Author Topic: "What the hell is this, and why do I need one?"  (Read 7157 times)

Offline Analog

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"What the hell is this, and why do I need one?"
« on: May 29, 2019, 02:53:27 PM »
https://oshpark.com/shared_projects/jY5VGW48





It is a gizmo that has a BNC connector, "special" magic circuit (that some idiot kid in Ireland could not understand and some British ponce said could never work and that I had never designed any RF gear in my life because no one would be that stupid yet every microwave radio I worked on used it), which then goes to a transformer that is suitable for SPDIF, and then it goes to something I am probably never going to disclose, and ends up going to a LVDS gate, that drives a coax so that anyone can make their own BNC SPDIF input, and hook it up to ANY RX chip. (Although you may need to stick a cap somewhere on the chip end, depending on how it is designed.) (OK, if it is designed to work on 3.3 V directly, it may need an extra gate.)

The neat feature is it will work with a +12 V supply.................or a +5 V supply, and put out a very clean signal (that won't screw with the actual SPDIF input), at a level that should not fry the SPDIF input on a RX chip.

(Remember, it is supposed to be 0.5V p-p. And Crystal...............in their infinite wisdom.....................the '8412 runs on 5V, and has internal clamps, the '8414 is like the '8412, but on 3.3v, and the '8416...................well, it is totally different, but can handle up to digital supply voltage.) (Not sure about any of the TI versions, because no one used them.) (Or the Wolfson, as they needed to be programmed, and most of the folks I know are almost as stupid as I am, and can't program diddly-squat. And the ones that can think I am more stupid that I really am. Which is hard...............!)

OK............back the inputs..................should work fine on a '8412/4, but you will probably need to stick a small cap in front of the input, as they are biased up to some voltage, and direct coupling will muck that up. If it already has a TOSLINK, it should already be there. So DON'T SCRAPE IT OFF THE PCB! The '8416 works on +3.3V, and the level should be high enough for it to work properly. In any case, you will need to check with the datasheet for the RX you have.

OK, putting all that aside........................the bottom line is this works better than any RX input on any commercial DAC that you have. Period.

While, in theory, you can buy 3 PCBs, from OshPark, for only $10, you won't have the schematic! And I am not going to give it to you. Plus, if we sell you one, it will be tested, and will come with a 1' coax pigtail, so it will be easy to make work.

If you only have +12 V as a supply, you will have to stick a crappy '7805 TO-220 regulator in the proper holes. If you have +5V, you can put the supply leads in the pads for the '7805 out and ground.

Simple, right?

And let's be honest......................we are not going to get rich selling these, so buy a few.

Oh...............we will also supply the stand-off, so that you can bolt it to the back of whatever. Without having to worry about how you are going to keep it from rotating, since none of you are likely to have a 1/2" D hole punch. Right? (Yeah, you know I am.)


Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #1 on: June 14, 2019, 02:52:48 PM »
"Now getting it ready for you.........................."



"Not yet ready for you......................."



"Anytime now..................almost ready for you................."


Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #2 on: June 14, 2019, 03:07:08 PM »
Yes, it is pretty much ready. There is a mistake on the PCB, which I should have caught, but didn't. And it may need some minor tweaking, but more about that in the next post.

So, anyway..........bidnis first..................

It comes with a BNC attached, so all that you have to do is make a 1/2" hole. Since very few of you have a 1/2" D hole punch, it comes with a reversible stand-off, so that it is used to both support the assembly, and prevent the BNC from rotating. (You can thank me later. Hell, just buy some.)

It can work with either a +5 V supply, or a +12 V supply. You can drop a TO-220 7805 style regulator in it, to supply the +5 V that it needs to operate. (NO! YOU CAN NOT PLUG 12 V DIRECTLY INTO IT, WITHOUT THE '7805 THINGIE. It will fry the little 3.3 V regulator.)

Also, it comes with the ferrite bead wrapped around the power leads. For some bizarre reason, there is some feedthrough (probably into the pulse transformer), that shows up on the input return loss. One of the weird things that we strive for is input/output circuits that do not go through wild gyrations, when the power is turned on. Not sure there is a pressing need to do it that way. We just do because we can and we are the ones who are actually weird. (But, you already knew that, right?)

Anyway...................there was some weird stuff going on, above 50 MHz. Power on......................power off.......................power leads just hanging around, not connected to the PSU.....................short them together........................

