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 $/โ‚ฌ, 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 ๐Ÿ™‚ ). 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.

102 Responses to “Blackstar Fly 3 Mods”
  1. Michael says:

    Is there a extension cable (phone cord male to female) or lan cord extension I can get to spread the cab further from the amp. They only give you about 22 inches of cable lead from the cabinet ?

  2. ChetP says:

    I’m interested in doing the external speaker output mod on a used Fly 3 Bass amp I just ordered. The seller said that the power led doesn’t turn on, but the amp works fine. Should I be concerned about the led?

    I’ll get back to you with questions about the external speaker mod after I receive the amp.

  3. Andreea says:

    Hey, thanks for the tutorial! The boost is beyond my skill level but the external speaker output turned out great. I managed to sneak the jack on the side, kinda where your boost pcb is, and didn’t need to extend the yellow ground cable. Cheers!

  4. Tommy says:

    Now I’m curious whether or not the extension speakers are active. If they are, then one could use a simple old school telephone splitter jack to run two or more extensions. If they aren’t, this might be risky in terms of lowering the impedance on the amp. Also, this RJ jack seems like it might be an easy thing to maybe replace with a 1/4″ jack in order to more conveniently run other types of extension cabinets, whether they need to be passive or active. Incidentally, my Fly + extension combo is my favorite pair of computer speakers ever. I use them much more that way than for guitar, which is why I think about getting more extensions, in order to distribute the sound to other rooms.

    • bancika says:

      it’s easy enough to check. Open the extension cab and check if there are any chips inside. I suspect it has a small daughter board directly on the speaker.

  5. Tony says:


    Thanks for this detailed write-up! I’m really enjoying my Fly 3, but would love to be able to hook it up to an external cab sometimes.

    Is it possible to use an adapter of some kind with the extension cabinet output instead of doing the mod? I know it won’t defeat the internal speaker, but will it drive an external speaker? Would it be 4ohms or 8ohms or something else?



    • bancika says:

      I don’t think you can do that. Not 100% sure because I haven’t played around that part of the amp, but I think that the native fly3 extension cabinet is active, not passive. That LAN connector they use for ext speaker passes DC power as well as the line-level signal and the second channel amplification happens in the extension cabinet.
      But that also means that you can build active cabinet using any low-power power amplifier chip that can work on 6.5-9V DC and a speaker of choice.


  6. Ian says:

    Will this amp work ok if powered by a 9v adaptor instead of 6.5v? I’d like to run mine off a 12v portable battery I have and getting 12v to 9v is easier off the shelf than 12v to 6.5

    • bancika says:

      Yes, it will work fine. In reality, the DC jack is connected to the same point where the internal battery compartment is connected and 6xAA batteries output 9V DC. It might even work with 12V, but I haven’t tried it ๐Ÿ™‚

  7. David says:

    I just blew mine up by connecting a neg centre psu, so I’ve taken it to bits. Good news is the power amp still works (and a 103 extn that was plugged in). For anyone who doesn’t know, the ‘daughter board’ on the speaker is actually the power amp, there are 4 connections of which 2 are ground(connected together and to the yellow ground wire), then the signal lead and finally the +ve which takes 5v. These class D amp modules should be mounted as close to the speaker as possible to prevent badness which is why they are mounted right on the chassis as they are. If you extend to a bigger speaker and intend to use that exclusively it’s best to move the board and extend the wire. The extension cab 103 also has this board and for hackers this is brilliant as they are cheap and you’ve basically got an active speaker that will run from a beefy USB supply which are dirt cheap. My guess if you do what I did and connect the wrong polarity supply is that it only burns out the regulator chip (the lump in the middle of the Fly’s main board that uses the copper land as a heatsink) so you could try replacing that and quite likely be good to go again. B* recommend a 6.5v supply probably so that it reduces the load on the regulator as the power amps run at 5v but it seems to be connected the same as the batteries so a 9v supply would be fine imo.
    I’m quite glad I burned my fly3, I have got a bit tired of the sound, like all solid state B* amps it just sounds processed to my ear. Look at the number of chips on the circuit board and it’s not surprising it sounds like that. I’m going to try replacing the preamp circuit with a discrete FET circuit with simple tone controls as I particularly dislike the ISF nonsense and then I’ll be able to use a proper mono send stereo return effects loop before a stereo master volume pot -as I use a lot of stereo effects this will be ideal for me.

  8. Peter says:

    It looks like a fun project though. And I do have the newer Bluetooth model. Not sure if that would still be compatible or would need some revising

    • bancika says:

      I haven’t gutted the newer version, but I would assume that the guitar input section is the same or very similar.

  9. Peter G says:

    I really wanna try your booster mod, but my electrical skills are lacking. I do have a soldier tho.. The proto board picture looks confusing haha.

    • bancika says:

      If you are not conformable with electronics, maybe it’s better to use a booster pedal in the front of the amp. It’s not as convenient, but the effect will be the same and you can have it footswitchable.

  10. aptfx says:

    I’m inexperienced with this and wondered in what way the external speaker mod is different to using the headphone out to an external speaker? I used a Marshall Kilburn at the headphone out and this works to the extent that it delivers more bass and volume.

    • bancika says:

      Marshall Kilburn is a powered (active) speaker and also a “hi-fi” full spectrum speaker. Headphone out works fine in that arrangement. External speaker mod is intended for actual guitar cabinets that are passive.

