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Old 21st October 2012, 04:53 PM   #1
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Join Date: Apr 2010
Location: Hungary
Default compact stackable relay attenuator - something new

There are many options when a DIY-er want volume control. Some of them are regular and some are very high-end. High-end options usually prevent the audio signal from going trough a potentiometer and uses fixed steps with more precise matching between channels.
What I show you is not entirely new, it is a relay based stepped attenuator.
Stepped attenuators can be very-very precise and can replace old potentiometers. In a regular stepped attenuator there are like 24-26 steps. This is why the relay based stepped attenuator is made, which can do easily 4x the steps, or more.

My idea was to design such an attenuator for my DIY projects but something hit my mind. Many of us likes the ODAC the USB DAC designed by NwAvGuy. When I first got my hand on it I was amazed how small it is. And it got me to think if I can do a layout for my attenuator in such a small form factor.

For this I had to use a 2 board stack design. But not only 2 boards are possible. The way I show You next is possible to have:
Single ended setup (most stereo setup)
Balanced setup (like some headphone amplifiers)
Multi-channel setup (home cinema)

To complete the specs.:
It supports 128 logarithmic steps, it has 2 channel input with source selector, remote control receiver and an external delayed relay drive (possible headphone pop protection).
Size: 58mm x 50mm x (stack high)

Click the image to open in full size.

I have a working prototype on my desk, it sounds excellent. I will make a few more.

Click the image to open in full size.

Next to do:
-buying long leg stackable female headers
-fine tuning layout
-taking more photos
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Old 22nd October 2012, 03:58 PM   #2
diyAudio Member
Join Date: Apr 2010
Location: Hungary
How do You guys like it?
Are there any live multi channel DIY projects I can check on?
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Old 22nd October 2012, 07:01 PM   #3
diyAudio Member
Join Date: Apr 2010
Location: Hungary
I have to correct myself as there was some misunderstanding on a different forum. The attenuator was made in sight of a company for an ODAC. Thus it was first planned only single ended, as the ODAC.
My plan was to build a small box, and a desktop amplifier with USB DAC, this way, the attenuator could be mounted below an ODAC to occupy the least space in the box.
Only in the design process it turned out it could be expanded to balanced or even multichannel (for an appropriate source).

Last edited by Earfanatic; 22nd October 2012 at 07:03 PM.
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