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Old 15th June 2006, 07:03 PM   #1
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Default .1uf cap twix pos/neg speaker posts

I see that the T-amp and other amps have a .1uf cap twix the neg/pos speaker terminals.

Is this a shelving circuit? I've looked in side my solid state amps and I don't see one. Are they omitted from SS amps or are they just relocated on the board somewhere?

I ask because I remember a tweak thread (at another site, a long time ago) concerning putting a low value cap in parallel with the speaker. I forgot what it was supposed to 'improve', but I think I remember it being called a shelving circuit.

The archives at this 'other' site do not go back that far. I would ask them, but they'd prolly be too busy putting green marker around the edge of their CDs.
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Old 16th June 2006, 05:32 AM   #2
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No, it is not a "0.1uF" cap in the T-amp, (I don't recall the exact default value but I'm sure it wasn't 0.1uF as stock on the one I had) and if you are assuming it is, I will wonder if you likewise assume any other small cap is a 0.1uF?

Such a cap essentially shunts HF noise, and is particularly important in Class-D amps because they are prone to having high frequency components inherant in the way they work. If some other amp did not have bandwidth restriction and/or had HF getting into the signal or feedback path somehow, then it too would need such a cap on the output, BUT it would be better to be rid of that HF before this point as much as possible.
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Old 16th June 2006, 06:21 AM   #3
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Quote:
Originally posted by !
No, it is not a "0.1uF" cap in the T-amp, (I don't recall the exact default value but I'm sure it wasn't 0.1uF as stock on the one I had) and if you are assuming it is, I will wonder if you likewise assume any other small cap is a 0.1uF?

mmm....OK....


After looking some more, I've seen two different schematics with two different values, .1ufd and .01ufd

http://www.michael.mardis.com/sonic/images/TA2040.gif

http://i79.photobucket.com/albums/j1...st/TA2024b.jpg

But sorry if I disturbed you.
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Old 16th June 2006, 07:59 AM   #4
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Quote:
Originally posted by 3-LockBox



mmm....OK....


After looking some more, I've seen two different schematics with two different values, .1ufd and .01ufd

http://www.michael.mardis.com/sonic/images/TA2040.gif

http://i79.photobucket.com/albums/j1...st/TA2024b.jpg

But sorry if I disturbed you.


Was it not a valid concern? Knowing that mine didnt' have 0.1uF, what can I conclude? Nothing yet until I draw out more info from you, why you are making such a conclusion. The links are not necessarily a T-amp though, are they? One is a reference schematic from it's looks, and the other I was too lazy to look around his site but could be a proposed circuit or mod. Anyway, if either were supposed to be the actual T-amp it looked like the 2nd was but it is the one mentioning 0.1uF which wasn't what the T-amp had.

So, I'm not disturbed but you need to not jump to conclusions based on some other schematic, possibly.
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Old 16th June 2006, 08:10 AM   #5
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Default The idea is to "tune" the coil using a capacitor in parallell

This produces some ressonance...in a practical way, spikes generated by a coil in movement, inside a magnet (generator) will be "eated" by the capacitor....normally it is capable to work under hi voltages.

People decided to put into the amplifier boards...this was done around the seventies.... in series with 10 ohm resistor, as a low impedance (not to low) drain of hi frequencies..... well, it works avoiding HF oscilations that may born inside the amplifier board...if the oscilation start, in a microsecond, the capacitor will "eat it" and will send it to ground througth the 10 ohms resistor....more adequate is 2,2 ohms (Dr. Graham Maynard), as this may produce a more large "troat" to eat the starting oscilations.... that are not more than a repeating charge-discharge cicle.

Those modern things..... maybe to populate the board, maybe because designers are always afraid of oscilations, as they use much higher frequency components than really needed...so, having the capacity, the capability to oscilate (work) into 100 Megahertz, some transistors having some small capacitances because the board copper lines in parallel.... having some inductances because those copper lines too.... capacitances related the ground...well....all this together start a very good oscilator, and them you can measure 10 or 20 or more volts into the output...all high frequency.... sometimes 10 Megahertz or more...amplifier turns hot, sound turns strange, compressed, poor, with small dinamics, as all transistors are overdriven.

