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Phono Stage Going Bad?

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furui_suterioo

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I don't start threads often, but a strange problem has developed recently with(I think) my kenwood 9940 receiver, there seems to be feedback in phono 1&2 but not in CD-4 mode after I lift the tonearm or clean the stylus. It is almost silent feedback(low frequency) vu needles jumping, the weird thing is that in RM the feedback alternates between front and rear channels and sq mode it seems to rotate. It does not do this in CD-4 mode so that's why Im thinking its main phono stage or is it my turntable/cartridge? Opinions appreciated.
 

furui_suterioo

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It has two phono inputs, the cd-4 slide-in demodulator uses phono 2 input but has it's own position on the selector, so I think it may have it's own separate phono stage. It also occurs in stereo and mono, if you temporarily change inputs it stops but will start again if you barely touch the needle and it will keep going. The receiver is old and does need servicing but I just wo der if anyone else have a similar issue.
 

Doug G.

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Many times, that kind of thing is caused by a loose, intermittant, or poor ground. I had to fix my Heathkit AA-2010 quad amp due to that. Poor solder connection on the input preamp board.

Doug
 

furui_suterioo

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I finally set up KR-9940 #2 and no more phono problem, so I'm pretty sure that means 9940 #1 needs preamp service(I was worried that my phono cartridge was going bad). One problem they both seem to have is tape monitor B output not working, both front and rear outputs, so my decoders have to share monitor A out, both A and B inputs are working so at least I don't have to mess with the 4 channel connections. If only there was a component in the loop with an extra monitor out or maybe even an auxiliary 4 channel input.. hint hint for SMV3 although that would be turning it into the Space & Image Composer! Need to open up 9940 #1 and try to figure out what is causing the problem with tape B output, service preamp board, decoder board also need recap but I dont really care since mostly use external decoders anyway. Makes me think about finding a way to Mickey mouse an Involve board in place of the original decoder board, they both have inputs and outputs so it can't be impossible. Might be worth a try since I have all of this recapping work ahead of me, yes, I probably belong on the quad funny farm.
 

Circular Vibes

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It is odd to me because I had a similar issue using my Sansui QRX7001. I can't remember how I fixed it. I thought I was gonna blow the woofer cones straight outta the baskets at reasonable volume. I think I moved components around or moved apartments. Also, at the time I was experimenting with a few cartridges. A NIB JVC 4MD-20X, JVC 4MD-5X with replacement stylus, Audio Technica AT-440mlb. I also replaced the turntable cables with genuine Technics replacements from KABUSA. All I know is that I went to an outboard CD4 demogitator for Strain Gauge carts and next time I tried MM carts again, the AT cart worked. If I hadn't been using recently made styli I would have suspected a failed cantilever suspension. Perhaps try cleaning the contacts wheree your demogitator connect to the receiver and clean the socket contacts too. It can't hurt.
 

furui_suterioo

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9940 #2 is set up in the exact same spot, connected to the same tt and does not have the issue(which only affected all non-cd4 phono modes and could be terminated by temporarily switching between phono sources) so I am thinking there is a faulty capacitor on the preamp board. I would looove to upgrade to strain gauge and direct drive, some serious dough.
 

Circular Vibes

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Keep an eye on Yahoo Auctions Japan for the cartridges and genuine Technics styli. They are often much cheaper tha ePay. I have 4 and 3 came from there, the 4th from a junked/trashed Panasonic changer at a local thrift shop for $25. Also keep an eye out on those auctions as they often come on dead arms from crumpack systems. In Japan there were quite a few models of 2 channel crumpacks that had the yellow conical stylus but are perfectly good for CD4 with upgrade stylus. Even Technics demogitators come up about once a month. Be aware that an affordable one will take patience but once you get one you may end up with more. I have 4 now, 3 that need restoration and one I have yet had the opportunity to test. You will want a step down transformer with Japanese gear in North America.
 

furui_suterioo

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Been waiting for a deal on Panasonic SE405, some have sold online for around $100 within the last two years, I would pay that price for one if it powers on. My 4DD-10 demodulator is a bit noisy with non-mint CD-4s but sounds a little cleaner after its warmed for awhile so I assume it needs recapping aswell. On the other hand, Kenwood slide-in demodulator is operating silently, right away, and handles used CD-4s much better(although JVC does have a bit livelier seperation than Kenwood on mint CD-4s). Lots of work to do with all these receivers and decoders but I wouldn't bother if I didn't think each has its own merit, whether it is being top of the line, rare, odd, or the best performing, these machines have earned their existence!
 

MidiMagic

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You might have feedback between the speakers and the turntable. The speakers cause the turntable to vibrate, shaking the pickup.
 
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