I keep watching for a complete digital signal path, which conflicts with the recording industry's goal of stopping pure digital copies, lmiting silicon availabilty for DIY.
Digital from the player goes over a digital coax or fiber to each speaker where there is digital Xover, room equalization and digital amp.
I'm always curious about the current SOTA in all digital audio.
Digital from the player goes over a digital coax or fiber to each speaker where there is digital Xover, room equalization and digital amp.
I'm always curious about the current SOTA in all digital audio.
Im Spanish
I am Spanish. My inglish is not very good (I use the translator of google).
It is almost impossible to read all post of this forum which they speak on the digital amplifiers (Hypex, LCaudio... etc)
I need to know pros and cons of each system DIY that there is in the market and whish is the best option.
Thanks
I am Spanish. My inglish is not very good (I use the translator of google).
It is almost impossible to read all post of this forum which they speak on the digital amplifiers (Hypex, LCaudio... etc)
I need to know pros and cons of each system DIY that there is in the market and whish is the best option.
Thanks
The Hypex UcD based modules seem easy to work with, and should not present an EMI problem. Some of the other modules that you ask about have large, air-core output coils. That could present an EMI problem. Whether you can tolerate that possibility, you will have to answer for yourself.
ICEPower modules are not available to the DIYer, so do not even ask.
Hope this translates ok..............
Jocko
ICEPower modules are not available to the DIYer, so do not even ask.
Hope this translates ok..............
Jocko
I think at present time, only the modified T-amps use aircore coils. Everyone else uses some kind of ferrite core.
But several use toroid cores with very low ferrite content.
Just to clarify.
It has been argued that only air coils are free from hysteresis distortion, but at this point we have achieved THD below 0.001% (with 4 Ohms 10W load). And that is the amplifier plus the ferrite coil's combined THD.
(Measured on a tuned ZAPpulse 700XE).
So i guess the hysteresis distortion can be extremely low.
But several use toroid cores with very low ferrite content.
Just to clarify.
It has been argued that only air coils are free from hysteresis distortion, but at this point we have achieved THD below 0.001% (with 4 Ohms 10W load). And that is the amplifier plus the ferrite coil's combined THD.
(Measured on a tuned ZAPpulse 700XE).
So i guess the hysteresis distortion can be extremely low.
Or iron powder, eg. microirons type 2.
I believe, since switching current is very high (several amperes) in your amp, so it "biases" the histeresis nonlinearity at low output level, just like in tape recorders. Low inductance helps to achieve low distortion too, but in an other amp there can be different (bigger) value, what makes distortion much higher, especially at high output level. (Saidly I experienced this in one of my early designes.) I think ultimate solution on this is UcD.
Pafi: Yes i know the old usual way of solving the THD problem: include everything you want to hide in the feedback loop, and the output signal will look nice on paper.
This is not only found in UcD, but in many other platforms as well.
Let's call this: the easy solution...
Anyway i have found even if you use this method, it can only help you so much.
Let me make an analogy, which i think many have thought of or tried at some point in their carreer as Audio DIY'er: You want to build a class B amplifier without BIAS, and to make good THD figures you use a lot of feedback to get rid of the cross over distortion. It works in theory, but will help you very little in the real world. It will still sound terrible, no matter how much feedback you use, right?
In this analogy the cross over distortion is the hysteresis distortion in the ferrite core. You can make it look nice on paper, by using feedback, but you can never make it to sound good, if there is a lot of unlinear distortion in the coil. That's why you have to use a low distortion coil even if you are using post filter NFB!
If you have an unlinear element in the feedback loop you can still get nice THD data using feedback, but the circuit will also act as a mixer, (like found in a radio input stage). A mixer blends tones together, and makes harmonics. So you can never get very good IMD, and the sound will never be any better, than without the feedback loop alltogether. Now i will say that UcD in particular has a quite low level of IMD, but that's not because of the feedback, it's more owing to the use of a good ferrite material in their output coil. Others are not taking so much consideration, and use sometimes very poor coils. As long as the feedback clears the THD, everything is good right ?
IMO True high performance demands a whole different approach.
This is not only found in UcD, but in many other platforms as well.
Let's call this: the easy solution...
