Cap Job

[Microbass]

My Trace Elliot V4 has been given a clean bill of health by my new tech and I'll be picking it up on Saturday morning.
There were two popped capacitors of which I assume may have been in the preamp or possibly smaller power board components as the charges for parts is only £10ish - I'll find out on Saturday what they were.

My V4 is a Mk1 '96 or '98 so we've passed that 20 year mark when people start to freak out about the filter caps. Since I've had this amp it has been my number 1 and put in a LOT of hours in rehearsals, my gigs and as backline, albeit for the last 2 years it didn't see any action and I also have a 4 year hiatus where it was only fired up a handful of times.

Tech has said visually and on the scope they are fine but he recommended I consider getting the work done in the next 6-18 months. We have a lot of gigs coming up this year already including a 12 date tour across the UK next month so I'll be looking at a service in 12 months for upkeep purposes, but am I at the stage where I should go ahead and get the work done on it's next service? I have the type of luck where if I get a service as normal, then I'll have a catastrophic failure a month later and have to pay for another bench fee+any damages..

 

[lug]

The caps in my 45 year old Acoustic 220 are fine. The whole idea that caps have a shelf life of 20 years is patently false, dreamed up by people who either meant well but were somewhat ignorant of electronic components, or shysters looking to make a buck on unneeded repairs. There are several types of caps built with various methods, and if used correctly can last a long long time. Caps are NOT wear items.

 

[beans-on-toast]

It sounds like your tech is recommending doing some preventative maintenance to ensure that there won’t be an issue during touring season. It isn’t unusual. If the caps test good and are not bulging, leaking, or have cracked seals, normally there’s no need to change them at this point.

Like with everything, it depends. Electrolytic caps come out of the same plant made to different specifications. They aren’t all the same. Some are good, some have shorter service lives and perform differently. If the tech knows that a particular type are prone to problems, they might recommend changing them.

 

[agedhorse]

The caps in my 45 year old Acoustic 220 are fine. The whole idea that caps have a shelf life of 20 years is patently false, dreamed up by people who either meant well but were somewhat ignorant of electronic components, or shysters looking to make a buck on unneeded repairs. There are several types of caps built with various methods, and if used correctly can last a long long time. Caps are NOT wear items.

Agreed, I typically design to a ~40 year minimum lifespan and so rarely see a bad cap in products I (and others) designed over 30 years ago that I generally recommend leaving things alone. I do see problems from folks that did a “cap job” and caused damage that did not exist prior to their work however.

There are of course designs where a part was inadequately specified or selected, and these always exists the potential for a defective part, but this is not as common as the internet might suggest.

 

[Lo-E]

Electrolytic caps are similar to batteries in that they will last longer and be healthier if they are in use and they are being charged and discharged routinely.

They are most likely to fail if they’ve spent a lot of time unused, with extreme heat and/or humidity also being potential problems.

While there are cases where electrolytics crap out after 10 years, those cases are very rare and, as @agedhorse stated, are usually due to poor design choices.

If the caps in your amp are showing no signs of failure and everything looks good on the test bench I see no reason to change them. Your amp never spent decades sitting in a hot attic or a damp basement. You should be fine.

 

[beans-on-toast]

Beware of the IC ecaps that a certain company is using in their Mexican made amps. I’ve seen them start to bulge after only a few years. The IC caps in their earlier US made amps do much better. An example of accountants shaving a few dollars off the cost to the detriment of the amp.

 

[agedhorse]

I have used IC (Illinois Capacitor) in some designs going back over 30 years and haven’t seen ANY problems with them, they have always been excellent parts.

Maybe there’s now a different “IC” but I am now aware of it.

 

[byacey]

PC board layout at the design stage can definitely affect the lifetime of electrolytics. For reasons unknown, some designers like to place electrolytics very close to heat sinks or power resistors that run hot, which slow cook the caps to death.

 

[beans-on-toast]

Last I heard, IC is owned by Cornell Dubilier both make good products. The caps found in the Mexican made amps that I mentioned are smaller in size than the IC caps in the American made products. Same models, same boards, different spec on the parts. Unfortunately, it seems that the ones now in use are not up to the job much beyond the product’s warranty. I’ve seen some fail at 2 years.

 

[beans-on-toast]

PC board layout at the design stage can definitely affect the lifetime of electrolytics. For reasons unknown, some designers like to place electrolytics very close to heat sinks or power resistors that run hot, which slow cook the caps to death.

If the PCB’s are not designed to suit lead free solder and high heat, there can be cracked solder joint issues.

 

[byacey]

Last I heard, IC is owned by Cornell Dubilier both make good products. The caps found in the Mexican made amps that I mentioned are smaller in size than the IC caps in the American made products. Same models, same boards, different spec on the parts. Unfortunately, it seems that the ones now in use are not up to the job much beyond the product’s warranty. I’ve seen some fail at 2 years.

That's a very dismal lifetime, considering caps in many other devices are still fine, 50 years later.

 

[Analogeezer]

The caps in my 45 year old Acoustic 220 are fine. The whole idea that caps have a shelf life of 20 years is patently false, dreamed up by people who either meant well but were somewhat ignorant of electronic components, or shysters looking to make a buck on unneeded repairs. There are several types of caps built with various methods, and if used correctly can last a long long time. Caps are NOT wear items.

