Mesa F series - understanding amp genealogy

post ideas here for things you would like to see a video on
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Joined: Wed Mar 30, 2022 4:34 pm

Mesa F series - understanding amp genealogy

Post by daft_dude »

Hi there, I am looking into amps because I find them fascinating as does everyone else here. In the last few years amps have gone up a notch with quality, especially noise and articulation. What I want to do is learn about amps enough that I can remake an amp I have but with a bunch of changes. I've just started watching the Blueglow video series on guitar amps and I was really impressed with the care given so that's why I'm here, that and you suggested on both videos to submit suggestions for amp schematics to look over and contrast. :D

The amp in question is the Mesa Boogie F series amps. Below I've given two links, one to the schematics and the other with an interview with Randall Smith of Mesa Boogie. ... 92QEP2l4nQ

During the interview he says a number of things I find interesting but don't understand. Below I've pasted those ideas for clarity.

“The F-50 uses one of my favorite sounding front-ends and I finally figured out how to get it quiet enough to use in a powerful rig. Plus it’s got a new pair of old-time tone controls, a pre-set EQ for the Contour, a twisted hi-fi driver and the 50- watt output section. The trick is to get everything working happily together. It’s a surprisingly versatile and familiar-sounding amp for deviating so far off the usual path."

"It’s simpler and more stripped down than the Mark II and the basic arrangement more resembles the Mark I. But while the Mark I sounded great, it didn’t footswitch very well and this patented new circuit sought to overcome that limitation. And it did so partly by placing a huge attenuation pad right in series with the incoming guitar signal, a very bizarre thing to do. That’s the source of both the tone and the noise. This pad increases the clean headroom of the input stage and cultivates a curvaceous tonal response, bursting with freshness and bouncy dynamics."

“When switched into the high-gain mode, the front-end operates largely like an original Mark I, except for that attenuation pad, which now adds an out-of-phase component that is surprisingly vital to the overall sound. After that, anyone familiar with amp circuits could see a pair of different tone controls, one for each channel, where the credit must be given to old Fender, because those tone stacks are unsurpassable even today, in my opinion. The clean channel uses the spankier Black Face type while Channel 2 uses the older tweed Bassman configuration altered to Dual Rectifier values, which contributes mightily to the F-50’s gain sounds.”

"I started to discuss the pre-amp layout, and I think you could say it’s one that deviates most from a traditional Fender as far as the circuit and the arrangement of the main elements."

“The way in which the reverb circuit interfaces with the dry signal chain is also unique, as is the phase-splitter stage driving the output tubes. That was something I worked up long ago for hi-fi use: it’s really warm sounding and the way it works with the bias supply delivers a lot of ‘envelope’. When you hit a note, you can hear a complex morphing of harmonics that gives it that elusive and interesting character. As far as the contour, that’s another carefully voiced EQ circuit that has been in Boogies for decades except this time – to keep it simple – it’s not user-adjustable. It’s preset in our classic ‘V’ curve, like the setting we’d use on an old Mark II-C for example. It’s there to help deliver a modern, aggressive overdrive from a sweet little old amp! I should mention also that the negative feedback changes too, depending on which channel is selected, and that’s part of it also.”

With regards on what I want to educate myself on eventually as I'm sure this takes a while to get:

- I don't like the spring reverb and never use it, so that would be edited out unless an element of the circuit needed to stay based on what is said in the interview
- change the effects loop from parallel to series
- remove the v contour switch or upgrade it to an adjustable one. I've heard that mesa's contour is more powerful than regular a 10 band eq in the loop?
- add a depth and presence knob to each channel
- add any easy and modern techniques to reduce noise
- make a 100 watt version with power scaling
- understand the difference between the power amp section in this versus a SLO100 or a Fryette as they're known for their power amps with mesa
- the front end of the gain channel being based on a Fender tweed bassman and if this is used in other hi-gain amps as a platform to start with? (I think the amp does have a unique sound)
- how to obviously turn this into a printed circuit board I can order

Of course I'm not expecting anything, if you happen to find this particular request interesting then at least you have something that I hope is a bit different on your hands.

Thanks for all the great work so far.
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