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AU–X701 dc offset

mkneidl

mkneidl

New Member
I recently fixed my 701, a broken 2SA1306 I could replace, some resistors with wrong values and at least I recapped the beauty. The amp sounds great and is not going into protection, bias is ok, dc offset for hot/cold is ok, voltages are as in the sm but I don‘t get cold/earth below 1V for both channels. Any ideas?
 
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mkneidl said:
but I don‘t get cold/earth below 1V for both channels. Any ideas?
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A very common problem with this and other models that use a similar design. This 1V - it has a mind of its own and wanders all over the place - is that correct? - if so that is quite normal - and nothing to be too concerned about. I don't think it was ever correct even when new, unless Sansui used an unbelievably stable mains supply when setting this adjustment. ;)

You can sometimes improve on the range of variation of that voltage by simply starting the adjustment process all over again. Note that the hot/cold and cold/ground adjustments interact with each other.
 
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Thank you John for your reply! That‘s what I guess. At all there‘s no reason to fix it because it sounds well. I was just wondering if there is a specific and common problem. I love the sound of these vintage amps but they have to be treated well and I am afraid of running out of parts.
 
Bourns multi-turn pots help quite a bit, at least to keep the swing down while you set it.

A little late to be mentioning it now, but if you ever take apart again, they're worth it.
 
Thank you! Yes that is to mention, i already replaced all the pots. If the pot is turned clockwise the reading is some volts and when i turn cow the voltage drops down to about the middle of the pot to 1V and from that point ist stays at 1V.
 
Are you sure the resistors you replaced were not factory installed?

Secondly, with my AU-Alpha707 (which is the Japanese version of the X901, which is very similar to your X701), I was unable to set DC offset until I cleaned up glue near the main amp input diff pair and replaced several transistors and resistors in the area which had green furry legs.

And another vote for multi-turn pots.

Also, if you are unfamiliar with setting alpha amps, note that the offset is a fiddly iterative process too; you need to set hot-cold, then cold-gnd. They effect each other a bit, so sometimes it's best to ho half-way in Nelson Pass style, as you go round and round. And as hyperion says, don't be surprised if it wanders, a lot.
 
mkneidl said:
If the pot is turned clockwise the reading is some volts and when i turn cow the voltage drops down to about the middle of the pot to 1V and from that point ist stays at 1V.
Click to expand...
Probably caused by that interaction I/we have mentioned, set the hot/cold first and then try the cold/ground.
 
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