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Boz preamplifier
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Old 9th November 2017, 08:08 AM   #1
Giovanni malluzzo is offline Giovanni malluzzo
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Default Boz preamplifier

Hello everyone. I'm young and I'm new to the forum. i'm sorry for some writing mistake but i'm using google translate. the reason for my thread is that I built a pre Boz and I have at the output i have a potentiometer of 50k ohm alps, rotating up to 99% all ok, rotating until end of the race at 100% feels a strong bang.I also tried an input potentiometer to reduce the strong signal of the cd, but I input potentiometer produces a slight mass noise during rotation, and at maximum rotation it bumps as in the output potentiometer. I read an article where they say that you can adjust the bias to the symmetrical clipping point, i have a dats with oscilloscope function but i do not know where to connect the two terminals. Thanks in advance for your answers!
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Old 9th November 2017, 09:51 AM   #2
AndrewT is offline AndrewT  Scotland
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maybe the wiper is lifting off just as it reaches the end stop?
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Old 9th November 2017, 12:12 PM   #3
Rodeodave is offline Rodeodave  Austria
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Boz preamplifier
BOZ has a lot of gain, resulting in very high input sensitivity (easily driven into clipping). There are several post on lowering the gain for the BOZ. See BOZ replacement parts post #22 for example.
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Old 9th November 2017, 12:16 PM   #4
Giovanni malluzzo is offline Giovanni malluzzo
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I do not know. what do you mean exactly?
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Old 9th November 2017, 12:18 PM   #5
PMA is offline PMA  Europe
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Boz is one of the simple Pass??

Re pot issue, make sure you have no DC voltage across the pot.
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Old 9th November 2017, 02:56 PM   #6
Giovanni malluzzo is offline Giovanni malluzzo
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thanks to everyone for help. regarding input distortion, I lowered the voltage to about 3v (original 4v). while I still have the potentiometer problem that just comes to maximum rotation makes the bang.
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Old 9th November 2017, 10:42 PM   #7
Giovanni malluzzo is offline Giovanni malluzzo
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thank you very much for the answers, and for kindness. I solved the problem. the bang that made the potentiometer rotated to the maximum was like the bang that makes the IRF610 when it lights up and goes off, under a certain voltage. I had set the trimmer to 2.85v at IRF610 SOURCE, and 30v at DRAIN, and maybe I was at the IFR610 ignition voltage limit. then I set the trimmer to 3v to SOURCE, and 28v to the DRAIN, and the potentiometer does not bother anymore.
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Old 9th November 2017, 10:50 PM   #8
Giovanni malluzzo is offline Giovanni malluzzo
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for the problem of input distortion, i do not know how to use oscilloscope, i hope the 3v adjustment to SOURCE of the IRF610 is fine, otherwise i will test ears or. said this, thank you mr. nelson pass, which gives us these very simple and cheap projects, but very well played. i am very happy with my BOZ and with a little money i have a pre that SUON !!
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Old 10th November 2017, 06:56 PM   #9
Nelson Pass is offline Nelson Pass  United States
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Boz preamplifier
Simple and Cheap. Love those words....

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Old 10th November 2017, 07:03 PM   #10
PMA is offline PMA  Europe
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Quote:
Originally Posted by Nelson Pass View Post
Simple and Cheap. Love those words....

Understood, especially those words
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