Bonsai, do you understand that your remark is inappropriate?
I have given the results of testing the amplifier of the author of the book under discussion with his permission.
Summing up Lynn Olson wrote in the article "The Sound of the Machine. The Hidden Harmonics behind THD" following:
It’s time to debunk the myth of "euphonic distortion" once and for all and discover the genuine and subtle sources of amplifier distortion that people are actually hearing. Once we find measurements that can actually help, rather than hinder, it'll be easier to build electronics that are friendly to the listener. I hope this article gets people thinking, and most important of all, listening for themselves!
Lynn Olson 1997, First published in "Glass Audio" magazine by Lynn Olson, revised in 2001 and 2003.
On the question of phase modulation (PIM).
Bob, as far as I know, you disproved the theory of phase modulation by Matti Othala and John Curl.
Here is my take on the effects of output inductance, including phase modulation.
In the presentation of the BC-1 amplifier indicates that it has a high load capacity and can operate at a load of 2 ohms. Let's take a Bode diagram with various loads from 2 ohms to 12 ohms (at high frequencies, the impedance of some speakers can have even more resistance, and the impedance drawdown can be up to 1 ohm or less). As you can see, even with such a range of load changes, the signal propagation delay time changes by a factor of 3, high-speed distortion increases by a factor of 5!
If we add a reactive load, then the group delay dependence becomes even more complicated - “ringing” is added at the resonance frequency “output impedance - load impedance”, and this will further increase high-speed distortion.
Bob, as far as I know, you disproved the theory of phase modulation by Matti Othala and John Curl.
Here is my take on the effects of output inductance, including phase modulation.
In the presentation of the BC-1 amplifier indicates that it has a high load capacity and can operate at a load of 2 ohms. Let's take a Bode diagram with various loads from 2 ohms to 12 ohms (at high frequencies, the impedance of some speakers can have even more resistance, and the impedance drawdown can be up to 1 ohm or less). As you can see, even with such a range of load changes, the signal propagation delay time changes by a factor of 3, high-speed distortion increases by a factor of 5!
If we add a reactive load, then the group delay dependence becomes even more complicated - “ringing” is added at the resonance frequency “output impedance - load impedance”, and this will further increase high-speed distortion.
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Still using the term "high speed distortion" after everyone has tried to explain that this is "slew rate limiting", or at least, simply a response due to a finite bandwidth?
You aren't even going to get an inductive speaker to react instantly either.
You can mitigate inductance effects with an RC network, too, as Bob described in his book, but won't increase the amplifier response speed.
You aren't even going to get an inductive speaker to react instantly either.
You can mitigate inductance effects with an RC network, too, as Bob described in his book, but won't increase the amplifier response speed.
Hi Petr,
For a clearer understanding of phase intermodulation distortion (PIM), please read the AES paper I wrote that is available on my web site at cordellaudio.com.
I did not prove or assert that PIM does not exist. Rather, I showed that PIM is not exacerbated by the use of negative feedback, or by large amounts of feedback or by small closed loop bandwidth. In fact, amplifiers with no feedback at all exhibit PIM.
Otala asserted that PIM is caused/exacerbated by large amounts of negative feedback with low open-loop bandwidth. That is what I disproved.
Cheers,
Bob
For a clearer understanding of phase intermodulation distortion (PIM), please read the AES paper I wrote that is available on my web site at cordellaudio.com.
I did not prove or assert that PIM does not exist. Rather, I showed that PIM is not exacerbated by the use of negative feedback, or by large amounts of feedback or by small closed loop bandwidth. In fact, amplifiers with no feedback at all exhibit PIM.
Otala asserted that PIM is caused/exacerbated by large amounts of negative feedback with low open-loop bandwidth. That is what I disproved.
Cheers,
Bob
Hello Bob!
in your work you write:
«Although the real-world validity of the assuptions on which the above exercises are based (most of
which are in the original theory presented by Otala) can be arqued, the thery does provide a good basis for
understanding the phenomenon of PIM due to negative feedback, including its relation to AIM, and shows
that feedback-generated PIM in excess of about 20 nanoseconds should not be expected in amplifiers of
reasonable design.»
You deny the influence of the first pole, the depth of the OOS and the broadband of the amplifier on the phase intermodulation. Here is a typical example of an amplifier that fits Otal's definition:
first pole 80 kHz;
loop gain is slightly more than 30 dB;
the amplifier is broadband, easily copes with a frequency of 2 MHz
group delay deviation when the load changes from 2 to 12 ohms is only 4 ns!
the output impedance is purely resistive, the amplifier does not need any inductance at the output
I can give many similar examples, but I do not want to bore the forum visitors
In the BC-1 amplifier, the group delay deviation is about 600 ns!
The first pole is below 10Hz, and the full power bandwidth is not more than 250KHz.
best regards
Petr
in your work you write:
«Although the real-world validity of the assuptions on which the above exercises are based (most of
which are in the original theory presented by Otala) can be arqued, the thery does provide a good basis for
understanding the phenomenon of PIM due to negative feedback, including its relation to AIM, and shows
that feedback-generated PIM in excess of about 20 nanoseconds should not be expected in amplifiers of
reasonable design.»
