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McIntosh 1900 Volume Control / On-Off Switch Replacement

SaturationPt,
Thanks for your thoughts, and compassion. Indeed, I am learning that this volume pot ordeal is a common one among these old Mac units. I continue to be puzzled that even the Mac company doesn't put much effort in supporting this dilemma. I get the feeling they are more interested in their current products than their 50 year old units. I suppose that is understandable. I suppose I better get used to the idea that some repairs for this old vintage equipment requires some compromise. After all, nothing lasts forever. Then some people are more critical that others. You, for instance, are not as critical. From the standpoint of a repair technician, I try to do the best I can, and that includes a reasonably accurate tracking volume pot. You're right, this may well be a case where the customer will have to accept something less than ideal.
Indeed, crossing my fingers that Joe's pot will at least be acceptable if not perfect. Again, Joe, thank you for your generosity and caring!
Stay tuned, everyone.....for the continuing saga of the mistracking volume pot!!
 
I am extremely critical, of my own work. If my C28 didn't track perfectly at low volume from the factory, and I don't know about it, I won't obsess. Such is the escape of OCD tendencies: not looking for something I can't fix or the C28 will be sold in the blink of an eye.

I agree it would be nice if McIntosh sold new perfect pots, but they don't. As they don't manufacture them their only option would be to spec them for a very close match or screen them and toss the majority of them for not being a close enough match. It is likely that they did screen them at one time, but at this point I'm just happy that they still carry parts for our old units. The available parts might be as close as they were when the C28 was new. I am ordering glass for a nearly 40-year-old amp from them, some optocouplers, thermistors for my 1960s amps, bought a tube-shield for another 1960s amp last year, ... I'm not complaining. I know that I can't go to Pioneer or marantz and buy a single part for a 1970s TOTL receiver, Mercedes no longer stocks parts I need for my classic cars, so McIntosh has been great.

I believe that adding a series/parallel resistor has been mentioned to compensate, I'm not thrilled with that option. Is there any way to disassemble and rotate parts in these pots to get them to the same starting point? I'm looking at an NOS 3-gang setup I have and it appears that each section is secured to the one below it with two tabs crimped into slots. What about doing a little trimming on these tabs to rotate then re-securing them?
 
Joe,
I received the pot today, and thank you for taking the time and mailing expense to send it to me. I carefully checked the tracking, and I'm sorry to say, it is faulty! It tracks fine from 7 o'clock to a little after that, but starts to mistrack at around 8 o'clock. By 10 o'clock the resistances are 284/189...a 33% difference! I think that would be very noticable in volume between left and right channels. Then, between around 10 o'clock to around 1 o'clock there is very little change in resistance...from 1 o'clock on the resistance goes up, but the 33% error persists. Bummer. Am I being too critical? I'm not aware of what tracking error is acceptable, but seems to me that something like 10% might be the extreme limit? I also wonder how many Macs out there have this issue without the owners being aware? For that matter, brands other than Mac...same sort of issue?
 
Hello
Many pot have this issue . I have many project but time is missing and I have customers waiting since a long time so I cal't loose my time to work on this problem now
The problem is that nobody want to wait
What is the emergency on a very old unit from sixties if you can get one perfect working pot in one month or 3 ?
 
Patrice:

Do you have a good volume-pot source? I’m looking for a C-28 pot, would love to find a good one that tracks well.
 
johnhoef said:
Joe,
I received the pot today, and thank you for taking the time and mailing expense to send it to me. I carefully checked the tracking, and I'm sorry to say, it is faulty! It tracks fine from 7 o'clock to a little after that, but starts to mistrack at around 8 o'clock. By 10 o'clock the resistances are 284/189...a 33% difference! I think that would be very noticable in volume between left and right channels. Then, between around 10 o'clock to around 1 o'clock there is very little change in resistance...from 1 o'clock on the resistance goes up, but the 33% error persists. Bummer. Am I being too critical? I'm not aware of what tracking error is acceptable, but seems to me that something like 10% might be the extreme limit? I also wonder how many Macs out there have this issue without the owners being aware? For that matter, brands other than Mac...same sort of issue?
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OK...We tried....I do have another one I will look for this tonight.
 
