Circuit for a Blackstar Fly 3 watt amp?
- microbailey
- Breadboard Brother
I've now found time to draw the schematic for the power supply section of the Blackstar Fly3, and add a bunch of circuit analysis around it.
For those interested, my schematic is here: http://www.midboost.com/workbench/black ... -schematic
There's a part of the circuit I just can't see how it works. It's the circuit that turns on the red Power LED!! The tranny TR1 measures as an NPN (on the board that is - I haven't removed it), but biased like this (base to ground through a resistor) I can't see how the LED ever gets any current when the +5v supply is on. My feeling is it should be a PNP, but that's not what my meter is saying.
The marking on the SMD tranny SOT-23 is "1F" in case that helps anyone. I reckoned it was a BC847 as shown in my schematic.
If anyone can explain how the NPN works in this configuration I'd be interested
Next, I'm going to write up some more around the grounding scheme Blackstar used to avoid internal noise.
For those interested, my schematic is here: http://www.midboost.com/workbench/black ... -schematic
There's a part of the circuit I just can't see how it works. It's the circuit that turns on the red Power LED!! The tranny TR1 measures as an NPN (on the board that is - I haven't removed it), but biased like this (base to ground through a resistor) I can't see how the LED ever gets any current when the +5v supply is on. My feeling is it should be a PNP, but that's not what my meter is saying.
The marking on the SMD tranny SOT-23 is "1F" in case that helps anyone. I reckoned it was a BC847 as shown in my schematic.
If anyone can explain how the NPN works in this configuration I'd be interested
Next, I'm going to write up some more around the grounding scheme Blackstar used to avoid internal noise.
"There's something about a Gucci loafer kicking on a fuzz pedal" Alex Turner, Arctic Monkeys
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It looks a bit like a common-base configuration to me.
https://www.electronics-tutorials.ws/am ... ifier.html
https://www.electronics-tutorials.ws/am ... ifier.html
I only give negative feedback.
- Manfred
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You are right with your feeling, it must be a PNP transistor, I made a simulation of this circuit, it actually only works with the PNP transistor.My feeling is it should be a PNP, but that's not what my meter is saying.
My guess is a BC857 and a low current LED.
- The G
- Grease Monkey
Manfred beat me to it
Did simulations in Tina TI - apparently it does work with a PNP transistor (I assumed a 5V voltage on "LC" pin):
I had to add a 390Ω resistor to limit the LED current to around 10mA.
It kinda resembles a constant current source to me.
Did simulations in Tina TI - apparently it does work with a PNP transistor (I assumed a 5V voltage on "LC" pin):
I had to add a 390Ω resistor to limit the LED current to around 10mA.
It kinda resembles a constant current source to me.
- Manfred
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In the post of the link from above the following is written:
I had also tried this with the LC on ground point to switch off and it worked.
The LED obviously always lights up with power on and no switchable.In any case TR1 must turn on when the +5V rail is up (I mean switched on) and provide a steady current to light the red LED . Blackstar have added a testpoint on the board here, labelled "LC" on the PCB legend. I'm not really sure what it's for since the LED doesn't need any special manufacturing test - it will be on when the power is applied. It either works or doesn't. Any suggestions on this part of the circuit are welcome!
I had also tried this with the LC on ground point to switch off and it worked.
- microbailey
- Breadboard Brother
Thanks guys and thanks The G for the SPICE sims. I had initially thought 'common base amplifier', but couldn't see any way the NPN could be biased on without some extra resistor from base to a positive voltage (with respect to emitter). I've checked and checked again and I can't see any such extra resistor. I agree it should be a current source, to ensure the LED gets the correct current.
So I'm starting to think I need a new multimeter
The second sim from The G gives numbers very close to what I had measured (before I took the amp apart) which was 1.6 volts across the LED when it was lit. I never checked the voltage on the "LC" testpoint, but I can confirm it is not wired to anything off-board, just the collector of TR1. I think I need to re-check the value of that 1k5 resistor on the collector.
Perhaps the "LC" pad is a way for Blackstar to check the factory current through the 1k5 and so the current through the LED?
I'll be putting the amp back together soon (now that I've traced the hell out of it) so I'll be able to make some more voltage measurements and get a better idea of what's going on.
