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A handful of noob questions

sigma25, sigma26, sigma24

A handful of noob questions

Postby ohshitgorillas » July 21st, 2015, 11:44 am

Hello,

As my first AMB project, I plan on building a sigma25 power supply for my gamma2 DAC (which I traded for, but am extremely impressed with, and is currently running off of a wall wart that is a subtle improvement over USB power). But I'm a noob to electronics in general... like I'm still reading and learning about some of the basic concepts... and I have a bunch of what are probably stupid questions.

Note that this isn't my first DIY project, I've successfully built a Bottlehead Crack with Speedball.

  • I want to use an epsilon24-controlled power button on the front. In order to power both the sigma25 and the epsilon24, I can use the same transformer/sigma24 right? (proper transformer selection is still something I struggle with)
  • Where does one get/make a suitable short cable for transferring power from the sigma25 to the gamma2? The two will be stacked on top of one another, so anything over six inches will probably be overkill. Which also reminds me....
  • I don't see a "recommended case" for the sigma24, but I'm wondering what/where to look for in cases that are at least the same width/depth as the gamma2? I realize it will probably be taller than the gamma2 itself.
  • I also want to mount a USB-powered USB to coaxial converter inside the box. Do the quality of these converters vary, or is it one of those "it's a digital signal, it's fine" kind of things. Anything in particular I should look for in a converter?

I apologize for asking questions that are probably lazy/obvious to most people, but I never really got a formal education with regards to electronics besides a laughable introduction to basic calculations in undergrad (about 7 years ago), so any literature would be greatly appreciated. I've done a lot of reading lately, but I'm also in the 4th year of my PhD so the amount of time I can dedicate to hobbies like this is... well, limited... no matter how hot the fires of DIY audio burn inside of me. I'm learning though!
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Re: A handful of noob questions

Postby amb » July 21st, 2015, 2:41 pm

ohshitgorillas wrote:I want to use an epsilon24-controlled power button on the front. In order to power both the sigma25 and the epsilon24, I can use the same transformer/sigma24 right? (proper transformer selection is still something I struggle with)

The voltage requirements are different. γ2 needs 5V regulated (so it needs a 9V transformer), but ε24 has an onboard voltage regulator for 12V, and needs at least a 12V transformer. You need two transformers anyway, in order to use the ε24. It needs to have power all the time, whereas the γ2's power is switched on/off with the ε24.

Where does one get/make a suitable short cable for transferring power from the sigma25 to the gamma2? The two will be stacked on top of one another, so anything over six inches will probably be overkill. Which also reminds me....

You can simply use two stranded copper hookup wires, cover it in shrink wrap or some other protective sheathing, and install the appropriate connector on each end.

I don't see a "recommended case" for the sigma24, but I'm wondering what/where to look for in cases that are at least the same width/depth as the gamma2? I realize it will probably be taller than the gamma2 itself.

The σ24/σ25 and σ24/ε24 are not designed to fit any particular case. You need to find something that they would fit in (with all parts installed, and with PCB standoffs and other items accounted for, such as IEC AC inlet, switch, etc). You might be able to fit these in a taller version of the same [url=http://www.boxenclosures.com/category/category_product.html?cats__id=730]Box Enclosure BEX series[/quote] that the γ2 is usually housed in. Check the B3-080 or B4-080 and do some measurements:

I also want to mount a USB-powered USB to coaxial converter inside the box. Do the quality of these converters vary, or is it one of those "it's a digital signal, it's fine" kind of things. Anything in particular I should look for in a converter?

There are definitely vast differences from product to product. What bit depths and sample rates does it support? Does it transfer data in adaptive or asynchronous (preferred) mode? What is its jitter performance, etc.,

I use the M2Tech hiface2 USB-S/PDIF converter. It supports all standard bit depths and sample rates up to 24/192, runs in asynchronous transfer mode, and is conveniently shaped as a USB dongle so it effectively becomes a part of your S/PDIF cable. It doesn't need to be "mounted" in anything.

