Hello friends...
Here in Brazil we have a very active diy audio community and due to research I am bringing a new circuit for your enjoyment.
It is a simple audio amplifier, polarized with diodes, with an option for ground suspension of the input signal, 100W, full CCS and differential current mirror
Around here in Brazil we have a lot of bad circuits that are shared on the web that leave DIY people very frustrated when they set up and it doesn't work, so whenever I can I share new tried and tested ideas.
Here are some data measured on a bench
Power: 100W @ 4 Ohm
Sensitivity: 380mV
Input Impedance: 47kOhm
Frequency Response: 10Hz~191KHz @ 3dB
Damping Factor: 995
Simulated THD: 0.02% @ 1KHz (real life measurement will happen soon)
Schematic:
PCB:
Prototype PCB:
SCHEMATIC UPDATED: 08/17/21
🙂 I am a happy DipTrace user🙂
Here in Brazil we have a very active diy audio community and due to research I am bringing a new circuit for your enjoyment.
It is a simple audio amplifier, polarized with diodes, with an option for ground suspension of the input signal, 100W, full CCS and differential current mirror
Around here in Brazil we have a lot of bad circuits that are shared on the web that leave DIY people very frustrated when they set up and it doesn't work, so whenever I can I share new tried and tested ideas.
Here are some data measured on a bench
Power: 100W @ 4 Ohm
Sensitivity: 380mV
Input Impedance: 47kOhm
Frequency Response: 10Hz~191KHz @ 3dB
Damping Factor: 995
Simulated THD: 0.02% @ 1KHz (real life measurement will happen soon)
Schematic:
PCB:
Prototype PCB:
SCHEMATIC UPDATED: 08/17/21
🙂 I am a happy DipTrace user🙂
Last edited:
I mounted and calibrated it this weekend. The sound is very nice, well distributed in bass, mid and treble. The current from the VAS is enough for a good performance and allows the transistors to run very cold.
It's worth built and listening to.
See the amplifier first run video:
HM100X FIRST RUN - YouTube
It's worth built and listening to.
See the amplifier first run video:
HM100X FIRST RUN - YouTube
Looks fun and straight to the point.
What diodes are you using for thermal tracking D6 and D7 ?
Where to you source 2SA1837 and 2SC4793 driver transistors?
.02 % sounds about right
If the amp still remains stable you could lower C4 to 47p to 62p
and likely improve THD
Also MJE340 is a incredible slow transistor for Vas
Most datasheets dont even list the Ft which is around 16 Mhz
Try using a Onsemi / Fairchild
KSC3503 for your Vas Transistor
With a Ft of around 150 Mhz
it should offer a big improvement in simulated THD
Otherwise I tend to enjoy simple fun designs such as this
C5 , C7 and C9 are shown as 100pF on the drawing
I think you might mean 100 N
What diodes are you using for thermal tracking D6 and D7 ?
Where to you source 2SA1837 and 2SC4793 driver transistors?
.02 % sounds about right
If the amp still remains stable you could lower C4 to 47p to 62p
and likely improve THD
Also MJE340 is a incredible slow transistor for Vas
Most datasheets dont even list the Ft which is around 16 Mhz
Try using a Onsemi / Fairchild
KSC3503 for your Vas Transistor
With a Ft of around 150 Mhz
it should offer a big improvement in simulated THD
Otherwise I tend to enjoy simple fun designs such as this
C5 , C7 and C9 are shown as 100pF on the drawing
I think you might mean 100 N
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WhiteDragon Questions
Dear WhiteDragon
Diodes used for thermal tracking are 1N4148.
In Brazil, transistors 2SA1837 and 2SC4793 are very popular even among large national manufacturers, so they are easy to find here. I don't know if where you live you find it easily.
Currently, on the Miller capacitor I'm using 47pF and I ended up forgetting to upgrade the schematic.
Still about transistors, the MJE340 is very easy to find here but the KSC3503 I can't find in any national store, just importing from Mouser or similar.
C5, C7 and C9 are actually 100nF. Sorry. I will update.🙂
Dear WhiteDragon
Diodes used for thermal tracking are 1N4148.
In Brazil, transistors 2SA1837 and 2SC4793 are very popular even among large national manufacturers, so they are easy to find here. I don't know if where you live you find it easily.
Currently, on the Miller capacitor I'm using 47pF and I ended up forgetting to upgrade the schematic.
Still about transistors, the MJE340 is very easy to find here but the KSC3503 I can't find in any national store, just importing from Mouser or similar.
C5, C7 and C9 are actually 100nF. Sorry. I will update.🙂
Dear friends
I make available to you the PDF with the photoliths for making the PCB of this project.
Enjoy! 🙂
THERMAL METHOD:
FOTOLITO.pdf - Google Drive
PHOTOGRAPHIC METHOD:
HM_FOTOLITO_FOTO.pdf - Google Drive
I make available to you the PDF with the photoliths for making the PCB of this project.
Enjoy! 🙂
THERMAL METHOD:
FOTOLITO.pdf - Google Drive
PHOTOGRAPHIC METHOD:
HM_FOTOLITO_FOTO.pdf - Google Drive
Last edited:
Dear friends
The amplifier circuit has been updated to the new revision with important fixes and changes for better stability. Follow the new circuit for everyone to enjoy.
