AM demodulation.
Hi Glen,
It was just a quick and dirty test. A bit too dirty btw, because the HF signal was erroneously also connected to one of the supply rails (hardly visible)
So I have to do the tests all over again.
Whether your method will produce more meaningful results, depends (of course) on what you are looking for, IM vs AM.
If time allows, I will also do it your way.
BTW, any idea which HF amplitudes are representative for worst case conditions in real life?
Cheers,
Edmond
Hi Glen,
It was just a quick and dirty test. A bit too dirty btw, because the HF signal was erroneously also connected to one of the supply rails (hardly visible)
So I have to do the tests all over again.
Whether your method will produce more meaningful results, depends (of course) on what you are looking for, IM vs AM.
If time allows, I will also do it your way.
BTW, any idea which HF amplitudes are representative for worst case conditions in real life?
Cheers,
Edmond
AM demodulation.
Hi Glen,
I've redone my homework and I can confirm your observations and/or reasonings. Much can be gained by using a better VAS (read: complementary).
I've also observed that things get worse if the input stage is "too good", because now the VAS is much easier overloaded by unattenuated HF signals.
Cheers,
Edmond.
Hi Glen,
I've redone my homework and I can confirm your observations and/or reasonings. Much can be gained by using a better VAS (read: complementary).
I've also observed that things get worse if the input stage is "too good", because now the VAS is much easier overloaded by unattenuated HF signals.
Cheers,
Edmond.
Re: Re: AM demodulation.
Hi Glen,
These are good observations and suggestions, especially the points you make about the susceptibility of the VAS to RFI conveyed to it by a wideband input stage.
In referring to amplifiers in which the input stage is rolled off as being more immune, I'm wondering if the topology I use (miller input compensation? - where the Miller cap is returned to the input differential pair) falls into that category as being more immune.
Cheers,
Bob
G.Kleinschmidt said:
Hi Glen,
These are good observations and suggestions, especially the points you make about the susceptibility of the VAS to RFI conveyed to it by a wideband input stage.
In referring to amplifiers in which the input stage is rolled off as being more immune, I'm wondering if the topology I use (miller input compensation? - where the Miller cap is returned to the input differential pair) falls into that category as being more immune.
Cheers,
Bob
Edmond
I hope you place your findings here, i am very interested in the results. Ive used that arrangement since i can remeber, i have no idea about its rf immunity effects but there are many other benefits including reactive loads and most importantly sonic|subjective benefits. Found this out when i was kid starting building kit amps and thanks to John linsey Hood. One does not always get the best distortion results but the sonics is in my opinion more important.
John i thought of mentioning this type of compensation, am not sure what the right term for it is around here, phase lead???, regarding lowering higher order harmonics on the ad797. Ive always used this type of compensation scheme on amplifiers and using this type of compensation with experimetal amp based on the ad797 topology with very interesting results. Did not mention it for fear of being lamblasted and asked many questions which i dont have all the answers for, i dont have 30,40 years of experience designing audio.
Alex
I hope you place your findings here, i am very interested in the results. Ive used that arrangement since i can remeber, i have no idea about its rf immunity effects but there are many other benefits including reactive loads and most importantly sonic|subjective benefits. Found this out when i was kid starting building kit amps and thanks to John linsey Hood. One does not always get the best distortion results but the sonics is in my opinion more important.
John i thought of mentioning this type of compensation, am not sure what the right term for it is around here, phase lead???, regarding lowering higher order harmonics on the ad797. Ive always used this type of compensation scheme on amplifiers and using this type of compensation with experimetal amp based on the ad797 topology with very interesting results. Did not mention it for fear of being lamblasted and asked many questions which i dont have all the answers for, i dont have 30,40 years of experience designing audio.
Alex
Re: Re: Re: AM demodulation.
So, getting back on topic, what about the RF susceptibility of an
open loop (locally degenerated) circuit such as Blowtorch style, as
compared to circuits with GFB?
From everything that has been said so far, it all appears to point
to the fact that they are potentially better.
- IP stage usually has more degeneration than closed loop designs.
- Each following stage has lower gain, if any.
- There can be multiple RF attenuation points through the circuit
without affecting stability, phase margin etc.
T
Bob Cordell said:
So, getting back on topic, what about the RF susceptibility of an
open loop (locally degenerated) circuit such as Blowtorch style, as
compared to circuits with GFB?
From everything that has been said so far, it all appears to point
to the fact that they are potentially better.
- IP stage usually has more degeneration than closed loop designs.
- Each following stage has lower gain, if any.
- There can be multiple RF attenuation points through the circuit
without affecting stability, phase margin etc.
T
OK Fellow Blowtorchers 
Slight (still relevant) diversion, back to transformers briefly, since they
are very good RF blockers if done with ES shields.
