How to make sense of the cascading gain stages in a 1980s solid-state combo.
I’ve got a strange question about an Ibanez GX20 combo. This has puzzled me since I bought the amp in 1984, so I hope you can help me finally resolve it. In addition to bass, middle, treble, and reverb knobs, this solid-state amp has two inputs—overdrive and normal—and three volume knobs: overdrive, normal, and master. It’s the volume knobs that bother me.
Looking at these three knobs, you’d think the overdrive volume would control the gain of the overdrive input, and the normal volume would likewise control the gain of the normal input.
And that’s correct if you’re plugged into the normal input. In that scenario, the overdrive volume has no function.
But if you plug into the overdrive input, the volume is controlled by a combination of the overdrive and normal volume knobs, as well as the master. The user manual shows a simple scheme to combine these volumes, but I just don’t understand how it works. Is it a pre-gain/post-gain thing?
Ad van Oyen
I typically don’t answer questions about solid-state amps, but I figured that because this is PG’s annual pedal issue and Ibanez made your amp, there might be a common thread here. While Ibanez makes many other products, they certainly left an indelible mark on the vintage pedal market with a couple of wildly successful stomps—the TS808 and the TS9.
Ibanez still makes amps, including a tube amp with a built-in Tube Screamer circuit, but your particular model comes from what I consider to be the second generation of solid-state amps. By the mid 1980s, solid-state circuits had improved from the 1960s, and more and more amps were combining the old transistor technology with the newer IC (Integrated Circuit) technology. Yours is one of these examples, though it only uses a 4558 IC (the same number as in a TS) as a reverb send and return. The rest of your amp consists of old-school discrete component design. One more cool and crazy fact: This amp, like many Ibanez effects, was also available in an identical model branded as a Maxon device. But so much for products with multiple identities. Let’s see if I can help you understand the different inputs and their associated controls.
You describe how both the overdrive and normal volume controls affect the sound when the guitar is plugged into the overdrive input, but if the guitar is plugged into the normal input, only the normal control functions. This is correct and intentional in design.
Look at Fig. 1, where I’ve traced out the signal path from the input jack in red. As you can see, it goes directly from the normal input to the input of transistor Q102. The output of this stage then goes to the tone stack (treble, middle, and bass knobs), and then to the normal volume control. The signal has completely bypassed the first gain stage based around Q101. In this mode, the input of the first gain stage (Q101) is also grounded—as shown by the green trace—to avert any added noise.
But as you’ll see in Fig. 2, things change once a guitar is plugged into the overdrive input. The red trace coming from this jack feeds the first gain stage (Q101). The output of this stage is connected to the overdrive control. The next red trace shows the output of this control going through one set of switching contacts contained in the overdrive jack, which are closed when a 1/4" plug is inserted into this jack. The signal then goes to the second gain stage (Q102) and, as before, on to the tone stack and then the normal volume control.
As you can hopefully see by now, this is why both the overdrive and the normal volume controls function when you plug into the overdrive jack. This jack gives you access to an additional gain stage, as well as the ability to control its level by using the overdrive control. The higher you set the overdrive control, the more the first gain stage will overdrive the second.
This is very similar to the first series of Marshall MV master volume amps—the 2203 and 2204. Plugging into the high gain input provides access to the first gain stage, which is disconnected when you plug into the low gain input. The only difference is that the level of the first Marshall gain stage is fixed, whereas on the GX20 you have the ability to control this level via the overdrive control.Here’s one way to think of the GX20’s overdrive input: It’s as if you’re plugged into the normal input, but have a gain-boost stompbox between your guitar and amp. I hope this alleviates any control confusion.
Kick off the holiday season by shopping for the guitar player in your life at Guitar Center! Now through December 24th 2022, save on exclusive instruments, accessories, apparel, and more with hundreds of items at their lowest prices of the year.
We’ve compiled this year’s best deals in the 2022 Holiday Gift Guide presented by Guitar Center.
The Oregon-based company extends their line of sustainably sourced models with an inventive new bracing system and a wallet-friendly price tag.
Myrtlewood grows in Oregon along a 90 mile stretch of the Pacific Ocean coast. It is Breedlove’s favorite tonewood for backs and sides. In addition to its highly varied color patterns extenuated by the thin Burnt Amber Burst finish, myrtle delivers surprising energy and extraordinary tonal balance. To further boost the high-energy sound, we chose a European maple neck—which is denser than mahogany—and an Ovangkol fretboard and bridge. Of course, the top is European spruce for responsive, powerful projection. We spared no detail, including brass inlays, Fishman Flex Plus-T Electronics, and a travel-ready hardshell case.
Looking for a compact, “noiseless” way to plug in and play guitar? Check out the brand-new Gibson Digital Amp, available only in the Gibson App.
The new Gibson App simplifies the learning process and brings guitar playing to life for the current and next generation of guitarists in a modern, comprehensive, and intuitive way. The Gibson App is the place to take your guitar playing to the next level. New to the Gibson App is the Gibson Digital Amp, the ultimate starting amplifier for beginners and a flexible amp on-the-go for intermediate players and pros to get their sound anywhere. The Gibson Digital Amp is an accessible amplifier for both acoustic and electric guitars, and is currently available for Apple/iOS users--an Android version will debut next year.
Use the Gibson Digital Amp’s jamming guide to get started and transform your sound with built-in effects and pedals, jam to backing tracks, or use it in lessons and songs. The Gibson Digital Amp only requires your phone, and wired headphones for the best playing experience, no cables are needed. The amp features 3 acoustic mic presets, 4 electric amp presets, and 6 effects pedals.
