HiFiStor

Quad 405 , what to say, probably one of the most commented and modified amplifier in HiFi community . For those who want to build this amp , due to many mod’s it is very hard to choose which version to build. In my build I have tried version which is as much as possible same as original one. I have choose to build this amp due to it is very well commented but also I noticed that most of builds has one , for me serious problem. Many of pcb’s which I have seen are built with ferrite core inductor’s . Ferrite can significantly impact the sound so my opinion is building this amp with ferrite core coil is wrong. Transistors used in original circuit are very hard to find this days , but most of them are not critical and have good modern replacement . In my build I have used next replacements (bolded are in final version):

TR1: BC214C – BC559C BC560C BC415C BC212
TR2: ZTX304 – BCX32 BC682 BC546B MPSA06 2N5551 BC300 2N2219
TR3/TR4: ZTX504 – BC556B BC303 BC212
TR5/TR6: BC214C – BC560C BC415C BC559C BC212
TR7/TR8: 40872 – 2SA740 BD242C BD244C 2N6134 TIP42C BDX78 BDX34
TR9/TR10: 17556 – 2SD424 2SD676 2N3773 MJ15003 BD245 BD249

Air Coil’s:

3 uH : 31 winding of 1mm enameled cooper wire on 10mm body or 17windings of 1mm enameled copper on 16mm body diameter

6.9 uH : 22 + 18 (double) winding of 1mm enameled cooper wire on 10mm body or 25,5 windings of 1mm copper wire on 16mm body diameter

OpAmp: TL071

Download: Schematic

Short test of my build I have on my facebook page Test #1 and Test #2