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Amplifier Distortion, DC-Offset, and You!

what am i supposed to be measuring? where do i put the meter? and what am i supposed to be touching? i have a sansui 9090...and could i get some pics of that Kenwood 700M amplifier? i have looked all over the internet for pics and i cant find any...i guess that thing must be really rare!
 
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Do a search for '700M' here at the forums and you'll find a few pics.

As far as 'what you're measuring', you're looking for unwanted DC voltage at the output of the amplifier...the speaker terminals. Read the first post in the thread for more info on procedure.
 
i have about 3 in the left channel and about 13 in the right...and that might be why my right meter is tracking .1w behind the left...any way to fix that?
 
The meter issue is something completely separate...likely just needs calibrating. The offset you see won't cause that.
 
oh...but how do i fix the other probelm? i know its no biggie but i want to have this thing perfect for ebay. what do i need to swap out to get that 13 to a lower number?
 
I'm assuming that you are measuring 13mV. Don't sweat it.

...and don't take this wrong, but I don't have much motivation to help repair gear so one can flip it on eBay. I want to help guys so they can make sure their own gear is as good as it can get...for the sole purpose of furthering their audio listening pleasure. Assisting in the repair of something so it can be sold for profit doesn't trip my trigger much...if you want to sell it to make a buck, then spend a buck and have a professional do it for you. Claiming something is in great shape when you're selling it because someone on some website that you've never met told you to do this and do that to things and for reasons you don't understand are a long way from offering a 'perfect' unit.

You have a personal piece of gear that you love and want to ensure that it's running its best? Start a post and I'll help out.

(I know you're going to see this as a smackdown, and I don't intend for it to be that way...I do repairs for a living, and I like to help others, but not so that they can make a buck on eBay. My time is valuable and I feel I should give it for the reasons I choose)
 
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ok...np...i dont take it personally. i just wanted it in tip top shape cause we are short on cash right now since my dad lost his job at ibm. but like i said...its no biggie.
 
Viper - My 2 cents:

As EW described in his 1st post, 13 mV is pretty darn close to splitting a hair on a gnat's arse, and is getting well into the inaudible difference category.

Also, the lack of precision with an old pot may not even allow you to get it any closer than that, and you might actually make it worse instead of better.

You have an excellent reading. So the old addage "if it ain't broke..." definitely applies here.

- jw
 
ok...and speaking of pots. i noticed there is a board behind the whole light tray that lights up the phono am fm etc...and the tuner. what does that board do and what does that pot do? i want to make sure that im not tuning things that dont need to be tuned...this board is removeable...
 
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i know to leave it alone cause i have no idea what it does. and like john was explaining..."if it aint broke...dont fix it." i just wanted to know what it did.

it does have a number on the top "F-2550" if that means anything to you guys.
 
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Viper - I wouldn't know myself, though some other Sansui guys may pipe in.

If not, and you are insatiably curious enough, you can spring the $10 for the pdf manual from Optimum Business Solutions, here.

(And be warned: Sansui manuals "no talk so good the English" sometimes! :D )

But if you are selling it anyhow, probably not a good investment. Although I do commend you for trying to make sure it's in proper shape before selling it! That is a rarity these days! :thmbsp:

Good luck,
jw
 
Just measured my recently acquired Sansui 350A
Left is about 35mv,
Right is about 20mv,
close enough for me as this is my free "hold me over until I figure out what is wrong with my G-5700" amp.
Will post measurements of my malfunctioning g-5700 and my $10 Pioneer SX-434 when I get a chance. Thanks again for this info... I may have read this earlier, but do you have to have schematics or service manuals to check the bias voltage?
 
I just got a hold of a AU 717 to go along with my existing TU 717 and I thought checking the DC offset before doing much more to the unit would be a good idea.

Prior owner said unit sounded just great and only has one small problem. He said Phono 1 works but Phono 2 has a problem in that only one side works. I figured the switch is dirty and bought the unit via eBay at what I thought a good price.

Anyway the offset measures 29 mV on one side and Negative 6.3 mV on the other side.

Can this be possible that you can have a negative voltage? I checked it with two meters and sure enough it is a negative voltage and sure enough it is negative.

Well I shut the unit down and fired off this post to ask the experts if this is ok and should just adjust the unit per SOP and not worry.

Overall the unit is in really pretty good shape and I really want to get this fired up and into my collection. What do you folks think can she be saved?

Many thanks,

sdz
 
Wonder if you can help me EW. I want to see the point at which my amps clip, but I don't have an oscilliscope. I've been down at the electronics store (Maplin) but the cheapest one they've got is a handheld one for £100GB (about $180US). Seems like an awful expensive way to determine where your amp clips! Is there any other way to do this apart from using an oscilliscope? Thanks.

PS - This thread has an awesome cult following!!!
 
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