Choosing the correct coupling capacitor

[abbey road d enfer]

I read somewhere that in tube stages much larger foil caps can sometimes be used to good effect with regards noise . The idea was that by making the cut off frequency of the filter much lower , the output impedence of the preceeding valve could help reduce low frequency noise at the following valve grid.
Anyone any thoughts on this ?

I believe it would be a sign of a defective tube (grid current?). Or wrong implementation (capacitive coupling?).

 

[Newmarket]

I never heard this before. So that's pretty much the case for all 500 modules. Interesting.

Well it rarely gets mentioned. And it's difficult to quantify and know if it's a significant factor or more academic.
IIRC I came across it some years ago at Power Supply Design Seminar hosted by one of the big semiconductor companies - likely International Rectifier or Texas Instruments. But I've still put boards into kit where the electrolytics are horizontal (vertical mount PCB).

On a related topic does anyone remember the "Capacitor Plague" problem ?

Capacitor plague - Wikipedia

I think it's worth bearing in mind that an ac coupling capacitor in an audio circuit gets a much easier life than one in a power supply etc.
The two things that really hurt them are heat and ripple current. Although I guess the temperatures inside 'Big' mixing desks can get pretty high.

 

[JohnRoberts]

Indeed. Other factors too eg standard 'wet' electrolytics are (arguably) best operated in a vertical position as this helps with the continual 'self-healing' process. But there are loads of cases in which they will be horizontally orientated eg a PSU pcb is mounted to a chassis vertically or they are on a PCB in a vertical rack type system (eg Schroff).

I never heard this in decades of work with electrolytic capacitors. Radial electrolytic caps are clearly designed to be used vertically, but I never saw a failure related to horizontal mounting.

I can imagine a heavy radial cap, mounted horizontally putting stress on the leads that would normally be relieved by resting on the PCB. Allowing my imagination to run wild, this lead stress may affect the bung seal and lead to electrolyte loss. But I repeat I never saw evidence of this.

Note, not that long ago, most electrolytic capacitors were axial and I am not aware of significant internal design differences other than lead attachment.

JR

PS: In hindsight this post is full of stuff I do not know, so caveat lector.

 

[Newmarket]

I never heard this in decades of work with electrolytic capacitors. Radial electrolytic caps are clearly designed to be used vertically, but I never saw a failure related to horizontal mounting.

I can imagine a heavy radial cap, mounted horizontally putting stress on the leads that would normally be relieved by resting on the PCB. Allowing my imagination to run wild, this lead stress may affect the bung seal and lead to electrolyte loss. But I repeat I never saw evidence of this.

Note, not that long ago, most electrolytic capacitors were axial and I am not aware of significant internal design differences other than lead attachment.

JR

PS: In hindsight this post is full of stuff I do not know, so caveat lector.

Yeah - I did experience a couple of electrolytic failures in horizontal, and in one case coincidentally did observe the actual failure. It was kind of aesthetically beautiful as the 'cross' in the top of the cap: ruptured and a spiral of electrolyte 'smoke' formed a moving spiral.
That was before I'd come across the idea that orientation was something to be considered.
But I'm not saying that the Horizontal was significant. I had inherited the design.
Actually the cap would have normally been vertical but the instrument was placed on its side for access to the electronics. Changed the capacitor based on ripple current rating and didn't see the issue again in several years. This was a serious power and voltage DC/DC converter non audio product.

But the idea is based on the wet electrolyte and gravity.
I did think of mentioning axial devices but thought I'd keep it short

 

[JohnRoberts]

Yeah - I did experience a couple of electrolytic failures in horizontal, and in one case coincidentally did observe the actual failure. It was kind of aesthetically beautiful as the 'cross' in the top of the cap: ruptured and a spiral of electrolyte 'smoke' formed a moving spiral.

The X scored in the top of the package is an intentional weakness to encourage ruptures from over-pressure to occur there (you don't want that pressure contained). That sounds like a ripple current, overheating stress failure rather that loss of electrolyte.

