Variable impedance device? - Page 2

drurb · #21 07-26-2007, 08:12 AM

Quote:

Originally Posted by shwashwa

so i guess what drurb is saying is that why not just buy something with the highest input impedance possible to insure maximum fatness (frequency response) and just use the tone controls later to eq it the way you like rather than using the variable impedance control?

Well, almost. I wouldn't opt for the highest impedance possible but 10 Mohms is a nice number. Yes, the idea is to load the pickup properly. Whether that results in maximum "flatness" (I'm assuming you didn't really mean "fatness"-- or did you?) depends upon the pickup. In the case of piezos, what such loading will do is preserve the low end. The way I approach this is to use one of these (actually an early prototype) followed by my EA iamp200 that has a very nice set of parametric tone controls. The input impedance of the iamp200 is 1 Mohm and that's just fine for my Rev. Solo pickup. I use the pre-amp because it includes a very useful high-pass filter that I use for blocking transduction of infrasonic frequencies. The pre-amp/HPF has a 10 Mohm input and costs all of $50. One of those variable impedance devices might end up producing a desirable sound but as I've stated before, it is hit or miss and may be highly dependent upon the particular combination of equipment with which it is used.

Jason Hollar · #22 07-26-2007, 08:19 AM

OK, so I guess I'm sorta konfuzed again.

What is better...a 10 Meg Ohm input impedance...or something like 3.5, or 2, or 1...?

Or does it all depend on the output of the particular pickup -- and the input of the particular amp/sound board, etc?

bdowd · #23 07-26-2007, 08:47 AM

Quote:

Originally Posted by drurb

I use the pre-amp because it includes a very useful high-pass filter that I use for blocking transduction of infrasonic frequencies. The pre-amp/HPF has a 10 Mohm input and costs all of $50.

I just signed up for one of these, should help my running my full circle into my eden head. I'm running the fc into a sansamp right now, of which the input is somewhere around 4.7megohm. I'm curious to see if there's an obvious difference between it and the hpfpre, while keeping in mind this new box has some other tricks that I hope will help out as well.

Joe Smithberger · #24 07-26-2007, 09:17 AM

IMO (read that as non-expert with ears) there is an optimum input impedence that will vary depending on the pickup and what its going thru downstream. To my ears (again IMO) an impedence that is too high can make the highs go brittle and the lows sound too wide. Anyone ever use the Raven labs 3 channel blender? It was 10Mohm with no EQ and it did nothing for anything. The new AI amps are only 1 Mohm, down from 10 in the previous series.

Jason Hollar · #25 07-26-2007, 09:55 AM

I had a Raven Labs PMB1 for a while.

Really couldn't see what was good about it.

It never really added anything to my tone other than gain. The EQ was strange and it even seemed to add (not remove) that mid-range pickup "glack" sound...which was a drag.

Consequently, I got better use out of an old Boss Bass EQ pedal and more recently an Aguilar DB924 18v pre.

This Art Tube MP is sounding pretty fine though...and I wonder if the 1 Meg Ohm is a proper match for all my gear.

I didn't realize the new AI stuff had that input rating as well...

drurb · #26 07-26-2007, 02:34 PM

Quote:

Originally Posted by Jason Hollar

OK, so I guess I'm sorta konfuzed again.

What is better...a 10 Meg Ohm input impedance...or something like 3.5, or 2, or 1...?

Or does it all depend on the output of the particular pickup -- and the input of the particular amp/sound board, etc?

With most piezos, once you get above 1-2 Mohms it hardly matters. The variation occurs largely with lower input impedances that are non-optimal. This is the region in which fooling with the variable-impedance devices would be expected to alter the sound.

It's worth revisiting this thread.

Jason Hollar · #27 07-26-2007, 03:00 PM

Thanks good Doctor,

Your wisdom inspires me...even though I'm afraid I'm too dense to comprehend the subtle science behind all this.

So in elementary school terms...is the 1 Meg Ohm input good/desirable?

Mark Perna · #28 07-26-2007, 03:10 PM

I talked to one of the guys at AI and they said they switched the input impediance from 10 to 1 Mohm because a number of people said they got a better sound out of the Realist at 1 Mohm (I guess it was screw anyone not using a Realist...)

