1900 On Off/Volume Control Replacement

[Fairlane]

Curious if anyone has tried the new replacement control being sold on the auction site.

They are not cheap but might be worth the money for a permanent fix. Anybody install one?

(No affiliation what so ever)

 

[Fairlane]

Guess I need to be the first.

 

[c_dk]

Mac parts has contracted with the Canadian firm PEC to build a generic volume control with a power switch and 50% loudness tap.

A previous poster supplied a eBay link for replacement pot that looks just like the one Mac parts supplies. I assume your question applies to the same.

 

[lowredmoon]

I ordered on over the weekend. We'll see.
Edit: I pulled out a PEC pot from my parts box and it looks different from those in the photos. I'll follow up when it comes in the mail.

 

[Fairlane]

That would be great. Hope its a good fit lowredmoon.

Love my 1900 but the volume thing is annoying on an otherwise great sounding receiver.

 

[c_dk]

Is it the one with two film caps in the picture for $164.00? Says made in Canada and sure looks like the last one i got from Mac parts for a C note.

 

[perryinva]

I bought one too (the ebay one , though without the film caps). Nice quality. Haven't installed it yet. It's in the rotation to do. I measured the L/R tracking and it was excellent.

c_dk: what is the amp rating of the on/off on the MAC one?

 

[c_dk]

I do not believe I have ever seen that part of the switch fail......in 40 years. I am sure they have, had a similar made speaker switch fail in a Mc2105 and the switches for the mC2205, but not a power switch for a C28,1900, 6100 or any of the tuner preamps.

 

[Fairlane]

Not sure of the policy posting links to the auction site but if you look up Mac 1900 you will see it listed; just the switch with no caps. Looks nice to me.

(Again no affiliation)

 

[lowredmoon]

Here are photos and measurements at 24 positions.
Resistance (ohms x 1,000)
Gang 1 | Gang 2 | Difference
791 | 793 | 0.3%
635 | 629 | 1.0%
505 | 530 | 4.7%
397 | 367 | 8.2%
321 | 292 | 9.9%
248 | 224 | 10.7%
203 | 181 | 12.2%
160 | 137 | 16.8%
113 | 93.1 | 21.4%
80 | 62.3 | 28.4%
56 | 28 | 100.0%
40.6 | 20.1 | 102.0%
25 | 15.4 | 62.3%
20.1 | 13.5 | 48.9%
15 | 10.5 | 42.9%
8.9 | 7.5 | 18.7%
5.5 | 3.37 | 63.2%
3.05 | 1.27 | 140.2%
1.88 | 0.71 | 164.8%
1.3 | 0.54 | 140.7%
0.55 | 0.154 | 257.1%
0.188 | 0.05 | 276.0%
0.004 | 0.04 | 163.3%

 

[c_dk]

Is it a alpha sourced product? One of the auction site devices was a PEC, you could read the writing when zoomed in.

 

[lowredmoon]

I'm not sure who manufactured it. I'm just a customer. The ad, and the box it was shipped in both say "Made in USA."

 

[lowredmoon]

I ordered it because my 1900 does not produce even sound out of both channels at low volumes, and for the first few degrees, equivalent to say, steps 1 and 2, the right channel doesn't come in unless I turn it up higher, then back it down, and even then it's pretty touchy. It's pretty annoying.
The previous owner said that a few months ago, he replaced the volume control with a part sourced part directly from McIntosh. I can tell that the part that McIntosh supplied him is a PEC. So you'd think it should be working correctly, but it isn't. It's either a design that is just as bad as the original, or its defective. I know PEC pots are very good pots, so I'm not sure what to expect with the new one. I ordered it in a "what the heck" moment.

 

[lowredmoon]

I'm going to sit down with the schematic and see if I can spot anything else that may be causing the issue.

 

[c_dk]

Typically the manufacturer's name will be stamped into the device.

The Mac sourced part is a generic device......it is sourced to replace I believe 5 different part numbers that were used in 7 or 8 different units.

I sounds like the previous repair tech did not customize it to the 1900 use.

 

[lowredmoon]

Typically the manufacturer's name will be stamped into the device.

The Mac sourced part is a generic device......it is sourced to replace I believe 5 different part numbers that were used in 7 or 8 different units.

I sounds like the previous repair tech did not customize it to the 1900 use.

It looks as though the unit was installed as if it is a direct drop-in, without modifications. I'm going to pull it out tonight and measure it. If you know of any further amendments that are necessary, please share.

 

[c_dk]

The original CTS design as well as the Alps Mac sourced in the late 80s conformed with the schematic's loudness tap at 60 % not the 50 % of the PEC replacement.

The resistor attached to the loudness tap to ground alters the taper of the control as a voltage divider and conforms it into a audio taper. If those resistances are not in spec the taper will be altered.

The loudness button adds a cap to the loudness tap to alter the bass response.

I decided to find the auction......strikes me as a auction hustle.......claims 1900 scare tactic failures I have never seen happen since I deliverd the last one we had in stock in 1978.

It does seem though that most CD players output will cause the control to be used where it's two channels taper is not optimized........it was expected to be used between 9:00 and 12:00, not down at 8:00 or 7:00.

 

[lowredmoon]

The original CTS design as well as the Alps Mac sourced in the late 80s conformed with the schematic's loudness tap at 60 % not the 50 % of the PEC replacement.

The resistor attached to the loudness tap to ground alters the taper of the control as a voltage divider and conforms it into a audio taper. If those resistances are not in spec the taper will be altered.

The loudness button adds a cap to the loudness tap to alter the bass response.

I'll check the resistors.
I just pulled the pot and it is a 750K PEC. One side does decrease in resistance a little quicker than the other side at first, but overall, it tracks surprisingly evenly.

 

[lowredmoon]

Both are 66K, so 6% deviation from the schematic's 62K.

 

[lowredmoon]

The PEC's tracks measure 755K and 791K, with the loudness tap at 46%.
The online auction pot's tracks measure 791K and 790K, with the loudness tap at 54%