Different ICs for Different Tone?

Different ICs for Different Tone

A different circuit could tweak it perfect ... 

by Chris Loeffler

Guitar players love to tinker with things and modify their gear to get the exact sound they want. Much like tone aficionados changes tubes in their amps to tweak the headroom or breakup characteristics of their amp’s tone, parts can be swapped in effects pedals to a similar end of modifying the characteristics of the effect. One of the most discussed examples of an effect that has been modified and customized to death is the Tube Screamer.

The IC (Integrated Circuit) chip opamp is the heart of TS-type overdrive circuits and one of the biggest factors in shaping their sound. While the stock JRC 4558 found in the original Ibanez TS-808 is considered to be the epitome of the ideal overdrive sound (especially when compared to the loathed 72558A or JRC 2043DD found in later TS-9 models), experimenters and modders have embraced alternative opamps in their quest for the perfect overdrive tone.

Effects maker PedalMechanic offers a unique take on the classic TS-808 circuit called the Bi-Polar Overdrive that includes the typical mods for increased bass and headroom, but adds a second 3PDT footswitch to switch between two different opamp chips, making it an ideal candidate to demo multiple chips. The two chips share the same Volume and Tone control but have independent Gain controls, making it easy to A/B chips throughout the gain range.

Please note the following observations are based on the narrow focus of how they performed in this particular version of the TS topology and the applications TS are used in, not overall judgment of the merits of the ICs. In testing different ICs with the goal of really hearing the slight differences, it is important to start with a high-fidelity guitar and a clear, relatively trasparent amplifier. I nasally vintage mini-humbucker into a mid-heavy Marshall is likely going to bury a lot of the nuance that would be revealed with high-output, neaturally voiced pickups and a clean Fender Silverface. That said, keep in mind some of quirks revealed in the transparent testing will marry perfectly with character-heavy gear, so don't mistake purity of testing with "the best" when it comes to individual setups.

The chips shipped with the B-Polar include the RCA 4558, LM1458, ST TL072, and a low noise 5532. A TA7558P and LM833N were also sourced for comparison.

Starting with the inimitable RCA4558 chip, the classic TS-808 sound was nailed in spades. It had headroom and crunch with a vocal, harmonically rich upper-midrange. Basically, SRV in a box, and the standard by which the rest of the chips were measured.

The LM1458, by comparison, seemed a bit cleaner and more sterile. While this chip excels in more transparent overdrive circuits, it came off as less colorful and a bit soulless in the TS.

The ST TL072CN, while sharing the clarity and reduced midrange content of the LM1458, had a bright, piano-like percussive bloom to it that had a good feel, but the overdrive was a bit less rich than the 4558.

The 5532 was the most bland and pedal-like of the group, with a boxy, two-dimensional overdriven sound.

The TA7558P, which is what is found in more modern TS-9s as the stock chip, added quite a bit of high-end and produced a grainy overdriven sound that had an almost fuzzy haze to the overdrive.

The LM833N was the final chip tested, and provided a clear, crunchy overdrive that was warm but a bit tighter than the typical OD. The tight clamping of the gain somewhat cut the sustain, and it felt more like a modern, gated drive than a classic, smooth overdrive.

In the end, none were terrible, and the differences were probably not going to be heard in a live performance at a loud bar, but the comparisons did give ideas for how those other chips could shine as well as the happy accident that was the implementation of the original 4558 (which was purportedly used in the original 808 because of its low cost and ready availability).

So other than a fun test, it is worth noting that an effect circuit is a concert of componants working together to create a specific sound. Upgrading caps, for instance, would have a much smaller impact than using a different value cap, and what's being fed into (and pulled out of) the IC was designed with that particular opamp in mind, so the circuit path that leads to glory with one IC may be unbalanced and weak with another. Like all great things in life, there is nothing better, just better suited to the moment. 

____________________________________________ 

Chris Loeffler is a multi-instrumentalist and the Content Strategist of Harmony Central. In addition to his ten years experience as an online guitar merchandiser, marketing strategist, and community director he has worked as an international exporter, website consultant and brand manager. When he’s not working he can be found playing music, geeking out on guitar pedals and amps, and brewing tasty beer.