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Parts List

IDQuantityPart nameSource (+ part number)
Transistors
Q1 2 2n5486 or BF245c or J112
please note the reversed pinout of BF245
mouser.com 512-2N5486
digikey.com 2N5486OS-ND
Allied Electronics 568-1097
Q3, Q5, Q762n5088 or BC550c recommended
(alt.: BC337c, 2n3904)
please note the reversed pinout of BC***
mouser.com 512-2N5088_J61Z
mouser.com 512-2N5088D81Z
mouser.com 512-2N5088TA
mouser.com 512-2N5088TAR
mouser.com 512-2N5088TFR
digikey.com 2N5088BU
Allied Electronics 568-0370
Q2, Q4, Q662n5087 or BC560c recommended
(alt.: BC327c, 2n3906)
please note the reversed pinout of BC***
mouser.com 512-2N5087_J18Z
digikey.com 2N5087
Allied Electronics 263-0462
Q8a, Q8b 4 MJE243 or 2sc3422y or BD137-16 recommended digikey.com MJE243OS-ND
digikey.com BD137OS
mouser.com 512-BD13716STU
newark.com 07F8371
Allied Electronics 568-4030 or 568-0339
Q9a, Q9b 4 MJE253 or 2sa1359y or BD138-16 recommended digikey.com MJE253OS-ND
digikey.com BD138OS
mouser.com 512-BD13816S
newark.com 07F8374
Allied Electronics 568-7858 or 568-0502
Resistors
R8a, R8b, R9a, R9b8 Metal film or metal oxide or carbon resistor
1W or 2W, 1% or 5%
2R2 ... 3R3 ... 4R7
mouser.com 282-2.2 or 282-3.3 or 282-4.7
mouser.com 594-5073NW2R200J
mouser.com 594-5073NW3R300J
mouser.com 594-5073NW4R700J
digikey.com 2.2W-1 or 3.3W-1 or 4.7W-1
Allied Electronics 648-0041 or 648-0043
please note note-4 (resistor quantities)
R12 SMD metal film resistor
1206 package, 1%, 1/4W or 1/8W
1K
mouser.com 71-CRCW1206-1.0K
digikey.com 311-1.00KFCT-ND
segor.de 1k0-1206-1%
Allied Electronics 895-1464
R2, R3, R4, R58 SMD metal film resistor
1206 package, 1%, 1/4W or 1/8W
220R
mouser.com 71-CRCW1206-220
digikey.com RHM220FCT-ND
segor.de 220R-1206-1%
Allied Electronics 895-1493
R6, R74 SMD metal film resistor
1206 package, 1%, 1/4W or 1/8W
10R
mouser.com 71-CRCW1206-10
digikey.com RHM10FCT-ND
segor.de 10R-1206-5%
Allied Electronics 895-1431
Misc
P12cermet trimmer, 2k, 1/4" (6mm), 74W series
top adjustment, 12 or 15 turn
mouser.com 652-3266W-1-202 (Bourns)
mouser.com 72-T63YB-2k (Vishay)
digikey.com 3266W-202-ND (Bourns)
rs-components.com 183-3053 (Spectrol)
rs-components.com 187-208 (Bourns)
rapidelectronics.co.uk 68-1108 (Murata)
conrad.de 42 39 63 (Vishay/Spectrol)
Allied Electronics 970-0092 (Spectrol)
in, out, V+, V-1 breakaway strip pins
conn header straight solder tail .100"
pins 0.65mm or 0.75mm
8 pins from 1 strip needed
(please note: assembly - alternate pins)
mouser.com 575-113120 (Mill-Max SIP strip tin plated)
mouser.com 575-010064 (SIP strip gold plated)
digikey.com ED7220-ND
segor.de SILST32
reichelt.de AW 122/20
Allied Electronics 900-6045 (Mill-Max SIP strip)
bias testpoints1 breakaway strip pins, 6 pins from 1 strip needed mouser.com 575-193164 or 575-113120
digikey.com ED7020-ND or ED7420-ND
Allied Electronics 900-6045
PCB1 printed circuit board group buy at HeadWize.com
more vendors:

Note 1: output resistors

  • rated wattage: at least 1W, 2W are the largest that fit the pcb
    lower wattage ratings (0.25W / 0.5W) may work, too, but the resistors can become fuses, particulary when the output gets shorted.
  • resistance: the lower the resistance the lower the distortion, down to the point where the buffer becomes instable and starts to oscillate. Once the buffer is instable adding psu bypass caps won't help, you'll have to desolder the resistors and replace them with resistors of higher resistance (with the risk of damaging the board while doing that). Don't go for the edge with 2.2Ω resistors, rather pick a higher value like 3.3Ω, especially when using high bandwith output transistors.