So I'm starting to think I need a new multimeter
The second sim from The G gives numbers very close to what I had measured (before I took the amp apart) which was 1.6 volts across the LED when it was lit. I never checked the voltage on the "LC" testpoint, but I can confirm it is not wired to anything off-board, just the collector of TR1. I think I need to re-check the value of that 1k5 resistor on the collector.
Perhaps the "LC" pad is a way for Blackstar to check the factory current through the 1k5 and so the current through the LED?
I'll be putting the amp back together soon (now that I've traced the hell out of it) so I'll be able to make some more voltage measurements and get a better idea of what's going on.
"There's something about a Gucci loafer kicking on a fuzz pedal" Alex Turner, Arctic Monkeys
- microbailey
- Breadboard Brother
As yoon_seri and others had asked earlier in this thread about the ground connections in the Blackstar Fly 3, I have put a section on the grounding, with diagrams, here:
http://www.midboost.com/workbench/black ... t-matters
which explains the reasons why the grounds are connected as they are (in a star).
Also because I got some questions about whether pedal power supplies can be used with the Fly I've added a small FAQ (very small actually, 2 questions ) on it here too
http://www.midboost.com/workbench/black ... upply-faq
Hope this all helps someone.
http://www.midboost.com/workbench/black ... t-matters
which explains the reasons why the grounds are connected as they are (in a star).
Also because I got some questions about whether pedal power supplies can be used with the Fly I've added a small FAQ (very small actually, 2 questions ) on it here too
http://www.midboost.com/workbench/black ... upply-faq
Hope this all helps someone.
"There's something about a Gucci loafer kicking on a fuzz pedal" Alex Turner, Arctic Monkeys
- microbailey
- Breadboard Brother
For reference I just added the Top Deck board (upper board) schematic on: http://www.midboost.com/workbench/black ... deck-board
Not that there's much on it
I've also added some discussion of the Blackstar Fly3 speaker design were I worked out (approximately) the bass reflex resonance.
Not that there's much on it
I've also added some discussion of the Blackstar Fly3 speaker design were I worked out (approximately) the bass reflex resonance.
"There's something about a Gucci loafer kicking on a fuzz pedal" Alex Turner, Arctic Monkeys
- microbailey
- Breadboard Brother
I've now finished tracing the Blackstar Fly3 practice amp. Was a bit more to it than I expected when I started
All the schematics are up on my website (see links below).
Here is a block diagram I drew up of the amp Probably more useful for everyone, here is an index of links to each schematic in some kind of sensible order (it is not in sensible order on my website )
Main PCB
Input stage. pre-amp, and clipping: https://static.ucraft.app/fs/ucraft/use ... 1609971056
EQ and Blackstar "ISF" tone-stack: https://static.ucraft.app/fs/ucraft/use ... 1604257987
Digital "Tape Delay": https://static.ucraft.app/fs/ucraft/use ... 1598721766
Mixer, headphone amp, and source switching: https://static.ucraft.app/fs/ucraft/use ... 1597009236
Power supply and filtering: https://static.ucraft.app/fs/ucraft/use ... 1606946210
Small PCB mounted on speaker
Power amp: https://static.ucraft.app/fs/ucraft/use ... 1594590407
The extension cab (for stereo) is just the same power amp board on a speaker in a box.
Discussion of bass ported speaker cabinet: http://www.midboost.com/workbench/black ... ase-design
Other PCBs in the amp
Pot and switch board: https://static.ucraft.app/fs/ucraft/use ... 1608304579
Extension cab connector / battery board: https://static.ucraft.app/fs/ucraft/use ... 1596058119
The web pages have lots more photos, SPICE sims, circuit analysis, and other info. See http://www.midboost.com/workbench/blackstar-fly-3 and http://www.midboost.com/workbench/blackstar-fly-3-pt2
Hope that all helps!!
And thanks for help with parts of the circuit on this thread
All the schematics are up on my website (see links below).
