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First amp build filter cap qustion...
First amp build filter cap qustion...
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Old 14th November 2011, 11:10 PM   #1
indiemojoe is offline indiemojoe
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Default First amp build filter cap qustion...

Hello all!

First post here. I am in the p2p layout stages for my build of a Trace Elliot Velocette/Gibson GA-15.

Scroll down for actual question, summary of the build is first.

Just sold my oh so heavy ga-30rvs because mu back hated me. Love, love, love the tone, hated the reliability issues. It was essentially two velocettes with a shared preamp and stereo power amp. I can get the same tone in a small, reliable p2p mono head and be loving life!

Schematic: http://tinyurl.com/d26f2bf

I will be removing the bright switch as the amp is freaking bright enough as is (brits...). I will also be blowing out the, quite nifty, if I may say, single tone control to a full TMB rather than fixed bass and dual ganged treble/reverse mid with a resistor strapped across the top to make it the correct value. I quite like the single tone control, it won't let you get a bad sound. In the studio, however, I figure it wouldn't hurt to have some more options, extreme as they may be, for an effect.


Filter cap placement. What are the up/down sides of using chassis mounted cap cans rather than a filter cap fiberboard? I don't need boutique, ultra-linear, $60/ea hi-fi filter caps for guitar applications so I have some can options.

My reason is to cut down on internal space allowing the use of a smaller chassis, my hesitancy is lines of flux surrounding the caps. I know the interplay between components can make a great circuit sound not so great, or help a mediocre circuit have that "magic".

I know its dorky minutia, but hey, that is what we do, right?!

Any input highly valued. (as long as it is of ample impedance )

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Old 15th November 2011, 12:03 AM   #2
aardvarkash10 is offline aardvarkash10  New Zealand
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Cap cans are fine if you specifically want that "old skool" look.

In practise, axial or radial standard construction caps will allow you to place them closer to where they are needed, reduce cost, and potentially ease component selection and replacement (if you intended using a multi-section can capacitor).

Sonically? Meh, I wouldn't think there's a lot to pick assuming similar value parts, but others will disagree.
"It may not be easy for some to not hear differences, even if they are not there." - Vacuphile,
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Old 15th November 2011, 12:15 AM   #3
indiemojoe is offline indiemojoe
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Alright, sweet. Thank you very much. Good points all. I tend to agree with your meh perspective of placement vs the "Eric Johnson" method. 1/2" mic placement change has 100x the affect of 4" cap placement change, though I figure if I am starting from scratch I can incorporate any superstition if only for good measure.

Any voodoo believers?
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Old 15th November 2011, 05:17 AM   #4
kevinkr is offline kevinkr  United States
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First amp build filter cap qustion...
Lots of guys should be able to help out with this over in Instruments and Amps where I am moving it per forum policy..
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 15th November 2011, 05:29 AM   #5
indiemojoe is offline indiemojoe
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BAH! My bad. I guess I didn't browse the forum as thoroughly as I should have.
Still interested in what the serious cap sniffers think of the placement. Those over here in inst & amps too?
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Old 15th November 2011, 08:05 AM   #6
Enzo is offline Enzo  United States
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FIlter caps, which is what your can cap was, can be anywhere. They are not going to pick up radiated fields. If you are going to have a problem with something picking up fields from transformers, it is going to be sensitive grid wires runing to the tubes, not filter caps.This is a guitar amp, not a NASA satellite receiver. In the old days, for a given value cap, caps were much larger than they are today. The can cap allowed them to be outside the chassis, so they took up almost no room. Can caps today are a lot more expensive than using several individual caps.

If this is your first amp project, I'd recommend getting the basics down and honing your construction skills before concerning over subtle nuance of cap selection. At this point in your career, you are more likely to have tonal or performance issues from wire dress and actual construction than cap variations.

Places like Antique Electronic SUpply sells can caps in values suited to guitar amps, so check them out, compare prices to the individual caps they would replace. The main issues around selecting a multi-section can cap versus individual caps are space under the chassis and cost. Cut a chassis hole about the same size as for an octal socket, and mount the can cap over it. Underneath there will be the several solder lugs for the cap sections. Individual caps can be mounted all over the amp, they don;t have to be in a group. Electrically I don't care either way, I see no difference.
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Old 15th November 2011, 09:56 PM   #7
indianajo is offline indianajo  United States
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When I recapped my 1968 organ in 2010 I used four can caps, $120, plus 66 of something else, radial lead electrolytics, under 10 uf film caps and ceramic caps (Aerovox gold 50V). The can caps aren't rated for life, and my experience with the ST70 amp says they are good for 8-10 years before power degradation and about 12-15 years before the water leaks out. I'm buying radial lead caps for my second third & fourth organ. I'm putting them on TRW terminal strips like those available from tubesandmore.com or electronicsurplus.com or triodeelectronics.com. The best selection of caps seems to be mouser.com, although newark.com has a lot of values. I'm putting the radials under the deck, in the case of cathode bypass caps right on the tube socket. I plug the can hole with a bit of steel mesh.
What is really cool about radial lead caps, you can buy them in 3000-8000 hour life rating. Maybe they aren't sealed with rubber! Maybe they will last more than 8 years !! Newark.com has the life rating in the selector table, mouser you have to download the pdf file. Note the end of life spec'd is triple the leakage current at United Chemicon, versus that used by panasonic, nichicon, & rubicon. If you're doing tubes, buy a little 600v wire at tubesandmore.com, they are way cheaper than mouser & newark on wire.
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 15th November 2011 at 09:59 PM.
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Old 21st November 2011, 09:30 PM   #8
escopunk is offline escopunk  United States
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See, I love this forum, get all kind of usefull info.
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