Since CH is no longer here to scream at me "Hey, man, don't use those ^$))%$^^#^%#$ ferrite pieces of crap! They are magnetic, and you know magnetic stuff sucks. Besides, they will eventually become DC saturated and will sound like crap."

Well....................maybe. Problem is, the return loss doesn't look that good (above 50-60 MHz) without it. We are talking about 10 dB difference. Maybe the next iteration will have that fixed. Maybe not. And then, there might not be a next iteration if no one buys these damn things.

Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #3 on: June 14, 2019, 03:22:06 PM »
OK, time to test this silly thing....................

First, we need an input. Grabbed an old SB3, and this is what its output looks like:



(Yes, it is unterminated, which it isn't supposed to be. You'll see why in a bit why I chose that.)

And here is what comes out of the silly gizmo:



It is also unterminated.......................

(I think now you will see why.)

So, this should drive any SPDIF RX chip, directly, without any changes. If you have to drive a 3.3 V (or worse, 5 V logic chip) directly, it will need to be boosted. But, most likely, you will just use it as-is.

And what about the input return loss?

Well, here it is, with the power off:



Anyone who followed the old "SB3 thread" on AudioCircle, might recall how hard this is to do.

And once power is turned on, and all those transistors (operating in a non-saturation mode.....................yes!, there is no way to saturate the input...............even if you cram 5V into it.) (Please don't..................the pulse transformer isn't very large, and will saturate worse. And don't put DC on it!) add in some stray reactance, and well, you get the picture.

(Oh, speaking of pictures................got sidetracked...........)



So, maybe, I'll look more closely what is behind that. Maybe not.

Offline tubesguy

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Re: "What the hell is this, and why do I need one?"
« Reply #4 on: June 15, 2019, 07:51:07 AM »
I'll need two, one for "the reference system" and one for the tiny Vanatoo powered speakers.

Hoping the Legato is appropriate to drive this gizmo.  ;)

Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #5 on: June 15, 2019, 05:01:49 PM »
Think I will just send you the one that is made up already, and see how it installs in your gear. I had some further ideas on how to make it more universal.

This was originally designed to be part of a specific product (well, that is how it was designed........................whether they used it or not...................at least we got paid), so we knew what the output needed to be, etc.

The problem gets to be when someone, anyone, wants to remove a wretched TOSLINK input, and replace it with one of these. Bet that a lot of those applications need 3.3 V logic levels to work.

You could do us all a favor and look at the gear you might want to put this in, and see how the inputs work.

Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #6 on: June 27, 2019, 08:43:26 AM »
We have a new member!

And they have a question...................

And since the reason we started this place is so that folks can ask questions, and get answers HERE, so that we don't have to answer the same question 10 times................

Right now, we are thinking about $60. The price is based on the cost of parts. Is it worth $60? We don't know. So, unless or until someone buys one, that is what we plan to charge.

If folks only want to pay $20 for it, well, we know how much the parts cost, so that is not going to happen. In which case no one will ever have to worry about it.

You might get lucky, and talk us into selling the one pictured above for only $40. We need feedback, there are mistakes on the PCB, and since this is now viewed as a "universal drop-in accessory", and not something intended to be dropped in the design of someone's product, the new version will be slightly different. So, $40 is $40. It won't pay any bills, but will put a few bucks in the company "pizza fund". Which is now a misnomer, as someone who shall remain nameless can no longer eat pizza, and is even more miserable than before!

If no one likes this version, well, see above statement.

Buy it now before someone changes their mind.

Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #7 on: June 27, 2019, 11:38:46 AM »
Attention, new member:

Please ask your questions here, and not via PM or e-mail, so that others can see the response here. That is the point of having a forum.

It also saves us from having to answer any question just once, and not 2 dozen times.

So, the answer, posted here is:

1.) Uh, if the problem was not fixed, then how did I make all the measurements that are posted here? It works. It just isn't pristine, and we do not want to throw it in the trash, so it can be bought at a discount.

2.) The final version will be different. Not better, not worse, just different.

"But what difference?"

Easier to change output level. You may not need to change the output level, but if you do, it will be easier on the new one. (That will depend if you use a '8412, '8414, '8416, some horrible thing made by TI, or who-knows-what RX chip. Which might even be the actual DAC chip itself.)

BTW, how did you find out about us?

