DOS Days

Retro Review: Crystal 3D Sound Card - Part 1

5th October 2025

 

This week's retro review looks at another sound card, one that is renowned for its buggy FM synthesis. I bought it specifically because of this (somebody has to). It is based on the Crystal CX4235 - a late ISA sound chip which is highly-integrated and supports Sound Blaster, Sound Blaster Pro and WSS compatibility.

 

Crystal 3D Sound
Bought in October 2025 for £12

The card I have here is actually Crystal-branded, and oh boy.. it's a no frills one. It doesn't even get a wavetable or IDE header, but that's actually quite understandable, given that it was manufactured in 1998. This was a time when Windows AC'97 audio was all the rage, and in Windows you may have just used 'soft' wavetables. It's quite similar to the Digimate 3D Sound, and is sometimes referenced with this name, despite it not being a Digimate product.

 

Quick Visual Inspection

Looking around the card, it's a very simple design given that almost everything is handled within the Crystal chip:

  • Crystal CX4235-XQ3 EP all-in-one audio controller
  • ST Microelectronics TEA2025B - stereo audio amplifier
  • A single 16.9 MHz crystal oscillator
  • Two white 4-pin headers for CD Audio-in (one for Mitsumi drives and a second for Panasonic drives)
  • One 4-pin header for Sony CD audio-in
  • Two jumpers at JP14 and JP15
  • Pads for a CS9236 wavetable chip
  • Pads for a 40-pin IDE header
  • Pads for a 26-pin wavetable header
  • Faceplate with Mic-in, Line-in and Speaker Out 3.5mm jack sockets and 15-pin game/MIDI port

Date-wise, the most recent date stamp on the card's chips is week 37 of 1998, so it was certainly no earlier than September 7th 1998 when this particular card was manufactured.

 

The Component Parts

The Crystal CX4235-XQ3 EP

The Crystal audio controller here came two years after the introduction of their first all-in-one controller/codec chip, the CS4232 in 1995. The CX4235 was one of their final ISA-based chips before the big move to PCI.

The CX4235 is actually a slightly later version of the CS4236B (also released in 1997), adding what Crystal called "CrystalClear" 3D audio. It supports full duplex, is Plug & Play, and has an integrated FM synthesizer on-chip which is fully compatible with Sound Blaster, Sound Blaster Pro and Windows Sound System (WSS) 1.0.

In addition to its codec functions, it handles other ancillary interfaces including a joystick port, MPU-401-compatible MIDI, and an optional CD-ROM interface.

A low-power version of the CS4235 was also released, called CS4239.

There are some notably excellent Crystal audio controllers that pre-date this one, including the CS4231 and CS4232. These were used prolifically on sound cards in the early-to-mid 90s, and produced pretty authentic OPL3 sound.

 

TEA2025B Stereo Audio Amplifier

The onboard audio amplifier produces up to 2.4W per channel in stereo mode, or 4.7W mono.

This same TEA2025B IC from ST Microelectronics can be found on many ISA sound cards including the Aztech Sound Galaxy BX/NX/NX Pro 16/Basic 16/Pro 16, Creative Music System (CMS), Sound Blaster 1.0/1.5/2.0, Sound Blaster Pro, Sound Blaster 16, AWE32, and various OPTi-based cards with 82C925/82C928/82C930/82C931 chipsets, to name but a few.

 

Pads for Wavetable IC

The 28-pin wavetable IC that would exist at U6 [if the card were more of a premium model], is the Crystal 9236CL. Also arriving in 1997, this was fully General MIDI-compliant with 32-note polyphony, reverb and chorus effects processing, and built-in RAM and ROM for samples, though I believe it's just 512 KB in capacity.

Other supporting components are of course missing. You would need a 4 KB EEPROM at U3, capacitors at C7 and C8, and an NPN transistor at U2. U8 and U5 can remain unpopulated. The EEPROM is necessary since the Crystal Audio System must be loaded with appropriate resource data to operate correctly in a Plug & Play environment such as Windows. This can be achieved in several ways, the most secure of which is from an external EEPROM, where the card will reload the stored resource information from the EEPROM when it's initialised.

The Crystal Oscillator

The Crystal CX4235 IC derives its master clock signal (called MCLK) from an onboard 16.9344 MHz crystal oscillator. If a CS9236B wavetable synthesizer IC were also installed, it too would use this as its clock source.

 

Headers and Jumpers

The four-pin header and two white header blocks at the top of the card are for CD audio-in from a CD-ROM drive. One of these would typically be used, depending on the interface your CD-ROM drive uses: Sony, Mitsumi or Panasonic. This feeds the CDA (CD audio) from the CD-ROM drive into the sound card so that the audio can be fed through the amplifier and out the Speaker jack.

The two jumpers at JP14 and JP15 are used to select the audio output as "Line-Out" or "Speaker-Out". Line-Out mode would mean the onboard amplifier circuitry is circumvented so the output would be unamplified while Speaker-Out is amplified. Why are there two jumpers? Probably for the 2 channels (left and right). The card is currently setup as Speaker-Out. For best signal-to-noise, it is usually preferable to use the unamplified "Line-Out" and connect the card to powered speakers or better still, a high-quality stereo amplifier, since a lot of noise is generated in a sound card's amplifier circuitry. Based on the card's silkscreen, the 'Speaker Out' 3.5mm jack is actually just 'Out', so you'd get "Line Out" of this if the card were jumpered to work that way. Another nice cost-reducing measure ;-)

Being a pretty cheap card, there are numerous missing header pins (just solder pads) directly behind the 3.5mm jack sockets. The tracks from these are connected to the Audio-Out, Line-In, and Mic-In jacks, so you you could have pins on these to connect a front panel connector.

In Part 2, I will install the DOS drivers and test just how bad that CX4235's FM output might be!