I have been trying to repair my Fender FM212R with little to no knowledge. Looking at the schematics for the first week was like looking at the Code in The Martix. So I went in search of info. I found more info (good and bad) about Tube Amps but Solid State seems to be an after though. I mean there are plenty of people offering their two cents about what's wrong and what to look for (and I appreciate all of you) but I was looking for info on how SS amps work. I finally came across an article that does just that. This fella goings from the beginning lays down the theory and the problems designers went through and how they overcame them. Its a great article if you are interested in stepping beyond guessing at what might be causing the problem into understanding what's going on within the circuits and opamps and so on.
I would like to have a discussion on this topic and maybe we can see what problems others have had and what they have tried to solve them. Maybe some of us can avoid making the same mistakes and such.
I would like to have a discussion on this topic and maybe we can see what problems others have had and what they have tried to solve them. Maybe some of us can avoid making the same mistakes and such.
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Keeping things cool
I have learned from this article why an SS amp has a + power rail, - rail and a ground terminal coming out of the transformer. AND with that explained, it goes on to explain that the motion of the speaker cone in and out is the result of transistors switching the circuit from the - rail to the + rail back and forth at a very high rate of speed. I always assumed the speaker moved because of a wave form being carried on the current in the circuit or something like that. This was a big eye opener to me.
The amp has a fair sized heatsink attached to the PC board, which is where four of the transistors are mounted because they get WAY hot. In fact the article states that these output transistors run hotter than they are designed to handle and still they work.
I am wonder if people have tried other methods for helping the heatsink to do its job. For instance, there is a device known as a Pertier
https://www.sparkfun.com/products/10080
I have used them in the past to keep an over clocked CPU cool.
You have to add a finned heatsink and a good fan to the hot side of the peltier. The result is the cold side gets real cold. I was always worried about moisture becoming a problem but it never was (to my knowledge).
BR
I have learned from this article why an SS amp has a + power rail, - rail and a ground terminal coming out of the transformer. AND with that explained, it goes on to explain that the motion of the speaker cone in and out is the result of transistors switching the circuit from the - rail to the + rail back and forth at a very high rate of speed. I always assumed the speaker moved because of a wave form being carried on the current in the circuit or something like that. This was a big eye opener to me.
The amp has a fair sized heatsink attached to the PC board, which is where four of the transistors are mounted because they get WAY hot. In fact the article states that these output transistors run hotter than they are designed to handle and still they work.
I am wonder if people have tried other methods for helping the heatsink to do its job. For instance, there is a device known as a Pertier
https://www.sparkfun.com/products/10080
I have used them in the past to keep an over clocked CPU cool.
You have to add a finned heatsink and a good fan to the hot side of the peltier. The result is the cold side gets real cold. I was always worried about moisture becoming a problem but it never was (to my knowledge).
BR
A useful article for the complete beginner, but bear in mind that the author is (hopefully!) still learning himself so some of the details are wrong or exaggerated. To be honest, it reads like it was written by an opinionated teenager. Good start, but then move on to Doug Self or Bob Cordell (via Horowitz & Hill).
You (or he) may be confusing Class D with Class AB/B.badraven said:
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Mooley, you are correct. It is a lot to read. But its not really a simply subject. In fact you will find within these pages just how inefficient amplifiers really are. AND how we are deceived by retailers.
I figure you have to read this thing at least three times. The first time to get the general idea, second to pick up on all the stuff you didn't catch the first time and third and subsequent times to put it all together in workable use. But hey, its worth it if you want to understand how these beasts work. Being able to repair a given thing means learning how it works and how to recognize what's really happening or not happening.
BR
I figure you have to read this thing at least three times. The first time to get the general idea, second to pick up on all the stuff you didn't catch the first time and third and subsequent times to put it all together in workable use. But hey, its worth it if you want to understand how these beasts work. Being able to repair a given thing means learning how it works and how to recognize what's really happening or not happening.
