Laney Pro Tube AOR/Non AOR channel switch gain mod

[Mr Fixit]

It is often said on internet forums that there is too much difference between the distortion levels available on Laney AOR Pro Tube amps when switching the AOR boost channel on or off. People often say that they use only one channel (or solid state pedals on the non-boost channel).

The way the AOR boost works is as follows.

The difference in boost level is controlled by am opto coupler channel switching chip which connects a 2.7K Ohm resistor across the preamp 1 volume control 100K Ohm pot in parallel to attenuate the signal.

Looking at the schematics Laney seem to have changed the resistor that controls the levels from 1K Ohm (early series 1) to 2.7K Ohm later. A higher value resistor gives a higher level of distortion on the non boost channel.

On the pictures (links below) there is the later value of 2.7K Ohm resistor (red/purple/red colored bands) next to a black 6 pin chip (marked H11F1) on the input socket side of the circuit board

AOR30

http://i217.photobucket.com/albums/cc10 ... G_2906.jpg" onclick="window.open(this.href);return false;

AOR 100 (also applies to ARO50)

http://i33.tinypic.com/ae0g90.jpg" onclick="window.open(this.href);return false;

If you look carefully at the pictures there is another resistor already wired in parallel across the control on the potentiometer itself reducing the value to 50K Ohms. When combined with the effect of the 2.7K resistor this reduces the overall distortion level quite a lot on the non boost channel.

To adjust the difference in gain boost this 2.7K Ohms resistor can be replaced with a different value. A lower value would give even less distortion on the non boost channel (maybe even cleanish?) and a higher value anything from 2.7K Ohms up to say 100K Ohms for more boost (but less difference between boost and non-boost channels).

Or the resistance could be made variable by removing the resistor and connecting the original connections from it to variable resistor which you could mount in a new or existing hole in the chassis.

I made my amp fully channel switching so it uses each of the channel 1 and channel 2 volume pots (actually gain controls) separately on channel 1 to control the relative level AOR boost/non boost (in the original design they are in separate parts of the cascaded gain stages and both interact).

There is quite a lot to describe for that so I will come back to that in another post.

[vince1971]

could you send me your AOR mods,exactly what I was looking for!Vincechassey@yahoo.ca

[dimbulb]

Mr Fixit, count me as another who's interested in the AOR mod you alluded to in your last paragraph:

"I made my amp fully channel switching so it uses each of the channel 1 and channel 2 volume pots (actually gain controls) separately ..."

Thanks - dimbulb