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Old 7th January 2010, 08:54 AM   #1
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Default TC Electronics Switch amp

Some time ago we decided to do our own switching poweramp based upon the TC elctronic switchamp module.
This module is also sold by LC Audio, but has nothing to do what so ever with the older ZAPpulse modules. LC Audio was aquired by TC Electronics some years ago, therefor the alternative outlet exists.

By now we reached a point where af few final decissions is to be made regarding design of PSU and the input buffer, but nevertheless some might find the project interesting anyway.

The module from TC was first presented to my by ts designer, who is a master of science who earlier worked @ Power House, which is the home of ICEpower, later he came to TC, where he developed this module.

The very interesting thing about this module is its design of the feedback loops, which I will come back to a bit later.

When I firstlistened to it, it was with a somewhat undersized SMPS and a standard buffer and in addition some safety circuits and ekstra filtering, but in spite of that, it sounded very different from other class D amps Ive listened to. To me the original ICE modules has a somewhat laid back sound, but endeed they are very clean and smooth.
This one sounds deffinately more neutral to me
So we devided to one ourselves, because its very upside was as mentioned the sound, but also its low energy consumption, which has to be held up against my Gravity class A amp, which consumes 1.2KW and runs @ 55dgr. C and heats up my listning room to around 26 dgr. C on cold winterdays, in the summer not much music is played, since only "nakedlistening" is possible, and we cant svcare the kids that way - can we?

So class D seems atractive, at least during the summer.
Well! back on track. The special thing in ICE power modules is their patended feedback principple, namely only ICE has 2 different feedback loops. One for high frequency control taking its feedback signal inside the outputfilter, the next loop is an audio frequency loop which takes its feedback signal outside the output filter. This is the very basic thing about ICE, all other makes do only have one feedback loop, which either takes its feedback signal inside OR outside the output filter, mostly inside. That makes the output filter a very critical component, and it leaves the designer with a huge problem, namely a very unlinear output impedance, and it can be hard to obtain good stability.
Also "dead time" adjustment can be critical especially over time.

If you want to know more about the ICE principle you can read more here: ICEpower — Ph.D. thesis
This is the Phd. on which the whole ICEpower business is built.

Looking at ICE power modules and their performance, youll find very high powerdensity and pretty nice data generaly, but looking at the output impedance, the ICE modules impedance also rises with frequency, though it has a damping factor @ 1KHz about 1.000 which has fallen to around 20 I think @ ca. 20KHz.
This is due to output filter and its limitation of the speed of the audio feedback loop, but still this is a lot better than amps with only one loop.
The ICE modules are this way superior regarding stability, output impedance and it can handle pretty difficult loads as long as they are not to close to purely capacitive loads.

Now comes the surprising part TC introduced a THIRD feedback loop - yes they did.
They feature a high speed feedback loop inside the filter, an audio loop aoyside the filter, and in addition a high speed loop outside the filter eliminating the downsides in the filter, which is rising impedance with frequency.
Still the output impedance rises though, but the level is much lower.
The output impedance @ 1KHz is only a few Ohms giving a damping factor that counts in MILLIONS
This is amazing even @ 20KHz the output impedance is still lower than I think what ever you might imagine, also THD+N is very low, and hardly affected by outputpower.
Unfortunately they filed a patent for this technology, so this is a TC only product.
The sound of this I think will amaze a lot of people, since Ive never heard anything perform with that ease and overview as this. and for the funny part, it does this in our prototype with an undersized linear powersupply @ 100VA and 18 panasonic FC smooting caps each 660F. The available peak power is much larger than one imagines though, but that is of course of short duration only. But this really makes one think twice about amps with large caps and monster transformers. In this case something completely different is at stake.
The prototype was actually just meant as an experiment, where we wanted to find out what the module is sensitive to. So we had much larger smoothing caps earlier we tried out RIFA PEH 160, PEH 200, EPCOS Sikorel 105 dgr. and also some Philips and a lot of bypasses.
The thing this module apparently is sensitive to is impedance, and in that way the bunch of FCs are much lower than any of the other ones, and this actually works much better. We will try out larger values in due time, but certainly it will be 20 or so small caps parallelled and from either Panasonic or Sanyo.

The buffer we made for the prototype is a discrete non feedback unity gain buffer with 2. order one point servo, decoupled with SMR caps from Evox.
We did not yet build an onboard regulator for it, this will come in a later version. For now we just regulate in one stage with 7812/7912 for both the buffer and the modules 12V supply. This is not optimized yet, the module has very high PSRR, but the buffer does not, therefor a high speed series regulator close to the buffer is called for.

So far i really like the switch monster which we named "BIGFOOT" .

If you might have experience with this module or good ideas for design details you are welcome to comment, inspiration is highly appreciated.
Also feel free to ask about details regarding the project.

PS!
There is not yet any schematics for the buffer, as it is not yet closed.


switch1.jpg

Switch 2.jpg
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Last edited by Kurt von Kubik; 7th January 2010 at 09:04 AM.
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Old 7th January 2010, 01:33 PM   #2
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I have a few ICE modules, stereo and the big monoblocks.

