Amek AT8 Hybrid Line Driver Questions

[Khron]

I have to move some of them further away from the IC pins than before

Which ones, and by how much? Only one that fits that description might be R2..?

Could move those power trace vias down to where the traces are closest to each other, and reduce the R2-to-R4 trace length even further...

 

[GreyboxAudio]

Which ones, and by how much? Only one that fits that description might be R2..?

Could move those power trace vias down to where the traces are closest to each other, and reduce the R2-to-R4 trace length even further...

This is what I ended up with this morning:



I aligned everything to the grid so that even components on different sides of the IC are at the same level. It looks pleasing but I also started to create more unnecessary space.

 

[GreyboxAudio]

I rotated the components and while it's aesthetically more pleasing I have to move some of them further away from the IC pins than before. This is where it gets philosophical. I'll sleep over it but in the end I will probably prioritize function over form.

I still haven't had time to do more reading about the power pins. The idea that current will pass in a straight line and will go into every component sequentially sounds very "romantic" to me. Even more so when we're talking about fractions of millimeters and when the current could physically choose an alternate path. Let's imagine a scenario where the power trace passes through the pad of the capacitor first, but the physical distance between the IC power pin and the beginning of the capacitive element are equal. Would current still run through the capacitor first just because we want it to? This thought experiment might get even weirder the more the package sizes between capacitor & IC differ. What if the IC is QFP but the ceramic capacitor is a through hole part? In that case the physical path "into" the capacitor might actually be longer/of more resistance, than the direct path into the IC.

I just watched a couple videos about decoupling and this one was very interesting! In the part from 55:50 Eric Bogatin talks about how the 100nF bypass caps are apparently redundant in SMD.

 

[Khron]

In the part from 55:50 Eric Bogatin talks about how the 100nF bypass caps are apparently redundant in SMD.

Context is paramount - "redundant" is very relative. As i understood the description around that timestamp, that may be the case assuming you already have similarly-sized 1uF and/or 10uF in place.

 

[GreyboxAudio]

Context is paramount - "redundant" is very relative. As i understood the description around that timestamp, that may be the case assuming you already have similarly-sized 1uF and/or 10uF in place.

Correct. I've now watched the rest of the video and if I understood it correctly I could drop in larger valued capacitors in place of the 100nF caps, remove the two 10uF electrolytics and as an added bonus I could shorten the supply lines quite a bit.

 

[Khron]

If anything, you could easily find 10uF / 25v ceramics in 1206 packages too / anyway

 

[GreyboxAudio]

I've now added the balanced line input as well and fitted everything onto a 50x100mm board:

 

[richiyobs]

I've now added the balanced line input as well and fitted everything onto a 50x100mm board:

View attachment 128570

You could also add Gnd plane on top side... Maybe It can be used to better screen components and so put small gnd vias around the surface where you change layer, it's a practice i saw in any tutorial...

 

[amplexus]

As an owner and maintainer of a 32ch BC3- albiet with spares- I am watching this topic with great interest

Re: Rupert’s involvement- my understanding was that he was responsible for the TLA preamp circuit (BC3, 9098 and others) and the AT8 driver, and the EQ of one or two desks of that era but otherwise not much else in terms of overall desk architecture pr design- however I may be mistaken and Matt is the obvious knowledge holder king here!

 

[GreyboxAudio]

Once

As an owner and maintainer of a 32ch BC3- albiet with spares- I am watching this topic with great interest

Re: Rupert’s involvement- my understanding was that he was responsible for the TLA preamp circuit (BC3, 9098 and others) and the AT8 driver, and the EQ of one or two desks of that era but otherwise not much else in terms of overall desk architecture pr design- however I may be mistaken and Matt is the obvious knowledge holder king here!

Once I have the first PCBs built and tested I will upload all the KiCAD files to GitHub

 

[GreyboxAudio]

Since it got very crowded on the PCB there were a couple of places where it was really hard to make out which label belongs to which component. So as an experiment I've oriented all ceramic capacitors vertically and all resistors horizontally. It still needs a bit of refinement but I think the idea might work out without too many compromises.

 

[GreyboxAudio]

I've added M3 mounting holes and have just ordered the first batch of prototype pcbs

 

[amplexus]

I've added M3 mounting holes and have just ordered the first batch of prototype pcbs

View attachment 128794

What’s the overall pcb size you ended up with?

 

[GreyboxAudio]

What’s the overall pcb size you ended up with?

100x50mm

 

[GreyboxAudio]

The boards have arrived and against all odds everything worked first try! I've published the KiCAD project here: https://github.com/greyboxaudio/Purrtico-TLA

 

[Khron]

The boards have arrived and against all odds everything worked first try!

Well that can't be right, that's not supposed to happen!..

 

[GreyboxAudio]

Well that can't be right, that's not supposed to happen!..

Right?! All the PCB-Design tips videos I watched on youtube seemed to agree that one should expect the first version to be a failed attempt. And while the PCB turned out pretty well (thanks to your help!) there were a lot of other potential sources of human error involved. From the drawing of the schematic to ordering the parts, exporting the correct files for manufacturing, working with a new opamp model for the first time, soldering SMD for the first time, using polymer electrolytics for the first time, wiring everything up correctly etc.

