OK so throughout a bunch of threads there has been discussion of a variable impedance box. (and preamps like the TD 100 that have them built in)
What i want to know is: Is there such a device or a way of making one that is a very high quality audio device that only does that. No preamp, or gain or color or tubes or anything. It seems like from the one time I tried a TD 100 that it would be a great thing to have. I use an Avalon U5 cause it sounds so damn good, but if most of that is the way it deals with impedance, then I'd love to have a much smaller unit to sit on top of the Focus.
I read the Steve Rodby quote where he says he has it built into his gear, but who builds them?

...What i want to know is: Is there such a device or a way of making one that is a very high quality audio device that only does that. No preamp, or gain or color or tubes or anything.

Yes, it is a piece of cake to build this as a passive device. It would, however, be subject to interaction with whatever follows it in the circuit. Personally, I would have little to no use for one. I prefer to load the transducer (pickup, microphone, etc.) appropriately and then employ well-designed tone controls to make desired alterations in the response. To be sure, varying the impedance will alter frequency response but, in my opinion, such an approach amounts to non-optimal gimmickry, the effects of which are unreliable and somewhat unpredictable across different combinations of equipment.

piro, check this out (http://www.talkbass.com/forum/showpost.php?p=4464056&postcount=202).

It showed up recently at the end of the Summit Audio TD-100 thread.

piro, check this out (http://www.talkbass.com/forum/showpost.php?p=4464056&postcount=202).

It showed up recently at the end of the Summit Audio TD-100 thread.

Anyone tried one yet? Do they work with bass piezos?

Joe S. (http://www.talkbass.com/forum/showpost.php?p=4467133&postcount=205) has apparently. Sorry to keep cross-linking these threads.

I kinda doubt it would work the same tonal magic as a TD-100 or the U5, but it is kind of interesting. Its effectiveness (like so many other amplified DB things) might depend a lot on what's in front of it and what's after it in the signal chain perhaps. Like how bad do you need impedance matching / adjustment from whatever pickup you have to whatever amp you have. Results might vary for various combinations of gear. I dunno.

Looks like the street price is $50. Slips on your guitar strap. ;)

Joe S. (http://www.talkbass.com/forum/showpost.php?p=4467133&postcount=205) has apparently. Sorry to keep cross-linking these threads.

I kinda doubt it would work the same tonal magic as a TD-100 or the U5, but it is kind of interesting. Its effectiveness (like so many other amplified DB things) might depend a lot on what's in front of it and what's after it in the signal chain perhaps. Like how bad do you need impedance matching / adjustment from whatever pickup you have to whatever amp you have. Results might vary for various combinations of gear. I dunno.

Looks like the street price is $50. Slips on your guitar strap. ;)

Gee, for that money you could buy one of fdeck's low-noise piezo pre-amp/high-pass filter devices with phase reversal. That would load the piezo properly, after which you could use tone controls to tailor the response. IMO, that's a much smarter way to go and it avoids all of the snake oil.

Personally, I would have little to no use for one. I prefer to load the transducer (pickup, microphone, etc.) appropriately and then employ well-designed tone controls to make desired alterations in the response.
I don't understand this point of view. (However it seems common, so I must be missing something)

Assuming that you've already got a combo or head with tone controls that you find adequate, why do you need more tone controls on a piece of hardware that you only need in order to match the impedance of a piezo pickup to the input jack of the combo or head?

I saw a "db 100" in a case the other day-- 19 bucks. No variable control. Has anyone seen one of these? From the case, it looked like '80s. I forget the brand-- rocktron?

Personally, I would have little to no use for one. I prefer to load the transducer (pickup, microphone, etc.) appropriately and then employ well-designed tone controls to make desired alterations in the response.


I don't understand this point of view. (However it seems common, so I must be missing something)

Assuming that you've already got a combo or head with tone controls that you find adequate, why do you need more tone controls on a piece of hardware that you only need in order to match the impedance of a piezo pickup to the input jack of the combo or head?

If I understand your response correctly, here is what you are missing. I was, in fact, referring to the tone controls on my head. I was not advocating for another device with tone controls that would feed the head. Having a variable impedance device represents what is essentially another tone control in front of the head and its operation would be unpredictable across combinations of pickups and amps. What I was advocating was a device that properly loads the pickup, whether that is the head itself or an outboard active pre-amp, followed by well-designed tone controls within the head.

If I understand your response correctly, here is what you are missing. I was, in fact, referring to the tone controls on my head. I was not advocating for another device with tone controls that would feed the head. Having a variable impedance device represents what is essentially another tone control in front of the head and its operation would be unpredictable across combinations of pickups and amps. What I was advocating was a device that properly loads the pickup, whether that is the head itself or an outboard active pre-amp, followed by well-designed tone controls within the head.

Ok So heres the uh...(d)rub, and the reason for my interest in such a device, if for example my AI Focus has a imp. of 1mohm or whatever, and I personally might chose a fatness level (I dont quite know how to describe what I think I hear when the imp load is changed) more or less on the sweep, or has happened recently where I changed pickups and want to be able to adjust the pickups response more than can be done with the subtle tone controls on the AI (and I don't want to bring the gentle giant Avalon U5) Would this little box (the radial for example) dial in the super fatness that can then be tuned with the HP filter....oh my god I can barely follow this myself...
Basically my fat sounding Full Circle broke and I had to go back to a somewhat thinner sounding Underwood. The FC has so much bass that it is easily dialed out with the HP filter. The Underwood can sound really good thru the U5 (and mixed with a fat mic) but the Damn U5 is huge. Will this variable imp device be able to dial that fatness into the Underwood? or Do I need to lay off the espresso and think about something else?

does anybody know more about the min and max impedance of the tonebone radial? if it is from 500Kohm to 1Mohm it will not help us AI-users to get a better sound!

