Diagram of a 2.1 preamplifier joined to an audio power amplifier, taken from a YouTube project; the doubled pdf extension is just a naming slip.

PDF schematic of 45.2 KB for a Dynatech V5000 SMD preamplifier with display section, plus an inverter design attributed to Pappu.

PDF amplifier circuit built around the Sanyo STK412-170 hybrid module, rated at 180 W in the name, which also marks it as OK, presumably a verified design.

Simple preamplifier schematic built around the NE5532 dual low-noise op-amp, a 405 KB PDF; the extra tag in the name only marks the source site.

Regulated power supply for a preamplifier, drawn in a 601 KB PDF schematic with a source tag in the name.

Preamplifier schematic, the file name being the Romanian word for preamp, delivered as a 574 KB PDF with no model or brand stated.

Schematic in PDF form for a stereo preamplifier with a loudness control, a common DIY audio circuit that boosts bass and treble at low listening volume.

PDF for the KA4558, a dual operational amplifier in the KA series, equivalent in function to the familiar 4558 dual op amp, size 121 KB.

Tone control circuit intended for a 2.1 channel audio system, in a 159 KB PDF. It shows the bass and treble adjustment network that sits between the source or preamp and…

Compact PDF schematic whose name points to a parametric equalizer combined with a subwoofer filter stage.

Service manual PDF for the Audio Pro TA150 receiver, matching the rec and sm tags in the name.

Datasheet PDF for the KIA324P with an additional F suffix in the name, 321 KB, filed under schematics.

Updated schematic for the IRS D900 class D amplifier, rated from 200 to 500 W and credited to Rat Net, in a 423 KB PDF.

Schematic PDF of 2.29 MB for a tone control circuit with low, mid and high adjustment plus a sub-woofer section, according to the name.

For the 2SD2098 transistor, this 159 KB PDF is categorised as a schematic but follows the usual naming of a part datasheet.

Sony SA-WGT5D schematic in PDF format, 15.9 MB in size. The name gives only the model, which follows Sony's SA- prefix for speakers and subwoofer units, so open the…

Document for the 2SD2536 transistor, a 71.6 KB PDF in the schematic category that is most likely its datasheet.

Datasheet-type PDF for the 3SK271, around 32.7 KB, catalogued in the schematic category.

Component PDF for the 3SK285, 22.2 KB, placed in the schematic section of the index. Only the part number is given.

Compact 42.7 KB PDF covering the 2SB1183 transistor. The JIS-style 2SB prefix identifies a PNP device designed mainly for low-frequency circuits, commonly found in power…

Compact 77.2 KB PDF covering the 2SB893 transistor. In JIS numbering the 2SB prefix identifies PNP transistors for low-frequency circuits, such as audio amplifiers and…

PDF datasheet for the 2SD879 transistor, roughly 106 KB, with no manufacturer indicated in the file name.

Datasheet PDF, about 180 KB, for the 2SB1481, filed in the schematic section of the index under its bare JIS part number.

The file name gives nothing beyond 2SC3460, a Japanese JIS designation in which the 2SC prefix denotes an NPN bipolar transistor.

Covering the 2SA1837, this 173 KB PDF is listed as a schematic but is expected to be a transistor datasheet.

Named for the 2SD1618 transistor, a 116 KB PDF listed as a schematic but most plausibly the part's datasheet.

Datasheet-style document for the 3SK302, a 26.0 KB PDF indexed as a schematic. The 3SK prefix in Japanese JIS numbering denotes a four-terminal N-channel field-effect…

PDF for the 2SD1992A NPN transistor, indexed as a schematic though the name points to a part datasheet.

Component sheet for the 2SA1940 transistor, provided as a 172 KB PDF and listed among schematics.

Small 33.0 KB PDF for the 3SK144, catalogued as a schematic but named for an individual semiconductor, so it is most likely a datasheet.

Component datasheet for the 2SK1057, packaged as a 55 KB PDF. The 2SK prefix marks an N-channel FET in the Japanese numbering system, and this number sits in the same…

This 93.0 KB PDF carries the part number 2SJ258 and nothing else. The 2SJ prefix, under Japanese JIS numbering, indicates a P-channel field-effect transistor, so expect…

A 214 KB PDF for the 2SA1429 part, catalogued as a schematic though most likely a data sheet.

Schematic in PDF form for a tone control board labelled NEWGEN TA2411B, where TC most likely stands for tone control.

Part datasheet for the 2SK2033, provided as a 296 KB PDF and filed under the schematic category. The 2SK prefix follows the JIS standard for N-channel FETs.

Datasheet-style PDF for the 2SD1302, 46.0 KB, listed in the schematic category. The 2SD prefix follows the Japanese JIS designation for NPN bipolar transistors in…

Compact 44.8 KB PDF for the 2SD1051, with an _E suffix in the name whose meaning is not stated, possibly a language or edition marker.

Datasheet for the 2SD669 NPN transistor in a small 32 KB PDF, maker not stated in the file name.

Named only 2SC4365, this 148 KB PDF is filed with schematics but should contain the manufacturer datasheet for that transistor.