Replacements for audio path through hole transistors are getting hard to find:
The KSA992 and KSC1845 transistors are common replacements for many small signal BJT through hole transistors where low noise and high gain are more important than medium or high current. For super-low signals (think MC cartridges), the ZTX951/851 is even lower noise. We use these in hundreds of applications in preamp, amplifier and other signal path applications.
Then there are even harder-to-find devices like the dual transistor 2sa798. Many have built their own replacements by mounting two devices (e.g. KSA1845) together and installing that assembly in place of the 2sa798.
But now we're running out of the replacement through hole devices, so this thread will share some pointers to solutions.
Using SMD or surface mount versions as replacements for through hole transistors
When you can't find these through hole devices (i.e. TO-92) and you get desperate, one option would be to use the surface mount, SMD or SMT versions (e.g. SOT-23, SOT-323, etc.) of the exact same transistor.
You'd need some kind of small adapter board, one that you solder the SMD device to and which breaks out the pins into PCB traces... that you then solder wires to in order to create the same pins or legs of the original through hole device.
How to mount a SMD device on one of these tiny adapter boards is covered in a different thread: https://audiokarma.org/forums/index...apters-for-through-hole-replacements.1079170/
If you need help designing or building an adapter, read this post by @Hipocrates and the help being offered. https://audiokarma.org/forums/index...-bjt-transistors.1067614/page-3#post-17462253
Here are the SMD versions or equivalents of the popular KSA992/KSC1845 and BC549/BC550/BC559/BC560 devices (and a few similar):
low noise audio amplifier BJT with in SOT-323 or SOT-23 plastic package:
Threads with a similar idea or method (i.e. using SMD transistors in place of through hole transistors):
SMD-based PCB boards with 2SA798 and similar:
@redk9258 and @Warren-Oates have shared that we have AK members contributing to, designing, building and offering PCB boards and fully assembled replacements for original devices like 2sa798 and 2sc992/ksa992 here (in Bartertown Parts forum) and places like eBay. Read further below for details.
Other dual transistor SMD replacements:
Other SMD replacements for through hole transistors:
While we are here, we should also recommend an SMD equivalent for the 2SC945, and for the 2SA733. An excellent match for the 2SC945 is the Isahaya 2SC5814 (which also features low CE-saturation voltage, like the 2SC945. Another one that may be more available is the ROHM 2SC2412 and 2SC4081.
For the highest gain 2SA733K I would go with the ROHM 2SA1576A rank S if possible. This is a really nice SMD part.
FET SMD replacements for through hole FETs:
Adapter boards and such for using SMD transistors in place of through hole THT transistors:
The KSA992 and KSC1845 transistors are common replacements for many small signal BJT through hole transistors where low noise and high gain are more important than medium or high current. For super-low signals (think MC cartridges), the ZTX951/851 is even lower noise. We use these in hundreds of applications in preamp, amplifier and other signal path applications.
Note: we have a list of modern, mostly available low noise transistors you may find suitable sometimes https://www.audiokarma.org/forums/index.php?threads/low-noise-small-signal-transistors.815432/
Then there are even harder-to-find devices like the dual transistor 2sa798. Many have built their own replacements by mounting two devices (e.g. KSA1845) together and installing that assembly in place of the 2sa798.
But now we're running out of the replacement through hole devices, so this thread will share some pointers to solutions.
Using SMD or surface mount versions as replacements for through hole transistors
When you can't find these through hole devices (i.e. TO-92) and you get desperate, one option would be to use the surface mount, SMD or SMT versions (e.g. SOT-23, SOT-323, etc.) of the exact same transistor.
TO-92 below
SOT-23 below
You'd need some kind of small adapter board, one that you solder the SMD device to and which breaks out the pins into PCB traces... that you then solder wires to in order to create the same pins or legs of the original through hole device.
