VG-8 & VG-88 Modifications
VG-8 SUBSONIC SENSITIVITY REDUCTION MODIFICATION
WARNING – If you blow anything up, its your fault, even if we told you to do it.
This article was found, in a donatory sort of way, by Gunnar Backman whose whereabouts (for the sake of this article anyway) are currently confidential. Not all the info you need to safely carry out suggested tasks is included as this would take up inordinate space. We are presuming you know all about Static Safety Precautions, RHoS compliance, and the WEE directive. Even so we strongly discourage the wearing of nylon clothes when using a soldering iron. Do not play the guitar in the bath.
VG88 – Ovation patch
Picture & mod info courtesy Gunnar Backman
RMC VG-8 INPUT FILTER MODIFICATION
This VG-8 modification is designed to remove the subsonic (very low frequency) content of the separate string signals (produced primarily by piezo hex pickups). This helps the VG-8 perform more cleanly and without puffyness, especially when using the detuning (pitch shifting) functions. There aren’t any negative side effects to this modification. Everything works the way it should, only better. Subsonic filtering is like what you may have in your stereo for the turntable preamp. It removes non-musical, mechanical vibrations that are detected along with the desired sounds and relieves the signal processing circuitry of a lot of useless, and sometimes unwanted, work. The result is cleaner attack transients. This modification consists of changing capacitor values in the analog “front-end” of the VG-8, which attenuates subsonic frequencies which can otherwise enter freely and upset the performance of the overdrive and pitch shifter in some cases. By changing 12 electrolytic capacitors in the analog front end, frequencies 25Hz and below are significantly reduced and the low-frequency saturation symptoms go away. This can be accomplished by a competent electronic repair technician. The VG-8 modification consists of changing these electronic components and testing the modified unit for proper function. – RMC / Richard McClish.
RMC don’t perform this modification any more. We simply provide the recipe. Please find it below. The VG-88 has similar circuitry and can be modified in a similar manner. The component numbers are different however, we are trying to locate this info, so be extra careful if attempting this from scratch.
There are 12 capacitors to change in order to reduce the subsonic sensitivity of the VG-8 and VG-88. This helps to significantly reduce the objectionable thumping and/or momentary distortion which may occur in the amplified sound when the string tension and/or the pickup to string distance is changed abruptly.
The same problem typically arises with a GK-2 in proximity of a tremolo bridge. Because the bridge moves up & down with changes in string tension as you move the tremolo arm, this produces objectionable subsonic signal components (which can be much larger than the useful music signals) and adversely influence the A/D conversion in the VG-8.
The mod is a simple capacitor substitution which is of no consequence in the audio spectrum. It simply helps to maintain the A/D converter in its linear mode of operation.
The following caps refer to the VG8 only:
1) Replace C25, C29, C33, C37, C41 & C45 (all 10uF) with 0.22uF (metal film, electrolytic or ceramic) capacitors.
2) Replace C201, C202, C203, C204, C205 & C206 (all 10uF) with 0.33uF (metal film, electrolytic or ceramic) capacitors.
The Roland p.c.board has legend information which makes locating the components easy. The work takes usually less than an hour to perform.
The parts are worth less than US$10.
You want capacitors somewhere between 16V and 50V (it’s mostly a size issue) and you want radial caps (with both leads at the same end like the originals, since these capacitors are standing vertically on the board).
You have a choice of either a standard aluminum electrolytic or a tantalum electrolytic cap. They both work well. If you just look for something small, it should work fine. This is not a critical application and the portion of sound you’re filtering is not in the audio spectrum. Let a competent electronic technician handle the capacitor selection if you have a problem deciding.”
Good Luck.Return to the Unfretted Archive