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Old 6th February 2016, 10:09 PM   #1
recepky is offline recepky  Turkey
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Exclamation Preamp or buffer advice needed

Hi friends,

First of all I want to explain my sound system and situation after that I will ask my suggestions.

My source is: Clock Modified Asus Xonar STX having 100ohms output impedance

My preamp is: DIY Aikido 12vac with stepped attenuator and input selector in front of it. (I dont know but this also have low output impedance, like my source)

My poweramp is: DIY 2x bang&olufsen 125asx2 modules bridged using a unbalanced to balanced converter in front of it. (10kohm input impedance)

My problem is with Aikido line stage has a slight hiss in the background that I can not solve, and when I connect my source directly to the poweramp I feel the music is much more neutral and natural. I like it more, but when I connect my source directly to poweramp there is too much gain so simply I cannot set the volume up to %10. I also need input selector because some times I switch to Playstation and TV

SO I need an active or passive preamp in front of my power amp simply to control several inputs and volume.

Last several days I read nearly all of the from post is the "analog line level" forum but I can not find the answer.

If I use passive preamp, because of the low input impedance of my DIY poweramp, I think I can not get proper results.
IF I use active line stage, this time there will be unnecesarry gain and I dont want this.
All I want is extremely transparent preamp to use as input selector and volume controller.

Stepped attenuator + buffer is a way to go? Or only passive pre?
Should I use LDR based passive pre?
OR nelson pass b1 is a good choice for me?

I am so confused need immediate help
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Old 6th February 2016, 10:40 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by recepky View Post
All I want is extremely transparent preamp to use as input selector and volume controller.
Sounds like you could use just a selector switch feeding a 10k volume control.
That would work well enough with a 10k Ohm amplifier input impedance, since the
maximum output impedance of a 10k control is only 2.5k (at a -6dB setting).
There would be NO hiss at all. I would try that first.

If you have very long audio cables going to the amplifier, you might need a buffer circuit
after the volume control. That could be added later.

Last edited by rayma; 6th February 2016 at 10:50 PM.
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Old 6th February 2016, 10:51 PM   #3
recepky is offline recepky  Turkey
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Quote:
Originally Posted by rayma View Post
Sounds like you could use just a selector switch feeding a 10k volume control.
That would work well enough with a 10k Ohm amplifier input impedance, losing only
about 2dB of gain. The maximum output impedance of a 10k control is 2.5k.
There would be NO hiss at all. I would try that first.

If you have very long cables to the amplifier, you may need a buffer circuit after the
volume control. That could be added later.
Hi rayma

Thank you so much for the quick answer. I have not any electronic enginnering background sorry if this question is stupid. 10k volume control will also output 10k impedance? Or what will be the max output impedance of 10kohm stepped attenuator?
Sorry for my stupid questions.

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Old 6th February 2016, 11:09 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by recepky View Post
10k volume control will also output 10k impedance? Or what will be the max output impedance of 10kohm stepped attenuator?
In most audio applications, we want a low source impedance, and a high input impedance.
A 10k control will have a 10k input impedance at most volumes, decreasing at high volumes down to 5k,
due to the 10k amplifier's input impedance loading it. That should be fine for most sources.

A 10k volume control will have at most a 2.5k output impedance, and that's only at close to full volume, at -6dB.
At lower volumes, the volume control's output impedance will be even lower, so the 10k volume control will be fine
for connecting to a 10k input impedance amplifier.

Asking good questions is never stupid. I have a good friend from Turkey here at our university.

Last edited by rayma; 6th February 2016 at 11:18 PM.
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Old 6th February 2016, 11:37 PM   #5
recepky is offline recepky  Turkey
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@rayma
Thank you again. I now understand how volume controller impedance works. Now i have to decide which passive preamp to choose.

Option 1: Khozmo Acoustics stepped att

Option 2: Tisbury Audio passive pre

Option 3: LDR based passive pre

Option 4: Aikido a3 stepped att.

Option 5: ALPS blue velvet based passive pre

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Old 6th February 2016, 11:47 PM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by recepky View Post
@rayma
Thank you again. I now understand how volume controller impedance works.
Now i have to decide which passive preamp to choose.

Option 1: Khozmo Acoustics stepped att
Option 2: Tisbury Audio passive pre
Option 3: LDR based passive pre
Option 4: Aikido a3 stepped att.
Option 5: ALPS blue velvet based passive pre
Think I'd go for a stepped switch type of volume control.
There's also an input selector board from Glassware/Aikido.
Select-5 Signal Selector Switch
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Old 11th February 2016, 05:50 PM   #7
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I wonder the same as you op

Im interested in using a passive pre with a tube buffer.
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