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Old 7th November 2005, 04:53 PM   #11
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I am having another sort of strange problem... The left channel (the one that was giving me fits before) is a little lower in volume than the right. My speakers are equal distances from me, so that shouldn't be the cause. Is it possible something could have been damaged during that time of no bias across the left channel?
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Old 7th November 2005, 07:01 PM   #12
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Default No effect

Try swapping the preamp leads. If the channels are out in level, there is a problem.
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Old 7th November 2005, 09:20 PM   #13
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Whew... I switched the inputs to the amp and the louder channel then became the left instead of the right. So, the problem resides with my computer sound card. Funny I never noticed it before when listening through my headphones... Glad to know the amp is not to blame. Now I just need to rig a preamp somehow so I can hook it up to my real CD-player...
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Old 30th September 2011, 02:40 PM   #14
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DC value on resistors for this model is 24-25mV, not 120.
With 120 there will be overheat with a lot of problems.
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Old 8th May 2017, 04:18 AM   #15
Doc777 is offline Doc777  United States
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Bump. One side of my Forte 1A is cold. Pot is bad. Can anyone confirm the factory bias voltage? I always set it at 47mv. Read it somewhere. Heatsinks are warm but never hot.
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Old 8th May 2017, 11:30 AM   #16
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Quote:
Originally Posted by Doc777 View Post
Bump. One side of my Forte 1A is cold. Pot is bad. Can anyone confirm the factory bias voltage? I always set it at 47mv. Read it somewhere. Heatsinks are warm but never hot.
Please see post #2.
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Old 19th May 2017, 06:43 PM   #17
Randy Y is offline Randy Y  United States
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Default forte 1a bias

My service manual says 140mV but Nelson Pass says to use 120mV but make sure you check them all both upper and lower.
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Old 19th May 2017, 07:23 PM   #18
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Depends on whether you are measuring across Emitter pins of complementary
parts or across individual power resistors.

Measure what you have and then increase it veeerrryyy gradually until the
amp operates at 50 deg C on the top of the sinks after 1 hour or more with
the top on.
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Old 22nd May 2017, 03:39 PM   #19
Randy Y is offline Randy Y  United States
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Default it is not pot and not transistors

What else should I check to find where bias will not adjust. I replaced the pot and the checked all the transistors. Not sure where to go next?
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Old 22nd May 2017, 06:46 PM   #20
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Here is the schematic.

If you can't develop enough bias voltage, then perhaps you want to
increase R11 or R12 or decrease R14. Easiest is to place some resistance
in parallel with R14. Take whatever the value is and put something about
10 times its value in parallel with it.

Be careful - that should bump up the bias quite a bit.
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