Quote Originally Posted by meBob View Post
Hello LDR,

Thanks for your reply.

Both board fuses are well and truly blown.

R40 is good at 2.689kohm. I'll change this to 15k as recommended.

R23/R16 are ok, R39/R2 are alive but out of range at 11.5 ohms (they're still in circuit so the readings might not be too accurate).

I've sent an email to Quad enquiring price of a new board, but i'd rather go down the DIY route. If not too expensive I'll probably go down that root to save time.

If the worst came to the worst with N1/N2 I've seen on Dada that desoldering N1/N2, C18/C19 and replacing R35/R36 with wire links would solve my N1/N2 problem?

C11,C15,C16 do you know if these are polypropylene or polystyrene?

Regarding N1 and N2 it is not just a simple matter of desoldering those parts. The parts Quad used in earlier boards at that position tell us that
substituting N1 and N2 requires then placement of earlier board components R26 75R , R24 22 ohms D3 a diode ,R27 a 15k, R28 a 75 ohm R25 a 22
ohm D4 and R29 15k which are all needed for the circuit to function correctly

As for R35 and R36 these are resistances of 0.91 an ohm each. Each part Quad used was arrived at to provide an amplifier with low distortion and ability
to drive loudspeakers.

You would need with any substitution ( other than the led current limiting resistor R40 ) to have ability to measure distortion before and after.
C11 is a 1 nanofarad capacitor , whereas C15 and C16 are 100 nanofarad. My advice is to use these exact values particularly observing voltage
tolerance. The construction of capacitance material is or should be way down your list of priority at the present time. MKP is one type of
capacitor where each value is available

Your best option is to restore the 405 to its original condition by installing a new board from Quad- forgetting things like removing current limiting and doing partial mods you have seen
at Dada. Quad amplifiers have a good reputation for reliability and performance, none of which can be achieved by removing parts.

Alternatively save up for either Net Audio 405 Mk 3 boards or indeed Dada boards, which I know in the case of Net audio boards offer improvement in lowering distortion
compared to a standard 405 board.