I don't think that spec is published. What the drag control does on the Radial active DI (I forget which model) is raise the input impedence. The Dragster is intended to do the same thing for a low impedence input like those on wireless units. If my understanding is right, it can't lower the impedence on the Focus, but it can raise it(?). To my ear it doesn't do much on the Focus which is already at 1 Mohm.

...Will this variable imp device be able to dial that fatness into the Underwood? or Do I need to lay off the espresso and think about something else?

It's difficult to tell. This is the unpredictable part I keep mentioning. What varying the impedance will do in terms of response depends upon the impedance of the pickup, the response of the pickup, and the interaction between the variable impedance device and the input of the amp. You may just find a sound you really like by playing with these passive devices but it is hit and miss.

It's difficult to tell. This is the unpredictable part I keep mentioning. What varying the impedance will do in terms of response depends upon the impedance of the pickup, the response of the pickup, and the interaction between the variable impedance device and the input of the amp. You may just find a sound you really like by playing with these passive devices but it is hit and miss.

What about this ART product? It has variable impedance and is a pre.

http://www.artproaudio.com/products.asp?type=79&cat=1&id=99

I noticed this when reading the manual online for that Art product:

"NOTE: the Input impedance control only affects mic/line inputs. The 1?4”
instrument input on the front panel is NOT affected by this control in
any way. The instrument input impedance is ALWAYS >1M Ohm."

Just throwing it out there, seems like it might be relevent.

I have the Art tube MP Project Series:

http://www.artproaudio.com/products.asp?type=79&cat=1&id=115

I got it for my AT Pro35 mic, but found it sounds quite nice as a preamp with my Full Circle & Barbera pups.

Is 1 Meg Ohm the right impedance? Is there a big difference between 1 & 2 -- according to the Steve Rodby device?

This thing makes my bass sound very smooth and loud...and was a whopping $65.

It also has phantom power, a 40HZ cut, limiter, and phase invert. All this plus a tube DI and gain & output levels. And cool lights -- can't forget that!

Got three upcoming casual jazz upright gigs this week & next...will report how it sounds in the trenches...

I noticed this when reading the manual online for that Art product:

"NOTE: the Input impedance control only affects mic/line inputs. The 1?4”
instrument input on the front panel is NOT affected by this control in
any way. The instrument input impedance is ALWAYS >1M Ohm."

Just throwing it out there, seems like it might be relevent.

Ah, rules that out.

I have an old Tube MP The Original from years ago. I remember liking it well enough, thinking it made the old Polytone sound better until the flimsy power supply wire died an early death.

BG

Yeah, I had one of those art tube mp's for a while, my p-bass sounded great through it, but it had a really short life also. The 1megohm input on the Art seems great, just seems there is some question to the lifespan of these things.

Yeah, I had one of those art tube mp's for a while, my p-bass sounded great through it, but it had a really short life also. The 1megohm input on the Art seems great, just seems there is some question to the lifespan of these things.

The unit was fine. It was just the "wall wort" power supply adapter had a flimsy wire that broke.

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? (which in effect becomes a variable frequency high pass filter.) my suggestions? there are several devices out there that have a 10 meg ohm input inpedance or higher with varying degrees of eq on them for people who want more or less. here's a list of things i know about in decending order from more eq to less:

1 the fishman platinum pro has 10 meg ohm input inpedance and graphic eq and a high pass filter. pretty nice sound on my basses too.

2 raven labs has one input channel with a 10 meg ohm input. and some eq. i use this as a buffer box and keep the eq flat and use the eq on my amp. the eq knobs on the raven unit itself can come in handy if i need more in a difficult room.

3 d-tar solstice. has 2 channels with 10 meg ohm input impedance. never used one, but i'm considering getting one because of the 2 channels of 10 meg ohms. i dont know how the eq sounds , but from the specs it seems to not be optimal for bass. i'd probably use the amp's controls, but this is the only unit i know of that has 2 10 meg ohm inputs.

4 the old BII fishman preamp. just volume bass and treble and a 10 meg ohm input impedance. i use this as a buffer box too and do the eq from my amp. it's pretty cheap. the treble slider can cut out finger noise. bass slider is very boomy on my basses. i use the amp's tone controls.

5 the demeter di box has a 20 meg ohm input and a gain control i believe. it's expensive but i would think it's a good buffer for those who want to use the tone controls on the amp. ( there are other di boxes with high input impedance too that could do the same thing. the avalon u5, however, which i own, is something like 3.5. i seem to prefer 10, but that's just me...)

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 (http://personalpages.tds.net/~fdeck/bass/hpfpre.htm) (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.

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?

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.

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.

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...

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 (http://www.talkbass.com/forum/showthread.php?t=215867&highlight=impedance) thread.

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?

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

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?

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.

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.

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.

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

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

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.