[quote author="Dale Manquen"]Some of the things we learned while designing the Martech EMT upgrade might be helpful:
Place the pickup preamps close to the pickup amps. This minimizes the cable capacitance and loss of signal. We used a FET op amp with a bit of EQ and 20 dB of gain as a buffer, then fed this to a balanced line driver.
We utilized the EMT HF equalization - a boost on the high end to compensate for the mass of the plate.
When we got to a really clean sounding, we found that the EMT high pass filter really wasn't desirable. We had half-octave selection, but most of the scoring stages in Hollywood (which all use Martech-upgraded EMT plates) run them flat on the low end.
We used an amplifier capable of 30 watts peak.
With a +4 dBm reference level, the narrowband dynamic range at 1 kHz was about 130 dB. We had about +26 dBm peak output capability. When operating on our Neve VR console, the noise of the plate was about at the same level as the noise of the mix busses.
Your driver is clever, but I have a couple of comments. Is the post attached to the plate so that it can push and pull equally well? I would be inclined to have a cone on the top of the dowel, trying to create a point source.
We included a warble tone generator that could be used to inject a line level signal for setting the driver and pickup circuits gains. This isn't hard to simulate if you have a function generator with a VCO input.
I can't tell where you have placed your pickups for stereo, but they should be asymmetric.
If you do things right, the output from the plate should sound like clean music, not a steel plate. You may have a problem until you get a damping plate rigged because of your long decay time.[/quote]
Thank's ! that information is very appreciated :grin:
I've kept the cables from the pickups as short as possible, then into a JFET-amp with about 20dB of gain + a buffer amp. The line-signal is unbalanced, but very silent though.
When you speak about the HF eq, do you mean the driver-signal ?
I've changed the low-cut to about 130 Hz, 6dB per octave.
It's easier for me to cut the low-end, rather than boosting the high-end.
Concerning the driver: the post is glued (super-glue) to the plate, since i didn't want to make a hole in the plate before I had tested it.
This is just a setup for testing, really. I took an old Hi-Fi speaker and cut the cone off.... but it works remarkably well :!:
I'll make a new post from metal I think. I'll also make it cone-shaped.
The pickups are placed about an inch asymmetric along the x-axis and symmetric in y-axis... is that correct, you think :?:
I'm working on the damping... how thick is the original damping-material ?
Thank's again for the feedback ! :guinness: :thumb:
