dude

Thanks guys. I can understand not being into the plain top. I originally intended to do an amber stain, but I fell in love with the plain maple once I got the finish off, and decided to leave it. It helps that I'm a bit of a Tom Scholz fan. If I do another, though, it will be an oceanburst top with cream plastics and zebra pickups. I saw a video of a guy doing a burst by hand on a huge chunk of figured maple and now I really want to try it. Maybe I'll buy some scrap maple and give it a go. Got plenty of tru-oil left...

So last year, Gibson introduced the LPJ Model Les Paul. This is their new entry-level Les Paul - one step below an LP Studio. Construction-wise, they are essentially the same as a studio save that the necks are maple, and the finishes are a cheaper satin nitro. In other words, Gibson sells a legitimate, well-playing Les Paul for a little more than half a grand. Not bad. I've wanted a proper Gibson Les Paul since before I could even play guitar, so this new model caught my eye very quickly. ...except that they're horribly ugly. Well, not ugly, per se; just not to my taste. The overall styling definitely targets the sort of "indie rocker" niche, as evidenced by their promo photos, and honestly, in that context, they look pretty great. But I didn't want a modern, indie Les Paul; I wanted a classic rocker. So I did what any self-respecting gearhead would do - I refinished an LPJ to look how I wanted. I found a seller on eBay who regularly has gibson husks (neck and body - no hardware) for pretty reasonable prices, and bought myself a red LPJ. Here she is on my kitchen table workbench: In person, the finish isn't actually that bad, though for some strange reason it does smell like a cherry popsicle. Here's the back: At this point I'm already drooling over the grain on the mahogany back. Its three pieces, and that top piece (the one with the switch cavity in it) is just gorgeous. Can't say much about the maple cap, yet. The finish is just too obtrusive. ...enter the acetone. After two hours and at least as many rolls of paper towels, I am left with this: ...which is great, because I really always wanted a pink Les Paul. (not really ... though now I kind of want to try a pink burst) At this point I went and bought myself a palm sander and went to town with ... 200 grit I think? Might have been 250. It's been a while. And then finally: Look at that plain maple top. Just look at it. I think I'm in love, and I haven't even started tru-oiling it yet. Tru-oil was, in fact, the next step. I had a couple of false starts before I figured out how thick to apply the stuff, but as I got going, she started looking like this: Here she is drying with some friends: When I finally got enough coats on and waited long enough for it to cure, I hit it with micromesh to give it a nice gloss. It ain't nitro, but it looks pretty good. Finally, I slapped some hardware on there -plastics and a bridge from GFS, a tailpiece from Stewmac, and tuners from Rondo. I had to learn how to notch a TOM bridge, which turned out to be easier than I expected - just a lot of careful measuring and re-measuring. And finally: That's an EMG 81 ( and 85 (n) that I pulled out of my old Schecter, whose frets are so bad it is unplayable. Here's another shot, hanging with some friends again: Conclusion: It would be pretty cool if Gibson sold the LPJ with a plain clear finish on it, but until then, DIY is more fun anyway.

Awesome, that's more-or-less what I was thinking (minus the grid stoppers, so thanks for that). Alright, I should be able to order some parts today. Hopefully I can get started soldering this thing up later this week. Thanks for all your help.

How important is the value of the grid resistors on the EL34s? Since I'm cathode-biasing my power tubes, I'm thinking I can probably just replace the 220k grid resistors that normally go between the grid and the negative bias voltage supply with a dual-gang 220k (or higher) pot for my PPIMV. Is that okay or is the grid current pretty big on these beam power pentodes? Also, for my 6au6 preamp stage: I'm thinking I'll run the first of the two bootstrapped as a triode, and then run the second with a high plate voltage in pentode mode (mostly because this is what's provided on the datasheet). My theory is that I'll get a bunch of gain from the first stage that will distort on the relatively low-gain second stage and give me some nice, tasty pentode distortion. That might be totally wrong though. EDIT: Actually its probably safe to run them both as pentodes. Datasheet shows the transconductance getting higher with lower grid#2 voltages (more "pentode-ey" operation). Granted I'll have a lower plate resistor, which will reduce the gain and max voltage swing somewhat, but I ought to be fine, I think.

Very cool. I'm not going to use any active filter controls (just the variable negative feedback knob), so that's okay with me. Though if I have room when I'm punching holes tomorrow, I'll just put in a PPIMV and a regular MV.

Nearly! Need to calculate my bias resistors for the two 6au6 stages and then order my components. I think I'll punch some holes in my chassis this weekend though. EDIT: I was toying with the idea of putting my master volume AFTER the phase splitter (use a dual gang pot), but I'm not sure how well that would work with negative feedback. I guess if the feedback isn't as intense as it would be for an op-amp, then adjusting the open-loop gain should still affect the closed-loop gain reasonably well. Does that sound reasonable?

Man I'm off today. You're right. It would just mess up the biasing on the phase inverter (when you turn the MV all the way down).

Oh oh oh. Right. My mistake. Good catch. That would have been an unpleasant mistake. Popping fuses left and right.

The tone stack preceding the master volume (right before "A") should block DC from the stage before (its the same circuit as the big array on the left). The 10k grid resistor was there based on sims I ran without the grounding cap. In fact, all of the weird mods I made to the phase splitter were essentially because I forgot to add that cap. So, yeah, I'll just use a traditional LTP and be done with it. I'm already doing enough weird things with this amp as it is.

