Mark IIB Gain/Footpedal

[gitapik]

Hi,

I heard that I can hook up a footpedal (I've got a Boss) to the effects loop on my Mark IIB and have it control my tone from crystal clear to the dirtiest overdrive.

"Cool", I said...so I gave it a shot and all it did was work as a great volume control.

Anyone know if there's a particular setting I'm supposed to have on the pots and switches. I've got the EQ and all the other extras on my Mark IIB from 1980.

Bob

BTW: How can I change that "Bottle Rocket" thang, below my Avatar, to "Mark IIB"?

 

[Boogiebabies]

The gain boost footswitch plug should be under the chassis. It adds an extra capacitor through the midrange pot.
It may even look like a reverb connector.

As for your second question, post a few hundred times and you wont be a bottle rocket anymore, bottle rocket.

 

[gitapik]

Kinda like a "freshman", eh...?

That's funny, but I can dig it...the only time in music is what you're playing to...

I appreciate the reply, BoogieBabies. I shoulda been more specific, though: it's not the footswitch I'm talking about. I've got the option with EQ/Gain. I'm talking about attaching a volume pedal to the effects loop. Here's a description. It's only on the Mark II and IIB models that this is available and I'd love to use it:

II): 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..."

I've tried it and had no luck, yet. Wondering if anyone could be a bit more specific about it. Maybe I'm missing something. I am, after all, just a li'l ol' bottle rocket. :wink:

 

[scandoslav]

William G. Sacks has written, "A cool and little-known option with the Mark IIB (or original Mark II): 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..."

Sorry to drag this up, but I thought it'd be better than starting a whole new thread to ask the same question. I saw the above quote on this site: http://homepage.mac.com/mesaboogie/MarkSeries.html. Does it hold any water? Where'd it come from? Who's this William G. Sacks fellow? Anybody tried it? Could anybody try it and report back with the results? The Mark Series wikipedia page (which seems to be a copy-pasted from that page) mentions it indirectly, saying that the IIC can't do it.

I'm looking to move from my F50 into the Mark series, and the pregain-pedal thing sounds kind of like magic.

 

[zodiac272]

I have heard about the volume pedal/FX loop thing, never had a IIB to try it. Maybe your IIB could use the FX loop mod.

scott

 

[gitapik]

Hey,
I've tried many times to get that feature to work, but had no luck. Just get a tinny version of the real sound.
If I use two cables going to and from the pedal and the effects loop, it makes for a kick *** volume pedal. Same as when I use one cable from the jack under the chassis, which controls the Volume I pot. Makes for a great, great volume pedal. You can keep the same tone but at different volumes pretty much through the entire sweep. I use the volume pot on my guitar to control gain.
All that said: it would be great to be able to do what Mr. Sacks is talking about and maybe someday I'll be told or find out that I just didn't hook it up right. But for now, the bottom line is that the Mark IIB is a fantastic amp. Especially in the clear channel. Besides the fact that it sounds so great, period...it also takes to any effects pedal I've plugged into it (I've used plenty), perfectly.
I'd be curious about the FX loop mod...

 

[scandoslav]

I can see using it like this: dime the amp, use the pedal to determine the amount of gain when the guitar is at 11, then use the guitar's pot to clean it up from there.

Maybe it's the "on the fly" part that William G. Sacks is going on about. In fact, I'm betting that's the thing, that it'd save the hassle of fiddling with the gain knob.

But why, for goodness's sake, would it be unique to the IIB? Is the IIB's FX loop in an unusual part of the overall circuit? What about the IIC's loop differentiates it from the IIB's, and what is this FX mod?

If I use two cables going to and from the pedal and the effects loop, it makes for a kick *** volume pedal.

I imagine that this as the way to do it. How do you like your IIB?

 

[glguitarman]

It might be that your IIB's loop has already been modified, that is why you are having trouble, but I couldn't be sure about that of course. I have read that what when a IIB is modified to sound like a IIC+, that pedal in the loop feature becomes null and void.

 

[glguitarman]

Not sure about any of this having never owned a IIB....

http://homepage.mac.com/mesaboogie/MarkIIB.html

...from that url you can find this....

Effects Send&Return: A useful feature to hook up external effects, or other Boogies.  Modified from the Mark II, the new patch points offer a low noise connection without overloading of effects.  The output is designed to have low impedance to ensure low signal noise and hum.  The signal comes in before the Graphic EQ. so shaping of the effects is possible.   Input will interupt signal so a loop must be completed.  Output however works alone and can be used to send a preamp signal to another Boogie.  A know issue is when the internal switching jack fails and cuts the signal.  To test this, place a cable from send to return.  If this solves the problem, the jack should be repaired by bending the contacts or replacing it with a Switchcraft 12A.

Gil Ayan writes: A cool and little-known option with the effects loop of a Mark IIB (or original Mark II): one 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 pre amp tubes' full voltage to pass into the power section.  As the pedal is backed off, it decreases the amount of pre amp signal allowed through the 'loop,' cleaning up the sound. To make use of this feature, setting the clean channel's pre amp to 9 and using an Ernie Ball pedal to vary the overall tone gives many different tone options.  In the Mark IIB mannual they describe this, but say that one should use the preamp/amp junction input underneath the chassis.

Not sure where I read about the IIB to IIC(+) mod changing all of this but it would stand to reason since the loop was an important difference between the B and C.

Hope this helps.

