Does Mesa Boogie Intentionally Falsify Schematics? EVIDENCE INSIDE! Bass 400 Service Postmortem
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- เผยแพร่เมื่อ 14 มี.ค. 2018
- Original video: • Amp Tech's Worst Night... I have been told by techs I trust that Mesa Boogie's Randall Smith made it a common practice to intentionally falsify or otherwise obscure published schematics to prevent copying or cloning of his amps. This Bass 400 EQ-180A board seems like one of those instances. Mesa is already notorious for being tight-fisted with their documentation, refusing to honor requests for schematics on current production amps to just anyone, examples include the Mark Series and Rectifier series.
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I draw documentation schematics for a living. I can't pick my jaw off the floor.
Thanks sincerely for taking the time to share your knowledge.
Sort of defeats the whole purpose of a schematic, eh?
Seen bad schematics numerous times on Mesa's, it's a big problem over here in the UK getting one repaired - the sole importer is useless and doesn't want to know. I've repaired quite a few, but it's always hard work. One that springs to mind was an old studio calibre 22. No signal to power stage and no schematic for the revision - it was similar to other versions but not the same. I found the problem - sneaky bastards had hidden 3 small signal diodes in series under two power caps that were siliconed together. Impossible to see without removing the caps or the complete board, center diode was open circuit and effectively switching off any signal output from pre-amp by killing DC to loop section and opto switch. Removing the board was the last option - every wire from the mains and output transformers would have had to be cut or unsoldered along with every wire to every pot which were blocked in by the PCB! Three other techs had looked at it and given up, two of whom were allegedly Mesa certified....
Westside distribution , otherwise known as "oh you have 1 non mesa brand tube in therem so youll have to buy an entire mesa branded retube set before we can even touch the amp" they charged me over £400 to repair a 290 and it broke within 4 months , fuck shipping that back to them again , £80 each way
That's akin to software developers releasing false source code for end users trying to diagnose errors decades later. It must be vindicating for you to learn that you were smarter than their deception and were able to fix the amp's problems despite the OEM's misinformation.
I can't say I have the last laugh considering what a pain in the ass troubleshooting was because of the error.
Considering how .. inspired.. they were by Soldano amps, it's funny they'd be so worried about people copying them.
As well as how Randall Smith started off by modifying Fender amps. The first Mesa Boogie amps were essentially modified Fenders, which meant the Mr. Smith probably had a schematic of them.They're hypocrites.
Most amp and effect manufacturers are. Some are are even hostile towards modders, like Mike Fueller (of Fulltone), which would often go after people on ebay selling nadmade builds of his circuits, which is why the OCD has 4 different versions with different circuitry, since Mike was desperate to get a patent on that pedal.
This is some years ago but the diy effects/stompbox community is no different lolz. I remember some ridiculous fighting and attacking (like hacking etc) as well as threats reg certain 'holy grail' type pedals or gooped up ones being degooped and reverse engineered. Community split in 2 iirc and the reverse engineers kept on reverse engineering. X'D (With surprising results in regards to how boutweak some of the boutique scheme really is/was).
Haven't been there in years but I remember a couple of amps being reverse engineered/verified, so if people are looking for confirmed schematics it's at worldwidewebz dotz byocelectronics dotz com/board/index.php
makes Mesa seem scummy.. + to anypone who doesnt know what hes referring to, the rectifier preamp is a Soldano clone.
I think it makes sense now... that cap you replaced is not on the schematic at all, but it needs to be there to keep the 21v negative bias out of the return of the FX loop. That's an obvious error on the schematic (the one that *is* shown on the schematic is behind the one you replaced.) The undocumented input cap had failed short -- you can't blame it, it was trying to make the circuit match the schematic after all!
All of which explains both why you were reading so close to zero at the base of Q1 and why the resistance to ground was only 14k (the 15k resistor up before the FX loop was shunting the bias resistors), and having the negative bias fed back up the FX loop would also explain:
- the reported weirdness with the FX loop that you mentioned at the start of the first video;
- unexpected interaction between the FX blend knob and the EQ
- why the bypass switch was so noisy (switching a DC offset in the signal chain.)
Yep, yep, and yep. All that stuff you just said.
Killer work man!
Thanks, Tom. I got there eventually. Only took an hour of total footage.
Minimizing variables... Always a good idea! On repairs like that, especially if I never opened one up before I dig into the circuit and do some math so that I am better prepared. Sometimes you can’t do that, but when you can it is helpful.