Joe,
I sure appreciate your concern and effort...I'm beginning to see this as a hopeless situation! My thoughts are now on considering "Audio Classics". They rebuild pots for $150. Based on my experience so far, I am reluctant to throw another $150 into this. Thankfully, Mac refunded my money, but the clown on ebay (hifiaudio) refuses to refund my $90. I wonder if my $150 with "Audio Classics" will also end up non-refundable??? Do any of you have experience with them? Are they reputable? Trustworthy? Will they refund me if the work they do is not satisfactory?
 
It's sad to hear that ebay hifiaudio / captfantastic isn't making good on his return policy:

Returns:
If, for any reason, you do not like this pot, I would be glad to accept it back and even pay for the return shipping fee!
 
Capt fantastic?? I don't think he deserves that title. As I mentioned above, he claims I damaged the pot by squirting faderlube deoxit into it, thus nullifying his return policy....OK, that is nonsense, of course, but let's assume he's right....should he not have warned me upon selling me a scratchy pot not to use deoxit? Capt hifiaudio, if you're out there reading this, how about standing behind your return policy?
 
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It was mentioned before that resistors can be used to compensate for a tracking error. All I can think of is installing a resistor in series with the pot that has the lower reading. In the case of Joe's pot, which has a 30% tracking error, this may work, provided the 30% error is more or less the same through the entire rotation of the pot. This is not the case. There is negligible error at the very low volume settings. Anyone....how about a schematic for compensating with resistors?
 
Thought about the suggestion to add a resistor, ... as they're voltage-dividers will it need a parallel resistor from wiper to one end and series on the other end to maintain the same total resistance to signal ground?
 
Any thought about just installing the best of the pots you have now and see how bad the tracking is in actual use?

Typically, you travel a certain range of the volume dial based on speaker efficiency, desired listening volume, room size, etc.

Maybe the actual usage range is on a better tracking portion of the pot or could be moved to a better portion of the pot using attenuators between the pre out and main in jumpers.
 
Here's an update from the guy who started this thread: The Audio Classics rebuild is nice & quiet, but mistracks badly; very badly. To their credit, they offered to rebuild it again, but I declined the offer as it is just too much trouble. My compromise solution is to rotate the balance control (approx 100 degrees of rotation!) so that channel outputs are audibly balanced. This compromise will have to be acceptable for now. Even though the pot rebuild was not satisfactory, Audio Classics stands by their work and is being most accommodating.

One other thought that I mentioned early on: that guy on eBay promised me that his 1900 VC was an exact replacement. I'm now glad I didn't test his promise.
 
bwv1 said:
<<snip>>One other thought that I mentioned early on: that guy on eBay promised me that his 1900 VC was an exact replacement. I'm now glad I didn't test his promise.
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He also told me that the 6A on/off switch he's selling is the right one for my amp that draws 12A, ... I believe that the proper term is "fire hazard".

I think I'll continue to steer clear of "captfantastic / hifiaudio
 
Great. I was hoping to use Audio Classics as a last resort. I'm very disheartened to hear they failed to provide a solid rebuild.
 
I watch threads about this topic - My original1900 pot exhibits the same behavior. From about 8:00 to 10:00 on FM much louder than other sources. I started using mine as a preamp though my 2255 and get the same. I can regulate the volume by being precise. Not ideal but livable.
 
okgood said:
Picked up a non-working (no sound) MA6100 on the cheap maybe 10 years ago and it sat for a couple years before I came across a local tech. First time around he replaced a number of caps and other parts, got it home and still no sound. After some research I read about the on/off/vol pot problem and told the tech. Turned out to be the problem. Ordered one of "those" pots from McIntosh for $100. After installation tech said that taper had a slight sound unbalance at the very start but then cleared up. After reading this post I realize he never said if he tested taper through the whole range and I never really paid attention. Been quite awhile since I used it so I may have to go back and give it a listen as I wasn't aware that there was a problem with Mc replacement pots, but that may be something new. The tech did tell me he was amazed that he clocked the output at 105wpc.
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Sounds like your tech was not experienced with McIntosh and I'm surprised he sent the amp home to you not working. I guess good techs are getting rare.
 
Emmbee said:
Great. I was hoping to use Audio Classics as a last resort. I'm very disheartened to hear they failed to provide a solid rebuild.
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AC is very familiar with this problem, maybe too familiar. You might call & speak to Ryan who I think would tell you truthfully what they could do for you.
 
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