Wurlitzer Cobra Phonograph Cartridge vs. Magnetic Cartridge

Wurlitzer Cobra Phonograph Cartridge vs. a Modern Magnetic Cartridge

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This is a before an after comparison of a Wurlitzer 2250 Jukebox that has been converted from using a Zenith Cobra to using a Stanton SM.V3 Magnetic Cartridge. The existing Cobra equipped tonearm was modified to use a Stanton SM.V3 cartridge. For more information on the conversion, click here. For the sample audio, the auxiliary amplifier output on the Wurlitzer 532 amplifier was used. This means that the audio path includes the ALC (Automatic Level Control) of the 532 amp but not the tone controls. The magnetic cartridge definitely sounds better, which was the primary reason for converting to a magnetic cartridge. There was an additional benefit to converting to the magnetic cartridge. With the Cobra it would pick up a noticeable hum on the lead out groove from the turntable motor and with the magnetic cartridge that hum is greatly reduced.

Below are some FFT plots that show the frequency spectrum of some samples taken with the Cobra and the magnetic cartridge. These plots do not necessarily represent the frequency response of the cartridges since the source material was music and not white noise. The plots do allow the two cartridges to be compared to each other. All of these selections are mono records and were chosen by how much high frequency content that they seemed to have when played back with the Cobra cartridge. One thing noticeable on the plots is that the magnetic cartridge had a higher output in from 1kHz and above with the exception of the 6kHz-14kHz range. I suspect that range had higher noise in that range due to the distortion from the cobra. I think the vane on the cobra has some odd resonance that can be heard in the output. Also, you can notice a narrow peak around the 120Hz range. This must be from the turntable motor. The peak at 120Hz is lower with the magnetic cartridge.

Comments:
While the plots do show the difference in frequency response relative to each other, they do not reflect the difference in distortion between the two cartridges. The audio samples included help somewhat to make that comparison. When it comes to playback through the jukebox, the difference is significant. There is better response with the higher frequencies and less distortion. Also, there is less worry about extra wear on stereo records because of the lack of vertical compliance and no problems with distortion (see stereo samples with distortion below). I would recommend this modification to anyone that is less than happy with the sound quality from their cobra equipped Wurlitzer or for playing stereo records in a cobra equipped Wurlitzer.

Wurlitzer Cobra Phonograph Cartridge vs. a Modern Magnetic Cartridge

Sample 1 FFT Plot: Cobra Cartridge vs. Magnetic Cartridge

Sample 2 FFT Plot: Cobra Cartridge vs. Magnetic Cartridge

Sample 3 FFT Plot: Cobra Cartridge vs. Magnetic Cartridge

Distortion when playing stereo records with the Cobra cartridge.