JUST A WARNING ABOUT THE SILICONE SEALANT - I'm only 3 minutes in but I thought I should mention something very important about the silicone sealant. Standard universal silicone sealant is acidic (you can smell that strong vinegary odour when you use it), and it can corrode components and PCB traces! I'm sure the plastic covers on the big caps would be fine with universal sealant, but getting it anywhere near the PCB traces can cause problems later on. It's always safest to use the electronics-grade silicone sealant - I think it's known as 'neutral cure', as it doesn't release acid when curing.
ForViewingOnly this is exactly what I was wondering when people were saying "you should put that right under the caps and stick the caps right to the board so you can't see the sealant." The acidic smell was a clue
That's why I left the amp wide open to cure for more than a day. Good point. The board is also laminated in this section, so the bits on the board shouldn't corrode as it cures. Thanks for the comment!
Every proper engineer knows that standard silicon sealer fumes can still be rotting copper over a year after it was put in there. No proper engineer would EVER use that stuff. Cowboy.
Wow, another no name anonymous troll...
Why do people do that and hide behind a mask?!
Electrofrying D, perhaps he works for Mesa :)
Thanks, man.
Love the content find your video's educational
Thanks, Jason.
Amen to that
Wow! Randall Smith puts more silicone in his amps than Dolly Parton. lol
I have a feeling many of your subscribers (including me) noticed the same discrepancies in the schematic
Yep ! The Graphic EQ is the Hart of the MK series Boogies an these bass amps. Thus Randall throughs a couple of zingers in the service schematics. If you ask Mike B at Boogie HQ , he will say its a mistake . But I've seen actual Erased and smudged component values and some just left out. Randall does have some Steve Jobs control issuies about his products. You should do a rant on Randall Smith's explanation of why he doesn't put Bias Pots on his amps ??? Because I put Bias Pots in all my Mesa Boogie's and recommend that all my clients do the same. Some things i've never seen on a schematic, like the Limit Knob on the back of some MK2C+ Colosseum's.
This brings up why I'm conflicted about Mesa Boogie. I love their products, but their practices regarding schematics and the way they bully those who possess them into taking them down makes me hate them. I also wish I could get my hands on a bunch of their amps, make correct schematics of them, and put them out on the internet for the world to see.
And what a contrast to what fender does, which makes their schematics freely available!! This makes and keeps me a loyal Fender customer!
Well, some of their schematics are freely available. For example, if you request a Bassbreaker schematic from them, you'll get a flat refusal from them instead.
nothing Mesa makes is superior. Fender, + many other better for clean sounds. Marshall, soldano, wizard, Bogner, Diezel, Friedman etc. better for heavy sounds. i will say the Mark 1 + 2 are pretty good.
I am not defending Randall Smith or anything but, I wanted to point out that Leo Fender took his designs directly from the RCA Receiving Tubes Manual. It wasn't stealing or shady business practices either. RCA compiled the manual with bunches of schematics intended for potential manufacturers to use freely so they could then sell them RCA Tubes. So, basically the tube amplifier designs are public domain. Not Fender, Marshall, Smith, Rivera or anyone else own the rights of tube amplifier designs except for certain ideas and improvements that they have added along the way that are worthy of a patent. As far as I know Vox is the lone exception.
@@MrSimondaniel3 Good Luck finding a better Class D Heads than the D800+,WD800, or TT800.
I wonder if there's any addendums for the schematics on the sites or forums where they are hosted? (And knowing there's intentional errors at times to discourage copying.) If not, you should give 'em a heads up on what you found.
2N3906 has max Collector-Emitter voltage of 40V so you're operating at or close to the max. I would increase that dropping resistor and get the voltage down if you are using those transistors (for long term reliability).
I'm looking, interestingly, at the biasing of those transistors; it wouldn't be difficult to vary the frequency response(s), which would add the ability to vary that board's 'range selection'. It's actually damned clever!
I'm not surprised by the way Mesa Boogie hides information from consumers. Had a mini mark 5 that was super noisy with switching and they told me that there was nothing wrong with it. After watching your video on another amp, I tried to get some info on the mute circuit and was refused any help from Mesa Boogie. I got rid of the amp and bought a Silver Jubilee.
It's surprising they wouldn't help you at least find a Mesa authorized tech nearby.
They most likely assumed the warranty was already void on the amp, which makes it not their problem.
I guess good used Mesa amps are their greatest competitor!
The stupid thing is they don't need a mute circuit ! I v'e ben using Relay switching in my 2 and 3 ch amps for years. Just using the old snubbing cap method keeps it plenty quiet while switching .
