Speed Freak Sound Board Question

From: Chris Leyson <cleyson_at_aol.com>
Date: Fri Jun 03 2011 - 15:47:44 EDT

Hi guys

As I've got some time on my hands I thought I would upgrade my FPGA CCPU
with some audio effects.
The design has been running on a Spartan 3E eval board since 2009 but
with no sound :-(

Thought I would start with Speed Freak because the vectors display
nicely on a TEK scope and the sound card is virtually all digital.

On the sound card the 78.125kHz clock from the main board (J4 pin 2) is
tripled to a jittery 234kHz and then divided by 32 to generate
7.324kHz (U18 pin10) and by 256 to generate 915Hz (U18 pin 8). The
manual mentions U18 pin 11, which would generate 3.662kHz,
but I am not convinced for the following reasoning

I analysed the sound from a YouTube video for Speed Freak and the two
tones for the horn sound would appear to be 458Hz and 333Hz.
This would imply that the clock to U17B is 915Hz (U18 pin 8) and that
U23 divides 7.324kHz (U18 pin 10) by 11 to clock U17A at 666Hz.

Would be nice if anyone could confirm the clock frequencies for U17A and
U17B and the clock supplied to the noise generator.
Also, what is the value of the mystery resistor connected to R21 and C20.

Best regards

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Received on Fri Jun 3 15:48:08 2011

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