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Laney AOR 50 aus zweiter Serie Modden?

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toxic_zombie:
Sorry, ich kann dir leider selbst nicht direkt weiterhelfen aber die Frage gab's im Musikerboard auch schonmal:


--- Zitat ---So, mein AOR brüllt wieder!!! Oh Gott was iss das nur für ein geiler Apparat!!!!!!!!! Hab jetzt auch mal die Gitarre komplett auf D gestimmt, statt nur Drop D
ABER, der Bass Boost ist einfach zu fett. Wenn ich den ziehe, erschlägst mich fast. Machst du ihn dann aus, klingt das Teil wie ne Blechtröte.

Hab einige Vorstufenröhren und ver. Kombinationen probiert (Auch mit ECC81) aber nichts zufrieden stellendes.

Daher mein Aufruf und Bitte an die Freaks mal den Schaltplan anzusehen, und mir vielleicht Tips geben wie ich den Bass Boost entschärfen kann

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Darauf kam diese Antwort:


--- Zitat von: aus dem metroamp-forum ---There are different versions of the AOR series. I’ll assume you have the 50W Head (as the Combo has 9 knobs) and that it is a series 1(as that is the one that most people find to have the excessive bass boost issue). If it doesn’t have series 2 written on the front panel then it is a series 1. I'm also assuming that you don't mean too much bass compression in the distorted sound for which there are other mods to make it tighter. I can also share these if you want.

The issue is that the tone boosts interact with the level of the master volume control and "borrow" some of the amps total volume when the master volume is set low. So with the bass boost on and the master volume between 0 and 2, the bass becomes very loud and dominates the other frequencies. This effect is reduced as the master is turned up but then the overall volume can get too high. As the boosts are part of the master volume circuit the normal tone controls don’t really control the boost levels directly.

Imagine playing a guitar with just a tone control and no volume control through a loud amplifier that has no controls. You want to turn down the volume but the guitar has no volume control so all you can do is turn down the tone control. The high frequencies are reduced but the lows are still loud.

Now imagine the same guitar with a combined tone and volume control. As you turn down the control the volume is reduced but so are the high frequencies leaving too much bass. So you turn up the control to get more highs but then the volume is increased and it all gets too loud again.

Music sounds better louder as the ear naturally hears more highs and lows. Loudness controls were developed on older hi-fi amps to give added bass/treble boost at low volumes. The combined effect of the master volume and tone boosts on the AOR amplifiers is a kind of loudness control.

The boosted levels of bass versus treble on the master volume can be controlled.

Solution 1

If you do not want to modify the amplifier you can use a volume pedal or an effects unit that has a volume control as an external “true” master volume in the effects loop of the amp. Then with the boosts on you can adjust the amps internal master volume to the overall volume/tonal balance you like – as it is increased from 2 to 5 the bass reduces and the treble increases. Above 5 the boosts cease to be effective.

If you don’t mind modifications then there are a couple of things you can try.

The tone boosts are passive but seem very powerful, particularly the one for bass on the series 1 as it has a sort of two stage bass boost.

Normally a master volume control has the low volume side connected directly to ground/earth. When the volume pot is turned down all frequencies are attenuated by the same amount.

However on the series 1 before connecting to ground the master volume low side connection instead passes though a 220nF capacitor (C16) which has a 22K resistor (R27) in parallel across it. When the boost is on this is just like a guitar tone control with the highs reduced.

There is also a second part to the bass boost circuit. From the high side of the master volume control there is a second bass boost connection going via a 33K resistor (R25) then through a 15nF capacitor (C15) to ground.

Laney reduced the amount of bass boost on the series 2 connecting the master volume low side directly to ground (and leaving out the 220nF capacitor/22K resistor) so they must have been aware of the issue.

Solution 2

You could try connecting a direct ground connection to the low side of the master volume control (and remove the existing wire going there – tape up the end safely). Or alternatively you could try a lower value resistor than 22K to reduce the boost.

Solution 3

If you don’t want to use an external volume pedal/control there is a second master volume control on the AOR50 (and AOR30) called “preamp 1 level” which could help control the overall volume when using the tone boosts. It is intended to control the volume boost heard only when the preamp 1 AOR channel distortion pull boost (or foot-switch) is engaged. So it is not active when the AOR boost is off. This control does not have the low volume side connected directly to ground/earth. In this case the low side first passes through an opto-coupler chip (VT2) which connects the ground to preamp 1 level control low side only if the AOR distortion boost is engaged.

To prevent the volume getting too loud overall I suggest wiring the preamp 1 level potentiometer permanently into the circuit by connecting the low end to ground directly. Since it actually comes after the amps master volume it now becomes the actual master volume control and lets you set the tone boost sound you want on the original M/V control at the volume you want using the preamp 1 level potentiometer. Remove the blue wire already there which goes to the opto-coupler switching i/c and tape it up safely.

This approach of having both master volumes on has the advantage of allowing a lot of bass at controllable volumes but does have the disadvantage that you lose the switchable master volume.
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Sieht so aus als käme man an etwas Lötarbeit nicht vorbei...

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