Re: Apple IIGS Stereo Sound Card - Interest?

[Steve <srkh28@gmail.com>]

Hi Drew,

Nice looking card! The fabricator has done a great job on the matt
green.

As for noise, I usually find power is a key contributor for noise.
Some low noise linear regulators (10uV/RMS) with high PSRR can really
make a difference, especially if you have stage gains around 20db and
above. Its amazing how much supply noise gets amplified up into the
output. Killing it at the source is easier than removing it from the
output.

Do you know for sure its white noise? (hiss) - is there any sign of
digital noise? When the floppy drive operates, do you notice any
change in the noise level for example?

steve


On Nov 24, 8:20 am, Drew <goggled...@gmail.com> wrote:
> On 2 Nov, 17:34, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
>
>
>
>
> > Drew wrote:
> > > On 2 Nov, 09:52, "Bill Buckels" <bbuck...@mts.net> wrote:
> > >> "Toinet" <antoine.vig...@laposte.net> wrote:
> > >>> Will your board allow sound input as well as sound output? I mean
> > >>> "numérisation du son" (sound digitization)
> > >> Hi Tony,
>
> > >> That would be good if Drew's board provided recording as well as playback
> > >> functionality. (i.e. ADC input as well as DAC output).
>
> > >> Bill
>
> > > Hi,
>
> > > At the moment it will be output only. I have thought about input, and
> > > i 'might' look at this at a later date. This is all new to me and am
> > > keen to get something produced and then look at how i can improve
> > > things maybe on a version 2.0 board, but to be honest if i was going
> > > to do the input i would need lots of help from the group :).
>
> > Since the Ensoniq ADC input (mono) is on the same connector as the
> > multiplexed outputs, you already have access to the input.
>
> > All that's needed is suitable amplification for your intended input
> > (required for a microphone input) plus an anti-aliasing low-pass
> > filter--probably another two op-amps as active filters.
>
> > The net impact to the bill of materials would be another two
> > or three op-amps (in one chip), about a dozen passives (resistors
> > and capacitors), and an input jack--plus a gain control if one is
> > not available off-card.
>
> > If a low-level (microphone) input is provided, some care should
> > be exercised in laying out the card to avoid noise pickup.
>
> > -michael
>
> > NadaNet 3.0 for Apple II parallel computing!
> > Home page:  http://home.comcast.net/~mjmahon/
>
> > "The wastebasket is our most important design
> > tool--and it's seriously underused."
>
> Hi,
>
> I have completed the prototype card (http://drewbiegs.blogspot.com),
> but seems the hiss that was on the breadboard is on the real card as
> well, specifically on the right speaker. I was wondering if anyone had
> some suggestions on a good starting point? possibly the layout of the
> board, but I am not expert on what can cause issues with audio on
> PCB...
>
> Any help would be appreciated :)
>
> Drew- Hide quoted text -
>
> - Show quoted text -