Technical data

APPENDIX - Level Problems

No Signal

This problem might be caused by balanced wiring. If the signal almost completely drops when the

alpha compressor is activated, it is probable that a pin of the XLR connector at the input is not con-

nected. As the input stages feature transformers, both pins have to be connected. The classic case

for this problem would be a balanced XLR connection that is connected to an unbalanced output

that only uses ground and pin 2. Connecting pin 3 to ground should solve this problem.

Slight Level Jump

Under certain circumstances, pushing the active switch may cause a small change of level. If there

is no noticeable dierence between Bypass and Active when in stereo mode with activated Direct

buttons and Mix controllers fully turned counter-clockwise, everything is OK. But if there is a small

change of level somewhere between 0,5 - 1dB, the input and output impedances of the devices

preceding and succeeding the alpha compressor might be the reason. A high output impedance

(approx. 1kOhm) of the preceding device and a low input impedance (<4700Ohm) of the succeed-

ing unit are especially critical. If the compressor is in Bypass, the preceding device will be loaded

with the input impedance of the alpha compressor itself plus the input impedance of the suc-

ceeding unit. This cumulative load might result in a decrease of level. If now the alpha compressor

is activated, the preceding device only “sees” the alpha compressor and no longer the following

unit. Therefore the load decreases and the level rises as a consequence. Especially tube equip-

ment tends to produce this phenomenon. Generally speaking, output impedances smaller than

150Ohm are recommended for a trouble-free signal chain.

Large Level Jump

In some equipment the output stage is designed in a way that the level will always stay the same

– no matter if it is hooked up with a balanced or an unbalanced connection. If pin 3 is connected

to ground, for example, the level at pin 2 will automatically become twice as loud as before. These

kinds of output stages are usually unproblematic. But there are also stages that cannot compen-

sate for that. In these cases the level at pin 2 will stay as it is, even if pin 3 is connected to ground.

If the alpha compressor is placed between a device with that kind of output stages and a device

with unbalanced inputs and with pin 3 connected to ground, it is possible that the level jumps up

by 6dB when the compressor is activated. As a general rule, input stages with balanced connectors

are always the best choice. In case these are not available, the rst attempt to solve this problem

should be to disconnect pin 3 at the XLR inputs of the alpha compressor and then connect it to

ground. This generates an unbalanced signal that should not shift the level anymore.