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Oh . . . a capacitah, eh?

subgenius

subgenius

Member
Been lurking for more than a year, so thought I'd finally join/contribute to the fun.

I got interested restoring turntables a couple years ago (done three so far) and found lots of help on forums (including this one). Besides hours of mechanically fiddlin' with stuff--soldering tonearm wires is no easy feat!--I eased into the electronics side with replacing a few capacitors and trim pots. This seemed pretty easy, so I kept reading/learning about restoring electronics.

By then I was starting to feel pretty smart, so I bought a recap kit on fleabay to "fix" my sisters somewhat tired and noisy Sansui 7000. I read all the stuff, then opened the cover to see a HUGE pile of electronic "thingies" . . . that's when my chest started feeling tight, and I put the cover back on. WAY more parts than a turntable!

I decided that the 7000 was too complicated for me, so I sent it to a "reputable" restorer, and bought a much simpler/cheaper, beginner project--Sansui au2200--to practice on. Now, I'm about 3/4's done with the 2200, but running into things that I need help with. I'm sure many members of this forum could finish the 2200 in less than a day, but I'm slow. When I have spare time, I have to read about things and try to figure them out, order parts, install them, see if they work--all under my wife's disapproving eye. But I love it!

I recently got the 7000 back from restoration with underwhelming results; more hum, overblown/distorted bass, hashy treble . . . I think it actually sounds worse. When I contacted the restorer, he said that it sounded fine when they tested it, that maybe it was just the "Sansui sound" that I wasn't used to. If the Sansui sound is like a cheap woofer in a rattley car trunk, then I'm definitely not used to it.

Rather than wasting more money sending the unit back to the "restorer" (to be fair, they did a good job of cleaning it and fixing/adjusting the tuner--which I don't really use), It's time for me to learn about replacing transistors/diodes and re-restore this unit all over again. So now I'm working on the two projects at once (with another two turntables waiting), and plan to post threads on these when I get a chance.

Reading the technical write-ups from the likes of Leestereo, Stereofun, and dlucy has been VERY helpful. And comments from other forum members--leesonic adds just the right amount of helpful sarcasm--have kept it fun.

Thanks everybody for making this forum such a great place.
 
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Welcome ! I think the sansui 7000 is a good amp to go about replacing capacitors on. Most sansuis from that time have some removable boards that are easy to get at, like the driver boards. I always start with the power supply board. Do one board at a time and check your work by listening . Sometimes I only do part of a board and then listen. Its a good way to know what is making a difference and if you make a mistake , it is easier to locate. Oh, I always set the bias and offset if direct coupled first. Download the service manual and study it before you do anything.
 
billyz,

Thanks for the advice and encouragement, everybody! Got the manual, read several restore threads, and ready to go. As for as offset (DC?), I'm not sure this is adjustable since the output couplers filter the DC, don't they? Many of the caps on this 7000, including power supply and coupling, were just replaced by the restorer, but I wonder about their choices.

For example, the stock output coupling caps (2200 uF/80V) were replaced with 10,000 uF caps that I think are letting a lot of extra bass content and distortion through(?), and it sounds terrible, loudness button on makes in unlistenable. MIJ_Pioneer said he upped the output couplers with good results, but not nearly as much (settled on 3300uF), and used smaller bypass caps as well. dlucy kept them the same value so they wouldn't "increase bass emphasis," and I believe him on this. I swapped the output couplers back to the smaller value, and this has helped clean up the bass some, but I suspect there is distortion coming from somewhere else . . . Transistahs?

So, I'm starting over one board at a time (like you suggest), and am almost done with the power protection board (thanks dlucy and MIJ_Pioneer for paving the way). I'll be sure and listen after putting it back in--before I start on another section--especially because twisting transistor legs around for different pinouts was quite confusing, I checked and re-checked about 6 times!

This was my first time with transistors, and I'm holding my breath to hear if it works when I put the board back in!
 
I did not look specifically at the 7000 to see if Capacitor coupled output or Direct. I was speaking in general terms.
Regarding the choice of capacitor values. I don’t usually deviate that much from the original design . I have increased the UF and voltage rating . When recapping , lots of the time you cannot find the exact values. Does not hurt to increase the voltage rating ( but I don’t go crazy either) I have increased the capacitance in the power supply but Usually not more than 50%. It could stress the rectifiers and power switch at start up. I seldom mess with other values especially in the phono stage and tone circuit , unless you really know what you are doing .
Capacitor coupled outputs are sensitive to the uf value though . That’s why I say do a few and then listen .
 
Thanks again! Yes, the 7000 is capacitor coupled and I had read a little bit about that, so you got me wonderin'? For fun I measured dc at the speaker connections, with speakers connected (on the au2200, also cap coupled--since I don't have the power protection board back in the 7000 yet) and sure enough, measured "O" VDC. Since I could definitely hear some hum through the speakers, it got me wonderin' again. Switched the meter to VAC and wha'd'ya know, (oops that was) 0.15V @ 120Hz! Who'd a thunk it! Nyuk, Nyuk! Learnin' things about this 'lectricity stuff everyday.
 
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