LesPaulopolis
New Member
Are you saying you were able to create replacement "MIDI switching chips" in case you experience the dreaded 6100 MIDI fail / stuck on one channel problem?
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6100 channel switching problem
- Thread starter bennieusmaximus
- Start date
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Yes, that is what copying an EPROM firmware to file and having an EPROM burner allows you to do. I do this with all of my stuff if it has a microprocessor / EPROM setup. Most of the time, I have found that on the 6100 series, it is not the EPROM that fails but the M5201 op-amps. Replacing those with NJM2121D switching op-amps usually solves this. The 93C46 OTP PROM in the 6100 per the datasheet will have a lifecycle of over one million startup cycles and is a very difficult chip to erase. Usually only a catastrophic failure (dead short) causes this chip to fail and loss it firmware program.
Jonathan Wilder
Well-Known Member
Ah I see it now! It's flash EEPROM!
I was getting the program ROM (the 2764) confused with the data EEPROM that they're using. Not sure why I didn't see it before, but of course this wouldn't need a backup battery as it is flash ROM.
So basically if I'm seeing this correctly, off of Port 1 of the 8031 they're psuedo-bit banging serial to communicate with it (since the on chip UART is tied to MIDI)?
Jon, correct. All three of the memory / processor bricks code files together only add up to about 5kb worth of machine code programming. Considering that in 1992 no other amp manufacturer was even doing anything like this for amp channel switching and damping circuit the amp was ahead of its time and the circuit to me seems to be unique due to that and some other features in the amp.
Regards,
Norm
Regards,
Norm
Jonathan Wilder
Well-Known Member
Got it.
Yeah I found it odd that they were making the JMP-1 around the same time and that they didn't just use a 6264 RAM chip/backup battery arrangement like the JMP-1 does. However, the JMP-1 is a bit more complex than the 6100 whereas the 6100 would be way underutilizing the capability of the uC/memory arrangement in the JMP-1.
I'm currently working on a MIDI decoder for one of my amp models that's still in the design phase. It will operate similar to the JVM in that everything will be "learned"...MIDI channel assignment, preset changes, etc etc. Unlike the JVM you will also be able to map the front panel buttons to instant access switches on MIDI controllers that are equipped with them. It's all based on the PIC uC family as they have an EEPROM on chip and they're easy to program.
One of these days I'd like to learn the 8051 family of microprocessors even though they're ancient. Seems that every guitar related MIDI device uses them for one reason or another.
Jonathan Wilder
Well-Known Member
Ya know it's interesting...I started a thread awhile back that was a poll to have a statute that only qualified techs should be posting up tech information in order to keep the tradition of the Marshall Forum having only correct, valid, corroborated facts for tech advice. There are far too many sites and forums out there that continue to spread nothing but misinformation about amps being all about so-called magic, mystique and mojo and we want to set ourselves apart from those sites, making it the best place to come for rock solid information.
The question was asked (not word for word but along these lines) -
"Well that's not really fair. I mean...who gets to decide who's qualified and who's not?"
And I stated -
"Very simple...if you know what you're talking about, you won't feel intimidated when you're challenged and you'll automatically be able to demonstrate that you know what you're talking about through the use of rock solid laws, math, engineering data, reference material, etc etc".
This thread is a PERFECT example of such! Norm came on here as a new guy and just by the things he was saying I could tell right out the gate he knew what he was talking about. Furthermore, I challenged him on something because he mentioned something I had never seen on the 6100 schematic.
Did he react in a way that showed that he felt intimidated, cornered, or get on a defensive? NOT AT ALL! He told me to take another look, which prompted me to do so. Sure enough...Norm had his bases covered and I figured out something I had previously overlooked!
THIS is how we decide who knows what they're talking about and who doesn't. The ones who do don't have to ask super basic questions like "Should I ground the chassis when draining filter caps?" or "My amp is dead. I know it's not the valves cause they're still glowing", "Can I operate my amp out of standby with no load connected and no valves installed?", "I tried biasing my amp by reading pin 8 and I get no reading" yet there's no 1 ohm cathode resistors installed, etc etc, don't get defensive or feel cornered/intimidated when challenged...and are able to demonstrate using nothing but solid fact are the ones who know what they're talking about. If you're asking questions such as the ones listed above, you get defensive when challenged on tech info, you have a tendency to use the "red hearing" approach to save face when proven wrong (i.e. calling a certain tech's name and reputation, how many people/big name people play their amplifiers, etc etc...into question)...that is a sign that you're not qualified to be giving tech information.
I hope this answers that question.
The question was asked (not word for word but along these lines) -
"Well that's not really fair. I mean...who gets to decide who's qualified and who's not?"
And I stated -
"Very simple...if you know what you're talking about, you won't feel intimidated when you're challenged and you'll automatically be able to demonstrate that you know what you're talking about through the use of rock solid laws, math, engineering data, reference material, etc etc".
