yes.
go through the route; signal ground, Zin, Q5 base to Q5 emitter.
If signal ground is at Zero Volts then all the points listed will be negative with respect to the Signal Ground.
Now look at the inverting input of the LTP.
Using the usual opamp rule; the two inputs will be at the same voltage for a zero output voltage.
and
The negative feedback will always try to ensure that both inputs are kept at the same voltage.
This implies that the quiescent voltage on the base of Q6 is also negative with respect to signal ground.
What voltage is sitting across the the NFB capacitor? What polarity is that voltage?
hint; the value of Zin and the input offset current can be used to define the quiescent voltage at the bases of Q5 & Q6.
If the LTP is made from PNP transistors then the input offset current is opposite to the NPN version. What is the polarity of the voltage across the NFB cap for a PNP LTP?
go through the route; signal ground, Zin, Q5 base to Q5 emitter.
If signal ground is at Zero Volts then all the points listed will be negative with respect to the Signal Ground.
Now look at the inverting input of the LTP.
Using the usual opamp rule; the two inputs will be at the same voltage for a zero output voltage.
and
The negative feedback will always try to ensure that both inputs are kept at the same voltage.
This implies that the quiescent voltage on the base of Q6 is also negative with respect to signal ground.
What voltage is sitting across the the NFB capacitor? What polarity is that voltage?
hint; the value of Zin and the input offset current can be used to define the quiescent voltage at the bases of Q5 & Q6.
If the LTP is made from PNP transistors then the input offset current is opposite to the NPN version. What is the polarity of the voltage across the NFB cap for a PNP LTP?
I do not want to sound abraisive or harsh, but I would agree with Andrew here. You have the kind of blogger's "up and at 'em" style of writing.
Judging by the detached style of writing, it doesn't seem like you're "all here" with us.
I think if you would take a calmer, more peaceful approach, you would make less nonsensical posts. Center yourself and keep both feet on the ground, don't move ahead of the group. This way, you can state your concerns without taking up as much space, as you have not already gathered up a bunch of questions.
Since you aren't much interested in amplifier design, you might as well just let us guide you to the finished project. If you were interested in designing the amp, it would be more appropriate that you worry about things like NFB or back-EMF. Generally, we know enough to keep your audio sounding good.
Judging by how enthusiastically you concern over these issues, I think you would make a swell amplifier designer if you put yourself to the task. You have experience with opamps, you have most of the theory and concepts already. Is it as if your brain starts putting together the pieces automatically? If so, you are either narcoleptic or you are more interested in amplifier design than you let off. This kind of interest is what makes good designers. If you are narcoleptic, get more sleep.
I had problems with it until I looked it up on Wikipedia.
Apart from this, patience, peace, and persistence are rewarded with smooth and steady resounding success.
With these values, we will get to the finished project smoothly no matter HOW you try and do it (within reason).
Best wishes,
- keantoken
Judging by the detached style of writing, it doesn't seem like you're "all here" with us.
I think if you would take a calmer, more peaceful approach, you would make less nonsensical posts. Center yourself and keep both feet on the ground, don't move ahead of the group. This way, you can state your concerns without taking up as much space, as you have not already gathered up a bunch of questions.
Since you aren't much interested in amplifier design, you might as well just let us guide you to the finished project. If you were interested in designing the amp, it would be more appropriate that you worry about things like NFB or back-EMF. Generally, we know enough to keep your audio sounding good.
Judging by how enthusiastically you concern over these issues, I think you would make a swell amplifier designer if you put yourself to the task. You have experience with opamps, you have most of the theory and concepts already. Is it as if your brain starts putting together the pieces automatically? If so, you are either narcoleptic or you are more interested in amplifier design than you let off. This kind of interest is what makes good designers. If you are narcoleptic, get more sleep.
I had problems with it until I looked it up on Wikipedia.Apart from this, patience, peace, and persistence are rewarded with smooth and steady resounding success.
With these values, we will get to the finished project smoothly no matter HOW you try and do it (within reason).
Best wishes,
- keantoken
AndrewT said:
Okay!
So, what else does your diode here do? http://www.diyaudio.com/forums/showthread.php?postid=1678237#post1678237
For some reason, I find this sort of thing really fascinating. Thank you!!
You're welcome.
Yes.
If you use a cap for DC filtering, like supply rails, you usually go one over the voltage you have.
But if you're going AC, your capacitor must be rated for twice the peak voltage, because -1V-1V is equal to 2 volts.
I didn't see the schematic, but I think the allows use of a cap with a lower voltage rating. Am I right?
I'm fairly sure I'm right on this.
- keantoken
Yes.
If you use a cap for DC filtering, like supply rails, you usually go one over the voltage you have.
But if you're going AC, your capacitor must be rated for twice the peak voltage, because -1V-1V is equal to 2 volts.
I didn't see the schematic, but I think the allows use of a cap with a lower voltage rating. Am I right?
I'm fairly sure I'm right on this.
