Do I just need a power resistor on micropeone preamp output? - diyAudio
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Old 14th October 2006, 05:28 AM   #1
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Default Do I just need a power resistor on micropeone preamp output?

I have a LM386 based microphone amp(schematic shown below). I know on the schematic it shows an 8 ohm speaker. What i am wanting to do is use the output of the amp as the input to my cars cd player. The reason being that I want to use the output of the mic-amp to go into the AUX input of the cd player. then the cd player send the signal to a 50watt car amp that powers a loudspeaker. I have it setup like that right now but the car amp seems to go into clipping because of the mic-amp. if i put a 500 ohm resistor on the output of the mic-amp, will that clear the problem up?

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Old 14th October 2006, 07:28 AM   #2
lineup is offline lineup  Sweden
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hello,
silentblackhat

No, you need not use a power resistor for that 10 ohm.

Together with 100 nF ( 0.1 uF ) film cap ( polyester )
this 10 ohm resistor make a Zobel Filter network at the output
to avoid eventual oscillations.
It is NOT involved in the music and output power.
It is there for safety and to save you from troubles that can sometimes happen
for those that think they get better music without safety net.

How wrong they are - how little they know.
Any sensible designer, commercial or DIY would recommend such a ZOBEL filter.
It is named after a wellknown audio man with last name Zobel.

You can use normal 1/2 watt, or even 0.25 watt resisistor for 10 Ohm.

If you want to know more about this filter,
search with www.google.com or this here at www.diyaudio.com
for:
zobel filter


Regards
lineup always uses 10 Ohm + 100 nF
- because he dont want his amplifier or loudspeaker to burn!
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Old 14th October 2006, 08:06 AM   #3
johndiy is offline johndiy  Greece
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Hi lineup
np is offline the one and only is missing from the forum
but the latest zen is awesome zv9 can be seen at
passdiy.com

your friend mastertech

cheers
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Old 14th October 2006, 10:51 AM   #4
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Default Here is an idea...this will work fine


Be happy with your microphone...attention with feedback.

Be carefull with your ears...can damage your ear drum.

regards

Carlos
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Old 14th October 2006, 05:51 PM   #5
lineup is offline lineup  Sweden
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Quote:
Originally posted by johndiy
Hi lineup
np is offline the one and only is missing from the forum
but the latest zen is awesome zv9 can be seen at
passdiy.com

your friend mastertech

cheers
Okay,
I goto www.passdiy.com

Is latest ZV9 in his articles or do you mean a new ZV9 built in the Gallery ?
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Old 15th October 2006, 03:53 AM   #6
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destroyer X, is that a schematic that i need to make? I dont have a headphone amplifier...the way i have it setup is that i have a microphone and the output of the LM386 amp goes into my car's cd player. The cd player outputs its sound to an external amplifier that powers a 8ohm loudspeaker.


do i need to make a zobel network to make the output of the amp correct? in that schematic it says to use a 8ohm speaker but i am imputting it into the Auxillay of my cd player
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Old 15th October 2006, 05:28 AM   #7
lineup is offline lineup  Sweden
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Quote:
Originally posted by silentblackhat
do i need to make a zobel network to make the output of the amp correct? in that schematic it says to use a 8ohm speaker but i am imputing it into the Auxillay of my cd player
If you are not using a loudspeaker or headphone
but plugging the output into a CD player jack
then you do not need the 10 ohm resistor + cap = Zobel.

It is only for inductive devices.
Like headphones and speakers have a voice coil = inductance
and this makes them inductive loads
and so they can upset amplifiers outputs. ( Making them become oscillators ).
So just remove those 2 components.

lineup
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