dude

The best guitar tone always comes from running parts out-of-spec

Yeah I'd agree, though a Twin Reverb has a gorgeous sound.

Fair enough. I think its a square formula actually, so it'd be more like 40% of the volume but that's about 50% anyway.

Right on. I'm still curious to try a 12" + 10" pairing or even a 15" and 8" pairing like a bass. You know - plenty of bass but with a crisp definition too. I bet it would be interesting if nothing else. Regardless of speakers I have an amp to build. Hopefully my parts will arrive soon. I am debating buying new iron so I can do this build completely from scratch (you know, for that sense of accomplishment). I'm sorely tempted to build an el84-powered amp because my current 50W head is simply too much for my apartment at the moment (and when I play out I'm on keys these days), and this one would be the same way. We shall see.

I've found that my ears generally appreciate the later-60s to 70s tone more than the 50s and early 60s stuff. I'm not a fan of speaker distortion as it turns out, or just pure fuzz pedals. I much prefer tube distortion. As an example I love Hendrix's typical rhythm tone, but his fuzzed-out solos (a la Purple Haze) sound kind of unpleasant to me. Tone wise. Not playing wise. Well, I've dialed back my revolutionize-everything idea and settled in on a design that I think will have a nice tone, with a smooth distortion at higher levels. I'll post the schematic when I get it.

That's been my thinking lately, actually. So much of what is considered "desirable" in terms of tone is simply the result of cheap design. Been wondering lately if a bit more modern approach could be made to create "good" sounding guitar, albeit different.

Aren't the studio monitors usually beveled though?

Another acoustics question: I've always heard that for HiFi speakers, rectangular cabs are bad, because you get standing waves inside, and hence a very nonlinear frequency response and weird harmonics. And yet virtually all guitar cabs with a closed back are big, 90-degree boxes. Bass cabs tend to be ported and such, but guitars pretty much have stayed the same since the 60s. Is this simply tradition, or is there a different reason for this? I'm considering having a pair of cabs built for 1x12+1x10 speakers with more conical shapes, no parallel walls, and possibly a small port on the 12-incher, just to see what happens. I'd do it myself but I have no woodshop. Thank god for craigslist.

Yeah, speakers are a whole new can of worms aren't they. Well, my current design strives to be as crystal clean as possible, but still open (minimal negative feedback), so an open back is probably a good way to go. On the other hand, a circuit with no negative feedback will be "tamed" somewhat by a closed cabinet ... so there's that option too. Perhaps I should throw some webers into my current 412 and perhaps get a 212 at some point to run open-backed. Or just take the back off my cabinet sometimes. I do plan to build a JMP clone at some point as well, so there's that to consider as well. One thing I always wondered is what would happen if you connected two speakers in a closed cabinet in reverse polarity. Do they resonate with each other then (since two would be pushing while the other two are pulling)? I'm guessing this would be dangerous, as it would essentially be abusing the cones of the speakers with twice the power it would on an open back. Could be louder - could oscillate and break your cones. I'm sure somebody has tried this (on purpose or otherwise.

I have an opinion question for y'all: Currently I'm playing my amps through the 4x12 from a "Crate Flexwave" solid state stack. As far as I'm aware it is the cheapest 100W+ halfstack on the market, and I don't think the speakers are very good (though I've not compared them directly to any others). Would it be worth my while to invest in new speakers/a new cab so I can properly test this (and future) projects? Okay, well I already know the answer, and its probably "yes". My follow-up question is which speakers to get. This is, of course, subjective, but I had a thought: My cab allows stereo play, so I could get two sets of different speakers with drastically different sounds so I can do a wider array of testing. I was considering a pair of greenbacks and a pair of vintage 30s (I haven't looked at non-celestions yet, but I will). Any thoughts on this?

Good information, Ansil, thanks. I'm particularly excited that the pentode has more headroom. In that case I have a new circuit design. Once I get it mocked up I'll post it. Planning on doing 2 channels as before, with a triode in front cascaded into a pentode for each channel. The pentodes will be direct coupled through a resistor network to a triode cathode follower driving the Baxandall. Then I'll have a single triode (the other half of the follower) acting as the phase splitter. I may or may not use negative feedback. I had a switch to turn it off on my old project and I loved the openness of the sound without it. We shall see. I was concerned before that the single tube splitter might have less headroom or something, but I guess it always sounded okay on my old project. I ordered parts last night. Lots of them. So I can change my mind on the design quite a bit until they get here without any problems

Question for you two (or anyone else with experience): what, sonically, are the differences between doing a long-tail phase inverter (as is seen on most big amps with two triodes) and a simple phase splitter (configuring a single triode with balanced anode and cathode resistors and taking the signal across each)? I'm playing around with some configurations, and one of the ones I'm rather fond of lands me with an extra half of a dual triode. Also has anyone ever tried using a 6n2p instead of a 12ax7 for your typical high-mu dual triode purposes? I've heard they're voiced in more of a hi-fi fashion (less mids), and break up a little less smoothly, but are much clearer than a 12ax7. Since this amp is (save for the pentode) intended to be mostly clean, I'm considering trying them out (I'll probably put jumpers on my pcb for easy swapping from 6n2p to 12a_7). Also they're pretty much free.