Anyway i have found even if you use this method, it can only help you so much.
Let me make an analogy, which i think many have thought of or tried at some point in their carreer as Audio DIY'er: You want to build a class B amplifier without BIAS, and to make good THD figures you use a lot of feedback to get rid of the cross over distortion. It works in theory, but will help you very little in the real world. It will still sound terrible, no matter how much feedback you use, right?
In this analogy the cross over distortion is the hysteresis distortion in the ferrite core. You can make it look nice on paper, by using feedback, but you can never make it to sound good, if there is a lot of unlinear distortion in the coil. That's why you have to use a low distortion coil even if you are using post filter NFB!
If you have an unlinear element in the feedback loop you can still get nice THD data using feedback, but the circuit will also act as a mixer, (like found in a radio input stage). A mixer blends tones together, and makes harmonics. So you can never get very good IMD, and the sound will never be any better, than without the feedback loop alltogether. Now i will say that UcD in particular has a quite low level of IMD, but that's not because of the feedback, it's more owing to the use of a good ferrite material in their output coil. Others are not taking so much consideration, and use sometimes very poor coils. As long as the feedback clears the THD, everything is good right ?
IMO True high performance demands a whole different approach.
Lars!
If you are really interested in my opinion: not really, (= not unconditionally,) but let this subject not to be discussed, since we are in ClassD group!
I knew you will grab my last sentence, but there is no a single state wich can be argued!
Of course, open loop distortion must be as low as possible, but if there is no chance to lower, feedback is definitely helpful (but it must be done in the right way, eg. with proper phase margin, without coupling spikes into error amp, etc...). And I'd bet on that your output filter distorts the signal significantly at large output current, and high freq! This is what I wanted to tell in previous post.
My listening tests said different unless the input stage causes the distortion.
But I attach a BIG IMHO! (I don't want to argue, and this topic is not intended for this either.)
If you are really interested in my opinion: not really, (= not unconditionally,) but let this subject not to be discussed, since we are in ClassD group!
I knew you will grab my last sentence, but there is no a single state wich can be argued!
Of course, open loop distortion must be as low as possible, but if there is no chance to lower, feedback is definitely helpful (but it must be done in the right way, eg. with proper phase margin, without coupling spikes into error amp, etc...). And I'd bet on that your output filter distorts the signal significantly at large output current, and high freq! This is what I wanted to tell in previous post.
My listening tests said different unless the input stage causes the distortion.
But I attach a BIG IMHO! (I don't want to argue, and this topic is not intended for this either.)
How large current are we talking?
Below is the THD curve (of the amplifier) at 100W in 4 Ohms (this is 7 Ampere peak).
An externally hosted image should be here but it was not working when we last tested it.
And here the THD curve of the exact same conditions, but now using the typical ring core coil used by most other manufacturers:
An externally hosted image should be here but it was not working when we last tested it.
Anyway if my coil did distort the signal, as you say, i would not be able to remove the effects of this distortion using feedback. So i would prefer working on the best possible ferrite material, to get as low open loop THD as possible instead of just throwing feedback at the problem.
Charles: I agree completely
Lars Clausen said:
The feedback after the coil (in UcD) is not only done to get lower distortion. Another very important reason is to make the frequency response of the amp independent of the load impedance. This is impossible with only feedback before the coil. As a result, an amp with only feedback before the LC output filter can have a different frequency response (and thus time response) depending on the speaker impedance at high frequencies, thus giving subjective a "better" sound on some speakers while objectively speaking the frequency response is distorted. Those kinds of amps also need zobel networks at the output to prevent that the Q-factor of the LC filter gets too high with a load that has a high impedance (such as dynamic drivers that have an inductive voice coil). These zobel networks have a tendency to burn out (the resistor) depending on how much high frequency material you feed the amp or in some cases when one gets oscillations. I managed to burn out a zobel network when I experimented with ZAP 2.2SE, when you get oscillations, as can easily occur in an experimental setup, the resistor can burn out in a few seconds. With a burned out zobel network, I don't want to use such an amp as it could generate very high output voltages that are amplified by the q-factor of the LC filter, these voltages could be deadly and protection is needed, I think such a kind of protection is now added in the newer ZAPs, correct?
Best regards
Gertjan
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