smurfer77
Super Member
Hello,
I have question about the output adjustment. In the service manual it is written that we had to apply a sinus 1000Hz to aux 2 and adjust vr801/2 until both crete are clipping.
When I try this setting, I have just the bottom crete that is clipping but never the both. Did I miss something ? Or is it an other way to make this settings ?
Sometimes the clipping at one side (crest or trough) is 'hiding' if your settings are way off centre.
You should be able to centre up so you have clipping at both top and bottom using just VR801 and VR802. Starting from a low volume, turn up the volume until you just have clipping on your one channel..... just a tiny bit of clipping on your bottom part of your sine wave. Then adjust the appropriate VR (801 for L, 802 for R) - turn in the direction such that your tiny bit of clipping disappears. (If the amount of clipping is unaffected by VR adjustment something is wrong, possibly with the VR, but it's unlikely both VRs are dead). Then turn up the volume a bit more and you will get clipping again... adjust VR again so that you remove the clipping and repeat and repeat. At some point both channels will clip. Make it so as you turn up volume you just go a bit into clipping on both channels at the same time. Repeat process for other channel (using other VR). Others have slightly different approaches. I like this way if you are really far off centre, to help find centre and it's quite precise to make onset of clipping occur at same volume for top and bottom of peak compared to visual approach of making clipping about the same level (as described in next paragraph and manual)
Another approach is much simpler and basically what the manual says to do - just push into clipping and adjust VR so that amount of clipping is even - you should be able to affect the clipping with the VRs. If you only see clipping on one side, turn the volume up further until you have clipping on both sides, and then adjust VR so that level of clipping is similar at top and bottom (then turn down volume so you are just at onset of clipping and match it up onset of clipping). If you turn volume up to max and still only see clipping on one side you are way off centre and you might need to turn up your input voltage so you get into clipping earlier on your volume control - proceed with caution in that direction - the amp might not like being driven too hard into clipping for extended periods.
There is a rough approach that you can use that people who don't have oscilloscopes can use, but since it sounds like you have a scope, might as well work out the proper way. if none of this works maybe start-up a thread on your issue and we can all help you
Cheers
David
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