I make update available to you the PDF with the photoliths for making the PCB of this project.
DOWNLOAD FILES
The amplifier circuit has been updated to the new revision with important fixes and changes for better stability. Follow the new circuit for everyone to enjoy.
I make update available to you the PDF with the photoliths for making the PCB of this project.
DOWNLOAD FILES
Sorry for my ignorance; what sets the low end -3dB frequency? Is it C3 and if so could it be increased?
Hello Jhon. The circuit as a whole generates this limit, but in general by lowering the value of the Miller capacitor you can go further in the frequency response, but it may fluctuate as well. The Zobel Filter also ends up limiting, having to recalculate to go much further.
I meant the 10Hz -3dB point. Because in any audio system there are several cascaded stages, e.g. source, preamp, power amp as a minimum, I like to see the -3dB point at 1 or 2 Hz for each stage.
I believe I have misunderstood what you mean. The frequency response is between 10Hz and 191KHz at -3dB and at these extremes the resulting power is half of the total power or -3dB
Without going into complicated calculations, in all simplicity
gain of the amplifier is set by R4 / R5
and any AC decoupling capacitor involved use simple RC 1 pole filter equation
R4/C3 and R2/C2
C3 100u / R4 1K form single pole high pass filter fc= 1/(2πRC)
= 1.592 Hz
Amplifier input is AC coupled with C2
C2 4.7u / R2 47k also form high pass filter fc= 1/(2πRC)
= .720 Hz
RC filter do not only restrict the bandwidth; topology, operation points and component choices also play a part.
The shunt cap, 100uF in your amp, also plays a big part in the low frequency gain. If you increase it to 1000uF you would notice the low frequency point will drop quite a bit.
The shunt cap, 100uF in your amp, also plays a big part in the low frequency gain. If you increase it to 1000uF you would notice the low frequency point will drop quite a bit.
What semis are they really ?
2SC4793/2SA1837 driver transistors are long obsolete now. What you fitted to your HX100 build are most likely Chinese copies of these but there is no indication of their actual specs or other datasheet features that should be available to a designer. It's doubtful that they will perform anything like the originals but if the design is adapted to those particular semis, it should work well enough. Unfortunately, that doesn't make them interchangeable with original Toshiba semis, as I found when I replaced a pair in friend's original Japanese amplifier and it went berserk with oscillation and overheating. I suspect the same goes for other semis in the kit but I guess its not a problem for a design that's adapted to suit the specific copies. The remaining problems are; what spec. are the copies anyway? Are all parts marked with with that part number all the same spec? What must I use for replacements? Why can't I buy these from bona fide parts distributors and so on?
In any case it's important to know you are working with parts that have credible, actual specs, particularly now that fake/unspecified copy semis are everywhere and no one knows for sure what they are buying from the local cheapo parts suppliers or the online generic parts sites. I don't need to add that parts that look the same don't necessarily work the same and no one wants to be disappointed that the amp they build from the schematic doesn't work like the designer or kitseller claims.
2SC4793/2SA1837 driver transistors are long obsolete now. What you fitted to your HX100 build are most likely Chinese copies of these but there is no indication of their actual specs or other datasheet features that should be available to a designer. It's doubtful that they will perform anything like the originals but if the design is adapted to those particular semis, it should work well enough. Unfortunately, that doesn't make them interchangeable with original Toshiba semis, as I found when I replaced a pair in friend's original Japanese amplifier and it went berserk with oscillation and overheating. I suspect the same goes for other semis in the kit but I guess its not a problem for a design that's adapted to suit the specific copies. The remaining problems are; what spec. are the copies anyway? Are all parts marked with with that part number all the same spec? What must I use for replacements? Why can't I buy these from bona fide parts distributors and so on?
In any case it's important to know you are working with parts that have credible, actual specs, particularly now that fake/unspecified copy semis are everywhere and no one knows for sure what they are buying from the local cheapo parts suppliers or the online generic parts sites. I don't need to add that parts that look the same don't necessarily work the same and no one wants to be disappointed that the amp they build from the schematic doesn't work like the designer or kitseller claims.
In Brazil these transistors (2SC4793/2SA1837) are very, very common. Most likely, as Ian Finch said, they are Chinese semiconductors clones of the originals. The amplifier was completely developed to use the BD139/140 or 2SC2690A/2SA1220A transistors but as the BD's are one of the most counterfeit transistors that we find in Brazil and the C2690a and its pair A1220A are not so much easier to find, I recommend the C4793 and A1837 , and these will need to be mounted inverted because they are pinned upside down. It's complicated, Brazil is flooded with low-quality Chinese junk and so we do what we can.
UPDATED SCHEMATIC FROM HX100 REV. 3.0
Q8 - 2SC2690A / BD139 / 2SC4793 > (INVERT)
Q9 - 2SA1220A / BD140 / 2SA1837 > (INVERT)
Hello There I Have Seen All Of Your Shematics You have Did A Great Job I Mostly Like These Type of Amplifiers Simple And Powerful I Have Added It to My current Project And Will Make Amplifier By using it Hope Its Performance Will Be Good..