Mesa Mod

MESA BOOGIE 20/20 "DEEP MODIFICATION" I finally figured out how to do the "Deep" modification a lot of reviewers talk about. If you own this amp and its out of the warranty period, I HIGHLY recommend this modification. If you do it while the warranty is still active, you will void it. If you don't know already, the 20/20 has a "boost" above 200 Hz (high bass and above) that is double the low range of the amp. Sounds good and cuts, but not "ballsy" enough. Doing this modification will give more low end "oomph", add richness, and open the treble a bit more. I find it gives you a more "modern" mix of vintage EL84 chime and new metal sound. This amp is a little too washed in the mid frequencies as stock. Here's how you do it (if you aren't tech / electronically inclined, find somebody who is!! Amps store high voltages even when unplugged and if you poke or prod the wrong thing, you can be electrocuted) 1. Take off the cover 2. Locate the 12ax7 input tube closest to the input jacks, this will be the farthest tube to the left if standing behing the amp with the tubes pointing to you. 3. Look at the circut board the input tube is mounted on. Slightly below the tube on each side of it, you'll see a series of capacitors / resistors. These are miniature "sausage" looking things about a 1/4" long, running up and down. Some are tan/brown with stripes, some aren't. 4. You'll see one in each grouping per side that is different. They are a bit smaller than the rest, NO STRIPES, and are a yellowish/tan color, and have tapered ends. THESE ARE THE ONES YOU WANT TO REMOVE. 5. One is very easy since its by itself to the left of the input tube. The other one on the opposite side is in between the other "sausage" looking devices (resistors). 6. I removed them by heating the back side of the circut board where its soldered in. Using very long, thin needle nose pliers (or a long thin screw driver). I disconnect on side of the capacitor from the circut board. Gently pry out the connection while applying the heat to the connection. 7. Repeat on the other side. Be careful not to damage the resistors next to it. Enjoy the sound. If you don't like it, re-solder the connection. Thats why its good to only remove one end, its easier to re-connect. You'll notice the perceived volume drops a bit. Thats because your ears aren't getting "slammed" with all the previous midrange. I like that because now I can open up my amp and preamp a bit more and not blow out my ears. You will have to modify your current bass and treble/presence settings since you've changed the overall sound.

I recently modded mine. Very easy to do. First off, I recommend that the last time you power off your amp, don't hit standby first, just hit the main power. In fact, you should always do this. (When powering up, however, have standby enabled so that the filaments warm up first). Helps to drain the caps. Now then, remove the top cover with the 20 or so screws. Looking in from the top, you'll see two small rectangular circuit boards standing on end. You can actually follow the wires leading from the inputs to these boards. You see on each board a very small round yellowish capacitor, smaller than a dime. Only one each per board. All you need to do is carefully clip one of the leads. Move the clipped lead away from contact with anything, including the top once it's replaced. Do NOT clip any of the larger mylar(I think) orange caps !!!Frankly, you'd have to be retarded to confuse them, but I wanted to mention that anyway. Be careful to stay away from the power supply area, you don't want to touch any of the components there either, in case it's still holding a charge. That's really all there is to it. Snip, snip. I'd say it sounds more responsive than before. I haven't had a chance to really crank it up though to test the lower end or headroom claims. It's easy enough to reverse the mod, in any case. I'd use needle nose pliers to form tiny hooks on the snipped lead ends, hook 'em back together, and solder. But I don't think I'll be doing that, frankly. It sounds pretty good. To anyone that has opened their 20/20 amp: Did you notice that either of the output trannies were loose? This was the case with me so I tried tightening up the screws underneath but they were already tight. It turned out the screw head was too small for the hole drilled into the chassis causing it to not be secured properly. I put a washer around the screws to give them a chance to grab the outside of the chassis which made it look a little ugly but stopped any potential rattles. Mesa designed this amp for use with their preamps. To do so they cut quite a bit of bass out of the 20/20. Don't worry, it's very easy to undo. You simply need to remove 2 cathode bypass caps (one per channel). They are very small 1uF capacitors that are located at the bottom of the tube circuit board, on each side of V1. They are smaller than the resistors. These caps boost the mids & highs to about double the level of the bass. So removing the caps will flatten down the mids & highs, to make them even with the bass. You may need to increase your 20/20 volume settings slightly to compensate. This mod will make your non-Mesa preamp sound the way it was intended to. Heck, it makes my V-twin sound way better through this amp. (Note: If you need extra volume then replace the 1uF caps with 10-22uF caps, but I find this unnecessary). I also have a tip regarding the presence controls. They are cut only controls. So if you set them counter clockwise you are choking out your extreme highs. Turn them all the way up and they won't affect the highs. I like to set them around 12 o'clock. This setting is very subtle, and helps take the edge off of the EL84 tubes. It makes them sound like EL34's. OR Get the Mesa 20/20, but do the following fat mod to it: Mesa put a 1uF Cathode bypass cap on each channel's input stage. This cap gives a boost to the mids & highs, and makes the low end sound a bit wimpy. Simply remove the cover, locate these two caps, and remove them. They are on the tube circuit board, below the tube that is closest to the input/output jacks. They are probably beige or tan colored, and about the same size as the 1/2 watt resistors in this amp. DO NOT ATTEMPT THIS MOD UNLESS YOU ARE QUALIFIED TO DO SO - LETHAL VOLTAGES INSIDE COULD KILL YOU!!! You don't need a resonance control, because the Chameleon has one in its speaker simulator - I think it calls it a reactance control. You can use the speaker simulator with guitar cabinets as long as you set its speaker to full range. Also, set the mic

