Zenductor 2 in 2U Modushop Galaxy Chassis

The plan is to use this thread to document my integration of a Zenductor 2 stereo pair into a Modushop Galaxy 1GX388 2U chassis.

Except for removal of the tall Mosfet heatsinks, relocation of the transistors to the chassis sidewalls and reuse of the speaker posts I tried to leave the Zenductor 2s unmodified, and make the assembly as modular as possible. DC power and RCA input connections are via connectorized jumper cables. A preamp mounted to the front panel can be optionally looped into the signal path via rear panel RCA input and output connectors. I integrated two digital bias current displays and a large illuminated push button power switch into the front panel.

Heatsinks and transistors after removal:
IMG_20250430_230815 - Copy.jpg

They look a bit sad, with their legs cut off. Will they ever run again? ;-)

The amps just fit with the jumper cable connections:
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Transistors mounted on sidewalls (1.4 K/W heatsinks, tested in https://www.diyaudio.com/community/...galaxy-1gx388-2u-chassis.426972/#post-7997356):
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A quick test to see whether the Mosfets survived:
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The 3-digit display shows the bias current. All four transistors survived, and get warm, but not hot. Definitely an improvement over the original heatsinks.

A thermal image:
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Lots of filing for the bias display cutouts:
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It's been a while since I had to do 'precision filing'; maybe I'll fill the gap later.

Almost finished (except for the preamp connections):
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With top cover:
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Rear panel, still with empty holes for preamp connections:
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The preamplifier (from ebay, using two NE5532 op-amp chips) is all wired up and works. As hoped, it puts out a little bit more than my Bluetooth receiver. For some reason the volume when streaming from a Macbook was insufficient. Must be an Apple thing?

The preamp gets looped in via two external 8 inch RCA jumper cables, which makes it easy to remove it from the signal chain.
1746243457775.png


Unfortunately one of the green 3-digit displays already fried itself and had to be replaced. At some point I'll probably switch the other display to yellow as well.
1746243604536.png

A recalibration of the voltmeters is probably in order as well.
 
IR images after bias adjustment to 1.13V over the inductors. The current sharing on the left side is perfect, on the right side the front transistor runs hotter.

Overview:
flir_20250503T110938.jpg

Left outside:
flir_20250503T110909.jpg

Right outside:
flir_20250503T110847.jpg

Right Mosfets:
flir_20250503T110705.jpg

Left Mosfets:
flir_20250503T110620.jpg


Front view, with both bias displays now in yellow:
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Final wiring:
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I moved the bias display ground reference to the inductor, to get rid of a 30mV offset. The cheap displays came pretty well calibrated (within 2%), contrary to what some of the reviews (on Amazon) said. Gluing the top panel nuts in place in the sidewall channels makes replacing the lid easier.
 
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Parts used:


To integrate the preamp:
 

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