The Gibson Digital Amp is the ultimate starting amplifier for beginners and a flexible amp on-the-go for intermediates and pros.
The Gibson App uses a unique two-way, interactive platform to teach guitar students how to do everything from playing their first note to shredding loads of songs. The Gibson App features interactive lessons with thousands of lessons and songs. Learn the songs step-by-step with video tutorials from superstar artists and pro guitarists in the “Gibson App Guide.” The Gibson App also includes the new Digital Amp, a built-in tuner, a metronome, Gibson TV, and new songs are added every week. New Gibson App Guides are added regularly and include Tommy “Spaceman” Thayer’s favorite iconic KISS guitar solos, Richie Faulkner’s (Judas Priest) “Guide to Metal,” Jared James Nichols’ “Guide to Blues,” CELISSE’s “Guide to Songwriting,” and more.
The Gibson App uses “audio augmented reality” to provide dynamic feedback to students as they learn and play. As you pluck a note or strum a chord, the Gibson App listens to your guitar and gives you real-time feedback on your playing. It also gives students a more contextual learning experience: Instead of learning chords and scales in a vacuum, you’re able to practice on a scrolling tablature that lets you hear how you sound with the backing of a virtual band. That means you can load up “Hurt” by Johnny Cash, “Brown Eyed Girl” by Van Morrison, “American Girl" by Tom Petty, “Nothing Else Matters” by Metallica, “Where is My Mind" by Pixies, “Country Roads” by John Denver, “I Hate Myself For Loving You" by Joan Jett, “Heaven” by Kane Brown, “Shape Of You” by Ed Sheeran, “Killer Queen” by Queen,“ Sweet Child O’ Mine,” by Guns ‘N Roses, “Run to the Hills” by Iron Maiden, “Roxanne” by The Police, and “Don’t Stop Believin’” by Journey, “Smells Like Teen Spirit” and “The Man Who Sold the World” by Nirvana, “Are You Gonna Go My Way” by Lenny Kravitz, and “Don't Look Back In Anger” by Oasis and hundreds more songs in a wide range of genres, to see how your play matches up with such seminal tracks.
As you’re playing, the Gibson App gives you feedback on timing and tone, ensuring that students are getting active input on how their play is developing. The Gibson App appeals to players of all levels, it’s not just for beginners looking to learn a few chords; the app can assist seasoned guitarists who are working their way through difficult riffs, want to learn their favorite songs, or polish their advanced techniques.
Players can also challenge themselves by speeding up or slowing the tabs. Like having a full-time guitar teacher, the Gibson App keeps track of all your progress and adjusts lesson plans accordingly. The Gibson App released a “backing track mode” which supports both lesson and song playback without headphones, so users can self-select what works best for their current environment. And that’s not all: the Gibson App also packs in a fully-featured digital tuner for guitar first-timers, there’s even a detailed lesson on how to tune your instrument, a multi-function metronome, players can connect to free one-on-one consultations with Gibson’s Virtual Guitar Tech team, and to direct links to the Gibson, Epiphone, and Kramer online stores for easy shopping for guitars, gear, apparel, and accessories.
Learn Guitar With The Gibson App
The Gibson App is more than a pocket-sized guitar teacher, it’s loaded with an archive of exclusive content and original programming from its premium and accessible award-winning online network, Gibson TV, featuring music icons telling their best guitar stories, with more episodes and installments added regularly. Users can watch Black Sabbath’s Tony Iommi share insights and tales from his decades-long career on the series “Icons,” dive into Joe Bonamassa’s assortment of legendary Les Paul guitars on “The Collection,” or see how Gibson’s iconic instruments are made in their Nashville factory from body to binding on “The Process.” There’s even a series called “The Scene” that focuses on backstage stories from hallowed music venues from coast to coast like The Troubadour and Grand Ole Opry.
The Gibson App free version features a few lessons a day; the premium version of the Gibson App offers full access and a 14-day free trial, then costs $19.99/£16.49 monthly or $119.99/£98.99 yearly.
For more information, please visit gibson.com.
This pickup captures the clear, bell-like single-coil chime of a classic P-90 when played clean and retains the tight mids and articulate low-end vintage growl and smooth sustain saturation when pushed into overdrive.
Belltone Guitars, as part of their Custom-Select System curated offering of pickups, has partnered McNelly pickups to create a one-of-a-kind retro-vibe P-90 pickup in the standard Filtertron size format. This pickup captures the clear, bell-like single-coil chime of a classic P-90 when played clean and retains the tight mids and articulate low-end vintage growl, and smooth sustain saturation when pushed into overdrive.
The McNelly P-90 Foil-Coil comes housed in a ‘raw’ nickel outer casing with a dull nickel foil face with metal mount screw gromets to complete the ‘new-vintage’ aesthetic, making it a perfect choice for your signature Belltone custom build. Available exclusively through Belltone Guitars.
Check out the Custom-Select System belltoneguitars.com to preview the McNelly P-90 Foil-Trons and all our standard and selectable components available to create your own signature Belltone. Then visit the Dream Lab on our website and select either model B-Classic ONE with its top binding or B-Classic TWO with its arm and body contours select your body color from our wide range of offerings, select your neck profile of either standard ‘C’ or thicker ’59 Round Back and either Maple or Rosewood fingerboard followed by your tuners, pickguard, and strings. Finally, review our curated custom-designed, and unique pickup selection to locate the McNelly P-90 Foil-Trons to complete your signature build.
Builds start at just over $2,300.00 with a custom case and shipping included.
For more information, please visit belltoneguitars.com.