ISP Technologies VECTOR 210 - Manual (Page 8)

SPEAKER LEVEL SYSTEM CONNECTIONS
When using the Vector 210 with a tube guitar amplifier and connected to the
speaker output, it is possible to have a micro-phonic feedback occur due to the fact
that the 4x12 speaker cabinet can act like a microphone on the input of the Vector
210. This can cause a low frequency howl (feedback) due to the fact that the tube
amplifier has relatively high output impedance. This high output impedance is
because the tube amplifier uses an output-coupling transformer to match the
impedance of the speaker with the correct output tap on the output transformer.
The lower the impedance of the speaker being driven, the less chance for this type
of feedback to occur, but there are a number of things that can be done to
eliminate this problem.
1. Reduce the output level of the Vector 210, which will reduce the gain
between the 4x12 speakers and the output of the Vector 210.
2. Move the location of the subwoofer away from the 4x12 cabinet.
3. Use a lower impedance cabinet to reduce the impedance drive from the head.
Comment [ISP1]: …it is possible to have
micro-phonic feedback occur due to the fact that…
Comment [ISP2]: The lower the impedance of
the speakers being driven, the less likelihood for this
feedback to occur.