Mystery regulator

hihopes · 23rd July 2007, 10:09 PM

Can anyone help me identify a component? It seems to be a positive adjustable voltage regulator, TO-3P package, capable of at least 100v input. There are absolutely no identifying numbers or logo's on mine, though a friend with the same amp has a small logo on his regulator that looks like it might be S something (SGS?) Input is on the centre terminal. (So it is NOT a TL783). The guy who built the amp is overseas and out of reach. Please help me ..... I am missing my music!!!!!!!!!!

analog_sa · 23rd July 2007, 10:12 PM

A picture of the board? Could it be a transistor?

hihopes · 24th July 2007, 10:33 PM

Thanks for the suggestion. You could be right. I will try to post a pic 2 morrow. If it is a transistor, it seems highly unlikely to be faulty as the B+ is only 90v.
As for a pic, I don't know whether anyone will be able to make out much from it as this is a hybrid design and the power wired and signal path comes and goes from the board making it a bit difficult to work out what's going on without the whole amp in front of you.
The problem is a distortion that seems about equal in both channels, which is why I suspected a power supply problem. It is not severe, but is noticeable. I have since laid hands upon another amp the same and found the voltage readings I took from it pretty similar, so now I am even more in the dark. I did replace the output mosfets and found the distortion slightly worse, so perhaps it is to do with setting the bias point of the fets (which I have no idea how to do).

hihopes · 28th July 2007, 03:38 PM

Hi AnalogSA. Sorry no pics. I figured that if anything was going to be damaged, it was not likely to be a power transistor, so assuming you were right, I replaced a TO92 transistor (MPSA42) and an electrolytic cap (100v 100Uf) and the problem was solved. Actually, the amp was better than ever, probably because I used higher value parts. The MPSA 42 was replaced with MPSA43 and the cap was replaced with 200v 220Uf (taken from a switching supply). The turn on thump that I have lived with from the beginning is also gone now. I have since added an extra bypass to the cap (.22uF polyprop) with good results. I may try a 1000uF cap soon, since I have one and it is the same size as the 220uF. It may give me a bit of an overblown sound, but the only way i can find out is to try.
Thanks for your help.

23rd July 2007, 10:09 PM	#1
hihopes diyAudio Member Join Date: Sep 2004 Location: Cape Town	Mystery regulator Can anyone help me identify a component? It seems to be a positive adjustable voltage regulator, TO-3P package, capable of at least 100v input. There are absolutely no identifying numbers or logo's on mine, though a friend with the same amp has a small logo on his regulator that looks like it might be S something (SGS?) Input is on the centre terminal. (So it is NOT a TL783). The guy who built the amp is overseas and out of reach. Please help me ..... I am missing my music!!!!!!!!!!

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23rd July 2007, 10:12 PM	#2
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	A picture of the board? Could it be a transistor?

24th July 2007, 10:33 PM	#3
hihopes diyAudio Member Join Date: Sep 2004 Location: Cape Town	Thanks for the suggestion. You could be right. I will try to post a pic 2 morrow. If it is a transistor, it seems highly unlikely to be faulty as the B+ is only 90v. As for a pic, I don't know whether anyone will be able to make out much from it as this is a hybrid design and the power wired and signal path comes and goes from the board making it a bit difficult to work out what's going on without the whole amp in front of you. The problem is a distortion that seems about equal in both channels, which is why I suspected a power supply problem. It is not severe, but is noticeable. I have since laid hands upon another amp the same and found the voltage readings I took from it pretty similar, so now I am even more in the dark. I did replace the output mosfets and found the distortion slightly worse, so perhaps it is to do with setting the bias point of the fets (which I have no idea how to do).

28th July 2007, 03:38 PM	#4
hihopes diyAudio Member Join Date: Sep 2004 Location: Cape Town	Hi AnalogSA. Sorry no pics. I figured that if anything was going to be damaged, it was not likely to be a power transistor, so assuming you were right, I replaced a TO92 transistor (MPSA42) and an electrolytic cap (100v 100Uf) and the problem was solved. Actually, the amp was better than ever, probably because I used higher value parts. The MPSA 42 was replaced with MPSA43 and the cap was replaced with 200v 220Uf (taken from a switching supply). The turn on thump that I have lived with from the beginning is also gone now. I have since added an extra bypass to the cap (.22uF polyprop) with good results. I may try a 1000uF cap soon, since I have one and it is the same size as the 220uF. It may give me a bit of an overblown sound, but the only way i can find out is to try. Thanks for your help.

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