That was before I'd come across the idea that orientation was something to be considered.
But I'm not saying that the Horizontal was significant. I had inherited the design.
Actually the cap would have normally been vertical but the instrument was placed on its side for access to the electronics. Changed the capacitor based on ripple current rating and didn't see the issue again in several years. This was a serious power and voltage DC/DC converter non audio product.

yup

But the idea is based on the wet electrolyte and gravity.
I did think of mentioning axial devices but thought I'd keep it short

Bung on bottom is so leaks make less of a mess, but there are no good leaks. IIRC the typical bung also serves as a pressure relief.

JR

 

[Newmarket]

The X scored in the top of the package is an intentional weakness to encourage ruptures from over-pressure to occur there (you don't want that pressure contained). That sounds like a ripple current, overheating stress failure rather that loss of electrolyte.

yup

Bung on bottom is so leaks make less of a mess, but there are no good leaks. IIRC the typical bung also serves as a pressure relief.

JR

The X scored in the top of the package is an intentional weakness to encourage ruptures from over-pressure to occur there (you don't want that pressure contained). That sounds like a ripple current, overheating stress failure rather that loss of electrolyte.

yup

Bung on bottom is so leaks make less of a mess, but there are no good leaks. IIRC the typical bung also serves as a pressure relief.

JR

Yeah - understand about the cross being a deliberate pressure relief thing. Agree that it was likely ripple current / internal heating due ESR. It was a new capacitor.

I've had the bung go too but I know that was a high voltage / PCB layout thing due to offset pins. Quite a mess on the PCB

 

[JohnRoberts]

Yeah - understand about the cross being a deliberate pressure relief thing. Agree that it was likely ripple current / internal heating due ESR. It was a new capacitor.

I've had the bung go too but I know that was a high voltage / PCB layout thing due to offset pins. Quite a mess on the PCB

Back in the 60s as a wet behind the ears junior technician I blew up a couple... One time on a dare from older technicians I plugged a small wet electrolytic cap into an outlet and it sounded like a rifle shot when it blew apart.
===
I blew up a second cap actually doing my job. Back then I was working on a very early DC to DC switching supply. We had a large metalized film cap across one of the transformer windings to absorb the inductive spikes. Luckily I was away from my bench across the room when that one blew up. It sounded like a fire cracker going off, and my bench was covered by a light sprinkling of what looked a little like snow.

Modern wet electrolytic caps have pressure relief engineered in to reduce damage, I never saw another film cap fail that spectacularly.

JR

 

[Newmarket]

I blew up a second cap actually doing my job. Back then I was working on a very early DC to DC switching supply. We had a large metalized film cap across one of the transformer windings to absorb the inductive spikes. Luckily I was away from my bench across the room when that one blew up. It sounded like a fire cracker going off, and my bench was covered by a light sprinkling of what looked a little like snow.

Oh yes - "Indoor Snow" I recall that filling a small industrial unit I was working in sometime in the 90s.
The prototype PSU was just sitting there during lunch but off it went !

 

[bone]

I remember back in the 60s I was responsible for the amps used by this Band and while on stage the PA amp (valve/tube) blew an elec capacitor in the cathode of one of the output valves. What a noise, and also a little panic fron the band and the audience. He he. Had to temporarily use the instrument amps for the mics as had no spare with us. Almost had to wash out the chassis to get rid of the bits of aluminium foil. Back up and running though for the next gig a week later. Remembered to bring spare amp this time

 

[T_Ray]

That's correct. There is a formula that anticipates the expected lifetime with lower ambient temperature, based on chemical activity. It says that lifetime doubles for every 10°C temperature drop.
A 2000h/85°C cap submitted to an ambient temperature of 40°C can be expected to live 5 years.
Which justifies using 105°C types, which would last 20 years. Actually, there maybe other causes of defect in a 20 years span. And who designs gear for 20 years of service, today?
Actually, many lytic caps that are supposed to be long past according to this law are still operating, probably not like the day they came out of the factory, but well enough for their owners to ignore it.

