Amek AT8 Hybrid Line Driver Questions

[GreyboxAudio]

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.....SHUT-UP & PAY ATTENTION!!! 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 on 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 onto 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:

------↓↓↓↓↓------
View attachment 129341

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 --
View attachment 129342
-- BACKSIDE --
View attachment 129343
-- TOPSIDE --
View attachment 129344
-- BACKSIDE --
View attachment 129345

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.

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The amount of accumulated toxicity makes my acid traps jealous

 

[MidnightArrakis]

The amount of accumulated toxicity makes my acid traps jealous

[The amount of accumulated toxicity makes my acid traps jealous] -- I am not quite sure what you are meaning here, but I think I have an idea. In any case, I was writing from a perspective of.....you were asking for advice and help, which other members on here were gladly providing you with, but then you were either arguing against or challenging the advice they were providing you with. So.....my comment was based upon -- "Here's my background in PCB-design and I will also offer you some help. But, if you also want to challenge/dismiss/ignore what I am offering you.....that's your choice"!!!

Now.....once again.....should you want to PM me all of your KiCAD files as other members have done, I will take a close look at your layout and see what's up with it. Other members on this forum have sent me their GERBER and N/C Drill data files while letting me know that one or two things "might not be quite right". Then, when I run their files through my "GERBER and N/C Drill Analyzer & Editing Program", it reports that their files actually have 8 or more fabrication issues within them. So.....I fix things up and create new fabrication files for them, ZIP everything back up and send them my new fabrication files back. When those members receive their new PCB's after using my new GERBER and N/C Drill data files, they send me a message saying, "WOW!!! THESE ARE THE BEST LOOKING PCB's I'VE EVER HAD"!!! ..... GEE!!! What an - AWFUL - person that I am, huh???

[I'll connect the mounting holes to the ground plane so that it can be connected to the case/shield if needed] -- ONLY CONNECT -- ONE -- MOUNTING HOLE TO THE "COPPER POUR" GROUND PLANE!!! .....Otherwise, you will be creating a "Ground-Loop" problem!!!

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[JohnRoberts]

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.....SHUT-UP & PAY ATTENTION!!! 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.

Free advice is ok, but polite civil discourse is required here.

Do not say "SHUT-UP & PAY ATTENTION!!! ".

JR

 

[MidnightArrakis]

Free advice is ok, but polite civil discourse is required here.

Do not say "SHUT-UP & PAY ATTENTION!!! ".

JR

-- Edited.

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[amplexus]

100x50mm

Ahh ok so a fair hike bigger than the OG modules. Those definitely won't clear inside my console!

 

[GreyboxAudio]

I have uploaded r01, including fabrication outputs for JLCPCB. The previously unused opamp now acts as an optional HPF. Since I don't want to require anti-log pots, the 100KA potentiometer is wired backwards. While being a bit counter-intuitive this gives a more usable range. I will order a batch soon so that I can test & verify everything.

 

[GreyboxAudio]

Ahh ok so a fair hike bigger than the OG modules. Those definitely won't clear inside my console!

Here's a rebuild of the AT8. The routing is pretty ugly because I spent already way too much time on it and my priority was to get it to a state where kicad doesn't spit any errors It's 46x20mm which is 4mm taller than the original AT8. All resistors & caps are 0805 parts and I've included the fabrication outputs for JLCPCB.

 

[thomasdf]

I am working a preamp design (see dedicated thread here : https://groupdiy.com/threads/rouge-un-my-attempt-at-a-red-lundahl-5534-preamp.88241/ ) and was thinking about using a AT8 output, that would allow me to use some LL1539 transformers I have... The work you have done here is amazing, and very handy... Thanks a ton !

 

[GreyboxAudio]

Thank you I have also refined the AT8 PCB a bit and the assembled PCBs should hopefully arrive next week. I'll publish the GitHub repository once I've tested the design.

 

[thomasdf]

I am curious / surprised about the value of R19 in your schematic. Shouldn't R8 and R19 have the same value so they "meet halfway" and the ideal position of the trim is in its middle position ?
How do you trim the CMRR ? Signal generator and triming for a symetrical waveform ?
Thanks again

 

[GreyboxAudio]

I am curious / surprised about the value of R19 in your schematic. Shouldn't R8 and R19 have the same value so they "meet halfway" and the ideal position of the trim is in its middle position ?
How do you trim the CMRR ? Signal generator and triming for a symetrical waveform ?
Thanks again

I haven't fully grasped that either. But on one of my original AT8 it's 3k1 and on another one it's 3k7.

 

[thomasdf]

Well it makes sense because 3k1 + 500k is approx equal to 3K7, (edit : was I drunk ?) give or take. But that implies the trim won't be centered and may even reach the end of course before an ideal setting, I suppose

 

[GreyboxAudio]

All the other resistive pads on my original AT8 PCBs are accurately trimmed to <0.1% tolerance. This and the fact that the other resistor going to the 500R trim pot is 2k2 makes me think that the difference between the outputs is actually somehow important.

 

[GreyboxAudio]

I've attached my spice simulation if you want to poke around

 

[thomasdf]

I've never used LTSpice, but installed it and toyed around... It's interesting and makes me want to learn how to use it properly, thanks

 

[GreyboxAudio]

My AT8 replacements have arrived and seem to be working as intended.

 

[GreyboxAudio]

Something isn't right. I put my second, unmodified (at least not by me) Mozart channel on the bench as a reference. Buss & Insert Outputs have completely symmetrical signals across the frequency spectrum. This seems to imply that I made a mistake somewhere and now I need to figure out where

 

[MidnightArrakis]

Something isn't right. I put my second, unmodified (at least not by me) Mozart channel on the bench as a reference. Buss & Insert Outputs have completely symmetrical signals across the frequency spectrum. This seems to imply that I made a mistake somewhere and now I need to figure out where

[Something isn't right] -- Maybe it might be this -- not fully-seated IC chip in its socket -- that could be doing something weird!!!


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[GreyboxAudio]

That one's just vibing. But there's something wrong with my reconstructed AT8 schematic. Unfortunately the original schematic is not in high quality, all the component values were missing and I don't even have another version for reference.
Edit: I did re-measure all the resistive pads on my two desoldered AT8 circuits and still get the same values. The two other AT8 are hard to measure in-circuit and I don't want to desolder them because those Amek PCBs are a pain in the backside to work with.

 

[jensenmann]

I don´t know if I posted this already: https://mae.tcrcloud.de/index.php/s/rq8Kxt2A27Rc2c4?path=/Amek/Amek BC3
Look through the files, maybe there are better readable schematics amongst.