Both AC and DC voltage are measured in V, mV etc. In a typical amp AC appears in two forms: power source and signals. The AC voltages specified at the test points will be so that you can trace a signal through and check that it is being amplified as it should, starting with 5mV at the input TP7.
The DC voltage at many of the test points should be small, as it arises only from opamp offsets. The exact value won't matter, provided it stays small (few mV or 10's of mV).
For other test points such as TP5 and 6 the DC value is what matters. These two measure the supply voltage to the opamps. The rails are +-16V because of the presence of the zeners. No zeners means +-42V, which would probably blow the opamps.
The DC voltage at many of the test points should be small, as it arises only from opamp offsets. The exact value won't matter, provided it stays small (few mV or 10's of mV).
For other test points such as TP5 and 6 the DC value is what matters. These two measure the supply voltage to the opamps. The rails are +-16V because of the presence of the zeners. No zeners means +-42V, which would probably blow the opamps.
Test Points
DF96
If I understand correctly these test points are not checked with the AC setting of my DVOM? I set to mV setting and check see what I get.
The values shown in the TP balloons are when I am running a signal, like an "test signal" or hooking the guitar up and plucking a note? And I assume that would involve using something that recognizes the signal being generated so as to trace or follow it through the circuit?
I thought R144 and R145 were what drops the 42V to 16?
If TP5 and 6 are what drops the voltage that means its being dropped to 16 into the ground rail? I don't get it. Sorry, I'm a novice.
BR
DF96
If I understand correctly these test points are not checked with the AC setting of my DVOM? I set to mV setting and check see what I get.
The values shown in the TP balloons are when I am running a signal, like an "test signal" or hooking the guitar up and plucking a note? And I assume that would involve using something that recognizes the signal being generated so as to trace or follow it through the circuit?
I thought R144 and R145 were what drops the 42V to 16?
If TP5 and 6 are what drops the voltage that means its being dropped to 16 into the ground rail? I don't get it. Sorry, I'm a novice.
BR
the power amp starts at Q8-9, there is an opamp right before it that drives the input diff pair.
TP means "test point".
Those resistors 144/145, do not "step down" anything by themselves.
They form a "divider" with the two zener diodes.
The zener diodes set the voltage.
The resistors limit the current, and also prevent too much current from passing through
the zener diodes, so they don't get too hot and blow up.
There are other ways to use a zener to handle more power, but that's something to look up.
IF those resistors are getting really HOT, then something may be drawing too much current from
one or both rails. You can check the current draw by measuring the vdrop across each resistor
and putting into ohms law, find the amps.
The mV figures along the way in the amp refer (most likely) to the test condition spec'd on the schematic,
with an AC signal input at a spec'd freq. See note 6. on the schematic.
Ok?
TP means "test point".
Those resistors 144/145, do not "step down" anything by themselves.
They form a "divider" with the two zener diodes.
The zener diodes set the voltage.
The resistors limit the current, and also prevent too much current from passing through
the zener diodes, so they don't get too hot and blow up.
There are other ways to use a zener to handle more power, but that's something to look up.
IF those resistors are getting really HOT, then something may be drawing too much current from
one or both rails. You can check the current draw by measuring the vdrop across each resistor
and putting into ohms law, find the amps.
The mV figures along the way in the amp refer (most likely) to the test condition spec'd on the schematic,
with an AC signal input at a spec'd freq. See note 6. on the schematic.
Ok?
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The zeners regulate the voltage to the values shown at TP5 and TP6. R144 and R145 must drop whatever voltage exists over those test point values; in that respect your above statement is correct. The resistors also limit current through the zeners.
Ground is not defined as the lowest voltage in a circuit.* This fact is especially appropriate for an audio amp, and reasons why should be easily determined from the article you linked.
I skimmed the article yesterday and will read it more thoroughly, but at this point I honestly couldn't characterize that last page as anything less than bizarre. But one bad apple blah blah blah
*mathematically speaking
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You can check AC signals with a DVM. Most have a 200mV AC range. It may be less accurate at very low or very high frequencies, but should be OK over the normal audio range.
To understand how zeners are used, first you need to understand potential dividers. To understand those, you first need to understand Ohm's Law. To understand Ohm's Law, you first need to understand voltage and current. Think of electronics as an upside-down pyramid, with things like Ohm's Law and a few other principles supporting a huge expanding structure above.
To understand how zeners are used, first you need to understand potential dividers. To understand those, you first need to understand Ohm's Law. To understand Ohm's Law, you first need to understand voltage and current. Think of electronics as an upside-down pyramid, with things like Ohm's Law and a few other principles supporting a huge expanding structure above.
emphatic
That is not true. I have replacement diodes on order. Just waiting for them to arrive.
That is not true. I have replacement diodes on order. Just waiting for them to arrive.
Hey, you! To criticize what other people do is very easy, but why don't you make one better that that???
I have other things to write about.
I said it was useful. It would have been unhelpful and misleading of me not to qualify that recommendation. Do we have to separate everything into utter condemnation or sycophantic praise? What is wrong with fair criticism? Critical faculties are supposed to be a good thing.
I said it was useful. It would have been unhelpful and misleading of me not to qualify that recommendation. Do we have to separate everything into utter condemnation or sycophantic praise? What is wrong with fair criticism? Critical faculties are supposed to be a good thing.
