Blackstar Fly 3 Mods

I was looking for a small, portable battery-powered amplifier that I could play anywhere in the house without having to plug into the laptop or my full rig. There are many portable amps to choose from these days. Some are very small like Marshall MS-2 and few dreadful Fender mini amps, but they all sound rather bad, partly because of simple circuits, partly because of tiny speakers. There are some amps that are very decent, but are a bit larger than I need, like Yamaha THR5, Roland Micro Cube and VOX Mini3 G2. Smaller amps tend to have simple (and bad) analog circuits and most larger portable amps these days feature digital amp simulations (which is not bad per se). And then there’s Blackstar Fly 3 that sits right between the two groups. It’s very portable, but still has a “real” analog two channel preamp, digital delay and a full-range 3″ speaker.

At around 60 $/€, the price is closer to those cheap and crappy Marshall and Fender amps than to bigger Roland, VOX or Yamaha. At this price point, as expected, there’s no vinyl-covered wooden box. The amp is housed in a dull looking black plastic box, but there’s a limited edition for the same price that features beige plastic box with British flag on the front grill. I went with the limited edition.

  • Analog preamp with two channels – clean and overdrive. Shared volume control, Gain control for Overdrive channel.
  • Single knob ISF EQ control.
  • Digital simulated tape delay with Time and Level controls.
  • Aux-in 3.5mm jack.
  • Line/Headphone out jack.
  • Proprietary jack (looks like LAN connector) for stereo extension cab (cab sold separately).
  • Runs on six 1.5V AA batteries or a 9V DC adapter with positive tip (not included).
ISF Eq Control

Instead of a conventional tone control or a tone stack, there’s a single ISF control that changes the character of the EQ as you turn it. It’s one of Blackstar’s selling points for their amps and they even had it patented (they had to patent *something* to brag about 🙂 ). In their bigger amps they usually combine ISF with a conventional Bass/Middle/Treble tone stack to add versatility, but in this case, ISF is the only control over the EQ. I would prefer a standard Bass/Middle/Treble but I understand that space and cost would be an issue. ISF is better than nothing, and probably better than a standard treble-cut Tone control.

I wanted to take it a step further and analyze how response of the amp changes when playing with ISF control. To do that, I hooked up Fly 3 with my laptop, connected audio interface output to Fly 3 input and then took the simulated output from Fly 3 and connected it to audio interface input. Then I played frequency sweep going from 50Hz up to 10KHz and recorded what comes out of Fly 3. This is repeated with 5 different positions of the ISF knob. Below are frequency responses of each take plotted on the same graph. Treble and bass roll-off is most likely part of speaker simulation circuit and doesn’t seem to be affected by ISF control.

As you can see, the response with ISF set to zero is very different than the rest of the pot travel, probably caused by the same effect that causes drastic change in tone with guitar’s tone knob at 0 when there’s no resistance in the network. That’s my favorite position for rock/metal and for riffs. It has a pronounced mid scoop that prevents it from sounding boxy, noticeable low end boost around 200Hz and it has the most clarity in the high end. As we turn the knob to the right, the scoop shifts and is less and less pronounced. At the same time, there’s less and less high end and the low end hump is less pronounced. For my taste, positions around noon sound the best for lead sounds. The extreme right position sounds a bit too dull for my taste, but could be useful for bluesy/jazzy stuff.

What I Like About Fly 3?

Analog preamp featured in Fly 3 is quite good. Cleans are nice and clean and overdriven sounds range from mild crunch to saturated gain, with about the same range of distortion as say a JCM800. The distortion is crunchy and smooth, almost tube-like, with no digital artifacts or fizzy character usually associated with cheap solid state amps. What’s great about it is the great dynamic range. With lighter picking (or playing with guitar volume control), it cleans up nicely without losing clarity. Harder picking pushes it harder and produces more distortion. Digital simulators in small practice amps rarely sound this good and usually have poor dynamic range. High gain models sound very distorter regardless of guitar you plug into or how you play it. You get the same sound, just louder or quieter. With Fly 3, my Ibanez with high power humbuckers can push the preamp quite far into saturation, even reaching the metal territory. With a Strat I can get nice SRV type of sound and classic distorted rock sounds with Gain control maxed.

