The R9 & R14 can be changed from 15K to 4K7, but
only if the added gain is needed, as it was in my system. If your system
has high line levels to the Power Amplifier, it may be a good idea to
leave as is, and change if needed. The original value is preferable as it
gives higher Headroom for the Input PCB.
R24 may vary from the standard 180K as used in
the Jaycar AA-0508 (Please Note,
it is recommended that you use
AA-0501 Plate Amp), but the Parts Express 300-793 will probably have 120K,
change to 180K as indicated above.
About the optional changes to the Power Amp
Module: Do not attempt to remove Power Amplifier PC Board. Re-assembly may
be extremely difficult. If in any doubt do not attempt this
The Input Coupling Cap which is C1 - in Jaycar
unit - is a cheap Electrolytic. Electros are not good caps to have in the
audio path at any time. I was able to change it by using a sharp pair of
pliers and cutting it in half, then pricing the remaining bits of it I was
able to access 1/4 inch leads to which I soldered a film 3.3uF cap. This
saved me from having to remove the whole Power Amp module, a very
complicated process where things could easily go wrong.
The 100uF Electro marked C4 - Jaycar unit - is
used in the feedback loop of the Power Amp circuit. It's there to reduce
the gain to unity at DC, so that the DC Off-set feed to the Speaker Driver
is kept very low. This unfortunately needs to be a very high value at
100uF and this makes it virtually impossible to use a film cap. So get the
highest quality Electro you can get, perhaps one that is claimed to be
'Audio Grade'. You could also use a Bi-Polar Electro as they are generally
better than normal Electros - but make it 100V rated as higher voltage BP
caps are generally better. Use same technique as C1 to solder onto PCB.
See Box Construction Page for detailed Drawings, Cutting Sheet and other
See Download Page Zip File
- you will be able to view entire Project off-line.
See Technical Page for in depth discussion of EQ approach used.
See User Setup Page for Operating Instructions.