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:
They look a bit sad, with their legs cut off. Will they ever run again? ;-)
The amps just fit with the jumper cable connections:
Transistors mounted on sidewalls (1.4 K/W heatsinks, tested in https://www.diyaudio.com/community/...galaxy-1gx388-2u-chassis.426972/#post-7997356):
A quick test to see whether the Mosfets survived:
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:
Lots of filing for the bias display cutouts:
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):
With top cover:
Rear panel, still with empty holes for preamp connections:
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:
They look a bit sad, with their legs cut off. Will they ever run again? ;-)
The amps just fit with the jumper cable connections:
Transistors mounted on sidewalls (1.4 K/W heatsinks, tested in https://www.diyaudio.com/community/...galaxy-1gx388-2u-chassis.426972/#post-7997356):
A quick test to see whether the Mosfets survived:
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:
Lots of filing for the bias display cutouts:
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):
With top cover:
Rear panel, still with empty holes for preamp connections:
Attachments
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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.
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.
A recalibration of the voltmeters is probably in order as well.
The preamp gets looped in via two external 8 inch RCA jumper cables, which makes it easy to remove it from the signal chain.
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.
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:
Left outside:
Right outside:
Right Mosfets:
Left Mosfets:
Front view, with both bias displays now in yellow:
Final wiring:
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.
Overview:
Left outside:
Right outside:
Right Mosfets:
Left Mosfets:
Front view, with both bias displays now in yellow:
Final wiring:
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:
- Burning Amp 2024 Zenductor 2 (pair), came with 16V switching power supplies (hopefully available soon in the diyaudiostore?!)
- Modushop Galaxy 1GX388 2U 330mm by 280mm by 80mm chassis https://diyaudiostore.com/products/galaxy?variant=12174834308
- 30mm double pole latching push button switch with ring light https://www.amazon.com/dp/B0CNYZ56ZG
- 5.5/2.5mm (NOT 2.1mm) DC power sockets & pigtail cables (2 of 3 sets used) https://www.amazon.com/dp/B0B6FFN4V5
- RCA feedthroughs (2-pack) https://www.amazon.com/dp/B004M4B7WA
- digital 3 wire 3 digit volt meters (5 pairs, 1 pair used) https://www.amazon.com/dp/B0BG31FBX5
- rubber feet (4-pack) https://www.amazon.com/dp/B08FD8TRPD
- RCA jumper cables, 6 inch, right angle to straight (pair) https://www.amazon.com/dp/B093PMLPPM
To integrate the preamp:
- NE5532 stereo preamp, single supply voltage https://www.ebay.com/itm/176909832601
- volume knob (pair, one used) https://www.amazon.com/dp/B0B375DC6Q
- insulated RCA sockets (8-pack, 4 used) https://www.amazon.com/dp/B08ZLQHGNS
- RCA jumper cables, 8 inch (pair) https://www.amazon.com/dp/B08PVSSPVM
Attachments
Thanks Dirk, it's the Bluetooth output. I think this Macbook (air, somewhat recent, i.e. a few years old) does not even have a headphone output. I did not dive in to see whether there are any output or driver settings associated with specific connected devices. I assume it's similar to Windows? It's my wife's macbook; it's been a while since I used a mac myself. I know my Windows tablet 'thinks' the DS220 bluetooth receiver are headphones, at least as far as the device name is concerned. But changing the category name does not seem to have an effect on that machine. I don't remember how to do that (list hardware devices and their drivers) on a Mac. For what it's worth, the DS220 does display maximum volume setting, as commanded by the mac, when the volume is still significantly lower than from my Windows tablet. I guess I also don't understand how volume is set and transmitted via Bluetooth. I would have naively assumed that the transmission uses the full dynamic range of the bit pattern, and volume reduction only takes place at the receiving end. But clearly the receiver thinks it's getting the full volume command, so the encoding must already be at a lower level, i.e. some of the dynamic range available (bit depth) is wasted in the transmission?
In any case, it's good to have a volume knob, and as far as I can tell the NE5532 is a very old but nevertheless competent audio amplifier. Of course there could be mistakes in the preamp design or layout, but nothing obvious that could hear. I guess at some point I will have to break out the old USB scope and look for myself...
In any case, it's good to have a volume knob, and as far as I can tell the NE5532 is a very old but nevertheless competent audio amplifier. Of course there could be mistakes in the preamp design or layout, but nothing obvious that could hear. I guess at some point I will have to break out the old USB scope and look for myself...