TurntablePSU.comReviews and Technical Analysis
Rega Neo TTPSU
Overview
The $395 Rega Neo TTPSU is a dual frequency supply that uses DDS to generate the 33/45 RPM sinewave signal. Despite the claim that the PSU uses DSP, it uses a conventional PIC processor and a dedicated Analog Devices AD9837 28 bit DDS. The PIC 16F1827 processor uses a 4.00 MHz ceramic resonator separate from the DDS cystal controlled clock. There are 2 buttons on the front panel, an on/off switch and another for switching between 33 and 45 RPM; the Rega Logo is back lit with a red LED for 33 and green for 45 RPM. The back panel has the 2.5mm barrel connector for power input, a 4 pin DIN connector for the motor, a momentary switch to put the unit into frequency program mode, an LED to indicate program mode and a rotary encoder to change frequency; the encoder switch uses a 1/16" hex drive (allen wrench) to make the adjustments (not included).
The TT-PSU is powered by a 120VAC input, 24VAC 500mA output wall wart and the PSU has one output (DIN PD-40S 4 pin) to the turntable with 24VAC on 2 pins and zero or 21VDC between the other 2 pins to switch the phase cap in the turntable between 33 and 45 RPM. Like most of the other PSUs on the market, the TT-PSU uses 50/60 Hz for 33 RPM and 67.5/81 Hz for 45 RPM, so the turntable belt must be installed on the small spindle of the pulley (33 RPM).
The Neo TTPSU is housed in a one piece aluminum extrusion with plastic front and rear panels.
Operation
The Neo TTPSU is factory set for 50/60Hz at 33 RPM and 67.5/81Hz at 45 RPM. There is an internal jumper (SK2) that selects 50Hz (jumper out) or 60Hz (jumper in). You must cycle power after changing the jumper. There are output level adjustments internally for both 33 and 45 RPM. Frequency adjustment is done in 33 RPM mode only, with a momentary press of the program switch recessed in the back panel. The program LED will be illuminated when in this mode. The rotary encoder is used to increase or decrease the frequency with a maximum range of +127 steps and -128 steps of ~0.015Hz per step for a total range of ±1.9Hz. Each step equates to ~0.01 RPM with a 50Hz pulley or ~0.00825 RPM with a 60Hz pulley. The rotary encoder has no stops and if you exceed 127 steps in the positive direction, it will roll over to the lowest frequency setting and continue counting up; if you exceed 128 steps in the negative direction, it will roll over to the highest freqeuncy setting and continue counting down. There is no indication of the frequency within the setting range. There is only one frequency setting for both 33 and 45 RPM (the same offset is applied to both speeds). When the speed is set correctly, a momentary press of the program switch will save the frequency setting and it is unaffected by power cycling. The program LED will blink every 10secs to indicate the PSU is not at the factory settings.
To restore the PSU to the factory settings, select 33 RPM; press and hold the program switch. The program LED will start flashing, then stay on continuously. Release the program switch. Momentarily press and release the program switch while the program LED is on continuously to restore the factory frequencies for both 33 and 45 RPM.
Circuit Description
The clock source for the Analog Devices AD9837 DDS chip is a 4.00 MHz 100PPM crystal so the frequency resolution is 0.0149011612 Hz. This is an odd choice for the crystal as it produces a frequency step that does not allow exact setting to 50/60 or 67.5/81 Hz. If they had used a 4.194304 MHz crystal instead, (a standard value), the frequency step would be 0.015625 Hz (1/64 Hz) and the PSU could be set to exactly 50/60Hz. The output of U6 pin 10 is a 630mVPP sinewave; VR2 and VR1 set the 33 and 45 RPM output levels. Front panel switch SW4 selects VR1/2 output and is amplified and filtered by U4B TLC072 dual opamp. The output of U4B drives a bipolar commplimentary push-pull amp consisting of TR5/6 and TR8/10. The output of the amp is one side of a BTL arrangement; an identical amp consisting of TR1/2 and TR3/4 provides the other output via inverter U4A. The 2 halves of the bridge are 180 deg out of phase and provide 24VAC from ±36VDC rails. The second half of SW4 (33/45 RPM switch) provides 21VDC when 45 RPM is selected on the output DIN connector pins 3 & 4 to switch the phase cap between 33 and 45 RPM on the turntable motor PCB.
