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Old 10th April 2013, 05:15 PM   #391
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...did not try, but with long dead time it is in the nature of a class D amp to allow it...
I am aware that most friends of classD are oriented to cheap, small and low idle losses. The poor musical reputation of classD is not just a myth, its a result of lots of scrap out there.
Fortunately in my hobby I am not bound to serve this LoFi mind setting.
Converting my design?
Low idle losses you can get by long dead time. ==> Just change two resistors.
Converting it to small and cheap would be more hard.
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Old 10th April 2013, 05:29 PM   #392
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I guess some ppl could argude that "whats the point of class d if it runs as hot as a similar power class ab amp"
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Old 10th April 2013, 06:35 PM   #393
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...hope here are not just some ppl who think 150W = 1200W.

Nevertheless, I will have a look to the popular LoFi adjustment as well.
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Old 10th April 2013, 08:14 PM   #394
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Quote:
Originally Posted by ChocoHolic View Post
...
The amp itself? - I designed and build it short time ago, I am afraid I am biased.
Sweet!
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Old 10th April 2013, 09:42 PM   #395
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Quote:
Originally Posted by ChocoHolic View Post
...hope here are not just some ppl who think 150W = 1200W.

Nevertheless, I will have a look to the popular LoFi adjustment as well.
If a well designed amplifier class D really lives up to its efficiency of 90% >
then im sure power loss should taken into account.

I must be honest I really don't have the money to build this amplifier at the moment I was just thinking of adapting the modulator to work with a pair of IRF540Z in the mean time and a +/- 40 supply for now, not PA level power design...
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Old 10th April 2013, 10:18 PM   #396
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Default Long Dead Time without heat sink

Here some measurements when you increase the dead time from 25ns to 80ns.
In short:
If 400W into 8R are sufficient and if you can live with higher distortion (still not catastrophic) then you just need the small angular piece, but no further heat sink.

More detailed:
In the first picture you see the power devices just mounted to the angular piece.
The freewheeling diodes on the back side were without any heat sink.

In the second picture you see the idle sloping.
Scales: 50V/grid, 50ns/grid
Dead time is 80ns. Sloping is still a slightly active forced event, but the IR chip does not offer a longer dead time.
It idles with 50C at the angular piece without heat sink.

In the third picture you see the amp playing music into 8R with clipping levels of 80Vp.
This corresponds to an amp rating of 400W into 8R.
Scales: 20V/grid, 5ms/grid
No heat sink. Playing music with this level for over 1h lets the angular piece stabilize at 70C.
(I disabled the thermal shut down for this, because it would act at 65C.)

Down side of the longer dead time is the increasing distortion level, especially at medium levels.
At 10W into 2R almost nothing changes. THD around 0.008%, IMD around 0.02%.
But at 100W into 2R THD grows from 0.01% to 0.04% and IMD grows from 0.025% to 0.14%.


@Reactance:
IRF540Z is a very good choice for +/-40V.
You can directly drive it from standard level shifters and can use the body diode, instead of the intensive arrangement of my high power switching stage.
You could club together with Tekko, I think he posted an universal power stage in the 25-1200W thread.
Attached Images
File Type: jpg noheatsink.jpg (138.0 KB, 538 views)
File Type: jpg sloping.jpg (126.8 KB, 512 views)
File Type: jpg 80Vp_8R.jpg (153.2 KB, 426 views)
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Old 15th April 2013, 07:11 PM   #397
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Quote:
Originally Posted by Reactance View Post
If a well designed amplifier class D really lives up to its efficiency of 90% >
then im sure power loss should taken into account.
Accurate measurement of efficiency is always difficult due to tolerances of the measurement equipment. Still I tried as careful as possible with my home meters and got the following results.
Set up as described above with long dead time.
Load 8R close to clipping: 91.3%
Load 8R and clipping (THD=10%): 98.1%, hard to believe.
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Old 27th April 2013, 08:24 AM   #398
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Hi, ChocoHolic.
Can you show THD measurements without feedback?
(half-br, open-loop mode, 400W, 4 ohm).
Maybe you can find an opportunity?
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Old 28th April 2013, 04:44 PM   #399
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Hi vovatver,
you will need patience, I have put your request on my backlog list during measurements on the next enhanced version.
You are asking for a lot of work:
1. Dissolder D312 & D313
2. Dismount the backplane
3. Open R222 & R216
4. Short C217 ==>disable the integrating gain
5. Resolder D312 & D312
6. Add offset adjustment and adjust it
Then doing the measurements and then reworking the amp again to the proper assembly with feedback...
I am even more reluctant to waste my time, because few postings ago it was very important to give evidence that also this classD amp acts like a normal classD amp can be adjusted for low idle losses and can run without heat sinks and has high efficiency.
For this I went through similar efforts like you are asking for - and after I posted the detailed examinations and measurements nobody did care about it.