Having a delay on-board is a big plus. It’s advertised as “tape” delay, but in most cases, “digital tape delay” is just a imperfect digital delay that has low fidelity, so it cuts high end and potentially adds distortion or digital artifacts. Fly 3, like most of other “warm digital delay” circuits uses PT2399 delay chip that is imperfect to begin with. Then they double the maximum delay time from ~300ms to ~600ms, degrading the quality of echoes even further. In this case, I can definitely hear that echoes are warmer sounding, but there’s no too much distortion or noise, meaning that they did a good job filtering the signal. Shorter delay time with level set to around noon can be used somewhat as reverb to add space to the sound and longer times with more pronounced level can be used as conventional echo.

3W amplifier delivers plenty of volume for bedroom playing. For late night playing I keep it at around 9 o’clock hoping not to wake up anyone.

What I Don’t Like About Fly 3?

The 3″ full-range speaker is good enough for listening to music, but I’d like it to have more punch and clarity with guitar. The preamp is voiced rather dark. It sounds decent for lead playing, but riffs can sound a bit dull. I’m guessing that they feared that the tiny amp would sound thin with more treble so they make it warmer. Sure, you can’t expect wonders in a small plastic box, but it’s still something I think can be improved (mods to follow).

I really miss the feedback control for the number of repeats on the delay. It’s preset to barely two repeats, which is fine for slapback-style delay, but for lead playing it would be nice to be able to have more. One more mini pot next to delay level would solve that.

Below are some of the mods I did. If you’re not interested, you can skip the section and jump to Sound Clips section.

External Speaker Mod

The minuscule size is one of the biggest strengths of Fly 3, but it’s also a drawback at the same time because such a small speaker cannot provide enough depth in such a small plastic box. Plugging it into a bigger guitar cabinet makes it sound much fuller and it’s relatively easy mod to enable this. The first thing we need is a switching 1/4″ jack. Regular open-style jacks will not fit because of the internal “ribs”, but plastic style jacks with lugs at the back will (just) fit. Make sure you have the switching type jacks that have three lugs instead of the usual two. The third lug allows us to disconnect internal speaker when external speaker is plugged.

Then we need to drill the plastic cabinet to find the right place for the jack. That’s not very easy to do because of the aforementioned ribs and battery compartment, but there are few places that we can use. One of those is marked on the photo below. If we drill the cabinet at exactly that spot, the hole will land right between the two ribs and you’ll be able to squeeze in the jack there. I drilled a small 3mm guide hole before going all the way to 9mm.

The next problem is getting to speaker leads. You can probably cut the ribbon cable and solder the wires there, but my approach was to desolder the small daughter board from the speaker and add more cables from the board to the jack and the speaker. These carry low impedance signal, so added noise from more leads is not a concern.

Note where the + and – terminal are on the speaker and where the corresponding solder pads are on the daughter board. After the board is desoldered, wire the jack sleeve lug together with – pad of the board and the – terminal of the speaker, wire the + pad on the board to jack tip lug and wire + terminal of the speaker to jack shunt (switch) lug. After all done, it should look something like on diagram below.

And here’s how my wiring looks like, admittedly the angle is not revealing enough.

The final result, with the jack is installed.

JFET Booster Mod

Pretty much the whole circuit is built using SMD technology and there’s no schematic available yet, so it’s really not really mod-friendly. However, with some analysis and patience, I was able to further improve the amp without killing it. I wanted to expand tonal range of the little Fly 3 and add more gain for high gain tones and to improve definition when playing rock or metal riffs. The stock preamp can get decent amounts of gain with higher output pickups, but I wanted to push it harder. I put together a simple JFET booster based on J201 with parts I had in my bin.