Very nice amps. The bass control on the big amps is amazing. Most be that super low output impedance. It really brings some speakers to life.

The TC stuff looks interesting.
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Old 8th January 2010, 12:05 AM   #3
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Quote:
Originally Posted by panomaniac View Post
I have a few ICE modules, stereo and the big monoblocks.

Very nice amps. The bass control on the big amps is amazing. Most be that super low output impedance. It really brings some speakers to life.

The TC stuff looks interesting.
yeah!
ICE power has a very nice bass control, due to the low output impedance, but so does my class A amp, which features 16 matched output transistors pr. ch. Which results in a dampingfactor @ around 400 from 20-20 KHz.
This is easily heard as a very controlled behaviour no matter what is to be done throughout the audible frequency area.
But this small fellow is somewhat of a beast in that regard
We still need to try out a few things regarding PSUs, but already now I can say, that it really has its moments.

Compared to ICE modules, I think the TC is sounding clearer and more lifelike.
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Old 8th January 2010, 01:17 AM   #4
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Hi Kurt von Kubik
Sounds interesting. The output filter impedance is definitely one hurdle to overcome and it sounds like TC has an interesting way of controlling the output filter impedance curve.

Kurt, what's the PSRR of this amp?
Does this amp have low reactivity to speaker load? If so, is it due to the implementation of the 3rd feedback loop?

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Old 8th January 2010, 09:58 AM   #5
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Quote:
Originally Posted by KLe View Post
Hi Kurt von Kubik
Sounds interesting. The output filter impedance is definitely one hurdle to overcome and it sounds like TC has an interesting way of controlling the output filter impedance curve.

Kurt, what's the PSRR of this amp?
Does this amp have low reactivity to speaker load? If so, is it due to the implementation of the 3rd feedback loop?

Hi KLe!

I also found the TC way of solving the output impedance problem sofisticated.
It is not so that they made it doing "clean and smooth" measurement results, but they did manage to get both THD+N and output impedance down to almost unimagenable values.

The PSRR is not stted by TC, but we,ve made experiments with very high ESR caps from Philips, resulting in ripple @ 5V and even more, without any influence on power delivery. This is due to the design, which if the supply voltage decreases, then the modulator will just increase time. So theoretically ripple is no issue for concern.
But a sitching amp do need power en very short jerks, wich makes the high frequency behaviour of the power supply pretty important. Therefor a very low impedance power supply is needed, and at best if it has low impedance at high frequencies as well.

The abillityy to drive difficult speakers speakers should be excellent, though I do not know how it responds on reactive loads. reactive loads is normally a challenge for switching amps. Ive also seen some trouble with switching amps, that cannot be turned on without load, I think Ive seen 3 or 4 switcing amps send out smoke doing that.
This one is perfectly stable in any regard, even if you pull the plug playing really loud, you just plug it again, the only thing that happans is: music - no music and so on. No blob bump fssst or anything at all.
TC states its max output current to more than 60A peak, and max power is 200 Watts @ 8 Ohm, DNR is a smashing 113 dB with standard buffer unweighted.

It is a very strong amplifier indeed, and I think it must be due to the third loop, because it lowers the outputimpedance that much, that is my belief.

The only special thing about this module is, that it requires an input buffer, because of a very low input impedance @ 2K Ohms. That will not go with most preamps without change in sound.
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Old 8th January 2010, 01:52 PM   #6
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Yeah, that is a low input impedance. I thought the ICE were a bit low at 8K.
An input buffer would certainly be a good idea.
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Old 8th January 2010, 05:15 PM   #7
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Quote:
Originally Posted by Kurt von Kubik View Post
Hi KLe!

I also found the TC way of solving the output impedance problem sofisticated.
It is not so that they made it doing "clean and smooth" measurement results, but they did manage to get both THD+N and output impedance down to almost unimagenable values.

The PSRR is not stted by TC, but we,ve made experiments with very high ESR caps from Philips, resulting in ripple @ 5V and even more, without any influence on power delivery. This is due to the design, which if the supply voltage decreases, then the modulator will just increase time. So theoretically ripple is no issue for concern.
But a sitching amp do need power en very short jerks, wich makes the high frequency behaviour of the power supply pretty important. Therefor a very low impedance power supply is needed, and at best if it has low impedance at high frequencies as well.

The abillityy to drive difficult speakers speakers should be excellent, though I do not know how it responds on reactive loads. reactive loads is normally a challenge for switching amps. Ive also seen some trouble with switching amps, that cannot be turned on without load, I think Ive seen 3 or 4 switcing amps send out smoke doing that.
This one is perfectly stable in any regard, even if you pull the plug playing really loud, you just plug it again, the only thing that happans is: music - no music and so on. No blob bump fssst or anything at all.
TC states its max output current to more than 60A peak, and max power is 200 Watts @ 8 Ohm, DNR is a smashing 113 dB with standard buffer unweighted.

It is a very strong amplifier indeed, and I think it must be due to the third loop, because it lowers the outputimpedance that much, that is my belief.

