CDP output signal too strong for AMP input?? - diyAudio
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Old 31st July 2005, 07:53 AM   #1
Florian is offline Florian  Germany
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Default CDP output signal too strong for AMP input??

Hello fellow members !!

I recently purchased a UnicoCD and did notice some unpleasant changes. On highy powerfull recorded music it seems to overdrive the input of the Pathos. My Sphinx Project 2 MKII Preamp comes back on monday or tuesday and i would like to know what i can do to reduce this problem. The problem does not happen with my Rega Planet 2000. My friend told me this


Quote:
the Unison might have a higher gain, which overdrives the input stage of the power amp

He suggested a passive-preamp in case it wont work with the Sphinx. Are there any other options out there exept buying a new CD-Player? How can i build a passive preamp or how can i lower the output of the Unison?

Thanks

Flo
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Old 31st July 2005, 08:30 AM   #2
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I have experienced the same problems albeit on different models of kit, there are two cheap and easy ways.

If your cd has a remote control, look for the volume controls and simply lower it, works great.

For no more than 40 you can purchase inline Attenuators, a -10 dB reduction usually does the trick and from my experience of the ones i purchased off a dealer on ebay did not detract from the sound quality whatsoever. In fact you will hear a lot more detail with a more equal volume level rather than booming bits that just sound loud and nothing else ! You can get them configured for cd output side or amp input side, i use them on my tuner output and enables the fm stereo side to now sound the way it should, and not like you are listeneing to the radio !

Hope this helps
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Old 31st July 2005, 09:54 AM   #3
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Hi Florian,

Find the input (differential) section of your amplifier / preamplifier.

Find R1 and R2.

Increase R2 to decrease the gain or
Decrease R1 to decrease the gain.

For the best results, slightly change the value for both resistors.

Cheers,
Extreme_Boky
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Old 31st July 2005, 10:17 AM   #4
guytou is offline guytou  France
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It' very dangerous to tent to decrease the gain by this way (i.e increasing the ratio feedback) . For an amplifier , there's a quick way to destroy it .
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Old 31st July 2005, 10:25 AM   #5
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Quote:
Originally posted by guytou
It' very dangerous to tent to decrease the gain by this way (i.e increasing the ratio feedback) . For an amplifier , there's a quick way to destroy it .

could you explain that mechanism of destroying amplifiers that way ?
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Old 31st July 2005, 03:05 PM   #6
guytou is offline guytou  France
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What happens if you increase the feedback ratio ?
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Old 31st July 2005, 03:07 PM   #7
guytou is offline guytou  France
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Likely the amplifier will oscillate & you'll burn the output transistors (at least).
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Old 31st July 2005, 04:11 PM   #8
Florian is offline Florian  Germany
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Thanks all for replying. I am going to wait till monday or tuesday and hope that it will work on the Sphinx. Ill keep you guys posted.

Thanks

-Flo
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Old 31st July 2005, 11:41 PM   #9
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Quote:
It' very dangerous to tent to decrease the gain by this way (i.e increasing the ratio feedback) . For an amplifier , there's a quick way to destroy it .
Hi guytou,

In fact, that is the proper way to set the gain of an amplifier.

It is possible to change the gain other ways - but none apart from the above affects only the gain - they affect linearity as well.

Maybe you've tried and fried the amplifier(s)?

This is an excellent read:
http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm

Extreme_Boky
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Old 1st August 2005, 09:03 AM   #10
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Quote:
Originally posted by guytou
Likely the amplifier will oscillate & you'll burn the output transistors (at least).

That is, if little or no phase margin is present. Decently designed amps have sufficient margin to increase feedback by a factor 2 or 3.

Indeed, you are right, those amps that don't have phase margin, will oscillate.

That way they disappear from the world, Darwins mechanism works here too :-)
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