Got a buddy that has wanted a Kenwood 700C preamp for ages. I found one that 'needed help', and we bought it. Seems that there are multiple issues, but the worst is that the really nice stock 20K TKD stereo volume potentiometer has been screwed with to beyond the point of no return.
So, I went searching. The only thing I could find anywhere close is a 20K Alps with NO loudness tap It's probably a Chinese counterfeit, but I'd take it if it meant at least getting the preamp back to functional. I was able to find a 50K Alps with a loudness pin, but although the auction showed a smooth 6mm shaft (what I need), what arrived was a split knurled shaft. I can't see a way to make the knurled shaft type work without having a very funky and wobbly volume knob. So that ain't gonna work.
Michael Percy Audio used to sell some nice Noble pots with a loudness tap...but no more.
So I'm out of ideas here unless someone knows a source that I haven't found yet for a 20K (or even a 50K) stereo pot with a 6mm smooth shaft and a loudness tap. Or if there's a way I can use the 20K that I have and rig something up that fakes the tap in a way that is at least somewhat functional.
A fixed resistor from the loudness network to the wiper, using a value that mimics the loudness at a normal listening level? Maybe a larger value tied to the input pin instead? I'd appreciate your thoughts...this is giving me a migraine.
So, I went searching. The only thing I could find anywhere close is a 20K Alps with NO loudness tap It's probably a Chinese counterfeit, but I'd take it if it meant at least getting the preamp back to functional. I was able to find a 50K Alps with a loudness pin, but although the auction showed a smooth 6mm shaft (what I need), what arrived was a split knurled shaft. I can't see a way to make the knurled shaft type work without having a very funky and wobbly volume knob. So that ain't gonna work.
Michael Percy Audio used to sell some nice Noble pots with a loudness tap...but no more.
So I'm out of ideas here unless someone knows a source that I haven't found yet for a 20K (or even a 50K) stereo pot with a 6mm smooth shaft and a loudness tap. Or if there's a way I can use the 20K that I have and rig something up that fakes the tap in a way that is at least somewhat functional.
A fixed resistor from the loudness network to the wiper, using a value that mimics the loudness at a normal listening level? Maybe a larger value tied to the input pin instead? I'd appreciate your thoughts...this is giving me a migraine.
Hi there! 
I've just run into the same problem with the turntable I'm doing up. Apparently you can just wire it up with a normal 3 pin pot and leave the loudness tap disconnected, which is probably what I'm going to have to do since a 50k pot with a 5k loudness tap is not easy to find!
To answer the question though, perhaps you could use a seperate potentiometer for the loudness tap? Trouble is you would end up having to drill extra holes in the front panel which would destroy the original look.
Good luck with it anyway, and post some pictures as it sounds like a nice project!
I've just run into the same problem with the turntable I'm doing up. Apparently you can just wire it up with a normal 3 pin pot and leave the loudness tap disconnected, which is probably what I'm going to have to do since a 50k pot with a 5k loudness tap is not easy to find!
To answer the question though, perhaps you could use a seperate potentiometer for the loudness tap? Trouble is you would end up having to drill extra holes in the front panel which would destroy the original look.
Good luck with it anyway, and post some pictures as it sounds like a nice project!
Not so easy with this one...
(scat here: http://elektrotanya.com/kenwood_700c_control_amplifier_sch.zip/download.html)
(scat here: http://elektrotanya.com/kenwood_700c_control_amplifier_sch.zip/download.html)
An externally hosted image should be here but it was not working when we last tested it.
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1) if you already got an electrically correct pot, by all means just USE IT , instead of inventing doubtful kludges.
2) as of:
Works perfect.
Not really necessary, but if you want extra peace of mind, you can epoxy or magic glue it in place.
The plastic strip I mean, not knob to shaft
2) as of:
piece of cake, I do it all the time, just cut a piece of proper thickness plastic sheet (old credit card is perfect) and insert it in the slot.
Works perfect.
Not really necessary, but if you want extra peace of mind, you can epoxy or magic glue it in place.
