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Frequently Asked Questions


In addition to the troubleshooting articles on this page, please also check the FAQ section in the Details menu.

Definition of mono, pseudo-stereo and stereo


In the realm of SIDFX the terms mono, pseudo-stereo and stereo are defined as following:

Music composed for one SID chip is always considered mono. Although SIDFX allows the audio from one SID to be output onto two separate channels this is still considered mono. Mono music only addresses one SID chip. However, if mono music is played by two different SID types and output onto two separate channels this may be considered pseudo-stereo.

Music composed for two SID chips is always considered stereo. Stereo tunes are often named 2SID. Stereo music always addresses two SID chips located at different addresses with SID 1 at $D400 and SID 2 typically at $D420 (but sometimes $D500 or $DE00).

No sound from SID 2 after installing SIDFX​


This may happen when you attempt to play standard mono SID tunes while SIDFX is configured for one of the stereo operating modes. What happens is that music data addressed for both SIDs (at $D400) only reaches SID 1 because SID 2 is located at either $D420, $D500 or $DE00 due to the chosen stereo operating mode. Please always configure SIDFX for either "Mono Auto" or

"Mono SID1+SID2" operating mode before playing standard mono tunes.

Garbled sound from SID 1 and no sound from SID 2 while playing stereo tunes

This may happen when you attempt to play stereo SID tunes that expect SID 2 to be located at $D500 while SIDFX is configured for the "Stereo $D420" operating mode. What happens is that music data addressed for SID 2 are also received by SID 1 because of memory map mirrors. Please always configure SIDFX to the "Stereo $D500" operating mode before playing stereo tunes requiring

SID 2 to be located at $D500.

No pseudo-stereo with SW1 in center position

This may happen when you use an intelligent SID player, for example SIDPlay64 and the built-in 1541U/Ultimate64 SID player.


The issue is caused by the mentioned SID players, which both have specific SIDFX support. They use the SIDFX API to detect which SID chips are installed and automatically selects the SID model for which the tune was composed. This provides the listener with the highest degree of authenticity and is in most cases the desired behavior.


However, the lack of pseudo-stereo may take some fun out of listening. We are not aware if the auto-detect/select feature can be disabled in the players, so unfortunately we must refer you to the respective authors with this question. Alternately use an older version of the player without SIDFX support to work around the issue.

No stereo output when SIDFX is connected to external mixer/amplifier

This may happen when you connect SIDFX to external equipment, regardless of SIDFX configuration and SW1 position.

The issue is usually caused by mono cables, mono adapters or mono inputs on the external audio equipment. Mono cables/adapters/inputs typically use one SIDFX channel and pass it to left and right at the output. SW1 may select which SID is active, but due to mono conversion only one SID is audible, also with SW1 in the center position.


Avoid using mono cables/adapters/inputs if you require stereo output from SIDFX.

Audible hum or slow moving video disturbances when connecting SIDFX stereo output

This may happen if multiple devices in your system are connected to earth ground. The issue is usually caused by ground loops in the audio or video cable which couples noise into the signals.

This issue is typical if you replaced the original C64/C128 power supply with a modern version with earth ground connection and you have another device, e.g. monitor or audio mixer which is also connected to earth ground.


To solve the problem try to lift/disconnect earth ground from one of the devices, for example using a ground lift adapter or an extension cord without earth ground connection. An audio isolator may also solve the issue without disconnecting earth ground.

Software detects an incorrect SID type

Software detection usually involves configuring voice 3 and reading the $D41B register. With two SIDs mapped at the same address space only one SID is allowed to respond to reads. Which one responds depends on the operating mode, switch 1 position and SIDFX batch (CPLD code revision).

Generally SID 1 responds when SIDFX is configured for "Mono SID1 only" or "Mono SID1+SID2".

Generally SID 2 responds when SIDFX is configured for "Mono SID2 only".

For early SIDFX units (CPLD code revision 68, sold October 2016 to June 2017) the above behavior applies regardless of the switch 1 position.

Based on customer feedback we decided to change this in order to make the detection behavior more intuitive.

For later SIDFX units (CPLD code revision 6A, sold November 2017 onward) the above behavior applies only when switch 1 is in the center position. Otherwise software detection follows the sound, i.e. SID 1 with switch 1 in the left position or SID 2 with switch 1 in the right position.

Our latest SIDFX configuration tool (version 1.2) is able to report the CPLD code revision by pressing the ‘?’ key. The latest configuration tool is available from our download page.

We offer a CPLD code upgrade for units with CPLD code revision 68 in order to give them the improved behavior of all newer units. Unfortunately the CPLD code is not user upgradeable so you need to send in your SIDFX unit if you choose to get it upgraded. We only charge a negligible service fee per unit plus return shipping. Please visit our online shop for more information and to purchase the SIDFX CPLD code upgrade service.

SID types are detected as unknown in the configuration tool

SID chip detection involves configuring voice 3 and reading the $D41B register. In case you have one or more SwinSID devices installed please refer to the section on SwinSID further down. In rare cases voice 3 or $D41B may be partially defective. Usually this would be audible but this may not always be the case. If you experience that genuine SID chips are detected as unknown then please contact us for help on how to solve the issue.

SwinSID is not detected in the configuration tool

SID chip detection involves reading the value of the $D41B register. This register is not implemented on SwinSID Nano and is not cycle-accurate on SwinSID Ultimate. As a result the SwinSID generations are incorrectly detected by SIDFX and shown as "NONE" (SS Nano) or "UNKN" (SS Ultimate) by the configuration tool. For SIDFX to support SwinSID the advanced edition of our firmware is required which allows manual SID type configuration. After installation use the configuration tool to manually set the SID type of any installed SwinSID to either 6581 or 8580 depending on the emulated SID type. Always leave any real SID configured to Auto. An incorrectly configured SID chip will not operate correctly and may be permanently damaged. The advanced edition of the firmware is available from our download page.

SIDFX is not found by the configuration tool

Please verify that SIDFX is properly installed in the SID socket of your motherboard. The orientation of SIDFX (the notch on the motherboard socket and on the SIDFX pin-header must match up) must be correct and all of the SIDFX pins must be fully seated in the socket. This may also happen if the SID socket of the motherboard does not offer a reliable electrical connection.

SIDFX seems to be faulty

Most often any problems that you may experience are related to installation-, configuration or system issues. Please always consult us prior to returning a seemingly defective item. With a bit of debugging help from us 99% of all problems can be solved. In the rare case that an item is actually faulty we will provide you with a RMA reference number and instructions on how to send in your item.


Did you not find an answer?

Feel free to contact us via e-mail at in case you have any questions.

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