Help to build a Passive Balanced Preamplifier (Volume control) - diyAudio
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Old 12th March 2015, 01:51 AM   #1
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Default Help to build a Passive Balanced Preamplifier (Volume control)

First, please excuse my terrible English.
I am a newbie as a DIY so I appreciate any help from the basic.

I have a DAC with a digital volume control and balanced outputs and a tube amplifier with balanced inputs.

I understand that, in order to have the highest performance from the DAC, the volume should be kept at its maximum, (best S/N ratio and “bit perfect” digital words…) and use a high-end analog volume control. I only have digital sources, so spending $2K or $4K in a high-end preamp seems paying for a lot of stuff I don’t need: big chassis, several inputs and outputs, power supplies, knobs, balance controls, displays…). So, I am thinking about building a high quality passive volume control.

Some system data:
DAC output Impedance: 4.7 ohm
DAC output voltage: 4 Volts rms at Max.
AMPLIFIER input Impedance: 215 Kohm.
Interconnect cables: balanced 3 ft.

The DAC volume control goes from 0 to 100. Normal listening levels, connecting the DAC directly to the amp, are between 60 and 80. Depending on the recording, the volume can be set to “100”, very loud but “Ok” to the speakers. I assume I don’t need “Gain” from a pre-amp, just attenuation.
My questions:
Am I aiming to the right direction to improve the sound ?
Regarding performance, Is there any other benefit in buying a finished pre-amp ?
What do respectable high-end manufacturers use as volume control ?
What do I need to build a Passive Balanced Volume Control, with just one balanced Input and one balanced Output ?

It is my basic understanding, that I would need a quad potentiometer, a pair of Female XLR chassis-mount jacks, a pair of Male XLR chassis-mount jacks, a chassis and some cable. Is it right ?

These are the potentiometers I am thinking about:
- DACT CT2-4 (Balanced Stereo) 10, 20 or 50 Kohm ? ~ $400
- ALPS RK50114A0001 (Quad unit) 50 Kohm ~ $700

I guess these are expensive components, Are these worthwhile ? Any suggestion ?
Where can I find an schematic diagram ?
How do I make this Volume Control work with a remote ?
Thanks!!
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Old 12th March 2015, 01:58 AM   #2
udailey is offline udailey  United States
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Try Elma for less expensive solution than $400. Or very inexpensive glass-ware.stores.yahoo.net/baat.html
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Old 12th March 2015, 02:09 AM   #3
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Save yourself a bit of money and go here
High Quality Audio & Industrial Attenuators and Passive Preamplifiers
Far better than the DACT, and complete passive preamps are cheaper. Go low resistance 10k should be fine.
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Old 12th March 2015, 11:15 AM   #4
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by J Corner View Post
Some system data:
DAC output Impedance: 4.7 ohm
DAC output voltage: 4 Volts rms at Max.
AMPLIFIER input Impedance: 215 Kohm.
Interconnect cables: balanced 3 ft.

The DAC volume control goes from 0 to 100. Normal listening levels, connecting the DAC directly to the amp, are between 60 and 80. Depending on the recording, the volume can be set to “100”, very loud but “Ok” to the speakers. I assume I don’t need “Gain” from a pre-amp, just attenuation.
................
You forgot to tell us the input sensitivity of the Receiver.
What voltage does it need to just not quite clip the output?
1Vac, or 0.5Vac, or 2Vac?
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Old 12th March 2015, 11:17 AM   #5
AndrewT is offline AndrewT  Scotland
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Read D.Self and ESP and Bruno Putzeys.
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Old 12th March 2015, 02:18 PM   #6
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Quote:
Originally Posted by AndrewT View Post
You forgot to tell us the input sensitivity of the Receiver.
What voltage does it need to just not quite clip the output?
1Vac, or 0.5Vac, or 2Vac?
Thank you, Andrew T.

It is an stereo tube amp. with just balanced Inputs. (BAT VK-55SE)

Input Sensitivity: 1 V.
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Old 12th March 2015, 02:39 PM   #7
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Quote:
Originally Posted by audiopro View Post
Save yourself a bit of money and go here
High Quality Audio & Industrial Attenuators and Passive Preamplifiers
Far better than the DACT, and complete passive preamps are cheaper. Go low resistance 10k should be fine.
Thank you Dan,

The Khozmo Passive Preamp looks great, (6moons review), but it seems its web page is not working ? Do you know where I could check and maybe order it ?

Thanks
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Old 12th March 2015, 02:46 PM   #8
rayma is offline rayma  United States
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Quote:
Originally Posted by J Corner View Post
The Khozmo Passive Preamp looks great, (6moons review), but it seems its web page is not working ?
It works for me, try it again.
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Old 12th March 2015, 02:48 PM   #9
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Quote:
Originally Posted by AndrewT View Post
Read D.Self and ESP and Bruno Putzeys.
Thank you Andrew T,

I will.
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Old 12th March 2015, 03:03 PM   #10
McLanz is offline McLanz  Germany
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Thumbs up Khozma is great!

Quote:
Originally Posted by rayma View Post
It works for me, try it again.
Hi Rayma,
to order Khozmo is the best idea - even better than building it yourself!

I recently ordered two Passive Pre's from Arek (Khozmo).

One was a double mono to minimally adjust left and right channel- one was Stereo.

The finish is awesome for the Money!! The Wood sides + Aluminium give a perfect contrast in every hifi rack.

Quality is superb too: I once purchassed the expensive "Seiden" Switches from Japan for a DIY pre but they do not compare to Areks 48 step double Gold contacts switch. They never create any noises during turning the knobs!

Sound is great - I chose the expensive version but I guess the Standard resistor Version is just enough.

Of couse you can built one yourself but for this money ist not worth to spend all the swet and for sure you have noises with a standard switch one day.

Jochen
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