BR
DF96
DF96
I would imagine that I am the one with the confusion. I'm not posting this to argue about whether the author is perfect. I am posting this because its a good start for me and other novices. No matter who authors something, someone else will always find faults, mistakes etc. Its not about that, its about learning. And this is the first tool I have found specific to SS guitar amps. So how about just enjoying the fact that someone out there spent a good amount of time to give us some insight. There will be plenty of time for finding the flaws. Thanks!
BR
DF96
I would imagine that I am the one with the confusion. I'm not posting this to argue about whether the author is perfect. I am posting this because its a good start for me and other novices. No matter who authors something, someone else will always find faults, mistakes etc. Its not about that, its about learning. And this is the first tool I have found specific to SS guitar amps. So how about just enjoying the fact that someone out there spent a good amount of time to give us some insight. There will be plenty of time for finding the flaws. Thanks!
BR
;3333323 said:
DF96
I have been reading the article and thinking about this "Opinionated Teenager" comment. I noticed when you posted that it was minutes after I posted the article. Unless you have seen the article previously you didn't have time to read anything more than a page or two. I think you skimmed over a few pages and based your assessment on the first page that could be construed as being biased towards solid state amps. If that be true that means you are biased toward tube amps and you took offense to the perceived statement. I'm not going to defend the author because that is for him to do. But I will say this: after having read the article and beginning back through, this is not about proving SS amps are better, worse or the same. It is simply an essay in amp electronics. It is quite fascinating for those willing to read and learn. I can not attest to it being 100% accurate because I am a novice concerning electronics. But I can say this: it is well written and most certainly NOT come off like someone with an arrogance issue. Its simply a training tool.
How about giving it a chance by reading it before you pass judgment. Then when you are finished we can all discuss the discrepancies.
BR
I have been reading the article and thinking about this "Opinionated Teenager" comment. I noticed when you posted that it was minutes after I posted the article. Unless you have seen the article previously you didn't have time to read anything more than a page or two. I think you skimmed over a few pages and based your assessment on the first page that could be construed as being biased towards solid state amps. If that be true that means you are biased toward tube amps and you took offense to the perceived statement. I'm not going to defend the author because that is for him to do. But I will say this: after having read the article and beginning back through, this is not about proving SS amps are better, worse or the same. It is simply an essay in amp electronics. It is quite fascinating for those willing to read and learn. I can not attest to it being 100% accurate because I am a novice concerning electronics. But I can say this: it is well written and most certainly NOT come off like someone with an arrogance issue. Its simply a training tool.
How about giving it a chance by reading it before you pass judgment. Then when you are finished we can all discuss the discrepancies.
BR
Are you trying to fix a guitar amp?
Or learn about solid state amplifiers.
I'd not suggest trying to mix the two together at the precisely same time.
They are related, but *not* quite the same skill sets or information sets.
I took a look at the schematic of your amp, it's a complicated circuit.
Also it is a $200-$300 retail unit, making the cost of repair close to the cost of replacement. So I can see why you might want to try to repair it.
If you state the exact symptoms, in reasonable detail, like what works and what does not, a few things that might work based on what you say.
Also state what the amp was doing when it "stopped working".
First steps:
Check fuses
Check output from preamp. BE CAUTIOUS, if there is a blown output component, there may be enough DC present on the pre-out to blow what you plug it in to.
SO, take ur DVM and check the DC level of the SPEAKER OUTPUT, with all input levels turned all the way down. Also check the DC level of the PRE-OUT, same conditions.
Assuming all are under 100mv MAXIMUM, you may have only and open component and not a shorted component.
It may be possible to find that and repair. But it is still rather unlikely.
To properly troubleshoot this amp, one would need at minimum a signal source, a scope, DVM and preferably a "Variac". Soldering iron, of course.
To be 100% direct, this sort of repair is likely way past your current abilities, and unless you either get very lucky or have the ability to acquire and apply new knowledge at an amazing rate, it's going to be so for a long time to come.
Otoh, if this provides the impetus to learn about solid state amps and venture into building circuits and trying them, all the better. This is a great place to do that!
Or learn about solid state amplifiers.
I'd not suggest trying to mix the two together at the precisely same time.
