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Topic: Polyester caps for tone controls? |
David Mason
From:
Cambridge, MD, USA
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Posted 30 Apr 2006 4:22 am |
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I am going to be building a new six-string this summer and I am wondering if it is appropriate to use polyester capacitors for the tone controls. I want to experiment with substituting a .015uf one for the usual .022, and a .033 for the .047. I can get them here: http://www.circuitspecialists.com/level.itml/icOid/957
Are these especially heat-sensitive or any other concerns? I have heard that film capacitors are less "harsh" than ceramic discs, are these a good choice? It seems somewhat wacky to me to pay $18 apiece for "vintage" capacitors from some place like angela.com, if they're not actually in the tone path. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 30 Apr 2006 6:39 am
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David. I wouldn't waste money on an expensive vintage cap, but I would recommend using a good cap. Actually, a tone cap IS in the signal path. It may be strapped across it instead of in series thru it, but it's still right there reacting to the direct signal imparting its tone character to the sound. I didn't belive it before I tried. It may not be drastic, but when you are using the tone control to mellow or darken, the cap quality does come into play. I really like the sound of those Angela tin caps. I generally like foil caps for that. If you're just getting a film cap, the polypropylenes sound a bit better than the polyester (mylar). Then polypropylene and foil are even better sometimes. Just avoid the ceramic disks.
I sure wouldn't want to spend more than 4 or 5 bucks on a cap though. You could buy some cheap ones to find the value you like, and then pick a good one at that value.
Brad |
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Robert Leaman
From:
Murphy, North Carolina, USA
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Posted 30 Apr 2006 6:06 pm
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| If you are going to select capacitors, select capacitors with the lowest dielectric leakage and the lowest dielectric absorption. There are no perfect dielectrics except a complete vacuum. All other dielectrics have some, if however small, conductivity. That conductivity acts as a parallel resistance across a capacitor and lowers its quality factor. Any good manufacturer lists these quality factors in their capacitor specifications. One can always add imperfection to a manufactured device but it is virtually impossible to improve quality after the device has been manufactured. |
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Bob Metzger
From:
Waltham (Boston), MA, USA
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Posted 1 May 2006 1:59 pm
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| I think the cap value is much more critical than the cap type but in a perfect world you can have both. |
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Geoff Brown
From:
Nashvegas
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Posted 1 May 2006 4:35 pm
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I agree that the ceramic discs should be avoided. I'd never spend the $$ on vintage caps either, unless I was restoring a vintage instrument. Orange Drops make great caps in guitar circuits and are inexpensive. Is it the 716 series?...I can't remember. Jensen, Mallory and Hovland also make very nice caps that are a bit more $$. Any of these would be fine.
Just a side note...try to make sure your pots are close to their rated value. Quality control is pretty loose on CTS pots...they can vary quite a bit. Some dealers check their pots to make sure they are at or slightly higher than their designated value. [This message was edited by Geoff Brown on 01 May 2006 at 05:41 PM.] |
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Dave Grafe
From:
Hudson River Valley NY
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Posted 2 May 2006 9:14 am
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While it is true that the mylar and poly caps have much better IM figures and tend to last longer as well, the electrical value of the caps is critical, as is the value of the pots - "tone" and other EQ circuits rely on a precise combination of resistance and capacitance to deliver the desired function.
A circuit designed for a .22mf cap will not do what you expect when you substitute a .15mf cap unless you also change the pot value to compensate, the more than 30% difference in value will make a big difference in what the control will do.
If you don't have the information available to make these design changes exactly then be very careful to follow the original design values if you want a usable product when you are through. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 2 May 2006 11:40 am
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Yea, the actual cap value is by far the most critical factor because it determines the rolloff frequency and the general voicing of the tone control. The cap "quality" is a subtler factor and deals more with the harmonic character or timbre of the tone control. Also since these tone controls are shunts or low-pass filters, the more you cut or darken the tone, the more the cap comes into play. Once you've upgraded to a film cap from ceramic, the actual tech specs of the caps are somewhat irrelevant. What matters is what they sound like. Polyester/mylar has a certain tone. In amps many Marshall geeks swear by these particular mustard colored mylar caps. The Orange drop 716p series are aluminum foil and polypropylene in a very hard epoxy casing and they have a bright, snappy quality. Other foil/poly caps have a different tone.
In these guitar treble shunt tone circuits we're talking about here, it can be a different story with regards to what sounds best. I've found that mellow foil caps sound real nice for this application. The old C.D. caps that you see inside old guitars (like old Push/Pulls) sound good for tone caps. The Angela tin caps are great. The old Fender blue cylinders are also nice. But honestly, the biggest improvement seems to be when you go to just about any kind of cap other than ceramic disk.
Brad |
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David Mason
From:
Cambridge, MD, USA
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Posted 2 May 2006 1:29 pm
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| Quote: |
| A circuit designed for a .22mf cap will not do what you expect when you substitute a .15mf cap unless you also change the pot value to compensate, the more than 30% difference in value will make a big difference in what the control will do. |
Making a difference is exactly what I'm hoping for - the people at angela.com themselves recommend subbing a .015 for a .022 to get more of the "woman tone" out of the lower reaches of the pot when using a humbucker, and I have a copy of an extended interview with Jerry Garcia in which he discusses changing the capacitors and pots around in order to get what he calls a "cello tone" with the knob turned down. As long as you avoid the "vintage", "collectable" insanity, even a decent poly cap is only 35c or so, so I'm just going to buy a sackful of different ones and fool around - I have a feeling my upcoming Warmoth is going to be an ongoing, mad-science experiment for a while here. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 2 May 2006 1:55 pm
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David. I actually have the ACTUAL schematic for Jerry's guitar. I got it directly from Gary Brawer at Real Guitars in San Fran about 10 years ago. He had it on his computer and he printed it out for me and scribbled a couple of notes on it. It's got the the exact cap and pot values that were in Jerry's Tiger and other main axes. Having read the same article you did, I asked Gary about that cap thing and he said although they messed around a bit, they settled on the common value of .05uF (or possibly .047uF) for the tone caps, and they were used with 500k pots. Also there is no volume pot loading the pickups down, only the tone pot thru the cap. The pickups only see the tone controls and the buffer preamp in the guitar. The volume pot is a 25k because of the lowered impedance from the buffer.
He had it wired with one tone pot/cap for the outer pickups and another pot/cap for the middle pickup which was Jerry's main pickup 90% of the time (split to single coil). I've got this entire schematic sitting right here in my lap. It's kind of scribbly, but very legible and has pretty much every detail with regards to the swtiching, splitting, looping, buffering, tone and volume control, battery hookup, grounding, etc. As soon as I can get my scanner hooked up, I'll be happy to scan it and post it on a webpage for any and all to see.
Pete Burak linked me to the latest buffer amp that Jerry was using. John Cutler makes these and they're quite reasonably priced. See here:
http://www.caesound.com/oldsite/CB1.html
A number of people have used rotary switches to engage different values of tone caps so you can pick the treble cut you want on the fly. On one of my guitars I've got a toggle that goes between a .022 and a .047. It's pretty handy. The .022 is kind of honky or horn like with strong mids but no highs. The .047 is a rounder, jazzier cut. Into distortion I find the .047 is more like what I think of as a "woman" tone. The .022 is kind of barky.
Brad
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