Good day sir. My first time in here so I hope this appropriate. I have a soundcraft delta dlx and a soundcraft 600. I have bought some “modded” input channels and I would like to mod the rest myself. Upon searching for the film/ceramic capacitors I’ve noticed there are many different types and most out of stock. They’re Wima capacitors. I’ve gathered that the FKP series are the best for audio. Im confused on a few things.

1. The difference between/when to use PET decoupling (FKP1/MKS) series caps vs the PP audio FKP2 caps. Are they interchangeable

2. As most are out of stock, the guidelines on the ratings. For example, one is a .047uf 630v 10% but all I can find is a .047 1kv cap. Will this higher rating cause problems or is it just capable of handling more voltage? Are both the uf and dc ratings to be strictly followed or can you go a little higher on one or both?

Any help would be greatly appreciated. I’ve also sent off a few modules to be modded and have permission from the owner of the company to do the rest myself as they are booked out for over a year. I have worn him out with questions and don’t want bother him if I don’t have to. Thanks, Tom.

 

[user 37518]

Good day sir. My first time in here so I hope this appropriate. I have a soundcraft delta dlx and a soundcraft 600. I have bought some “modded” input channels and I would like to mod the rest myself. Upon searching for the film/ceramic capacitors I’ve noticed there are many different types and most out of stock. They’re Wima capacitors. I’ve gathered that the FKP series are the best for audio. Im confused on a few things.

1. The difference between/when to use PET decoupling (FKP1/MKS) series caps vs the PP audio FKP2 caps. Are they interchangeable

2. As most are out of stock, the guidelines on the ratings. For example, one is a .047uf 630v 10% but all I can find is a .047 1kv cap. Will this higher rating cause problems or is it just capable of handling more voltage? Are both the uf and dc ratings to be strictly followed or can you go a little higher on one or both?

Any help would be greatly appreciated. I’ve also sent off a few modules to be modded and have permission from the owner of the company to do the rest myself as they are booked out for over a year. I have worn him out with questions and don’t want bother him if I don’t have to. Thanks, Tom.

The higher voltage rating shouldn't be a problem unless size makes it unpractical. Yes, PET an PP are interchangeable but PET tend to produce more distortion than PP, another alternative is PPS.
Are you using them in the EQ section? if so, you do not want to change the capacitance value and make sure the tolerance is the same. If its being used just to block DC (ac couple) you can go higher in value. Also make sure the footprint size is the same.

Hope this helps

 

[moamps]

I'm not Abbey but I thought you (or someone else) might find my opinion useful. First, I’m not exactly a fan of Wima capacitors. If finances allow, I prefer to use Vishay or Kemet for positions where film capacitors are used. Lately I've been really liking Kemet's MPS capacitors. For decoupling I use Vishay MLCC. I use Nichicon UFG for electrolytic capacitors. I can’t give any measurements of where these selected capacitors turned out to be better than the others, it’s probably some very small difference, maybe completely subjective.

I think that the most change for the better can be obtained by changing old electrolytic capacitors. If possible, higher values should be used, the operating voltage may remain the same.

And I'm not sure that changing the decoupling capacitors can lead to some improvements, only if the opamps are changed with some more current demanding ones.

 

[Ike Zimbel]

I'm not Abbey but I thought you (or someone else) might find my opinion useful. First, I’m not exactly a fan of Wima capacitors. If finances allow, I prefer to use Vishay or Kemet for positions where film capacitors are used. Lately I've been really liking Kemet's MPS capacitors. For decoupling I use Vishay MLCC. I use Nichicon UFG for electrolytic capacitors. I can’t give any measurements of where these selected capacitors turned out to be better than the others, it’s probably some very small difference, maybe completely subjective.

I think that the most change for the better can be obtained by changing old electrolytic capacitors. If possible, higher values should be used, the operating voltage may remain the same.