Also, if the converter will sit inside the power supply box, how are you going to get its output into the γ2? Panel mount RCA jack?
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Re: A handful of noob questions

Postby ohshitgorillas » July 21st, 2015, 4:14 pm

Thank for your reply. Some follow-up questions to make sure I've got this right:

1. So I'll need a 120VAC>12VAC transformer for the epsilon24. Is there any purpose/benefit to using two sigma24's as transformers, one for epsilon24 and one for the sigma25? Is it just form factor (that's enough for me) or is there more to it?
2. If I'm reading this correctly, the epsilon24 takes 12VAC in and puts 12VDC out, correct? So the sigma25's power supply would need to be a 12VDC > 9VDC converter?

Does all that sound right?

I'm on the fence about the USB to S/PDIF converter, but it would be interesting to see if there's a difference. Maybe I'll just leave some room and someday throw a gamma1 in USB to S/PDIF mode into the same case, or maybe I'll even make a standalone unit from some of the Twisted Pear Audio modular chips.
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Re: A handful of noob questions

Postby amb » July 21st, 2015, 4:54 pm

ohshitgorillas wrote:1. So I'll need a 120VAC>12VAC transformer for the epsilon24. Is there any purpose/benefit to using two sigma24's as transformers, one for epsilon24 and one for the sigma25? Is it just form factor (that's enough for me) or is there more to it?

The σ24 is simply for convenience if you use EI-30 style PCB-mount transformers, and it allows you to stack the σ25 or ε24 on it. Just watch the height of the stack. It may be too high to fit into certain cases.

2. If I'm reading this correctly, the epsilon24 takes 12VAC in and puts 12VDC out, correct? So the sigma25's power supply would need to be a 12VDC > 9VDC converter?

No. As I said, you'll be using a transformer with 12V secondary to power the ε24 (it has a built-in voltage regulator). This transformer must be always on. Then, use another transformer with a 9V secondary for the σ25, set up to output 5VDC for the γ2. The primary side of this transformer will be switched by a relay, which is in turn controlled by the ε24.

All that said, do you really need a momentary pushbutton power switch (or any power switch at all) and all the complications associated with it? It's not like the γ2 would really change your monthly electricity bill significantly. Just build it so that it's on as long as it's plugged in to the wall, and be done with it... Or use an IEC AC inlet with a built-in rocker switch.
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Re: A handful of noob questions

Postby ohshitgorillas » July 22nd, 2015, 6:38 pm

I probably don't need one, no, but I do love those Bellari illuminated buttons. Anyway, I'm ordering from Mouser and I'm having a hard time finding a transformer that isn't this one (http://www.mouser.com/Search/ProductDetail.aspx?R=VPT18-1390virtualkey55310000virtualkey553-VPT18-1390)... it's the most modest toroidal transformer with a 9V secondary I could find on their site. And it's already quite large. If I'd have to buy stuff ANOTHER one of those into the case with everything else, forget it... I'll just find a nice LED-illuminated on/off rocker switch.

I was really hoping that those small form factor EI-30 transformers, but they seem to only be sparsely available and usually with the wrong output voltage.

Dumb question, would it be possible to just chain 1.5V batteries in series to supply the delta25 with 9V?
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Re: A handful of noob questions

Postby ohshitgorillas » July 22nd, 2015, 8:24 pm

I found a miniature toroidal with a much smaller footprint, and placed the order from AMB and Digikey! I'm skipping the epsilon24 until I can find a miniature transformer... I may just use a wall wart for it, though....
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Re: A handful of noob questions

Postby amb » July 22nd, 2015, 9:12 pm

ohshitgorillas wrote:I was really hoping that those small form factor EI-30 transformers, but they seem to only be sparsely available and usually with the wrong output voltage.

Allied Electronics has a selection of EI-30 transformers.

Dumb question, would it be possible to just chain 1.5V batteries in series to supply the delta25 with 9V?

You certainly can, but those batteries won't run long before becoming depleted.
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