Coupling capacitors

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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.?
 
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.
 
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.

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:

Sy,
You are the resident chemist, Please share if you will.
We audio geeks speak of Mylar and polyester as if they are different things. We even see capacitors listed in catalogs with different pricing under the different headings. Construction differences aside, is there a difference between the quality of DuPont Mylar capacitors and generic polyester. If so what is it?
DT
 
DT, "Mylar" is just a brand, albeit a good and reliable brand, trademark of Dupont. Lots of other polyester films out there- and to be clear, I'm using "polyester" to mean "polyethylene terephthalate," aka PET. Same material that's used for soda bottles and disposable water bottles. PET is manufactured by quite a few other companies (Mitsubishi, 3M, and I wouldn't be surprised if there were some lousy ones out there- but any PET from a major manufacturer will perform well. I used to get Melinex from ICI, but I understand that Dupont owns that brand now as well.

PEN is also a polyester, though chemically a bit different but in common electronics parlance, it's usually not called that. Made by Teijin, marketed by Dupont.
 
Just another Moderator
Joined 2003
Paid Member
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.

Not that I know anything about tube amps, but But PPS caps certainly fit the bill for the bolded bit, and some of the manufacturers even mention that they are good for coupling in audio applications in their datasheets :)

Not sure if they are still available (my normal suppliers no longer stock them) but this is what I have used in the past. Evox Rifa SMR series

Tony.
 
Last edited:
Thanks for all the input. Seems poly-anything (mylar) would suit my needs and it's typically the type of cap I find in the mainstream amps. I just wanted to make sure there isn't something else (or better) I hadn't heard of before I go buy myself a large assortment of them.

When I finish this preamp I'll post some audio samples. It's pretty impressive now but I haven't dialed it in yet. I don't even play guitar anymore. Some people get better at it over time but I didn't. I'm building this for a friend who's also making a portable 12vdc rig for outdoor jams like drum circles. The preamp's heaters can run off 12vdc and I'm using an invertor from an automotive neon light for the high voltage supply. Rectified and filtered, it sat open circuit at 910vdc. I'll have to make some adjustments. :) The power amp will just be a bridged (or stereo for effects) Class-AB automotive amplifier of 100rms/ch or 200w bridged. Maybe a bit overkill for a drum circle. He's into metal but even clean this thing has a very clear and open sound to it. For those who know amps I'm aiming for an Engl Blackmore or Peavy 5150 sound.

Something along these lines (although poorly recorded).
SVS Tube Distortion TD 3 - YouTube

He gets the sound right from 0:14-0:20 then screws it up.
 
Lazzer408,

For cheap capacitors see the GE and other cap at the top of this link. Madisound Speaker Store

Now the confession: Much of the stuff I build is what if design stuff, the stuff you are talking about. I buy what I can find cheap.

Also check out these items. (keep an eye on the voltages)
AXON True Cap Metallized Polypropylene Capacitors
Solen Fastcap: PPE, PPM & PESG Series, Metalized Polypropylene Cap

Sy,
Thanks for the level of detail in your reply. In my day job I deal with plastic pipe; PE, HDPE, PVDF. I am always suspired at the price of the high tech polymers, even more expensive than the stainless steels.

M Gregg,
I have used Orange Drop capacitors. They are the entry-level real deal polypropylene and foil capacitor. Nice

DT
 
Disabled Account
Joined 2010
Lazzer408,

For cheap capacitors see the GE and other cap at the top of this link. Madisound Speaker Store

Now the confession: Much of the stuff I build is what if design stuff, the stuff you are talking about. I buy what I can find cheap.

Also check out these items. (keep an eye on the voltages)
AXON True Cap Metallized Polypropylene Capacitors
Solen Fastcap: PPE, PPM & PESG Series, Metalized Polypropylene Cap

Sy,
Thanks for the level of detail in your reply. In my day job I deal with plastic pipe; PE, HDPE, PVDF. I am always suspired at the price of the high tech polymers, even more expensive than the stainless steels.

M Gregg,
I have used Orange Drop capacitors. They are the entry-level real deal polypropylene and foil capacitor. Nice

DT

I think the problem with using Audio grade caps is the size....
It would be nice if you could get good audio caps at a similar size to standard. Don't know how the size of the orange drop compares..

Regards
M. Gregg
 
Sy,
Lots of Kynar pipe goes into clean rooms and research labs. It is Kynar to M.E. too.

M Gregg,
I think that much of the bulk is due to voltage ratings, higher voltage means higher bulk. Another factor that adds to the bulk is separate layers of plastic or paper and metal. Metalized capacitors tend to be smaller. For 715 type capacitors: We are locked into the voltage requirement effects on size. They have separate plastic and metal layers that make them bigger. They are epoxy dipped, that tends to increase the size as well. My best guess is they are as large as any. Check the manufacture cut sheet to be sure.
I am purposely thinking of going with lower voltage to include this capacitor in a tube RIAA preamplifier. This capacitor worked out well in the Salas Jfet version.
Vishay R. Film Caps

DT
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.