Mesa 20/20 Deep Mod

[Tripoutski]

Have any of you played around with different speakers in your cab to also compensate for lack of beef in the 20/20, or are we all pretty much in love wtih V30's and no way around that? I've thought about switching to G12H30's or something to get a little more bottom end, but the V30's just have that certain sound so I don't know.

Not speakers per se, but the cab itself. I purchased a Genz Benz 212 G-Flex and I have not used my Deep Mod at all with it. That cab works very well with the stock 20/20 because of the tuned ports. The BG uses GBE 1240-V75 speakers. Although GB generally uses Eminence speakers, I understand that the GBE 1240-V75 speakers are manufactured in England by a licensing deal with Celestion (or perhaps just the cone is). I don't know this for certain, though. I have never pulled them to look at them closely.

 

[D2dark]

I've cut the back of my cab to give more air to the speakers, so they can move more low frequency, that helped a lot. I also did an other version of the deep mod, I just change the low cut freq. to around 40hz.

 

[Dewdman42]

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I've cut the back of my cab to give more air to the speakers, so they can move more low frequency, that helped a lot. I also did an other version of the deep mod, I just change the low cut freq. to around 40hz.

Usually a closed back gives a bit more low end then open back, when you say "cut" do you mean just a small opening to allow some air in, while still mostly bouncing the low end forward? Some closed back cabs will put air ports on the front for this reason. What mod did you do to get 40hz cut?




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[D2dark]

I used this idea :

OUps,

You are right that is a misunderstood.
if you remove the cap, you will cut the HI frequency.
If you want more Bass add a Bigger CAP.

At this time,
THe fc~ 100Hz,
if you replace by a 10uF instead of 1uF
the fc~ 20Hz.
Personnally, i already tried but i do not like the Bass.
But that is a personnal choice.

And a 10uF work great

 

[Dewdman42]

Does anyone here know, after doing the bass mod, I'd like to add a little mid back in with an EQ. What frequencies should I boost to kind of bring back some of the 20/20's original character?

 

[j4q0]

I actually had the same question.
Here's my experience:

I installed a DPDT to switch between the normal mod (just removing the 1uf cap) and the mod using a 10uf instead. Like the 10uf WAY better.
I'm using and comparing a Rocktron Piranha, stock MP1 and a MP1 3TM. Even with the deep mod the 20/20 still colors the sound in the midrange area.

I'm after that chunky powerful mid range sound but with thick tight low end, the 3TM has this tight end but as it has this scooped sound the modded 20/20 is a good complement.
Both the stock MP1 and the Piranha have this thick sound in the mids and they are better paired with a more transparent power (the only one I've been able to test is Peavey classic 50/50 which sounds really good IMHO), thought they are not as tight in the low end register, but that only comes into play if you are doing any modern metal or detuned riffs I guess.

So about that mid to be brought back, it seems to be around 350hz (just a couple db), which works great with the MP1 3TM.

I leave some more questions here:
-What would the difference be between the use of a 22uf instead of the 10uf cap? Would that add more low frequency response? As in tighter?
-What preamps are people using with the 20/20?

 

[Dewdman42]

The cap doesn't add bass response, it removes bass response, a lot or a little. removing it entirely will give the most bass response. But having some kind of cap in there will basically flow more electricity through the circuit and minimize signal drop that some have experienced by removing the cap altogether. That being said, I can't vouch for different caps, but it sounds like some caps will roll off less bass then others.

At any rate, to get that chunky sound, you want to boost in the 150-250 range, and then again you have to boost up around 2.5-4k, which is where the "attack" comes through. the upper stuff also adds presence, so you might want to back off on presence from other parts of your signal chain first.

Doing them both will get you closer to a tight low end sound, but in my opinion this amp will never sound like an ENGL so be realistic.

I tried that BECOS kit, I was having some issues, so I removed it again, might try it back, but right now I just have the cap removed and then I'm using an external 6 band parametric EQ to fine tune the sound just before hitting the 20/20. What I found is that the no-cap bass mod (without EQ) is too boomy anyway. If just using it that way I would rather just use the amp stock.