Here is a block diagram I drew up of the amp Probably more useful for everyone, here is an index of links to each schematic in some kind of sensible order (it is not in sensible order on my website )
Main PCB
Input stage. pre-amp, and clipping: https://static.ucraft.app/fs/ucraft/use ... 1609971056
EQ and Blackstar "ISF" tone-stack: https://static.ucraft.app/fs/ucraft/use ... 1604257987
Digital "Tape Delay": https://static.ucraft.app/fs/ucraft/use ... 1598721766
Mixer, headphone amp, and source switching: https://static.ucraft.app/fs/ucraft/use ... 1597009236
Power supply and filtering: https://static.ucraft.app/fs/ucraft/use ... 1606946210
Small PCB mounted on speaker
Power amp: https://static.ucraft.app/fs/ucraft/use ... 1594590407
The extension cab (for stereo) is just the same power amp board on a speaker in a box.
Discussion of bass ported speaker cabinet: http://www.midboost.com/workbench/black ... ase-design
Other PCBs in the amp
Pot and switch board: https://static.ucraft.app/fs/ucraft/use ... 1608304579
Extension cab connector / battery board: https://static.ucraft.app/fs/ucraft/use ... 1596058119
The web pages have lots more photos, SPICE sims, circuit analysis, and other info. See http://www.midboost.com/workbench/blackstar-fly-3 and http://www.midboost.com/workbench/blackstar-fly-3-pt2
Hope that all helps!!
And thanks for help with parts of the circuit on this thread
Last edited by microbailey on 06 Jan 2021, 22:20, edited 1 time in total.
"There's something about a Gucci loafer kicking on a fuzz pedal" Alex Turner, Arctic Monkeys
- bmxguitarsbmx
- Cap Cooler
Once again, excellent work Microbailey. Very interesting.
On this op-amp in the preamp: Is this a TLV272? Or Possibly a TLC2272? I haven't been able to find a TLV2272, as notated on the scheme. The TLV272 does seem to fit the bill. Rail-to-rail mos op-amp. I was impressed with how good this stage sounds. It made me rethink low voltage stomp boxes. It even seems to clean up with volume roll-off.
On this op-amp in the preamp: Is this a TLV272? Or Possibly a TLC2272? I haven't been able to find a TLV2272, as notated on the scheme. The TLV272 does seem to fit the bill. Rail-to-rail mos op-amp. I was impressed with how good this stage sounds. It made me rethink low voltage stomp boxes. It even seems to clean up with volume roll-off.
- microbailey
- Breadboard Brother
Hi bmx, glad this trace is helping you.bmxguitarsbmx wrote: ↑06 Jan 2021, 01:44 Once again, excellent work Microbailey. Very interesting.
On this op-amp in the preamp: Is this a TLV272? Or Possibly a TLC2272? I haven't been able to find a TLV2272, as notated on the scheme. The TLV272 does seem to fit the bill. Rail-to-rail mos op-amp. I was impressed with how good this stage sounds. It made me rethink low voltage stomp boxes. It even seems to clean up with volume roll-off.
For the preamp IC1 - here is a close up photo of the actual markings on the package As you can see it is marked 2272C and its made by TI.
When I searched the TI website I found what you found - TLC2272. What has happened is when I drew up the schematic in KiCad the standard op-amp library in KiCad came up with TLV2272 so I just used it.
Thanks for spotting this!
I've changed the schematic on my website to read TLC2272, and I've updated the link in my earlier post to point to the new schematic.
If you see anything else which looks wrong let me know
"There's something about a Gucci loafer kicking on a fuzz pedal" Alex Turner, Arctic Monkeys
- bmxguitarsbmx
- Cap Cooler
Thank you microbailey! I really appreciate you verifying that. So, that is interesting. I have a whole bunch of TLC2272. I shot them out with some buddies in the Friedman BE-OD circuit and in blind test, the TLC 2272 sounded the least good. (The stock tl072 sounded best). I really wanted to like the TLC2272 because it is "Mos" you know? I will try this circuit at 5V. That may be what these rail-to-rails prefer to sound good. Possibly.
- microbailey
- Breadboard Brother
Interesting. Actually the TL072s are pretty solid op-amps even if not the quietest in input stage applications. I used to use them a lot in pedal designs back in the '80s.bmxguitarsbmx wrote: ↑07 Jan 2021, 22:05 Thank you microbailey! I really appreciate you verifying that. So, that is interesting. I have a whole bunch of TLC2272. I shot them out with some buddies in the Friedman BE-OD circuit and in blind test, the TLC 2272 sounded the least good. (The stock tl072 sounded best). I really wanted to like the TLC2272 because it is "Mos" you know? I will try this circuit at 5V. That may be what these rail-to-rails prefer to sound good. Possibly.
