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...

 

[krabbencutter]

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.

 

[krabbencutter]

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.

 

[krabbencutter]

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

 

[krabbencutter]

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!

 

[krabbencutter]

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

 

[krabbencutter]

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.

 

[krabbencutter]

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?

 

[krabbencutter]

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

100x50mm