Hi all,
Since there have been some inquiries, here I document how I built
the Purifi amp with big meters based on Purifi Eval1. Some of the below have already been mentioned, but it would be more convenient to put them all together in one place.
Case
The case is BZ3809H. It is available from Ali Express and Ebay. I got it from Ali. It's fairly cheap. I got it for 73USD including shipping (to Japan).
It is also
available from Audiophonics. It may be cheaper if you are in Europe.
Sticker
To mark where to drill holes on the panels, I used transparent sticker films like
this one. That is, I printed lifesize outlines of the holes using an inkjet printer and stuck it on the panel. The Purifi sticker was an afterthought when there were a few sheets of the films left. I just printed the logo from the Purifi website.
Tools
To cut the holes, I used mostly
a handheld power drill I already had. For the big, non-round holes I used
a jigsaw I bought a few years ago when I built the wooden amp rack you can see in the picture. With these tools, the precision is not that great. So I bored considerably smaller holes and filed away the rest. I started with the back panel so that I would get better by the time I tackled the big hole on the front panel. It was a pretty ardous process. For more effortless and cleaner machining,
sattlermanufacturing.com and
sendcutsend.com have been recommended by other members. I considered outsourcing the cutting to local machining shop, too; but the cost seemed too high relative to the price of the case. Besides, I already had the necessary tools.
Knobs
I made the three round knobs on the front panel from a solid aluminum rod with a diameter of 13mm. It was quite cheap with USD5 for 30cm length. I cut them to maybe 25mm long and put each in a drill (as if it were a drill bit, i.e., using the drill like a lathe) and filed it while rotating it. I also drilled a hole in the center of one of the cross sections so that the push switch and the VR could be screwed into it. (The left two knobs on the front panel are push switches. The one on the right is a VR/switch that changes the illumination of the meter and turns it off when it is rotated to the leftmost position.) This is however a tricky process and needed quite a bit of trial and error.
Meters
The meters are two of
these. I took off the transparent plastic cover of the meter and also the blue meter panel (made of thin plastic, just attached by a tape). The remaining part is basically a white plastic board with a meter mechanism. I connected two of them side by side and made one big panel. I printed a new big meter panel on
a plastic label that looks like a hairlined silver panel. I drove the meters using a control board called
TS-VU001. I bought the meters and the driver from Ali Express. As the driver needs a DC power at 12V-16V, I used the switching regulator M78AR15-0.5 that happened to be available at the local shop I bought electronic parts from. I built the recommended circuit in its data sheet on a universal pcb to regulate 15VDC from the unregulated VAUX (at 19VDC when the main is 100VAC), available as J5.3 on the power supply Hypex SMPS1200A400. The signal input to the meter comes directly from the XLR input. For illumination, the meters came with white LEDs but I broke some of them experimenting. So I bought some more LEDs that are more diffuse and had more yellowish color. I concocted some light diffuser from some white plastic (the spine of a plastic paper file) that were around.
PS Standby
The Hypex SMPS1200A400 goes into standby when 3.3-5.5VDC is applied to J5.1. But the voltage has to come from some other source than the SMPS itself. I used an iPhone AC adapter (5V). The 5VDC is switched by the latching push-button (on the left on front panel.) I verified that the power consumption of the whole box is less than 1W when it is on standby.
Parts
I chose the necessary parts mostly by availability, trying to buy from as few shops as possible to minimize shipping. Because the parts are cheap, I didn't want to pay more for shipping than the price of the parts. I bought most of the electronic parts from a local (Tokyo) electronic parts shop (although I didn't actually go there, buying via web), but they are generic parts that can be had from any of e.g. Amazon, Ali Express, or Audiophonics.
Gain switch
When I basically finished the build, I used the amp for a while and found out that the meters hardly moved at the audio level I usually listen to music. Since the meters show the input level from the DAC (Topping Dx7pro), and the gain of the Purifi is fixed, I could turn up the digital volume on the DAC to see the meters moving, but that was too loud. Then I realized I could bypass the buffer of Purifi EVAL1. I bypassed it by changing the jumpers J14 and J15 as instructed in Purifi EVAL1 User's Guide and was mostly satisfied by the result: now that the gain is about 14dB, compared to 27dB when the buffer was not bypassed, I could turn up the DAC volume for another 13dB for the same level of speaker output, and the meters moved much more. However, for some sources, especially classical music with a large dynamic range, I found that the 14dB was not quite enough gain. So I wanted a handy way to change the gain without opening up the case and changing the jumper setting. So I concocted a circuit to use a few relays to simulate the jumper change. I used another universal pcb, which can be seen over the Purifi buffer board at the back of the case. The relays are controlled by the second push switch from the left on the front panel. They are latching relays that only need current when changing the switch position, which is not very often. I was worried about adverse effect on the sound quality of the longer circuit that the signal goes through, but I can't tell the difference. Only after I made this addition did I realize I could use the signal after the buffer for the meter input.
That's it. Have a nice holiday!