[Hi.
Sorry, but I beg to differ. I have just designed a valve pre driving 2 250 watt Class D power amps and took thiem to a high end HiFi consultant. He used a Copland CD player and Pro-ac Response speakers. It's not valve or Class D in presentation. It's something a bit special according to him. Class D IS HiFi if you surround it with the appropriate kit.
Ricky.
Sorry, but I beg to differ. I have just designed a valve pre driving 2 250 watt Class D power amps and took thiem to a high end HiFi consultant. He used a Copland CD player and Pro-ac Response speakers. It's not valve or Class D in presentation. It's something a bit special according to him. Class D IS HiFi if you surround it with the appropriate kit.
Ricky.
[Hi.
What's my idea of a linear amplifier? My idea of a linear amplifier is either a conventional Bi-polar or Mosfet design that uses a + an - power rail. Class D seems to behave in a very similar way to Class A. That is to say that it draws current all the time. On the ones I use, they are fed from a well regulated single rail supply of 48volts. If you place a meter on either of the output terminals and the other to 0volts, you read half the supply voltage i.e. 24 volts. In a linear circuit, voltage or current only flows when a signal is applied to the input (with the exception of Class A).
I have to say that the sound, with a valve pre-amplifier driving it, is something I have never heard before. Fast, tight and the bottom end is extremely well controlled unlike some "linear" designs I have heard where the supply rails drop as you ask for low frequencies. The result is un-controlled low frequencies or "One Note Waffle" as one critic wrote a few years ago.
Ricky.
What's my idea of a linear amplifier? My idea of a linear amplifier is either a conventional Bi-polar or Mosfet design that uses a + an - power rail. Class D seems to behave in a very similar way to Class A. That is to say that it draws current all the time. On the ones I use, they are fed from a well regulated single rail supply of 48volts. If you place a meter on either of the output terminals and the other to 0volts, you read half the supply voltage i.e. 24 volts. In a linear circuit, voltage or current only flows when a signal is applied to the input (with the exception of Class A).
I have to say that the sound, with a valve pre-amplifier driving it, is something I have never heard before. Fast, tight and the bottom end is extremely well controlled unlike some "linear" designs I have heard where the supply rails drop as you ask for low frequencies. The result is un-controlled low frequencies or "One Note Waffle" as one critic wrote a few years ago.
Ricky.
ANY amplifier is linear, as it is nothing more than a linear system multiplying the signal with a constant.
It does not matter how the linear system is constructed, so in case of a class a,b,c or d amplifier it is al the same.
The problem of non-linearity lies in the fact that due to the linearity curves of (mainly) tubes and transistors there are serious problems to overcome which are most prone with class b and class c amplifiers (class c is not used in audio circuits).
Class d is special in the sense that it is in fact a very fast thrown switch. There is a relation between the switching frequency and the signal frequency you want to amplify. As long as the switching frequency is relatively high, the class d amplifier acts as a linear system.
The fact that most amplifiers drawn current whether or not they are actually "amplifying" has nothing to due with fidelity in itself. It follows from the way you design it. In so far there is a relation with linearity that you use some bias currect to get out of the nonlinear curve-part of tubes and transistors. Or you have some losses due to the fact that switching takes time, like in the class d circuit.
Due to the way you design, all systems (amplifiers) have their pros and cons and so a right to exist.
Class d is not actually "new", but could not be realized before due to the fact that there were no fast (enough) power switches.
So listen to a good class d amp, you may like it!
It does not matter how the linear system is constructed, so in case of a class a,b,c or d amplifier it is al the same.
The problem of non-linearity lies in the fact that due to the linearity curves of (mainly) tubes and transistors there are serious problems to overcome which are most prone with class b and class c amplifiers (class c is not used in audio circuits).
Class d is special in the sense that it is in fact a very fast thrown switch. There is a relation between the switching frequency and the signal frequency you want to amplify. As long as the switching frequency is relatively high, the class d amplifier acts as a linear system.
The fact that most amplifiers drawn current whether or not they are actually "amplifying" has nothing to due with fidelity in itself. It follows from the way you design it. In so far there is a relation with linearity that you use some bias currect to get out of the nonlinear curve-part of tubes and transistors. Or you have some losses due to the fact that switching takes time, like in the class d circuit.
Due to the way you design, all systems (amplifiers) have their pros and cons and so a right to exist.
Class d is not actually "new", but could not be realized before due to the fact that there were no fast (enough) power switches.
So listen to a good class d amp, you may like it!
Ricky said:
This has nothing to do with Class A. You are simply seeing, as with any bridged amplifier, that each output of a bridged channel will sit at an average DCV of 1/2 supply rail, to keep the net across the load at zero volt. You will measure exactly the same with any bridged amp running off a single rail, whether Class A, B, AB or D.
Lukas
marconist said:
Quite right, Lukas! (If you replace bridged by balanced .....
In my "theoretical view" I missed that point. Thanks.
I have to say that I find all of your comments fascinating. I could spend hours on her but I don't have the time or want to pay the phone bill!!! I do agree with your comment though. Try a good Class D amp sometime.
While I was having my amp appraised at the dealer's place I mentioned, I listened to a Class T driving Wilson WATT/ Puppy 7's. Not sure about what my ears were receiving. Didn't make music for me.
Keep it coming. I'm learning one helluva lot.
Ricky.
Ricky said:
Ricky,
From the experience I have had with small class T amps I suspect all of them have problems driving complex loads like any speakers with crossovers. This is probably due to their output filters not being in the feedback loop. I personally have never actually sat down and listened to the Watt Puppies but they are respected. I also suspect they do have a complex crossover network with all that implies sonically and load wise.
My experience with this situation is the sound becomes strained and irritating with real problems around the crossover point. Was this the kind of thing you heard?
With good single driver/no crossover speakers the class T can be dazzlingly good! A truly worthy replacement for 2-15 watt class A triodes at the price of one good tube too boot!
Roger
Hi Roger.sx881663 said:
I have to say that I didn't have this problem because these class D's produce a full 250watts into a 4 ohm load. The WATT's are quite efficient so the amps were never pushed that hard. It's an interesting point though. I'll see if I can duplicate what you've said with Inductive/resistive load on the bench and measure it with a scope.
Ricky
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