I started out with buying an ICEPower 300AS1, since that would fit into the base of the Penta.
My idea is to keep the functionality (not the display, since I’m not using it) of the Penta, i.e. automatic on/off, possibility to relay speaker cable from one speaker to next and the front green/red LED.
First thing was to take one of my “spare” Penta’s and connect the ICEPower to my setup (my output is from the Almando Surround unit). https://almando.com/support/support-multiplay-surround-switch-2
It worked immediately and sounded really good & crisp – but the volume was much lower than for my other Pentas…
So, first problem to solve was gain. The data sheet of the ICEPower is good, but didn’t really help me to change the input sensitivity. And since I didn’t feel like buying & integrating a pre-amp, I started to measure up the input circuity on the ICEPower. Sure enough, the op-amp have a 2,2kohm vs. a 120 ohm resistor (=18 times gain). I managed to lift the 2,2kohm resistor (very small surface mounted…) and replaced it with a 10kohm potentiometer. Then, connecting the speaker again and trying to find the same volume form this amp as from the other. Came up with some 3.7kohm. Resulting in a gain of 31, so almost double from what it was. So I replaced the pot with a 3,7kohm SMD resistor. You really need some magnification, good light and a steady hand, to work with these miniature pieces. At least I have two out of the three pre-requisites 😊
The ICEPower is both an amp and a power supply, all on one board. The PCB fits nicely inside the now empty Penta base, in a standing position. But in order to fix it in place, I had to make holders, which made use of my Fusion 360 and 3D printer. After *many* trial & errors, I came up with four holders, keeping the PCB in a nice standing position, allowing air to pass through, and keeping a healthy distance to the metal walls.
Then, I got myself a 5mm dual color LED, for the front panel. The ICEPower already supports this function, so the electronics is easy, but – again – I had to create a holder for the LED, which took me some more time with 3D printing trial & error. The holder fits inside the front lid of the Penta base, so the LED is in the same place as the original.
I decided to keep the PCB with the two DIN connectors (and some other connectors as well), all in order to get the functionality and connectors of the new Class D Penta amp, to be the same as original. Again, this called for a 3D printed piece to hold the power cable in place, and for the new mains fuse holder.
Now, I’m in a stage where all pieces are in place, and I have a class D Penta amp, hopefully working as well as the original.
I already know that it will have a *little* less power, since the 300AS1 is 260W @4 ohm, so probably more like half of that for the Pentas 8 ohm. I will make a long-time test and replace one of my 4 Pentas with this, and see how it takes a bit of abuse.
-Would be nice to hear if any of you ever tried something like this?
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