Yep me too......(same amp, same situation).

A couple of years ago I did a full cleaning and LED meter bulb replacement on my Allen and Heath System 8 console. I am the second owner, it was originally purchased in 1988.

I had the bottom plate off and was checking all the components, needless to say a ton of caps in there and not a one was bulging or leaking.

What WAS interesting was about 10% of the caps were different (different brand), at first I thought these had been replaced but you could tell looking at the soldering points they were the original factory parts.

All I figure is they used up one batch of caps when the console was being built and switched over to the new batch.

The other reason I figured this was the case was all the caps that were a different brand were installed in the last four channels closest to the outside of the console (technically channels one through four).

Analogeezer

 

[byacey]

If the PCB’s are not designed to suit lead free solder and high heat, there can be cracked solder joint issues.

That's one issue, but when a cap is placed within a 1/4" next to a heat sink running at 130F continually, this is just plain bad design practice.

Edit: This isn't really a fault of the cap or manufacturing quality, more of a design fault.

 

[agedhorse]

Every manufacturer has lines of miniature and sub-miniature caps, each series has specific characteristics and use different internal construction. When you design around these parameters, there’s no problem. When a designer or contract manufacturer randomly chooses or substitutes components, unexpected problems can result. This is not a capacitor problem.

 

[beans-on-toast]

The capacitance was the same. Other specs must not have been since there was a high failure rate with the smaller footprint caps. They’ve since moved to a different product but it took some time to do so. As you said, substitute components can have unexpected consequences. Not necessarily right away but down the road.

 

[agedhorse]

The capacitance was the same. Other specs must not have been since there was a high failure rate with the smaller footprint caps. They’ve since moved to a different product but it took some time to do so. As you said, substitute components can have unexpected consequences. Not necessarily right away but down the road.

I'm not familiar with this supposed issue.

 

[Patrice B]

I'm not familiar with this supposed issue.

It’s like some « urban myth » me think. Same goes for Sprague Atoms in some tube hifi circles… I could be wrong though…

 

[Microbass]

Picked up the amp yesterday and the blown caps were in the preamp. Discussed the filter caps in a bit more detail and cost wise was definitely not as bad as expected and the discussion was really that if I stick to a yearly service, barring any issues cropping up before that time he’d be checking the caps fully every time anyway and doesn’t necessarily need to be rushed.

Now the really interesting thing was an old Ampeg imported from the USA at some stage in its life now owned by Mogwai. The previous owner had retro fitted a new transformer onto the chassis (without removing the original) to suit our 230V mains. It looked insane and was about half the size of the original transformer. Amazing no one died using or working on that thing!

 

[Wasnex]

Picked up the amp yesterday and the blown caps were in the preamp. Discussed the filter caps in a bit more detail and cost wise was definitely not as bad as expected and the discussion was really that if I stick to a yearly service, barring any issues cropping up before that time he’d be checking the caps fully every time anyway and doesn’t necessarily need to be rushed.

Now the really interesting thing was an old Ampeg imported from the USA at some stage in its life now owned by Mogwai. The previous owner had retro fitted a new transformer onto the chassis (without removing the original) to suit our 230V mains. It looked insane and was about half the size of the original transformer. Amazing no one died using or working on that thing!

Probably the hardest part is done.

AFAIK the preamp filter caps are the hardest to get to. I believe you have to remove the preamp to get to them, which is a significant hassle because the controls and jacks are fastened to the front panel.

There are also four big caps on the output board, but these protrude through the top of the chassis. It may be possible to remove and replace these without pulling the output board. Even if the board must be taken out, it looks like less hassle than removing the preamp. Probably safer to remove the board.

There are also two small caps in the bias supply. This is the small board in the upper left. May be a bit more hassle than the output board (or not).

Any noticeable difference in the level of hum after replacing the preamp filter caps?

 

[Microbass]

Probably the hardest part is done.

AFAIK the preamp filter caps are the hardest to get to. I believe you have to remove the preamp to get to them, which is a significant hassle because the controls and jacks are fastened to the front panel.

There are also four big caps on the output board, but these protrude through the top of the chassis. It may be possible to remove and replace these without pulling the output board. Even if the board must be taken out, it looks like less hassle than removing the preamp. Probably safer to remove the board.

There are also two small caps in the bias supply. This is the small board in the upper left. May be a bit more hassle than the output board (or not).

View attachment 4669562

Any noticeable difference in the level of hum after replacing the preamp filter caps?

Tech said the bias and power amp filter caps were all good.
Regarding the hum: our studio space doesn’t have the best electronics and I didn’t actually run without my pedalboard attached, alas that almost signature Trace hum was still there. I Played for about 30min before packing up and heading to our gig last night. What I will say is the immense shift in volume. This amp has never been louder. It was almost wild. I like to run the pre at 1 o’clock and then output to suit and had to turn the master down 2 notches compared to the typical gig setting I’ve been using for years. Got to play on a big stage in a decent sized venue to boot - everyone was impressed. Paired up with a SuperTwin and my trusty Grabber my sound has never been better!