J E M box information

[Mcneilwaeasteel]

I would like some information on the JEM box I have from the early 1980's, basically what it could do to enhance my steel guitar, any technical information on it would be appreciated.
Answers please on the use of it as described in lay mans terms for " dummies " in other words what do the knobs do?
Would it be suitable for use with Rickenbacker horse shoe pickups?
Cheers Robert

[Danny Mitchell]

Robert I've got no technical advice to offer, I'm afraid. I'm guessing it's some kind of an impedance watchamacallit.
My approach would be open it up, see if it requires a battery, stick it in line between the guitar and amp (no volume pedal), turn controls full up and A/B the sound with and without said gizmo.
This should reveal it's capabilities and let you decide if it's bringing anything to your tone.
And; to quote Brother Geoff, our wise man in the east,'if it sounds good then it is good.'

[Malcolm]

Robert it runs on two 9volt batteries, as Danny said run it between guitar and volume pedal, I had one some years back but it made no significant difference to my tone ( large magic wand needed for that). Good for subtle changes with out having to get up and alter amp settings. Built in UK, Uncle Roy was involved in it if I remember rightly.

[Mcneilwaeasteel]

I had previous knowledge on the batteries and fitting the two 9 volt batteries has stretched my technical skills to the limit, now it's the use of the knobs that puzzle me.
Like Malcolm I do not possess a " magic wand " but I'm also like Glen Milller trying to get that "sound"
After long deliberation I set up a zoom camera and recorded my guitar with and without the JEM box, the blue knob seems to alter the tonal qualities and the red one increases the sustain, but cloth ears don't help me in reaching this conclusion
I would share my efforts with you but when I tried to upload the two video clips the dreaded words
" the extension MOV is not allowed " in a pronounced red colour prevented this miracle from taking place
Unless someone can inform me otherwise I'll have to accept my own conclusions regards tonal difference, meanwhile I'll just have to twiddle my knobs a bit more!

[Arcada]

I would share my efforts with you but when I tried to upload the two video clips the dreaded words
" the extension MOV is not allowed " in a pronounced red colour prevented this miracle from taking place

You can only upload images to the forum, not video clips. For video you'd have to upload it to YouTube first, then viewtopic.php?f=27&t=30

[Mcneilwaeasteel]

Here comes my recording efforts for what they are worth, first using the JEM box

And now without the box

I could ask for answers on a postcard as to what sound is better, but I'd be giving my age away, so any helpful comments ( good,bad or ugly ) would be appreciated

And lastly my newly set up recording "studio" put together in a day out of necessity, using a zoom Q3hdi recorder on a tripod held horizontally by the weight of a lap steel on the shelf, the cables were hanging everywhere from the amp as it is all confined in a space about 3' square surrounded by useful rubbish. This was all done on the spur of the moment to see if it would work, as a great " master " once said " grasshopper you can be a recording engineer or learn the steel guitar, but to do both is not advisable " even so the great master is playing steel after being a sound engineer
Thanks for your advice Mark, I have taken a crash course on video compression joined Utube learned how to add videos and now I've managed to post them on here, after this lot I'm going to lie down for a week at least.
Problem is by tomorrow I will have to try and remember what I have done to get this far

[Jif]

Robert, my guess is that it's a unity gain current amplifier, in other words it doesn't alter the amplitude of the voltage of the input signal but increases the current, (amps), of the output signal, it probably also presents a high impedence to the pickup which decreases the loss of high frequency signal from the pickup. The higher current through the cable also decreases high frequency losses, overall giving a brighter sound.

This can be proven through the use of ohms law, combined with the equation for frequency response.

I've used a few instances of this type of circuit in a variety of guitars and have installed one into my MSA and it certainly has this effect. It's not adding anything, it's just cutting down on high frequency losses and so you get a more accurate response over a wider frequency range.

It's then a matter of taste whether you like the tone change it creates.

[Will C]

Geoff, what you have described is what I would call a buffer, pure and simple. As you say, it would have a very high input impedance so as to defeat what is usually called "tone suck" when the upper register is lost if the pickup is loaded appreciably, and a low output impedance so it will drive the VP and a decent cable run without adverse effect. You could certainly call it a current amplifier, although the words "unity gain" would then I guess be referring to unity *voltage* gain.

I could trace out the circuit diagram if you can spare it for a wee while, Mr McNeil! It would then be possible to work out what the controls are meant to do.

[Mcneilwaeasteel]

Thanks for your kind offer Will, P M sent to you.
regards
Robert

[Jif]

Geoff, what you have described is what I would call a buffer, pure and simple. As you say, it would have a very high input impedance so as to defeat what is usually called "tone suck" when the upper register is lost if the pickup is loaded appreciably, and a low output impedance so it will drive the VP and a decent cable run without adverse effect. You could certainly call it a current amplifier, although the words "unity gain" would then I guess be referring to unity *voltage* gain.

I could trace out the circuit diagram if you can spare it for a wee while, Mr McNeil! It would then be possible to work out what the controls are meant to do.

Indeed Will.

I use a single FET source follower with a 10M ohm input impedence for my version. Nothing fancy required!