Is it possible to damage the input amp....

[daz]

....on a SS amp but hitting it with too hot a signal? I have a modeler and i tried jacking the volume and gain on a tube screamer type pedal with the gain lowered on the amp and after that it started sounding like blocking distortion. I'd hit a note and it would be low in volume then a slit second later jump up to normal volume. turned the amp off and the problem was gone when i restarted it. But now and then it starts happening again usually after playing it longer than usual which makes me wonder if theres a op amp thats damaged at the input that once hot enough causes this. But if i turn the amp off and back on it stops, so why would it stop? It's only got a few seconds of cool down restarting it and then it doesnt do it even after more time playing.

[Enzo]

Do you know how LARGE a too hot signal would have to be? Your typical SS amp has 15v rails. To exceed those, your signal would have to peak OVER 15v. That is over 10v RMS of signal. Can your tube screamer pedal produce 10v RMS? If it runs on a 9v battery, it only has about 4.5v headroom. That is 10v short of the 15v cap. and only about 3vRMS of signal.

SO I really doubt you are even overdriving the input, at least in terms of signal level and clipping. Can you be hitting it with signal too large for it to amplify it well? Sure, why not. But that won't damage it, it will just clip the signal.

Now what if I did put 16v of signal into that IC running on 15v? Most modern designs have clamping diodes on the inputs, and for that matter, even on the outputs.

DO you have a selection of PV schematics? A few examples common enough you may already have: XR600B, Combo 300, Bandit (most any version), Heritage VTX, KB300. That is enough, you have any of those? Pick one and look at the input circuits. From the input line you will see a pair of diodes, one to +15 and the other to -15. Those are normally reverse biased to they are not conducting, and are invisible to the audio. If some voltage hits the input and goes above 15v (either polarity), then the diodes conduct and shunt the excess voltage into the low impedance of the power supply. That prevents the input pin of the op amp from being more positive than its power pin. if the input were allowed to exceed the power supply voltage, the IC would think it had reversed power supply. Damage could result.

Now look at a power map like the PV 400BH. You will see reverse biased diodes from the output to either power rail. They do the same thing. Not concerned the amp will drive the output past its rails, but the inductive kick of a speaker sure could.

If your modeling amp does funny things, since most of the amp takes place in the digital world, I'd be more thinking there is some gating or other level control inside the program. ICs have no memory. Well, not unless they are memory chips.

[daz]

Thats what i figured but it would be a coincidence of monumental proportions if thats not what caused it. You know your stuff damn well and i don't doubt you. But maybe this amp is different, bad design at the input or such? Lets look at the facts.....owned it (fender mustang GT) since it debuted about 8 months ago. Been thru numerous updates sometimes forcing the same update thats installed, even going back to the original and updating from there. All to try and solve other issues. (tried a forced UD for this issue, time will tell if it helps) And thru all that time and updating it never once did this. Then one day i tried what i said with that pedal and soon as i did within seconds the symptoms started. Since then it's done this now and then bet never before this. The only think i can think of otherwise makes no sense to me, but i'm not a programmer or such so maybe it;s possible? That being the thought that somehow a very hot input signal could affect the firmware? Is that even possible? If it is maybe the forced update will indeed do the trick, but like the idea that a hot input signal could cause hardware damage, this too seems impossible.

I never imagined a pedal could do this but as u can see from what i said about the timeline it looks impossibly coincidental that it didn't. Like i said, i don't doubt your knowledge but theres got to be some reason why in this case your theory given the details i just outlined. I don't have a schematic and i don't think fender has released one for it, as it's i believe designated non field repairable. Thanks for your input.

[Enzo]

Well, everything works until it doesn't, and amps are most likely to fail while in use. SOMETHING is happening when anything occurs. If the car across the street happens to honk its horn at the same moment my cable goes out, should I find them related? Maybe there is some related factor I have not considered, but I believe in Occam's Razor.