The future enhanced version will be on the same PCB, but make use of the Infineon MosFet IPP110N20N3. ..going for an adjustment with higher fs, faster filter and faster frequency compensation ==> further improved step response.
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Old 29th April 2013, 03:12 PM   #400
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Quote:
Originally Posted by ChocoHolic View Post
I am even more reluctant to waste my time, because few postings ago it was very important to give evidence that also this classD amp acts like a normal classD amp can be adjusted for low idle losses and can run without heat sinks and has high efficiency.

For this I went through similar efforts like you are asking for - and after I posted the detailed examinations and measurements nobody did care about it.
Apologies Mr Chocolate

Firstly thank you for making all the effort answering most of the the time with questions we personally ask, I give you the all gratitude.. (I understand it takes time to do this, take the amp apart eveytime, remove the thermal compound, setup the scope, start the analysis process, document and reconstruct the amplifier again for listening pleasure) hopefully you wont get tired like eva, she has lost energy and patience and moved on with other priorities. (its understandable, not all of us like me here makes money off electronics its only for fun..)

Quote:
Originally Posted by ChocoHolic View Post
Here some measurements when you increase the dead time from 25ns to 80ns.
In short:
If 400W into 8R are sufficient and if you can live with higher distortion (still not catastrophic) then you just need the small angular piece, but no further heat sink.

More detailed:
In the first picture you see the power devices just mounted to the angular piece.
The freewheeling diodes on the back side were without any heat sink.

In the second picture you see the idle sloping.
Scales: 50V/grid, 50ns/grid
Dead time is 80ns. Sloping is still a slightly active forced event, but the IR chip does not offer a longer dead time.
It idles with 50C at the angular piece without heat sink.


In the third picture you see the amp playing music into 8R with clipping levels of 80Vp.
This corresponds to an amp rating of 400W into 8R.
Scales: 20V/grid, 5ms/grid
No heat sink. Playing music with this level for over 1h lets the angular piece stabilize at 70C.
(I disabled the thermal shut down for this, because it would act at 65C.)


Down side of the longer dead time is the increasing distortion level, especially at medium levels.
At 10W into 2R almost nothing changes. THD around 0.008%, IMD around 0.02%.
But at 100W into 2R THD grows from 0.01% to 0.04% and IMD grows from 0.025% to 0.14%.

This is rather expectable levels of behaviour considering you dealing with a "programmable" DT.

@Reactance:
IRF540Z is a very good choice for +/-40V.
You can directly drive it from standard level shifters and can use the body diode, instead of the intensive arrangement of my high power switching stage.
You could club together with Tekko, I think he posted an universal power stage in the 25-1200W thread.

I decided to go the UCD route instead in favour of its simplicity (and im on a budget so optimisation and simplicity rules in favour) , diagram is from the bender post (with pole/zero compensation modifications) I haven't simulated it yet but, it seems legitimate thus far not sure for sure.
Click the image to open in full size.[/URL]

As for the class d filter core, Micrometals cannot send me even samples cause here are no dealers and they wont ship it for free , not a famous core but my local electronics dealer on deals with Arnold cores.(I have looked through the forum and eva recommended this)
Click the image to open in full size.


Off the topic, interesting toys has reached me today as well, Analog Devices just sent me 2 AD1442 SigmaDSP Digital Audio Processor(s) (I have the SigmaStudio designer tool as well which works great and has loads of functionality !! It will put the Hypex and Mini DSP to shame ), I shall be doing some DSP stuff in this year (hopefully if time allows) for DIY DSP research should be fun.
Click the image to open in full size.
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Last edited by Reactance; 29th April 2013 at 03:19 PM.
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