CVX4 "Covox Speech Thing" Compatible Parallel Port Sound Card

CVX4 "Covox Speech Thing" Compatible Parallel Port Sound Card

CVX4 is a "Covox Speech Thing" compatible Parallel Port Soundcard for IBM Compatible computers without ISA expandability, such as vintage laptops, PCs with proprietary desktop form factors and modern PCs with Parallel Ports.

OPL3LPT connects to your Parallel Port and offers extensive tuning options for a high quality "Covox Speect Thing" Analogue Line Out port intended to for use with amplified speakers.

Device Features

  • No efforts, no expenses spared: CVX4 is the fourth revision in our quest to produce the highest quality Covox Speech Thing clone!
  • CVX4 uses high quality, high precision (0.1%), same value resistors and a professionally reverse engineered, Serdaco designed schematic (based on a real original Covox Speech Thing) for excellent 8-bit sound.
  • CVX4 offers significantly better audio compared to other DIY clones which use 1%-5% resistors and unauthentic schematics. There is no comparison! (But if you really feel like comparing, you will be pleasantly surprised!)


Dip Switch Settings:

Dips 1-5: Low Pass Filter

Dip 1: 1nF: Moderate Low Pass Filter
Dip 2: 4.7nF: Heavy Low Pass Filter
Dip 3: 10 nF: Very Heavy Low Pass Filter
Dip 4 : 0.1nF: Very Subtle Low Pass Filter
Dip 5 : 0.47nF: Subtle Low Pass Filter

Dips 6-7: Extra Volume Divider

Dip 6: 56k (1/2R)
Dip 7: 27k (1/4R)

Dip 8 : Bypass Coupling Capacitor

Dip settings for authentic Covox Speech Thing sound: Dip 7 On, All other dips Off.

Example DIP switch settings :

E-D-D-D-D-X-X-X low pass filter set medium
D-E-D-D-D-X-X-X low pass filter set heavy
D-D-E-D-D-X-X-X low pass filter set very heavy
D-D-D-E-D-X-X-X low pass filter set very low
D-D-D-D-E-X-X-X low pass filter set low
X-X-X-X-X-E-D-X extra volume divider set half
X-X-X-X-X-D-E-X extra volume divider set a quarter
X-X-X-X-X-X-X-E bypass decoupling capacitor

Legend: E=(E)nabled or On; D=(D)isabled or Off; X=Doesn't matter

Audio Samples

  • CVX4 Demonstrations by Serdaco:


  • CVX4 Review by Phil's Computerlab:

  • CVX4 Review by The 8-Bit Guy:


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