Blackstar Patents - ISF – What is ISF and How Can You Use It

Blackstar Patents - ISF – What is ISF and How Can You Use It

The ISF is a patented feature that appears on a lot of the Blackstar Amplification range, but what does it do?

If you have an ISF control on your amp and you want to know how to get the best of it, keep reading.

ISF stands for Infinite Shape Feature.

Before we can understand what the ISF does, we first need to understand how the tone controls on amplifiers work. If you think of any amp brand, you probably have a “signature tone” in mind. These signature amplifier tones are created by varying component values inside the amplifier circuit on the part of the circuit that handles the tone you hear.

Depending on what component values you choose, this creates different start and end points for specific frequency bands. Therefore, some amps have a brighter treble control than others, or some have a more prominent midrange.

These “snapshots” of that potentiometers tonal range is a small part of a larger spectrum of frequencies. Even though you can adjust the controls on an amplifier, the components used in the circuit determine how far across that spectrum the control is able to take you. You cannot go outside of this “snapshot”.

Therefore, Amplifier A can never sound like Amplifier B, and vice versa.

The ISF works by shifting the whole tonestack response so that each of the controls react differently. You can break the ISF down into two main positions. Fully counterclockwise is the “American” setting and fully clockwise is the “British” setting.

The American setting is tighter, more focused, and percussive and the British setting is woodier, warmer and has a softer crunchy breakup. You can also set the ISF to anywhere between these 2 extremes to create new combinations.

The bass, middle and treble controls are reactive to this. In the American position, the controls react more like an American snapshot, and In the British position they react more like a British snapshot.

With this control, you can match the snapshots of whatever amplifier you want, as well as blending it in new positions to create the sound in your head.

Let’s look at a few settings you can use to dial in a few different tones using your ISF control. For all the examples in the video, the EQ controls have been left straight up at 12 o clock to show off the ISF at work. You can use this as a starting point to tweak the EQ to your own tastes.

60s/70s American Low Gain Drive and Blues Tones


Keeping the gain low with the ISF to the American side gives a lovely, soft breakup. If you pair this with a Telecaster style guitar, you get a great Rolling Stones style rock tone. Pair it with humbuckers and you can play all your favourite American blues licks.

60’s British Light Overdrive and Classic Rock Tones


On the British side of the ISF, paired with a Telecaster, you get an early Led Zeppelin style tone. The bite from the Telecaster and the prominent mids of a British voiced amp make for a great rock tone.

If you choose a humbucker loaded guitar, you instantly get transported to the mid-1960s British Blues Invasion. Dust off those Eric Clapton and Jeff Beck licks!

70s British Classic Rock Tone


If you push the gain slightly, you get a rich, full classic rock tone. Think Led Zeppelin, Aerosmith, AC/DC. This tone calls for big riffs and big chords.

80s American Thrash Scooped Metal Tone


This is the only tone where the EQ has been changed. American metal tones are typically scooped in the mid-range so this tone has had the mid pushed back to about 3. The gain is halfway and the ISF all the way to the American side.

Pair this with a high output humbucker guitar and you’re straight into the middle of the 80s thrash scene.

80s British NWOBHM Metal Tone


If you shift the ISF to the British side and put the mids back in, you get a rich, warm British 80s metal style overdrive. Think Iron Maiden, Judas Priest and all your other favourite NWOBHM bands. This is a great British heavy rock tone and sounds great with humbuckers.

About The Author

Leigh Fuge is a professional guitar player from Swansea in South Wales that has written and created content for many high-profile guitar brands and publications such as PMT, RSL Rockschool, Trinity College London, and more.

He works with to provide high quality guitar content for guitar players of all abilities from around the country. To date, has successfully generated over 32,000 student enquiries for their network of music teachers around the country. Find a local teacher in your area today.