Has anyone thought of using a zero field transformer at the
IP of a power or (high level) pre amp. These have far lower distortion
than conventional transformers but I believe still all the advantages.
T
Slight (still relevant) diversion, back to transformers briefly, since they
are very good RF blockers if done with ES shields.
Has anyone thought of using a zero field transformer at the
IP of a power or (high level) pre amp. These have far lower distortion
than conventional transformers but I believe still all the advantages.
T
I have used ZF xfomer inputs, and one of their strong points is RFI and galvanic isolation. There are issues though, ie one needs to use a I/V circuit behind them, with a negative impedance to cancel the copper resistance, or alternatively use ultra low secondary winding resistance. The neg impedance or plain I/V can be done with opamps (straightforward approach) but with discrete I/V circuits as well. One point is that one usually needs a cap coupled I/V input, otherwise LF/DC noisegain skyrockets with the associated problems.
- Klaus
- Klaus
Yes, these are the nude Vishay S102 resistors from www.texascomponents.com
The ones I have used and use are called TX2352.
There are SMD versions of the bulk metal foil resistors. Actually, there are many types.
Texas Components has a few of them, and Vishay has all of them.
I have not tried them yet.
Jonathan Carr spoke highly of them.
There is now another nude bulk metal foil resistor which has another geometry of the foil. This resistor is called the TX2575.
Now, even Vishay has seen the potential and released a nude version called the VAR. Same as the TX2575 as far as I can see.
I have a few of these new TX2575s but have not had a chance to test them yet.
They are said to be fragile but I have not destroyed even a single one of them during the past 5 years.
I do not pick up SMD resistors that I drop on the floor, but I do pick up the TX2352s that I drop on the floor.
Sigurd
The ones I have used and use are called TX2352.
There are SMD versions of the bulk metal foil resistors. Actually, there are many types.
Texas Components has a few of them, and Vishay has all of them.
I have not tried them yet.
Jonathan Carr spoke highly of them.
There is now another nude bulk metal foil resistor which has another geometry of the foil. This resistor is called the TX2575.
Now, even Vishay has seen the potential and released a nude version called the VAR. Same as the TX2575 as far as I can see.
I have a few of these new TX2575s but have not had a chance to test them yet.
They are said to be fragile but I have not destroyed even a single one of them during the past 5 years.
I do not pick up SMD resistors that I drop on the floor, but I do pick up the TX2352s that I drop on the floor.
Sigurd
john curl said:
RFI
Hi Alex & Glen,
Before I'm doing that, I like to get some input from experts in this field. (Pavel?). The problem is that I haven't a clear picture of which HF frequency (or range of frequencies) I should use, which amplitude, where to inject the signal into the DUT? Then, what should be measured or simulated (AM, IM?) and how.
If I investigate someone else's design, Bob's front-end for example, and I do it the wrong way, much change that my erroneous results, wrongly 'discredits' his amp. Then he gets 'hissy'. Therefore, I need more information how to do it.
Cheers,
Edmond.
homemodder said:
Glen said:
Hi Alex & Glen,
Before I'm doing that, I like to get some input from experts in this field. (Pavel?). The problem is that I haven't a clear picture of which HF frequency (or range of frequencies) I should use, which amplitude, where to inject the signal into the DUT? Then, what should be measured or simulated (AM, IM?) and how.
If I investigate someone else's design, Bob's front-end for example, and I do it the wrong way, much change that my erroneous results, wrongly 'discredits' his amp. Then he gets 'hissy'. Therefore, I need more information how to do it.
Cheers,
Edmond.
Re: RFI
Hi Edmond.
For a start, just mix (sum) the RF carrier in with the audio input signal.
Do 0.1MHz to >100MHz in 1,2,5 steps from 100uV to >100mV also in 1,2,5 steps.
Mix this with a 1kHz sinewave input signal of an amplitude that produces, say 1/4 of full power output.
Just measure the 1kHz THD. No stage within the amplifier can do a good job linearly of passing a 1kHz signal (or any audio frequency signal for that matter) if it is being heavily or over driven with a RF signal, so this will immediately show when the amplifier is under stress.
Have fun
Glen
PS, maybe continue this discussion in the Negative Feedback thread?
Edmond Stuart said:
Hi Edmond.
For a start, just mix (sum) the RF carrier in with the audio input signal.
Do 0.1MHz to >100MHz in 1,2,5 steps from 100uV to >100mV also in 1,2,5 steps.
Mix this with a 1kHz sinewave input signal of an amplitude that produces, say 1/4 of full power output.
Just measure the 1kHz THD. No stage within the amplifier can do a good job linearly of passing a 1kHz signal (or any audio frequency signal for that matter) if it is being heavily or over driven with a RF signal, so this will immediately show when the amplifier is under stress.
Have fun
Glen
PS, maybe continue this discussion in the Negative Feedback thread?
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