Some key take-aways so far:
- soldering SMD is fun! Yeah, it's a bit fiddly, but not having to flip the board all the time is amazing!
- I specced all passive SMD components for 1206 knowing that some MLCCs I bought are 0805. Soldering 0805 parts to 1206 pads worked well
- orienting the electrolytics all in the same direction was a really good idea
- I started with the ICs and tested all leads for continuity. Then I soldered the MLCCs & resistors, which I also tested for continuity afterwards. Last but not least I soldered the electrolytics, trimmers and connectors
- the layout of the reference labels worked well and I managed to solder everything to the correct pads without any confusion. Having the resistors oriented horizontally and the MLCCs vertically was a good idea imo
- the purple PCB with the blue trimmers and blue/silver polymer caps looks great!

Improvements for r01:
- I already made some changes to the power traces and ground plane (see attachment). (@Khron that's basically what you suggested at the beginning, but it took me a while to stop being scared of vias and the ground plane xD)
- I'll copy the reference labels of the electrolytics to the bottom silk screen as well
- the bottom layer needs test points to easily test continuity of the electrolytics
- I'll connect the mounting holes to the ground plane so that it can be connected to the case/shield if needed
- I might take a look at the reference labels, because the order is pretty arbitrary right now
- some friends of mine will get a PCB + components and we'll assemble it together. Maybe they also have some additional ideas

All in all I'm pretty happy so far!

 

[MidnightArrakis]

I rotated the components and while it's aesthetically more pleasing I have to move some of them further away from the IC pins than before. This is where it gets philosophical. I'll sleep over it but in the end I will probably prioritize function over form.

I still haven't had time to do more reading about the power pins. The idea that current will pass in a straight line and will go into every component sequentially sounds very "romantic" to me. Even more so when we're talking about fractions of millimeters and when the current could physically choose an alternate path. Let's imagine a scenario where the power trace passes through the pad of the capacitor first, but the physical distance between the IC power pin and the beginning of the capacitive element are equal. Would current still run through the capacitor first just because we want it to? This thought experiment might get even weirder the more the package sizes between capacitor & IC differ. What if the IC is QFP but the ceramic capacitor is a through hole part? In that case the physical path "into" the capacitor might actually be longer/of more resistance, than the direct path into the IC.

I am just a "Beginner PCB Designer" since I only have 40+ years of designing PCBs for aerospace/avionics companies, defense contractors, medical electronics firms, NASA, R&D laboratories and others, so you can take my comments here with a "grain-of-salt", OK??? First off.....I would suggest that you pay attention to the comments of "Khron" and others who have offered you advice as their suggestions to you have been completely correct!!! If you are truly wanting to learn more about "How To Design PCB's Correctly", then.....DON'T ARGUE WITH EVERYONE & LEARN FROM THEIR ADVICE!!! What you will end up learning on this forum for - FREE - would have cost you at least several hundred Euros, if you would have taken a class or a webinar to learn this exact same stuff.

A lot of my PCB-design work has been in various "RF/microwave" environments and the many engineers I have worked with all had top-level engineering degrees in categories you didn't know existed from colleges and universities that you have never heard of!!! The point being is.....-- ALL -- of these engineers stressed upon me time and time again that you -- ALWAYS ROUTE TO A CAPACITOR FIRST -- before any other component!!! So.....you need to force yourself to create a components placement with this in mind, while also keeping a "mental eye open" with how the developing components placement might be affecting the eventual routing. In other words, while you are moving and placing the components around on your PCB, you -- ALSO -- need to be "imagining/visualizing" how the routing will be taking place at the same time!!! And.....doing this TAKES SKILL.....Buddy!!!

One "RF" company I worked at was involved with designing highly-specialized communications equipment for "unknown and unheard of" U.S. Government secret agencies. YES!!!.....working at this company had finally verified for me that there are actually all sorts of "covert intelligence-gathering" U.S. agencies that nobody knows about!!! Real spooky stuff!!! In any case, the engineers at this company would perform tests on existing "RF" PCB's and log their test results. Then.....they would have me completely redesign these PCB's.....with the components placement and the routing.....GOING TO THE CAPACITORS FIRST!!! When the new PCB's arrived and were assembled, the engineers would then re-run their tests again. While the engineers were performing their tests, they would invite me over to their workbench areas and they showed me their test results of the new PCB's as compared to the previous PCB's. I could then see for myself the lower noise, faster slew rates, overall higher performance of the circuits.....just by simply placing and routing to the capacitors FIRST!!! But, again.....what do I know??? You can either take what I have written here at its own value.....or.....you can believe that I am just making all of this up!!! Your call!!!

In general.....I would fatten up your tracks.....JUST BECAUSE!!! Doing so lowers both the track resistance and its inductance. In addition, you should really try to avoid entering/exiting component pads like this:

------↓↓↓↓↓------


Doing this creates what are called "Acid Traps" and over a period of time, these can cause the track and/or pad to come loose or, delaminate, from the PCB material. In other words, these are called a "NO!!!-NO!!!".

There are some other issues with your layout that I was going to mention, but I would end up writing a small booklet in trying to cover all of the pertinent details. Therefore.....why don't you just ZIP-up all of your KiCAD files connected with this layout of yours and send them to me via a PM and I will look them over for you. That will be MUCH easier!!!

And.....just in case you may be wondering.....these are the typical types of PCB's I have been involved with designing:

-- TOPSIDE --

-- BACKSIDE --

-- TOPSIDE --

-- BACKSIDE --


NOTE: These PCB's were used in signal-processing equipment as the signals from The HUBBLE Telescope and the various Space Shuttle missions were received here on Earth and processed for use by NASA facilities around-the-world.

/

 

[GreyboxAudio]

Lol, I'm out.

 

[ultra-alex]

All in all I'm pretty happy so far!

well done. cheers mate!