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by John Gatski

  Like the hot-rodding of cars that has gone on for as long as there have been cars, guitar amp hacks and mods have been pursued for that ultimate “golden tone.“ Most mods from amp specialists or the tech-savvy do-it-yourself-er are designed to give that vintage tube tone from the 1950s-60s, the so called "golden age."

  The Copperhead Audio custom capacitors are designed, according to Owner Doug Weisbrod, to improve the tone of any amplifier — from a Fender Tweed to Silverface, to Marshall JCM’s and everything in between. Yes, even the new Fender reissues — such as the Deluxe, Twin and Princeton Reverb 65’s — are candidates.

 These custom cap kits were developed, according to Weisbrod, because amplifier mod/repair customers were constantly asking him if there were small signal capacitors available that would be upgrades for the stock capacitors.

CAE offers custom voicing caps in different values

  In the audio capacitor world, there are the “audiophile capacitors.” “orange drops,” stock replacements like “Illinois Capacitors,” and recreations of the “Fender Blues,” and the “Marshall mustard's.” That’s about it. The replacements are cheap metal film types and the recreations suffer from the same flaws as the originals. The “audiophile capacitors” are often poorly made, standard manufacture variety that offer little in the way of sonic improvements. They are just made from more expensive materials, that may offer some benefit, but they do not take advantage of construction techniques that will make them  the best in terms of sound.

  The effect of tone capacitors on guitar amp tone is significant, yet subjective. One kind of tone may be liked by one owner, but the next guy may not like it at all. That is why making a good cap that has wide appeal is tricky.

Bit by the Copperhead

  Capacitors are an integral part of many audio components including guitar amps. They are used in the power supply, phase coupling and tone stages of tube guitar amplifiers. Most capacitors are made from electrolytic, film and foil, metalized film, ceramic or mica.

  Copperhead Audio capacitors are made from a special material formula created by Weisbrod, and are claimed to the lower the Equivalent Series Resistance (ESR), Dielectric Absorption and Corona effect, all of which Weisbrod believes can negatively affect the sound of an audio circuit.

A CAE Fender amp "cap" mod kit

  Tone cap mods in guitar amps have been offered for many years, but Weisbrod said the Copperhead caps open up the midrange/treble sound of an amp — with a significant smoothing  — and the change tightens the bass to the point that you can turn up the tone controls to lessen the filtering effect when it is used extensively. Copperhead Audio capacitors also increase sustain by reducing ESR and mechanical distortion when the part is under load, Weisbrod added.

The upgrade

  So the guinea pig for the Copperhead mod was my 1966 blackface Deluxe Reverb (AB763). Doug had done a basic tune up, a year before, which was mostly filter cap replacement and a few resistors. With a Jensen Neodymium speaker and stock value tubes, the Deluxe Reverb sounded like a typical BF Deluxe, but I could never use the treble control to open up the sound because the midrange sound gets too hard. Most stock Deluxe Reverbs sound the same in stock form.

  With the Copperhead cap mod, Doug replaced all the tubes, and replaced all the tone and bypass caps with the Copperheads.  He only did just the reverb channel, since it is more widely used in the Deluxe Reverb amps. According to Weisbrod, my Deluxe Reverb amplifier was received with the original Fender “Blue” capacitors. Also original ceramic values of .47pF (Bright) and .10pF (Reverb Filter) were there. There was one non-original capacitor which was a .01uF “Orange Drop” at the phase inverter input. That should have been a ceramic .001uF.

  The Copperhead mod’s sonic improvement becomes more evident as you turn up the amp. In stock form, the congested dynamics of the 6V6’s limited output, combined with stock caps, made for reduced dynamics. The Copperhead mod’s sonic output was not so grungy.

  Ultimately, Weisbrod did two rounds of mods: Round 1 — the Fender “Blues” were replaced with the CAE Coppers. The non-original Orange Drop was swapped with a CAE Black .001uF. The ceramic .47pF and .10pF were replaced with Silver Mica. Doug said Ceramic and Silver Mica both have a gritty audio nature and have both been used by Fender over the years. Silver Mica has a lower ESR and, therefore, allows a bit more sustain. Silver Mica caps are also more expensive than ceramic types — which is why Fender prefers to use ceramics. Currently there is no film and foil improvement for these values — with the exception of the old Phillips film and foil polystyrene and aluminum capacitors. While these are better-sounding materials than Silver Mica or Ceramic, they have a variably higher ESR, since the leads are “laid in” rather than soldered — making the internal lead connection resistance rather high.