Firmware is the memory IC that stores the program. It is a digital version of an instruction manual. The signal, good bad or indifferent, has no way to change the program stored in ROM, any more than playing one's amp can alter the schematic.

Sometimes coincident things ARE related, but correlation is no proof of causality.

The following is a true story. I was working on something once, and I could hear a beeping sound, so I turned it off and the beeping stopped. I looked at the manual for a clue, maybe it was an indicator? Turned it back on, and the beeping returned. A few seconds of that and I turned it back off and opened it up. Ready with my scope and meter, I turned it back on, and sure enough the beeping returned, but this time when I turned it off, the beeping continued. WTF? I unplugged it even and still beeping. And about then I realized that there was a dump truck out in the street, and it just happened to back up at exactly the same time I had turned my unit on and off. The sound was bouncing around and sounded like it was coming from my bench. I had heard the beeping truck. Total coincidence, totally unrelated, shit happens.

I can't tell you nothing happened to your amp from signal level, I just think it unlikely.

Another true tale from the bench. (I know I have told this before) I was working on an amp and about every 45 seconds, it made a hum noise out the speaker. Lasted just a few seconds then stopped. But 45 seconds later it does it again. I spent an hour or more trying to track down that intermittent hum. At one point I left it running and stepped out on the front steps for some air. I could still hear the hum cycling on and off. I happened to look down the street, and noticed the hum was exactly timed with the traffic light at the corner. Turns out there was a noisy triac (or whatever they use) for the yellow light on one direction. And whenever that light was on, it sent a bunch of noise down the electrical wires. Plugged the amp into a mains line filter, and voila, noise gone. SO there was an example of a correlation that WAS a causation too.

[daz]

Those things don't surprise me I've experienced my share of electronic ghosts. I think this is a bit too focused tho. Happened right when i tried that pedal cranked fully as never before, so i know thats got to be what caused it at that point. Whether or not the random continuation of this issue is related would be coincidence i suppose, certainly more so than that first time. But i doubt it. I just wish i had a damn schematic for it !

[Jazz P Bass]

Maybe there is something wrong with the pedal.

[glebert]

Does the problem occur if you are plugged in straight (no pedal)?

[daz]

Does the problem occur if you are plugged in straight (no pedal)?

yes, i did that and even removed the footswitch so nothing but the guitar was plugged in.

[loudthud]

Got a link to a schematic? The chip that digitizes the signal might behave badly when the analog input is driven beyond the chip's rails.

[daz]

Got a link to a schematic? The chip that digitizes the signal might behave badly when the analog input is driven beyond the chip's rails.

No, like i said above "i wish i had the schematic". But it's N/A far as i know. The question isn't whether a chip in there acts badly, it's whether it's damaged. Because it started by that incident with the pedal, but the fact is when it randomly does it not it's when i'm just playing normally, no boost, just a fender with vintage single coils.

[Chuck H]

You cooked it's 9's (Steve Martin fans will appreciate that one).

Basically a digital amp is interpreting what your guitar is saying and translating it into a code that can be read by the computer to playback the "this sound" program or "that sound" program. Since the amp isn't failing to read your pick attack all the time I think it amounts to a glitch in the digital arena. If it were one of the analog amplifiers I would expect the problem to occur full time. So, do you have or can you get (online) an owners manual for the amp and does it have a "reset" or "reboot" procedure (maybe to "original parameters" or whatever). You may lose your presets, but it may fix the problem.

[daz]

You cooked it's 9's (Steve Martin fans will appreciate that one).

Basically a digital amp is interpreting what your guitar is saying and translating it into a code that can be read by the computer to playback the "this sound" program or "that sound" program. Since the amp isn't failing to read your pick attack all the time I think it amounts to a glitch in the digital arena. If it were one of the analog amplifiers I would expect the problem to occur full time. So, do you have or can you get (online) an owners manual for the amp and does it have a "reset" or "reboot" procedure (maybe to "original parameters" or whatever). You may lose your presets, but it may fix the problem.

