eric343
Member of the Trade: Audiogeek: The "E" in META42
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- Jun 23, 2001
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Recently, I modified my Arcam CD72T player by adding an opamp socket that would allow me to easily swap the opamps in the output analog stage. While my Arcam was open, I pulled out a very sensitive vibration sensor and hooked it up to my Tektronix 7000-series mainframe oscilloscope (which I set to 5mV scale). Placing the sensor on the clock crystal and then on the actual transport itself revealed that there was very little vibration damping inside the CD72T itself, as the sensor picked up nearly equal vibrations in both places.
Therefore, I began testing. Placing squares of foam (non-sorbothane stuff, the kind used for packing) under the feet caused a seriously noticeable decrease in external vibrations - at least 80% to my eyes. (external vibrations being defined as those caused by the noisy little muffin fan sitting on the bench vise) Note that the sensor was still able to pick up the vibration caused by my stamping hard on the cement floor of my workshop... I then slid a square of the same foam under the main PCB, so that it would be directly under the clock crystal. Placing weights in various places in the bottom of the metal case or on the transport or near the clock crystal caused very little decrease in vibration, probably around 10% at the most. I did not have any sandbags to try.
The breakthrough came when I noticed a very heavy plumb-line weight with attached string on my shelf. I ran the line over the front panel (which stuck approx. 1cm out over the edge of my bench) to the back corner (the back panel had been removed in order to remove the mainboard) and around the left side to pinch between the front-left foot and the foam blocks under it. This eliminated a good 70-90% of transport-induced vibrations as measured *on top of the transport itself* despite the plumb weight's string never coming into contact with the transport, making the plumb weight the most effective vibration damper I tested. Oddly enough, however, the plumb weight did not seem to decrease vibration at the clock crystal very much.
Any comments? Questions? Flames?
Therefore, I began testing. Placing squares of foam (non-sorbothane stuff, the kind used for packing) under the feet caused a seriously noticeable decrease in external vibrations - at least 80% to my eyes. (external vibrations being defined as those caused by the noisy little muffin fan sitting on the bench vise) Note that the sensor was still able to pick up the vibration caused by my stamping hard on the cement floor of my workshop... I then slid a square of the same foam under the main PCB, so that it would be directly under the clock crystal. Placing weights in various places in the bottom of the metal case or on the transport or near the clock crystal caused very little decrease in vibration, probably around 10% at the most. I did not have any sandbags to try.
The breakthrough came when I noticed a very heavy plumb-line weight with attached string on my shelf. I ran the line over the front panel (which stuck approx. 1cm out over the edge of my bench) to the back corner (the back panel had been removed in order to remove the mainboard) and around the left side to pinch between the front-left foot and the foam blocks under it. This eliminated a good 70-90% of transport-induced vibrations as measured *on top of the transport itself* despite the plumb weight's string never coming into contact with the transport, making the plumb weight the most effective vibration damper I tested. Oddly enough, however, the plumb weight did not seem to decrease vibration at the clock crystal very much.
Any comments? Questions? Flames?
