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Should I Use A Buffer With A Long True Bypass Box?

#41
Toasted said:
That's because you dont understand the subtle yet important difference between what a clean boost and a buffer do.

A good buffer has a high impedance input (typically around 5meg) to act as a magent to "pull" your guitar signal towards it and eliminate the effect of cable capacitance between guitar and buffer. It also has a very low impedance output (even right down to 100 ohms) to "pump" your guitar signal through the cable to the am pand eliminate the effect of cable capacitance between buffer and amp.

A clean boost increaces the amplitude of the audio signal wave passing through it - more volume. That's it, nothing to do with eliminating the effects of capacitance.

Therefore, in my opinion the best pedals for couteracting treble and bass loss in cables with passive basses are pedals that are both a clean boost, have a high input impedance and have a low output impedance. Like the Barber Launch Pad.
Click to expand...

Thanks that makes perfect sense.
 
#43
What Toasted said is only true when using European voltage. The strength of the magnetism in the lower American voltage system changes the amount of amplitude one gets, and would in an entirely different impedence. What you'd need to get would be an impedence conditioner. I recommend the Barber Ohmlet box- it's an active impedence-conditioning buffer with a passive true bypass switch, and has a really awesome paintjob and 5-month waiting list. Your tone will suck and your pedalboard won't be complete without one. Unless you're using European magentism that is.
 
#46
Toasted said:
A clean boost increaces the amplitude of the audio signal wave passing through it - more volume. That's it, nothing to do with eliminating the effects of capacitance.

Therefore, in my opinion the best pedals for couteracting treble and bass loss in cables with passive basses are pedals that are both a clean boost, have a high input impedance and have a low output impedance. Like the Barber Launch Pad.
Click to expand...

I think MOST pedals are designed such that their input impedance is high and the output impedance is low. How high or low may be a matter of debate, but i think all of them do something beneficial impedance-wise, compared to a passive bass output. Any pedals with a low input impedance and a high output one?

Bryan R. Tyler said:
What Toasted said is only true when using European voltage. The strength of the magnetism in the lower American voltage system changes the amount of amplitude one gets, and would in an entirely different impedence. What you'd need to get would be an impedence conditioner. I recommend the Barber Ohmlet box- it's an active impedence-conditioning buffer with a passive true bypass switch, and has a really awesome paintjob and 5-month waiting list. Your tone will suck and your pedalboard won't be complete without one. Unless you're using European magentism that is.
Click to expand...

Hilarious.
 
#47
Toasted said:
That's because you dont understand the subtle yet important difference between what a clean boost and a buffer do.

A good buffer has a high impedance input (typically around 5meg) to act as a magent to "pull" your guitar signal towards it and eliminate the effect of cable capacitance between guitar and buffer. It also has a very low impedance output (even right down to 100 ohms) to "pump" your guitar signal through the cable to the am pand eliminate the effect of cable capacitance between buffer and amp.

A clean boost increaces the amplitude of the audio signal wave passing through it - more volume. That's it, nothing to do with eliminating the effects of capacitance.

Therefore, in my opinion the best pedals for couteracting treble and bass loss in cables with passive basses are pedals that are both a clean boost, have a high input impedance and have a low output impedance. Like the Barber Launch Pad.
Click to expand...

Sold!

Or at least added to GAS list!:hmm:

Thanks Toastmeister.:)
 
#48
niftydog said:
You may choose to "set" the input impedance of a non-inverting follower by putting a resistor to ground on the input - the impedance of the non-inverting input itself is enormous, so the impedance effectively becomes the resistor value.
Click to expand...

hmmm how does that work? my understanding: opamps take no current into the inputs, so when you put the resistor to ground in front of it, all of the current goes through that, because there is a voltage difference across it, so there must be current through it. But I don't really understand how that sets the impedance to the opamp...

I'm not really understanding what everyone means by impedance in this context. To me it sounds like they really mean what the current will be, with a high impedance the current would be lower, assuming the impedance means resistance. So a low impedance would mean high current. (voltage = current * resistance)
 
#50
ehque said:
I think MOST pedals are designed such that their input impedance is high and the output impedance is low.
Click to expand...
Precisely why I've been saying all along that virtually any pedal will work as a buffer.

Sir Edward V said:
hmmm how does that work? my understanding: opamps take no current into the inputs, so when you put the resistor to ground in front of it, all of the current goes through that, because there is a voltage difference across it, so there must be current through it. But I don't really understand how that sets the impedance to the opamp...

I'm not really understanding what everyone means by impedance in this context. To me it sounds like they really mean what the current will be, with a high impedance the current would be lower, assuming the impedance means resistance. So a low impedance would mean high current. (voltage = current * resistance)
Click to expand...
Ok... yes, op amps take virtually 0 current into the inputs, all the current is forced through the resistor and a voltage is developed across the resistor - it is this voltage that drives the op amp input stage. As far as the input signal is concerned, the impedance of the op amp is SO high that it's practically an open circuit, so the ONLY impedance the signal "sees" is the resistor.

