Hood 1969 Simple Class A Amplifier

Hello. I am new to DIY audio and I believe the Hood 1969 class-A amplifier is a good place to start off due to the ease of construction. I am currently taking an online course to KiCAD like a Pro.

I believe the challenge right now is to find the modern counterparts for the transistors. So far I’ve got three alternatives which I am comparing with the specs given by Hood (I have discrepances on the open-loop gain, output impedance and THD, but I haven’t figure out the reason yet).

However, what I would like to do is to select the definitive transistors to build the amp. Does anyone have experience with this amp?



Welcome @fran
Thank you for sharing.

I built a Linsley Hood Class A back in 1970. Fifty years on it is difficult to remember the details, but I am pretty sure I used 2N3055s for the output transistors, since I had a plentiful supply of ex-equipment examples. It was used in a mono system for my sister, and she only retired it about a decade ago because it sounded so good. A useful portal for a lot of information about the amplifier and its variants is at Simple Class A Amplifier


You’re welcome. I hope to have soon the BOM for the veroboard prototype. I will be posting as I move along.

Thanks for your feedback and the resource to the website. It is also great to go beyond the specs and have someone telling how great a sound this amplifier can produce.

I look forward to watching your progress. All I have ever done was to assemble kits, such as Hafler’s, and build lots of cables.

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:slight_smile: In truth, at that time the Class AB amps were not brilliant. They were quasi-complementary and it wasn’t until 1975 that the Baxandall diode was introduced to cure the asymmetry between the push and pull halves of the output. Around then the availability of PNP power transistors also meant that complementary outputs became more common.