It’s important that customers understand that advertised record weights – be they 200 grams, 180 grams, 150 grams or so on – are in fact approximations based on the die and stamper profiles used for the pressing of that title. Record weight will vary from title to title based on a number of factors explained below.
There are three main parts to the equation of a pressed record.
The first part of the equation being the pressing die or molds used to press the record. One mold is used for each side of the record. The cut of each mold must match a chosen surface profile, which determines the shape of the record. At Quality Record Pressings, our pressing die profile, like most others, has a thick label area matched in thickness by the outer edge of the die. This allows the pressed records to stack without the groove area touching while the record cools prior to inspection and packaging. If you placed the two molds together (face to face) you would see an area that is the same shape as a pressed record. The idea being that once a stamper is mounted to each of the molds the hot vinyl can be inserted between the molds and pressed to fill this cavity between the molds to produce a record. As the molds squeeze the vinyl, the groove guard at the edge creates backpressure that allows the vinyl to mold to the stamper surface and not just exit out the edge of the molds (low or no backpressure equals non-fill in the pressed record). We have worked closely with Bob Roczynski, president of Record Products of America, in developing a die profile that will allow for 200 grams of vinyl to fill this void between the molds.
The second part of the pressing equation is the nickel stamper. The pressing mold has a pitch from center to edge that must be matched by the stamper, producing a flat pressing surface that, once the stampers come together with vinyl in between, will then mold the vinyl record.
The third part of the equation is the groove geometry. Dynamic range, volume levels and type of music are all factors in determining how the record will mold and finally have a lot to do with the weight of the pressed record. A wide dynamic range produces a groove that can vary greatly in depth and width from the beginning to the end of a side. On the stamper, a cut groove is inverted so as to produce a groove in the pressed record. This inverted groove produces a barrier to the vinyl as it spreads from center to edge during the pressing sequence. If the groove geometry varies greatly the vinyl will actually spread at different rates across the stamper surface. The pressing cycle is then adjusted to compensate and mold the vinyl evenly across the stamper surface. This is why pressed records will vary in weight from one title to another even though the die and stamper profile stay constant.
In short, our 200-gram profile is just that; a profile that will produce records of varying weights. As we adjust to the innovations we have come up with here at QRP we fully expect our record weights to vary less, but they will vary.
In the case of the Cat Stevens Tea for the Tillerman LP, groove geometry definitely came into play. From loud vocals to very low-level acoustic guitar to a tight, intense bass, this one ran the gamut. We had to squeeze and work the vinyl a bit more than usual to allow the vinyl to mold from the inner diameter to the outer edge and everything in between. Usually, you will find a recording will have one or two tracks that might give molding fits. In this case, virtually every track presented challenges to molding a good LP. You might say that the mastering engineers may have showcased what can be done with today’s cutting electronics. Even with the backpressure created by our groove guard, we still lost more than the usual amount of vinyl out the edge and into the flashing (the trimmed-off portion) of the LP. This resulted in a record that just did not want to mold at 200 grams. In the end, a recording has a sweet spot where it will press a listenable LP, and that’s not always at the exact planned weight. We use a mold that should produce a 200-gram vinyl record. Depending on the musical content and dynamic range it should be close to 200. In the case of Tea for the Tillerman we weighed one randomly and it was 186. Now, if we had used the 180-gram mold, it could have turned out to be 166.