Sausui 9090 Bias issue

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#46
MR Overclock said:
What I actually Think more important than same current both sides npn pnp, is that you measure the BE voltage of your output trasntiors, Both trasnisotrs should have same voltage, BE voltage indicates how turned on the transitors are, more BE voltage more idle current it is drawing.

Some times theres a extra pnp or npn trasnitor used, so its we want to have same BE voltage not same idle current both sides.
Click to expand...

To correct my self, if the transitor is in common collector set up which most amps are in for outputs, you need to measure BC voltage to be same on both npn pnp, that means both devices are drwaing same current.
 
#47
Just got back to this project. Had planned on putting in a larger main caps to see if it diminishes buzz. Got 2 12000uf I pulled out of a nak amp. The originals are 6800uf. Will this risk damaging anything just for test purposes?Just trying to see if problem goes away then order new 10000uf if this is problem.
 
#48
No it will not damage anything, if you stay within 50 000 uf per channel your more than likely allright.

I have 152 000uf hooked into mine and with only a 6 amp diode rectifier no plorbems at all

Larger capacitors should take away buzz, but for buzz to fully dissapear in tweeters I assume that you'll need about 40 000uf or more

(Some times circuit tuning can take away buzz, mostly would be bias related tuning)
 
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#49
Hey Craig,
Do you still have the 9090 handy? ZD1 on power supply board is 1/2 watt according to service manual but appears large for a 1/2 watt. I couldn't find reference for the markings on it. Mine has 135NR on it. Do you know what value it is?
 
#50
Usually you can tell by the lead size, 1N47xx or 1N52xx but this one is on the large size for a 1/2W. All of the spec sheets for the EQA01 series say 1/2W.

By the way I just put the 9090 back together this morning and then you posted, what timing, bad timing that is.

Craig
 
#53
Put in the larger main caps and didn't solve issue. My scope is bad but I measured 40mv ac on main supply rails with a meter. I don't see much in line with main power such as chokes or twisted wire or magnets that you see on more modern receivers. Is it possible that I have noisy house wiring that is being picked up by this receiver that is being filtered by my other modern equipment?
 
#54
Just got back to this project. Noticed that when using a preamp to power this that no buzz. Also when jumpers remove no buzz. What's strange is when you remove cable from board going to positive lead of output jumpers you still get buzz. It's only 3 inch cable. How is that possible? Could tuner section be interfering with this cable somehow?
 
#55
Do you mean buzz or hiss? Hiss coming from the pre amps in these old Sansuis is very normal, and not fixable. If you want hiss-free operation, disable the pre-amp entirely by going into the power amp directly. I am currently listening to a very hissy Sansui AU 8500, with a DAC connected to the power amp section. Sounds lovely, and no noise.
 
#57
I just put 9090 in home system and now realize buzz is only about 2 feet away from tweeter. It's inaudible beyond that. I had my shop speakers right there which made it seem more pronounced. I'm thinking now maybe normal? I can live with it in any case. I noticed the unit does need tuner aligning which I do not have the equipment to properly do. Main issue is max tuner signal only goes to 3.5 on meter and you have to be exactly on station to receive it(no wiggle room here). Is there way to align it using strong station?
 
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