Mesa Boogie Maverick mods?

[steeve_a]

I've been drooling over these amps since they first came out but now that I've had one since September I feel the urge to take soldering iron and dremel tool to the circuit board... Is there a 12 step program I should enroll in?

The Clean channel is great- I would just like it to be more like the blackface circuit that it resembles. One quick fix- replace the .001uF Fat cap across the treble cap with a 500pF mica cap.

The Lead channel has that creamy sound that will sustain for days- some people have compared it to a Dumble. I love that about it. But as you back off the gain the signal doesn't clean up like on a D'clone. With a .001uF cap to ground on the input signal you have already thrown away the sparkle in your guitar. So I would probably remove that altogether, replace the 500pF cap in the first (virtual) tone stack with a 330pF cap and maybe increase the 56k slope resistor. The second (real) tone stack has what appears to be a 47k slope resistor on the schematic. It might not be a bad idea to use a trim pot to fine tune the resistance of both slope resistors.

When I was looking at the schematic I was thinking "3 gain stages, hmmm... I bet a Trainwreck Express preamp circuit would work great in there!" You actually would not have to change too many parts to turn it into an Express. But having a second tone stack after the 3rd gain stage would cut the signal level down by maybe 10dB to 20dB- would that signal be sufficient to drive the PI? I guess you could bypass the tone stack with a Preamp Boost switch as on an ODS if you needed more signal... The gain in the Maverick Lead channel looks like it would be close to the Express until we hit the 3rd stage where the un-bypassed 10k cathode resistor would result in much less gain than from the Maverick with the 1k5 cathode that is bypassed with a 1uF cap. But then again the OD channel is pretty damn loud to begin with- I really wouldn't mind if I lost a few horsepower...

Question for the day: it is "common knowledge" that a Fender tone stack will cause a 20dB drop in signal level. If that is true, I wonder what settings of the controls that they were using? Probably everything at 12:00 noon since it was engineers doing the measuring. You can hear an increase in volume when you turn up the bass and mid controls. And with a Marshall tone stack using a 500pF treble cap and a 33k slope resistor I think that the insertion loss would be much less than the nominal 20dB we hear all of the time. Any thoughts on this?

Thanks!

Steve Ahola

P.S. I just noticed the 22k resistor in series with a .001uF cap going to ground right at the output from the treble control... Geez Louise- I think we found where the rest of the high frequencies went! (BTW I have always been a Fender guy who was never that crazy about Marshall and the Lead channel is voiced like a Marshall. )

[selloutrr]

Make sure the schematic version matches your PCB's. several versions of schematics and production models, they don't all match up.

I'm not a fan of mods for the mesa amps. They have enough of a following that modifications, other then factory authorised, destroy the value.

The truth is mesa amps do "the mesa swooped mids sound with mid gain crunch/ compression" but it's only that, the rest of the features are fluffy to help sell the amp. They are a bitch to work on, requiring total board removal in most cases to do it properly. The best thing you can do is add an adjustable fixed bias and pick your own tube compliment to voice the amp. If you don't love it for what it is, give it a new home.

Mesa amps are some of the hardest amps I've ever come across to dial in. they have a very small window of "sweet spot" on most models. if you can dial it in they are great if not they are frustrating. I've had best results with humbucker pickups and heavy weight guitars running a compressor foot pedal on the front end.

[steeve_a]

Make sure the schematic version matches your PCB's. several versions of schematics and production models, they don't all match up...

Thanks for the suggestions! I was going to take the schematic I have*** with a grain of salt and trace the circuits from the tube pins, correcting my schematic as I go.

To simplify my game plan I'd probably start by removing the 0.001uF caps to ground on the input and output of the Lead channel. Is that a 62k resistor on the tail of the first tone stack (the virtual one with fixed resistors)? I think that reducing that to maybe 25k would give that channel more clarity (soldering a 39k resistor across the 62k mid resistor would bring the value down to ~24k). It seems to me that with a 62k mid resistor why even bother with the virtual tone stack since you are practically bypassing it with the "beer belly boost" of the early Boogie amps...

For the Clean channel quick'n'dirty fixes could be removing the 500pF cap to ground on the input and reduce the resistance from the input jack to the first stage grid to something like 33k-68k (it looks like there is a 1M series resistor bypassed with a 1?0pF cap). If 33k series and 1M to ground on the input was good enough for Leo then it's good enough for me. I think that Mesa had to put all of the crap on the input because of the pedals that someone might use ahead of the amp. Soldering a 330k across the 150k(?) slope resistor would bring it down to 103k; a 220k resistor would bring it down to 89k, a 180k resistor would bring it down to 82k and (of course) a 150k resistor would bring it down to 75k. (I didn't need to use a calculator to figure out the last one!)

Removing the 250pF to ground on the wiper of the Clean gain control and the .005uF cap -> 330k resistor from the grid to the cathode of V4b would pretty return the design to Blackface territory.

"So why not just buy an amp that you like???" If they made one and I could afford it I would...

Steve Ahola

*** The one that reads "There's nothing missing here all these parts go to sig[nal ground]" on the Preamp Part 1 page.

Disclaimer: I have not looked inside the chassis to see if any of this is feasible. When I looked inside my V-Twin to change just one resistor I closed it back up, shaking my head...

