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Post by svart on Jan 7, 2015 19:51:58 GMT -6
"all of the same mechanical constraints" if this is true, then you have answered your own question. You are the one who knows . Yeah, but sometimes thinking out loud where people can critique those thoughts is good practice. When I'm at work, I always run my ideas by the other engineers simply because we tend to get too close to our ideas and it's hard to see any other options. I think I'm going to go ahead with the production amount once I do another check. I will print out the layout, place parts on the paper to see how everything fits, and double check the X/Y locations of the mechanical parts(TRS connectors, Coax connector, screw holes, etc) to make sure they are exactly where they should be. Also, I've received some of the mechanical prototype materials like captured nuts/studs and such. Looks like I've found the part I'll use or have used if someone else makes these. I was able to drill and press these in about 10 minutes. I figure if I make a jig to drill the holes exactly, then it will take less than 2 minutes to do all the holes and press the studs.  |
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Post by kcatthedog on Jan 7, 2015 20:16:28 GMT -6
oh I get it. i work as a analyst; all well and good to know what I think much better to have some constructive criticism !
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Post by svart on Jan 7, 2015 20:20:00 GMT -6
oh I get it. i work as a analyst; all well and good to know what I think much better to have some constructive criticism ! It's kind of a gamble really. The monetary price would be the same if I had to do two orders of production quantities or if I did a prototype set (of 4 boards..) and then another production quantity. So really I'm betting that the first boards will be OK and I'll save half the money I would have normally spent, and the time would be cut in half. If I lose the bet, I'm out the same money, but adding 10 more days of manufacturing time. |
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Post by Martin John Butler on Jan 7, 2015 22:39:27 GMT -6
10 days seems worth the risk. If it was 10 months.. maybe not.
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Post by svart on Jan 8, 2015 11:58:50 GMT -6
OK, today is a big day! I got my first production worthy ADC boards and solder paste stencil! Don't get too excited just yet, there is still plenty of work to be done. I have to build at least one of these for testing before anything else. Once one of these is working, I'll be sending the DAC board to be made by the same company. I still need to have the LCD board made too. I'll likely send both in the next few days. Still need to draw the chassis in CAD, although I have a number of the measurements worked out already.   |
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Post by Johnkenn on Jan 8, 2015 15:33:03 GMT -6
I'm pumped up about this, Svart!
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Post by svart on Jan 8, 2015 15:49:43 GMT -6
I'm pumped up about this, Svart! I populated the power supplies on one board. Everything is A-OK so far. I'll get the rest done tomorrow and hopefully test over the weekend. |
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Post by tonycamphd on Jan 8, 2015 17:00:58 GMT -6
i just saw that previous post, i'm sure you got it licked, but i should still say the one thing about those ADA4898 is they run hot, i hope you put provisions into the board for carrying and keeping heat away from those?
looks awesome man! i too am pumped for this, it's so cool to be watching it unfold like we all are here! Thanx!
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Post by svart on Jan 8, 2015 22:09:26 GMT -6
i just saw that previous post, i'm sure you got it licked, but i should still say the one thing about those ADA4898 is they run hot, i hope you put provisions into the board for carrying and keeping heat away from those? looks awesome man! i too am pumped for this, it's so cool to be watching it unfold like we all are here! Thanx! Yep, taken care of. I'm still not sure why these get so hot. The datasheet doesn't really spec them as getting too warm unless the outputs are shorted, and then it's only 130mA or so. Anyway, even when an opamp swears that they are unity stable, they rarely are perfectly stable especially when they have a reasonably fast slew rate and high bandwidth like these do. It makes me wonder if there aren't some small oscillations in certain circuits that cause them to be hotter than usual, but not show overtly bad symptoms. Even datasheets get it wrong sometimes. Might have to study these a bit once I get the new board populated. |
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Post by jimwilliams on Jan 9, 2015 10:15:19 GMT -6
Do you have film cap bypasses for the large input blocking caps? El caps absorb low level transients. A small quality polyprop film cap will stop that. If the layout is set in stone a small WIMA MKP-2 .01 uf could be attached to the rear of the pcb.
Will you use MELF metal film SOIC resistors? I see the layout is for metal oxides. Those will add THD and noise to the system as they have poor linearity.
On the DAC, a very high quality I/V stage resistor is needed like a Dale CMF55 or a Vishay bulk foil for best resolution. A quality film feedback cap like a WIMA FKP-2 is also recommended.