They are related, but *not* quite the same skill sets or information sets.
I took a look at the schematic of your amp, it's a complicated circuit.
Also it is a $200-$300 retail unit, making the cost of repair close to the cost of replacement. So I can see why you might want to try to repair it.
If you state the exact symptoms, in reasonable detail, like what works and what does not, a few things that might work based on what you say.
Also state what the amp was doing when it "stopped working".
First steps:
Check fuses
Check output from preamp. BE CAUTIOUS, if there is a blown output component, there may be enough DC present on the pre-out to blow what you plug it in to.
SO, take ur DVM and check the DC level of the SPEAKER OUTPUT, with all input levels turned all the way down. Also check the DC level of the PRE-OUT, same conditions.
Assuming all are under 100mv MAXIMUM, you may have only and open component and not a shorted component.
It may be possible to find that and repair. But it is still rather unlikely.
To properly troubleshoot this amp, one would need at minimum a signal source, a scope, DVM and preferably a "Variac". Soldering iron, of course.
To be 100% direct, this sort of repair is likely way past your current abilities, and unless you either get very lucky or have the ability to acquire and apply new knowledge at an amazing rate, it's going to be so for a long time to come.
Otoh, if this provides the impetus to learn about solid state amps and venture into building circuits and trying them, all the better. This is a great place to do that!
Oh how do solid state amps work?
Simple. Really.
little wiggles on the input ---> big wiggles at the output.
You take some amplifying devices (transistors), set them up with bias so that they conduct, and then sequentially create stages, each one take the signal up in voltage and/or current, until the requisite level is reached. Along the way there are things like "level shifting" so that stage one can "wiggle" the input of stage two and also set the bias... then there is feedback from the out back to the input (to reduce distortion and
increase effective bandwidth, and drop gain to a fixed value).
That's "all" there is to it.
Along the way the stupid details muck everything up royally, since nothing works quite so cleanly or simply, but nearly so.
Around here folks chat about "linearity".
It's like peeling a glass onion... layers upon layers, upon layers...
but repair is a different game.
Simple. Really.
little wiggles on the input ---> big wiggles at the output.
You take some amplifying devices (transistors), set them up with bias so that they conduct, and then sequentially create stages, each one take the signal up in voltage and/or current, until the requisite level is reached. Along the way there are things like "level shifting" so that stage one can "wiggle" the input of stage two and also set the bias... then there is feedback from the out back to the input (to reduce distortion and
increase effective bandwidth, and drop gain to a fixed value).
That's "all" there is to it.
Along the way the stupid details muck everything up royally, since nothing works quite so cleanly or simply, but nearly so.
Around here folks chat about "linearity".
It's like peeling a glass onion... layers upon layers, upon layers...
but repair is a different game.
Bear
Bear
Thanks for the input. This thread is not about repairing my amp. I already have a thread concerning that matter. And no, a solution has not been reached yet. The shorted output transistors have been replaced and the amp works now but its still having an issue. If you are interested, here is a link. http://www.diyaudio.com/forums/instruments-amps/226463-fender-fm212r-problems-11.html
I would welcome some insight. I have received plenty of off the cuff advice and a couple different techs have helped me find the short but for some reason the ball has been dropped in the last 10 days. Why I don't know, especially since the main problem has been addressed and corrected. But anyway...
My first and foremost desire is to get my amp working because I can hardly stand the amp I am playing because it sounds like ****. The Fender, despite it being a lowly SS amp, sounds quite good. I mean I would rather have a tube amp but its not in the financial cards at the moment.
My other interest is learning electronics, especially guitar amps. So, this obviously gives the motivating force to learn faster, which I am doing. In the last two weeks I have gone from looking at the schematic with a deer in the headlights stare to understanding parts of the circuit. Now I am learning the power flow and rectification and manipulation. Its like anything, learning to see and recognize what you are looking at. Yeah I know its a lot to take in but hey, the amp is on the bench and I have time and I like to learn. I just wish it wasn't my Fender.