I took it to the only tech in the province and got it back 3 months later with the same issue. The roadster that you fixed was 100% silent and my mark 5 still made noise. Long story short, I want to thank Mesa Boogie for steering me back to Marshall
Interesting schematic errors. The schematics I've found online for my Mesa's (original 3ch Recto, Studio Preamp) appear 100% correct, at least for the work I've done on them. Either way, Mesa crams so much on their pcb's - working on them is truly a test in patience. Nice work buddy!
Thank you for the update. I'll never buy a Mesa amp. I want my amps to have accurate schematics. So they'll be easier to repair.
I had heard this rumor from several techs, but never saw it personally until now.
Don't know if it is intentially. My experience is that a lot of designers are just very inconsistent (especially in the older days). Errors were just fixed by hand on paper.
True, it is very difficult to tell whether these mistakes are careless or intentional ones. How can we ever know for sure?
esquehill . I don't really see a reason why someone would do these things on purpose. It's not rocket science to figure out the correct values etc
im not aware of other amp schematic errors.
Coupling capacitors sometimes drive me crazy; When I'm using my pedal chain with my modified clone of vibrochamp sometimes accidentally short the out pedal jack with the tip of the cable and it just stop the signal until i short the first coupling capacitor on the amp. I finally modify the circuit to drain slowly that cap when it happens and avoid open and open my amp to short it manually. I think it has relationship with the pedals power source, the high noise when the jack short happens, but i don't know exactly why. In this case that mix of voltages with solid state and tubes maybe can cause something like that, just a theory i don't know.
Same with current Marshall schematics. I needed one a for a JVM 210C, good luck!!. A customer wanted a choke added to which I have it figured out but trying to get a schematic would be like getting a pardon for Charles Manson.
I was looking at the schematic for the Engl Fireball recently and thought the same thing. Seems like the one that’s publicly available wouldn’t work … or would at least sound terrible.
Nice!!
I'm confused about the transistors Q1, Q2, Q3 being "DC Coupled" meaning they don't have any Inter-stage Capacitors? Any reasons or Advantages of using "DC Coupled" transistors in a row because most audio circuit have those inter-stage block capacitor per each stage section to block dc voltage from the previous stage output to the next following stage input, which Mesa Boogie used DC Coupled topology instead for a reason or advantage.
It's funny how Mesa jumped on you for working on it. Not surprising.
On the eq circuit, what role do the inductors play? Do they act as filters for certain frequencies?
You're the man. Thanks again.
5:50 - looks like the conductor track near the electrolytic capacitor is damaged.
Just as well you were awake to it bro.
That is some barebones discrete op-amp there ;-) I wonder why Randall Smith didn't go for gyrators instead of inductors, maybe BJT's were still a little pricy back then?
He he he , There was a guy in Japan , who was nuts about Mesa Amps so much so , that he started a company called Mesiah Engineering , and built stuff that looked like Randalls stuff , but was off on component values ,and such . It did use the same tube compliment ( although Jap , , NEC brand ) ,and an imitation of that big 12 inch speaker. I have the 100 watt version of a MK 2 , ish , and he made a 50 watt version . Randall Smith went over there , and unleashed some legal shit to stop him .. Since then its been like ,, Oh , Poor Randall ,, now show us on the dolly where the Naughty Japanese man touched you.. Seriously , the guy does things that have been done for years , and patents it as his own technology..
Randal made some good amps too.
Minute 9:02: looks like a trace is lifted right at the negative lead of the 160V 10uF cap.
What other tech channels do you subscribe to? Besides fanlab.
Question. I have a Peavey xxx used to sound great but now it's a buzz bomb and has a squelching pop when cut off. I re soldered the tube sockets but didn't help but I noticed two out of the four tubes burn blue other aren't. Switched them into the different sockets and the same sockets that burn blue had the ones that weren't burning blue. They all use to burn blue. Resistors?
To reply to myself. It was the resistors
one thing else you should consider,
a leak in the circuit board itself !
I have come across this myself.
You can tell that there is something fishy about this schematic right away - Q4 has no connection to the output except for a 10 pF capacitor, and that's just not right. Q2/3/4 form a simple operational amplifier, with Q2+3 being the differential stage and Q4 the VAS, with a negative feedback network going from Q4 emitter to Q3 base. Q4 emitter (plus maybe an output coupling capacitor + series resistor) should be the output, with a decent amount of current drive capability at audio frequencies. A 10 pF makes a good coupling capacitor at VHF, not audio...