This thread is a PERFECT example of such! Norm came on here as a new guy and just by the things he was saying I could tell right out the gate he knew what he was talking about. Furthermore, I challenged him on something because he mentioned something I had never seen on the 6100 schematic.
Did he react in a way that showed that he felt intimidated, cornered, or get on a defensive? NOT AT ALL! He told me to take another look, which prompted me to do so. Sure enough...Norm had his bases covered and I figured out something I had previously overlooked!
THIS is how we decide who knows what they're talking about and who doesn't. The ones who do don't have to ask super basic questions like "Should I ground the chassis when draining filter caps?" or "My amp is dead. I know it's not the valves cause they're still glowing", "Can I operate my amp out of standby with no load connected and no valves installed?", "I tried biasing my amp by reading pin 8 and I get no reading" yet there's no 1 ohm cathode resistors installed, etc etc, don't get defensive or feel cornered/intimidated when challenged...and are able to demonstrate using nothing but solid fact are the ones who know what they're talking about. If you're asking questions such as the ones listed above, you get defensive when challenged on tech info, you have a tendency to use the "red hearing" approach to save face when proven wrong (i.e. calling a certain tech's name and reputation, how many people/big name people play their amplifiers, etc etc...into question)...that is a sign that you're not qualified to be giving tech information.
I hope this answers that question.
Tickling neurons I guess could be a good thing. I agree with Jon, I have seen this site for many years and have never posted. I decided to post for two reasons, my love of Marshall amps, their tone and glory inspire me every day and got me interested in electronics and two to try to get the right information out on the net about stuff I have seen that is just incorrect. Hopefully somebody got some information from me and Jon discussion today and can get their amp up and playing again because believe me a Marshall 6100 deserves to be played.
Regards,
Norm
Regards,
Norm
Jon, that is an interesting idea on the midi decoder to be a memorized fuzzy learned logic. It's gonna need more then 5kb of code to do that, that's is for sure. I would like to hear more about it.
Things have come a long way with logic chips and good algorithm programming. I believe the day will soon be here when an amp manufacturer comes out with a firewire or usb controlled tube amplifier circuit that can configure itself to be any type of circuit and not be a modeling amp. Hope everyone sees the humor in that statement.
Things have come a long way with logic chips and good algorithm programming. I believe the day will soon be here when an amp manufacturer comes out with a firewire or usb controlled tube amplifier circuit that can configure itself to be any type of circuit and not be a modeling amp. Hope everyone sees the humor in that statement.
Joey Voltage
Well-Known Member
while certainly possible, and an inexpensive fix, the thing that doesn't sit right with me is that the op stated that when it is stuck, it is stuck on channel three, and the gain pot doesn't work, while the rest of channel three does (channel volume, and tone controls), in this circuit there is really no isolation between channels except the IC's.... which would be the most "likely" suspect, however my spidey senses are tingling a bit and am not too quick as to dismiss their drive/trigger circuitry either.
I really hope you are right!
Joey,
At .65 cents an op-amp plus USPS shipping all you will be out is about $8 so you will have a box of rocks that cost $8 bucks more if it doesn't work! If it works you have an amp back, you fixed it yourself from "free information" on the internet, it only cost you $8 and you didn't pay some tech who will tell you one of two things, he fixed it and it was the most complicated repair in the world and is gonna require another economic stimulus (out of your pocket again) to pay for it or he will tell you he can't fix it and is still gonna charge you a smaller economic stimulus (once again out of your pocket). Hope you get my drift.
Good luck,
Norm
Jonathan Wilder
Well-Known Member
Oh believe me...MIDI has gotten a bad rap as most think it processes the audio itself when all it does is give you a means to control analog audio.
I code in assembly and believe it or not I've got the code learning the presets with nowhere near even 2K of ROM. It doesn't read the pot settings. It only does the function switching like Channel Select, Solo Select and FX Loop Select. You can create presets that call up those 3 functions in different combinations.
Say you want a dry clean preset. Select the clean channel and switch the FX loop off, then program that preset.
Then you wanna be able to go from that to wet overdrive with solo boost active. Select overdrive with solo active, select the FX loop, then program that preset.
Also, the panel switches that control each function are mappable to instant access buttons on controllers that are equipped with them so that you can switch each function on/off individually. It's made to work with everything from the dumbest of dumb MIDI controllers to the most sophisticated of MIDI controllers.
On top of all that, you can also have it learn the MIDI channel as well as restore the pre-loaded set of defaults as well.
Joey Voltage
Well-Known Member
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My apologies. What were you trying to get across to me? I will be glad to help.
