audio research ls 27
- Thread starter decca61
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arts
Addicted Member
Richard,I seriously doubt that there is anything that can be done to ''upgrade'' this unit. It was only introduced about five years ago,and carried a suggested retail price of $7K
USD. Other than perhaps replacing the tubes,which may need replacing at this point if original,I do not believe for one second that Audio Research left any areas lacking in this product.
If by ''upgrade'' you mean a better preamp entirely,there's always the Reference series
USD. Other than perhaps replacing the tubes,which may need replacing at this point if original,I do not believe for one second that Audio Research left any areas lacking in this product.
If by ''upgrade'' you mean a better preamp entirely,there's always the Reference series
and give me that MID- FI preamp to go with the Dual 75 i picked up !!!inline_phil
New Member
I picked up a used LS-27 several months ago and yes, it is a VERY NICE preamp. But as things would have it, trouble brewed under the cover.
Every now and then, it would spontaneously go into MUTE mode. Contacting ARC, they said another model using a similar mute circuit had a problem with the 4-wire power cable to the front panel. Poor crimp, poor colder joints on both PC boards were stated as the source of this problem and recommendations were to re-solder everything and solder the crimped connections too.
It was quite a challenge to remove everything and access not only the solder pads for the cable but also the solder pads for the 4-pin connector on the front panel. But doing so with a lot of patience proved to be fruitful. No more spontaneous muting.
While inside, I looked at the grounding scheme and discovered it was not single-point grounded [yikes!]. The ground wire from the IEC jack ran to a nearby stud on the rear of the chassis and another ground ran from the PC board power supply through a standoff to a different part of the chassis. The simple fix was to disconnect the IEC wire to the chassis, add a longer length of wire to the IEC jack ground pin and connect it to the power supply board screw via a ring lug at that standoff post. Ground loop gone.
The other thing I noticed was that the power transformer wires, while twisted, were not twisted tight. Marking the orientation [phase] of the wiring first and then removing the wires from the PC board, I tightly twisted them and re-soldered them carefully into place. I also tightly twisted the wires to the power switch that runs underneath in the same way.
Lastly, I added non-inductive snubber circuits [thank Nelson Pass] to the output side of each diode bridge [10 ohm + 0.1uF].
This simple upgrade turned a very nice preamp into a great preamp. All I can say is that ground loops are the bane of high-end audio. Fortunately, ARC does not use one of those computer optimized PC board layout programs that build a ground plane and along with it countless numbers of ground loops.
Still thinking of other mods but for now this is it.
Every now and then, it would spontaneously go into MUTE mode. Contacting ARC, they said another model using a similar mute circuit had a problem with the 4-wire power cable to the front panel. Poor crimp, poor colder joints on both PC boards were stated as the source of this problem and recommendations were to re-solder everything and solder the crimped connections too.
It was quite a challenge to remove everything and access not only the solder pads for the cable but also the solder pads for the 4-pin connector on the front panel. But doing so with a lot of patience proved to be fruitful. No more spontaneous muting.
While inside, I looked at the grounding scheme and discovered it was not single-point grounded [yikes!]. The ground wire from the IEC jack ran to a nearby stud on the rear of the chassis and another ground ran from the PC board power supply through a standoff to a different part of the chassis. The simple fix was to disconnect the IEC wire to the chassis, add a longer length of wire to the IEC jack ground pin and connect it to the power supply board screw via a ring lug at that standoff post. Ground loop gone.
The other thing I noticed was that the power transformer wires, while twisted, were not twisted tight. Marking the orientation [phase] of the wiring first and then removing the wires from the PC board, I tightly twisted them and re-soldered them carefully into place. I also tightly twisted the wires to the power switch that runs underneath in the same way.
Lastly, I added non-inductive snubber circuits [thank Nelson Pass] to the output side of each diode bridge [10 ohm + 0.1uF].
This simple upgrade turned a very nice preamp into a great preamp. All I can say is that ground loops are the bane of high-end audio. Fortunately, ARC does not use one of those computer optimized PC board layout programs that build a ground plane and along with it countless numbers of ground loops.
Still thinking of other mods but for now this is it.