Critical faculties are a good thing; in fact they're required for anyone to grow in knowledge and experience in any field. And the sooner constructive criticism is given, the less time wasted.
Not everyone knows how to criticize, nor how to handle criticism. But it is pretty simple ... if there is something wrong, say so. And if you (or I) are wrong, accept that we are wrong sometimes, learn, and move on.
It is not a crime to be a "teenager" who writes about what he knows or believes. But it is somewhat of a crime to let errors or hasty conclusions go without comment, so that people can learn from both his youthful ideas and what is really what.
I did not think the author of that paper would disagree. From the first page:
" ...
Many professional audio providers and audiophiles have mis-conceptions about how a solid state (transistor) amplifier functions. Mis-conceptions occur because basic principles are not understood.
..."
Pretty much what has been said in this thread already. And if the author truly believes what he has written there, he would not object to constructive criticism. However I see by reading it that he has already closed his mind to certain things. That is a mistake, and it betrays his opening statements.
To the OP:
It's an interesting read but definitely it would be a shame to consider it conclusive. If used as an introduction to electronics, maybe a decent start. But more advanced texts, well written to be easily understood, again as suggested in this thread, is a good idea (explaining what you know is far from easy when you have a good grasp of a subject; it's difficult to remember what it was like to not know, so you tend to assume people know things they do not, which confuses them).
Anyone who can convey special knowledge so the student quickly grasps the concept is a rare individual, and it's a great gift if someone points you in their direction. They are saving you time, money, grief and effort. Take advantage.
Not everyone knows how to criticize, nor how to handle criticism. But it is pretty simple ... if there is something wrong, say so. And if you (or I) are wrong, accept that we are wrong sometimes, learn, and move on.
It is not a crime to be a "teenager" who writes about what he knows or believes. But it is somewhat of a crime to let errors or hasty conclusions go without comment, so that people can learn from both his youthful ideas and what is really what.
I did not think the author of that paper would disagree. From the first page:
" ...
Many professional audio providers and audiophiles have mis-conceptions about how a solid state (transistor) amplifier functions. Mis-conceptions occur because basic principles are not understood.
..."
Pretty much what has been said in this thread already. And if the author truly believes what he has written there, he would not object to constructive criticism. However I see by reading it that he has already closed his mind to certain things. That is a mistake, and it betrays his opening statements.
To the OP:
It's an interesting read but definitely it would be a shame to consider it conclusive. If used as an introduction to electronics, maybe a decent start. But more advanced texts, well written to be easily understood, again as suggested in this thread, is a good idea (explaining what you know is far from easy when you have a good grasp of a subject; it's difficult to remember what it was like to not know, so you tend to assume people know things they do not, which confuses them).
Anyone who can convey special knowledge so the student quickly grasps the concept is a rare individual, and it's a great gift if someone points you in their direction. They are saving you time, money, grief and effort. Take advantage.
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After reading it further, I have to revise my conclusions about the paper. It starts out reasonably well if a little narrow-minded and over-confident, but quickly deteriorates into pure opinion, and not well-founded opinion at that. It ends in a bizarre summary that the author should probably have kept to himself. I can ignore the politics but the electronics are too often just plain wrong.
The OP should maybe ignore it completely. Check out the other suggested texts.
I am pretty sure if you hired the author to build you a guitar amplifier, you would hate it, while at the same time he would insist it was perfect and demand full payment.
The OP should maybe ignore it completely. Check out the other suggested texts.
I am pretty sure if you hired the author to build you a guitar amplifier, you would hate it, while at the same time he would insist it was perfect and demand full payment.
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You should come clear of the facts if u need help. If u read the later posts, it implies something else.
Gajanan Phadte
True. This thread is an example; people seem unable to handle criticism of what someone else wrote.Johnny2Bad said:
I never said it was. I find it interesting that factual errors and unsupported assertions in the original article are somehow regarded as less important than my use of the word 'teenager' to attempt to give the author the benefit of the doubt for factual and stylistic problems. Have I offended the Equality gods?
I have no idea who the author is and, as far as I am aware, he is not on this forum so it would be improper to give detailed criticism where he can't see it and respond. I have better things to do with my time anyway. Can I say again that the article, despite its problems, would be useful for a complete beginner. It is useful, it just isn't perfect.
Now you are being even more critical than me! Will you give us a detailed list of errors and corrections, as you demanded of me? Will people now queue up to criticise you, as they did me?
Let us drop the fruitless discussion of this article, and get back to the point of this thread. Otherwise I am out.
Hey guys!
DF96 is the forum member that helps people like no other.
Spend his time correcting mistakes.
There are days when his style is somewhat harsh, it is because he knows a lot and certainly some opinions bother him.
Those who know him, take their criticism with a different philosophy, and we can always learn something.
In the past we had differences, but believe me, he is a good man and is intended to help.
Take advantage of his advice and do not get angry.
DF96 is the forum member that helps people like no other.
Spend his time correcting mistakes.
There are days when his style is somewhat harsh, it is because he knows a lot and certainly some opinions bother him.
Those who know him, take their criticism with a different philosophy, and we can always learn something.
In the past we had differences, but believe me, he is a good man and is intended to help.
Take advantage of his advice and do not get angry.
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