Note 2: output transistors

NPN PNP fT
[MHz]
IC
[A]
UCE
[V]
description
MJE243 MJE253 40 4.0 100 well balanced, neutral to slightly warm sound. very stable due to moderate bandwidth.
default recommendation.
BD 135 -16 BD 136 -16 190 1.5 45 warm sounding, rich to tubby signature, little lack of detail, recessed highs. cheap and easy to source (at least in Europe).
BD 137 -16 BD 138 -16 190 1.5 60 neutral to warm sound, strong bass, yet detailed. cheap and easy to source (at least in Europe).
default recommendation.
BD 139 -16 BD 140 -16 190 1.5 80 slim sound, a little on the bright side. cheap and easy to source (at least in Europe).
BD 787 BD 788 50 4.0 60 not tested yet
2SC 3419 y 2SA 1356 y 100 0.8 40 strong bass, warm to dark sound. not that bright and rough highs like 2SC3421/2SA1359
2SC 3421 y 2SA 1358 y 120 1.0 120 strong bass, hard punch, recessed mids. highs tend to sound a little rough and pronounced.
2SC 3422 y 2SA 1359 y 100 3.0 40 strong bass, neutral to warm sound.
good choice if you prefer rocky sound with slam
2SC 4935 2SA 1869 100 3.0 50 not tested yet
note reversed pinout!
2SC 5171 2SA 1930 200 2.0 180 warm to dark sound, yet detailed, slightly pronounced bass, smooth highs
note reversed pinout!
2SC 2344 e 2SA 1011 e 100 1.5 160 crystal clear and airy, rather bright but not piercing bright. good detail and instrument seperation. well defined bass. sounds clean and analytical.
note reversed pinout!
2SC 2238 y 2SA 968 y 160 1.5 100 neutral and balanced sound, tight bass. detailed and clear highs without being bright, easy to listen to
excellent choice but note reversed pinout!
2SD 313 f 2SB 507 f 8 3.0 60 strong bass, smooth highs. warm to dark sounding.
sensitive to bias, consider 5k pots and 3.3Ω output resistors or jfets with lower IDSS
not recommended, note reversed pinout!
2SD 669 d 2SB 649 d 140 1.5 120 not tested yet
KSC 2690 KSA 1220 165 1.2 160 recessed, soft bass. bright but smooth highs.

Note 3: hFE matching of BJT transistors

  • Transistor matching is not a necessity, most probably it doesn't make an audible and just a measurable difference
  • Since we are using bipolar junction transistors (BJT) matching is done by their hFE values.
  • Matching is done within a single channel only, you don't have to match the channels
  • Match input stage Q6 / Q7 (good chances of success)
  • Match current mirror Q2 / Q4 / Q3 / Q5 (medium chances of success)
  • Match output stage Q8a/b / Q9a/b (poor chances of success, little benefit)
  • The small signal transistors used in the input stage and the ccs mirror (2n50xx ... BC5xx) are cheap (~ 5 cent ea.), get about 30 to 50 of each to find decent complementary pairs among them.
  • For the large transistors used in the output stage it's unlikely to get perfect matching pairs, probably npn and pnp types are more or less off each other. Don't get frustrated if the ranges not even overlap, group them as good as possible but don't buy too many surplus.
  • The easiest way matching transistors is to measure their hFE values with a DMM that has a transistor socket and supports this mode. There is a nice transistor matching thread at head-fi.org and a page about BJT transistor matching on my site if you want to read more about this topic.

Note 4: quantities

  • small signal BJTs: they are cheap, so it doesn't set you back too far if you buy more than the needed 6 per board. About 20 to have spare in case you solder them reversed by mistake and destroy them while desoldering. 30 to 50 to have a decent basis for matching complementary pairs.
  • JFETs (2n5486/BF254C): you may consider to buy a few more than the needed 2 per board. In case you accidentally fry one it's salving to have a spare one in your box.
  • large output transistors: it's unlikely that you fry one of these, nevertheless it won't hurt to have one or two spare.
  • output resistors: it's recommended to buy a second set of resistors with higher resistance values, e.g. if you're going to pick 2.2Ω it's good to have a set of 3.3Ω resistors up your sleeve when the buffer doesn't run stable with 2.2Ω