The only special thing about this module is, that it requires an input buffer, because of a very low input impedance @ 2K Ohms. That will not go with most preamps without change in sound.
are we talking now about the current LCaudio Class D module?
Is it available yet?
What are the actual technical data?
how much current (rms) caoul you get out of them?
I mean are they capable of driving 4 ohm loads in Bridge mode?
and more likely, are they now (if I read your post correctly) using post filter feedback? (e.g. the frequency response is load independent??)

Thanks,

Tamas Tako
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Old 8th January 2010, 07:29 PM   #8
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Quote:
Originally Posted by ttako View Post
are we talking now about the current LCaudio Class D module?
Is it available yet?
What are the actual technical data?
how much current (rms) caoul you get out of them?
I mean are they capable of driving 4 ohm loads in Bridge mode?
and more likely, are they now (if I read your post correctly) using post filter feedback? (e.g. the frequency response is load independent??)

Thanks,

Tamas Tako
Yes it is the current LC module, but it is not designed by Lars Clausen.
Have a look here L C Audio Technology / Forside

Data
Standard setup med 500VA toroid og PredatorXE supply output power 8 Ohm 230 Watt RMS
Bridged output power 4 Ohm 1200 Watt RMS
Peakcurrent >60 Ampere
Frequency response 20-20khz +/- 0.2dB
THD+N, 20-20khz, 1W i 8 ohms < 0,004%
THD+N, 20-20khz, 100W i 8 ohm < 0,1%
THD+N, 20-20khz, 250W i 4 ohm < 0,1%
Gain with buffer 35dB
DNR, with buffer, uvejet 113dB
Indputimpedance with buffer 10 kOhm
Without buffer buffer 2 kOhm
Supply voltage +/-48-70 Volt DC
Efficiency, 300W i 4 ohm ~93%

About the feedback, they are using pre AND post filter FB, 3 loops with different properties in conjunction.

The modules are available for DIYrs, LC Audio is the outlet.
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Old 8th January 2010, 08:48 PM   #9
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Quote:
Originally Posted by Kurt von Kubik View Post
Yes it is the current LC module, but it is not designed by Lars Clausen.
Have a look here L C Audio Technology / Forside

Data
Standard setup med 500VA toroid og PredatorXE supply output power 8 Ohm 230 Watt RMS
Bridged output power 4 Ohm 1200 Watt RMS
Peakcurrent >60 Ampere
Frequency response 20-20khz +/- 0.2dB
THD+N, 20-20khz, 1W i 8 ohms < 0,004%
THD+N, 20-20khz, 100W i 8 ohm < 0,1%
THD+N, 20-20khz, 250W i 4 ohm < 0,1%
Gain with buffer 35dB
DNR, with buffer, uvejet 113dB
Indputimpedance with buffer 10 kOhm
Without buffer buffer 2 kOhm
Supply voltage +/-48-70 Volt DC
Efficiency, 300W i 4 ohm ~93%

About the feedback, they are using pre AND post filter FB, 3 loops with different properties in conjunction.

The modules are available for DIYrs, LC Audio is the outlet.

Hi,

is this 60A peak = 42.5Arms????
meaning the max Prms to be 42A x 42A x 4Ohm in bridge?? (=7700W) meaning, that just the DC voltage rails are the limiting Factor? (70V/1.4142 x 2= ca 100V in bridge mode =2500W rms??)
i highly doubt these 60A peak seeng just 1 TO220 device there per switch...

Thanks,

Tamas
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Old 10th January 2010, 10:14 AM   #10
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Quote:
Originally Posted by ttako View Post
Hi,

is this 60A peak = 42.5Arms????
meaning the max Prms to be 42A x 42A x 4Ohm in bridge?? (=7700W) meaning, that just the DC voltage rails are the limiting Factor? (70V/1.4142 x 2= ca 100V in bridge mode =2500W rms??)
i highly doubt these 60A peak seeng just 1 TO220 device there per switch...

Thanks,

Tamas
Well!
I do only have the data provided from LC Audio, so I do not really have any Idea of under what conditions the peak current is available.
But I talked to the designer, and he also mentioned 60A peak current.

About the two TO220 FETs in the switch, one must understand, that the switching principle completely eliminates the need for dozens of transistors and bulky heatsinks.

In linear design you can gain sound quality by oversizing both your amp and the PSU, therefor measurement condition for linear amps is often much harder than any condition they will face in real life. I.e. for class A/B amps, 1/3 power for one hour @ 1.000Hz sine wave is the preconditioning routine @ stereophile, which is the worst possible thermal condition.
If the amp copes with that, it is correctly sized and it will normally behave both strong and with authority in real life situations.

Switching amps behaves completely different, youll win absolutely nothing by oversizing it to meet the conditions mentioned above. The point is that the switch does not perform significantly worse @ high power than @ low power delivery, hence th normal oversizing does not make any sense in this case.

How much power it can deliver on long term basis is very dependend on cooling, since the remaining 7% not delivered to the speaker, discipates as heat in the switches. But careful thermal design will indeed make it very strong.
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