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In Reply to: RE: What tubes to use with this Interstage Transformers? posted by dave slagle on September 04, 2016 at 20:06:14
No matter from where I look at (i.e. From the input pin of the transformer or from the output pin of the FG, I only get the same answer). That resistor is in series with the input pin of the transformer. Thus, creating a current limiter and (variable) voltage drop across it depending on the load impedance of the transformer based on the different frequency.
That's the way I see it no matter where I look at.
Now, what is that wonderful Engineering marvel FG of yours? I would like to look it up and see what kind of circuit it is constructed with.
Have you ever opened it up and see the impedance selector switch selects different resistors or resistance values? And are they the series resistor inside the FG box with the value of 550, 250 and a short wire?
I wonder why no Engineers from HP, and Tektronix never send a box of resistors along with the FG for the end user to transform the source impedance like you mentioned. It would be very useful for sure.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Follow Ups:
I think you just need to come up with a fundamental understanding of what source impedance is because you keep defining it over and over and then say it cant be.
that pesky variable voltage drop is exactly what you are looking for and is caused by a finite inductance working against a known source impedance. If we drove everything from perfect voltage source then we would get bass response down to DC.
The signal generator is a wavetek 288 and there are switched resistors right at the unbalanced output. I asked a guy at audio precision how they define their source impedance and he also said they switch a "resistor" at the output. I'm sure the guys at HP and tek are also smart enough to put those resistors (or an equivalent sand device) inside the box.
dave
"No matter from where I look at (i.e. From the input pin of the transformer or from the output pin of the FG, I only get the same answer). That resistor is in series with the input pin of the transformer. Thus, creating a current limiter and (variable) voltage drop across it depending on the load impedance of the transformer based on the different frequency."
That's right but what you are not understanding is that the output impedance of a stage is always in series with the "input pin of the transformer".
What this means is, if you have,
1. a source circuit with an output impedance of 5050 ohms
or
2. a source circuit with a output impedance of 50 ohms with a 5000 ohm series resistor added
They will both have a total output impedance of 5050 ohms and will behave the same.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre,
What you said is only true if you connect your source to the purely resistive load. You can't even start to think they are a real AC impedance source has an open ended series resistor connected to it.
And how is the load connected to the source (series or parallel)?
Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
The C and R and L are in parallel with each other and together they constitute the load that's being driven by the source.The load looks like it's in parallel with the 5050 ohm source to me. (the audio generator with 50 ohms of output impedance, in series with the 5000 ohm resistor constitutes the 5050 ohm source)
What does it look like to you?
BTW I ran the sim sweeping 20 to 20kHz with the generator having 5050 ohms output impedance with no series resistor and the way it's shown.
There was no difference in the results.
Either way, a large cap value causes the high frequencies to fall and a low inductance value for the choke causes the low frequencies to fall and all by the same amount at the same frequencies.
It doesn't matter if I start with a generator of high (5050)output impedance with no series resistor or a low output impedance (50) generator with a large value (5000) series resistor. It gives the same result either way.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/05/16 09/05/16
I see that as C1, L1, R1 are in parallel with the series resistor R2 of 5K. FG as the AC impedance source.You follow the path the current flows and see what the current sees (i.e branches out).
So, the voltage / current come out of the + end of FG and goes into the 5K resistor in your circuit and then the current see the branch with C1, L1, R1. So, current decided to chop itself off 3 portions and follow through the path according to the value set by R1, Xc, and Xl and then to the Ground.
Regardless of how components are placed (the R2 on top of the FG), where is the actual load begins at? Where is the point the load meets with the FG?
Most sim can't simulate an actual AC impedance source to the actual circuit (most sim software have unlimited current and voltage capability at any impedance you define because of programming limitations and the use of purely mathematical formulae).
If it can simulate a real 5000ohm Zout or a 50ohm Zout, I highly doubt that you will see the same thing between the 5000ohm impedance FG and 50 ohm impedance FG in series with 5K resistor. At the very least, you will see a very varied phase angle between the results from a real 5K ohm FG or source and a 50ohm FG with a 5K series resistors.
And as always, it also depends on where you probe your Scope and what you are looking at.
Regards,
James
.
.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Edits: 09/05/16 09/05/16 09/05/16 09/05/16
"If it can simulate a real 5000ohm Zout or a 50ohm Zout,"
It can.
"I highly doubt that you will see the same thing between the 5000ohm impedance FG and 5K ohm impedance FG in series with 5K resistor."
I think you mean a 5000 ohm impedance FG vs. a 50 ohm impedance FG in series with a 5k resistor.
Well, no. The one has a output impedance of 5k ohms and the other has a output impedance of 5.05k ohms.
Other that that they will be the same.
"At the very least, you will see a very varied phase angle between the results from a real 5K ohm FG or source and a 50ohm FG with a 5K series resistors. "
No, the phase (just like the Fc and amplitude loss) was the same as well.
