Doom fuzz 18 watt circuit?

[Crowbar]

Hello all,

This is my first post here, I have built a number of guitar pedals, and now I want to step up and try to build my first tube amplifier. I'm no electronics expert, so please bear with me

I mostly play doom/sludge metal on down tuned guitars, and I thought it would be nice with a small lunchbox size amp made specifically for that. I want it very simple, both to make it easier to build, but also because I like the purity of just plugging the guitar directly to the amp and just doom away.

So a single channel amp, no clean or edge of breakup tones needed, just all out fuzz assault. Something sounding a bit like an Acapulco Gold or Meathead pedal. Thick fuzzy distortion with lots of low end.

I plan on going for a 2xEL84 power amp, it seems like a simple circuit with no bias adjustments, and at 15 or 18 watts you can run it cranked up high to hopefully get some power tube distortion going, and it should be loud enough for band practice with a good 412 cab.

So, I am looking for suggestions for what circuit design I should go for. I was looking at the Orange Tiny Terror, its a simple circuit with few components, and Orange amps in general tend to have a bit of that round fuzzy sound that I want. But maybe there is an even better design I should look at, or if the Tiny Terror can be tweaked towards more fuzz?

Of course I could build a clean amp and simply put an Acapulco Gold in front of it, but I really like the idea of just using an amp without pedals, and also its fun to build something a bit unique I think.

Thanks for reading all this, all input is greatly appreciated

[JMPGuitars]

18W amps are still plenty loud, so keep that in mind.

Do you want an EQ or a simple tone knob?

Personally, I think the TinyTerror sounds like a tinytoy.

[Crabman]

If you are really into fuzz then you may have to integrate solid state hard clipping somewhere in the mix. The easiest approach would be to use a solid state fuzz pedal to push a relatively clean tube amp to get what you’re after.

The Mercury Rising pedal is a mix of vacuum tubes and germanium diode clipping. If you can find a schematic for that pedal, you may be able to use that to influence how you could construct a tube preamp that has some sort of built-in fuzz and feed that into a tube power section of your choice.

While not a fuzz type of clipping, the José mods used in the 80s to juice up Marshall amps from that era involved diode clipping as one of the options. This was inserted just before the EQ section. You see this type of approach used in modern amps, particularly as an option to enhance clipping in a number of Friedman amps.

It may be that a similar type of approach could be used with a hard clipping mechanism to produce fuzz. This would require some trial and error in order to figure things out, but may be fairly difficult for somebody with little experience experimenting with tube circuits.

[Crowbar]

18W amps are still plenty loud, so keep that in mind.

Do you want an EQ or a simple tone knob?

Personally, I think the TinyTerror sounds like a tinytoy.

I was more looking for changes to the actual circuit, to drive it to more aggressive clipping.

I have actually never tried a Tiny Terror, so I dont know if it sounds like a toy. But a few other EL84 15 watt anps like 6505 mh and Engl Ironball and those sounded quite good.

I will be using a substantially bigger output transformer, dont know if that will make any difference.

[Crowbar]

If you are really into fuzz then you may have to integrate solid state hard clipping somewhere in the mix. The easiest approach would be to use a solid state fuzz pedal to push a relatively clean tube amp to get what you’re after.

The Mercury Rising pedal is a mix of vacuum tubes and germanium diode clipping. If you can find a schematic for that pedal, you may be able to use that to influence how you could construct a tube preamp that has some sort of built-in fuzz and feed that into a tube power section of your choice.

While not a fuzz type of clipping, the José mods used in the 80s to juice up Marshall amps from that era involved diode clipping as one of the options. This was inserted just before the EQ section. You see this type of approach used in modern amps, particularly as an option to enhance clipping in a number of Friedman amps.

It may be that a similar type of approach could be used with a hard clipping mechanism to produce fuzz. This would require some trial and error in order to figure things out, but may be fairly difficult for somebody with little experience experimenting with tube circuits.

