POWER AMP Altec Lansing 9444B patulong po

[snider]

POWER AMP Altec Lansing 9444B

kapag mahinangmahina ung volume mron sound pero distorted

mron syang protect indicator at naka ilaw ung LED both channel

mron pa isang indicator CLIP kapag nilalakas ko ung volume iilaw ung clip LED tapos mawawalan na ng sound kahit mahina wala na

lahat ng transistor na check kona ok nmn.

ito po ung schematic diagram.

http://www.altecpro.com/pdfs/vintage/ElectronicsAndTransformers/powerAmps/9444B%20Power%20Amplifier%20Service%20Manual.pdf

[audiomachines]

swap op amp with a good channel to verify, QSC circuit ang ginagamit nito grounded collector wlang mga mica insulator ang output trannies. klimitan pag distorted ang sound, ok output tranies ung op amp sa front end ang culprit

[snider]

both channel po sira,distorted pag nilakas volume mag clip na.

[audiomachines]

my gumawa nba ng amp na 2?, ndi kya pinihit ung mga trimmer ng negative at positive current limiter adjust? pki check sir ang supply ng mga op amp kung ano value ska ung sa filter/ouput capacitors dapat equal ung voltage nila i.e. Vcc+ to ouput node, Vcc- to output node

[snider]

my gumawa na sir pero nung buksan ko kabilang channel lang ung my hinang,pero both channel sira eh,tapos sa trimmer hindi ako sure kung ginalaw..equal po ang voltage sir.

[audiomachines]

ok sir pki verify kung nsa near midpoint ung wiper arm ng mga trimmer ng current limiter, ok nman po bas ir supply ng mga op amps? +/-15Vcc

[danny]

sori late na ako i just got your PM ngaun lang
sensiya na

lets say ok mga outputs mo
check mo din muna yung mga supply
ng opamp mo like what audiomachines said
pag nde ok naka sibak zener or resistors etc.
usually front end na encounter ko pag sa mga commercial
poweramps, minsan resistors lang kung ok ang mga outputs at front end.
make sure na balance ang rail voltages mo?
ingat lang sa pag sukat at baka maputukan ka ng output.
also a reminder na pag mag kakalas ka discharge ka ng mga capacitors
(safety reminder lang) we dont want you to get hurt

by the way, may oscilloscope ka ba?

[snider]

@audiomachines
icheck ko sir post ko ulit kung anu balita.

@danny
ok lang po hindi nmn nagmamadali ^_^.

samalamat po.

[TinTopHack]

@snider

Meron ka bang mas malinaw na schematic.

@audio
OK din tong QSC na innovation. If I remember correctly ito yung connected ang speaker between ground and center tap ng power transformer. Tama ba?

[akosiikem]

Bro nung pinagawa mo ba ito eto na yung dati nyang sira?

[audiomachines]

@TinTopHack

 yes sir npaka simple ng ckt ni pat quilter pti ung protection scheme kinacurrent starve nya ung op-amp sa front end pag bumaba ng sobra ung load impedance hence limiting voltage drive sa output stage. download na lng kyo sa QSC website ng schematics. Lahat naman ng topology ng amp nila ganan grounded collector wlang mga mica insulator kya wlang thermal inefficiencies na inherent sa mga nka mica insulator na power devices 

[snider]

@TinTopHack
sir yan lang po ung nakita ko sa net nag search nako same lang ganyan lahat.

@akosiikem
bro ako ung gumagawa ngaun,hnd ko alam gaano history ng ampli.

@audiomachines,danny
mga sir hindi ko pa na check ung ampli busy pa dito sa shop hindi ko maisingit,pag na check ko post ko po result.

thanks po sa lahat ng nag rereply.

[danny]

ok no problem   

[snider]

na check kona po ulit ung amp,hindi equal ang supply sa filter capacitors

[danny]

wala ka bang leaky na filter caps kaya
gaano ba kalaki ang difference
madalas ako makagawa sa
mark levinson ng leaky filter caps
actually you can see na lumalabas talga yung chemical sa screw terminals
unbalance supply as much as 20 to 30v difference
yung mga diode ok naman

can u check the supply seperately
saka minsan  dont get confuse yung ibang supply ok pag walang load
pero pag naka load na saka nag dodrop supply

[snider]

38v+ 42v- both channel same ang voltage,4700uf 100v ung filter..

medyo confuse na nga  po ako sa ampli na toh hindi ko kasi kabisado ganitong design hehehe.

[snider]

hindi din stable ang supply pag ginagalaw ko volume,

[danny]

maliit lang ang difference pero dapat as much as possible close yun
what do u mean nde stable ang supply pag ginagalaw volume?

[snider]

tumataas bumababa po ung supply,nahihilo na talaga ako sa amp na toh,hindi kagaya ng ibang amp usualy my shorted transistor lang of busted resistor...kung sa bias po ba ang problema kaya ba syang ibias ulit kahit wala scope.

[TinTopHack]

Some suggestions:

** Please check what is the total supply voltage measured between +V and -V. If your filter E-caps are OK the total voltage should not change too much - maybe a drop of 5V when volume control is increased to max.
** If total supply voltage between +V and -V does not vary too much then any imbalance between +V and -V will have something to do with the adjustments of the trimpot on board. If you read the manual, R23 and R24 controls the + and - current limit. These also have effects on the + and - clipping. Which means the adjustment of these 2 trimpots affect the balance of the +V and -V WITH RESPECT to ground. This is an inherent characteristic of this amp design because ground is NOT the center tap pf the power transformer. If R23 and R24 have been misadjusted, your amp maybe going into current limit mode too early in a way that the upper and lower current limits are unbalanced. This will definitely cause distortion and create imbalance between your +V and -V. Increasing the volume will also create more imbalance which is what you are probably seeing right now. -- This is the most logical explanation because if the amp does not go into current limit mode, any imbalance between +V and -V (offset) will be corrected by the negative DC feedback from the output to the input opamp (NE5532). The amp is like a big opamp with global negative feedback.

Mahirap i-correct yan without the equipment recommended in the manual. I would not recommend adjusting the bias trimpot R26 unless you know the effect of adjusting it counter clockwise and clockwise. Logically counterclockwise means reducing the bias (less Q current) and clockwise means increasing the bias (more Q current). But sometimes this is not the case. Baka masira output trans mo kung masobrahan ang bias. Besides you should not adjust the bias when the current limit of the amp is active because you will get incorrect results.

If you are the adventurous type, there might be a way to adjust the trimpots to disable the current limit but it will require extreme care in your part. Would you like to try this adventure?