- keantoken
I think they do, a band called Dream theater produced back
EMF of sufficient level to be measured on the diodes of my peerless sub amp and popped a 7amp fuse shortly after.
So on that amp I keep the diodes. (10lb. magnet/3" voice coil)
As far as the cap , why not use a NPO . I use 100u to 220u
NPO's , a little bigger and costly but they eliminate the issue.
Also if you use a 63v cap nothing could fry it. If space is an issue
2 diodes and a 16v NPO would be just as safe..
I blew one of my amps and had the honor
of observinghow it burned
, I am relieved to report just semiconductorsburned (quickly,pinhole spark) NO caps.. then out went the fuse.
So far, came up with a "ballpark" figure of 560R+1N4148 to go in parallel with the NFB cap (with the resistor "towards" the input, and diode "towards" the 0v). Is that anywhere close, and if not, what's closer?
P.S.
Can't tell if its a proportion of the NFB cap or a proportion of the gain. So, for reference the amp tested on had 22uF+2.7k, with 120k feedback.
P.S.
Can't tell if its a proportion of the NFB cap or a proportion of the gain. So, for reference the amp tested on had 22uF+2.7k, with 120k feedback.
Dan, if two components are series then it does not matter which component is towards which end. The current through both and the voltage across them will be the same.
The gain is set by the proportions of the feedback resistors, not caps. The caps are for frequency compensation and for stability so it won't oscillate.
... I don't understand what you are trying to do with the diode thing but I get the feeling you're missing the point. What is the 560r resistor for?
- keantoken
The gain is set by the proportions of the feedback resistors, not caps. The caps are for frequency compensation and for stability so it won't oscillate.
... I don't understand what you are trying to do with the diode thing but I get the feeling you're missing the point. What is the 560r resistor for?
- keantoken
I'm mystified by this diode across cap thing going on. I have never heard of an issue here, nor have I ever measured anything close to what is being talked about.
Firstly, are we talking about the electrolytic cap that goes to ground in series with the ground (or common) leg of the voltage divider we use to sample the output voltage with? If so, you do realize that there is a higher value resistor in series with it, right?
The only time I have ever seen this cap (if it's the one) ever damaged is when the amplifier fails DC and does not blow any fuses.
-Chris
Firstly, are we talking about the electrolytic cap that goes to ground in series with the ground (or common) leg of the voltage divider we use to sample the output voltage with? If so, you do realize that there is a higher value resistor in series with it, right?
The only time I have ever seen this cap (if it's the one) ever damaged is when the amplifier fails DC and does not blow any fuses.
-Chris
MJL21193 said:
Its because I plugged in the soldering irons and tried it. It was like add the resistor and "dial it in" to taste.
Very nice!!! I'm un-fixated now, and just sitting back enjoying the music. Got a bit nicer bass. I'm a happy guy thanks to Mr. AndrewT! The neighbors came over to tell me that this rumble bass was nicer than all that booming. That was kind of embarrassing although it was more fun use of the components than trying to protect a cap from +0.002vdc. No more fixation needed. EDIT: Although, it would be nice to know why there was a difference like that.
Dan, you've discovered Audio Enhancement!
Such things a Jammix for Winamp do this.
I seem to remember something where DestroyerX did this...
You might want to add a switch however so you can turn it off if you want.
This was quite unexpected, Dan.
You should inform us if you plan on experimenting like this.
Technically, I think this would be distorting the sound (but not sure where you put it) and so any true audiophile would burn you at the stake for this.
We can probably give you all sorts of suggestions for sound "enhancement", audio engineers hear many strange noises over the years resulting from unintended modifications...
I believe it works like this: the diode and cap probably act like a rectifier for the bass, causing all sorts of weird things to happen. I guess it's something to try and simulate.
- keantoken
Such things a Jammix for Winamp do this.
I seem to remember something where DestroyerX did this...
You might want to add a switch however so you can turn it off if you want.
This was quite unexpected, Dan.
You should inform us if you plan on experimenting like this.
Technically, I think this would be distorting the sound (but not sure where you put it) and so any true audiophile would burn you at the stake for this.
We can probably give you all sorts of suggestions for sound "enhancement", audio engineers hear many strange noises over the years resulting from unintended modifications...
I believe it works like this: the diode and cap probably act like a rectifier for the bass, causing all sorts of weird things to happen. I guess it's something to try and simulate.
- keantoken
keantoken said:Dan, you've discovered Audio Enhancement!
Such things a Jammix for Winamp do this.
I seem to remember something where DestroyerX did this...
You might want to add a switch however so you can turn it off if you want.
This was quite unexpected, Dan.
You should inform us if you plan on experimenting like this.
- keantoken
Ah, no. Not an enhancement, but more of a very mild patch. My cap was undersize. EDIT: Question is, why did this fix it?
An enhancement would have altered the gain. I didn't do that. Hey, but if you want to do it, I'd love to hear it.
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