The plastic strip I mean, not knob to shaft
Tried that. Won't stay straight...wobbles like a clown car wheel no matter how I try (and I spent hours fiddling with it). Just too sloppy a fit. Tried wrapping the shaft in Teflon tape as well, and it helped a little, but it's just...well...weak, for lack of a better adjective.
I take it the pot in question is one with the knurled spine and a split shaft. I found slipping a small right angle bracket in the slot is a tight fit and there is just enough room to fit the other end into a vice so you can file or machine a flat surface if that style of pot is what you require. The type of bracket is shown here Metal Right Angle PCB Standoffs Pk 8 | Jaycar Electronics New Zealand.
Other than that you might try electronics disposal stores. I have a centre tapped pot purchased from the major store in New Zealand when I was living in Auckland unfortunately it is not the value you are seeking. The thought has occurred that one could add a resistor in parallel with the pot to fake the 20 k with the 100k type I have. To do that I would arrange the faking resistors between the centre tap and either end of the pot.
Here is a link to some 20k pots this store is selling - apparently for simplicity the images are the same for all groups in the range so whether or not they have something suitable is not evident but you could find out. https://www.surplustronics.co.nz/products/1688-20k-ohm-alps
Other than that you might try electronics disposal stores. I have a centre tapped pot purchased from the major store in New Zealand when I was living in Auckland unfortunately it is not the value you are seeking. The thought has occurred that one could add a resistor in parallel with the pot to fake the 20 k with the 100k type I have. To do that I would arrange the faking resistors between the centre tap and either end of the pot.
Here is a link to some 20k pots this store is selling - apparently for simplicity the images are the same for all groups in the range so whether or not they have something suitable is not evident but you could find out. https://www.surplustronics.co.nz/products/1688-20k-ohm-alps
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I don't get a choice of where to put the screw. Gotta go 'here' if I want the volume control notch to line up with the faceplate display.
I may have found a solution. I filled the split with some dense cardboard, and wrapped the knurled shaft with copper foil that I use for PC board repairs. No wobble if I carefully tighten the set screws evenly.
Not my preferred solution, and I'm really bummed out over the loss of the nice Noble AP25 pots. But unless buying a Goldpoint for $130 (DIY) or $165 (assembled), I can't some up with an alternative.
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Model engineering suppliers usually carry thin-walled brass and other metal tubing in standard OD like 6 or 6.35 mm. It may be difficult to find the correct combination of ID and OD but a little ingenuity with slitting the tube lengthways may wind up in a good, concentric fit.
If that is all too hard, heat-shrink tubing should be obtainable in a fairly hard plastic grade and various shrunk wall thicknesses. It doesn't really matter if the locking screw penetrates the plastic and it's not difficult or expensive to experiment with what's available.
If that is all too hard, heat-shrink tubing should be obtainable in a fairly hard plastic grade and various shrunk wall thicknesses. It doesn't really matter if the locking screw penetrates the plastic and it's not difficult or expensive to experiment with what's available.
The brass tubing in model shops is invariably designed to telescope into each other. So if you find a size that fits the shaft you should be fine. I think it's possible there's a 6mm vs. 1/4" issue here too..
I dug through my bag of old pots, only got this:
50k, dual log pot, 1/4" (6.3mm) shaft, 27mm long shaft (no chamfer but center-split..it's very old, a Ducon made in Australia), complete with a loudness tap. You'd need to change the chassis tab mount over to a thread/nut mount like the last pot pictured, but it may do the job. It's smooth and tracks ok.
Any help?
-John
50k, dual log pot, 1/4" (6.3mm) shaft, 27mm long shaft (no chamfer but center-split..it's very old, a Ducon made in Australia), complete with a loudness tap. You'd need to change the chassis tab mount over to a thread/nut mount like the last pot pictured, but it may do the job. It's smooth and tracks ok.
Any help?
-John
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Don't know if this will work, but Don Sachs had some nice custom pots made for upgrading HK Citation I's. If these don't work, maybe you can get a custom made one also?
