exxos's Atari, Amiga & retro forum

I'm just in the process of doing the C-Lab audio mod to my Falcon. Today I (almost) finished the bottom side with all SMD changes, the "standard" 10K resistor and the four ceramic caps between audio ports and the filters L33-L38.
What remains to do on this side is changing the two caps C26 and C79 from the ceramic 0,47µF to (what I've seen in all pictures so far) 22µF/16V tantalum caps, see picture (from a user of german atari-home.de).


As there are a few C-Lab Falcon owners here (hopefully ^^), do you know of any schematics or documentation why these two caps have changed?
Even in the latest Rev. L schematics I found in the 115MB Service guide from here, these caps remain untouched.
All other changes of the audio mod were in this Rev. L schematics.
The SMD part of the mod can be found in the Cubase Audio manual or here, but also without C26/79 changes! :?

Btw, I aim for the "version 2" (as I call it) of the filter modifications, leaving the old L33-L38 in place. Less soldering and because I haven't found any infos about these L33-L38 replacement ferrites, which are shown in Rev. L schematics.
Just like in these pictures (see that in this version the four ceramics on the bottom side are not soldered to GND, the outer ring, like they are in the version with ferrites!)

That's way to many caps to warp my head around :)
I have a MKX board I could photograph areas of interest if it would help.

T'PAU wrote: 21 Dec 2022 19:24 As there are a few C-Lab Falcon owners here (hopefully ^^), do you know of any schematics or documentation why these two caps have changed?

Assume they are on the 5V rail and just adding more bulk capacitance to the rails. I would have gone with ceramics though. Tantalums tend to catch fire.

I photographed and wrote in detail about the following Clab board if it helps:
https://exxosforum.co.uk/forum/viewtopi ... =59&t=3809

Also I agree with Exxos, tantalums are a bad choice. Use ceramics or lyrics.

There are 22uF SMD 1206 ones with 6,3V max. These are for the Mic In (Line In). The OP Amp run at 9V DC ...

https://en.wikipedia.org/wiki/High-pass_filter

exxos wrote: 22 Dec 2022 10:35 I would have gone with ceramics though. Tantalums tend to catch fire.

Really? If you put them in with wrong polarity, or even with correct orientation? :o

Steve wrote: 22 Dec 2022 11:42 I photographed and wrote in detail about the following Clab board if it helps:
https://exxosforum.co.uk/forum/viewtopi ... =59&t=3809

Also I agree with Exxos, tantalums are a bad choice. Use ceramics or lyrics.

Already saw this, thanks. Especially the detail photo from the bottom side was quite helpful, as this is about the third C-Lab Falcon I saw with these Tantals.

I have finished the modification now! "Only" needs to be tested... tomorrow or so. ;)


I put R68 on top of C59 as I lost a solder pad of R68 while desoldering. Collateral damage you know! :D


The tantals have the exact size of the pads! The C-Lab ones are quite big. Maybe there were no smaller ones in the 90s. ;)

@T'PAU Since you're going to all this effort having the motherboard out etc, have you not considered re-capping the board at the same time?

Steve wrote: 22 Dec 2022 18:59 @T'PAU Since you're going to all this effort having the motherboard out etc, have you not considered re-capping the board at the same time?

Steve, are you yet offering this service, including the audio cap upgrades for the MKX? This is a builder, functions. No other mods yet. May request low profile NVRAM socket installed and MIDI/KB ACIS to have socketed access. (Works with my bus mod.)

Rustynutt wrote: 22 Dec 2022 19:22

Steve wrote: 22 Dec 2022 18:59 @T'PAU Since you're going to all this effort having the motherboard out etc, have you not considered re-capping the board at the same time?

Steve, are you yet offering this service, including the audio cap upgrades for the MKX? This is a builder, functions. No other mods yet. May request low profile NVRAM socket installed and MIDI/KB ACIS to have socketed access. (Works with my bus mod.)

No Sorry, haven't done any work for over a year. Too busy at work.

@Steve This came to my mind, but I think I'll leave that for now and do it only when necessary.
Btw. I should have done re-capping before this audio mod, as several filtering ceramics are directly soldered to some electrolytics.
Well, at least C6 and C24 are new (the ones which were soldered in with wrong polarity from Atari). ;)
I also did a recap of the PSU with the exxos kit.

After close inspection of my pic of the bottom side compared to C-Lab pics, I realized I missed two caps C613 and C614! :shock:
They are in schematic Rev. L, but aren't listed in the instructions in Cubase Audio manual or here.
As I don't have 560 pF caps I plan to use a 470 and 100 pF in parallel, giving 570 pF.
I have these from the modifications at the microphone side of things (I always buy way more components than needed ^^).
These caps should be soldered on top of R124 and R131 (that's how I recognized it in the pictures). Fortunately there are solderpoints in parallel to these Rs, which I could use to at least solder one of the two caps there instead of making a "triple sandwich".

Not quite sure though, if I can put 570 pF (+/- 5% tolerance each) instead of 560 pF in there. Any thoughts? :?: