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Please Note, it is now recommended

that you use AA-0501 Plate Amp  

  THE INSTRUCTIONS ARE CLEARER AND EASIER TO DO 

Earlier Sub Plate Amplifiers are no longer available. But PartsExpress makes what looks like a suitable amplifier, part number 300-804. According to the PDF file, the stock unit without any changes will give you good all round performance being -1.5dB @ 20 Hertz. But if you limit the subwoofer for only audiophile use, change R35 from 24K to 15K and R36 from 150K to 470K.

The box cut-out for the amplifier now need to be 216mm by 216mm.

  AA-0508 

COMPONENT CHANGES TABLE

Component

Original

Value

New

Value

Options

Comments

 

Input PC Board

R9, R14

15K

4K7

Set Extra Gain

See Text

R23

18K

82K

Critical Value

Flattens 30Hz Peak

R24

This may vary

180K

Critical Value

Boost Level

C13, C14

0.1uF

Leave alone

Critical Value

Sub-Sonic Filter

 

Frequency & Volume Control Module

R1, R2

6K8

1K

Critical Value

Controls Freq Range

C1

0.082uF

0.33uF Film

Critical Value

Controls Freq Range

C2

0.15uF

0.33uF Film

Critical Value

Controls Freq Range

Add the Following Filter to the Input Before R1 on the F/V Control Module

This adds a fixed Low-Pass Filter

 

Power Amp Module

Optional & May Be Very Difficult - See Text

C1

4.7uF Electro

3.3uF Film

3.3uF to10uF Film

Must be Film, get rid of Electro Cap

C4

100uF Electro

100uF Bi-Polar

Keep Value Same

Change to Bi-Polar or Audio Grade Electro

 

'See Text' Comments:

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.

Optional Because It's Tricky!

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 option!

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 Box Diagrams

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.

 

Send mail to joeras@vacuumstate.com with questions or comments about this web site.
Copyright 2003-10 Joe Rasmussen & JLTi
Last modified: Sunday June 07, 2015

Just had a terrible thought. If "intelligent design" is unscientific, then who will design our audio equipment?