Current handling capability: big F&T power supply caps vs new design Nichicon

[SoulFetish]

Electrolytic Cap life is dependent on their internal temperature which has a drying effect on the paste electrolyte.

Caps self heat according to Power = current squared x resistance, in this case the current is the ripple current and the resistance is their ESR (equivalent series resistance).

They also absorb heat from adjacent components.

To give some idea about this we see an equivalent idea in aircraft wiring standards, wire rating is based on temperature rise. If 2 wires are bundled together so they can heat each other then the current rating of each wire is reduced to 0.94, if 3 wires bundled to 0.86 etc. Source is Fig 11-5, AC43.13-1B Chapter 11 "Aircraft Electrical Systems".
So don't bundle all your high ripple current caps together (like in Fenders "doghouse") and keep away from other heat sources.

I said above that I use Panasonic ED but have also use Nichicon and Rubicon. Higher Voltage Caps, in general, have higher ripple current ratings. Don't be afraid to use a cap with much higher voltage rating than absolutely required.

Cheers,
Ian

Good stuff Ian. Along with high ripple current ratings, aluminum electro's life can be extended as well by operating the cap at a lower voltage that it's max rating. Although, according to data published by Illinois, this is limited by a ratio of 2:1, even when the cap is run at 50% of it's voltage rating.

[NoelW]

"MY" opinion... Well, maybe you can state a spec of 105C no matter how mediocre it's performance at that temperature, as long as you state what it's actual performance is at that temperature. I wouldn't be at all surprised if some caps rated at 105C are no better under such conditions as many 85C rated caps. I think I've actually seen some of that in derate specs. But I don't actually know if there's any stringent criteria for being able to print a 105C rating outside of disclosing performance.

Good point and that is true; the temp rating doesn't tell the whole story.
It could be a 105C rating with a lifespan of 100 hours or, of 10000 hours or, ?

I guess that answers my question.

[NoelW]

Electrolytic Cap life is dependent on their internal temperature which has a drying effect on the paste electrolyte.

Caps self heat according to Power = current squared x resistance, in this case the current is the ripple current and the resistance is their ESR (equivalent series resistance).

They also absorb heat from adjacent components.

To give some idea about this we see an equivalent idea in aircraft wiring standards, wire rating is based on temperature rise. If 2 wires are bundled together so they can heat each other then the current rating of each wire is reduced to 0.94, if 3 wires bundled to 0.86 etc. Source is Fig 11-5, AC43.13-1B Chapter 11 "Aircraft Electrical Systems".
So don't bundle all your high ripple current caps together (like in Fenders "doghouse") and keep away from other heat sources.

I said above that I use Panasonic ED but have also use Nichicon and Rubicon. Higher Voltage Caps, in general, have higher ripple current ratings. Don't be afraid to use a cap with much higher voltage rating than absolutely required.

Cheers,
Ian

Very informative Ian; about wire rating too.
Maybe it would be good to measure the operating temperature of caps, as a gauge of their internal temp while working hard.
Keeping them away from heat is always preferred.

[NoelW]

Thanks to you all, for your replies.
They tend to confirm that my approach, of using electros with manufacturer stated "Lifetime@Temperature" ratings of more than 8000 hours, is a good approach.

Cheers, Noel

[Justin Thomas]

Given I'm usually building true PTP, I try to stay away from skinny-lead lytics, so it's F&T for the big guys for me for sure. I could go with Atoms, but quadruple the price is a bit of a deterrent...

Justin

[R.G.]

Best cap does not mean the best sounding amp.

That is 100% true. It's CIRCUITS that affect the sound.

F&T's have a good reputation among guitar amp repairers, builders and upgraders. If you look at the specs, they are not the best cap to make the best power supply, they have faults and weaknesses but "I" think they actually improve the sound without making it too sterile.

I'll insert my standard complaint about anecdotes: reputation is interesting, but by no means definitive. You can't measure reputation, and that means you effectively can't figure out what to do to make it better or worse.

I absolutely respect your opinion about what makes something sound better to you. But what, exactly, does "sterile" mean? Less distorted? Less 120hz ripple in it? Les subliminal 180hz or 240hz? "Sterile" is probably something like pure, unadulterated, absolutely true to the original, maybe. We know how to make that really dirty, but I suspect that's not what you're after either. What do we mix in to make it less sterile?

I mentioned once before, there was a website where they had a good sounding Fender Bassman, they tested the power supply for a bunch of parameters. They then tried to duplicate this power supply with some lab equipment and subbed it into the amp. The sound changed.