It's a bit of an odd design anyway. Q2 seems to be geting all its collector current from Q4 base with no extra resistor, leaving differential stage balance at the mercy of Q4 beta variation. Yeah, it obviously works, and it's not hi-fi anyway, but...
I ran a small sound company based on good tech the representative of buggy amps brought his sample by is had a problem in its EQ so he got me copy of the factories schematic it was wrong I went round and round with it till I realized the information was wrong them it was a easy fix so why to there do this to themselves?
Its alive!! ITS ALIVE!!!!!!
Interesting about Mesa messing with the schematics. Because of that, I will never buy one. That’s just ridiculous.
Well ain’t that some shite. I called it. It’s a handicap to start you in a hole with your repair... wait Brad, didn’t you test the orange cap on the eq board with the tiny tester and it showed “shorted”? I was thinking you had... oh well, you are still rocking in my opinion!
This is the usual....Moog did it, also roland and korg in their vintage stuff, but mainly to keep out these "MeeToo" copy engineers/companies at the time, not to confuse the repairmen....but these "altered" schematics are what is to be found out the net...as these copy companies usually filed and sold all of their stuff to someone else who only was interested in making more money...so they also sold these formally hart to get stuff for a usually tripple digit count....and that´s what we have to deal with today...all these "altered" schematics...
So the best thing is: always draw your Amps circuit first and then check it against the one you got from the net somewhere and always use common sense when doing repair...it´s not as complicated in an amp, but way more complicated in a (modular/polyphonic) synthesizer with 5 or more PCBs, my personal mighmare was the memory moog, known to be unstable due to heat and bad PCB design....also there´s no free to download schematics which are known to be correct. you alsways need to contact a professional and authorized schematic comany, or you need tio know a tech who already did ona these without failure....
Brad the cap you replaced looked to be a coupling cap from eq switch and i also didn't see that cap on the schematic.
That's what it was...a coupling cap designed to prevent DC leakage back into the main board circuit, including the effects loop! So if that cap was already leaky and on its way out, it makes sense that the customer would have experienced issues with the effects loop.
Man, that looks very heavy besides its sound.
Roland 120 choures ???? xoxo
Send all Mesa repairs to Mesa cause I ain't touching them.
Been standing in the street naked screaming "Long live the guitalogist." (as suggested), for the last 2 hrs. You probably lost a few subs, and I've got to submit to a court ordered psych evaluation. Lol
But it was fun though, right? ;)
The Guitologist yeah, i usually run around the neighborhood naked, with a rubber glove on my head yelling "Help, im a squid!!" . That was probably much more fun than you had restling with this mesa. amp.
Many put errors in their documents. Even DaVinci did it.
Mesa admitted to me they were doing this in the early or mid 80s.
Service Above Self.
Shucks...now i have a strange craving for tic-tacs...wierd😲
I thought I saw a cold solder joint next to the capacitor you replaced, Brad. Am I wrong? Look at the footage really closely. Those two resistors. Maybe the two 3.3k resistors? Maybe the pad lifted? It's connected to the one next to, what's it say? 1992? 1982? Then the next rail and then the next transistor? Another cold solder joint? I see that in the video right after position 8:44? Tell me anybody if I'm seeing things that can be misconstrued by a video. I'm not anybody that can be anything near Brad. One reason I watch his videos is because I hope I can learn from him. Js. Ugh.
Did you silicon the EQ caps?.
I wasn't going to, but might not hurt to do the two larger ones.
Yeah you know how gravity works lol.
I do. Thanks for reminding me.
The small electrolytic cap on the EQ board seems to be connected to a trace that is lifting off the board. Might be worth another look.
I dont know why they do that!!! Specially with the Rectifier since they basically copied Soldano´s SLO preamp LOL
You are on point but need more views ? AMP PORN or baby metal rig or live shock fun day?? great job as a n amp luther ??xoxoxo
I hope that was natural cure silicone, not acid-cure, otherwise those PCB traces are at risk of acetic acid attack.
Mark Tillotson Absolutely. Electronic grade, 100% pure Silicon neutral cure is the only way to go. Brad would be onto that.👍
One of the major tube web sites had a page for M*sa/b*ogie schematics and recently i went there and found a letter from M*SA threatening prosecution if the drawings were not removed.
So i know they are rather tight with there stuff.
I've always used a hot glue gun. Is there a benefit to using silicone?
