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Old 6th May 2004, 12:40 PM   #11
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i ran a multisim bode plot (1Hz to 100kHz) using 10R and 0.1R resistances with 0.7uH inductor -- the load was the ESP simulated speaker, with simulated inductances, capacitance and resistance for 10 feet of Monster Cable -- the "gain" is the difference in gain between the two versions:
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Old 6th May 2004, 12:56 PM   #12
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maybe this is a little clearerrrrrrrrrrrrrrrrr -- the attenuation of the 0.1R and 10R on the simulated speaker/cable
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Old 6th May 2004, 01:23 PM   #13
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10x for the advice

Need advice on someting else.

how to mesure the output power of the amp in Volts?

my pre amp is integrated on my sound card and my amp is working on 1V input signal max.
I need to know what will be my siound card output max voltage...
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Old 6th May 2004, 01:35 PM   #14
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Quote:
Originally posted by Hybrid fourdoor
Whats the wattage rating on the resistors if using <0.5 Ohm? 5W? 3W?

Since most of the current is going through the choke at low/mid freqs, the resistor can be small wattage. If you use the resistor as 'body' for the coil just chose the resistor from that pov. The resistor DOES carry the current for high freqs, but these signal levels are very low (avarage) anyway, so again the resistor choice is more determined by the required physical dimentions. A 1 W res would do anyway.

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Old 6th May 2004, 02:37 PM   #15
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Quote:
Originally posted by peranders

You MUST have resistors if you connect the LM3886 in parallel but if you only have one IC you can have nothing or the inductor. This depends of your load and cable lenght. You can have this resistor also if you wish but start with as little as possible at first. My examples gives you a DC resistance of 5 mohms.

Hi peranders,

I am currently building my latest stereo GC project that uses only one IC per channel and already bought a pair of 0.1 and 0.22 ohm 5W resistors and several 10 ohms 2 watts. I also have some spare magnet wires from a passive crossover network project so I have the things that I need. I am seriously considering the inductor.

My last question is, for capacitive loads (such as cables), is the inductor only any good?

Regards,
JojoD
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Old 6th May 2004, 09:24 PM   #16
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Quote:
You need to "protect" your power amp from capacitive loads that would cause instability (typically "ringing" ).
This small value resistor at the output doers nothing to protect the amp from capacitive loads.
GC is very sensitive to this kind of loads.Take a pair of speaker cables that measure more than 1000p (there are many on the market) and connect "not easy" speakers withe them to GC.It will crack /distort like hell no matter the resistor is there or it isn't.
Only Zobel fixes that ,but it makes the amp sound worse.

Bartek
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Old 7th May 2004, 08:46 PM   #17
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Quote:
This small value resistor at the output doers nothing to protect the amp from capacitive loads.
I am sorry "zygibajt", but a small resistor (0.1 - 0.5 ohm) does indeed protect your amp from capacitive loads.

Try the following experiment. Take a amp with no kind of output resistor or inductor. Connect it to a resistive load, like 8 ohm. So far you should be fine. Now connect a capacitor at about 100 nF across the resistive load. If you are "lucky" you can see evidence of unstability as sign of oscillation in the 100-500 kHz area. You might have to "adjust" capacitor to make it happen.
(with your "crack /distort like hell " it should not to to difficult)

When you have the "oscillation" put the small resistor between the amp and load. You "oscillation" are completely gone.

Quote:
Only Zobel fixes that ,but it makes the amp sound worse.
Hmmmmmmmmmmmmmmmm, how surprisingsly it may sound, the Zobel network "protects" the amplifier from inductive loads and I have a very hard time seeing how it can make the amplifier sound worse, so please explain.

Thomas
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Old 7th May 2004, 09:26 PM   #18
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All I'm saying is based on my experiments with GC,not theory.
GC doesn't like high capacity speaker cables,and with some speakers going with the cables higher than some 400-500p makes GC crack and distort.I have some audophile quality cables that measure 1,4nF for 3meters long.It's impossible to listen to the GC on that cables,it distorts like hell.In every case of GC distorting small series resistor made no diffrance.Only 100n in series with 1ohm resistor to ground fixes this.With Zobel at the output even those high capacity cables sound fine,but that Zobel makes the amp sound worse,checked it many times.


Bartek
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