emt 140 plate sounds dark, muffled.

My friends  emt 140 plate sound muffled. I have not looked into it due to schedule but I did get to hear it.  Compared with his second plate, it's much different.  It sounds super dark.  Since  it is on both outputs of the plate,  I wanted to rule out the plate electronics(solid state) and I am thinking that it would either be a broken clip causing a tension issue. or that there is a pick up problem.

Anything I should check out or does anyone have an EMT 140 service manual?

Get the side off it.  You might find that some or one of the tiles has become unstuck from the damping plate & is impeding the free movement of the plate.  Or something else might be against it.

Rob Flinn said:

Get the side off it.  You might find that some or one of the tiles has become unstuck from the damping plate & is impeding the free movement of the plate.  Or something else might be against it.

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Will do.  Thanks...

Well we pulled it apart and there are no loose tiles, there are no broken clips and the plate has free movement.
We plan to check electronics,  but it would be unusual to have both outputs(returns from plate back to desk) sounding dark. I am convinced that there is a transducer issue, or pickup issue, but that is only because I convinced myself of that. As far as I know the electronics are fine.  We have a spare set of electronics that once I get tubes for, we can swap and see if that makes an improvement.

Just thinking out loud but you could make a cable with one end for the drive transducer connector and the other end for the pickup transducer connector and then integrate a simple resistor load / attenuator into the cable that loads the driver correctly with a resistor and then another 3 resistors for a t-attenuator of -60dB (or whatever the level difference is). So the load impedance at one end is 8 ohms (or whatever the drive transducer impedance is) and then the impedance of the other end is whatever the impedence of the pickup is (no idea, 10k-ish maybe?). Then use that cable to bypass the transducers and plate and listen to it, take a frequency response measurement, noise measurement and so on. Then you can determine definitively if it's the electronics or transducers / plate.

Swap the electronics, does it change the sound? If it is still bad then Tap the plate, is the sound OK?  If OK, then is the DRIVER out of alinement and or JUNK in the gap can cause a bad sound.  Are all of the tension torque the same.

Audio1Man said:

Swap the electronics, does it change the sound? If it is still bad then Tap the plate, is the sound OK?  If OK, then is the DRIVER out of alinement and or JUNK in the gap can cause a bad sound.  Are all of the tension torque the same.

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Hello duke, Yes a physical tapping on the plate yields an expected good sounding plate.  Yes tensions on the plate  and clips are the same.  Yes I thought about the driver as a culprit,  But have not tested that yet.  It's not a bad sound it's just a dull/dark sound, the high end is easily not there. Compared to a second plate that is known good the high end is really not there.

This is crude, but does your “tapping” test have similar top end to “tapping” on the good sounding plate?  If so, it’s most likely driver related. (Or something on the “send” side of things, at least.)

I have an ecoplate that I use two ways - the original mounted driver and a small speaker hanging about 10" away. Sound very similar.
Easy way to test if the driver is the problem. Just put a speaker close to the plate and see if the output sounds good.

Drivers on plates get blown. They are basically a speaker coil. Might need a re-wind.

We do have a spare driver, I don't know if it's working or not. I will try the speaker test too and see.  This is my first foray into handling a plate reverb. While I am good with the electronics side and as simple in theory as a plate is, there is a lot going on.

pucho812 said:

We do have a spare driver, I don't know if it's working or not. I will try the speaker test too and see.  This is my first foray into handling a plate reverb. While I am good with the electronics side and as simple in theory as a plate is, there is a lot going on.

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Almost as simple as looks in principle... one transducer wiggles the sheet metal, another reads it.

You can tell that the receive end appears OK so problem is with send amp or transducer.

JR

You can narrow this down quite easily without swapping anything out.  If you tap the plate with a screwdriver you will know whether the playback side has any top end when you listen to the output(s).    If you have top end then the problem lies with the driver, if you don't have top end then look at the output side of things.

Rob Flinn said:

You can narrow this down quite easily without swapping anything out.  If you tap the plate with a screwdriver you will know whether the playback side has any top end when you listen to the output(s).    If you have top end then the problem lies with the driver, if you don't have top end then look at the output side of things.

Click to expand...

already did that yesterday

JR

Some drivers have an alignment adjustment and if it is out of adjustment, the driver will rub. (like a speaker coil rubbing).

yes, and that will reduce high end a lot

there are alignment rings that can be used,
or wear a pair of headphones and listen to the plate as you move the driver.
you will hear the high end come back as it centers.