And I'm not sure that changing the decoupling capacitors can lead to some improvements, only if the opamps are changed with some more current demanding ones.

Ah, careful there...when replacing electrolytic caps in older equipment you want to make sure that the original caps were spec'ed for the optimal voltage and not just because they were small enough to fit. EVERY vintage API module that I have ever been into had 15 volt decoupling caps on the 16 volt supply rails and every single one of those I've seen has been completely dried up, empty, no capacitance.
I have also seen MANY blown up 220uf/25v output coupling caps (often in Drawmer 1960's and related gear, some Focusrite gear...). I've never been 100% sure if they got that way from accidentally being exposed to 48v phantom power or if they just didn't like sitting on the outputs of 5532's for years at a time but I think it's the latter. So some times increasing the voltage rating can be a good idea.

 

[moamps]

...So some times increasing the voltage rating can be a good idea.

No doubt. But, I believe the problem with the capacitors at 5532 output was in the small reverse polarity (negative DC offset).
Your post reminded me of a faulty professional CD player from about 20 years ago that completely lost its first decade. it turned out that the output capacitors were completely dried due to the phantom voltage that was turned on at the input of the console (the console was not exactly optimally designed).

 

[T_Ray]

The higher voltage rating shouldn't be a problem unless size makes it unpractical. Yes, PET an PP are interchangeable but PET tend to produce more distortion than PP, another alternative is PPS.
Are you using them in the EQ section? if so, you do not want to change the capacitance value and make sure the tolerance is the same. If its being used just to block DC (ac couple) you can go higher in value. Also make sure the footprint size is the same.

Hope this helps

Thank you! I had leaned myself to thinking that I needed the PP’s but there are 0 stock for the 630v so my closet option was 1kv. I’m trying to use the exact things but it also seemed like there wasn’t one of the FKP PP’s even made in the uf/v rating of one of capacitors, only in MKS. I’m going to try to get pics tomorrow, maybe that will help.

 

[T_Ray]

Ah, careful there...when replacing electrolytic caps in older equipment you want to make sure that the original caps were spec'ed for the optimal voltage and not just because they were small enough to fit. EVERY vintage API module that I have ever been into had 15 volt decoupling caps on the 16 volt supply rails and every single one of those I've seen has been completely dried up, empty, no capacitance.
I have also seen MANY blown up 220uf/25v output coupling caps (often in Drawmer 1960's and related gear, some Focusrite gear...). I've never been 100% sure if they got that way from accidentally being exposed to 48v phantom power or if they just didn't like sitting on the outputs of 5532's for years at a time but I think it's the latter. So some times increasing the voltage rating can be a good idea.

Thank you! I’ve never been on these forums before and I’m trying to figure it out so I picked abbey because he sounded like he would know. Im not wanting to change anything as I know the guy that did the mod knows what he’s doing, but the capacitors don’t say FKP or MKS etc so I think I need to get some pics and figure out what part of the signal he’s changed. There’s a lot of them and I think many are for EQ. I really appreciate it and I’m amazed at the knowledge on this site.

 

[T_Ray]

The higher voltage rating shouldn't be a problem unless size makes it unpractical. Yes, PET an PP are interchangeable but PET tend to produce more distortion than PP, another alternative is PPS.
Are you using them in the EQ section? if so, you do not want to change the capacitance value and make sure the tolerance is the same. If its being used just to block DC (ac couple) you can go higher in value. Also make sure the footprint size is the same.

Hope this helps

Thank you! I’m going to try to pics tomorrow and look at the schematics to see what all he did and maybe that will help. I was just wanting to start ordering the parts as it’s probably going to take awhile to get with short supplies. Can’t tell y’all how much I appreciate it as this very important to me.

 

[T_Ray]

Ah, careful there...when replacing electrolytic caps in older equipment you want to make sure that the original caps were spec'ed for the optimal voltage and not just because they were small enough to fit. EVERY vintage API module that I have ever been into had 15 volt decoupling caps on the 16 volt supply rails and every single one of those I've seen has been completely dried up, empty, no capacitance.
I have also seen MANY blown up 220uf/25v output coupling caps (often in Drawmer 1960's and related gear, some Focusrite gear...). I've never been 100% sure if they got that way from accidentally being exposed to 48v phantom power or if they just didn't like sitting on the outputs of 5532's for years at a time but I think it's the latter. So some times increasing the voltage rating can be a good idea.

Thank you! I’ve never been on these forums before and I’m trying to figure it out so I picked abbey because he sounded like he would know. Im not wanting to change anything as I know the guy that did the mod knows what he’s doing, but the capacitors don’t say FKP or MKS etc so I think I need to get some pics and figure out what part of the signal he’s changed. There’s a lot of them and pretty sure m

I'm not Abbey but I thought you (or someone else) might find my opinion useful. First, I’m not exactly a fan of Wima capacitors. If finances allow, I prefer to use Vishay or Kemet for positions where film capacitors are used. Lately I've been really liking Kemet's MPS capacitors. For decoupling I use Vishay MLCC. I use Nichicon UFG for electrolytic capacitors. I can’t give any measurements of where these selected capacitors turned out to be better than the others, it’s probably some very small difference, maybe completely subjective.

I think that the most change for the better can be obtained by changing old electrolytic capacitors. If possible, higher values should be used, the operating voltage may remain the same.

And I'm not sure that changing the decoupling capacitors can lead to some improvements, only if the opamps are changed with some more current demanding ones.

All noted and thank you! Thats another question I didn’t ask. It seems like every piece of modded audio equipment has the red wimas but I was wondering which other brands were dependable. I’m going to get some more info and pics tomorrow but I greatly appreciate your help.

 

[T_Ray]

Good day sir. My first time in here so I hope this appropriate. I have a soundcraft delta dlx and a soundcraft 600. I have bought some “modded” input channels and I would like to mod the rest myself. Upon searching for the film/ceramic capacitors I’ve noticed there are many different types and most out of stock. They’re Wima capacitors. I’ve gathered that the FKP series are the best for audio. Im confused on a few things.

1. The difference between/when to use PET decoupling (FKP1/MKS) series caps vs the PP audio FKP2 caps. Are they interchangeable

2. As most are out of stock, the guidelines on the ratings. For example, one is a .047uf 630v 10% but all I can find is a .047 1kv cap. Will this higher rating cause problems or is it just capable of handling more voltage? Are both the uf and dc ratings to be strictly followed or can you go a little higher on one or both?

Any help would be greatly appreciated. I’ve also sent off a few modules to be modded and have permission from the owner of the company to do the rest myself as they are booked out for over a year. I have worn him out with questions and don’t want bother him if I don’t have to. Thanks, Tom.

Thank you! I’ve never been on these forums before and I’m trying to figure it out so I picked abbey because he sounded like he would know. Im not wanting to change anything as I know the guy that did the mod knows what he’s doing, but the capacitors don’t say FKP or MKS etc so I think I need to get some pics and figure out what part of the signal he’s changed. There’s a lot of them and pretty sure m

All noted and thank you! Thats another question I didn’t ask. It seems like every piece of modded audio equipment has the red wimas but I was wondering which other brands were dependable. I’m going to get some more info and pics tomorrow but I greatly appreciate your help.

Thank you! I had leaned myself to thinking that I needed the PP’s but there are 0 stock for the 630v so my closet option was 1kv. I’m trying to use the exact things but it also seemed like there wasn’t one of the FKP PP’s even made in the uf/v rating of one of capacitors, only in MKS. I’m going to try to get pics tomorrow, maybe that will help.