Let us know if you hear a difference with the 2272s running at 5v - I'd be interested.
"There's something about a Gucci loafer kicking on a fuzz pedal" Alex Turner, Arctic Monkeys
- The G
- Grease Monkey
Nice summary about op amps from @teemuk himself:
teemuk wrote:
Re: Different opamps in the OCD (08.02.2018 11:03, on DIYStompboxes)
It may seem obsessive but the OpAmps are not all equal and do behave differently in certain conditions. Which can explain why they sometimes introduce different "tones".
Besides few details (of which most matter very little in "LoFi" -effect design) OpAmp circuits operate pretty much "uniformingly" as long as their feedback loop remains operational (no pun intented). This is pretty much the sole purpose of an operational amplifier to begin with. This all, of course, changes if the OpAmp is overdriven outside its linear range. This is the region where circuit architecture differences of the OpAmps begin to display themselves.
- Different OpAmps have different limits in how close to supply rail voltage(s) their output signal can swing. It is common for these limits to have some degree of "asymmetry". e.g. positive half wave swings within 1V and the negative swings only within 2V.
- Some OpAmps "latch to supply rail" when overdriven to clipping. The poor recovery characteristic introduces much "nastier" harmonc content than plain brickwall clipping,
- Some OpAmps reverse phase of conduction when their common mode voltage is exceeded. This generates sort of an "octave effect"
- Some OpAmps may introduce "ringing" oscillation bursts at sharpest waveform corners
- Low slew rate can prevent the gneration of most obtrusive very high order harmonics
- Noise ratio is usually an issue in "high-gain" -design
- Current limiting circuits may begin to operate if the opamp's load becomes too low in impedance.
- "Rail-to-rail" -type opamps are - for obvious reasons - designed to have decent overdrive characteristics (they pretty much just brickwall clip without any "side-effects") but their low limits of operating voltage can pose practical designing challenges.
Ok, where do we encounter overdriven opamps...
- Stages configured for sole OpAmp overdrive should be pretty self-explanatory.
- "Shunt clipping" circuits driven by an opamp gain stage. (Isn't OCD in this category?) These can often be deceiving. The opamp stage WILL overdrive with high-enough input signal or gain levels (though typically this happens well above clipping threshold of the shunt circuit). So, with "high gain" settings dialed in overdrive of the opamp stage is very much a possibity. The shunt clipping circuit will limit signal peaks exceeding its clipping threshold as usual, but it can not prevent any of the "ill-effects" it's driver stage introduces when overdriven. These may contribute to total distortion in certaim conditions.
- Feedback loop clipping in non-inverting configuration. If these circuits are overdriven excessively the opamp stage begins to clip to rails.
Could be some other examples too.
- bmxguitarsbmx
- Cap Cooler
The PAM8304 can drive a 3 ohm speaker. AFAIK, the internal speaker is 4 ohms, so you cannot drive an additional speaker in parallel without adding another power board (available very cheaply on Ebay).
Keep in mind that this little amp is compensated for this speaker. Specifically it cuts out a ton of top end that would sound buzzy otherwise. So, if you wanted to instal a switched jack to drive a 4x12, that compensation would cause your tone to be very dark. You could use a switched jack to drive various full range speakers- which might yield some great results or just be a fun experiment.
- microbailey
- Breadboard Brother
The amp circuit board is essential for the speaker - it contains the power amp.
You could remove the existing speaker and re-wire another in its place - but note bmxguitars' comments.
The whole pre-amp is EQ'd for the speaker + enclosure the Fly3 is housed in.
I think I saw a video on YouTube where someone had run a 1x12 in an external cab off the Fly3 speaker leads.
I've not tried an external speaker but I'd have thought a long run of cable (to an external speaker) might cause interference to other devices as this thing radiates a high frequency.
"There's something about a Gucci loafer kicking on a fuzz pedal" Alex Turner, Arctic Monkeys