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Minimax - DB Bias won't change? Help!

post #1 of 12
2/6/10 at 11:12pm
Thread Starter 
Hi all,
I finally built my Minimax kit from beezar and finally got to setting it up and biasing.
I followed the steps correctly, first turning down the DB bias 20 turns etc. Once I turned it on, the DB bias was around 19-20 mV for both sides. From there, I knew it was safe to go and do PS voltage which went fine. Then I went back to turning up the DB bias for both. This is were it gets weird. I turn the trimmer counterclockwise, and the the measurement doesn't change! I did try the other way, nothing much. I tried turning them both ways, spinning them quite a bit and nothing. There was a slight change but it didn't make sense which side was increasing or decreasing. I'm rather in a state of panic.. after several nights of work. Any tips or advice will be helpful. :-/

edit: I hope I am reading them correctly. I'm putting neg end of multimeter into ground and pos end into the db bias reading
spots. Using 200V range which says is Resolution 200mV. http://www.cyberpoet.net/ebay/centech.html
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post #2 of 12
2/6/10 at 11:33pm
from the millett minimaxwebsite :
when biasing the DB, you point the ends of the multimeter at TB1L or TB2L with TA2L, TB1R or TB2R with TA2R.

When I did it the first time same thing happened to me
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post #3 of 12
2/6/10 at 11:47pm
Thread Starter 
I tried that and I'm getting no readings. I flipped the pos and neg ends and tried that but no go.
Did I fry the transistors? Or I how could I check? Silly mistakes make a huge mess, oh boy.
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post #4 of 12
2/6/10 at 11:54pm
Don't worry, I've made a few mistakes assembling my minimax as well. What is the reading exactly from multimeter exactly? Which setting is your multimeter turned to now?
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post #5 of 12
2/7/10 at 12:05am
Thread Starter 
It was reading 0.00. its set at 200V on DCV.
and which end of the multimeter goes to which hole on the minimax?
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post #6 of 12
2/7/10 at 12:22am
I had the same problem a few weeks ago... I put the power transistors (2SC3422 & 2SC1359) in wrong. Not saying this is your problem but it is worth checking out before you do any damage like I did...
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post #7 of 12
2/7/10 at 12:36am
Thread Starter 
Haha Oberst, THANKS!
I set the multimeter to 2000mV and seems like that was the prob! I turned it on, checked and
the meter said around 40. I check the other side and similar. But this time, turning counterclockwise actually changes the voltage! THANK YOU both of you guys. I will post back once I get to the listening stage and I *actually* hopefully hear something coming from the amp.
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post #8 of 12
2/7/10 at 12:45am
Glad you seen that post before I edited it out.
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post #9 of 12
2/7/10 at 1:01am
Thread Starter 
I know.. I noticed. In the process of tuning up, (didn't sound yet) but I'm already so excited.
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post #10 of 12
2/7/10 at 1:30am
Thread Starter 
Ok, I got everything tuned up, DB bias at the moment are at 90mV.
So I go and plug in my bantamDAC, select the sound card under Audacious (On linux)
and I only hear buzzing through the headphones. Going to try reboot into windows,and try there. Hoping its a software prob.. argh
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post #11 of 12
2/7/10 at 1:33am
Bummer. Try to connect the the computer output directly to the amp first?
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post #12 of 12
2/7/10 at 2:58am
Quote:
Originally Posted by Inner View Post
Ok, I got everything tuned up, DB bias at the moment are at 90mV.
So I go and plug in my bantamDAC, select the sound card under Audacious (On linux)
and I only hear buzzing through the headphones. Going to try reboot into windows,and try there. Hoping its a software prob.. argh
Tell us the other measurements, too. Before you hook it up to anything again, measure the offset at the headphone jack and make certain that you don't have something amiss. Remember that the relay won't kick in until about 45 seconds from a cold start.

I'm not familiar with Linux, but there are several users who've confirmed the suitability of the BantamDAC with Linux, so that shouldn't be an issue.
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