So from searching I believe the

The higher voltage rating shouldn't be a problem unless size makes it unpractical. Yes, PET an PP are interchangeable but PET tend to produce more distortion than PP, another alternative is PPS.
Are you using them in the EQ section? if so, you do not want to change the capacitance value and make sure the tolerance is the same. If its being used just to block DC (ac couple) you can go higher in value. Also make sure the footprint size is the same. it appears that mods are on the

The higher voltage rating shouldn't be a problem unless size makes it unpractical. Yes, PET an PP are interchangeable but PET tend to produce more distortion than PP, another alternative is PPS.
Are you using them in the EQ section? if so, you do not want to change the capacitance value and make sure the tolerance is the same. If its being used just to block DC (ac couple) you can go higher in value. Also make sure the footprint size is the same.

Hope this helps

so there’s wima mks pet caps that are used on the input stage

The higher voltage rating shouldn't be a problem unless size makes it unpractical. Yes, PET an PP are interchangeable but PET tend to produce more distortion than PP, another alternative is PPS.
Are you using them in the EQ section? if so, you do not want to change the capacitance value and make sure the tolerance is the same. If its being used just to block DC (ac couple) you can go higher in value. Also make sure the footprint size is the same.

Hope this helps

By searching all the retailers sites I believe that all the wimas are mks series pet’s as they don’t offer the fkp’s in these specs (that I can find) so that would mean they’re being used for coupling/decoupling correct? And there are a lot of these yellow ceramic caps, mainly on/around the opamps and resisters next to the opamps. They’re on the input section, eq section, and output section.

 

[T_Ray]

Thank you! I’ve never been on these forums before and I’m trying to figure it out so I picked abbey because he sounded like he would know. Im not wanting to change anything as I know the guy that did the mod knows what he’s doing, but the capacitors don’t say FKP or MKS etc so I think I need to get some pics and figure out what part of the signal he’s changed. There’s a lot of them and pretty sure m

All noted and thank you! Thats another question I didn’t ask. It seems like every piece of modded audio equipment has the red wimas but I was wondering which other brands were dependable. I’m going to get some more info and pics tomorrow but I greatly appreciate your help.

Are these the Vishay

I'm not Abbey but I thought you (or someone else) might find my opinion useful. First, I’m not exactly a fan of Wima capacitors. If finances allow, I prefer to use Vishay or

Thank you! I’ve never been on these forums before and I’m trying to figure it out so I picked abbey because he sounded like he would know. Im not wanting to change anything as I know the guy that did the mod knows what he’s doing, but the capacitors don’t say FKP or MKS etc so I think I need to get some pics and figure out what part of the signal he’s changed. There’s a lot of them and pretty sure m

All noted and thank you! Thats another question I didn’t ask. It seems like every piece of modded audio equipment has the red wimas but I was wondering which other brands were dependable. I’m going to get some more info and pics tomorrow but I greatly appreciate your help.

for positions where film capacitors are used. Lately I've been really liking Kemet's MPS capacitors. For decoupling I use Vishay MLCC. I use Nichicon UFG for electrolytic capacitors. I can’t give any measurements of where these selected capacitors turned out to be better than the others, it’s probably some very small difference, maybe completely subjective.

I think that the most change for the better can be obtained by changing old electrolytic capacitors. If possible, higher values should be used, the operating voltage may remain the same.

And I'm not sure that changing the decoupling capacitors can lead to some improvements, only if the opamps are changed with some more current demanding ones.

They are different opamps than the original me. Are these the Vishay MLCC that you mentioned?

Ah, careful there...when replacing electrolytic caps in older equipment you want to make sure that the original caps were spec'ed for the optimal voltage and not just because they were small enough to fit. EVERY vintage API module that I have ever been into had 15 volt decoupling caps on the 16 volt supply rails and every single one of those I've seen has been completely dried up, empty, no capacitance.
I have also seen MANY blown up 220uf/25v output coupling caps (often in Drawmer 1960's and related gear, some Focusrite gear...). I've never been 100% sure if they got that way from accidentally being exposed to 48v phantom power or if they just didn't like sitting on the outputs of 5532's for years at a time but I think it's the latter. So some times increasing the voltage rating can be a good idea.