Aha! I was missing the cap to keep the grid of the second triode at AC ground. That's pretty important. Thanks for running that. I think I'll go with the standard, and upon further consideration I AM going to add negative feedback. I may make it variable with a pot, though. I've got a switch on my old project amp, and the ability to change the amount of feedback gives you tons of variability in tone.

I'm not sure which resistor you are referring to here. I started with the more traditional circuit with a 1M on each grid and a 100k/78k on the respective plates, but I ran into a few problems as I tweaked it. The first was a high frequency roll-off (bad on the positive triode, REALLY bad on the negative triode). The second was a pretty unequal output amplitude (I think I was seeing more like a 3dB difference - about double the amplitude). I know the circuit I started with is pretty tried-and-true (especially since you knew the dB difference off the top of your head), so there was probably something flawed with my simulation (might have been the transience in the capacitors. I only simulated the first 20ms most of the time), but I'm intrigued enough by this setup that I think I'm going to try it. If it is horrible, I'll just copy the standard Fender/Marshall/every-tube-amp-made-in-the-60s power amp and be done with it. In the sims I ran, this LTP circuit has a gain of only about 2-3 (which is fine), but it is pretty closely matched accross the full audio spectrum. It also can provide a pretty huge voltage swing on the output (~60v pk-pk each), so I should have a decent bit of headroom, I think, though I don't have a lot of frame of reference here. I assume this is because at 100k they are horribly matched with the output resistance of the EQ in front of them, and I will suffer a huge gain loss as a result? Yes, I will increase them. Is there any reason not to make the jump all the way up to 1M? Then I could use only one value of pot across the board.

Alright, I've knocked together a more final schematic here. Looks like I forgot to calculate the bias resistances and such. Well, that can be taken care of later: I did a factor-of-ten modification to the RC values in the EQ, and it made a huge difference. The boost and EQ now have a very good response, and the controls seem to behave as they should. I get a (normalized) +5dB at max, -5dB at min, and 0dB at center (log). We'll see how it acts in practice. The long-tail phase splitter took me a lot of fiddling and simulation, but it seems fairly good now. The signals are very close to balanced, and I should be able to have a lot of clean headroom if I want it. I'm using EL34s for the power tubes, and I am cathode biasing. I may add a switch to change bias resistors so I can swap for 6L6 conveniently later. No negative feedback for now. On my other project amp I have a switch to turn feedback on and off, and I really like the sound without, so I'm going to start there and add it in if I decide I need it. Overdrive will work better with feedback. I picked the values for the bias and grid #2 resistors based on an EL34 datasheet. I'm going to look a bit more into this, though, because I'm not convinced these are correct. And because I want to understand everything. (time to read the power amp section of the Audio Cyclopedia again ) I dropped a gain stage, as the music I've been playing lately has been more in the "crunch" range and less in the "lead" range of overdrive. Lastly, I'm moving the first EQ to before the preamp volume (like on a fender or mesa) and putting the main gain stages (2 pentodes) after. This will put the two EQs firmly before and after the gain section. I don't THINK there will be any problems putting the preamp gain immediately following the EQ with no buffer, but I could be wrong. Any thoughts on the design are, as always, deeply appreciated. I'm about ready to order my components (the only thing I haven't got yet) and get building! EDIT: I forgot to draw in a 1M series resistor before each band's 1M pot on the EQ. There should be one on each band.

Throw in an adjustment on the negative feedback and you've got yourself a pretty cool amp. Might have to try that next. Something lower-wattage this time. I've got some power dual triodes sitting around that I REALLY want to use in a push-pull power section.

Okay, well I'll need to mess around with some values and see if I can get something that works well. Though honestly what I have now looks alright. I'd rather have a flatter response though. Ansil, I like that circuit a lot. When I was reading up on vactrols I started thinking of ways to use them to shape the amp strictly from electrical control. I had a dream once of building a modeling amp that simply rearranged the circuit inside to model different famous amps. Hook a microcontroller up to a bunch of conveniently-placed vactrols, and get instant switching from Fender cleans to Marshall Crunch to Vox Bark. Of course you might need a motorized door on the back of your cabinet too EDIT: and yes, I'm using the built-in 12ax7 model, however good that may be. I used to have a link to a page that had SPICE models for a LOT of tubes (even the obscure TV scanner pentodes and such I've got lying around). I'll have to see if I can find it.

Yes, the "10" is 10%. The Pots are 100k. If I increase the R values of my filters I'll probably have to go with 1M pots instead. I can also reduce the output impedance by splitting the 150k cathode resistor into something large on top and something small on bottom, and then bypassing the larger, upper resistor with a good-sized capacitor. Trouble there is that if I do a 150k resistor on top and a 1k resistor on bottom, I need about 4u for the bypass, which is a little silly. But, I just ran a simulation and it works alright. I'll try increasing the filter R values tonight. I expect that will have better results. Plus, using smaller C values will make getting the right parts a bit more convenient. I'd probably be able to use ceramic caps all around. The reason I didn't try that before is because I have a bunch of 100k log pots sitting around, but oh well, I can order some 1M.