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CH2 29th August 2003 05:58 AM

X-BOSOZ noise
Hi all

I have just built henrik's version of X-Bosoz using point to point.

Everything is as according to Henrik's plan but for the output caps I used a 47uf instead of a 33uf.

When I turn it on, it has a noise level of 2mv. This leads to audible noise from my speakers (91db).

I don't think the noise level of 2mv is normal. Under the scope it is even more drastic. The fluctuation is in 100mv with a frequency of 33khz.

Is there anyway that I can determine the source of the noise?

Hock Hua

Henrik 29th August 2003 04:05 PM

I will take a look at the problem tomorrow.
regards Henrik.

Henrik 30th August 2003 09:44 AM

Hi CH2

I havenīt measured the noise in my xbsoz, but my guess is that it is more like 2uV than 2mV, which is too much.

My xsoz has about the same voltage gain as an Aleph-X (is that your poweramp?), and my tweeter Dynaudio D28AF has a sensitivity at about 89dB, wich is a little under your 91dB, so in broad terms it shoud be comparable to your system. When I put my ear right on the D28 I can hear some noice from the xbosoz, but at a distance at 10-20 cm it is gone, so in my setup noice isnīt a problem, so I guess somthing is going wrong in your setup, but exactly where is hard to tell.

You can get noise from resistors, caps, bad solderings and powersupplys.
What kind of resistors and caps are you useing, in PS as well as in the xbsoz?
Have you measured yor powersupply alone?
What kind of fets do you use?

I hope you will get rid of the noise, one way or the other.

Regards Henrik.

CH2 31st August 2003 04:19 PM

Hi Henrik

Thanks alot for your reply. I guess could be due to bad soldering. I just started on DIY. The caps and resistor are pretty standard. As for the mosfet, I am using irf620 and 520.

I measured the PS noise, which is about 0.8mv.

I guess I will try to rebuilt the circuit again. By the way, is there any way for me to trace the source of the noise?

Thanks again for your reply.

Hock Hua

Henrik 31st August 2003 04:50 PM


You will allways get a little noise from powermosfets, but under normal circumstances it shoud be no problem.

As I recall, the xing of the bsoz causes a little more hiss. So while you are rebuilding, try to make the original bsoz so you can compare the noiselevel. If the xbosoz makes too much noise in your system compared to the bsoz, you can reduce the xfeedback and add some sourcedegeneration to keep the voltage gain down and still keep the X.

Your choise of fets seems okay to me.


Henrik 31st August 2003 05:17 PM

2 Attachment(s)

I took a closer look at IRF620 and 520, and they seems to have too much input capacitanse, the -3db highend rolloff will be around 75 kHz and 32 kHz, which isnīt good enough. The X is very sensitive to the fets input capacitanse.

Attaced scematic with reduced feedback and some sourcedegeneration.


CH2 1st September 2003 12:59 AM

Hi Hendrik

Thanks a thousand for your respond. I will try the changes to see if it reduce the noise. Actually, I was suspecting that my soldering skill is the main culprit for the noise.

Thanks again for the help. Really appreciate that. This forum really rock. :cool:

Hock Hua

Henrik 1st September 2003 11:06 AM


Just one thing, in the scematic from 3 october 2002 I forgot to draw C3 and C4 (from Nelsons original scematic) which is caps at minimum 10000 uF, if you dont have them in you wil get a lot of noise.
One cap with plus connected to the node R101/R102/R118 and minus to Gnd, and an other one with plus to Gnd and minus to the node R104/R106/R117.

This could be your problem.

Regards Henrik.

CH2 4th September 2003 02:15 PM

Hi Henrik

Sorry for the late reply, my comp was down. Damn the virus.!!

Thanks for the pointer. I am using 880uf as according to the original circuit.

After I rebuilt the circuit, the noise is still there. I guess I must be having some really bad caps then. Will have to redo it again :cannotbe:

Anyway, really appreciate your help.

Hock Hua

Henrik 4th September 2003 02:22 PM

sorry to her you still have this noise!
And you are right, the last supply cap is minimum 1000uF not 10000uF, but anyway I uses 4700uF before and after regulation.

I hope you will find a solution.

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