SMD to through hole PCB adapter board below
SMD transistor mounted on a TO-92 (kinda) PCB adapter board below
How to mount a SMD device on one of these tiny adapter boards is covered in a different thread: https://audiokarma.org/forums/index...apters-for-through-hole-replacements.1079170/
If you need help designing or building an adapter, read this post by @Hipocrates and the help being offered. https://audiokarma.org/forums/index...-bjt-transistors.1067614/page-3#post-17462253
Here are the SMD versions or equivalents of the popular KSA992/KSC1845 and BC549/BC550/BC559/BC560 devices (and a few similar):
low noise audio amplifier BJT with in SOT-323 or SOT-23 plastic package:
2sa992/ksa992 2sc1845/ksc1845 equivalents:
FJV992 PNP & FJV1845 NPN
120v/120v/5v 50mA 300mW 50-110MHz
hFE codes P=200-400 F=300-600 E=400-800 U=600-1200
BEC pinout
bc560/bc559 bc550/bc549 equivalents:
BC859W PNP & BC849W NPN 30v/30v/5v
BC850W PNP & BC860W NPN 50v/45v/5v (higher voltage version)
100mA/200mA 200mW 100MHz NF=4dB
hFE codes W=220-800 BW=220-475 CW=420-800 (e.g. BC859W vs BC859CW vs BC859BW)
BEC pinout
BC859(A,B,C) PNP & BC849(A,B,C) NPN 30v/30v/5v
BC850(A,B,C) PNP & BC860(A,B,C) NPN 50v/45v/5v (higher voltage version)
100mA/200mA 100mW/200mW 100-300MHz NF=4dB
hFE codes A=110-220 B=200-450 C=420-800 (e.g. BC850A vs BC850C vs BC850B)
BEC pinout
ztx851/ztx951 equivalents:
dzt851/dzt951 (obsolete) so use ZXTN2010G/ZXTP2012G (validated by simulation and direct substitution in a simple design. Indeed, they are slightly quieter. @wyn palmer )
more low noise BJT audio small signal transistors in SMD packages:
2sa1163 PNP & 2sc2713 NPN 120v/120v/5v
100mA 150-200mW 100MHz NF=1dB
hFE codes GR=200-400 BL=350-700
BEC pinout
Threads with a similar idea or method (i.e. using SMD transistors in place of through hole transistors):
SMD-based PCB boards with 2SA798 and similar:
@redk9258 and @Warren-Oates have shared that we have AK members contributing to, designing, building and offering PCB boards and fully assembled replacements for original devices like 2sa798 and 2sc992/ksa992 here (in Bartertown Parts forum) and places like eBay. Read further below for details.
2SA798 dual transistor SMD replacement below
- 2SA798 --> Toshiba HN4A06J(TE85L,F)
- 2SA798 --> 2SA1873 on a SOT23 breakout board
- Gerber files for the 2SA798 adapter board and photos in use here: https://audiokarma.org/forums/index...-bjt-transistors.1067614/page-4#post-17547231
Other dual transistor SMD replacements:
- 2Sc1583 --> HN4C06J-BL(TE85L,F (slightly lower max dissipation)
Other SMD replacements for through hole transistors:
Through hole --> SMD
- 2SC1815-BL --> Toshiba 2SC4116-BL
- 2SC2878 --> 2SC3326-B,LF
Complementary (NPN + PNP) pairs
- 2SC2458/2SA1048 --> 2SC4116 in rank GR and complementary part 2SA1586 (hfe200-400)
- 2SC1815/2SA1015 --> 2SC4116 in rank GR and complementary part 2SA1586 (hfe200-400)
- KTC3199/KTA1267 --> 2SC4116 in rank GR and complementary part 2SA1586 (hfe200-400)
- KTC3198/KTA1266 --> 2SC4116 in rank GR and complementary part 2SA1586 (hfe200-400)
- 2sa992/ksa992 2sc1845/ksc1845 --> FJV992/FJV1845
For the highest gain 2SA733K I would go with the ROHM 2SA1576A rank S if possible. This is a really nice SMD part.
FET SMD replacements for through hole FETs:
- 2SK100 --> JFE2140 (using custom, tiny PCB by @Nashou66 )
- 2SK184 J-Fet --> 2SK209 (same die in a TO-236 package) but 2SK209 only rated at 150mW compared to 200mW for the 2SK184
- 2SK30A low noise JFET --> 2SK118 --> 2SK208 --> 2SK879 (last two still in production)
Adapter boards and such for using SMD transistors in place of through hole THT transistors:
- SOT-23 breakout
- SOT89/223 breakout
- 2.54mm right angle connector (these work great on newer equipment with 2.54mm pcb holes - like Denon/Onkyo)
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