[steeve_a]

I sketched out the Rhythm channel and plotted out which components (mainly caps) I want to remove from the circuit. Most of them go to ground and I think it should be easier and safer to desolder that end (less chance of screwing up another connection and those parts are certainly crammed in there.) And I scoped out the Lead channel and there are 2 caps I want to remove plus the mid resistor on the first (virtual) tone stack. It is 62k and I want to cut that back to maybe 18k. I haven't found it on the board yet but it would be cool to mount a trimmer pot across it so I could dial in the gain and distortion I want.

As I was looking at the Rhythm channel I was thinking "3 stages... I could turn that sucker into an Express!" I think it would work better than trying to "wreck" the Lead channel, which has the "real" tone stack after the 3rd stage. (If the pcb wasn't so damn crowded I probably could reconfigure it as an Express or Rocket.) But I would hate to give up the blackface Fender sound. Who knows- I might go for it after all!

Steve

[steeve_a]

While looking at schematics I noticed that the Maverick Clean channel preamp (Rhythm in Mesa terminology) is practically identical to that of the Subway Blues, which in turn is like the clean channel of the Subway Rocket. Not a terrible clean channel but certainly nothing to write home about!

I had also looked at the 2003 Lone Star schematic and noticed that the Clean channel was very similar to an AB763 Super Reverb. Hot damn that is what I want! I was kinda bummed out because I just bought the Maverick head in September and was wondering if I should have passed on that and waited for a LSS head at a good price. Looking into it further, although most people love the BF sound of the LSS Clean channel, there are not a lot of big fans of the LSS Lead channel. While the Mav lead channel is regarded very highly as a poor man's Dumble.

So why not just rewire the Mav clean channel as a blackface, and have the best of both worlds- the Lone Star Clean and the Maverick Lead channels?

The first step was creating a layout of V1 and V4, showing the location of each component in the Maverick clean channel. And then I figured out how to transform the Mav circuit in an AB763 SR. One problem kept coming up- the Mav clean channel has 3 gain stages while the Super Reverb only had two. I would have to attenuate the signal so it wouldn't overpower the Lead channel. And then it occurred to me to wire it up as the Vibrato channel of the Super Reverb, with the 2M2/12pF reverb splitter between the 2nd and 3rd gain stages. Even though there was no reverb circuitry connected to the two ends of the splitter. And that game plan worked really well- I am very happy with the amp knowing that what I have is better than the stock Mav or the stock Lone Star Special. I can live without the Solo circuitry and the option to drop the power to 15W or 5W. (If I really wanted to I could interrupt the signal going to the grid of one pair of EL84's for a 15W mode.)

For the Mav Lead channel I removed the .001uF cap to ground right at the input which really opened up the sound for me, making it much more responsive. And I can always turn down the guitar tone control to get the effect of the .001uF cap. And I removed the 120pF caps across the PI plate resistors to get back some of the high frequencies at that end of the amp. (There is still a 250pF snubber cap between the two PI plates to help with possible oscillations and squeals although I think I could cut that down to 120pF or 150pF.)

I figured out how Mesa came up with the unusual circuitry at the input of the Maverick clean channel: instead of a typical series resistor of 33k or 68k there was a whopping 1M5 resistor bypassed with a 180pF cap. The Subway Rocket has that on the input to isolate the signal coming and going from the added gain stage for the Lead channel (not unlike the reverb splitter on the Fender reverb amps). So Mesa included that signal-robbing circuit in the Subway Blues and Maverick as well to offer a consistent clean channel in all three amps. IMO they intentionally crippled the clean channels of the Subway Blues and Maverick to sound no better than the Subway Rocket (which would cut into its sales if people could hear how crappy it was). Fender could get away with their 3M3/12pF reverb splitter because the signal had already been amplified by 2 gain stages. To put a 1M5/150pF splitter at the input is really going to suck tone from passive pickups. (The input circuit also has the 1M grid load bypassed with a 500pF cap- 250pF for the Subway Blues for further loss of high frequencies.)

In any case although some of the circuitry in the Maverick leaves much to be desired, I have no complaints about the construction of the amp- it is built like a Mack Truck!

I will draw up some pictures showing the location of the components to change out for this mod.

Steve Ahola

P.S. I got the Maverick head for $600. The Lone Star Special head sells for around $1700 new and maybe $1300 used, and I think what I have now is better than that.

[steeve_a]

I have been pleased as punch with the blackfaced Rhythm/Clean channel but now I am getting bored with the Lead channel, which sounds great but is pretty much a one trick pony, er, maverick. I like overdrive channels that clean up when you back off the volume on your guitar or the gain on your amp (preferably both).

I kept looking at the Lead channel schematic hoping for some inspiration but was coming up with nothing since I have never seen a circuit like that. And then I thought "3 gain stages- I could rewire the lead channel as an SLO!"

I figured out an easy way to remove the fixed tone stack after the first stage- desolder the 56k slope resistor and the 100k resistor going to the "bass control" from the "treble control". Very easy to do- and very easy to undo if I don't like the results.

I downloaded some pix of the loaded Maverick pcb from the Boogie Board and will be adding reference numbers to all of the resistors and capacitors in the tube sections of the audio signal path, as a road map so to speak for anyone else who wants to fine-tune or completely rewire the circuit.

Steve Ahola