Lumin AMP (Class AB)

BlueFox said:
Does class AB mean it operates in class A up to some point, and then goes into class B after tha point? If so, how far into A does it operate?
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The strict definition of what a class AB amplifier is does not mean that it operates in class A up to a certain point and then transitions into class AB. Class AB means the the two transistors in the simplest of output configurations conduct for a little more than 180 degrees of the input wave form but much less than the full 360 degrees of conduction in a class A amp. What this does is get rid of cross over distortion and improves efficiency over that of a pure class A amp.

I have heard of amplifiers designs that operate up to class A to a certain point and then transition to another class of operation but this is not the strict definition of what a class AB amp is.

Wyklie can correct me if I am wrong and/or let us know what Lumin's definition of what class AB is to their design engineers.
 
dznutz said:
correction... class A amps do not have cross-over distortion
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Right you are. What I was trying to say was that, with a complimentary pair of transistors operating in class B, there is significant cross over distortion when one xisitor turns off and the other one turns on. The class AB biasing works to almost entirely minimize this distortion hence the naming convention class AB.
 
BlueSky said:
Right you are. What I was trying to say was that, with a complimentary pair of transistors operating in class B, there is significant cross over distortion when one xisitor turns off and the other one turns on. The class AB biasing works to almost entirely minimize this distortion hence the naming convention class AB.
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Think about the signal is the upper half and lower half. p and n channel transistors repsosible for upper and lower part of the signal, Pure B, is no overlapping, AB is where the signal has a slight overlapping. Where class A is complete overlapping. The overlapping range is closely related to the output magnitude of the signal. So for the Lumin amp, it is true to say it is pure class a up to a certain point, and class AB for the rest of the output power.

I am one of the designer behind the lumin amp and the sound tuning engineer for the X1.

A.
 
BlueSky said:
Wklie can correct me if I am wrong and/or let us know what Lumin's definition of what class AB is to their design engineers.
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I'll leave questions or support requests on Lumin AMP to @lscangus.
 
lscangus said:
Think about the signal is the upper half and lower half. p and n channel transistors repsosible for upper and lower part of the signal, Pure B, is no overlapping, AB is where the signal has a slight overlapping. Where class A is complete overlapping. The overlapping range is closely related to the output magnitude of the signal. So for the Lumin amp, it is true to say it is pure class a up to a certain point, and class AB for the rest of the output power.


I am one of the designer behind the lumin amp and the sound tuning engineer for the X1.

A.
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Iscangus, thanks so much for the response and I thank you especially for the the audio magic you have created with the tuning of the Lumin X1's sound!

A class A amplifier is an amplifier in which the output device(s) are biased in the middle of their "load lines" and conduct for the full cycle of the input signal so they never have to cut off and transition to a complementary transistor that would be typical in a class B amplifier to handle the other phase of the input signal. So, if I am to understand you correctly, in the Lumin implementation of it's version of class AB, one of the devices (P or N) at low signal levels is biased so that that single device handles all 360 degrees of the input? If that understanding is not the case and both the P and the N devices are always conducting for at least a portion of the input waveform regardless of how small the input signal is, then I would still say that the amplifier never really enters into a class A mode of operation.

Again, my thinking could be flawed and I will seek to learn more about it just to satisfy my own understanding.

Thanks again!

Joe
 
BlueSky said:
Iscangus, thanks so much for the response and I thank you especially for the the audio magic you have created with the tuning of the Lumin X1's sound!

A class A amplifier is an amplifier in which the output device(s) are biased in the middle of their "load lines" and conduct for the full cycle of the input signal so they never have to cut off and transition to a complementary transistor that would be typical in a class B amplifier to handle the other phase of the input signal. So, if I am to understand you correctly, in the Lumin implementation of it's version of class AB, one of the devices (P or N) at low signal levels is biased so that that single device handles all 360 degrees of the input? If that understanding is not the case and both the P and the N devices are always conducting for at least a portion of the input waveform regardless of how small the input signal is, then I would still say that the amplifier never really enters into a class A mode of operation.

Again, my thinking could be flawed and I will seek to learn more about it just to satisfy my own understanding.