You deny the influence of the first pole, the depth of the OOS and the broadband of the amplifier on the phase intermodulation. Here is a typical example of an amplifier that fits Otal's definition:
first pole 80 kHz;
loop gain is slightly more than 30 dB;
the amplifier is broadband, easily copes with a frequency of 2 MHz
group delay deviation when the load changes from 2 to 12 ohms is only 4 ns!
the output impedance is purely resistive, the amplifier does not need any inductance at the output
I can give many similar examples, but I do not want to bore the forum visitors
In the BC-1 amplifier, the group delay deviation is about 600 ns!
The first pole is below 10Hz, and the full power bandwidth is not more than 250KHz.
best regards
Petr
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No, the differential pair input stage is fundamental to this topology. Virtually all high-quality amplifiers are based on a differential input stage in one form or another. There are numerous different ways to do the differential input stage, however.
Cheers,
Bob
Bob, I understand that without a differential cascade it will be a different topology. It's about parameters. Not every Lin topology amplifier has good parameters on a real audio signal.
Cheers,
Petr
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You must have seen this already:
http://www.renardson-audio.com/mjr7-mk5.html
If wide current swings aren't needed from the input stage, a non symmetrical input stage can be perfectly adequate.
http://www.renardson-audio.com/mjr7-mk5.html
If wide current swings aren't needed from the input stage, a non symmetrical input stage can be perfectly adequate.
the vast majority of amplifiers have non symmetrical input stages, and the amplifiers themselves are not symmetric. The exception is a small percentage of amplifiers, including John Curl.
https://en.wikipedia.org/wiki/Hung-Chang_Lin Hung C. Lin held more than 60 U.S. patents. Among his inventions is the quasi-complementary (transistor) amplifier circuit
One voltage amplification stage. The second stage is a current amplifier.
US2896029A Semiconductor amplifier circuits
Electronics 1956
One voltage amplification stage. The second stage is a current amplifier.
US2896029A Semiconductor amplifier circuits
Electronics 1956
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μA709 (1965), LM101/μA741(1967-1968) - Widlar, R. J.
https://web.ece.ucsb.edu/Faculty/rodwell/Classes/ece2c/resources/an-a.pdf
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That circuit is going to clip at about 40VPP from a 60V supply, ie about half the potential output power. And I'm sure Bob will not be impressed by slew limitations from the lack of drivers.
You are right, besides this shortcoming, Mike Renardson's circuit has a number of other shortcomings: a large signal delay time, which determines the low speed of the amplifier. Therefore, it does not cope well with switching distortion and has a high level of intermodulation products in the audio band.
Distortion at low power (1 Watt) is also high and has a wide spectrum (measured on the 4th period).
There are two big differences between the steady state distortion that AudioPrecision shows and the real distortion that can only be measured with a compensation method.
p.s. OldDIY, thanks for the extra info
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I looked on the Cordell Audio website but couldn't find a list of Errata for the 2nd edition. So I don't know whether this has been reported before or not. Apologies if it is old news. And double apologies if it is wrong!
I think there might be a drawing mistake in Figure 4.2 , showing the output stage portion of the BC-1 amplifier schematic. I think the contact portion of the output muting relay is probably drawn incorrectly. As shown below, when the amplifier is muted, its output is shorted to ground (!!) by the relay. Lots of current can flow when you short a power amp's output to ground.
Maybe the original intention was to have the relay contacts' swing-arm attached to the amplifier's output jack. In the "play" position, the output jack (swing arm) becomes connected to the amplifier output (L1) and the amp drives the loudspeaker load. In the "mute" position, the output jack (swing arm) becomes connected to ground, and the amplifier output (L1) is floating. When muted, the amplifier is not connected to the loudspeaker.
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I think there might be a drawing mistake in Figure 4.2 , showing the output stage portion of the BC-1 amplifier schematic. I think the contact portion of the output muting relay is probably drawn incorrectly. As shown below, when the amplifier is muted, its output is shorted to ground (!!) by the relay. Lots of current can flow when you short a power amp's output to ground.
Maybe the original intention was to have the relay contacts' swing-arm attached to the amplifier's output jack. In the "play" position, the output jack (swing arm) becomes connected to the amplifier output (L1) and the amp drives the loudspeaker load. In the "mute" position, the output jack (swing arm) becomes connected to ground, and the amplifier output (L1) is floating. When muted, the amplifier is not connected to the loudspeaker.
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Hi Mark
You are correct the relay is drawn incorrectly, the swinger or common contact is supposed to be connected to the speaker and the Normally closed contact is to be grounded. Somehow that snuck through the editing. I made sure it was correct when I designed the protection pcb for the Bc-1 reference build. One other note is that if you use a S/S relay to replace the mechanical relay you are not able to do this grounding of the speaker.
You are correct the relay is drawn incorrectly, the swinger or common contact is supposed to be connected to the speaker and the Normally closed contact is to be grounded. Somehow that snuck through the editing. I made sure it was correct when I designed the protection pcb for the Bc-1 reference build. One other note is that if you use a S/S relay to replace the mechanical relay you are not able to do this grounding of the speaker.