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Oh no, Sony TA-1120

Frank Solem said:
Thanks for clarification, when you say it like that, its quite obvious! The way the resistors are arranged on the board, I was thinking they were two in series. o_O The good thing is that im getting good at being embarrassed :)
I will dive into why I have a voltage potential between pin 3 & 4. (Wich is between emitters on X118&X120)
Click to expand...

I'd think that potential is created by unmatched transistors. One transistor conducting a bit more, or even unmatched resistors having slightly diferent voltage drop. Anyway, it's an extra insurance to double check everything you don't trust. Specially after a short circuit.
 
Regarding the steps to power the amp after the DBT, well, a bit of experience helps, but basically, if the DBT is a bit glow, brighter than it should be, or you suspect any anomaly, bias adjustements not responding as expected, excessive DC offset, anything you don't trust, don't feed with full power. I usually connect speakers and do some audio tests even with the DBT and bias on the low side.

Then, when feeding full power, I keep a DMM connected to the bias test points, since some amps can raise the bias a lot. If bias raises too much, I unplug fast, and adjust the trimpots before powering again.

Then, a good practice is to give full power while watching the boards, one hand on the power button or on the main plug, and look for a couple of seconds. If you see any smoke from anything, unplug immediately.
 
Thank you, I did have very low ratings on my transistor-tester when testing HFE, so you are probably right.. The glow from the 40W bulb i suspect is a tad to shiny. But everything acts as normal, the bright light at startup, then almost completely dim, before it settles on a glow. I will wait for silica plates to arrive and change all of them out before I go to full power :)
 
40 W is a bit small. If you have something like 60 or 75w, you could test with that before full power. I use a 56W bulb for average small amps, sometimes 75W.
 
Thank you again, i changed to a 60w bulb and everything became more normal. Reduced bias a little bit, before I connected to mains outlet. Everything went fine this time.

So, now I have 91V rail voltage, somewhat high centre voltage at 47V, but not sure how to adjust. Bias set a little bit conservative at 20ma, DC offset as good as 0,0mv.

Now I have two problems.

Starting with the worst: When playing with two speakers, balance at centre, the sound is dull. I would say very dull.

If I turn balance to left or right, I'm guessing the volume comes up 20% and the speaker comes more to life! It sounds wonderful and rich! unbelievable good!

Balance back to middle, and it gets dull again. Almost like it doesn't have power to run both speakers..




The other problem i guess is obvious. I changed out C174, C178 and C181 on left power board. I changed to mica and wima, but the bass is muddy on the lift side now. not very, but noticeable. The original film caps on 50, 100 & 300pF are silver film caps. What can i replace them with?
 

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I bypassed the preamp with another external pre again, and both problems ara gone. So I guess the mica's can stay in the left main amp.

Then I have done something wrong on the pre-amp board, EQ board, OR I have mixed up the wireing. Some of the wireing was disconnected when I got it. Included the volume control.

Well, I actually got a un-touched one from Osaka, Japan some days ago, so I will be able to do a A/B comparison on the wireing :) I can see its 100% original. I will take a lot of photos before I start, to have the original layout documented.
 
Frank Solem said:
Thank you again, i changed to a 60w bulb and everything became more normal. Reduced bias a little bit, before I connected to mains outlet. Everything went fine this time.

So, now I have 91V rail voltage, somewhat high centre voltage at 47V, but not sure how to adjust. Bias set a little bit conservative at 20ma, DC offset as good as 0,0mv.

Now I have two problems.

Starting with the worst: When playing with two speakers, balance at centre, the sound is dull. I would say very dull.

If I turn balance to left or right, I'm guessing the volume comes up 20% and the speaker comes more to life! It sounds wonderful and rich! unbelievable good!

Balance back to middle, and it gets dull again. Almost like it doesn't have power to run both speakers..




The other problem i guess is obvious. I changed out C174, C178 and C181 on left power board. I changed to mica and wima, but the bass is muddy on the lift side now. not very, but noticeable. The original film caps on 50, 100 & 300pF are silver film caps. What can i replace them with?
Click to expand...

If both channels sound good when the balance knob is set to one side or the other, at 1st your problem sounds like speakers out of phase. But if with a different preamp the problem goes away, it must be some mistake at your internal preamp. Sounds like something out of phase, cancelling between channels.

Try the amp in "mono", also try with headphones.
 
I was just thinking, since most of the issues have been related to me being an idiot, can this issue be releted to me using a couple of bipolar caps where I'm not suppopsed to.C104, C105 C115 & C116 are nichicon muse BP caps. The green once.

EDIT: Never mind, i installed a phase tester, and my right speaker is left and vice verca.
I have to continue checking cables and connections I guess.
 

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Start with the simplest things. Follow the wires from the RCA input to the preamp. Compare both channels. It's almost sure you mixed some wiring. The PCB itself won't invert the phase. But some mistake wiring the boards, potentiometers, function selectors, could cause that issue.
 
In for the final trip across the finish line.

Pics are welcome once you get a handle on this classic, sir.
 
I need a break.
I got the sound as intended by switching polarity on one speaker. Using a phase tester on youtube made it very easy to hear. Its called
speaker polarity check - test tone

I would say this was a wreck, but is now working 100%, with some cheating.

What needs to be done is sort out the phase-issue, might take me some time.
I need to fabricate some heat sink for X116. I've replaced it with 2N5322 and it gets hot.
Since i replaced the brackets for the outputs, I need to find a solution on a space-issue. They were a bit deeper.
I need to put thermal compound to the diodes on the back of the power boards.
Terminate the cables going to the main cap and generally tidy up the cap's mounted to chassis.
Oh, and the left power board came with Elna Silmic II caps. Some had the wrong values, I changed those, but left most of them, just to see if I could hear any difference. I cannot, but will also change them so everything is 100% symmetric.
I'm guessing 10-20 hours left to get it perfect.

I dont know how to express my gratitude, so Im just going to post some pic's :)
What I can say, I never would have made it alone!


P_20221129_090536.jpg P_20221129_090645.jpg P_20221129_090525.jpg P_20221129_084419.jpg P_20221129_084405.jpg P_20221129_084412.jpg P_20221128_183906.jpg P_20221128_181338 (1).jpg P_20221129_084356.jpg View attachment 2726723
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Now I cant wait to start with the next one. I thought it was untouched, but behold...
 
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The new one, not so untouched o_O
Look at the pins on transistors... For reasons unknown to me, all the transistors on line board looks like this.
P_20221128_190349.jpg
 
Started stripping the ''new'' one today.
P_20221121_124212.jpg


I dont know why, I like to start with the power amp sections

P_20221129_143613.jpg


I do both at the same time :)

P_20221129_143926.jpg


Cant remember seing wiskars on a resistor before. It's supposed to be 220ohm, but measures 265, so out with it. Found 3 of them..

Screenshot_20221129-182108470.jpg


I know that not everyone like this, but I clean with water and lots of the strongest alcohol I can buy. I make sure it dries superquick.
P_20221129_173243.jpg


My ex's toothbrush finally come to use :) :) :)

P_20221129_174046.jpg
 
Are you checking all the carbon comp. resistors as well ? They can have an annoying tendency to age 'high' over the years.
 
I am extremely happy to say that all measurements are now perfect and the sony plays like a dream. I finished four hours ago, but since it plays so magically, I haven't been able to break away yet. I'll be back with a fuller report over the weekend :) PS, this is a really good amp!!!
 
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