The .pdf attached is the datasheet for the NJM2121D switching op-amp used in the 6100 series VCC controled channel switching circuit for the 6100 series amplifier. This circuit is a very smart design! Some would say it is flawed because it uses this op-amp instead of a switching relay. For the 6100 circuit all low level signal voltages from the three pre-amp channels route through these op-amp switches. The switch is also an amplifier, hence the objections from some that it ruins the tube "tone" of a guitar amp because you have essentialy replaced the tube signal output of the three pre-amps with a op-amp or solid state device. The switching function is controled by the VCC circuit output from the 8301 microprocessor CPU. If you would like to discuss further how this circuit works, I will answer all questions.
Regards,
Norm
Seems the file is to large to upload to the forum server. If you would like to get the file just Google or Bing NJM2121D and you will find sites were you can download the datasheet for your own use.
Regards,
Norm
Seems the file is to large to upload to the forum server. If you would like to get the file just Google or Bing NJM2121D and you will find sites were you can download the datasheet for your own use.
Last edited:
Jonathan Wilder
Well-Known Member
A lot of people flame SS devices due to their transparent nature and the way they distort. Me personally, an SS device located after a valve preamp that's running from a supply with more than enough headroom to reproduce the signal fed into it without clipping is just fine. It's only reamplifying what you're feeding into it. It's not "coloring" the tone if the circuitry around it is transparent.
But some people don't get this.
Valves in and of themselves are not transparent as they exhibit a non-linear region in their operating curves whereas SS devices do not. SS devices are tonally transparent...but we guitar players claim not to like this. However, it all depends on where you place it in the signal path! If the signal was first ran through a valve preamp, all of the overdrive and tone shaping was done in the preamp, then through a high headroom SS circuit, the SS circuit is only amplifying it exactly how it came in.
However, it is when SS is used for overdrive and tone shaping that it becomes undesirable. As long as SS circuits are kept 100% transparent, they can be a very good thing.
For the record...FETs and MOSFET transistor act very much like valves.
SigurdTheGreat
Member
This thread is internet as its best. As a 6100 owner, it has restored my faith in humanity. Thanks, gentlemen!
A lot of people flame SS devices due to their transparent nature and the way they distort. Me personally, an SS device located after a valve preamp that's running from a supply with more than enough headroom to reproduce the signal fed into it without clipping is just fine. It's only reamplifying what you're feeding into it. It's not "coloring" the tone if the circuitry around it is transparent.
But some people don't get this.
Valves in and of themselves are not transparent as they exhibit a non-linear region in their operating curves whereas SS devices do not. SS devices are tonally transparent...but we guitar players claim not to like this. However, it all depends on where you place it in the signal path! If the signal was first ran through a valve preamp, all of the overdrive and tone shaping was done in the preamp, then through a high headroom SS circuit, the SS circuit is only amplifying it exactly how it came in.
However, it is when SS is used for overdrive and tone shaping that it becomes undesirable. As long as SS circuits are kept 100% transparent, they can be a very good thing.
For the record...FETs and MOSFET transistor act very much like valves.
Well said Jon. I have no problems with the SS device after the tube pre-amp stage. People who get upset about it and then plug an effects rack into the effects loop are not seeing the hypocrisy of that action. It is doing the exact same thing as using an op-amp to buffer and control the pre-amp section that Marshall used for this circuit. I am working on ideas and product data to find and install a better op-amp switch at these locations because this series of op-amp is becoming obsolete, they are "old and slow" by today's standard of op-amp audio performance, hence there is room for improvement in what I saw in 1992 as a revolutionary audio switching circuit.
This thread is internet as its best. As a 6100 owner, it has restored my faith in humanity. Thanks, gentlemen!
You're welcome.
Regards,
Norm
Joey Voltage
Well-Known Member
Norm,
with all do respect, I am aware of how the circuit works, and the implementation of the M5201A "switching" opamps which Marshall has used in probably every amp they had produced in that time period. I agree that it would be a cheap fix, and great if it works, however I have some doubts that the opamps themselves are the true culprit, and with shotgun approaches you sometimes never do find what truly caused it. I personally would just do some basic poking before replacing anything. especially around the outputs of the D flip-flop when the fault occurs, which is routing the switching supply/trigger for the opamps, channel LEDS, amongst other things.
another thing... you don't find the op stating that the gain control of channel three doesn't work a little odd? when everything else for that channel does.... , the gain pot theoretically should work shouldn't it? if the channel volume, and tone controls for channel three do when it's frozen on three. There is no other isolation between channels prior to that opamp switching block Except for one thing.......the FET which shunts the gain pot for channel three with that massive 220n capacitance, the same trick Marshall used to pseudo isolate channels in their primitive 80's switchers 2205/2010, and guess where it's gate is connected? one of the outputs of that D Flipflop, which to me is the least common denominator before trouble shooting the dreaded.....
so my point, and my spidey senses where telling me to urge that measurements be taken, and poke there... and to keep options open, not jump to conclusions so much. nothing more, and certainly no pissing match, if thats what it happened to seem like. all of which also too are provided without the fee of stimulus monies
-Joey
