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Mark Levinson has odd choice for cap upgrades in one of their service bulletins. Why?

Pursuant to one of the Mark Levinson service bulletins, for Model 331, 332, 333 etc, they have outlined one of many things that should be performed on any amp that comes in for service.

One of the line items has me baffled. They recommend replacing four caps on each voltage gain / input board. These eight caps are PP type of .01uF @ 160v. They recommend replacing them with Ceramic X7R .01uF @ 200v. These are axial configurations.

This is not an expensive upgrade but I thought to myself that polypropylene caps had low failure rates and good longevity compared to other types especially if they were used in a proper operating envelope.

I just finished watching and reading some information on the perils of using ceramic caps in certain applications. For one, they tend to drift heavily with temperature changes. In a monster like the Model 333 there will definitely be a large temperature swing. The ceramics also tend to exhibit piezo effects with vibration. While vibration is only inducing small voltages, I can imagine the sum of many caps being subject to vibration not being a good recipe for an audio signal.

ML has stated that the ceramic replacements should be installed with spacers to keep them lifted from the circuit board. I am guessing that this could address temperature concerns, vibration or parasitic capacitance issues. They do not provide any reason.

I would really like to learn a little more behind their reasoning as it seems this particular "upgrade" is counter-intuitive. Can anyone shed some light on this?
generatorlabs

Showing 6 responses by erik_squires

erik_squires
16,644 posts
 
By the way, important to note that thermal stability ant temperature/longevity are not the same thing.

You can have a very stable cap that has a low thermal rating.

Also, who cares. These are RF filtering bypass caps. You could use 1 or 4 and the audible effects would be 0.  A cap with 20% variance in value is just fine here.
erik_squires
16,644 posts
 
If you absolutely can't stand the idea, get Cornel Dubelier PP.
erik_squires
16,644 posts
 
You guys are getting nuts. Please look at the original capacitor value again:

0.01uF or 10 nF

Most boutique caps don’t even come that small. 0.1uF is usually the lowest they go. I can pretty much guarantee it is not in the audio path.

To put this in perspective, a tube preamp output cap is usually at least 2 to 4 uF. That’s 200 to 400 x larger than this de-coupling cap. Also, the ceramic is probably 10-20x physically smaller than any boutique cap would be.

Before doing any more arm chair upgrade discussions I would strongly suggest finding out what the cap actually does by looking at a schematic. For all I know this is part of the LED driver

Sheesh.

Best,


E
erik_squires
16,644 posts
 
Not every part in an amp has to do with sound quality. For all I know this could be a bypass cap on an IC which controls relays and has nothing to do with the audio signal path.


Best,

E
erik_squires
16,644 posts
 
Hi Gnerator:

Yes, you are overthinking it. :) These are probably PS de-coupling caps, and size and heat resistance are most likely the dominant factors.

The location matters. It is quite possible that those caps are exposed to unusually high heat. The temperature in an amp isn't the same at every point, it is quite possible the caps are in a particularly bad hot spot. Also possible that the manufacturer of the originals was too optimistic re: heat / failure rates. ML seems to have learned something and chosen to act proactively.

Second, it's not just about thermal stability it is about failure. Caps with higher thermal ratings last longer.

Esoteric caps are huge by comparison to their "normal" counterparts, AND honest to god, it's quite probable that in this application they make no difference at all.


Best,

E
erik_squires
16,644 posts
 
The answer indeed seems to be heat, but it’s also important to understand the application.

0.01uF adds microscopic amounts of capacitance, so I assume they are merely RF filtering, power supply decoupling caps. Ceramics should be fine.

Best,

E
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