Driving the tone filter with a follower is probably a good idea. Even passive filters start to get weird with high-amplitude signals, and reducing loading is always a good thing. The 6au6 will probably get enough "juice" after the follower to sound nice and distorted still. And hell, I'm simulating this all so I can even check on that. Ansil, I actually decided to go with a baxandall after you suggested it a while ago. I looked into them and they seem like a very good choice. I think I'm going to keep things simple for this build (I've been on a pretty big strip-down-and-simplify kick lately. You should see my project guitar), but I am interested in seeing the diagram of the tone stack you've just described. Sounds cool.

Ask and ye shall recieve: the 6L6s aren't pictured, but they'd go right after the phase inverter. For now I just have resistive loads on each of the triodes there to show their output signals in simulation. Also missing is the second channel, but that will be mixed in at the volume control, so the gain will actually be reduced somewhat from what I've simulated, which is fine. I have my pots represented as resistor pairs at the moment as well.

Quick update: Circuit design is complete. It will be 2 channel (because I've got an extra half of a 12ax7 sitting there, and I've always liked the whole "jump-the-channels" thing on the old Marshalls), with one tone stack (Baxandall) and one volume per channel. Tubes include 2 12ax7s, 1 6au6, and 2 6L6s. Ordering parts tomorrow. Hopefully she'll be operational in a couple of weeks. ...I'll take pictures

That is a BEAST of an amp. I remember you talking about the compressor idea on my last amp thread (when I REALLY had no idea what I was doing). It sounds like a pretty nifty idea. I don't think I'll use it on this first amp, but I may have to look into it in the future. I've got a bunch of triode-pentodes in noval packages lying around from old TVs. I guess they're intended to drive the electron beam in a CRT, but hey, they'll probably be just fine for audio. I think I'll use one of them. I'm thinking I'll drive the tone stack as is typical with a dual triode (one stage direct coupled at the plate to the driver stage, which is used as a cathode follower to drive the tone stack). the triode will drive the tone stack, and the pentode will drive the triode. I think I'll put one 12ax7 stage in front of that (possibly in a two-channel arrangement), and then follow the tone stack with a phase splitter and a power amp. For the power amp this time I think I'll use a pair of 6L6GC tubes, though sometime soon I want to try this one tube I recently found (6080) which is a dual power triode. Each triode is good for something like 12W, so you could pretty reasonably build a 15-20W push-pull amp with a single power tube. Pretty neat.

That's a pretty cool idea. I was toying with a similar idea a few months back, though I was thinking I'd use an el84 (or a slow-cutoff pentode from a tv, since they're REALLY nonlinear) instead for the smaller form factor and (I think, though I don't know off the top of my head) the lower ideal quiescent current. Might be fun to try. Hell, I could even just put in a solid state power amp in that case, since the power tube distortion would already be there. That would save a bundle on transformers. The caps I am considering simply because I built a paper cap out of newspaper, mineral oil, aluminum foil, and wax a while back and was surprised to see that it actually worked. My buddy and I built the thing in a half of a paper towel roll, and it came out to about 0.8 uF. Considering most coupling caps in a guitar amp are usually going to be on the order of .02 uF, it got me thinking it might be fun, and not too hard, to build an amp using only diy caps for coupling. This would probably be better done after building it with factory-made caps, however, so you could do a proper comparison. Maybe I'll build a jtm45 clone sometime and make the caps for it.

Well its been two years since I started this thread. One electrical engineering degree and a fair bit of study and work with tubes, and I'm thinking its time to take another crack at this amp. For the record, you all were right last time - the problem was unbalanced power tubes. In this case, of course, "unbalanced" means "one is completely dead". This has been known to cause a less-than ideal sound. Now, when I say "another crack at this amp", what I really mean is I'm going to yank the PT and the OT and build from scratch. I'll also be designing from scratch, because I can do that now. Why make a SLO-clone when I can be original, right? It will be a bit before I start the physical work here because I'm going to simulate everything first, but I'll keep y'all posted in case there's some interest. Edit: Oh, also there will probably be custom paper caps involved, dependent on whether I can get the formula right. They're not hard to make, but I'm not completely certain I trust them to block 300vdc.

Hi All, I've posted a few times on here for help with amp conversions, but this time I'm just here to show off a completed project. For my embedded systems course this year, we had to design and build some kind of final project. Naturally, my partner and I chose to make a digital effects processor for guitar. You can see our demonstration here: This summer, I plan to expand upon this idea, using 16- or 24-bit sound instead of 8-bit, and using a more powerful processor chip. I'm also going to package it in a floor unit with a backlit LCD and some pushbuttons that will act as stomp switches. It should be cool.

I really like that Strat. Makes me want to play some Hendrix. Nice art.

I kind of like it without the controls. It gives it a kind of serene elegance.

I've been thinking about doing something similar with a KAOSS pad, though I haven't really researched it much. However, most devices that take a midi input will tell you what midi signals correspond to what functions on the device (so look in the manual to your Whammy). I'm fairly certain there are midi controller libraries for C which you could use to fairly easily program a small microcontroller to work with 2 buttons (or more) and send the MIDI signals you need through a midi port. The PIC microcontroller might be a good place to start. They're pretty cheap, and fairly widely used. I wouldn't buy one until you find out if there are MIDI libraries available.

The ones on stewmac are 1/2".

How would you recommend? I assume NOT by hooking up a current meter in series and looking for DC current.

Not really. I replaced the electrolytics with no result, but I should probably check the rest. Power tubes first though, I think. I swear I WILL find the time this week to try some of these things. Or if nothing else next week. School's been busy recently.