EMG EXG Expander

[Doughboy]

I just put this into as a guitar with passive pickups & even in the off position, it's affecting the tone, making it a bit more trebly.

Does anyone have an EMG EXG Expander with passive pickups & experiencing this problem?

 

[swarfrat]

I'm guessing but I expect you're experiencing buffering. An unbuffered passive pickup into an amp probably has a 68k-220k load. Going into an opamp buffer it essentially has no load. They have crazy high input impedances.

 

[Doughboy]

I'm guessing but I expect you're experiencing buffering. An unbuffered passive pickup into an amp probably has a 68k-220k load. Going into an opamp buffer it essentially has no load. They have crazy high input impedances.

According to EMG, the EXG Expander should have no effect on the tone of a passive pickup when installed. However, it definitely does change the tone.

What do you suggest? Do you think it's a faulty unit?

 

[Cagey]

I'm just guessing here, but if the "off" position ends up being a bypass (which is quite likely), then I would fully expect it to leave the guitar sounding brighter than you're used to. Some folks even use "no load" pots or eliminate the tone control altogether to get that effect on purpose, as even a tone control turned up to "10" will still bleed off some high end.

 

[Doughboy]

I'm just guessing here, but if the "off" position ends up being a bypass (which is quite likely), then I would fully expect it to leave the guitar sounding brighter than you're used to. Some folks even use "no load" pots or eliminate the tone control altogether to get that effect on purpose, as even a tone control turned up to "10" will still bleed off some high end.

I spoke to the tech at EMG & he said such a thing is impossible & he's never heard of it. This sounds a little suspect to me, as I also saw this problem in a review on Musician's Friend on this product.

What do you think can be done to fix this?

 

[Cagey]

Manufacturers, politicians, and little kids often say things designed to absolve themselves of any responsibility. I'd be suspect, too.

When I said "bypass" position, I meant more along the lines of "take the thing out of the circuit", which in the case of a tone control usually means opening the circuit altogether, not shorting it out. So, the EMG tech may be playing word games depending on the terminology you used to describe your problem. If you used the word "bypass", that's his out. it would be nearly impossible for the problem you describe to occur.

I don't think the thing is defective, but not having such a device handy I can't say how to mitigate the effect you're getting. Depending on the design, it may not even be reasonably possible.

I will say this, though. As I mentioned earlier, a lotta folks actually purposely work at getting the effect you're getting because it's not necessarily a Bad Thing. You may want to live with it for a bit, and see if it doesn't work out for the better for you. It may just take some getting used to.

 

[Doughboy]

Manufacturers, politicians, and little kids often say things designed to absolve themselves of any responsibility. I'd be suspect, too.

When I said "bypass" position, I meant more along the lines of "take the thing out of the circuit", which in the case of a tone control usually means opening the circuit altogether, not shorting it out. So, the EMG tech may be playing word games depending on the terminology you used to describe your problem. If you used the word "bypass", that's his out. it would be nearly impossible for the problem you describe to occur.

I don't think the thing is defective, but not having such a device handy I can't say how to mitigate the effect you're getting. Depending on the design, it may not even be reasonably possible.

I will say this, though. As I mentioned earlier, a lotta folks actually purposely work at getting the effect you're getting because it's not necessarily a Bad Thing. You may want to live with it for a bit, and see if it doesn't work out for the better for you. It may just take some getting used to.

I've lived with it for 2 weeks & I don't like the brittleness & excess treble. The passive PUs now sound more sterile than before.

Would it work to have a push/pull knob that would take the EMG pot out of the circuit when off & then back in when on?

 

[Cagey]

As I mentioned, I suspect the EMG thingy is taking itself out of the circuit and that's why you're getting the effect you are. If that's true, doubling up on the idea isn't going to improve anything except your soldering skills.

The vast majority of the complaints I read about the thing talk about it making things muddy, but if my theory is correct, that's likely while it's in play, not while it's defeated.

Maybe it's just the wrong thing for what you're trying to accomplish. It happens. Plus, there's a lotta snake oil (and snake oil salesmen) in the world, and nothing is a cure-all. People are always looking for a $20 fix to a $200 problem, so there will always be those seeking to satisfy that market.

Also, bear in mind I'm just guessing. I don't have one of the things or a schematic of how it's designed so I'm just driving while blind and going by what I know of electronics in general.

 

[line6man]

They have crazy high input impedances.

Not quite. The input impedance is probably comparable to a standard amp input. 1M or maybe 500k Ohms. If you allow input impedance to climb too high, then things get noisy, because thermal noise is proportional to resistance.


In any case, I would recommend throwing a resistor of value comparable to passive controls, parallel to the input of the buffer. That will take the edge off.

 

[line6man]

I just checked, and the input impedance is a low 250k Ohms.  That should be enough to prevent the tone from being too bright, but since it isn't, go ahead and load it down further.

If that doesn't help, another option is to throw a capacitor parallel to the buffer to shave off some highs.

 

[pabloman]

I've had two. One was in the Gilmour set. It was great. The second I put in a Dinky with Dimebuckers and it sounded like poo. My experience echoes most of the reviews. Clean singles, it's great. Dirty buckers gets ya poopie tone.

 

[Vallhagen]

I'm guessing but I expect you're experiencing buffering.

I'd say this is the best qualified guess so far. I didn't know about the product until i read this thread, but i googled a bit and read up on the manual offered by EMG, so let me continue the guessing: Theres no schematic, but as the unit is active and doesnt have an on/off-switch (only a basic 3-legged pot), AND affects your impedance (input 250k, output 2k) it most likely consists of three stages (maybe two): input buffer - EQ section - (output buffer). The EQ section might be zeroed with the knob CCW, but the buffer(s) will still be in your signal path (there is no "true bypass" going on here).

And as the buffer affects your impedance, it will affect your tone. Typically (but not always!) buffering is a good thing, providing less treble loss in long signal chains.

Good reading about buffers: http://www.muzique.com/lab/buffers.htm

Cheers

 

[swarfrat]

Judging from http://www.emgpickups.com/exg.html#info

I'd say it's a summing amp with a 250k input summing with a fixed notch at 950Hz and 20db gain.  That'd be my first stab at copying it.  250k  should appear for all practical purposes like a volume pot, and shouln't be overly bright. Sounds like the pot isn't taking it all the way out of the circuit. 

 

[Doughboy]

Judging from http://www.emgpickups.com/exg.html#info

I'd say it's a summing amp with a 250k input summing with a fixed notch at 950Hz and 20db gain.  That'd be my first stab at copying it.  250k  should appear for all practical purposes like a volume pot, and shouln't be overly bright. Sounds like the pot isn't taking it all the way out of the circuit.

I'm actually beginning to wonder if it's a faulty pot. The EMG tech swore he hadn't heard of my problem in the 14 years he's been working there & said he would replace the unit. I will try this out & see what happens.

I have one in my EMG PU guitar & it sounds fine, but then again, it's active PUs already so maybe it is changing the tone slightly.