placement to zero (off). The 20/20 has 2 inputs - 1 per channel. You can use its slave outs if you ever want to hook up to another amp. I think you'll really appreciate its great tone (especially with my mod), and compact size. But don't let the small size deceive you, this amp plays as loud as a 50 watt Marshall. But Why? I never understand that mod, I like mods, but coherent mods, in my point of view trying to get more bass on the 20/20 is a nonsense in my opinion. I think that before you do any mod you must to look all your enviroment, for example 20/20 uses the el84 tubes, that tubes are the british classical tubes in class A amps. The british sound is a totally balanced tone between bass, middle and treble. On the other hand tubes like 6v6 or 6l6 has a rock standard tone, with great highs and strong push bass ( the V eq settings ). One of the nice tones of the british tubes designs are the presence middles. Once a time I test the 20-20 power amp from marshall, with the same tubes. That amps sounds great but when you activate an extra low frecuencies punch it sounds amazing the first minute ( " hey mom It sounds like Steve Vai ") but the later minute I said " wait, wait, wait, where are the singing mids that are on every el84 tube ", that extra punch circuit killed all the feeling of the el84. I think that if mesa wants on the 20/20 an american rock tone they will designed the 20/20 with the 6v6 like fender amps. But I think that they were looking for a more british sound. The tone of the 20/20 is perfect, it is warm and vintage and this tone is the only reason to buy that amp, the triaxis with that amps achieve the perfect clean and semisaturated tones for country, funk, blues and jazz. And I think that if the tone is not correct for you, try to test a 2:90, because it has million functions than the 20/20 except that pretty vintage tone. If you really want more low end response I could recomend to you replace the boogie el84 tubes and try the jj el84. I've had this mod on my 20/20 for some time now. (I've also installed a circuit to allow the TA to switch the deep mod in and out) I find that the deep mod makes the amp's sound more subdued. The lows do increase, but the mids level out as well, and the highs stay the same, which makes them somewhat more prominent, since the bass and mids have decreased some. One thing I noticed is that the amp's "snap" is decreased as well, as if the dynamics are a bit subdued as well. This works great for a mellow, jazzy sound (but with crisp highs) on the neck pickup, or an acoustic with piezo pickups. I think that if you really want a bit more bass with the jj are enough, enjoy the 20/20 in my opinion is the best tube power amp of mesa Once you get the 20/20 I suggest retubing with JJ EL84s as they are one of the better EL84's produced today. There is one thing you may be interested in as far as mods go. Mesa put out a "Deep" mod for the 20/20 and most of the people that have done did not go back to stock. Now, don't get this associated with typical "deep" mods that one would think increases bass this actually just reduces a mid hump that makes the tone more linear instead of a bit mid heavy. It just balances the tone a little better and sounds great to my ears. If you want you can even make this feature switchable. The schematics and photos on how to perform the mod are on the Triaxis yahoo group. It's a great combination and I believe that, the 20/20 is the better deal. I have had my 20/20 modded though: it has the so-called deep-mod in the input filter section and my amp tech put a variable bias circuitry in it. The fixed bias thing Mesa raves about is basically a hoax designed for you to always buy Mesa tubes. My power tubes (EL 84) are running way hotter now (like they should be) and that makes them sing like they've never done before. This applies to most Mesa combos and poweramps.

Yes, this deep mod works and makes a pretty big difference. The 20/20 has a cut in the low end when it leaves the factory. By removing the 2 capacitors (1 for each channel), the virtual mid boost (due to less bass) is being reduced resulting in a deeper sound. As always, it's a matter of personal taste. When I modded my 20/20, I removed only 1 capacitor and compared the channels, 1 being original and 1 being modded. I liked the modded channel better and removed the other cap as well.

Oh, if you want to stick your hands in a tube power amp, there's a serious risk of being electrocuted - even when it's disconnected from the AC outlet! Here's a useful trick: -

connect the poweramp to the AC socket and to one or more speakers

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turn the amp ON (standby switch also ON)

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set the volume anywhere above 0.

pull the AC plug out with all switches still ON and wait for at least 1 minute. This should drain all charges.

Robert