Thing to keep in mind here is that most components used in audio circuits are "voltage driven" - meaning the important thing to do is transfer the most voltage from one stage to the next. The current is deliberately kept low in the input stage because pickups simply cannot generate large current flow.
 
#53
Okay, so I had my first band practice with my new pedal board and Barber Launch Pad and things didn't quite sound and react the way I was expecting them to.

I set up the Launch Pad for "buffer" according to the confusing one page instruction memo that came with unit. I thought I was set up for unity gain, but somehow my overall sound was louder even though I turned my amp down to a lower level.

My tone also seemed to be much more dynamic in volume, soft touch stuff was quiet, digging in was cutting --- yet, felt more distant. Less lows, more "artificial" sounding highs. It felt like my sound was squashed by bad compression, but still had sensitivity.

Sorry if that doesn't make any sense, I'm just trying to troubleshoot here and would love any advice.

I currently have my Launch Pad at the front of my chain, all other pedals are true bypass. Should I move it? Do I have it too high? I just want my straight jacked sound that I am happy with while being able to have some effect options added in...
 
#54
Less lows could mean that it's got the same low freq. attenuation problem that many guitar effects have. Perhaps it's just not happy being used for bass?

So, you set sensitivity at minimum and tweak the + volume, right? You were plugged into the + output?! And how did you set it for unity gain? Switch it on and off and compare levels?
 
#55
scotch said:
No way man! Educate me at least, I want to know more.
Click to expand...
Well, ok, but YOU asked for it!

First thing to understand is that impedance is related, but distinctly different to resistance. Resistance is only for DC voltages, impedance is for AC voltages. Audio signals are AC voltages, hence, we deal with impedance. Impedance is also frequency dependent, so it can vary depending on the frequency of the input signal - in fact, different frequency components making up a signal will "see" different impedances. Thus, impedance is never completely constant over a range of frequencies.

So, when a manufacturer gives a single value as an input impedance, it is actually a nominal or average value of the measured impedance over a range of frequencies. The true impedance over a range of frequencies can only be properly represented by a a graph of impedance vs. frequency. But this is very rarely, if ever given, especially in the context of musical equipment.

Input impedance is in parallel with the signal - Output impedance is in series with the signal. Below is an amplifier, with an input and output impedance represented by resistors.
Code: 
         |\    ___
    --o--| >--|___|--
      |  |/
     .-.
     | |
     | |
     '-'
      |
      |
     ===
     GND
For most audio applications the ideal is to have a very high input impedance, and a very low output impedance - this gives the best transfer of voltage from one stage to the next. A high input impedance means that more of the signal will pass directly into the amplifier, rather than being 'lost' to ground via the impedance. A low output impedance means the amplifier can produce a stronger output signal before it reaches the limits of it's operation. Notice how the high input impedance is in parallel with the signal - stopping the signal from being 'lost' to ground. Also note how the low output impedance is in series with the signal, directly 'impeding' it's passage through the circuit. Already you can see why it's important to have a high input and low output impedance.

Now, I could blather on all day, but the important thing for most of us to understand is how impedances interact. So, let's put two amplifiers together.
Code: 
         |\    ___        |\    ___
    --o--| >--|___|-------| >--|___|-
      |  |/            |  |/
     .-.              .-.
     | |              | |
     | |              | |
     '-'              '-'
      |                |
      |                |
     ===              ===
     GND              GND
Notice now that the output impedance of the first amp is connected directly to the input impedance of the second amp. The first amplifier is generating the signal, the signal on it's way to the next stage passes through the output impedance, and then encounters the next stages input impedance, before entering the 2nd amplifier. This can be represented like this:
Code: 
    SIGNAL
      o
      |
     .-.
     | |
     | |
     '-'
      |
      o-----o TO NEXT STAGE
      |
     .-.
     | |
     | |
     '-'
      |
      |
     ===
     GND
This arrangement looks just like a thing called a voltage divider - which literally 'divides' a given voltage by the ratio of the two resistances. This is the crux of the whole matter, so PAY ATTENTION!!! :p

Lets look at the ideal situation; the output impedance (top resistor) is 0 ohms - in other words, it's not even there, it's a short circuit, or just a piece of wire. The input impedance (bottom resistor) is infinitely high - or in other words, it's not there either, as if it's been removed from the circuit - an 'open circuit.' So, what you end up with is just a wire direct from output to input - the resistors effectively do not exist and ALL of the signal passes to the next stage.

The voltage divider ratio in this case is calculated as infinity divided by infitiy+0, which is equal to 1. The next stage see the input signal times the divider ratio (ie; input x 1 = output)

Sadly, this ideal situation does not exist in reality, it's purely theoretical. In reality you might have, for example, an output impedance of 100 ohms, and an input impedance of 10,000 ohms. The ratio of this arrangement is 10,000 divided by 10,000+100, which is 0.99. This is still a very good result as the output equals 0.99 of the input (ie; output = input x 0.99).