And yes, I have quickly come to learn that this amp is a cluster "you know what". This was my first "Good Amp" and it was a big step up for me back then. All I knew was I wanted a real amp and I asked the retailer and I was directed to "The Real Amp". So next time I guess I'll be purchasing a "REAL" real amp... lol
With all that said, and to answer your question: Everyone has a book or blog or something explaining how tube amps work, are modded etc. This forum is about learning how SS amps work and sharing that info with anyone that has the same interest.
BR
Bear
Thanks for the input. This thread is not about repairing my amp. I already have a thread concerning that matter. And no, a solution has not been reached yet. The shorted output transistors have been replaced and the amp works now but its still having an issue. If you are interested, here is a link. http://www.diyaudio.com/forums/instruments-amps/226463-fender-fm212r-problems-11.html
I would welcome some insight. I have received plenty of off the cuff advice and a couple different techs have helped me find the short but for some reason the ball has been dropped in the last 10 days. Why I don't know, especially since the main problem has been addressed and corrected. But anyway...
My first and foremost desire is to get my amp working because I can hardly stand the amp I am playing because it sounds like ****. The Fender, despite it being a lowly SS amp, sounds quite good. I mean I would rather have a tube amp but its not in the financial cards at the moment.
My other interest is learning electronics, especially guitar amps. So, this obviously gives the motivating force to learn faster, which I am doing. In the last two weeks I have gone from looking at the schematic with a deer in the headlights stare to understanding parts of the circuit. Now I am learning the power flow and rectification and manipulation. Its like anything, learning to see and recognize what you are looking at. Yeah I know its a lot to take in but hey, the amp is on the bench and I have time and I like to learn. I just wish it wasn't my Fender.
And yes, I have quickly come to learn that this amp is a cluster "you know what". This was my first "Good Amp" and it was a big step up for me back then. All I knew was I wanted a real amp and I asked the retailer and I was directed to "The Real Amp". So next time I guess I'll be purchasing a "REAL" real amp... lol
With all that said, and to answer your question: Everyone has a book or blog or something explaining how tube amps work, are modded etc. This forum is about learning how SS amps work and sharing that info with anyone that has the same interest.
BR
Ok, all good then!
The problem is that after the basics, it spins rapidly out of control. Or at least that is my problem. Yours may turn out different. Books start piling up like cordwood at a lumberjack's house... understanding them is another thing.
You can get pretty far with online stuff and what is here.
There was a mention of Horowitz & Hill, "The Art Of Electronics". It will cover much more than just analog and solid state amps, but the writing is superb, so you can actually understand it by just reading. Pricey, go for used if you can find. First edition might be better for basics, and price.
You can build tube guitar amps, even from kits... if you want a pricey type guitar amp... etc...
The problem is that after the basics, it spins rapidly out of control. Or at least that is my problem. Yours may turn out different. Books start piling up like cordwood at a lumberjack's house... understanding them is another thing.
You can get pretty far with online stuff and what is here.
There was a mention of Horowitz & Hill, "The Art Of Electronics". It will cover much more than just analog and solid state amps, but the writing is superb, so you can actually understand it by just reading. Pricey, go for used if you can find. First edition might be better for basics, and price.
You can build tube guitar amps, even from kits... if you want a pricey type guitar amp... etc...
I am a fast reader. 35 minutes would have been enough time to read most of it, but I quickly checked through the first third or so. My comments were quite unrelated to any views the author and I may or may not have about SS vs. valves. You are jumping to conclusions. It is not well written but a bit clumsy in places, which is why I (giving the author the benefit of the doubt) thought it might be by a teenager. The author, whoever he is, is certainly opinionated. I notice this even in the areas where I happen to agree with him. I didn't say he was arrogant; that is your word.badraven said:
Giving a list of discrepancies would not be helpful. As I said, it is a useful article for the complete beginner. The reason I made critical remarks too is that I didn't want anyone to be misled by it or start quoting it as some sort of authority. If you read it carefully you will learn from it. When you learn more from elsewhere you may begin to see its weaknesses too.
