Kenwood KA-7300 volume very intermittent

Vader82

New Member
I've scoured the forums looking for answers on why my KA-7300's volume knob is so intermittent. There are some volumes where I can hear both channels, and some where only the right channel works. I tried tightening the tabs on the pot behind the volume/balance knob once but that made the problem worse, not better. I also tried RatShack contact cleaner and that didn't seem to help either.

I have experience the turn-on thump delay circuit problem which I half-solved by replacing the relay. This was about 10 years ago, long before I knew about this site and before I had much electronics experience. I've since gotten my EE and am less stupid in such matters.

I measured the DC offset to be 20.1mV and 21.3mV in case EchoWars is listening.

Does anyone know of a suitable replacement pot for the volume/balance? I'd be content to kill of the balance and go to straight volume if that made sourcing a part any easier. I love this amp and I just want to figure out how to make it reliable.

Realistically any suggestions at all are welcome.
 
Before replacing the volume/balance pot, have you done any cleaning yet?
See the Deoxit tutorial in General Audio for a checklist. I personally use Deoxit followed by Faderlube on the volume and other rotary pots. It isn't just the obvious volume/balance pot that can affect balance. Various switches, contacts and selectors in the audio path can also contribute to problems. If I recall jiggling one of the turnover switches next to the Volume knob affected the balance. So I always clean everything -- using the check list cleaning inside and the rear connections.

Don't be surprised if you need to reclean every now and again.

Sometimes the problem weak channel can recur or sometimes it may need some jiggling or a few hours to slowly build up. This could mean that other parts replacement is called for and not the volume pot.

After cleaning my KA-7300 it is no longer as intermittent. But it may still take a few minutes to "warm up" and be fully balanced. It likes to be frequently used. I might jiggle it with the balance all the way to the weak channel until I hear it come up. And flipping that turnover switch I mentioned earlier. Or I might turn the balance knob to bring up the weak channel -- that is what it's for after all. And it may later "warm up" get louder in the weak channel and I can move the balance knob back to center again.

So unless you get it somewhat restored by replacing capacitors or whatever is needed, it may be like the old cartoons trying to get a vintage car started. It is what it is.
 
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btw I use the 2nd text box option Search AK with Google under the Search feature.

Try "KA-7300 echowars" and you should get several threads where echowars talks about the KA-7300:
http://www.google.com/custom?client...a-7300+echowars&sitesearch=www.audiokarma.org

btw your DC measurements sounds great but I don't think there's a way to adjust it with any trimmers anyway. I believe echowars covered that in one of the threads that that was one of the disappointing things about the 7300.
 
I has a similar problem with a KA5500. Cleaning the controls solved it and everything has been great since then :thmbsp:
 
Sounds like dirty controls/switches, and perhaps a speaker relay in need of replacement.
 
Did some cleaning

I've now cleaned it quite thoroughly and tightened the tabs on the volume pot again. Once the tabs were tight, no left at all. I've been trying to get this knob off for some time now and had no luck. I pulled the set screws from the knob and I've been pushing and pulling and twisting and nothing makes it budge.

I actually pushed it hard enough that the tabs popped loose again and suddenly the left channel works. I am quite confident that this is a bad pot. I can pull on the knob and the left goes out, push on the knob and the left comes on. This now works for all volume levels.

I must have -- in my vigor to remove the knob -- moved one of the pot contacts away from where it's supposed to be.

So I guess now I'm curious if anyone can tell me precisely how to remove this knob so I can get at the pot? I'll have to either try and fix it or replace it and get this delicious amplifier working properly again.
 
Many of the volume knobs have two set screws. Hopefully, you've missed one and it's a simple matter of loosening it as well to get the knob off. A drop of penetrating oil into the holes may help as well.

If that's not the case, I'd wait till a replacement volume control popped up before I battled it any further. I have had to destroy volume controls in the past to get a knob off. Problem in this case is that the combination balance/volume on the 7300 is a bit unique.
 
EchoWars, thanks for the quick reply. I did pull both set-screws already. It took a bit of work to get them loose but it happened. The knob now does turn slightly past what the pot does but it's not much additional play.

I guess I'll try some penetrating oil down the set-screw holes and see if that helps. And maybe shoot some WD-40 in between the balance and volume.

I am completely willing to sacrifice the balance to get this working again. The channels are already quite well balanced as my DC bias measurements show and I've never really found myself in a terribly asymmetric listening situation. The problem is that I've got to keep pressure on the knob to keep the left channel on right now. Not terribly conducive to enjoying the sound that's now in stereo.

I've done some searching on the net to see if I can find either the part number or the specs necessary and I'm not coming up with much. There are service manuals available on eBay for about $25 plus probably $20 shipping. I will pay that if I need to, but I was hoping the power of the internet might help a little here.
 
What you are describing still sounds like dirty pots.

