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Old 12th February 2009, 12:41 AM   #1
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Unhappy SL-10 Noise

Has anyone experienced an increase in noise from the line stage of their SL-10? It must be the output stage since it does not change with the level control. The power supply voltages are spot on. One channel is a little worse than the other. It is definately audible through a Threshold SA 3.9 driving WATT 5/Puppies.
Thanks,

Also, are there any good quality schematics of the SL-10 online? The only one I found is hard to read and the link to the one on the Pass Labs site is broken.
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Old 12th February 2009, 10:45 PM   #2
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www.passdiy.com/np/threshold/sl10-sch.tif

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Old 13th February 2009, 11:42 AM   #3
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Thank you Nelson! I've done a little measuring and the noise is definately in the high level gain stage. The DC offset is fine (<.001V) and the power supply is quiet so I'm guessing some transistor noise. I'll get some more and try some "plug and pray".

Thanks again!
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Old 13th February 2009, 06:33 PM   #4
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What kind of noise?
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Old 13th February 2009, 07:18 PM   #5
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Hi Nelson,
The noise is kind of a gritty white noise in the right channel (brown noise?) and the left channel is a lower level white noise. Relative to 700mV output signal, with the volume at 10:00, it is about 78db down in the left channel and 72-70db down in the right channel. With the volume pot all the way down it doesn't change. The phono stage (MC) is almost quieter than the line stage. Its those silly WATT/Puppies. Their just too efficient.

Thanks,
Doug
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Old 13th February 2009, 11:09 PM   #6
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No they're not.

Start by resoldering every connection on that channel.

After that, start replacing parts beginning with the front end and
feedback parts.

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Old 14th February 2009, 02:13 AM   #7
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Will do!! It may be a rainy day tomorrow so that will be a good day to dive back into it!

Thanks again!
Doug
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Old 16th February 2009, 12:32 PM   #8
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Swapping the input transistor on the High Level gain Stage did the trick so that now both channels have the same noise measurement. Unfortunately the noise in both channels is still fairly audible in our system. It is real quiet out where we live and the SA 3.9 has beau coup gain when paired up with the WATT 5s. I measured the SL-10 using 1v-out as a reference to compare it with some SL-10 specs that are on the web. Of course 1v out would blow the windows out of the house with the 3.9! On the RIAA stage with 24mV in and 1v on Tape out I measured -74db S/N unweighted and -82db Wtd. On the Line stage with 1v on Tuner In and Volume Pot set for 1v on Main Outputs I measured -82db S/N unweighted and -89db weighted. Since I can blow the windows out with the volume at 9:00 I may just build an attenuator to plug into the input of the SA3.9. That will give me a little more range on my preamp volume control and knock the noise down also. I guess Iím just an old fart now and I donít listen at the levels that I used to!

Thanks for the advice. And happy listening!!!
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Old 16th February 2009, 09:23 PM   #9
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Hooray!
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