The circuit resembles a simple triode gain stage from tube amps and provides at least 6db of gain. 4.7uF capacitor in parallel with the source resistor further boosts the output for most of the sound spectrum except for the very deep lows, as we don’t want the sound to get too muddy. I built it on a small 3-per-pad 1″ proto board, ready to be installed in the amp. The plan is to somehow inject it between the input jack and the rest of the circuit and have a bypass switch that would return the amp back to the stock voice (which is nice in its own right).

After using the booster for a few months I further improved the design by adding a 68K input resistor which eliminated radio interference that I was getting sometimes and some of the white noise. I also added a 220K/10nF low pass filter at the end that cuts some of the treble, as I was finding it too shrill most of the time.

Analyzing the Fly 3 circuit board, I identified the crucial points on the board. “A” is the circuit ground, “B” is input jack’s tip connection, “C” is the input leg of the input capacitor and is connected to “B” and finally, “D” is the power connection after the power switch. Powering our booster directly from batteries would drain them even when the amp is not turned on, so we want to make sure to get the point in the circuit that’s downstream from the power switch. “D” is exactly that.

Now the tricky part. We want to break connection between “B” and “C” so we can inject our booster circuit in between them. There’s a thin copper trace on the other side of the board that connects input jack to 22nF input capacitor and also connects the 2.2M reference resistor to ground. We want to cut the trace right next to the capacitor and break that connection without damaging the adjacent trace. Using continuity check on the DMM, I verified that the input jack and input capacitor are no longer connected.

Next is the bypass switch. Use the smallest DPDT toggle switch you can find because there’s not much room there. I drilled a 6mm hole exactly between the “Input” and “Level” labels and as far down as it could go. That position is perfect for installing the miniature DPDT switch.

Here’s now it looks like from the inside. Note how the middle terminal of the switch gets perfectly aligned with the point “B” on the board. The two terminals on the right side of the switch should be connected together, that’s our “bypass” side.

Now we can connect the middle two terminals of the switch to points “B” and “C” on the board, as shown below.

And the final step is to install the booster board. I used a piece of strong double sided foamy tape that works well for attaching two surfaces that are not perfectly flat and provides electrical isolation. Booster input and output leads are soldered to the two terminals on the left side of the switch, ground is soldered to point “A” and power supply to point “D” on the board. And voila, we’re done!

The mod worked great. Not only did the little amp survive my butchering, but it sounds even better now. The switch turns it effectively into a four channel amp – stock clean, boosted clean (sounds slightly broken up, but still very lively and not as compressed as overdrive channel), stock overdrive and boosted overdrive (great for high gain). Boosting the overdrive channel makes the sound more aggressive and present. It’s great for riffs, heavy lead sound and metal. Pinched harmonics jump out of the fretboard with ease. Sure, the same can be achieved by using a separate booster pedal, but for me it wouldn’t really work. Fly 3 is a tiny portable amp and adding any other pedals to the signal chain makes it much less portable. Having everything contained in a single unit is a big plus for me.

DC Output Mod

Fly 3 can be powered by batteries or an optional power adapter (regular pedal adapter will not work as it requires 6.5V DC and uses a non-conventional 2.5mm jack with positive tip), but to me batteries make it a great portable amp. However, if we wanted to use additional pedals in front of the amp, we’d need to get extra batteries for them. Luckily, there’s a way to use the amp to power additional effects from the same batteries used to power the amp. The way DC jack is wired, it disconnects ground lead coming from the batteries when we plug the jack, but if we defeat the switching, we can have the DC input jack work as DC output when batteries are installed, or as a regular DC input jack when there are no batteries. By doing that, we can use DC jack to power additional pedals.

