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Giovanni malluzzo 9th November 2017 08:08 AM

Boz preamplifier
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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!

AndrewT 9th November 2017 09:51 AM

maybe the wiper is lifting off just as it reaches the end stop?

Rodeodave 9th November 2017 12:12 PM

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.

Giovanni malluzzo 9th November 2017 12:16 PM

I do not know. what do you mean exactly?

PMA 9th November 2017 12:18 PM

Boz is one of the simple Pass??

Re pot issue, make sure you have no DC voltage across the pot.

Giovanni malluzzo 9th November 2017 02:56 PM

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.

Giovanni malluzzo 9th November 2017 10:42 PM

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.

Giovanni malluzzo 9th November 2017 10:50 PM

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 !!

Nelson Pass 10th November 2017 06:56 PM

Simple and Cheap. Love those words....


PMA 10th November 2017 07:03 PM


Originally Posted by Nelson Pass (
Simple and Cheap. Love those words....


Understood, especially those words :p

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