Hi,
Your one to talk about jumping to conclusions.
For a document that is attempting to be factual
it is littered with opinions rather than real facts.
rgds, sreten.
Bear
Bear
Yes you are correct, it all turns in to a big tailspin once the basics are set aside. Of course everything in life does that, in my opinion.
I am having a problem identifying the preamp and the power amp section on my schematic. It looks to me that the sections are intermixed. I know where the output transistors are (Q 20 and 21) And I see where the circuit from the guitar input leads in but trying to see the flow through the circuit is hard.
There is something you could clarify for me (us) if you would. On the schematic section D8 - 6 The test points list mVAC for measurements. I don't understand why its listed as AC, this is the DC part of the circuit. And isn't mV a DC measurement? Do you measure AC in mV? I mean if I understand correctly AC is supplied, then rectified Sec. A8 - 6, and then we have DC rails -42, +42 and grnd. then R144 and 145 step down the Voltage to 16 - and +. So either there is AC in other parts of the amp or I am misinterpreting the lingo.
I understand that the act of transistors switching a circuit from the + rail to the - rail could in a sense be considered an AC circuit but I am confused here.
And in Sec. B6 the 16v rails are connected in several spots via caps. And I understand that there is no physical connection between the terminals of a cap and I understand that caps are generally used for smoothing out a signal or lessening a ripple. What I don't understand is why TP5 and 6 connect the two rails through the zener diodes. The diodes are 16v and being zeners means they are there to restrict voltage to 16v but I don't get why the - and + are connected in the first place or why we need a 16 v restriction when both rails are already 16v.
Your comment about a amp kit. Yes, I am seriously thinking about purchasing such a kit.
Thanks!
BR
Bear
Yes you are correct, it all turns in to a big tailspin once the basics are set aside. Of course everything in life does that, in my opinion.
I am having a problem identifying the preamp and the power amp section on my schematic. It looks to me that the sections are intermixed. I know where the output transistors are (Q 20 and 21) And I see where the circuit from the guitar input leads in but trying to see the flow through the circuit is hard.
There is something you could clarify for me (us) if you would. On the schematic section D8 - 6 The test points list mVAC for measurements. I don't understand why its listed as AC, this is the DC part of the circuit. And isn't mV a DC measurement? Do you measure AC in mV? I mean if I understand correctly AC is supplied, then rectified Sec. A8 - 6, and then we have DC rails -42, +42 and grnd. then R144 and 145 step down the Voltage to 16 - and +. So either there is AC in other parts of the amp or I am misinterpreting the lingo.
I understand that the act of transistors switching a circuit from the + rail to the - rail could in a sense be considered an AC circuit but I am confused here.
And in Sec. B6 the 16v rails are connected in several spots via caps. And I understand that there is no physical connection between the terminals of a cap and I understand that caps are generally used for smoothing out a signal or lessening a ripple. What I don't understand is why TP5 and 6 connect the two rails through the zener diodes. The diodes are 16v and being zeners means they are there to restrict voltage to 16v but I don't get why the - and + are connected in the first place or why we need a 16 v restriction when both rails are already 16v.
Your comment about a amp kit. Yes, I am seriously thinking about purchasing such a kit.
Thanks!
BR
I'm happy to talk about amps. I thought you wanted to talk about opinions, by objecting to what you assumed to be my opinion.
I have been contributing positively to this forum for some years. Sometimes people don't like what I say. This is unsurprising, as a debate where all agree from the beginning tends to be short and unfruitful. I have learnt from others. Others have learnt from me. Some refuse to learn from me or anyone else. Life is like that.
I have been contributing positively to this forum for some years. Sometimes people don't like what I say. This is unsurprising, as a debate where all agree from the beginning tends to be short and unfruitful. I have learnt from others. Others have learnt from me. Some refuse to learn from me or anyone else. Life is like that.
DF96
Well thank you for clarify that. Since your honor has now been vindicated perhaps we can discuss guitar amps.
Well thank you for clarify that. Since your honor has now been vindicated perhaps we can discuss guitar amps.
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