Hot glue is considered the wrong material for this application by techs because it can be corrosive, can become conductive, and doesn't hold well long term under heat.
Silicone doesn't melt when it gets hot. Never use hot glue on any amp.
Lately , I've been using liquid electrical tape . I only use it to bed down a large component .
I've seen lots of errors from reputable manufacturers. Intentional? Can't say. But I'll bet the collector of Q4 goes to the EQ output as well, which is not what's shown. The output cannot come from the base of Q3. Q3 is the negative feedback input side of a differential amp. Lots of things not right with that schematic. Guess we'll never know unless you get another one on the bench.
It ain't no SVT. The heater connections near the pcb often break.I'm done with Boogies.All of them.
the cooling fan would really annoy me if i could hear it, id have to swap that out, is there any benefit to cooling the tubes with a fan ?
When there are SIX of them and this was in a rack, the fan would be almost necessary on hot days at outdoor gigs, for instance.
Cooling fans don't seem necessary until they are.
In my younger years (before I knew you could fix solid state amps) I had a gk700rb. The fan went out on it and it'd easily over heat in our conditioned practice spaces. We were in high school slightly before the internet was a big deal and we couldn't find a fan that fit.so I left the cover off- so I took a giant floor fan pointed down over it everywhere we went. I never had a problem after that but it looked ridiculous and was a pain to haul.
It's a bass amp. If you can hear it you're doing something wrong!
When cranked at 400 watts, if you can hear the fan, you are way too close.
Most electronics like the cool.
another reason I do not like Mesa
I hope my Tri-Axis never needs service, it's a freakin nightmare inside
It's also possible that the schematic was accurate at one time, and they changed the design without documenting it. Wasn't Boogie fairly well known for flying by the seat of the pants on some of their designs?
Mesa HAVE ALWAYS FLOODED SCHEMATIC SITES WITH INACCURATE FILES. I do work on mesa amps and they will send me schematics that are watermarked with my details and I have to sign a contract saying I will not pass the files on.
Now mesa is no longer anything to do with Randall...how about you let off some accurate schematics and help out those poor sufferers?
What did Randall Smith and his wife thumb this down? Who would thumb this down? WTF
Oh Randall must have got one of his kids to jump in to there is now 3. SMFH!
Wow Randall must have the whole family in here too.
I would just be happy to have a schematic to begin with, how many electronics can you get schematics for,almost none.
Errors are common on schematics and to think they are purposeful is tin foil hat shit
Don't know why he'd do this boogies aren't that great
It’s more likely that whoever drew up the schematic (and it does look hand drawn, to me), probably was in a rush, and forgot to copy down the component values. As for “errors”, this could have been for a different board revision. Given how simple something like this guitar amp is compared to, say, a computer motherboard, it’s too easy to reverse engineer a “true” schematic from a working prototype. We’re talking point-to-point wiring and single-layer PCB’s here. As long as there aren’t burned-up (or missing) components, or semis with the part #’s rubbed (or etched) off, it’s pretty trivial (if tedious) to make a schematic for this. It makes no economic sense to make deliberately “fake” schematics; the company would risk having these end up in “authorized” repair centers too - or worse - make it back into internal “official” documentation! Then they’d be buggered! 😎
wow this isnt common practice? I guess its a dick move if you ask for the schematics and they agree but send you wrong ones on purpose, but who knows happened, they do it all the time by default in other industries like software, obscuring code, map makers would put errors in their maps to see if anyone just copied so from that perspective i can understand gaurded attitude of some of this technology although i prefer open source I dont see the big deal
A good reason not to buy a Mesa.
I would be pissed getting my amp back from service and seeing silicone all over the place like that what you should have done is to put a small bead under the cap prior to soldering it in so it would be direct contact to the board then there would be no need for it on the top and all over the place at all.
If your Knowledgeable enough to open the amp and check the repairs and the vanity of them why would you send it out rather than repairing it yourself?
Amps are not my specialty, I'm a master computer hardware tech been in IT and electronics for over 25 years so I know a thing or two
Boogie make constant minor changes to their amps - I think that’s more likely than deliberate falsification - great video!
Welllll really now ewwwwwww lol...not to my knowledge man lol
If the schematic is not accurate.why bother including them. Corp are evil.
nothing but photo of eq Schematics for hole vidio
as if someone would like to copy this farce of an amp... incosistent,floppy, slow,expensive,...
I was looking at the schematic for the Engl Fireball recently and thought the same thing. Seems like the one that’s publicly available wouldn’t work … or would at least sound terrible.