From Don Sachs website:
"I have now managed to fit the excellent 48 step Khozmo attenuators in very neatly and cleanly. These have hard gold contacts good for 10,000 turns! I was able to get Arek, the fellow who makes the Khozmos to do a special version with a knurled shaft to fit the original Citation I volume knob. He even tapped the attenuator at about 70K so the loudness contour switch still functions."
Also, this quote from the same page, just above the section about the Khozmos:
" A new modern volume pot. A signifcant number of Citation I preamps have volume pots that are failing. The symptom is that channel balance is off and will vary with the volume setting. The new pot costs $19, has a loudness tap for the contour switch, and is an Alps Blue Velvet copy (a conductive plastic pot). Immediately you will notice a wider sound stage and more clarity, detail, and air. There is a significant difference...REALLY!"
From Don Sachs website:
"I have now managed to fit the excellent 48 step Khozmo attenuators in very neatly and cleanly. These have hard gold contacts good for 10,000 turns! I was able to get Arek, the fellow who makes the Khozmos to do a special version with a knurled shaft to fit the original Citation I volume knob. He even tapped the attenuator at about 70K so the loudness contour switch still functions."
Also, this quote from the same page, just above the section about the Khozmos:
" A new modern volume pot. A signifcant number of Citation I preamps have volume pots that are failing. The symptom is that channel balance is off and will vary with the volume setting. The new pot costs $19, has a loudness tap for the contour switch, and is an Alps Blue Velvet copy (a conductive plastic pot). Immediately you will notice a wider sound stage and more clarity, detail, and air. There is a significant difference...REALLY!"
Got a buddy that has wanted a Kenwood 700C preamp for ages. I found one that 'needed help', and we bought it. Seems that there are multiple issues, but the worst is that the really nice stock 20K TKD stereo volume potentiometer has been screwed with to beyond the point of no return.
So, I went searching. The only thing I could find anywhere close is a 20K Alps with NO loudness tap It's probably a Chinese counterfeit, but I'd take it if it meant at least getting the preamp back to functional. I was able to find a 50K Alps with a loudness pin, but although the auction showed a smooth 6mm shaft (what I need), what arrived was a split knurled shaft. I can't see a way to make the knurled shaft type work without having a very funky and wobbly volume knob. So that ain't gonna work.
Michael Percy Audio used to sell some nice Noble pots with a loudness tap...but no more.
So I'm out of ideas here unless someone knows a source that I haven't found yet for a 20K (or even a 50K) stereo pot with a 6mm smooth shaft and a loudness tap. Or if there's a way I can use the 20K that I have and rig something up that fakes the tap in a way that is at least somewhat functional.
A fixed resistor from the loudness network to the wiper, using a value that mimics the loudness at a normal listening level? Maybe a larger value tied to the input pin instead? I'd appreciate your thoughts...this is giving me a migraine.
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Did you try Goldpoint? 24 or 47 step attenuators...
Detailed Information
Looks like it has what you need, pics show smooth shafts and they are listed as 6mm?
$165 may be more than you wanted to spend though... but that Kenwood is worth it....
http://www.goldpt.com/compare.html
http://www.goldpt.com/prices.html
"You can choose from the many places which are available along the perimeter of the stepped attenuator.
Use an ohm meter to test your old, worn out potentiometer to find where the tap was made. Then you use your ohm meter to choose the closest matching tap point on the V24.
If you have the standard V24 which has surface mounted resistors, take care to not overheat the small pad (which is one side of the SMD resistor) when attaching your tap wire."
Detailed Information
Looks like it has what you need, pics show smooth shafts and they are listed as 6mm?
$165 may be more than you wanted to spend though... but that Kenwood is worth it....
http://www.goldpt.com/compare.html
http://www.goldpt.com/prices.html
"You can choose from the many places which are available along the perimeter of the stepped attenuator.
Use an ohm meter to test your old, worn out potentiometer to find where the tap was made. Then you use your ohm meter to choose the closest matching tap point on the V24.
If you have the standard V24 which has surface mounted resistors, take care to not overheat the small pad (which is one side of the SMD resistor) when attaching your tap wire."
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