 

[gitapik]

Well...this is where I often get raised eyebrows, so I don't often mention it. But, seeing as we are all Mesa brethren, here, I shall expound and bear the consequences:

As much as I do love my IIB (somehow you caught that, did you, scandoslav?), I always felt that the distortion feature left something to be desired. Especially when compared to the clear, which is excellent. It just didn't catch the nuances of the pick attack as well as I liked and was dark for my taste. I used my Big Muff Deluxe, Real Tube, countless Boss, etc distortion and overdrive pedals instead, for a long time. They sounded great...but I kept wanting the distortion sound of the Mark IIC or III.

Keeping the amp untouched, mod-wise is the key to resale value. But the bottom line is that I want my stuff to sound "right" if I'm gonna use it. So I went to my electric everything repair guy who'd told me for years that I should let him install a mod. Just a couple of small changes and I could keep the capacitors if I ever wanted it changed back. I don't know if it's the IIC mod...but he's brilliant with amps, so I decided to take the plunge.

He did not disappoint. The amp is a monster, now. Clear tone's still the same and the distortion's amazing at any volume. Still the Boogie sound, but so much clearer and defined with more of the color spectrum to choose from. It's just a complete amp, now. Still got the pieces he replaced, should I ever decide to sell it. But as long as it's mine, it's staying like this.

But…it sounds like the mod might have disabled that so cool pre-amp on the fly option. I had a feeling that might be it and, if what giguitar's saying is true…then it's a loss.

I'll take the trade off, though. The sound's worth it. I'd love to hear from someone who's using that feature.

Here's a shot of it, btw:

 

[BMcNibbnles]

Yeah, I think a previous poster had the right idea. I had a Mark IIB, but never tried this and always wondered about it. I think that it works like this: the gain is cranked, but when you attach a volume pedal to the effects loop, it controls the amount of gain being used. So, you can get, "on the fly" distortion (or, lack of distortion) without having to roll back the guitar's volume or screw with the amp's knobs. I think it's more of a convenience thing rather than a, "added tone" thing, for lack of a better description.

 

[chipaudette]

What I think is interesting, is that the schematics on the web for the Mark IIB, do not seem to suggest that this volume-pedal-as-gain-control should work.

Here's one for (I think) a Mark IIb: http://www.srl.utu.fi/~tke/MesaBoogie/Manuals/SchematicDiagram.gif

Note that the effects loop comes off the cathode of the mixing stage (V2A). This is the point after the clean channel circuit path and the lead channel circuit path join each other. If one were to stick a volume pedal here, it would allow one to cut back on any distortion that happens downstream from its location. Therefore, if this schematic is correct, the volume pedal would only be able to control the amount of distortion that occurs at V2B. I just don't think much of the distortion happens there. I think that it all happens V3B (in the lead circuit) and at V2A itself. So, because the volume pedal trick does seem to work, the schematic must be wrong...very wrong.

To get the volume pedal trick to work, I would think that the effects loop would have to happen before the tubes in the lead circuit (in this case, before V3B). This was the case for my original IIC (prior to its IIC+ upgrade). My schematic for the IIC (not +) is at: http://picasaweb.google.com/chipaudette/20090628MarkIICGuts#5357903106123784114

I would think that the volume pedal trick would have worked based on this kind of schematic. Unfortunately, I never tried it.

So does anyone know about the IIB schematic? Is the one on the web that wrong? I know that it had a reputation for a few errors, but if the effects loop is really in a different position than shown on the schematic, that's a huge huge misleading error. Anyone know?

Thanks

Chip

 

[gitapik]

Interesting post,Chip. I'm out of town right now. Pretty sure I've got the schematic at home. If so, I'll scan and post it when I get back.

 

[gitapik]

Knew I had it. Hopefully it's different than the one you found online. Doesn't mean much to me. I'm eternally grateful to my techies. 8)

Big enough to read or should I email it to you?

Bob

 

[chipaudette]

Wow, that's a nice and clean schematic. Thanks for sharing.

The location of the effects loop is the same as I saw in my schematic. I just don't understand how putting a volume pedal in that effects loop would affect the amount of gain/distortion...except, as I mentioned, any distortion generated at V2B, which I claim is likely to be small. It would be much easier to understand the effects loop "trick" if it were in an earlier location.

Has anyone actually opened up their Mark IIB and seen, for themselves, where the effects loop connects in? BB, are you around anymore? Anyone else?

Inquiring minds want to know!

Chip

 

[gitapik]

My techie, who I mentioned in my "mod confession" is a wiz with amps and pedals. When I mentioned this feature to him he'd never heard of it. The main techie at Mesa said the same thing. I mean, there was gain control when I tried it, but it was such a tinny sound, I figured "why bother?".
I'll be visiting Jeff this weekend. Will bring him the schematic and ask where the effects loop hooks in.
I just remembered in the original manual they mentioned why the loop worked. Might have mentioned something there...I'll give that a look. It would be nice to figure it out.

 

[gitapik]

Just talked to my techie. He said the effects loop connects between the Preamp and Poweramp. Just tried it again and came up with no sound whatsoever, this time. Got frustrated, so I plugged the volume pedal into the jack under the chassis and am happily using it as a volume pedal. It's really nice: same great tone but at a lower volume. Then boost it and fly.

I'm hoping someone can figure this out, 'cuz I'm reaching the end of my rope and just want to appreciate this amp for what she is: great. The gain on the fly would be fantastic...but I can't seem to make it work. So I'm just gonna play and stop looking, for now. Thanks to all who have been and continue to get into this thread.