I have a Focus II with both a 10 and 1 Mohm input and I can tell a huge difference between them with a BP100, Bassmaxx and an Underwood. A-Bing is obviously really easy. The 1 Mohm has a noticable loss of bass response below about 200 Hz and a slightly less noticable but present loss in the 400-600 Hz range. The sound is edgy and thin-that old time '70's pickup sound. At 10 Ohm, the sound is round and fat with very little edginess and no noticable loss of low frequencies.

With the Realist, the differences are much less noticable. In fact, they both sound different but good. The 1 Mohm input produces a slightly thinner sound but since the Realist is so bottom heavy, it sounds good. The 10 Mohm input produces a really big fat sound but it is almost too big as it requires a lot of EQing to thin the bottom out to a useable level.

I ordered a Focus III but requested that they modify the input to have a Z of 10 Mohm.

I'm really glad this thread is getting some discussion. I saw the Rodby article as well and was looking around for a commercial variable Z device. I'm glad I saved my money.

mark

shwashwa · #29 07-26-2007, 03:22 PM

after reading that last post my thought would be this: get something with as high as sensible input impedance, perhaps 10 meg ohm, in order to accomodate the most pickups out there, and use the eq or high pass filter in case you're getting too much low end. my understanding is that by lowering the input impedance, you're bringing up the corner frequency on the inadvertant high pass filter you're creating, thus you hear a "sweet spot" depending on which pickup you're using. i'm saying that if you use a 10 meg ohm input and a seperate high pass filter, or just a eq section on your amp, you can create that sweet spot with EQ, and not use the impedance to EQ and by having the 10 meg ohm input impedance you have more flexability with which pickups you can use.
thoughts?

drurb · #30 07-27-2007, 07:23 AM

Quote:

Originally Posted by Jason Hollar

Thanks good Doctor,

Your wisdom inspires me...even though I'm afraid I'm too dense to comprehend the subtle science behind all this.

So in elementary school terms...is the 1 Meg Ohm input good/desirable?

Wow, an inspiration?

Thanks for the kind words. Yes, for most piezos, 1 Mohm is quite desirable.

drurb · #31 07-27-2007, 07:27 AM

Quote:

Originally Posted by shwashwa

after reading that last post my thought would be this: get something with as high as sensible input impedance, perhaps 10 meg ohm, in order to accomodate the most pickups out there, and use the eq or high pass filter in case you're getting too much low end. my understanding is that by lowering the input impedance, you're bringing up the corner frequency on the inadvertant high pass filter you're creating, thus you hear a "sweet spot" depending on which pickup you're using. i'm saying that if you use a 10 meg ohm input and a seperate high pass filter, or just a eq section on your amp, you can create that sweet spot with EQ, and not use the impedance to EQ and by having the 10 meg ohm input impedance you have more flexability with which pickups you can use.
thoughts?

Yes, indeed!!! The tone controls can, of course, be used to tailor any aspect of the response, be it the low, middle, or high end. That inadvertent filtering you mention is, as I've repeated ad nauseum here, also likely to differ across combinations of devices.

mje · #32 07-27-2007, 03:53 PM

Nice design. I built fdeck's original preamp- the front end of this box- into my Azola. Much more linear volume control, and yes, nice overload characteristics. I also built it into my Fender Precision A/E to buffer the piezo transducer.

Eric S · #33 07-28-2007, 01:35 PM

FWIW - stumbled on this. Looks interesting albeit pricey.

http://www.sarnomusicsolutions.com//page2/sgbbpage.html

* Variable input impedance - 33kΩ to 1MegΩ

"The Steel Guitar Black Box™ is the ultimate tone enhancer for amplified musical instruments. It is a simple device using a single vacuum tube, yet it has a profound effect on just about any instrument signal that you pass though it." ...blah blah blah

Jason Hollar · #34 07-29-2007, 08:57 AM

Wow -- that Black Box looks cool...but $300+! That puts it in the used Summit range.

Jason Hollar · #35 07-29-2007, 09:05 AM

On another note...

I did use my Art Tube MP preamp this weekend.

I played a loud beer hall drummerless trio date on Friday. The preamp gave me much more gain and clarity in my bass signal...but alas, once you get past a certain volume the bass starts to sound like mud anyway. Good thing the guys I played with were hip to the volume thing.

On the quiet stuff though, it really shines, but you almost don't need a preamp on really quiet gigs if you have a decent amp.