"Like" AX84 on facebook

'Capacitors'
Author:fewjr (registered user: 49 posts )
Date: Fri, Nov 02nd, 2007 @ 02:51 ( . )

Hi again guys,
I have started putting the parts on the board and came across a part that I think is wrong. I bought most of my passives a couple of years ago and got sidetracked with ...well life! Kids, work, etc. The part that concerns me is Caps C12 and C16. I bought Nichicon 1uf/50V. The BOM calls for 1uf/25V and on the board layout C3, C4, C5, C6 & C7 need to be polarized. The rest of the caps do not need to be.....do they? Is this what they mean by "Audio Capacitor"? Anyway, for C9, C10 & C15 I used Solen Fast caps...the black ones that say France on them, but for C12 & C16 I have the Nichicon 1uf/50V, which are polarized electrolytic caps. Where can I find non-polarized caps at 1uf/25V. All I have found so far in 1uf are like 250V, 350V, 650V, etc. Alot of the images I've seen of other's builds use those yellow caps. Hovland maybe, I don't know for sure. I'm still looking though. Thought I'd hit you all up for some wisdom.

-- REPLY: [With No Quote] --- [With Quoted Text]

'Capacitors'
Author:Cliff Chappell (registered user: 3209 posts )
Date: Fri, Nov 02nd, 2007 @ 08:50 ( . )

The part that concerns me is Caps C12 and C16. I bought Nichicon 1uf/50V. The BOM calls for 1uf/25V and on the board layout C3, C4, C5, C6 & C7 need to be polarized.


The caps marked with a + are polorized electrolytics. Using a cap rated at 50V instead of 25V is OK. In the case of 1uF caps, they are right on the borderline between film (non-polorized) and electrolytics. You can find 1uF/16V and 25V caps, but they are big.

The rest of the caps do not need to be.....do they?


No, the rest of the caps can be film. The pF caps will usually be mica. You really need to read Gary Anwyl's P1 construction guide here: [link]
It covers these questions.

Is this what they mean by "Audio Capacitor"? Anyway, for C9, C10 & C15 I used Solen Fast caps...the black ones that say France on them, but for C12 & C16 I have the Nichicon 1uf/50V, which are polarized electrolytic caps. Where can I find non-polarized caps at 1uf/25V. All I have found so far in 1uf are like 250V, 350V, 650V, etc. Alot of the images I've seen of other's builds use those yellow caps.


The Solen's will work, but they are generally considered "too clean" for guitar amps. That's subjective, of course, so YMMV. The yellow caps you see in the Build Guide are Mallory 150 Film caps. Try a bunch of different ones once you get your amp up and running. As long as you stay away from expensive "audio" caps, it's fairly cheap. The two most common film caps you see are probably the Mallory's and Sprauge Orange Drops.


-- REPLY: [With No Quote] --- [With Quoted Text]

'Capacitors'
Author:Francis Vaughan (registered user: 712 posts )
Date: Fri, Nov 02nd, 2007 @ 09:41 ( . )

Where can I find non-polarised caps at 1uf/25V. All I have found so far in 1uf are like 250V, 350V, 650V, etc.


Just to add to what Cliff said. In answer to the above - nowhere. If a cap is non-polarised it is going to be a film cap, and you simply can't make them with that low a voltage rating. The film would be so thin it would be non-existent. In pretty much any design there is never any issue with using a part rated for a higher voltage. Times where it does are when the part is physically too big, or you are penny pinching and it is more expensive.

There are second order effects that do come into play with more critical circuit designs (radio frequency and similar) where the precise design of a capacitor is important, here we need to know the effects of self inductance, effective series resistance, dielectric absorption, and lots of other stuff. Mostly this is of no import for guitar amps.

OK, there are non-polarised electrolytic caps - but these are simply a pair of polarised electrolytics connected back to back in the same package. In general one tries to avoid electrolytics wherever possible. If only because they are a long term reliability problem.

-- REPLY: [With No Quote] --- [With Quoted Text]

'Capacitors'
Author:fewjr (registered user: 49 posts )
Date: Fri, Nov 02nd, 2007 @ 14:16 ( . )

Thanks for the quick response guys. You know, after I posted this question I noticed that on the schematic C12 & C16 did show a + sign on the tube side of them. The board layout doesn't show it though. It does for C3,4,5,6 & 7. Thats why I thought I had the wrong kind of caps. So am I ok leaving the polarized caps in then at C12 & C16? I will read the faq again...its been awhile since I read that one.

-- REPLY: [With No Quote] --- [With Quoted Text]

'Capacitors'
Author:fewjr (registered user: 49 posts )
Date: Sat, Nov 03rd, 2007 @ 14:18 ( . )

I have been doing alot of reading the last couple days, and I think I am learning quite a bit. I have only had basic electrical training over the years (high school, Navy, etc.). This is something I wanted to do to keep my mind active, as I am a Plant Engineer. Operating boilers and chillers can make you a little stagnant...lol. I believe I understand more fully which caps are coupling the different stages now. Comparing the chassis/board layouts and the schemo, I am starting to get it all through to the grey matter. Like I said, I started to get into this a couple years ago, and now I am finally starting to do it. I appreciate all the help you guys provide for us that need the help. You have a wonderful community in here.

-- REPLY: [With No Quote] --- [With Quoted Text]


--- 33 Users Online --- 26 Recent Unique Posters

Q69=1485234024 - Threads: / 1485234024