Re: [AH] Behringer - Vocoder and String Ensemble VC340

From Oakley Sound
Sent Wed, Jan 10th 2018, 09:51

 > https://www.diyrecordingequipment.com/products/l2a

This is a useful device but not because of its impedance transforming 
abilities.

Hi-Z or high impedance generally refers to input resistances of over 
47,000 ohms or 100K. For a guitar amplifier input it is generally a lot 
higher, perhaps even a few millions of ohms. Lo-Z is usually lower than 
2000 ohms. It's not that common on anything other than microphone 
pre-amp inputs.

Most mixers and audio interfaces will be around 47,000 ohms. High but 
not as high as a guitar amp input or a pedal input.

Passive pickups and microphones will work their best when plugged into 
amplifiers/pedals that have an impedance that the pick up is designed 
for. So for most electric guitars they'll be wanting a high impedance of 
over 1 million ohms. Any less and the volume pots will start working 
strange and it'll not sound right.

But we're synth players and most synths will have low 'impedance' 
outputs because they are driven by active electronics. That means the 
synth won't care a damn whether it's plugged into a high resistance or 
low resistance input. You'll get a little less output level when driving 
even a low-Z input but it should not affect the sonics.

So what's with the need for these re-amp units? When being used to drive 
guitar FX pedals they are being used as volume changers. So that's 
nothing really to do with resistance but signal level. The reason a 
guitar FX pedal distorts when you plug a synth into it is almost always 
because it is being driven too hard. Turning the volume down on the 
synth will usually have the same effect as will adding a -10dB in-line pad.

There are, I'm sure, some curious vintage pedals behave the way they do 
when driven from a passive pick up... maybe some 60s wah pedals. But the 
rest are quite happy being driven from a low impedance source if the 
volume level is correct. After all, consider what happens when you have 
two pedals in series with another. The second pedal doesn't start to get 
all distorted when driven from the low impedance output of the first.

Re-amp units like the one shown are useful for breaking ground loops, 
adding some transformer saturation, adding a bit of low frequency cut as 
well as volume changing. Handy things to have for sure, but when all you 
need is a passive volume control, there may be easier ways to get what 
you want.

Tony