Thanks again!

Joe
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BlueSky said:
Iscangus, thanks so much for the response and I thank you especially for the the audio magic you have created with the tuning of the Lumin X1's sound!

A class A amplifier is an amplifier in which the output device(s) are biased in the middle of their "load lines" and conduct for the full cycle of the input signal so they never have to cut off and transition to a complementary transistor that would be typical in a class B amplifier to handle the other phase of the input signal. So, if I am to understand you correctly, in the Lumin implementation of it's version of class AB, one of the devices (P or N) at low signal levels is biased so that that single device handles all 360 degrees of the input? If that understanding is not the case and both the P and the N devices are always conducting for at least a portion of the input waveform regardless of how small the input signal is, then I would still say that the amplifier never really enters into a class A mode of operation.

Again, my thinking could be flawed and I will seek to learn more about it just to satisfy my own understanding.

Thanks again!

Joe
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If I understand correctly. You are right with the Class A situation. A Class AB is basically the same as Class A but the overlapping area of the P and N channel is less than the full rated output.

So if the signal is small enough too be accommodated in the overlapping area, then both channel are always conducting and you get a pure class A operation.

Angus
 
Hi Lumin Team!
For the last few days I have a very loud hum in both loudspeakers coming from Lumin AMP.
Can you give me any hint or do I need to contact local dealer for warranty service?
I am sure it is caused by Lumin AMP - hum is in loudspeakers even if anything else is disconnected.
 
Since it's under warranty take it to the dealer. Has anything changed in your system that would cause a ground loop that wasn't there before.
 
Nothing has changed in the setup. Hum has been there occassionally before, but only in one loudspeaker. Now it has become permanent, very loud and in both speakers. Unless I hear more from Lumin team, I will send it to a dealer.
 
Jsa said:
Nothing has changed in the setup. Hum has been there occassionally before, but only in one loudspeaker. Now it has become permanent, very loud and in both speakers. Unless I hear more from Lumin team, I will send it to a dealer.
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Sorry about the issue you are having. I wonder if I can have more detail about your system/setup?

Angus
 
Hi Angus,
Many thanks for coming back.
My setup is following:
Lumin A1 -> XLR Red Dawn (first version) -> Lumin AMP -> speaker cables Auditorium A23 - > Usher Mini Dancer Two

I have tested that the issue of hum is only via XLR, it is completely silent if I connect via RCA.
However clearly XLR connection is a different ball game in terms of sound quality than RCA between A1 and AMP.

Please let me know in case you have any hints. Does it have something to do with power supply inside AMP?
 
I can also add that I have tried with other XLR inteconnects and the issue stays the same.
In the past hum was occasional and only in one channel, now it is permanent and in both channels:-(
Some good advice will be highly appreciated. Is it purely ground loop issue or some internal AMP design of faulty element?
 
Jsa said:
I can also add that I have tried with other XLR inteconnects and the issue stays the same.
In the past hum was occasional and only in one channel, now it is permanent and in both channels:-(
Some good advice will be highly appreciated. Is it purely ground loop issue or some internal AMP design of faulty element?
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Hi, Thanks for your quick reply. As you have no issue with RCA input, I wonder if you can tell me which XLR interconnects you have tried?

The Lumin amp input section is a true balanced design. The RCA input is basically an XLR input with the negative pin short to the ground.
 
I have tried following XLR interconnects: another pair of Red Dawn, Valab Pure Silver Litz, Mogami, and DIY Klotz. Same issue with each of them. Should we move to private message with our further conversation?
 
Jsa said:
My setup is following:
Lumin A1 -> XLR Red Dawn (first version) -> Lumin AMP -> speaker cables Auditorium A23 - > Usher Mini Dancer Two

I have tested that the issue of hum is only via XLR, it is completely silent if I connect via RCA.
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Do you have the A1 and AMP plugged into the same power strip or outlet, or different ones? Are you using some sort of isolating power conditioner?
 
It turns out it is a classical ground loop problem. So nothing wrong with otherwise brilliant Lumin AMP.
Cheers to all!
 
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