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Post by svart on Jan 9, 2015 12:52:42 GMT -6
Do you have film cap bypasses for the large input blocking caps? El caps absorb low level transients. A small quality polyprop film cap will stop that. If the layout is set in stone a small WIMA MKP-2 .01 uf could be attached to the rear of the pcb. Will you use MELF metal film SOIC resistors? I see the layout is for metal oxides. Those will add THD and noise to the system as they have poor linearity. On the DAC, a very high quality I/V stage resistor is needed like a Dale CMF55 or a Vishay bulk foil for best resolution. A quality film feedback cap like a WIMA FKP-2 is also recommended. The input caps are not going to be used. Direct coupling, unless a customer specifically asks for it to be AC coupled. Thin film SMD resistors and MELF leadless are the same technology. I'm using thin film SMD resistors where needed. I also use them in up to 4Ghz transceivers that operate down to -80dBm without a lot of noise issues, and thick film for most other places that don't need low noise or low tolerance. Resistor noise is about inclusions (impurities) in the resistive material and the crystalline structure of the material impeding smooth flow of electrons. If this is what you mean by (non)"linearity", then yes, I agree. Although, Johnson noise is an issue in a lot resistors being used in high gain stages, I'm not sure it's a big deal here. What IS a big deal is that high bandwidth opamps are very sensitive to feedback, and it seems that a lot of designers ignore the proper value scaling of resistor networks in favor of achieving higher bandwidths than necessary, or simply swapping in higher bandwidth parts as a blind "upgrade". Now, that can cause increased noise moreso than the type of resistor. Arguing about this is almost purely marketing points and/or academic as system noise is pretty assuredly higher than resistor noise of modern parts. If this were a preamp with 80dB of gain, I'd be more inclined to agree that resistor choice is a bigger concern, but it's a buffer with almost no gain. Proper input current setting is of more importance here, as is the feedback resistor value. We could talk about how the inclusion based noise is less for foil wound resistors, but I can counter with the inherent inductance of those parts becoming a potential LCR tank coupled with wideband opamp. ESR is a common topic for most internet engineers, but very few have met with it's harder to defeat sibling ESL (equivalent series inductance). ESL comes from the long leads(long is relative, and can be 1/2 of a mm in some cases..) of axial resistors and foil wraps in capacitors and "low noise" resistors. MELF foil resistors still have the foil wraps and internal leads to the capped ends still introduce some inductance. To squash higher frequency oscillations we need more capacitance in the feedback loop to bring the feedback knee down and keep the opamp happier. So you trade (academically) lower noise for a much degraded bandwidth. In the design world, you always have to balance one thing with another. At least to me, I find that a good COG/NPO cap sounds better than a film, and thus is what I'm using. Threads upon threads of audiophile forums have agreed, and a lot of disagreed too. You really can't please everyone when everything is subjective. Also, I have to reiterate that this is NOT a 10000$ Weiss converter. This is a 1000$ price/performance balance. |
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Post by Johnkenn on Jan 9, 2015 13:52:40 GMT -6
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Post by Johnkenn on Jan 9, 2015 13:53:17 GMT -6
Oh - MELF - sorry.
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Post by svart on Jan 9, 2015 14:56:37 GMT -6
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Post by Johnkenn on Jan 9, 2015 15:06:31 GMT -6
It's a Metal Milf...(no idea...stock google image when googling metal milf)
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Post by kcatthedog on Jan 9, 2015 15:51:59 GMT -6
It's a Metal Milf...(no idea...stock google image when googling metal milf) shit John its me Kcat !! svart and Jim; really appreciate the frank design and part selection conversations; thx ! |
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Post by tonycamphd on Jan 9, 2015 16:48:46 GMT -6
svart "The input caps are not going to be used. Direct coupling, unless a customer specifically asks for it to be AC coupled."can you school us on the differences/advantages either way, sonically or otherwise?
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Post by wiz on Jan 9, 2015 16:59:03 GMT -6
Metal Milf
LOL
8)
Cheers
Wiz
PS i can't wait to hear this thing.
