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Old 11th November 2011, 07:57 PM   #1
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Default Coupling capacitors

There's alot of information online about the types of coupling capacitors used between tube stages but I'd like some opinions from you guys.

I'm not building a hi-fi amplifier so there's no need for expensive capacitors offering minimal benefits. The values are of much greater importance then the quality. The circuit is for guitar distortion using 12ax7 tubes. Much of it's design is based on how it sounds to the guitarist.

That said, I'm looking for cheap capacitors so I can order multiple values for testing. They should be stable at wide range of operating temperatures and offer long life expectancy. Values range from .001 to 1uf.

What are some pros and cons with current materials like polyester, polypropylene, tantalum, metallised poly, ect.?
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Old 11th November 2011, 08:03 PM   #2
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Tantalum is generally not considered very good. Polyester is the worst of the modern plastics. It does get better with burn in. The only other to avoid is all ceramics except COG types.
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Old 11th November 2011, 08:12 PM   #3
SY is offline SY  United States
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Since it's a distortion application, most of the hifi considerations don't mean much. I'd go for polyester or ceramic. Polyester is low-ish distortion (though higher than polypropylene). Cheap ceramic caps can be somewhat microphonic, a disaster in hifi but potentially a useful color for guitars.
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Old 11th November 2011, 08:19 PM   #4
TheGimp is offline TheGimp  United States
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Keep in mind that many old guitar amps were built with ceramic, polyester as well as Mylar coupling caps. They weren't shooting for Hi-Fi.
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Old 11th November 2011, 08:21 PM   #5
kevinkr is offline kevinkr  United States
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Panasonic makes a line of inexpensive high voltage film caps that some of my friends who build guitar amps apparently like, another popular choice is the orange drop..

Vishay Sprague Polypropylene 72 piece Orange Drop Capacitor Kit | Polypropylene Film Capacitors | Guitar Files(TM)
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Old 11th November 2011, 08:32 PM   #6
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Quote:
Originally Posted by SY View Post
Since it's a distortion application, most of the hifi considerations don't mean much. I'd go for polyester or ceramic. Polyester is low-ish distortion (though higher than polypropylene). Cheap ceramic caps can be somewhat microphonic, a disaster in hifi but potentially a useful color for guitars.
That is an important point to make. I'm aware of ceramics being microphonic and indeed it does color the sound. It colored it so well the guitar couldn't be heard over the feedback. Where they are placed is important if you're using them strategically to color the tone. I would place them after any major gain stages.

This is a pedal/preamp project. Ceramics may be more usefull in a combo or a head.

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Originally Posted by TheGimp View Post
Keep in mind that many old guitar amps were built with ceramic, polyester as well as Mylar coupling caps. They weren't shooting for Hi-Fi.
Isn't Mylar just a type of poly film?

Last edited by lazzer408; 11th November 2011 at 08:53 PM.
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Old 11th November 2011, 08:56 PM   #7
DF96 is offline DF96  England
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Mylar is a brand name for a type of polyester?
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Old 11th November 2011, 09:07 PM   #8
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DuPont?
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Old 11th November 2011, 09:09 PM   #9
SY is offline SY  United States
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Yes.
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Old 12th November 2011, 02:21 AM   #10
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Actually most people building guitar amps would toss the ceramics, all distortions are not created equal I guess. Polypropylene is more stable than polyester and does not cost much more.
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