  11. Bob says:

    Hi Bancika: I just downloaded and reviewed the Blackstar Fly3 PDF manual in which it is shown that a positive center pin is the polarity that the amp requires…. Your words above say a negative center pin – polarity – is required. “Runs on six 1.5V AA batteries or 9V DC adapter (not included, pretty much any adapter with negative center pin will work).” The info in the manual contradicts your statement. I wonder which power adapter polarity I should use? Will you please let me know your ideas?

  12. GnsMrk says:

    It will be safe to use the external speaker mod with a Jensen speaker (4 Ohms 25 watts) ??

  13. Retro says:

    This looks awesome, thanks for the write-up. I’d like to build the external booster, where I can get the protoboard from?

    • bancika says:

      Any perforated proto board will work. I like these 3-per-pad boards with plated holes. They are top notch quality and can make compact layouts with them. Try to search for ‘1″ Square Proto Board’, I see the same ones available on ebay at the moment.

  14. William says:

    Did the external mod this morning. Works great! Thank you for your help with this!!!


  15. William says:

    Where did you get the switching jack with the leads in the back? I can’t find one…


    • bancika says:

      Hm, what do you mean by that? It’s a standard switching jack like this, I soldered the leads on.

      • William says:

        The only “Switching” 1/4 mono jacks I can find on the internet have the lugs on the bottom not the back and would not be able to fit between the ribs where it needs to go.

        BTW thanks for your quick response. I appreciate that.

        • bancika says:

          You can easily get them, depending on where you are. One of the best ones available are switchcraft 112AX, you want type 2A that is switching, normally closed jack.

          • William says:

            I had seen them but wasn’t sure they were the right item. Thank you for clarifying. Just got them! Appreciate the help!


        • bancika says:

          I hope they fit, I don’t remember where I got mine and which brand they are ๐Ÿ™‚

          • William says:

            Got the jack. Fits fine.. So I have wired a few guitars but that’s the extent of my electronic know how. I was able to mod the Katana mini but this is a bit more involved. Any possibility of being a little more detailed in the description of what you did? Maybe more pictures of the wiring part? With the Fly, the speaker wires are both bare copper and I can’t tell from the pcb board which is + or -. This could be just my inexperience and for that I apologize but as far as I can tell you are the only one who has a tutorial out for this. No one else has done it.

            Thanks again,

        • bancika says:

          hm, did you follow the article and desolder the daughter board mounted directly on the speaker?

          • William says:

            No. I took the amp apart and looked and saw no obvious + or -. Are you saying if I go ahead and desolder the pcb board there will be an indication of + and – ? Again, I’m not really experienced with this and didn’t want to mess it up…

        • bancika says:

          It may be possible to do it without removing the daughter board, but I’m not sure. I removed it and explained it in “External Speaker Mod” section.

          • William says:

            I want to do it the same way you did. Just not clear on the procedure as explained above.. I admit this is probably my inexperience.

        • bancika says:

          I updated the article with a wiring diagram. Just desolder the daughter board from the terminals and do what’s on the diagram.

  16. Steve says:

    Hi Bancika I have no knowledge of circuits or wiring. My problem is I have had the blackstar fly for over a year now and this week the led light on the on button stopped working with the batteries but works with the adapter. I canโ€™t figure out what has caused this . I have a little soldering iron and if itโ€™s a loose wire I would be able to do a basic fix. Could you please point me to the possible cause and solution bancika as we busk on the streets with this and the batteryโ€™s are the reason I got the fly 3. Thanks Steve.

    • bancika says:

      Hm, I don’t think it’s possible to have it work with the adapter and not work with the batteries. Are the batteries fresh alkaline kind? I noticed that the light goes faint as the batteries die.

  17. Huscarl says:

    Hey, so i took my amp apart for another project i ahve since abandoned and i want to put it back together, except i cant remember where the power leads connect to. Could you point me in the right direction

    • bancika says:

      I don’t have the amp in front of me. Check my photos from the article, point D on one of the photos is the voltage supply, but after the power switch. You’ll need to trace that node and see what the power switch connects it to.

  18. Rascarcapak says:

    Hi! first thank you forw these mods.
    I would like to know if it is possible to have the fly 103 (extention cab) AND your external speaker mod plugged at the same time.
    cheers and thanks again!
    PS : please excuse my poor english

    • bancika says:

      Hi, your English is good, don’t worry ๐Ÿ™‚
      Yes, you can use the extension cab together with the external speaker. In that arrangement you’d get stereo between the external speaker and extension cab.

  19. LaFaro says:

    I have the Fly3 bass pair, with the Fly3 Guitar pair in the post. When I plug a jack into the Emulated output, the speaker cuts out. I’m thinking, if I can get both the bass speakers to work, plus send the emulated out to the Guitar pair, I can have the bass play through 4 speakers and the guitar just through 2.

    What mod would be needed to have the main speakers and the emulated(headphone) out play at the same time.

    • bancika says:

      I think you should be able to do it, the headphone jack is breaking a connection to the speaker when something is plugged in, you just need to figure out which two points are getting disconnected and bridge them permanently with a small wire jumper. You can do that by measuring resistance between each two pins on the headphone jack where it’s soldered to the PCB. First try with the jack unplugged and find pairs of pins that measure zero resistance. Then plug the jack and see which connection(s) get broken…then jumper them.

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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.