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Post by wiz on Jan 9, 2015 16:59:54 GMT -6
svart "The input caps are not going to be used. Direct coupling, unless a customer specifically asks for it to be AC coupled."can you school us on the differences/advantages either way, sonically or otherwise? Caps sound different to No Caps. 8) cheers Wiz |
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Post by svart on Jan 9, 2015 17:53:07 GMT -6
svart "The input caps are not going to be used. Direct coupling, unless a customer specifically asks for it to be AC coupled."can you school us on the differences/advantages either way, sonically or otherwise? Direct coupling is simply using no caps to block DC. Most devices have input and output caps for protection against DC offsets from other devices. I figure that most audio equipment already has a set of caps on the output blocking any back feeding DC, so why add another set to the input of this device? Anyway, there are loads of forums full to the top of folks arguing about caps and their effects on audio. You can't get a straight answer out of any of them IMHO. There have been studies with more scientific data presented, but still, it's up to each person how they feel about various "sounds" of caps. The short answer is that caps do affect sound, but it's a very small effect if the cap is a quality part. Those who wish to sell you upgrades will surely tell you otherwise. Some of the worst performing caps, tantalum, are used by some of the most revered and loved devices (Neve, etc) yet if someone were to attempt to use a tantalum coupling cap today in a "audiophile" type device, they would be laughed at, made fun of, and then laughed at again. Same pretty much goes for most any high end device. The pseudoscience seems to get a lot more fanfare than the actual science. Anyway, I don't necessarily need to use caps here, so I don't, although there IS 2VDC offset on the inputs to the unit. I may decide to put caps on the input for the sake of "safety", or I might make a big disclaimer. I'm undecided as of yet. The thought behind caps being bad is that their parasitic qualities tend to act like a LPF and their dielectric tends to be "slow" when moving charge from lead to lead. This, of course is the loudest argument you'll hear, but you won't hear that this is in the MHz range and that the audio spectrum has almost no such problems with modern caps, even electrolytics. This can cause some high end loss, or it can cause transients to seem to be rounded off (the LPF effect). It can also cause distortions and non-linearities due to changing impedances over frequencies. This is why the myth of bypassing with film caps is so pervasive, that the lower value film has lower ESR and will therefor shunt higher frequencies around the lossy electrolytic cap. However, there is not much proof this works in practice as most people that have been pleased with the result had previously been expecting a pleasing result.. Well respected folks like Doug Self and Cyril Bateman have covered this and thoroughly debunked most of this stuff, so I don't give it much thought either. As I mentioned before, there are ESR issues, and sometimes ESL issues if the frequencies get high enough and the compensation isn't good enough on the opamps. Now this *could* be a problem at the higher ends of the GBW of the opamp, especially in the feedback sections. If the cap is inductive (leaded) and isn't of sufficiently high value to swamp the inductance, then you'll get frequency peaking and oscillation. But again, it's arguing academics. How do they sound? The honest answer is that I'm willing to bet that 99% of the people who would do a blind test wouldn't be able to distinguish different types as long as the circuit was not affected by the parasitics of the cap type. Unfortunately, selling gear means playing to the crowd too, so while a lot of designers know they don't need to use any special caps, they will simply because they are expected to. A good read and it covers a lot more scientific detail than I care to type about: sound.westhost.com/articles/capacitors.htm |
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Post by svart on Jan 9, 2015 18:58:00 GMT -6
Another teaser:  This has one ADC board in the ADC slot and another taking the place of the DAC so that I can get measurements. |
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Post by kcatthedog on Jan 9, 2015 19:02:40 GMT -6
yo svart thx for keepin it reel !!
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Post by tonycamphd on Jan 9, 2015 19:33:37 GMT -6
Another teaser: I like the white pcb's, are those smd caps in the analog audio path portion of the ADC? |
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Post by svart on Jan 9, 2015 19:37:31 GMT -6
Another teaser: I like the white pcb's, are those smd caps in the analog audio path portion of the ADC? No, those are for bulk decoupling for the various sections of the circuit. Since it's a small design, each opamp and active part got it's own decoupling and bulk capacitance.. Possibly a little overkill, but nobody can say it's underpowered! There are no series caps in the audio path. There are only COG/NPO ceramics in the opamp feedback filters. |
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Post by LesC on Jan 9, 2015 19:49:46 GMT -6
Another teaser: This has one ADC board in the ADC slot and another taking the place of the DAC so that I can get measurements. I dunno, I've heard the pink polka-dot circuit boards sound sweeter with a hint of cinnamon. Sorry for the technical talk, jimwilliams and I are just trying to keep you honest. |
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