Modifying the EJ-10 Crab box

Discussions around meetinghouse sound systems, microphones, assisted listening devices, and translation equipment
russellhltn
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Modifying the EJ-10 Crab box

Postby russellhltn » Sun Oct 04, 2020 1:54 am

As many of you know, the EJ-10 is a useful idea, but it can fall short. The sound is "audible" but tends to fall short of "adequate". I've had expeerence in the past with it sounding "muffled". Meanwhile, the EJ-8 will get volumes close to "youth dance" level.

Least you think I'm exaggerating, some time ago, shanebankhead ran some tests and found a 30dB difference in the output. In terms of the human ear, that will be perceived as 8 times louder.

What's the difference? I finally sat down and compared the schematic. As it turns out, there's not much difference. I can't tell if there's a difference in the transformer, but I'm guessing it's a 1:1. There's only 4 component values different. I changed them out for a cost of $1.25 in parts. Wow what a difference! I didn't do a direct comparison with the EJ-8, but it's more than loud enough. I'm calling the modified box an EJ-8T. The "T" is because the telephone interface is still connected. Surprisingly, it doesn't make much if any difference. If I were to disconnect it, I'd have to do something to make it obvious, such as removing the RJ-11 jacks. (I hate when someone disables something and fails to leave a note for the next person.) So, it appears the trouble if disconnecting it isn't worth it.

See the attached photo for what needs to be changed. If you're handy with a soldering iron, it's well worth it.
EJ10 mod.jpg
EJ-10 modification
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Mikerowaved
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Re: Modifying the EJ-10 Crab box

Postby Mikerowaved » Sun Oct 04, 2020 11:39 pm

Bless you! The phone patch on our stake center's EJ-10 has never been used or even tested to my knowledge. I wished many times we just had an EJ-8. There have been times when I've had to run to another building to fetch an EJ-8 because the EJ-10 maxed out would not allow enough audio through to be heard over the sound system. One time was with a visiting GA on a Sat evening session of stake conference. Not fun!

Your research is much appreciated!
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jimbo3san
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Re: Modifying the EJ-10 Crab box

Postby jimbo3san » Wed Feb 17, 2021 12:12 am

Do you happen to have the schematics or a reference link to them? I found one for the EJ-10 but not for the EJ-8. I opened the EJ-10 and started mapping out the circuit board but I haven't finished yet. The one I have is a different version thatn the one shown in your pic too. I think it is pretty close to the same thing but the components are laid out differently.

A schematic diagram from EMTech would be the easiest to work with.

Thanks!


Jim B.
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russellhltn
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Re: Modifying the EJ-10 Crab box

Postby russellhltn » Wed Feb 17, 2021 11:14 am

There are at least two versions of the EJ-10. I need to create directions for the "Rev B".
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CalS201
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Re: Modifying the EJ-10 Crab box

Postby CalS201 » Fri Feb 19, 2021 2:26 pm

jimbo3san wrote:Do you happen to have the schematics or a reference link to them? I found one for the EJ-10 but not for the EJ-8.


This forum post includes the schematic for the EJ8
https://tech.churchofjesuschrist.org/forum/viewtopic.php?f=140&t=5933&p=49884&hilit=ej8+or+ej10#p49884

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Mikerowaved
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Re: Modifying the EJ-10 Crab box

Postby Mikerowaved » Sat Apr 10, 2021 1:00 am

Attached below are the modifications for the EJ-10 "B".

I found replacing the 470Ω resistor with a wire had only a slight increase in volume, so I recommend just leaving it there to reduce the risk of lifting a trace. Replacing the other three parts will have the significant volume increase we're after.

If anyone would like an EJ-10 upgrade kit for cheap containing two 4.7KΩ 1/4W Metal Film resistors and one 0.0047µF (4.7nF) 100V Mylar Polyester Film capacitor (suitable for audio), send me a private message. I have enough parts to upgrade about 100 EJ-10s. US and Canada only, please.

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