DYNAMIC SOUNDS ASSOCIATES Phono III
Page 32 of 38
USER MANUAL
It will be noted from the curves shown in Figure B.2 that the largest difference between the RIAA
EQ and the others is at the LF end of the audio spectrum. At 10 kHz the differences between all of
them is on the order of
2dB, whereas the differences at 50Hz are 4-5dB, with the RIAA EQ
providing excessive LF boost for some, and not enough for the RCA (Old). With reference to the
older EQ curves in Figure B.1, the differences between the RIAA and the other EQs are
significantly greater.
The following from reference [4] is a guide to identifying some 1950's recordings that used the
RIAA EQ standard.
“ORTHOphonic” or “New ORTHOphonic” (after August 1952), “NARTB” or “New NARTB”
(after June 1953) or “New AES” (after 1954) indicate RIAA equalization.
The following labels should have used only RIAA: Argo, Bethlehem, Classic Editions, Chess,
Clef, Composer Recordings, McIntosh, Montilla, New Jazz, Norgram, Prestige, Romany,
Roulette, Savoy, Vocalion and Walden [High Fidelity Magazine, MidiMagic].
A “HIFi+” sticker on American Columbia's or the catalogue number written in an inverted
triangle on German records (like Deutsche Grammophon) is a symbol for RIAA.
B.3
DESIGNING EQ CURVES FOR THE PHONO III
B.3.1 Design Approach and EQ Curves
For the original Phono ONE, and later the Phono II, Dynamic Sounds Associates (DSA) designed a
highly accurate RIAA EQ curve for playback. In addition, the Phono ONE also included the option
of adding a 3.18μsec time constant to the playback, which would roll-off the decreasing HF
response at about 50 kHz. This was supposed to correct for some cutter-head issues; however,
this has largely been proven unnecessary, and is not part of the RIAA EQ. This option is not
included in the Phono II or the
Phono III
.
In designing the DSA
Phono III
, our desire was to complement the RIAA EQ curve with the addition
of additional EQ curves that can be selected by the user at time of playback. However, a decision
had to be made regarding the number of alternate EQ curves and which ones were to be
included. To allow for the addition of other alternate EQ curves in the future, it was decided to
develop a "plug-in" module for this purpose instead of a "hard-wired" solution.
In reviewing the information on the various EQ curves shown previously, it became apparent that
there was a good degree of commonality between EQ curves that could be combined into two
"groups" identified as those based on 78 RPM EQs, and those that were after that period but prior
to the universal adoption of the RIAA EQ curve. In addition, there was considerable commonality
between the t2 time constant used by Columbia and Decca/FFRR during these two periods which
led to the decision to base the design of the "stock" EQ module for the
Phono III
on the EQ curves
from these two vendors.
Table B.1
shows the time constants associated with the two groups of
EQ curves, and how they compare within each group and with the RIAA standard.
Based on
Table B.1
, a plug-in module was designed that incorporates all five of the EQ curves
shown. The selection of a particular EQ curve is done for each input by using a pair of switches
located behind the lower central door on the front panel of the
Phono III
. (This is shown in detail
in Section 3.5.) The EQ curve selection follows the selection of MC or MM cartridge loading for
each input.
