carli@munich.dec.com (Bernardo da Vinci - the Amiga genius) (08/10/88)
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
mjg@client1.DRETOR.UUCP (Michael Grau see jimt) (08/16/88)
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
grr@cbmvax.UUCP (George Robbins) (08/18/88)
In article <917@client1.DRETOR.UUCP> mjg@client1.UUCP (Michael Grau see jimt) writes: > 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? > > Well here it is, the hardware fixup for the A1000 from Amazing Computing V3N4. ... The usual warning: When entirely removing the anti-aliasing filter, be careful that something in your audio output path is providing bandwidth limiting. The unfiltered Amiga output can include substantial 15 KHz and ultrasonic frequency components. If you pass the output thru a reasonable quality hi-fi system, these may damage your tweeters or prove irritating to your or your pets... -- George Robbins - now working for, uucp: {uunet|ihnp4|rutgers}!cbmvax!grr but no way officially representing arpa: cbmvax!grr@uunet.uu.net Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
mriley@pnet02.cts.com (Mark Riley) (08/30/88)
To disable the audio filter on an Amiga 1000 snip one leg of capacitors
C103 & C104. These capacitors should be right next to each other. If
you are more ambitious you could hook up a DPST switch to switch the
filter capacitors in and out. Make sure you use shielded cable that has
two internal conductors for each capacitor. The shielding should be
hooked up to ground. BTW, the capacitors are located beneath the
"daughter board" so you'll have to remove it first to access the
two little beasties. If for some reason this doesn't work for your
1000 version than all you'll need to do is put a tad of solder on the
snipped leg and all will be back to normal.
-Mark-
UUCP: {ames!elroy, <backbone>}!crash!gryphon!pnet02!mriley
INET: mriley@pnet02.cts.com
"Hey, I don't _use_ programs, I write them..." ;-)