A simple ide is to add clipping diodes between the drive stage and the phase inverter. Maybe on a rotary switch with a few different configurations, like led, assymetric diodes, symmetric diodes. Like on an EQD life pedal, or a Rat.

What needs to be figured out then is what kind of diodes to use, to get the right amount of clipping. Im guessing the voltages are different than in a 9 V guitar pedal so I need to find diodes with the correct forward voltage.

[JMPGuitars]

18W amps (that this site is primary focused on) also use EL84 tubes. That's not an issue.

You started by saying you didn't know which circuit to build, and now it sounds like you're set on something, but haven't stated that clearly. If you have a specific circuit in mind, share it here if you want feedback on it.

[Crowbar]

18W amps (that this site is primary focused on) also use EL84 tubes. That's not an issue.

You started by saying you didn't know which circuit to build, and now it sounds like you're set on something, but haven't stated that clearly. If you have a specific circuit in mind, share it here if you want feedback on it.

Ah, yes, sorry for the confusion. I think I will go for the Orange Tiny Terror circuit. 2x12AX7 plus 2xEL84. Its a very simple circuit with few components, and I like the Orange sound in general so I thought it could be a good start.

I have limited knowledge but I believe its,a quite normal 18 w design, one 12AX7 as drive stage and one as a long tail phase inverter. The EL84 part looks almost identical to the typical Marshall 18 w power amp.

[JMPGuitars]

That's fine if that's what you want. However, a better choice would be the 18W Superlite TMB or 18W Lite 2b(ish) (build docs for both in the Downloads section).

Both use 2 EL84s and 2 12AX7s, and both sound better than the TinyTerror. Don't get me wrong, I like Orange, but the TinyTerror is maybe the worst thing I've ever heard with the Orange logo on it. YMMV.

Thanks,
Josh

[Crowbar]

That's fine if that's what you want. However, a better choice would be the 18W Superlite TMB or 18W Lite 2b(ish) (build docs for both in the Downloads section).

Both use 2 EL84s and 2 12AX7s, and both sound better than the TinyTerror. Don't get me wrong, I like Orange, but the TinyTerror is maybe the worst thing I've ever heard with the Orange logo on it. YMMV.

Thanks,
Josh

Thanks, this is good information. I looked at the Superlite schematic, to my untrained eye it looks quite similar to the Tiny Terror. The first gain stage looks almost identical, also the phase inverter and power amp are seemingly the same design, with some variation in component values. I understand this is a simplified view and the devil is in the details.

A few differences i did notice:
- the TT has a double gain pot, one part between gain stages like the Superlite but also a second, after the second gain stage. I have no idea why or what it achieves
- the TT has its master volume after the phase inverter, I guess this is actually useful for driving the phase inverter to clipping?
- obviously the TT lacks the 3 band EQ, just a very basic tone control. It is also located after PI, I wonder if that has any significance.

I'm sure I have misunderstood at least half of this, but its interesting to discuss and learn

[Bieworm]

In my world fuzz is very different from overdrive. If you want tube saturation it’s called overdrive. I think , by the sound you describe, you’d be happier with transistors in the preamp. Go germanium for more mellow organic distortion, or silicon for more agressive buzz. Normally you do this with pedals, but what’s keeping you from integrating this into the circuit?

[Crowbar]

A bit of a follow up, I have now built the Tiny Terror amp, and its working very well except for the tone control that seems to be doing nothing.

I made a few small changes from the original schematic, the anode resistor on the first 12AX7 stage is 120k instead of 100k, for some more gain, and a few capacitors are larger for some more low end.

And it actually sounds really good, at lower gain it has like a British overdrive sound but gain past 75% it turns to a very nice fuzz. It sounds very similar to my Frost Giant Architect of Reality pedal, but a bit rounder and fuller. A very good doom sound. And this amp is insanely loud for being just 15 watt, I use it with a 412 cab with Jensen Electric Lightning speakers and Im sure I can use it for band practice with real drums.

[Iain T]

That's really neat!

One benefit if using tagboard is radial caps become much easier to use - costs are a bit lower and more choices on form factor.