My Latest Build

[JazzGuitarGimp]

It's been a few years coming, but I have finally started my next build. This started as a Weber Deluxe Reverb x2 kit. Four 6V6GTs, and 5AR4. But I've taken it in a whole new direction. There will be three 12AX7's dedicated to the preamp: The clean preamp is based on the 6G12-A, and the OD preamp is based on the #102 RF pre. An active effects loop is also planned, though, at the moment, the first phase will be to build the power amp, and the clean preamp. Phase II adds the loop, and Phase III adds the OD pre.

Before I move on to Phase II, I plan on trying it with a pair of 5881's - I've got some NOS Sylvania's on hand.

I am suddenly reminded of how much I dislike wiring the filament string! And the "slant face" chassis is a bit of a bummer too....

Some pics:

[JazzGuitarGimp]

Here are a few more pics:

[JazzGuitarGimp]

I'll get a schematic posted in the next few days, while waiting on parts.

[JazzGuitarGimp]

And here is the schematic:

Edit: hey guys, I forgot to mention when I posted the schematic, that this is my initial draft of the circuit, and so is unproven. As I work through the build and tweak process, I will keep the schematic updated with any changes.

8-22-15: Added switch logic for A/B & Y switching. Still needs DC to DC converter to up the 3.2V supply to 12V.

2-14-16: Added R132. Replaced 5AR4 with 1N4007 x 4.

[Smokebreak]

Looks like fun ! I recently used that same shiny chassis. I'm sure I don't have to tell you to watch out for that sketchy IEC they send. Their BOM suggests "USE GLUE"

[jcsifu]

I like that there are 2 independent channels, the ODS has that flaw (a flaw in my opinion anyway). I frequently have issues dialing in the tones that I like and also facilitate not having a big volume jump when switching channels. I have wanted to do something like this for a few years now. Thanks for the schem.

[jcsifu]

BTW, are you setting this up for strats?

[JazzGuitarGimp]

Smoke, use glue from plastic to steel - now that's funny. Actually, the IEC inlet connector is so snug on mine that I had a heck if a time removing it when it came time to wire the tube socket under it. The convenience outlet, on rhe other hand, has so much slop that when it's centered in the hole, there's a full 3/32" gap on both sides! Can you say "I think the paper clip slides in right her.....ZAP!"? but not to worry, with the terminal strips I added along the back wall of the chassis, there's no way the outlet is going into the amp anyway. The gaping hole will be tended to when it's time to have faceplates made.

Jcsifu, i have a friend who has a two rock modified black face bandmaster head. It has been dumblized, and I agree - it's a total compromise between getting a great clean tone, and a great OD tone. Keep n mind, and I should have made this clear when I posted the schematic, that this is an unproven design at this point. But as I massage the amp into maturity, I will update the schematic. And yes, it will be strat-tuned as I am a strat player through and through.

I forgot to mention I have a fourth build phase in mind: Phase IV will occur after both channels are working to my satisfaction, and it is a four channel MOSFET source-follower circuit on a +/-70V supply that will be DC coupled to the output grids - each channel having a bias trim pot. I'm going to see how much power I can squeeze out if four 6V6GT's (and / or two 5881's) in class AB2 mode! I am going to lay out a pcb for this add-on circuit. If there is any interest in this, perhaps I will make the board available for sale, with a complete documentation package.

Cheers,
Lou

[10thTx]

Lou,

"da Geezer" did essentially the same thing with a Twin Reverb where he had a traditional Fender "clean" & then a Dumble OD. (meaning Dumble clean into Dumble OD as you are doing).

he used an A/B box for switching channels.

The sound clips he sent me sounded just incredible! Beautiful tone with both a true clean and a true D-style OD.

He used 3 gain stages for his Fender true clean tone similar to the vibrato channel on an AB763.

IF you PM'd him, perhaps he would share his schematic with you? He is using a d'lator with his.

With respect, 10thtx

[cbass]

Dang Lou thats quite a project . I'm impressed

[JazzGuitarGimp]

Thanks, 10th. I want to make it work with two gain stages because, if you notice, i have two footswitch inputs: one to engage the clean pre, and the other to rngage the OD pre, which gives me the ability to do A/B/Y channel switching, so I need to keep the two channels in-phase.

Cbass, thanks, it kind of feels impressive when working the cramped confines of that chassis!

[Smokebreak]

Looking forward to seeing how the MOSFET follower works out. I'm doing a 12ax7 CF now, between PI and outputs, so it'd be nice to eventually A/B them in that spot.

[JazzGuitarGimp]

Hi Smoke,

This design has been through so many revisions in the last few years - I was trying to figure out just what it wanted to be when it grows up The previous iteration employed a 12AU7 DC-coupled driver, but I nixed that idea because of the four output tubes. Each half of the AU7 would have to push two output grids. I just figured I wouldn't get very far with that implementation, so I opted for four IRF820's instead.

You might want to keep the 12AU7 in mind as an alternate for your design, as it can deliver more current than the AX7, and since the CF is going to be at unity gain anyway, you don't need the extra gain of the AX7.

Cheers,
Lou

[JazzGuitarGimp]

I'm getting restless waiting for parts. I added a new page to the schematic that replaces the footswitching arrangement: It used to be one footswitch engages the Clean Channel, and the other footswitch engages the OD channel. Now, the left footswitch will switch between Clean and OD (with a green LED for Clean and a red LED for OD), and the right footswitch engages Y-Mode (with a blue LED), regardless of the status of the Clean / OD switch. Whichever Clean/OD LED was lit before entering Y-Mode stays lit, so you know if you're coming back to Clean or OD when leaving Y-Mode. And while it Y-Mode, you can change the Clean/OD status without affecting Y-Mode.

I still need to a DC to DC switching boost supply to get 12V from my 3.2V supply.

[10thTx]

Here is a sound clip of DaGeezer's amp demonstrating the clean (with 3 gain stages) vs. the D-style OD.

Don't know it for a fact, but I am wondering if the 3 gain stage clean does a better job of allowing comparable volumes between the clean and OD? Just a thought?

https://soundcloud.com/dageezer/twin-ultraphonix-test-1

Sounds amazingly good to me! Plus I am a huge fan of his playing!

With respect, 10thtx