Should I post screen shots of the sims? Or I could post the file and you could run it yourself?
Do you have and use spice? I use LTspiceIV. It's free and pretty easy to use.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Thanks for pointing it out. Yes, I meant 50ohm. It was a typo and I corrected it. I also added a few more lines to that post so please reread it.LTSpice and all of the sim has it's own limitations. First of all, they can presume pretty big numbers (voltage source / current source) since it uses purely mathemtical formula and it has almost unlimited current and voltage capability at any frequency and any impedance you set at.
It's very different from actual voltage source in life.
You need to compare the results with different voltages on the LTSpice model to about 1V to 30V. Compare the results. I don't need to do anything with your Spice sim models. I know where the limitations are at.
I used with play with LTspice and many sims very long time ago. I don't use any of them for a long time so I need to relearn again.
But I can do basics circuit analysis from the top of the head so I don't need to draw up schematic or model in Spice unless it is a very complex circuit I need to deal with.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Edits: 09/05/16
Here's the top one again so you can see them side by side.
The solid line is frequency response and the dashed line is phase.
The probe is at the top of the load(s).
As you can see, they are both the same.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/05/16
Tre,Put the scope in time domain mode and compare the measured waveforms. Don't look at bode plotting. It doesn't say much for the reflection from the load to the source.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Edits: 09/05/16
I think what you need to do is build it and measure for yourself.
Dave and I have tried to help you but you just want to argue.
I'm done.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre,I did not argue with both of you. I am only correcting the wrong here.
What is the 12V DC source? It is the 12V Battery, right? Where does the voltage come from and how is it measured?
Current comes from the positive terminal of the battery to the negative terminal of the battery, right? And we measured the voltage at the two terminals. No resistor added, right?
What is the 12V AC Source? Same thing, right? We again, don't measure with any series resistor, right?
Is there anywhere in any text book did you see that battery voltage is measured with a series resistor and call that resistor as part of the DC source?
The text book might refer to the battery internal resistance but it's not an actual resistor attached to it.
Such simple principles. Why do I need to argue with you over it?
And you can sim like I said and you can post results if you want. No one is stopping you. But like I said, Sims have it's own limitations.
I can post real test data if you like.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Edits: 09/05/16
"The text book might refer to the battery internal resistance but it's not an actual resistor attached to it."
No it's not.
But a battery with 1 ohm of internal resistance vs. a battery with .5 ohm of internal resistance and a .5 ohm series resistor attached to it will behave the same.
If you have all the answers why did you come here asking questions?
"I can post real test data if you like."
I think you should.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Here are 4 pictures.
The top yellow trace is the actual waveform coming out from the FG. It sets to about 20V at roughly 20Hz.
The bottom blue trace is for the measured waveform with the probe.
Probe hookup / measured points can be seen in the picture.
Take a go at it.
.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
What is the inductance of the IT?BTW In LT spice you can set the resistance of the DC source to any value. Same for a AC source.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/05/16
I don't know the inductance at 20Hz on the primary. I also don't know the capacitance at 20Hz on the primary. I also don't know any inductance of the secondary at 20Hz. I also don't know the capacitance of the secondary at 20Hz. Repeat that all the way from for DC to Daylight (whatever it is) Hz.I also don't know the size of the magnetic wire, the turn count of the wire on primary and secondary side, the magnetic core materials (Amophous, Permalloy, HyperMalloy, M9, M6; whatever) used, what core type (EI or C or Toroid) it use; etc.
I know it is 10K Zp transformer with step up ratio of 1:4. I also know the DCR of the primary and secondary but I am not going to tell you yet (not yet now).
Why? Because no transformer manufacturer tells you any inductance value or capacitance value or DCR values.
They only tells you the wattage it can handle, the impedance of the primary and the secondary, the insertion loss (if you are lucky), and the FR and Impedance curve (if you are really lucky).
Almost all of them also failed to mention that maximum voltage it can be operated for and the bandwidth.
So, I can't tell you all of them. But these 4 pics I posted have more than enough information to synthesize what's going on there.
You don't need to churn out numbers for me. Tell me what's going on at the probe point at the input of the transformer from these pics.
Again, it is a 10K primary transformer, open load on the secondary.
Yes, I recall you can set the values. But it doesn't mean it's almost accurately taken into account.
Anyway, I did tell you to try at different voltage levels and observe the waveform like in my screen shot.
.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Edits: 09/05/16
Internal resistance of the battery is not the same as the external series resistors! Some battery may have 0.0001ohms, some may have a little higher.
But in SIM, battery have extremely low resistance value like 0. A little smarter sim let you define the resistance.
Is it the same for you?
Yes, I will post pics. Do the AC analysis for me when I do.
.
.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
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