Replace Decoupling Caps as Well as Coupling Caps on MCI538C?

dbbubba · 27th July 2008

I am re-capping my MCI 538C and I am probably going to replace all of the coupling caps in the audio path.

I am wondering if I should also replace the shunt or decoupling caps as well.

Doing all of the coupling caps between audio circuits will be expensive enough with high grade caps.
Adding the cost of all of the shunt or decoupling caps will add quite a bit to the total cost.

Most are on the NEG INPUT of the ICs (2003s or 5534s) right before a 1K resistor going to GND.

I am wondering how important they are in the scheme of things.
Anyone have any input on this?

Jim Williams · 27th July 2008

They are very important, to the point that the original parts, if still operating correctly are far inferior to those available now. As to power decoupling, use the new low impedance tantalum replacement types, Rubycon Z, Panasonic FM or Nichicon HE series. Increase the values. I use the 220 uf 25v FM's, about 10 cents each in larger quanities. Add a .1 uf 50v mono ceramic across them. These are also good audio coupling caps, but I would consider replacing the 5534/2 opamps with low offset devices like the National LME series, that would allow bridging the coupling caps in several places. Bypass audio coupling caps with Wima MKP-2 .01 uf 250 v. Those can be placed on the rear of the pcb.

Jim Williams
Audio Upgrades

27th July 2008	#1
dbbubba Banned Joined: Sep 2005 Posts: 7,099 Thread Starter	Replace Decoupling Caps as Well as Coupling Caps on MCI538C? I am re-capping my MCI 538C and I am probably going to replace all of the coupling caps in the audio path. I am wondering if I should also replace the shunt or decoupling caps as well. Doing all of the coupling caps between audio circuits will be expensive enough with high grade caps. Adding the cost of all of the shunt or decoupling caps will add quite a bit to the total cost. Most are on the NEG INPUT of the ICs (2003s or 5534s) right before a 1K resistor going to GND. I am wondering how important they are in the scheme of things. Anyone have any input on this?

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27th July 2008	#2
Jim Williams Voiding warranties Joined: Feb 2004 Location: beautiful Carlsbad, CA Posts: 10,070	They are very important, to the point that the original parts, if still operating correctly are far inferior to those available now. As to power decoupling, use the new low impedance tantalum replacement types, Rubycon Z, Panasonic FM or Nichicon HE series. Increase the values. I use the 220 uf 25v FM's, about 10 cents each in larger quanities. Add a .1 uf 50v mono ceramic across them. These are also good audio coupling caps, but I would consider replacing the 5534/2 opamps with low offset devices like the National LME series, that would allow bridging the coupling caps in several places. Bypass audio coupling caps with Wima MKP-2 .01 uf 250 v. Those can be placed on the rear of the pcb. Jim Williams Audio Upgrades