The capacitance in the output is always present, because the wires used, parallell wires, have some capacitance, and depending the length, this capacitance can be very big...but there is resistance too, the coil inductance....well...the reality is a big mess...and the inclusion of a capacitor in parallel with speaker is a very good idea...to use non parallell audio output cables, with low resistance and short length is another good idea....also to keep the damn 0.1 with the 10 ohms resistor is adequated...as transistors are turn faster and faster...and amplifiers are turning more and more "Radio frequency linear amplifiers"...and that care can avoid problems.

Audio is not perfect....never perfect, but it is nice.....but stop to analise deep those things as i use to do, because you will loose half that deep love, because there's a lot of spurious...a lot of spikes and crazy distortions everywhere...starting our own listening place, followed by aging effects and was inside ears....and zillions of distortions and non perfect things.... the challenge is to produce the "nice distortions"...this is the trick.

regards,

Carlos
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Old 16th June 2006, 06:27 PM   #6
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Quote:
Originally posted by !
So, I'm not disturbed but you need to not jump to conclusions based on some other schematic, possibly.
You're quoting me from vague memory and I'm quoting documentation,
and I'm jumping to conclusions?

Alllllrighty then!
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Old 16th June 2006, 11:13 PM   #7
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Photo of the beast. His is marked 0.15 K63, my own is marked "L50 154" and '154' is 150,000pF, 150nF or 0.15uF. I've replaced mine with 0.1uF with no apparent change in quality. Not intentional, I just didn't have the 0.15uF values to hand. The SI has undergone a few revisions, I've no reason to doubt the one analysed by audio1st you link had 0.1uF fitted (and they're +/-20% tolerance parts ffs).

It is part of the output filter system to remove Class D supersonics, rather than let them into the speaker cables and the outside world. A 'normal' Class A/B audio amplifier wouldn't/shouldn't have the high level of supersonics there in the first place, so the zobel capacitor is adequate for any traces that are present.
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Old 17th June 2006, 12:48 AM   #8
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Quote:
Originally posted by 3-LockBox


You're quoting me from vague memory and I'm quoting documentation,
and I'm jumping to conclusions?

Alllllrighty then!

That's just it, the first link you provided is NOT documentation of a T-amp. It is a reference schematic from the datasheet. This alone when provided as evidence is a clear sign you jumped to conclusions.

Similarly, we could look at a (LM3875 for example) datasheet, see a 20K resistor on it and write "Why did Peter Daniel put 20K resistor in his Gainclone", it would be just as wrong, if we only ASSUMED he had used it based on something other than the real amp & corresponding schematic itself.

Was my first post as gentle as possible? Probably not, it was meant to get straight to the point instead of dancing around stroking your ego. Jumping to conclusions will be problematic for you sooner or later, and your attitude when it seems you either don't have or can't be bothered to check an actual T-Amp is a bit bizarre.
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Old 17th June 2006, 02:28 AM   #9
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Quote:
Originally posted by !
Was my first post as gentle as possible? Probably not, it was meant to get straight to the point instead of dancing around stroking your ego. Jumping to conclusions will be problematic for you sooner or later, and your attitude when it seems you either don't have or can't be bothered to check an actual T-Amp is a bit bizarre.

In a few more days perhaps. I ordered one this week, though mine is a SI Super T and may be different altogether.
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Old 17th June 2006, 07:13 AM   #10
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Quote:
Originally posted by !


Was my first post as gentle as possible? Probably not, it was meant to get straight to the point instead of dancing around stroking your ego. Jumping to conclusions will be problematic for you sooner or later, and your attitude when it seems you either don't have or can't be bothered to check an actual T-Amp is a bit bizarre.

Just my opinion, but you're (!) the one sounding more than a tad irrational. Not in your point so much as your delivery. It takes a lot of effort/guts to be amiable/mature when you feel like pouncing on someone. Try it one day.

..Todd
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