DIY AUDIO LDR kit projects

DIY StereoCoffee plus Class D amplifier.

 

I had an unused OEM Hypex NC122MP module that I can’t resell. When I discovered it in a cupboard I had a momentary brainwave and decided to combine it with my new passive StereoCoffee LDR boards but wasn’t confident that the NC122MP would be sensitive enough to take advantage of the LDR purity and it’s increased adjustable dynamic range. It was.

 

Dim the lights, close the windows, lock the doors and warn the neighbours! The result astounded me because the dynamics and purity seem to have multiplied without introducing noticeable distortion at any volume level, despite the enormous dynamic range available. Louder is better!

 

Eliminating output connectors by wiring the Hypex input directly to the LDR board output seems to showcase complex musical performances even more impressively than with my tethered DIY Holton.

 

The Build

The StereoCoffee LDR kit has been refined over many years and performance has improved dramatically during the last 12 months from my experience.

 

I chose a Class D amplifier module and Ghent connectors because of it’s low distortion which is a match made in heaven with the purity of LDR attenuators.

Note: My Hypex is an OEM product that I had left over from an ESL experiment I was working on in conjunction with an Aussie manufacturer and not available for retail sale.

 

Other retail Class D modules are available but I have no experience with them so check reviews before you lash out.

 

All components were mounted on a thin sheet of aluminium from Jaycar ($20). The sheet acts as a heat sink for the Hypex module which DOES get hot and I recommend getting several small self adhesive heatsinks from Jaycar for additional cooling. A larger heatsink would probably be better but mine runs much cooler now and only took a few minutes to add to the bottom of the chassis.

 

The chassis can be removed for repairs and is held attached to the support strip by screws in each corner.

 

The red StereoCoffee power board is mounted on 20mm standoffs so wiring can be passed underneath to keep things neater.

 

Note: Power supply requires a 15v dual wind, low power toroidal transformer or two 15v plug packs to provide individual power supplies to the input and shunt LDR control circuits.

 

Cases can be very expensive if bought online and I wasn’t sure if my project would be successful so I made my case from 12mm x 85mm dressed pine from Bunnings for about $7.50 but I had to make a few workarounds because it is too thick for pot mounts and interconnect sockets.

 

The sheet aluminium chassis is from Jaycar and the ventilated aluminium mesh on top is from Autobarn.

 

The black 3mm perspex front panel is used to mount the selector switch etc and covers the cutouts in the timber front which is too thick for chassis mounted components.

 

The SQ customisation adjustment knobs are mounted diagonally to differentiate their positions during unsighted adjustment while listening. * I actually made the cutout too small but it ended up as a bonus

 

How difficult is this project?

• Soldering (average skill)

• Inputs/Outputs = 12 solder joints

• Selector switch = 4 solder joints or tight fitting slide on connectors

• Volume control = 3 solder joints

• Timber case (I muddled through by spending lots of time fixing my mistakes because I can’t drill two holes in a straight line)

• Metal case required skilled drilling

 

Warnings

If you aren’t experienced building projects that use 240v ac power, find someone qualified to do this work for you. It could save your life!

*The top grill of my build now has additional sheeting to keep the Hypex power supply protected from prying fingers.

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Be prepared to take your time and plan positioning of components so they aren’t crowded.

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Make sure the enclosure has plenty of internal space. *My build is 300mm x 300mm. 350mm x 350mm would be better. *DoodleCad is free and allows dimensions to be added to assist designs on screen.

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Keep the red board away from enclosure sides because you will need space to insert wires securely into the screw terminal blocks. *My boards are too close to the sides and I have to lift the red board to ensure wires are fully inserted.

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SUMMARY

I won’t bang on about the StereoCoffee LDR performance too much because owners already understand what it can do. 

 

This version of StereoCoffee has several improvements that not only take the SQ and dynamics to a new level but also make it more user friendly. Sensitivity seems to have increased but I imagine this is due to improved impedance matching.

 

The difference between the Feb 2023 kit and previous versions is that power board circuitry has been refined to provide optimum current for the LDRs as required. This has made adjustments easier, volume control smoother and increased the dynamic power available to an even more impressive level on my NEAT SX3i speakers than i expected.

 

Relay LDR Input Switching (optional)

The rotary input selector switch controls power to three input LDR’s. Because of the low currents involved, perfect contact is desirable to ensure consistent performance. The optional LDR relays ensure optimum contact continues over time.

 

Ability to Customise SQ (included)

External SQ controls are simpler to use and allow me to fine tune balance the bass to sub bass ratio any time. I found this handy for balancing the explosive isobaric bass available with the SX3i speakers while keeping the mids pure. This isn’t a tone control but part of the new current management circuitry. Why don’t high end amps have this feature?

 

START Control (Feb 2023 tweak)

The position of the volume control knob can now be managed externally instead of using the simple trim pot previously required. Start point is also much easier to adjust over a wider range, giving a smoother transition.

 

I chose to listen with my volume control around 12.00 for optimum enjoyment, but I can adjust it to happen earlier or later. This would be a great asset when an amplifier or speakers are less/more sensitive.

 

The Hypex NC122MP is less sensitive than the Anthony Holton dual mono block amplifier that it replaced and the START adjustment has been a bonus for me as I can increase volume at the same volume knob position.

 

An unexpected improvement is that volume control is smoother and more progressive throughout its range instead of getting a bit twitchy at certain positions.

 

To Adjust START

Play a well recorded track that has subliminal bass and acoustic instruments or voice (Hans Zimmer live performances work well). 

 

Adjust FINISH

The FINISH adjustment is fine tuned by rotating the control knob until sub bass is first detected, then rotating it back in minute increments until any bloated mid bass that isn’t necessary is reduced to your satisfaction.

 

Every DIY StereoCoffee kit is a hand built in small numbers by Chris Daly and is not a NOT a mass produced, off the shelf, product so you may have to be patient if you order one.

 

If you take your time and assemble the kit carefully you will reap the reward of superbly addictive music for a bargain price whether it’s integrated or free standing.