Re-examining my effects pedals after a long layoff, I thought I might add a clean boost and drop in a few more true-bypass switches. Then came Darkhorse with his advice on line buffers, and my eyes were opened to the joys of low impedance. My question is: Where is the line between "low" and "high" impedance? Boss units put out 1k ohms -- is that low enough to act as a decent buffer. My Ibanez TS9DX has a "buffer amp" in the schematic, but output impedance appears to be 10k ohms... is that low?
I'm not sure what I need, how to find out what I need, or whether I already have what I need....
Help? Please?
"You can't write a chord ugly enough to say what you want to say sometimes, so you have to rely on a giraffe filled with whipped cream." - Frank Zappa
1kohm is about the highest source impedance allowed for a line-level connection. 'line-level' has undergone some redefinition over the years, but 1 kohm or less source (output) and >10 kohm minimum load (input or sink) have become the de facto unbalanced (hot and neutral return/shield) audio signal impedances. on the source, even lower is better. on the load (input), higher is only better to a point -- and going much beyond 10 k to 25 k for the most part simply increases vulnerabilities to interference.
in the case of your guitar output, 10 kohm is definitely not a low output impedance for a buffer amp. 10 kohm will not drive a cable any (if at all) better than a plain ole vanilla passive humbucker. but it's possible Ibanez intended exactly that, as that would cause your guitar to interact with standard effects boxes and amplifiers that "expect" to "see" impedances that appear to be passive humbucking pups (most likely to approach about 10 kohm). a 10 k ohm output cannot be considered buffered to line level impedances. if you want line-buffering, you still need to add a buffer amp after your guitar.
btw -- what leads you to believe the guitar's buffer amp output is 10 kohm? specs? schematic? reading the resistance off a buffer amp schematic can deceptive unless you understand how the feedback circuits work.
hope this helps.
-=Greg
-=tension & release=-
Greg, thanks for the reply.
btw -- what leads you to believe the guitar's buffer amp output is 10 kohm? specs? schematic? reading the resistance off a buffer amp schematic can deceptive unless you understand how the feedback circuits work.
That 10kohm refers to an Ibanez Turbo Tube Screamer; I got that number & schematic info via Google. None of my instruments have active electronics. My boxes are: Ibanez TX9DX Turbo Tube Screamer > MXR Distortion Plus > In-Line Effects XE601 Extra Distortion > Electro-Harmonix Small Stone Phase Shifter > Vox/Thomas Organ Cry Baby > MXR Analog Delay > DeArmond volume pedal > amp. I also have some rack-mount items, but I'm not sure I would ever pack them up for a gig. (DOD flanger/doubler, Yamaha multi-effector, Tapco stereo spring reverb, stereo 10-band EQ.)
"You can't write a chord ugly enough to say what you want to say sometimes, so you have to rely on a giraffe filled with whipped cream." - Frank Zappa
sorry I misunderstood -- it actually makes sense that a Tube Screamer would have a 10kohm output impedance as it is suppose to be able to boost the guitar's signal somewhat transparently (if necessary). part of achieving that would be looking somewhat like a guitar impedance-wize. of course, the Distortion Plus between the TS and subsequent stages changes that.
-=tension & release=-
The Tube Screamer and the Distortion Plus aren't used simultaneously. (I grew out of that phase.) I know a line of effects can suck tone, and I think I know that things like active pickups & line buffers solve this with a "low impedance" signal. I don't know how low is low, however.
I don't think I'm in any danger of gigging in the foreseeable future. Think I'll just spend a few hours plugging things into & out of one another. Good times. :)
"You can't write a chord ugly enough to say what you want to say sometimes, so you have to rely on a giraffe filled with whipped cream." - Frank Zappa
for buffers, low impedance output impedance should be less than 1 kohm, preferably closer to 100 ohms.
a little more specifically: for a modern line buffer. I would design (or expect to buy) a line level buffer with output impedances of 50 to 200 ohms unbalanced (tip-sleeve, 1/4 inch cable connex) or 300 ohms balanced (150 positive to gnd / 150 negative to gnd, XLR connex).
-=tension & release=-
Thank you -- exactly the info I needed (and couldn't find in about five hours of Google searches)!
"You can't write a chord ugly enough to say what you want to say sometimes, so you have to rely on a giraffe filled with whipped cream." - Frank Zappa
for buffers, low impedance output impedance should be less than 1 kohm, preferably closer to 100 ohms.
I see a number of pedals specifying output impedance "<1k ohms" just like that. "Less than." No hard number. Is it variable? Or are the manufacturers just being dodgy for some reason?
Crow, here's a good article on buffers: http://www.muzique.com/lab/buffers.htm
And another on pedal impedance: http://www.muzique.com/lab/imp.htm
If you are into DIY stuff, you can build your own quality buffer with a few parts:
http://www.muzique.com/lab/superbuff.htm
I've thought about breadboarding one of those, but haven't have the time ... nor do I really have the need ... :wink:
"Everybody got to elevate from the norm."
don't know if it's purposely dodgy or not, but the implication (from an engineering PoV) would normally be that as long as it's less than 1 kohm, it's meeting all requirements and will function equally well in all typical use scenarios. But I don't really believe that's true in this case, as an output impedance in the range of 1 kohm in not truely low enough to be insignificant if driving a line-level input, which some might decide to spec imprecisely as >10 kohm. and all of this says nothing about driving cable capacitances and other frequency dependent parms.
IMO, what would be very useful would be the ability set the output impedance to a selection of values between 100 ohms and 10 kohms (from good buffer to overwound pup resistance), say 100, 300, 1k, 3k and 10k ohms, this would change the interactions with subsequent stages and cable … changing timbre and dynamics. that would be a very "boutiquey" feature, applicable to input impedance adjustments as well (e.g., adjustable from 10kohm through 1 Mohm).
-=tension & release=-
