Testing direct drive turntables
Turntables to be tested
Turntable -> Carver C-1 preamp ->Audigy 2 ZS
Audacity + Creative WaveStudio 7. Recording
Test of the background noise of recording track after turntable
Image 1. No signal on open AUX input, soundcard itself:
That pick at the 60 Hz will be carried out in all spectrograms
2. No signal on MC open input
3. No signal on open MM input
4. MM Cartridge connected.
much within Carver’s specs for phono stage to have about 80 dB noise floor in
the main audible region.
Part I. Motor without plinth. Arm in the pod standing alone.
A. Technics EPA 100 tonearm.
5. No signal on MM input with Stanton 681 connected (recorded with Audacity)
comparison I had the same signal recorded by Creative. No difference in
Spectrogram on the Image 5 has to be taken as the common background
for all following measurements.
6. Needle on the table, motor is not spinning (Recorded with Audacity)
7. Needle on the table, motor is spinning 33 (Audacity)
of the spectrograms 6 -7 showed an unexpected for me results: there is big (20
dB) component of the noise in the 6 – 40 Hz region that present even when motor
is not spinning. I had no idea where it came from. So I’ve decided to change my
setup a little.
B. Marble base under tonearm, rubber spheres under SP-10.
Image 6 and following. Needle is sitting on the aluminum block on the top of
the motor unit:
The same exact effect, even with another tonearm
8. Just Arm (Signet):
9. Arm on the motor, no spin
needs to continue, something is wrong here. The only valuable data is existence
of the free arm resonance at the 20 Hz. To check if there is something
originated that signal in the motor, I’ve tested the case when needle is rested
directly on the table.
same result. The problem is not in the SP-10 unit. Let’s try another setup.
Setup C. To exclude possible influence of the vibrations coming from the
floor, I put a 60 lb granite slab on the table.
on the marble base is sitting on the aluminum block.
10. Arm in the air
11. Arm’s on the table. Motor is not spinning.
Image 12. Arm’s on the motor spinning 33.
curve with additional 10 dB added in the region below 100 Hz. Now, when I’ve
isolated influence of the base, the only possible source of those resonances
could be only air. Nothing can do about it right now.
check it again, two tests without the SP-10. Granite slab 60 lb as a base.
13. Tonearm itself, cartridge in the air
14. Tonearm on the base, cartridge lowered on the aluminum block sitting on the
same strange behavior. Time to test stock unit.
Part II. Original Technics obsidian plinth SP-10B3, EPA-100 tonearm
15. Arm itself
Image 16. Arm on the motor without spin
main difference is that resonance of the arm returned back to the expected 10
Hz. Other than that everything looks the same.
17. Arm on the motor spinning 33
Conclusion: When you
subtract spectrum 15 from 16, and then result from the 17, the only area that
showed 2 – 5 dB increase of the noise signal (potentially associated with the
rumble) is from 20 Hz to 40 Hz.
Bottom line, this method of the “in home” rumble measurement is
inaccurate and not conclusive.
Part III. My budget “universal” plinth
To Be Continued .....
for a comparison a few spectrograms taken when playing some records:
record, 1 KHz test signal
record, “Quiet” groves
Sinatra recording 1.
Sinatra recording 2:
can see that spectrum easy goes up to 20 kHz even without proper cart-arm
adjustment in my primitive setup.