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Old 24th April 2016, 04:23 PM   #1
JoeDJ is offline JoeDJ  United States
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Default Attenuators after a phono pre amp?

Are there any issues involved in putting (quality) attenuators in the line out of a phono pre amp ?

I ask this because my phono pre amp output has a bit too high of an output level .

I have also read conflicting opinions about if it will effect high frequencies.
I tend to believe it does not as it is no different than an amp's gain control .

Last edited by JoeDJ; 24th April 2016 at 04:26 PM.
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Old 24th April 2016, 04:57 PM   #2
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A pair of resistors forming a ladder is all you need. Say 10k and 10k to ground, that will give you a 3dB loss, halving the signal and halving any noise.
No frequency degrading will happen.
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Old 24th April 2016, 05:02 PM   #3
Mooly is offline Mooly  United Kingdom
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Jons suggestion is very workable in the real world.

If you have a circuit for the preamp then we might be able to suggest a simple component change to lower the gain of the amp. Doing that would preserve the (presumably) low output impedance of the unit.
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Old 24th April 2016, 06:13 PM   #4
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Are not all inline (RCA) attenuators just resistors? .

I prefer not modify any components if a simple inline attenuator will do.
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Old 24th April 2016, 06:18 PM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by JonSnell Electronic View Post
A pair of resistors forming a ladder is all you need.
Say 10k and 10k to ground, that will give you a
3dB loss, halving the signal and halving any noise.
No frequency degrading will happen.
Hi, to be specific that will give you - 6dB, rgds, sreten.
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Old 24th April 2016, 06:20 PM   #6
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by JoeDJ View Post
Are not all inline (RCA) attenuators just resistors? .

I prefer not modify any components if a simple inline attenuator will do.
Yes, but they are a network of two resistors configured as a divider and not just a single resistor in series.
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Old 24th April 2016, 06:22 PM   #7
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Quote:
Originally Posted by JonSnell Electronic View Post
A pair of resistors forming a ladder is all you need. Say 10k and 10k to ground, that will give you a 3dB loss, halving the signal and halving any noise.
No frequency degrading will happen.
Two resistors of same size will do 6dB, not 3 (half the output).
Degradation of the highest frequencies may happen if the load
capacitance is high at the output.
Yes,an "inline attenuator" will do, better connect this at the line input.
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Old 24th April 2016, 08:49 PM   #8
GDO is offline GDO
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Quote:
Originally Posted by JoeDJ View Post

I ask this because my phono pre amp output has a bit too high of an output level .
Don't understand the bit too high outputlevel issue...

What do you need attenuate for?
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Old 24th April 2016, 11:29 PM   #9
JoeDJ is offline JoeDJ  United States
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Quote:
Originally Posted by GDO View Post
Don't understand the bit too high outputlevel issue...

What do you need attenuate for?
what do you not understand about that?

Actually, it not "too high" .
It's just that what I got it input into would be a bit happier with a slightly lower input.

Last edited by JoeDJ; 24th April 2016 at 11:37 PM.
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Old 25th April 2016, 12:56 AM   #10
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Quote:
Originally Posted by JoeDJ View Post
Are there any issues involved in putting (quality) attenuators in the line out of a phono pre amp ?
Yes - you don't want to raise the output impedance too high or you'll create HF roll-off in conjunction with the cable capacitance as well as increase your noise susceptibility. You don't want to go too low or dynamics of the source will start to suffer.

Better to use a step down transformer.
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