Boogie MKIIA Rev Eq 60/100W

[mark2boogie]

Here are some additional pics of the hardwood cab - there's only a number inside at the bottom (= 593) :

And the original tolex cab which came with the amp - it seems to be made from pine plywood :

As you can see, there is no plate nor holder in any of them... So they looks to be original, and are reputedly considered as, but there is no evidence... At least to me ! So, again, what's you opinion about that ?

It would be interesting to learn, simply for my knowledge.

A+§

 

[mark2boogie]

Hi again,

In addition, I am working to reduce hum in my MKIIA - particularly in the reverb circuit : I am about to find a solution. It's surprising that none of you has faced that non-negligible reverb hum problem...

A+!

 

[megavoice]

Well it's a little bit dark on that pics, but can't you probably see any little holes on the left side, when looking in ? Maybe the holders have been remooved.
Those four screws on the right make me also wondering, because at that height ther wouldn't be any room for a fan because of the speaker-magnet. Mine is placeed fairly deep down at the bottom. Perhaps the fan had been fixed previously upright, or maybe another type of fan.

I don't know what this number means that is written inside, but have you removed the rear plate and looked upon the inside surface ?

The dovetails look pretty good from that distance so this should also stand for Mesa-quality.

As spongerob said, the sidebars either of my hard-wood and also in the tolex are tucked with metal-clamps. So this is the main difference to yours.

 

[megavoice]

I've a Mark III, I have no problems with my reverb so I can't give you any advice, but as I know there's a solution. Hope someone else replies.

 

[mark2boogie]

megavoice,

You're right : there is additional holes in the cab, at the left and at the right, as shown on the pictures below.

But there is no mention of the wood on the rear of the back panel, as also shown on pics...

I do not see any metal clamps, the wooden side bars are screwed - hope I undertand what you mean there !

Here is some closer views of the upper and lower dovetail joints :

The reverb hum problem is reputedly only found on MKIIA and B, but I have found by myself a satsfactory solution to reduce the hum very significantly - I'll explain it in another thread, if it is of interest to tech-minded MKIIA Boogie owners...

A+!

 

[SpongeRob]

Hi Mark2Boogie!

My final word. Aftermarket Hardwood cab. If you look closely to the dovetails it was used a dovetail router with "precutter". Don't know if such router are also available in the US. But Mesa don't use and never used such router! I had several Hardwood Products from Mesa and they never had this kind of dovetail joints. Sorry to tell you that. That's my opinion about the hardwood and also my experiences on this. I heard of someone in South Germany who does such Hardwood Cabs. And i saw a few Amps on Ebay sold in such Hardwoods. There are a lot of people who doesn't know the orginality of these products because they're not familiar with Mesa Hardwood products. But in this case it's a quality issue in my eyes! And Mesa uses Machines who cut the dovetails into the 1/10 mm exactly. They're perfect! This was made by hand, which doesn't mean that you can't get the quality of Mesa. But it will need the right machines and the "perfect" adjustments to all machines to get this Dovetails made with the same quality. And everything looks really nice on your hardwood but in this case the router just shorten the quality a bit. Still a nice Cab.

Hope i could help with the info!

 

[megavoice]

Mark2boogie !

Immediately after viewing the blow-up of the the dovetails I said to myself, no, that's not Mesa-work.
First, looking at original Mesa hardwood-cabs they look like "one-piece" at the dovetail-joint unlike yours.
Second, Mesa usually took one plank for all three sides, left, top and right, and if there s.th. had been interresting, they placed it on top. So as I know, the hardwood-cabs had been made out of one piece. This is not the case when looking at yours.

But as spongerob said, it's a very fine cab nevertheless. Enjoy !

 

[igfraso]

Mesa's hardwood early cabs have both the type of wood and the month and year of fabrication in the back panel (i.e. imbuya 7/82).
Most recent cabs have no legend at all.

Al least, this is my experience.

 

[mark2boogie]

Thanks SpongeRob, megavoice, igfraso for sharing your advice and knowledge +++ !

In addition, I bought a flycase which contained an all original MKI amp for my MKIIA, and :

1 - the Tolex cab which came with my MKIIA enters exactly in the flycase.

2 - the Hardwood cab is a little bit higher, circa +8mm, so I can't close the flycase.

Moreover :

3 - the output transformer touches the right wooden side bar on my hardwood cab, which is in fact slightly thicker than the ones on my Tolex cab.

So this goes in the same direction as your verdict : obviously, this cab is not a Boogie-made one, but an aftermarket model - even if it's not of a major importance for me, as the cab is nice and in good condition.

