Lookie lookie – An (almost) all-ceramic capacitor A1200 - Page 3

demolition · 26 January 2016, 11:58

No caps in the 1200 sees a voltage above 12V (ok, maybe 12.5V depending on the PSU), so there is no problem replacing a 35V version with a 25V version. You could even use 16V, however 10V versions can only be used for the ones seeing 5V.

There could be a size issue though as a 16V cap might be too small for a footprint meant for a 35V version.

olav · 04 February 2016, 07:52

Since this is the audio circuit, could not the voltage be higher?
Have to make sure the capacitor withstands the largest output from the audio amplifier..

ajk · 04 February 2016, 07:57

But it's not that kind of amplifier. You don't directly drive speakers from the Amiga audio output, it's line-level. I don't think it should ever go beyond a few volts.

olav · 04 February 2016, 08:18

Right. There is no amplification going on there.

seb132 · 04 February 2016, 10:56

Thanks to Stefan (in south Germany), all my A600s and A1200s have their capacitors changed for ceramic ones and all working like charm...

Definitely thumbs up!!

demolition · 04 February 2016, 14:02

Quote:

Originally Posted by olav

Since this is the audio circuit, could not the voltage be higher?
Have to make sure the capacitor withstands the largest output from the audio amplifier..

Looking at the A1200 R2 schematic, C334 and C324 are the AC decoupling caps. The voltage across them should be close to 0V most of the time, however due to DC offsets in the various components, there could be a few 100 mV, which is why they have been put there as this voltage would otherwise be seen as a DC offset on the audio output.

The supply decoupling caps C303 and C304 sees about 12V constantly.

Stedy · 05 February 2016, 01:08

Hi,

Something to be aware of with Ceramic capacitors, as the voltage goes up, the capacitance drops. Look here:
https://www.maximintegrated.com/en/a...ex.mvp/id/5527
This is most common in the X7R/X5R dielectrics.

Ceramic capacitors in AC coupling of Audio circuits are not recommended, the Piezo effect distorts the sound. I think the reason the audio capacitors fail more often is they have so little bias. The potential difference across electrolytics is a few 10's of mv. To keep Electrolytics in good condition, you need a reforming charge at least once a year. Switching on the computer will do this for most capacitors, except the audio. I should try this bus connecting the Audio output to ground via 10R resistor, and using a test tone might give enough potential difference to help reform the parts.

The Audio caps are the only ones I've had to replace in my Amiga 600, the others tested fine.

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26 January 2016, 11:58	#41
demolition Unregistered User Join Date: Sep 2012 Location: Copenhagen / DK Age: 43 Posts: 4,190	No caps in the 1200 sees a voltage above 12V (ok, maybe 12.5V depending on the PSU), so there is no problem replacing a 35V version with a 25V version. You could even use 16V, however 10V versions can only be used for the ones seeing 5V. There could be a size issue though as a 16V cap might be too small for a footprint meant for a 35V version.

04 February 2016, 07:52	#42
olav Registered User Join Date: Dec 2015 Location: Oslo / Norway and Tokyo / Japan. Posts: 23	Since this is the audio circuit, could not the voltage be higher? Have to make sure the capacitor withstands the largest output from the audio amplifier..

04 February 2016, 07:57	#43
ajk Registered User Join Date: May 2010 Location: Helsinki, Finland Posts: 1,341	But it's not that kind of amplifier. You don't directly drive speakers from the Amiga audio output, it's line-level. I don't think it should ever go beyond a few volts.

04 February 2016, 08:18	#44
olav Registered User Join Date: Dec 2015 Location: Oslo / Norway and Tokyo / Japan. Posts: 23	Right. There is no amplification going on there.

04 February 2016, 10:56	#45
seb132 French in Australia Join Date: May 2012 Location: Gold Coast Age: 52 Posts: 507	Thanks to Stefan (in south Germany), all my A600s and A1200s have their capacitors changed for ceramic ones and all working like charm... Definitely thumbs up!!

05 February 2016, 01:08	#47
Stedy Registered User Join Date: Jan 2008 Location: United Kingdom Age: 46 Posts: 733	Hi, Something to be aware of with Ceramic capacitors, as the voltage goes up, the capacitance drops. Look here: https://www.maximintegrated.com/en/a...ex.mvp/id/5527 This is most common in the X7R/X5R dielectrics. Ceramic capacitors in AC coupling of Audio circuits are not recommended, the Piezo effect distorts the sound. I think the reason the audio capacitors fail more often is they have so little bias. The potential difference across electrolytics is a few 10's of mv. To keep Electrolytics in good condition, you need a reforming charge at least once a year. Switching on the computer will do this for most capacitors, except the audio. I should try this bus connecting the Audio output to ground via 10R resistor, and using a test tone might give enough potential difference to help reform the parts. The Audio caps are the only ones I've had to replace in my Amiga 600, the others tested fine.

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