Not sure why you are so interested in pulling off the volume knob.
But there are two set screws that are actually quite deep within the Volume knob close to the shaft itself. So you need to use hopefully align the long end of your hex wrench and hope it catches. It is tricky and requires patience aligning the hex wrench to loosen. But once loosened it should be easy to pull off.

Did you actually remove the cover to clean the volume pot from inside?
You should see a round pot and square enclosure. That's where you should be spraying.

And I am serious about cleaning all the other switches and selectors from inside. Especially the turnover and presence switches.

The only reason you would be removing the Volume knob is if it is pressing or rubbing against the Balance knob.
 
My only source for manuals: http://www.stereomanuals.com/

I'm not sure what good the Kenwood part number might be (R24-9001-05), as these parts have pretty much been NLA for a decade & 1/2 or more.

It is possible, if you found a volume control that would fit (the control needs a loudness tap, unless you plan to bypass that also), to bypass the balance on the PC board (then the balance ring could be carefully mounted on the faceplate to retain the cosmetic look).

Edit: The stock control is 150K, but a 100K would work fine. Michael Percy Audio sells a nice Noble AP25 volume pot with a loudness tap that might do the job.
 
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Just for reference:
1050volume.jpg

As said, there are two set screws. Before reassembling to make it easier, I turn the set screws so they are flush with the inside and I leave the hex wrench inserted so I only need to do a little turn to tighten.
1052wrench.jpg

1055pots.jpg
 
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terra1: I pulled the cover off this amp and sprayed all kinds of DeoxIT on the volume/balance pot. I definitely know which one it is. I've Deoxit'd the other pots and switches as well.

There used to be SOME play on the volume knob. I opened the amp up a couple of years ago and tried tightening down the tabs that hold the volume pot together as they were a bit loose. That completely shut off the left channel so I loosened them back up. Left started working again (most of the time).

Today I just deoxit'd the crap out of the volume pot and then tried tightening the tabs back up again. Once tightened, no left channel. loosened again the left channel shows up ONLY when the volume knob is pressed back. This pushes the pot out to the end of the play provided by the tabs and enables the left contact in the pot stack to touch and thus work properly. When the knob is pulled out rather than pushed in, the left is off completely.

I believe that this is because I tried to pull the knob off some years ago before I knew much of anything. In doing so I think I moved the contacts inside the pot around a bit (bent something maybe?).

EchoWars: thanks for the part number. I didn't realize that it was going to be something so esoteric and unobtainable.

I really appreciate you guys helping me try and troubleshoot this problem. I'm probably going to pick up that Noble AP25 for when this pot completely gives up the ghost. Until then I think I'm going to see if I can rig things inside such that the necessary pressure is applied constantly rather than me jiggling it every 5min.
 
terra1: In the bottom picture you clearly show the volume/balance pot.

There are tabs nearest to the front-plate that seem to hold the whole stack to a fitting attached to the front plate. Those are the tabs which if loose permit the left channel to work. If tight, the left channel can't be coaxed into making noise no matter what switches I flip or how I jiggle the volume.
 
EchoWars: thanks for the part number. I didn't realize that it was going to be something so esoteric and unobtainable.
Esoteric? Not really...we're just talking about parts for a 35 year-old piece of consumer gear. It's the same as anything else: the older it is, the harder it is to get parts for.
 
I have determined that the round things nearest the faceplate are the balance pots and that the bigger, boxy portion closer to the transformers handle the volume.

I am redoubling my deoxit efforts focusing on those pots but I'm not terribly optimistic. I tightened the tabs up really well once I got the knob off. Now the right is normal and the left will only make the tiniest bit of noise if I throw balance all the way left and turn the volume to max.
 
On my KA-7300 the reason I mention the Presence toggle switch is that when I slowly move it up or down there is sometimes a sweet spot where the weak channel gets louder. And once jiggled, it seems to help balance things to even out the channels. I don't know why, but it does. I suppose as old as these are there are miscellaneous quirks for each unit.

You said pushing the volume knob in and out affects it, so is that no longer the case?
If it's a matter of pushing the knob in or out, I wonder if applying a washer might provide enough friction to hold it in place? Either an e-clip type or rubber one that you can cut to wrap around the shaft? Just brainstorming at this time. So forgive me if this just sounds stupid. :D
 
After doing still more investigation I've determined that there are a pair of wiper arms for each of the boxy chunks at the back. Those are the volume pots (or attenuators). I've deoxit'd them pretty hard and now I'm trying to figure out which one has the contacts which are loose. I just might be able to salvage this.
 
IF the balance is the source of your grief, you may bypass it (permanently or temporarily) by jumpering pin 13 to pin 15, and pin 19 to pin 17.
 

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EchoWars I think you actually nailed it on the head. I've got the end of a plastic dental pick (with floss!) wedged into the pot closest to the front of the stack (closest to the faceplate) and it's holding the gap open nicely. Now the left is back on and seems fairly stable through the whole range of volume.

Seven years of school for engineering and I determine that what my amp is missing is a bit of plastic. Kill me now.
 
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