Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Discussion about old sound cards, MIDI devices and sound related accessories.

Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Benedikt » 2019-3-15 @ 21:09

matze79 wrote:
root42 wrote:God we need someone with a tool for making custom brackets. But yeah, looks lovely!


ah i already have a solution for that into mind :)

root42 wrote:Then also make some for the snark barker!!

Would slot bracket No. 9204-1 by Keystone Electronics do? (mouser link)

Keystone Electronics appears to have quite a nice assortment of slot brackets.
If any of them fits – or you design your PCB, accordingly – you won't even need a custom bracket.
Otherwise, blank ISA bracket No. 9202 (mouser link) might be a good starting point.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby root42 » 2019-3-15 @ 21:28

Yes, I have a bunch of the blank Keystones. And usually if only round holes are needed, I am fine. But the Snark Barker (and matze's new design) require a slot for the volume wheel. That is a bit more difficult...
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-06 @ 11:43

Next PCB is on Order..

i figured out the SN76489 is sounds quite different to IBM PS/1 3 Voice Sound.
Also got my hands on tandy 1000, sounds slightly different but only minimal.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Lord Nightmare » 2019-4-07 @ 22:34

AFAIK there's a bunch of differences between the NCR8496 and PSSJ, vs the SN76489/89A/96, but it boils down to a few things, I believe:
1. The Noise channel LFSR is significantly different; on SN76489/89A/96/etc the LFSR (assuming a leftward-shifting Fibonacci LFSR where bit 0 is the rightmost bit, where the new bit gets shifted into on the next clock) has feedback taps on bits D and E, output tapped from E, XOR function. The NCR8496 and PSSJ, the LFSR has feedback taps on bits A and E, output tapped from E, XNOR function.
2. The Noise LFSR on the TI chips is reset on any write to register 6, regardless of what is written and what the contents of register 6 were. On the NCR8496 and PSSJ, writing to register 6 only resets the LFSR if the value of bit 5 (the periodic vs white noise select) changed vs the previous register contents.
3. Writing to registers which do not have a 'second half' (registers 1, 3, 5, 6, 7) with bit 7 cleared on the NCR8496 and PSSJ does absolutely nothing, while doing so on the TI chips causes the low 4 bits written to 'mirror' to the 4 bits of the first half of those registers. (For register 6, writing to the second half on TI chips also resets the LFSR, like a normal register 6 write would.) This 'writes with bit 7 cleared do nothing on NCR/PSSJ' fact still needs hardware testing to verify its behavior exactly, and whether it applies to all 5 of those registers or just some of them.

There may still be other differences yet to be noticed.

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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Scali » 2019-4-08 @ 00:27

The PS/1 runs the SN76489 (or equivalent) at a different base frequency. That also affects how the noise channel sounds.
See here for more info: viewtopic.php?t=18327&p=356139
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-08 @ 06:02

Anyone knows what frequency PcJr runs ? is it similar to PS/1 ?

The PcJr VGMs sound pretty good on the PS/1, and out of tune on the Tandy.

EDIT:
http://nerdlypleasures.blogspot.com/201 ... -chip.html
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Scali » 2019-4-08 @ 07:11

matze79 wrote:Anyone knows what frequency PcJr runs ?

PCjr runs at the same frequency as Tandy, an NTSC frequency: 3.58 MHz.

The only difference between PCjr and Tandy is the noise channel. Most Tandys use the NCR 8496 clone, which has a different noise channel implementation, as explained above by Lord Nightmare.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-08 @ 07:46

Yeah and which i can not find to purchase.. :)

Thanks!
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-13 @ 13:51

i trying to convert everything to kicad now.
As i have not enough space to fit everything on free eagle version.
Especial if i want to add the bracklet to the design.

unlikly everthing is different in kicad so i need to figure out howto i get my ground planes working..
EDIT: Fill all Zones -> Found it.

tandy_sound.jpg
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Great Hierophant » 2019-4-13 @ 16:30

It seems to me that unless one of these testers was using a genuine NCR8496 chip, that you may get lucky with a chip marked TI SN76489 if you want the behavior that makes Maniac Mansion and some other games sound like they would sound on a later Tandy 1000. Either Texas Instruments changed the behavior of the noise channel at some point or someone is using a remarked clone.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Scali » 2019-4-13 @ 16:42

I have both SN76489 and SN76496 chips for my clone card. I didn't test specifically with Maniac Mansion, but I didn't notice any difference in sound at all, last time I tested.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Great Hierophant » 2019-4-13 @ 17:10

If you use a SN76496 with the clone card, shouldn't its audio input pin be grounded to avoid picking up noise?
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Tiido » 2019-4-13 @ 18:33

All the TI PSG chips have the "Audio In" pin, including the early ones where the datasheet doesn't tell it is one. The pin connects to the negative input of the internal amplifier and cannot be tied to GND or other stuff that forces a DC offset or the internal reference gets messed up and you get garbled or no sound. Connecting a 68pF capacitor from output to that pin will stabilize that amplifier and oscillations seen in the output will stop, increasing sound quality, this works on all the TI PSG flavors.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-13 @ 18:50

oh i will try that, maybe it will stop sound problems.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-17 @ 16:28

Thanks this does the Trick, the oscilations magically disappered.
i used a Busdriver, a 7805 and decent filtering before to archive nearly same result..

i played populus a bit, and it sounds much better!

populus.jpg


i cancelled the pcb order and will adjust the smaller one now :)
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Tiido » 2019-4-17 @ 17:14

That is nice to hear it helped ~
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-18 @ 14:09

Indeed! also works perfect on dreamblaster TNDLPT Plug :)
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-19 @ 11:25

prototyp_r9.jpg


Stereo ? :)

it finally works the way i wanted.

Now PC-Speaker Output remains working when sn76489 is cut from amplifier.
The 1N4001 will be omitted, its only because i only had 3V OMRONs.

i now want to test activating the audio signal from SN76489 by pulsing OE with multiple writes to 0c0/2c0/1e0 in a certain pattern.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby Tiido » 2019-4-19 @ 11:53

I have had best results with gating the clock of the PSG chip, no need to put anything in the audio path that way and you can do it with only digital components too.
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Re: Tandy 3 Voice Sound - SN76489 ISA Soundcard Project

Postby matze79 » 2019-4-19 @ 12:13

So it would suffice to just connect the 7474 Clock Generation circuit to the Tiny13 hmm.
Just pull CLR/PRE to GND or VCC.

This never came into my Mind :)
at some point i had the idea to control clock, but then i found out i can use bypass pin on the lm386. which did not work on SMD LM386.
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