Boogie early history & more

[chipaudette]

Awesome piece of writing. Very cool... It was nice to see you used one of my old Mark IIA's as a reference photo. I sold that one to a cat in Australia last year. As a side note...you have a simple typo in the Mark I control description... Input 1 is the cascading high-gain channel whereas Input 2 would be known as the lower gain Fender-ish, Bassman-ish channel. Very concise and enjoyable read!

I take a small issue with the characterization "Bassman-ish". Assuming that we're talking about the classic and hallowed late '50s Fender bassman (the 1959 bassman is considered to be a holy grail), I think that there is very little that is Bassman-ish about the Fender-derived Boogies. From a circuit design perspective, I think that it is clear that all of the Mark series Boogies are derived from the classic 60s blackface Fender amps, not the late-50's bassman.

For example, in blackface Fender amps and in the Mark-series boogies, the preamp structure goes: gain -> tone knobs -> gain. But, on the late-50's bassman (and on Marshall amps), the pre-amp goes: gain-> cathode follower -> tone knobs. Also, the circuit values, the cutoff frequencies, and the insertion loss for the tone knobs are exactly the same between the Boogie and the blackface fender. They're quite different from the late-50's bassman.

These electrical design features of the pre-amp circuit have an important effect on the sound and feel of the amp as it is pushed into (by today's standards) mild overdrive. Some feel that these differences in the pre-amp between a classic Fender and a classic Marshall (which is derived from the late-50's bassman) are as important as Marshall's choice to switch from 6L6 to EL34 power tubes. So, we're not talking trivial differences here.

The only thing in the Boogie that is like the late 50's bassman is the inclusion of a "presence" knob. None (?) of the classic blackface Fender amps have this feature, though many of the Fender amps from the 50s did have it, including the late 50s bassman. But, the presence knob certainly wasn't unique to the bassman, and Fender started to re-introduce the presence knob on later amps (silverface?). So, I don't think that the presence knob is what the article was referring to as being "bassman-like".

So, to get back to my original point...I think that it's misleading to suggest that the early Boogies had anything to do with the late 50's bassmans.

But, if the reference was meant to point to the 60's bassmans, well, that's a whole different story. But did guitarists care about the 60's bassmans the way they did about the late 50's bassmans?

Chip

 

[VoodooGuitar]

Chip is spot on, the early Boogie amps have much more in common with the Fender AB763 circuit found in BF & SF Deluxe, Super Reverb, and Bandmaster amps, among others, but not the 5F6 "Holy grail" Bassman or even the later Bassmans.

 

[gts]

Chip is spot on.
This post of his explains it pretty well too:
(copied from this thread http://forum.grailtone.com/viewtopic.php?f=3&t=72930&p=494426#p494426)

The marks are a direct descendent of Fender amps

This is the answer. The tone knobs (with treble pushed in, bass pulled out) are exactly the same as on a classic blackface/silverface Fender. Randall Smith (founder of Mesa Boogie) started out by modifying Fender amps. Then, when he made the the Mark I (simply known as the Boogie from Mesa), it was a souped-up Fender. The design of the tone knob circuitry followed Fender's design. Hence, the template for the whole rest of the Mark series was set.

Once Mesa started to increase the gain on the amps, they added the push and pull pots to modify the knob's EQ frequencies to make it friendlier for higher and higher gain, but the basic behavior was set from its Fender roots.

In British style amps (Marshall and derived amps such as Soldano and Mesa Rectifier), the early parts of the circuit (where the Mark series has its EQ knobs) are hard-wired to cut most of the bass and low-mids. Since pre-gain bass is bad, the relative lack of bass in Marshall-style amps made them sound too thin at low volumes, but made them sound awesome when turned up to the point of distortion. Hard rock!

By contrast, have you ever turned up the volume on a classic Fender amp (or reissue of a classic)? Have you ever turned it up to the point of getting a really distorted sound? On those classic-style amps, I think that it getting it to the point of heavy distortion makes it sounds really mushy and kinda bad. The primary cause for the mush and flab is that the guitar signal has too much bass, which makes the distortion get flatulent. It's the same kind of effect that you get with the lead channel on a Boogie if the bass knob is incorrectly turned up.

Guitars and guitar amps are full of historical "features" such as this. They're full of vestigial tailbones and appendices waiting to burst. If you're into circuits, they're fun to learn about.

Chip

 

[VoodooGuitar]

Many of the BF Fender-derived amps (Boogie, Dumble, etc.) changed the huge 25uF cathode bypass capacitors to 4.7uF for a much more controllable low end. Smaller coupling caps can help, too.

 

[lovetoboogie]

Awesome piece of writing. Very cool... It was nice to see you used one of my old Mark IIA's as a reference photo. I sold that one to a cat in Australia last year. As a side note...you have a simple typo in the Mark I control description... Input 1 is the cascading high-gain channel whereas Input 2 would be known as the lower gain Fender-ish, Bassman-ish channel. Very concise and enjoyable read!

I take a small issue with the characterization "Bassman-ish"...

I agree...It's a holdover from some of the many ways to describe the lower gain input 2 on early Mark I's. Not to be confused with the original Princeton that was purportedly modified as an actual Tweed Bassman. I believe the Bassman-ish(darker) reference took root because of the availability of the Volume/Master Volume matrix on Input 2 which when pushed hard comes up with a slightly overdriven tone with a noticable bump in the mids, similar to tweed and blonde Bassmans, maybe even a BF/SF Bassman Head... but clearly not as much as input 1. Speaking purely in terms of tone without the circuit analysis input 2 could be described as Deluxe Reverb-ish...or Silvertone 1492-ish...or Ampeg B-15-ish..., etc. It's easier to just describe input 2 as cleaner and leaner....but with some "teeth"!

 

[igfraso]

Chip:
as you were correctly saying.

This is a Mark IIC preamp block diagram I copied from one of Mesa's old brochures. Probably a IIC+ since the effects loop appears to be after the Lead mode circuit.

Lead mode has a First Gain (Input) - Tone (and Treble shift)/Volume1 - Gain makeup - Lead Drive volume - First Lead Gain - Tone shaping - Second Lead Gain - Tone shaping - Mixer Amplifier Gain - Lead Master volume - Reverb (Rev. Driver & Rev. Return Amp) - Effects Send/Return - Effects buffer gain - Master1 Volume - Graphic EQ path

Rhythm mode has a First Gain (Input) - Tone/Volume1 - Gain makeup - Rhythm Tone shaping - Mixer Amplifier Gain - Reverb (Rev. Driver & Rev. Return Amp) - Effects Send/Return - Effects buffer gain - Master1 Volume - Graphic EQ path

Preamp then goes to Driver Amp and power tubes.