Additionally, I reworked the reverb circuit, the heater circuit, and some other details with success, mainly about the ground. The amp is now much quieter, even if all my SF Fender are superior on that point. It's amazing to see the misconceptions in the grounding schedule of the MKIIA... (Leo Fender wouldn't have done that).

Nonetheless, It's a great sounding amp, with a wonderful clean tone and reverb. The lead channel is smooth and bluesy (but would need more reverb level compared to the clean : I'll see what can be done) and you can have that magic Santana sustain... Most of the Mesa/Boogie I had for service were not able to sound as cool like the MKIIA (I mean : deep and unagressive), but shared with the MKIIA... A questionable S/N ratio !

A+!

 

[igfraso]

It's a very nice cabinet mark2boogie so enjoy it!

Regarding the MkIIA, Mike Bendinelli has always praised this model. He says it has a very unique sound in the Mark series.

 

[mark2boogie]

Thanks igfraso,

The hardwood cab needs some slight adaptations, and the chassis too, in order to meet themselves... I will post here the informations and picture when it will be ready, in the case of somebody else would have the occasion to.

For the moment, I am working on the electronics :

- now the reverb is at the same level both in Lead and Rhythm mode, with - the most important - the same tonal qualities ! (there was just a right resistor value to search).

- I doubled the gain on the Lead stage (V3a) by decoupling Rk with a 22µF 25V. The effect is not tremendous in terms of gain, of course, but the drive is a more sustained, with the same tone, so it's a benefit.

- there's sometimes an AF oscillation when the Presence control is maxed - I'll have to check that : probably an unwanted coupling somewhere...

- the reverb tank needs shielding and acoustical insulation to avoid sometimes Larsen effect and crashes - soon !

- I have a simul-class recipe that can take the place of the ground switch, as we don't need it in Europe. It would give 15/30/60/100W power choice, at the flick of 2 switches. I have to make some test to see if it's OK (it works well on Fenders SF and RI) - soon also !

- the fight against hum and noise remains open... and this is not the easiest task !

A+!

 

[mark2boogie]

Well... Decidedly, the Boogie MKIIA - almost mine - is really to be considered as "an artisanal product which tried to shift from a prototype to a production model" : I am debugging various misconceptions about shielding, ground routings, unwanted couplings which were hum or parasitic oscillation sources - that's amazing !

One example : the reverb transformer is close to the power transformer, and it receives magnetic induction = hum. I displaced it and turned it (closer to the output transformer, you have all the room for it) so I eliminated that induction hum... How can't we call that misconception ?

Another one : if you look to the wiring of the MASTER 1 and LEAD MASTER pots, you will find that these are wired in variable resistor, and even if these are LOG pots, the settings are very touchy to adjust (around 1-2). I rewired the MASTER 1 as a conventional LOG pot, and wired the LEAD MASTER pot in variable resistor but on the top, not on wiper of the MASTER 1 : this gives a great improvement in progressivity when you want to adjust or balance volume... Why was it not done on later models ?

Some problems will be very difficult - even impossible - to cure : the EQ coils seems to be induced by the power transformer, and so there is significant hum when you place the sliders up or down mainly on the 80Hz and 240Hz, and even on the 750Hz. Unfortunately, to displace the EQ coils far away from the power transformer resembles a nightmare...

Any of you MKIIA owners notice that EQ hum problem as I described it above ?

A+!

 

[mark2boogie]

Hi again,

The hum fight continues : this time I completed the modification of the GND points to the chassis from... 14 "randomly displayed" points (!!!) to 2 concentrated GND sections : the input jacks , the speaker jacks.

The GND schedule is accordingly divided in 2 sections : the input/preamp/reverb/Eq , the power/speaker. These are directly wired to the PSU filtering section, which has correspondingly no GND to chassis now.

The result is a NEAT improvement in the hum ! Simply imagine - to mention a few - that the power amp was fed stock from the PSU through the metal of the chassis via a bolt and a speaker jack ! No wire... So no equipotentiality... So hum !

The hum decreases, but the tone increases... So the hum/noise fight is not ended...

Additional question : with a 8 ohms single speaker (the EVM12L of the cab), what speaker out do you prefer to plug in ? 4ohm or 8ohms ?

A+!

 

[mark2boogie]

Last Hi,

I have worked again on my MKIIA, and now this amp is dead quiet - no more unacceptable hum - like a brand new Princeton Reverb (or a well restored vintage one), with the exception of the unavoidable - but now acceptably reduced - hiss when Lead Drive is maxed due to the gain of the MKIIA versus the PR , and at high volume setting (on stage).