I did a forced update which basically reloads the same firmware that was already in it. (it was already on the latest) There IS a procedure that goes back to the original and wipes out the presets i have made. But the problem with that is they had a change i believe in the server for the firmware and after a certain update (there have been 4 or 5) they said if you don't update by such and such a date you eill not be able to without getting a cable and using some app. It's a wifi update system so like i said, i think that update changed the server location. Thats just my theory but in any case if i go back i will have to buy a cable and download some app and jump thru a bunch of hoops. This amp has had me wearing out a set of hoops at this point so i'm tired and ready to sell it if i have to do that. So if the forced update i did doesn't work it's gone. I would think it should be as good as a reset because a forced update reinstalls the complete firmware, not just the parts that are new as a normal update does. So if it IS a firmware issue i think thats as likely to fix it as a reset. I've had more issues with this thing than i can count and i'm not willing to go any further if this forced UD doesn't fix it. I had the predecessor to this one for 5 years w/o a single hitch !

[Chuck H]

It reminds me of trying to use Windows 10 with my old pooter. Just too many old drivers that weren't compatible with the new OS and too many new drivers that weren't compatible with the old hardware. So I switched back to 7, but it was never the same. The switch back was supposed to be complete, but somehow it never was and I had snarky little gremlins ever after. Nothing that would keep me from using it effectively, but occasional annoyances. That sort of thing would be absolutely unacceptable for the creative process or in a live playing situation when it comes to amplification. That said (and you knew someone would say this ) I never had an encoding error with any of my tube amps.

[daz]

That said (and you knew someone would say this ) I never had an encoding error with any of my tube amps.

True, but I had other problems with tube amps and i find modeling today as good sounding/feeling in some ways, better in others, and not as good in others. (actually just ONE other i can tell) The overall verdict....just as good but with a zillion advantages. My combo weighs 22Lbs, and thats not a typo ! Every built in effect imaginable including 3 different EQs. Built in tuner. Switching between a bunch of different sounding models and effects. No biasing, no blown tubes or $ spent on them, i could literally go on and on. And trust me, it FEELS like tubes and responds like tubes with the same dynamics that let me roll my volume down and go from clean to total dirt on 10 or control dirt with attack. Actually does that better then most master vol tube amps. Theres one thing tube amps, at least most of them do better....they tend to have a more natural and extended top end. But not ALL tube amps. Just like there are trade offs with a tube amp, there is that one with a modeler. But thats the only one i can think of. The majority of those who feel tubes are better IMO feel so because they are using FR amp/speakers. IMO the trick is to have a regular analog output stage and guitar speaker and cab as mine is. IMO FR solutions will never sound quite right because using a regular guitar output and speaker/cab lets you ignore that part of the equasion and concentrate on getting the amp model itself right. There are tons of guys who weren't happy with the helix that finally found nirvana using the combo i have or a katana combo after having tried a tone of FR's. Speaks volumes. Modeling is here, and those who don't believe it just haven't heard the right one tweaked correctly, which can and does take time. Thats thier disadvantage....many walk away thinking tubes are best because they have played tubes forever and know what they can do but never really heard the modeler even after spending hours playing them. They have infinite possibilities for tweaking and can be tweaked to sound mediocre far easier then great ! Being a amp designer you should understand this. Think of tweaking a modeler like designing an amp. It's not easy is it? But once you do then people can buy your amp and have great tone immediately, using the 5 knobs just to fine tune it in minutes. With a modeler you're presenting the user with a blank turret board and a box of resistors and caps and YOU have to design it. Having done both i can tell you theres really no difference except that you use a data wheel instead of a soldering iron ! Thats what keeps modeling form totally dominating tubes IMO. But that time is coming and fast as companies start working around that as a few now are like the kemper 'profiler" with custom profiles not designed for 12 year olds in thier bedrooms with 63 effects going simultaneously.

[Chuck H]

Glad you like it. Sorry it's broken.