Offline alexm

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Re: "What the hell is this, and why do I need one?"
« Reply #8 on: June 27, 2019, 12:50:42 PM »
Thank you!!!

I'd like to buy this one.
How can I pay for it (paypal or something else)?


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BTW, how did you find out about us?

Fortunately! Yesterday, I was lucky to have had email conversation with the author of the schema and he shows me this forum. And made sensible advice!
(I was trying to use AD830; but having no related knowledge, experience and equipment makes that task almost impossible.)



Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #9 on: June 27, 2019, 01:22:25 PM »
Oh, wait...................are  you the guy who sent us an email, for El Jocko Schmucko? (That was forwarded on to him.)

Now it all makes sense.

AD830? That reeks of that other guy. Now it makes more sense.

(That is all that we need. Those 2 troublemakers showing up, just like Jake and Elwood Blues, at the fancy French restaurant, trying to get "Mr. Fabulous" to join "the band!". Please................noooooooo!!!!!!!!!!!!!!!!!!!!!!!!!)

"Your women, your women, I want to buy them. How much for the little girl?"



Yes, we take PayPal. Where are you located?

(Hmmm...........the only problem with that photo is El Jerko Schmucko is the short, but skinny one, and the other guy is both the tall and fat one!)

(And at least one of them still has long sideburns.)

Offline alexm

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Re: "What the hell is this, and why do I need one?"
« Reply #10 on: June 27, 2019, 01:32:15 PM »
 :) I should watch that movie (https://www.youtube.com/watch?v=ZLUiK2lbN2s)

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Yes, we take PayPal. Where are you located?

I'm located in Ukraine, but with the shipping address in Port Reading, NJ (meest.us).
« Last Edit: June 27, 2019, 01:46:13 PM by alexm »

Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #11 on: June 27, 2019, 02:42:09 PM »
THE UKRAINE!!!!!!!!!!

Do you have any idea how hard it is to get stuff to the Ukraine?

I guess you do, since you have some sort of expediter.

We used to do a fair amount of bidnis, in Russia, until around 2010, when the international postal regulations changed. Our customers wanted to blame "King O'Dumbo" (as he is called down here), but as much as I wanted to blame him, he had nothing to do with it.

Losing Russia, and the rest of the countries in that region, cost us some money.





Uhmm..................what to do................I guess I will PM you, so that I can get your email address.

Postage rates went up, the other day, so it will now cost $8 to mail it.

Offline Analog

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Re: "What the hell is this, and why do I need one?"
« Reply #12 on: June 27, 2019, 02:49:18 PM »
OK, so we are on the same page..................this is going into a RX chip, that normally takes 0.5 V p-p, right?

The coax that is on it should be long enough. If not, you can probably use a twisted pair. (No, I am not talking about El Jerko Schmucko and that other guy.) You can cut it to fit, but be careful when you solder it. The dielectric melts very easily.

I will include a 6-32 screw, flat washer and lock washer, so that you can use either end of the male-female standoff on the PCB or the chassis.

I will need to include a nut, for the BNC.

Are you going to power it from +5V or +12V? If it is 12V, I will stick in the cheap regulator that drops it to 5V, for the main reg.

(You can tell me all of that here. Except, of course, your email address.) (And any other questions or concerns. It isn't like you can call me on the phone [ha!] and I can talk you through it, if you have problems.

Of a mechanical nature, of course!)

Offline alexm

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Re: "What the hell is this, and why do I need one?"
« Reply #13 on: June 27, 2019, 03:00:27 PM »
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Do you have any idea how hard it is to get stuff to the Ukraine?
I guess you do, since you have some sort of expediter.
That's true. The only reasonable way I've found.

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I guess I will PM you, so that I can get your email address.
I'll be grateful!

Thank you!
 

Offline alexm

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Re: "What the hell is this, and why do I need one?"
« Reply #14 on: June 27, 2019, 03:08:09 PM »
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this is going into a RX chip, that normally takes 0.5 V p-p, right?
Yes

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The coax that is on it should be long enough. If not, you can probably use a twisted pair.
I'll use coax longer than 2m


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Are you going to power it from +5V or +12V? If it is 12V, I will stick in the cheap regulator that drops it to 5V, for the main reg.
I'm going to power it with +5V.

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It isn't like you can call me on the phone [ha!] and I can talk you through it, if you have problems.
Yes :)
« Last Edit: June 27, 2019, 04:11:05 PM by alexm »