Initial impressions

  To make sure that the tube change was not changing the sonic variable more than the caps in the Deluxe, I listened to the mod with the old tubes and the new tubes. Other than taming some noise, the tubes did not make that much difference. After the first phase of the mod, I played the Deluxe with a number of guitars using my normal demo Wireworld Micro-Solstice guitar cable, the most transparent cable I have ever used (excellent high frequency extension and zero microphonics). Guitars included the first-year production Fender Mark Knopfler Stratocaster with Fender 60th anniversary ’54 pickups, a 2001 American Series Telecaster and a modified 2008 Gibson  Les Paul Studio (Seth Lover pickups and a Bumblebee Cap kit /CTS pot upgrade).

  Upon playing the Knopfler Strat, I immediately noticed a tighter, focused sound from the 50-year old Deluxe using the CAE caps. I could finally turn up the treble controls without it sounding so harsh. Upper-end detail from lead picking, as well as bridge pickup rhythm, was so much more apparent with the cap upgrade.

  On the negative side, the amp lost a bit of the compressed warmth sound that the blackface are noted for, and there was still a tinge of midrange grittiness. I enjoyed the openness and the ability to use the tone control, but I wanted back some of that 6V6 character. A delicate balance, to be sure, but I was confident that Doug could get me there.

Tweaking the caps

  On the second round, the Silver Mica .250pF treble input capacitor was replaced with a CAE Black in both channels.  Doug said that during this round of cap tweaking, he made a switch to the CAE Black .250pF, which he believed would cure the midrange grittiness of the stock .250 pF Silver Mica cap.

  After a week of tweaking the Deluxe, Doug returned it to me for good. And wow, what a difference the final selection of tone caps made! As mentioned, the bass was much tighter, yet full,  to the point where you could actually turn the control to  “5.” The same with the treble control. The high-mid and low-treble opened up, as I could hear more string/pickup harmonics, yet it retained the vintage tune smoothing that we all love in a Fender BF.

  Upon playing the Knopfler Strat, I immediately noticed a tighter, focused sound from the 50-year old Deluxe using the CAE caps. I could finally turn up the treble controls without it sounding so harsh. Upper-end detail from lead picking, as well as bridge pickup rhythm, was so much more apparent with the cap upgrade.

  It took me a while to dial in exactly where my favorite tone control positions needed to be with different guitars — since the old settings no longer applied. Instead of treble between 2 and 3, it could now run at 4-5, depending on guitar. The bass I could now run at 5 without the flabby tone that the old caps imparted. This also improved the lower-mid’s impression.

  On all guitars, the opening up the top allowed me to hear more of the guitar, and less of the filter effect of the stock cap amp circuit. My Yamaha SA-2100 ‘335 clone, with Seymour Duncan Seth Lover humbuckers, really came alive with the Copperhead mod, less midrange edge and more air, yet still classic tube.

  The Mark Knopfler Strat — with the limited edition Anniversary 54 pickups, the best set of Strat pickups ever made (IMHO) — rang like a bell with the cap upgrade. BTW, the Copperhead mod’s sonic improvement becomes more evident as you turn up the amp. In stock form, the congested dynamics of the 6V6’s limited output, combined with stock caps, made for reduced dynamics. The Copperhead mod’s sonic output was not so grungy. Shall I dare say, the old Deluxe was, er, articulate. If you swap out the 6V6’s for a set of 6L6’s and rebias (which I did try), the dynamics improve even further.

The verdict

  The Copperhead capacitor modification for the vintage 1965 Fender Deluxe Reverb reverb channel resulted in a nearly perfect balance of vintage, yet truer-to-the-guitar/pickup tone, than the stock, replacement tone caps that were in the amp. The parts cost, excluding new tubes, was $240, the labor was another $200. But that is with Copperhead Audio doing the actual work. Do-it-yourself-ers can save the $200, and according to Weisbrod, those who are handy with a soldering iron and can read a schematic, it is pretty easy to swap out the caps.

  All types of guitar and pickup combinations revealed the improved sonic transmission of the Copperhead Cap mod, including the Les Paul, a P90-equipped SG Special, Gibson L5 jazz guitar, and Telecaster. The upper-end harmonics of my Mark Knopfler Stratocaster showed a marked decrease in mid harshness, but yet had a more-open top-end without being edgy. You could turn up the tone control and let through more treble. Equally impressive was the dynamic tightening of the bass, which also allowed me to turn up the bass tone control.

  Kudos to Copperhead Owner Doug Weisbrod for coming up with an inexpensive way (if you do the work yourself) to improve the tone of classic and modern amps. I can’t wait to try the mod in a modern amp, such as an Orange or Marshall. This cap kit is an Everything Guitar Network Grade A Award winner.

  Copperhead Electronics is located in Manassas, Va. The web site is http://www.copperheadaudioengineering.com. Phone number is 540-439-3162. ©All original articles on this site are the intellectual property of the Everything Guitar Network. Any unauthorized use, via print or Internet, without written permission is prohibited.