Schematic coaching needed

[mrdon]

I need a schematic coach to tell me if I got this layout correct. Here's the layout.

Here's my interpretation of the layout:
1. One end of the 3300pf cap is connected to Pin 20 (FILT) and the other end is connected to Pin 21 (AGND).
2. One end of the 470ohm resistor is connected to Pin 20 and the other end is connected to the 220nf cap. The other end of the 220nf cap connects to Pin 21.

Please be kind to me.

Thank you!

 

[thrice]

Sort of.

Quote:

Here's my interpretation of the layout: 1. One end of the 3300pf cap is connected to Pin 20 (FILT) and the other end is connected to Pin 21 (AGND). 2. One end of the 470ohm resistor is connected to Pin 20 and the other end is connected to the 220nf cap. The other end of the 220nf cap connects to Pin 21.

Both pins are actually going to AGND, which I'm assuming means analog ground since you're deling with a DAC chip?

In that case your instructions should read:

1. One end of the 3300pf cap is connected to Pin 20 (FILT) and the other end is connected to Pin 21 which is also connected to AGND.
2. One end of the 470ohm resistor is connected to one end of the 3300pf Cap (it needs to come after the cap so: Pin 21>cap>resistor) and the other end is connected to the 220nf cap. The other end of the 220nf cap connects to AGND.

 

[mrdon]

Thanks Stephen for the correction. It is greatly appreaciated!

Now let's see if I got it right. Here's a picture layout.

 

[thrice]

Not quite. The lead coming off pin 21 and the lead from the 220nf cap go to ground, not to each other.

 

[mrdon]

So like this?

I guess I am a little confused as Pin 21 is analog ground, but the analog ground connection other than pin 21 on the CS8412 chip would be something like an RCA ground?

 

[Garbz]

This is a receiver chip not a DAC chip. The pins do not often return to analogue ground. This is something you'd would need to check with whatever device you are playing with. Usually just straight ground.

MrDon what are you doing here? Are you modifiying a device with a CS8412. If so you need to remember for this modification to have a positive effect you need to keep the component leads VERY short. The datasheet actually recomends surface mount devices as close as technically possible to the pins in question.

 

[thrice]

What Garbz said...but yes, it would go to ground.

 

[mrdon]

Quote:

Originally Posted by Garbz This is a receiver chip not a DAC chip. The pins do not often return to analogue ground. This is something you'd would need to check with whatever device you are playing with. Usually just straight ground. MrDon what are you doing here? Are you modifiying a device with a CS8412. If so you need to remember for this modification to have a positive effect you need to keep the component leads VERY short. The datasheet actually recomends surface mount devices as close as technically possible to the pins in question.

This is a modification of an Entech Number Cruncher 203.2 DAC using the Wildmonkeysect filter mod talked about here
and here. To keep the leads short, wildmonketsect suggests using Wima type film caps. But I guess I am wondering how to run very short leads to ground? Going to the RCA's will be too long. The other issue is it appears the schematic is not available for this device. Any ideas where to run leads to a AGND?

BTW, here's a picture of the ENC 203.2 inside.

 

[Garbz]

Sorry was thinking CS8416, the 8412 definitely does not recomend SMD but the warning stays the same anyway, high speed digital filter, make leads very tight.

If I were you I would trace out the current filter path find out what is there, and remove the components and see if you can not find a replacement which actually fits into their holes.

For the capacitor, ignore all audiophile crap. As much as I hate them even for analogue work in the digital domain all they do is add size, and thus inductance. There is no real reason you should need to get WIMA caps over generic ones here, that said providing the package size is small they should work. I'd be inclined to try and find a ceramic plate capacitor, but that value may be too difficult, and too large in which case back to the MKT film caps.

When locating ground do NOT return it to the RCAs. As I mentioned before this is a digital chip and the datasheet mentions AGND, but this filter being very much digital will often not return to AGND. It either gets its own ground or returns to the digital one. Trace the path from the current pin21 and find out where it goes. If you can not find a suitable place to terminate, then run it back to pin 21 and solder it directly to the pin.

 

[mrdon]

Thank you both for you help and your coaching.