It is remarkably difficult to do unbiased A-B comparisons when you have to go muck around with components between tests. I have no doubt that the perception of the sound changed. The question is - how? And was it the parts or the people? This is a really crucial question for any attempt at engineering "betterness".

[Chuck H]

It is remarkably difficult to do unbiased A-B comparisons when you have to go muck around with components between tests.

+1
You really do need an instant change facilitating an A/B comparison. That's why when my amp doesn't sound quite snuff I don't open it up and start changing values. I just cup my hands and box my own ears about five or ten times really hard. Very fast and almost always changes the tone.

[eschertron]

+1
You really do need an instant change facilitating an A/B comparison. That's why when my amp doesn't sound quite snuff I don't open it up and start changing values. I just cup my hands and box my own ears about five or ten times really hard. Very fast and almost always changes the tone.

I prefer the 'drink a beer' mod. Sometimes it takes two or three before I'm satisfied that the amp sounds as good as it can. A funny side effect: my intonation gets better too (source: Joe's Garage, parts I and II)

[HaroldBrooks]

...when we micro-analyze caps like this, it is a similar matter.

I think Enzo makes a very good point. I woke up to this just last year, when we included another Led Zeppelin song into our repertoire ( What is and what should never be off the second album), and I started using one of my really old Valco amps miked up, instead of a more modern "cleaner" sounding distortion.

If you listen to the guitar outro on that song, the amp has some horrific intermodulation breakup, and to me it's perfect for that song, as it adds a mysterious and brutal sounding guitar tone, in conjunction with a Big Mystical Gong Swell - (LOL, hey this is Led Zeppelin after all !). The Outro starts at 3:30 ---

https://www.youtube.com/watch?v=WnMiXsRtsfc

Take that same type of amp setup-(their live performance sounds very close so I think the breakup it's mostly from the amp), and use it to play some other stuff, as in say a later Zeppelin songs like "The song remains the same", and all of a sudden, the amp you loved before will now sound like crap, and you will be looking to "Fix" it, so it can now sound like the pristine Marshalls used later on... Go back to the early stuff again, and a Marshall would sound too clean, and it would lack the artistic impact the "dirty" intermodulation distorted sound adds.

This is a good example IMHO of how context is very important when judging an amplifier's tone, so shooting for perfection in ripple reduction and hum may just well be the same as shooting your foot, in some instances.

[Chuck H]

Ok... On the subject of things that change the tone of an amp but can't be measured I'll nominate rainy days. My amps ALWAYS sound best on rainy days!?! Not like when rain starts, but really soggy days when the weather is already socked in. I'm not the sort that suffers mood changes with weather and it's consistent enough that I think there may be a physical reason, but I don't know what it is. About the only component that might change it's behavior under conditions of low pressure and high humidity would be the speaker/s. So that's always been my belief.

[HaroldBrooks]

Ok... On the subject of things that change the tone of an amp but can't be measured I'll nominate rainy days. My amps ALWAYS sound best on rainy days!?! Not like when rain starts, but really soggy days when the weather is already socked in. I'm not the sort that suffers mood changes with weather and it's consistent enough that I think there may be a physical reason, but I don't know what it is. About the only component that might change it's behavior under conditions of low pressure and high humidity would be the speaker/s. So that's always been my belief.

My guess is the speaker, as you already guessed ! there has to be some changes in absorptive materials based on high humidity, I would think. Add weight to a cone and you will change the tone !

And as you stated, changes to barometric pressure. That sounds reasonable as well.

[Justin Thomas]

Mine sound better after sitting in the car on a sunny day for a few hours.

Jusrin

[catalin gramada]

...btw talking about speakers...something for mythbusters..

https://m.youtube.com/watch?v=P4grDEC_Uj0

https://m.youtube.com/watch?v=CDy2dwPQAFs

https://m.youtube.com/watch?v=GIjyiIjvXFk

[Chuck H]

...btw talking about speakers...something for mythbusters..

https://m.youtube.com/watch?v=P4grDEC_Uj0

https://m.youtube.com/watch?v=CDy2dwPQAFs

https://m.youtube.com/watch?v=GIjyiIjvXFk

I wonder if the playback on the speakers for the before and after clips is done at a volume that might better exploit cone changes. It seems to me that a softened cone would demonstrate it's relative "softness" more when pushed harder? Anyway...

IMHO the only way to properly break in a speaker is to play through it. I can hear the difference in the LF on the speakers in the video, but odd to me is that there is no difference in the HF. Odd to me because my own experience breaking in speakers by playing through them has demonstrated tonal changes in the HF that are more pronounced than those in the LF. This is part of why I've never jumped on the band wagon with the low frequency AC break in.

[mikepukmel]

Yeah, same here: why "burn in" and not just play through it?