10,000 / (10,000 + 100) = 0.99

Now lets imagine we replace the first amplifier stage with a passive bass guitar pickup. Passive pickups by design have a very high output impedance - maybe something like 2,000 ohms. Now the ratio is;

10,000 / (10,000 + 2000) = 0.83
output = 0.83 x input

Suddenly, it's not looking quite as good. Reducing the input impedance has a similar effect. Lets go back to a 100 ohm output impedance, but lets reduce the input impedance to 1,000 ohms.

1,000 / (1,000 + 100) = 0.91

Now, imagine the worst of both, so input impedance is 1,000 ohms, output impedance is 2,000 ohms - notice now the output impedance is higher than the input impedance.

1,000 / (1,000 + 2,000) = 0.33
Ick! 2/3 of your signal is being lost, shunted to ground, gone forever.

Hopefully that's just enough to illustrate the concept for you. Keep in mind that all of this is frequency dependent, so just knowing a devices average input impedance doesn't necessarily mean it will respond equally to all frequencies.
 
#56
Re: less lows, "artificial" highs... IME changing the input impedance on my preamp(s) can have the effect of increasing the amount of high-frequency information into the amp, which can actually sound pretty terrible compared to the "naturalness" or "smoothness" of the subtle HF attenuation of a normal bass amp input.

Also with a very high z in the low frequencies don't have to "work as hard" (draw as much current) to transfer into the amp, which may (I'm just speculating) change the way the circuit actually handles the signal, resulting in a change to the way we hear it. Or maybe it's just a form of EQ pre-shaping.
 
#57
niftydog said:
Less lows could mean that it's got the same low freq. attenuation problem that many guitar effects have. Perhaps it's just not happy being used for bass?

So, you set sensitivity at minimum and tweak the + volume, right? You were plugged into the + output?! And how did you set it for unity gain? Switch it on and off and compare levels?
Click to expand...
Yeah, plugged into the + volume, turned down the "sensitivity" knob and adjusted the + volume knob to where it was at unity with the bypassed volume.
bongomania said:
Re: less lows, "artificial" highs... IME changing the input impedance on my preamp(s) can have the effect of increasing the amount of high-frequency information into the amp, which can actually sound pretty terrible compared to the "naturalness" or "smoothness" of the subtle HF attenuation of a normal bass amp input.

Also with a very high z in the low frequencies don't have to "work as hard" (draw as much current) to transfer into the amp, which may (I'm just speculating) change the way the circuit actually handles the signal, resulting in a change to the way we hear it. Or maybe it's just a form of EQ pre-shaping.
Click to expand...
It sounds to me somewhat like my tone travelling through too many pedals, but instead of remedying the loss, it does an artificial job of "fixing" it. I just want my straightjacked tone.:(
 
#58
niftydog said:
Well, ok, but YOU asked for it!
Click to expand...

So, based on what you wrote, the ideal situation is to NOT have an input resistor to ground and NOT have an output resistor. Clearly nobody does that, is it because the capacitance creates its own unpredictable ground impedance that needs to be tamed with something that has a more linear response?

If not, please elaborate.

Thanks for the engineer hat, I need to buy a book or something, but for now I would appreciate sapping the knowledge off of you.;)
 
#60
I've been using a VHT Valvulator for years as my buffer. I have a pretty extensive pedalboard and often have 50 feet or so of cabling before my signal hits an amp or DI. The Valvulator has worked great. It retains the inherent tone of your instrument & has a cool tube-amp like feel to it (as opposed to what you get when you plug straight into a console...).

I recently retired the Valvulator as I invested in a true-bypass looping system. I didn't think I'd miss having a buffer.... but I sure did! When all my pedals are bypassed, I'm still often looking at long cable runs & I had a feeling my passive basses were suffering a little high-end bleed. The Valvulator is a little large for my current pedal configuration, so I had one of these sent:
IMG_1563.jpg

It's a Barge Concepts GLZ-1 Volume/Impedance/Signal Buffer.
Link Removed

It's a pretty cool little tool.... It is:
1) A passive volume control +
2) A preamp with 15 db clean boost +
3) A signal buffer with adjustable output impedance

It's also true-bypass, but I intend to leave it on all the time.

So far I'm super impressed. The tone is as uncolored as I can detect & I'm not experiencing any weird high-frequency emphasis. The impedance control is pretty cool for matching active basses to fuzz/distortion effects. From the Barge sight: "As a passive signal emulator: The GLZ’s variable impedance control alters the resistive output of the buffering stage, to make the output signal appear more like a passive signal. This is particularly useful for bassists and guitarists with active pickups that want to send a 'passive-looking' signal to vintage effects that may not respond well to buffers."

For $99 you really should check one out for your buffering (as well as volume-management) chores!
 

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