amp behind it, ... it's pretty awesome...

Is it a starved voltage design?

If it is, maybe what you're hearing is a good SS Distortion colored by the tube slightly.

I'm not really sure to be honest with you. I just assumed it's great tone and hadn't taken a few minutes to figure out what's it's doing. I guess the 5E3, Epi VJ, 18 watt, P1Xtreme, and Champ builds took all of my time... I'll have to spec it out, I'm curious now. I don't remember seeing any transistors in it, so I don't think it's SS but I never really looked too close. It gets A LOT of drive from just the 1 12AX7 (I use a AT7 to tame it down, actually), I bet it's pretty similar to the P1Xtreme preamp milking every ounce of gain it can. I'll get on drawing up a schemo and taking some voltage measurements...

I owned a Mesa V-Twin for a while, and my first impressions of it were pretty favorable. Sounded pretty great with a Twin Reverb, I called it "the two twins tone." Man, I'm a nerd. Anyway, the SIB Varidrive I got as a loner when the Mesa broke (optocouplers failed, go figure) completely blew it away, so I bought it and Ebayed the V-Twin.

[zaphod_phil]

Anyway, the SIB Varidrive I got as a loner when the Mesa broke (optocouplers failed, go figure) completely blew it away, so I bought it and Ebayed the V-Twin.

There's a picture out there I've seen of Paul Ruby's V-Twin pedal that failed on him during a gig. I think he smashed it with a hammer.

[pylet2000]

Agreed, there is far too much flaky technology going on inside the V-Twin for a simple tube pedal. A hammer is probably a fair end for a V-Twin.

Another thing that really peeved me about it was the delay in the channel switching. There was nearly a half second delay between a button click and an actual channel change. "And this thing costs how much?" I remember thinking... Ebay was an easy decision.

[rjgtr]

Agreed, there is far too much flaky technology going on inside the V-Twin for a simple tube pedal. A hammer is probably a fair end for a V-Twin.

Another thing that really peeved me about it was the delay in the channel switching. There was nearly a half second delay between a button click and an actual channel change. "And this thing costs how much?" I remember thinking... Ebay was an easy decision.

The delay is because they use a muting circuit to cover a bad switching methodology. If they'd done the design a little better they wouldn't have all the issues they have with them.

[pylet2000]

The delay is because they use a muting circuit to cover a bad switching methodology. If they'd done the design a little better they wouldn't have all the issues they have with them.

He can keep his patents on that.