Ortofon measurement test chain.
How we at Ortofon perform the tests of cartridges during the production process.
The Ortofon measurement test set-up is a PC-based test system
Prior to testing, the cartridge is mounted on a special headshell, that has been optimized for repeatable and reproducible use.
The cartridge is connected to an amplifier, that is adjusted for an input impedance of either 100ohm, 200ohm or 47kohm/220pF (cable capacitance incl.) depending on two following elements:
- The impedance characteristics of the cartridge
- The type of cartridge, i.e. Moving Magnet or Moving Coil
Then the signal is amplified with a gain of +40dB for MM and +60dB for the MC types.The amplifier has a switch for measurements with/without RIAA-equalization. For lower frequencies below 1kHz the test is being performed with the RIAA equalization curve set on the ON/automatic switch. For high frequency tests the switch is set on OFF allowing maximum bandwidth since the records have been cut linear and non-equalized.
Subsequently the signal is converted through an AD-converter and filtered for optimal use of the PC capacity. Finally, the data is stored on a hard disk.
For each MM/MC model a set of limits, reflecting the performance of the cartridges, is being used.
After the system has been hooked up, a calibration sequence is initiated and the data stored. The sequence compensates for changes in the temperature, humidity etc. The calibration sequence also compensates all cables, impedances, gain etc in the measurement chain from the headshell to the PC
Three sequences of the measurement test
1. Testing sensitivity, channel separation and balance: we use track 1 and 2 on the DUAL PVK 321. The measurements are performed at 1kHz with a speed of 5cm/s. The AD-sampling is at 40 kHz, an average of 1000 measured data is used. The filter is a Bessel IIR Band Pass of 6th order with cutoff frequencies of 50Hz and 10kHz
2. Testing tracking: we use track 4 on DIN 45549. Detection of tracking is performed at 315Hz. It is chosen to register on the 4th, 5th and 6th harmonics in an FFT signal analysis. The filter is similar to what is applied in the first test sequence.
3. Testing frequency response: we use the Technical Record Series from JVC -1005 track 1-6. For this test the sampling is performed at 250 kHz, and an average of 3000 measured data figures is used. The filter is a Bessel IIR Band Pass of 3rd order with cut off frequencies of 500Hz and 80kHz.
The steps in the Ortofon measuring chain are subsequently:
1. Cartridge mounted in test headshell and/or tonearm
2. Amplifier with RIAA switch
3. AD converter
4. BandPass filter: 6th order Bessel (IIR)
5. PC (Results for QC)
6. Store Data on HDD
Test equipment applied by ortofon (subject to changes):
Record Player Acoustic Solid - Classic Wood
Vibration damped table Ortofon Design
Tonearm SME IV / Ortofon TA-110
Headshell Special Ortofon Design
Amplifier Modified Lehmann Black Cube with a RIAA switch
AD converter National instruments PCI-6280 18 bit Sample rate of 625kS/s
Program Special Ortofon design in Labview
Test records used:
DUAL PVK 321 Track 1 and 2
DIN 45549 Track 4
JVC - TRS 1005 Track 1 to 6
Ortofon Test Record
Due to record wear, test records are replaced with a fresh example every 6 months.
Environment during testing:
Temperature: 22-25 degrees
Humidity: 40-80% R.H
Calibration equipment (subject to changes):
Function Generator Agilent 33210A
Multimeter Hewlett Packard 3478A
Frequency Counter Hewlett Packard 5316A