Looking at the photo above, there’s a small PCB that hosts the extension cab socket and DC input jack. Black and red leads are coming from the battery pack and are connected to the two terminals of the DC input jack. The third terminal at the bottom is connected with the circuit ground. When there’s nothing plugged in, battery ground is connected to circuit ground. As soon as we plug the adapter, connection to battery ground is broken and instead it connects adapter’s ground to the circuit ground. But if we jumper the two ground terminals, we are bypassing the switching mechanism of the jack and we can use the jack to output power for external effects. It’s possible to solder a jumper wire without having to disassemble the whole amp, we just need to remove the screw that holds the mini PCB in place, and lightly pull it up as far it will go. Have in mind that you shouldn’t connect power supply AND batteries at the same time and also note that power switch of the amp does NOT affect the DC output jack. It is permanently connected to the batteries, so we need to make sure that the device(s) we power can switch the power on and off by themselves, or we need to unplug the DC plug when we’re not using it.

Sound Clips

Stratocaster with neck (Kinman AVn-56) and middle (Kinman AVn-62) pickups, ISF set to noon. Played without the boost and then with the boost engaged.

Telecaster with DiMarzio Chopper in bridge position. Gain set to around noon, without boost, ISF set to 0, then the same riff with the boost engaged.

Ibanez with DiMarzio Crunch Lab in bridge position. Gain set to around noon, without boost, ISF set to 0, then the same riff with the boost engaged.

Stratocaster with neck (Kinman AVn-56) and middle (Kinman AVn-62) pickups, ISF set to noon. Played without the boost.

130 Responses to “Blackstar Fly 3 Mods”
  1. Merlin00 says:

    To reduce the volume, for evening playing, there is a trick, a power limiter, which can be connected in series with a speaker and equipped with a switch or a switch.
    In series with the speaker, connect a light bulb with a suitable voltage, for example 6V 0.3A or 6V 0.5A…
    For very quiet night limitation 12V 100mA, or for a slightly stronger volume 12V 250mA, /two parallel 12V 100mA/
    This creates an effective performance limiter.
    low volume levels, or soft playing, when the bulb has a cold filament, will not manifest itself in any way.
    If the power is increased above about 0.6W, the bulb will start to burn and absorb the power.
    All noisy spikes, bangs and rude awakenings will be absorbed.
    You can experiment with light bulbs.
    An interesting finding is that the amplifier, driven to max gain, sounds quite pleasant and the speaker is not saturated, if you turn it to maximum, through the bulb.
    However, a much nicer sound can be achieved if you use a larger and more pleasant center and sensitive speaker.
    Cheap, for example monacor SP-205/4 (SP-205/8), Monacor SPM-200X/4
    Tesla ARO689, BG 20,..
    If you dare, on your own box, have the balls to experiment, then let them try the Jensen P8R.

  2. Craig says:

    How would I go about bypassing the f1 fuse as my fly isn’t working with batteries or dc.TIA

  3. Mgee says:

    I am looking for the pinout of the extension speaker. The + & – to hook up an extension speaker. Which leads are to the speaker out of the RJ45 plug? Thanks if you have the info.

  4. Mark says:

    Thanks for the great report. I salute you from Japan for your efforts and knowledge.

    By the way, I have one problem. Japanese houses have difficulty producing loud sound, and that includes 3W amplifiers. I would like to lower the volume of FLY3 to about half.

    What modifications should I make to achieve this?

    In case you are wondering, I have enough knowledge to DIY a pedal.

    • bancika says:

      The easiest way would be to add some resistance in series with the speaker to “eat” some of the output. I would get few values and experiment – 2.2ohm to 4.7ohm, 3w or 5w resistor and wire it in series with the speaker.

  5. ck says:


    I’ve noticed that the power output in wattage is 9.75W. Does that mean that you can drive a second extension cabinet using an RJ11 splitter making it a 9W combo?

    Thank you for your reply

    • bancika says:

      what makes you think that it has that much power? It is advertised as a 3w amp.

  6. Carlo says:

    Hi, there’s another option you can look into for mini amps that sound decent. The Boss Katana mini, i’m sure you are aware of this by now. This beats the fly 3 in about every aspect and they are almost the same price range. I have both and use them for stereo setup.

