Path: utzoo!dciem!dretor!client1!mjg From: mjg@client1.DRETOR.UUCP (Michael Grau see jimt) Newsgroups: comp.sys.amiga.tech Subject: Re: how to improve sound capabilities Message-ID: <917@client1.DRETOR.UUCP> Date: 15 Aug 88 19:12:51 GMT Article-I.D.: client1.917 References: <8808100911.AA07219@decwrl.dec.com> Reply-To: mjg@client1.UUCP (Michael Grau see jimt) Organization: D.C.I.E.M., Toronto, Canada Lines: 182 Summary: better then 5.5kHz sound In article <8808100911.AA07219@decwrl.dec.com> carli@munich.dec.com (Bernardo da Vinci - the Amiga genius) writes: > Has anyone the Amazing Computing issue (april?) with an article > how to improve the sound capabilities of the amiga? > (ya know that nasty filter that won't pass any frequences higher > than 7kHz...) > I'm desperately seeking for a cheap solution to set the cut off > frequency of the filter to 14kHz or higher. It shouldn't be a hard job, > but without any printsets it isn't a simple task (for me). > Maybe someone tried it allready - I don't want to reinvent the wheel. > As far as I know can this filter be turned off on newer A500 or A2000 > with the LED PD-Programm. So CATS, what do I have to do ??? > > Any recommendations would be appreciated. > > Bernhard > Well here it is, the hardware fixup for the A1000 from Amazing Computing V3N4. PAULA ----- |------| | | | | | | |TL084 | | | TL084 |-|\ | |AUD|-----|\ 2| >--@-------->>--- L | A | 13| >---X--R90--R98--R97--R96--R89-@--|/ 1 | | | |--|/ 14 | | | | | 3 | | | | 12 C110 C106 C109 C105 C104 | | | | | | | | | | | | | GND | GND | GND | | | | | | | | | | |---------@-------------| | | | | | | | | | |------| | | | | | | | | |TL084 | | | | TL084 |-|\ | |AUD|-----|\ 6| >--@-------->>--- R | B | | 9| >---X--R87--R91--R92--R93--R88-@--|/ 7 | | | |--|/ 8 | | | | | 5 | | | | 10 C107 C101 C108 C102 C103 | | | | | | | | | | | | | GND | GND | GND | | | | | | | | | | |---------@-------------| | | V Ref | | | | | | A1000 Audio Schematic ----- PAULA ----- |------| | | | | | | __________________________ |TL084 | | | TL084 / \ |-|\ | |AUD|-----|\ | | 2| >--@-------->>--- L | A | 13| >-@-X--R90--R98--R97--R96--R89-@--|/ 1 | | | |--|/ 14 | | | | | 3 | | | | 12 C110 C106 C109 C105 C104 | | | | | | | | | | | | | GND | GND | GND | | | | | | | | | | |---------@-------------| | | | | | | | | | |------| | | | | | | | | __________________________ |TL084 | | | | TL084 / \ |-|\ | |AUD|-----|\ | | 6| >--@-------->>--- R | B | | 9| >-@-X--R87--R91--R92--R93--R88-@--|/ 7 | | | |--|/ 8 | | | | | 5 | | | | 10 C107 C101 C108 C102 C103 | | | | | | | | | | | | | GND | GND | GND | | | | | | | | | | |---------@-------------| | | V Ref | | | | | | A1000 Audio Schematic Modification 1 ----- PAULA /RES========================================< L #2 ----- / | |------| | | / GND | | | | / |TL084 | | | TL084 / |-|\ | |AUD|-----|\ | 2| >--@-------->>--- L | A | 13| >-@-X--R90--R98--R97--R96--R89-@--|/ 1 | | | |--|/ 14 | | | | | 3 | | | | 12 C110 C106 C109 C105 C104 | | | | | | | | | | | | | GND | GND | GND | | | | | | | | | | |---------@-------------| | | | | | | /RES========================================< R #2 | | | / | |------| | | | / GND | | | | | / |TL084 | | | | TL084 / |-|\ | |AUD|-----|\ | 6| >--@-------->>--- R | B | | 9| >-@-X--R87--R91--R92--R93--R88-@--|/ 7 | | | |--|/ 8 | | | | | 5 | | | | 10 C107 C101 C108 C102 C103 | | | | | | | | | | | | | GND | GND | GND | | | | | | | | | | |---------@-------------| | | V Ref | | | | | | A1000 Audio Schematic Modification 2 ----- RES - 4.7 Kohm 1/4 Watt R90,R87 - 750 ohm R98,R97,R92,R91 - 3.3 Kohm R96,R89,R93,R88 - 36 Kohm C110,C107 - .047 uf C106,C109,C108,C101 - .01 uf C105,C102 - .0047 uf C104,C103 - 220 pf TL084 - UG5 on the board < - phono plug (must mount a new set for Mod 2) X - Test Point @ - connection = - shielded miniature cable Modification 1 : Simply locate chip UG5, and solder an insulated wire (22 - 24 Gauge) to connect pins 14 & 3 and 8 & 5. Modification 2 : Solder the resistors to pins 8 & 14 of UG5. Solder the resistor to the center wire of the shielded cable and cover with heat shrink tubing(to protect from accidental contact). Drill two holes in the back of the A1000 and fasten the two new phono plugs. Run the shielded cable along the ground traces on the board avoiding chips susceptible to noise, use black plastic electrical tape to fasten cable to board and run to back of A1000. Fit the cable between the two connectors for the original audio connectors on the motherboard. There should be only enough slack to feed the cable around and no more. *** note: also a .0047 uf capacitor can be connected to the gound and main wire of the shielded cable to form a simple low pass filter (outside ground better). *** Before completely finishing any modification, check it over to see if there are any problems (loose wires, gounds touching connections,...) then test it before completely closing up the machine. By the way, UG5 sits underneath the kickstart board and therefore it must be removed. Mike -- DCIEM - Summer Employer (does not bear the responsiblity for this message.) {utzoo|mnetor}!dciem!dretor!mjg