Reverb is now balanced in level between Clean and Lead channel, on a wide range of settings, and of course no reverb hum;

Master 1 really acts now as the master volume, not modifying the clean/lead level balance when re-adjusted;

the Pull Bright Lead is plentyful when pulled (modified circuit, not the original treble damper when pushed);

no larsen tendency on the deep reverb even at 10, on any volume setting (acoustic insulation);

neatly reduced hum on the Eq at 80 and 240Hz sliders extreme settings;

no more oscillation with the Presence control at 10, plentyful effect, even at max volume;

Some slight modifications to increase a bit that singing sustain in Lead mode (non-agressive gain amelioration);

four selectable power : 15/30/60/100W "multiclass" at a flick of 2 switches (one take the place of the GND SW);

That's done... The Great Sound of the MKIIA is really worthwhile... Once you have got rid of the issues... Exit !

A+!

 

[igfraso]

mark2boogie,
have you already tried this?

QUOTE
William G. Sacks has written,
"A cool and little-known option with the Mark IIB (or original Mark IIA): while the effects loop isn't worth much as such, you can run the output of a volume pedal (without your guitar being plugged into its input) into the 'return' jack, and get on-the-fly preamp gain control! This is a feature that very few tube amps have ever had, even inadvertently - it uses the pot in the volume pedal as a passive limiting device, such that when the pedal is 'wide open,' it allows the preamp tubes' full voltage to pass into the power section. As the pedal is backed off, it decreases the amount of preamp signal allowed through the 'loop,' cleaning up the sound. One of my best friends sets his clean channel's preamp to 9 and uses an Ernie Ball pedal to vary the overall tone.
Oh, I wish we could convince Mesa to make this a regular option on their new models..."
UNQUOTE

 

[mark2boogie]

Not yet, igfraso. I was really busy debugging my MKIIA... Some little improvements in the search of quietness have occured since (notably mains phase permutation switch and separated relay PSU). But it's an interesting feature worth to try when I can borrow a volume pedal for it !

A+!

 

[mark2boogie]

Well... For those MKIIA "technically minded" owners - we are less than very few, it seems...

I borrowed to a friend some ALTEC 417-8H for a trial.
I made a A/B comparison between an ALTEC 417-8H and the original ElectroVoice EVM12L, with my MKIIA.
Why ? Carlos Santana is reputed to have used a 417-8H on many of its great recordings. So I wanted to listen by myself... That's all !

Verdict :
- obvoiusly more efficiency for the EVM12L, wider sound, more linear, no tone variation when the volume increases, even a lot.
- more warmth for the 417-8H, with a little "grit-bizz" on the top high when in lead mode, like on many Santana's recordings.
- I wouldn't change my EVM12L for a 417-8H, but the ALTEC is nonetheless a excellent speaker as it is complementary to the EVM12L, for example if mounted in an additional 1x12" open cab, IMHO.
- to make a variant, I also tried a Celestion Vintage 30, and I founded it so dull and unable to cut through the mix in comparison of the two others that I discarded it soon. It's only interest was it's... relative lightweight, and just a lightly more efficiency than the 417-8H.

A+!

 

[McBarry]

Nice stuff, and for more breakup as volume increases, the 417-8C is also good (or bad dep on your taste).
AND, it's a little lighter.. nice for those of us not built like we used to be....

"For the technically minded", I'd love to see what the actual work was to achieve the results mentioned earlier.. that would be really interesting..
Dave

 

[mark2boogie]

Hi McBarry,

Nice stuff, and for more breakup as volume increases, the 417-8C is also good (or bad dep on your taste).
AND, it's a little lighter.. nice for those of us not built like we used to be....

My friend has also a 417-8C, but I didn't tried it because of it's lower power capacity (75W, according to him) for fear of damage it, and if it break-up earlier (which I translate in French by "distortion due to overload giving a wanted tone dirtyness" - hope I am clear !), I don't think it is what I am searching for, but I may be wrong... An nonetheless, or unfortunately, the Boogie remains as heavy as an anvil to carry !

"For the technically minded", I'd love to see what the actual work was to achieve the results mentioned earlier.. that would be really interesting..

I apologize for my approximative english understanding, but... What is your request ???

A+!

 

[McBarry]

D'accord,
je ponce, qu'est que vous faites dans le circuit pour faites les...umm modifications mentioned above..
God, I think I better stick to english.. it's been 20years since I wrote french.. and it shows...LOL
Basically, what exactly did you change/replace/modify to create the modifications listed in this thread??
Cheers,Dave