Measurements
The output frequency at 33.3 RPM measured 49.993/60.007 Hz and 67.472/80.988 Hz at 45 RPM. No load voltage was 24.1VAC; the output dropped to 24.0VAC at 3W.
Specifications
Nominal Speeds............................33 and 45 RPM
Speed Stability..............................0.01% (100 PPM)
Distortion (Freq Generator).............0.065%
Distortion (24VAC output)...............0.1%
Pitch Control.................................±1.9Hz (±1.0 RPM with 60Hz pulley)
Output Power................................3W
Output Impedance........................<1 Ohm
Reduced Voltage...........................Internal Adjustable 17-35VAC
Turntable Connection.....................24VAC on a DIN PD-40S 4 pin connector
Outboard Supply...........................120 or 240VAC input 24VAC 350mA output
Dimensions...................................5.2"W x 3.8"L x 1.5 H
Weight..........................................8 Oz.
Retail............................................$395
Rega TT-PSU
Overview
The $395 Rega TT-PSU is a dual frequency supply that uses 2 fixed frequency crystals to generate the 33/45 RPM sinewave signal. The clock source for 33 RPM is a 3.93216 MHz crystal (60 Hz) or a 3.2768 MHz Crystal (50 Hz). The clock source for 45 RPM is a 5.32021 MHz crystal (60 Hz) or a 4.433618 MHz crystal (50 Hz). All crystals have a frequency stability of .01% (100 PPM). There are 2 buttons on the front panel, an on/off switch and another for switching between 33 and 45 RPM; the Rega Logo is back lit with a red LED for 33 and green for 45 RPM.
The TT-PSU is housed in a one piece aluminum extrusion with plastic front and rear panels.
The TT-PSU is powered by a 120VAC input, 24VAC 500mA output wall wart and the PSU has one output (DIN PD-40S 4 pin) to the turntable with 24VAC on 2 pins and zero or 21VDC between the other 2 pins to switch the phase cap in the turntable between 33 and 45 RPM. Like most of the other PSUs on the market, the TT-PSU uses 50/60 Hz for 33 RPM and 67.5/81 Hz for 45 RPM, so the turntable belt must be installed on the small spindle of the pulley (33 RPM). The manual advises the user to start in 33 RPM mode and switch to 45 RPM rather than starting in 45 RPM mode. There is no tempo or calibration adjustment for either speed.
Circuit Description
The selected crystal is divided down by a 14 bit digital counter and 2 flip flops for a total divide ratio of 65536. The crystal frequencies used for 33 RPM divide down cleanly to 50 or 60 Hz, but the crystals used for 45 RPM do not divide to exactly 67.5 or 81 Hz. Standard value crystals are used and the output frequency is 67.65 Hz and 81.17 Hz. The outputs of the divider chains are square waves so this must be filtered by a 2 stage 4 pole Sallen-Key low pass filter with cutoff frequencies of 37 Hz (33 RPM) and 45 Hz (45 RPM). One of the 2 frequency outputs is selected by the front panel switch and sent to an NE5532 opamp driving a complimentary bipolar push pull amp in bridge tied load (BTL) mode to develop 24 VAC from ±20VDC rails.
Measurements
The output frequency at 33.3 RPM measured 60.00 Hz and 81.2 Hz at 45 RPM. No load voltage was 23.8VAC; the output dropped to 21.2VAC at 3W.
Specifications
Nominal Speeds............................33 and 45 RPM
Speed Stability..............................0.01% (100 PPM)
Distortion (Freq Generator).............0.65%
Distortion (24VAC output)...............2.4%
Pitch Control.................................Not adjustable
Output Power................................3W
Output Impedance........................23 Ohms
Reduced Voltage...........................Not available
Turntable Connection.....................24VAC on a DIN PD-40S 4 pin connector
Outboard Supply...........................120 or 240VAC input 24VAC 500mA output
Dimensions...................................5.2"W x 3.8"L x 1.5 H
Weight..........................................8 Oz.
Retail............................................$395