But I do like that I can use my EQ to tone down the boominess to my liking. Putting the cap back is too much bass rolloff though, without question. So I'm able to find the happy place with just the right amount of bass. While I'm at it my EQ fine tunes some other areas, so I can roll off everything under 100hz and everything over 5k. Then I boost in the 150-250 range and the 3k range, as described above. I also drop a bit around 800hz and 1.2hz which are supposedly bad frequency areas for guitar.

but I am still wanting to find the magic mid area that gives the stock 20/20 sound print, maybe I will get a floor pedal for boosting that occasionally, I really like the way the 20/20 sings in stock form, and its wonderful for doing Voxy Beatlesque sounds. But far more often I need that marshall chunky sound, and I feel I'm getting darn close with the above EQ

 

[j4q0]

I guess it all depends on what preamp you are using and what type of music you are playing.
Sincerely I don't know who said anything about making it sound like an ENGL, at least I don't want to make it sound like an ENGL, it's not realistic and not what I'm looking for. I was curious about this mod that everybody talks about so I decided to try it and I agree with you Dewdman, the mod that removes the cap makes the amp too boomy, not of my liking to me. That's why I liked putting the bigger cap, I do feel the difference in low end response and it serves it's purpose to me. I'm just wondering what would the difference be with a bigger cap.

What you say about the 250Hz is correct, although I felt the 350Hz range worked better with my setup.

I also agree that the stock 20/20 has a very nice singing sound so I'll find some time in the next couple of weeks to install a switch so I can switch between the stock cap, the 10uf cap and the 22uf cap, that way I will be able to properly A/B between the 3 options and have a better judgement of what works better for me, I'll share my experience here so people can have an idea of what the mods do.

 

[francm]

I have made a stereo mod for Mesa Boogie 20/20. You can view all the details here. It also has three options for each channel.

Nice job on taking my mod and making a product out of it :roll:

 

[francm]

Nice to see that so many of you tried this mod.

In terms of tweaking the cap value, there's a lot of room for experimentation and really, depending on your preamp, you might want to cut some bass out to tighten things up.

In saying that, my view is that the power amp shouldn't need to cut anything out. Shaping the tone and frequencies is the preamp and EQ's job, not the power amp's job. With a preamp like the JMP-1 or ADA MP-1, the 20/20 sounds real nice with the cap removed IMO. YMMV.

 

[francm]

If you merely remove the cathode bypass cap you'll lose some gain, so it's better to replace it with something around a 22uf 16V or better cap. They're polarized so watch that when you do this, and watch out for any stored charge in the power supply filter caps (best to discharge them or have a pro do the job etc!).

I've done this to mine and it makes the deep mod much better IMO now that it doesn't lose any gain.

Actually, the drop in gain is negligible and can be worked around by setting the preamp volume louder (very simple) or the power amp louder. In a practical, real life setup, this should not be an issue.

If it bugs you from a theoretical standpoint, another way to get a little more gain would be to drop the cathode resistor's value. The larger cap value should be fine though. 10uf is plenty large.

 

[j4q0]

Finally installed a switch to have the option of using 10uf, 22uf and no cap.
I found that there is no difference between the 10uf and the 22uf. However they do add gain to the power and I agree with Francm in that it shouldn't be a problem in practical real life setup, just set up the amp's volume.

 

[fengen]

Thanks for this post, it did the trick.
I had a slight issue with a nasal tone - and I might have to figure out how to mod the mid controls on the Formula Pre.
Still feel that they give a git to nasal sound.
But doing this went a long way on clearing it up.

Thanks a bunch.

 

[sgtreese]

Hi,
I understand that many really love the deepmod.

I have finally found a 20/20 and it has the deep mod. In order to learn more about the sound that it produces, I'd like to compare it with the original sound without the deep mod. Does anyone know the specification of the original caps that have been cut away from my 20/20? Could anyone provide a picture of the deep mod, thus where the caps are located on the circuit board. I looked in this thread for such a picuter but they seems to be unavailable.

 

[Linke]

Before you go clipping cap legs realize that cap has other effects more than just filtering. The cathode bypass cap eliminates the negative feedback loop and that amp stage will have more gain with the cap than without it.
I would recommend replacing it with a higher value cap rather than eliminating it. You will get the tonal quality that you seek without any loss of gain. I’d try a 20uF, 22uF, or 25uF 16VDC electrolytic cap.

 

[JammyDodger]

Could someone repost a schematic and photos of where the caps are? I just got a 20/20 and would like to mod it.

Cheers, Mike

 

[Petit scarabé]

Hi!
Here is the 2 caps.

You can solder a capacitor of 100uf 100v on this 2 caps. You will get more low frequencies.

 

[Petit scarabé]

If you want really more bass you can try this.
Sheers.

 

[edge59AlnicoIV]

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[JammyDodger]

Thanks so much!