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Variable impedance device?

Discussion in 'Amps, Mics & Pickups [DB]' started by flatback, Jul 24, 2007.


  1. flatback

    flatback

    May 6, 2004
    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?
     
  2. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    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.
     
  3. bolo

    bolo

    May 29, 2005
    Apex, NC
    piro, check this out.

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

    flatback

    May 6, 2004
    Anyone tried one yet? Do they work with bass piezos?
     
  5. bolo

    bolo

    May 29, 2005
    Apex, NC
    Joe S. 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. ;)
     
  6. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    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.
     
  7. dar512

    dar512

    Mar 25, 2005
    Chicago, IL
    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?
     
  8. Standalone

    Standalone

    Jan 17, 2005
    New Haven
    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?
     
  9. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004

    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.
     
  10. flatback

    flatback

    May 6, 2004
    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?
     
  11. 16fuss

    16fuss

    Apr 25, 2005
    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!
     
  12. 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.
     
  13. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    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.
     
  14. bribass

    bribass

    Jan 25, 2006
    Northern NJ
    Endorsing Artist; Arnold Schnitzer/ Wil DeSola New Standard RN DB
    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
     
  15. bdowd

    bdowd Supporting Member

    Oct 27, 2005
    New Hampton, NH
    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.
     
  16. Jason Hollar

    Jason Hollar It Don’t Mean A Thing... Supporting Member

    Apr 17, 2005
    Central Pa
    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...
     
  17. bribass

    bribass

    Jan 25, 2006
    Northern NJ
    Endorsing Artist; Arnold Schnitzer/ Wil DeSola New Standard RN DB
    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
     
  18. bdowd

    bdowd Supporting Member

    Oct 27, 2005
    New Hampton, NH
    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.
     
  19. bribass

    bribass

    Jan 25, 2006
    Northern NJ
    Endorsing Artist; Arnold Schnitzer/ Wil DeSola New Standard RN DB
    The unit was fine. It was just the "wall wort" power supply adapter had a flimsy wire that broke.
     
  20. shwashwa

    shwashwa

    Aug 30, 2003
    NJ
    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...)
     

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