    I modded my fly 3 power simply enough, I rerouted the wires for the battery compartment and hooked them into a standard 2.1mm female jack (positive on tip), then bought a 5V to 9/12V usb adaptor. Now i can use it with either a power bank brick or a phone charger. It is a bit tricky to turn on the amp though, I have to turn the On button first before plugging to the charger or power bank or it will not work. Must be an issue with the current because the usb adaptor is only rated for 1A, i think the fly uses about 1.2A that’s why they use 1.5A in the specs.
    Confuses me though because the Boss Katana mini only needs about 300mA 🤦‍♂️

  7. mickey says:

    have you tried replacing the speaker with an Eminence Alpha 3 speaker?

  8. Ed says:

    I wonder did you get around to adding the pot on delay to adjust the number of times it echoes as you mentioned should work?

  9. What size is the DC adapter fitting, to plug a power wire into it. I want to use a USB cable from a cel bank to the power adapter. I need the exact fitting size of the male output in millimeters on the back of the amp.

    • bancika says:

      Mentioned in the article – “6.5V DC and uses a non-conventional 2.5mm jack with positive tip”

  10. b02laire says:

    There actually is a small SMD fuse on the main board labeled “F1”, located a few millimeters away from the ribbon coming from the DC jack.
    Look closely has it might be hidden beneath the hot glue used to secure the ribbon

  11. dan says:

    did you attempt to bias the pt2399 chip hotter, perhaps improving the tonality. the jfet is a good reasonable mod. any room for this in the cab? lobed in half.

    • bancika says:

      hmm, not sure how biasing PT2399 hotter would improve anything, or even how to bias it hotter. It’s a digital chip.
      As for that preamp, I doubt it.

  12. Anthony Kluyskens says:

    As the driver of the blackstar is a full range driver, could it power a vintage 60’s 8 inch 16 ohm 10w speaker? Will it sound better than a dedicated guitar speaker?

    • bancika says:

      Sure, I tried Fly 3 with a 6″ and 10″ speaker and it could drive them great. Whether it would sound better or worse, it’s hard to tell, as I haven’t tried it with that particular speaker. In my cases it sounded better with bigger speakers. Fuller.

  13. zepyaf says:

    hello ! thanks for all this information about the great Blackstar !

    I am an airline pilot and travel a lot with my guitar and amp – to save room in my suitcase and avoid the batteries, i am looking for another power management solution – do you think that it is possible to supply it with power from USB ? which adapter ?
    Thanks for your help.

    best regards.

  14. joe says:

    I recently accidentally plugged a 300ma 12v adapter into my fly 3 bass and now it no longer powers on with batteries or adapter, no LED, no sound. Any ideas what I should test to fix it? Thanks!

    • J Faustus says:

      I bought a used Fly 3 from a young chap who’d repaired it from the garbage shelf at the local guitar store, where his dad works. He said (and I have not verified this) that it had broken when an incorrect adapter was used, and the returned amp was a “write-off and replace” item for the store. Blackstar didn’t want the failed units.

      He disassembled the Fly 3 initially out of general interest with no thought of repair, but spotted a tiny surface-mount fuse that had been blown, presumably by the power-adapter mixup. He repaired it, found that the amp now worked, and then sold me the Fly 3. It’s still my after hours faffing / Zoom meeting / waiting for Godot amp, sitting at the back of my desk for at least the last four years.

      That’s as much as I can tell you, in the absence of direct experience making the repair. Our host here may have photos of the internal electronics that would illustrate the (still hypothetical to me) fuse.


      • S Bell says:

        I tried this mod and ended up frying my Blackstar. Not a huge deal, I knew the risks. I’m not sure what I did, but it won’t power on now. I took it all apart since its broken anyway, and I could not locate a fuse anywhere on any of the boards. I can’t imagine why someone would make that up, but mine doesn’t seem to have one.

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    The idea behind this site is to share my experience with Do It Yourself approach to guitars, amplifiers and pedals. Whether you want to save a couple of bucks by performing a mod or upgrade yourself instead of paying a tech, or want to build your own piece of gear from scratch, I'm sure you will find something interesting here. Also, this is the home of DIY Layout Creator, a free piece of software for drawing circuit layouts and schematics, written with DIY enthusiasts in mind.