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McIntosh MA6100

amr2

amr2

Well-Known Member
Hello

I'm finishing the restoration of this beauty. The unit is in very good cosmetic condition.

IMG_8508.jpg

The main caps and the bridge diodes were damaged. I did a full recap, changed all bad parts, new bulbs, etc. I will post some pics once finished.

But I have a big problem. The volume pot. Parts of the resistive wafer are missing :eek:

IMG_0075.jpg

I have contacted Mcintosh, and shipping cost to Europe are about 100€, plus the cost of the pot, which is similar to the original. The potentiometer brand is CTS, dual 700K log with loudness tab, and rear switch. I'm thinking in change only the resistive wafer if I am able to find something similar. Some help is required ;)
 
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If your pot as one good wafer measure it. I have found that they measure as 1 meg, linear with a loudness tap.

The replacements Mac currently supplies are made in Canada, are generic, and therfore need some customizing to work as replacements for 5 different originals.

I have looked around for some repacement wafers but ultimately it comes down to time vs money.

You would think that Alps or Alpha might make something that fits but I haven't found anything.

The replacements cost $100.00 US plus $6.00 for shipping......obviously your local tarrifs are not kind to US imports.
 
I have just measure it. It’s very close to 700k. At midpoint it measures almost half of the impedance, but it is not linear, at least the first quarter.
 
The times I have measured the intact ones from many units they typically measured closer to 1Meg.

The resistance increased in a linear manner not a log or audio taper where more resistance was on one part of the rotation. The loudness tap was at a 60/40 split.

I think I posted a picture years ago.

In this control scheme by tying the center tap to ground along with one "side" of the resitative trace a log type voltage divider taper is created. By adding a capacitor to be switched in a loudness compensation circuit is available.
 
I found some old CTS pots, 1M log. I'm going to see if I can use the resistive wafer. But the problems is the fourth tap. A tapped pot is used in this circuit so that the loudness function is progressive, giving more bass boost as volume decreased. I can disconnect the loudness circuit, but I would like to leave some kind of compensation. What do you think about connect the tapped point to the 'hot' end of the pot, perhaps with a series resistor?
 
Another option could be the CTS 450 Series, it can be ordered in tandem configuration with power switch. But without loudness tab.
 
I did experiment with Rod Elliot's better volume control idea, without a loudness tap and a pair of Alpha wafers. It was under whelming used in a MX115.
 
c_dk said:
I did experiment with Rod Elliot's better volume control idea, without a loudness tap and a pair of Alpha wafers. It was under whelming used in a MX115.
Click to expand...

Yes, I know that article, I have used it in the past.

I have to think about that, but the idea of a 450 series potentiometer with some kind of fixed loudness compensation can be a good compromise solution, although it is not ideal.
 
Has it been determined that your government is adding a 100 euro tax on the import of this part? So if you bought the part from AC or a eBay seller the tax would still be applied.

Certainly FedEx isn't charging 100 euros so either it is your local importer for Mac or local taxes.

Bypassing taxes is illegal, buying from, in this case, a grey market supplier is just questionable.
 
It is my local importer for MC who wants to charge 100€ for shipping + fees + manipulation + ...
I have bought from the US several times and that amount doesn’t make sense
 
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In the meantime I’m doing some tests. I disassembled a new CTS pot that I had in stock. And the resistive wafer is interchangeable, it fits perfectly. The cons are that they are only available in 500k or 1M audio tape. And no loudness tab.

IMG_0102.jpg
 
Well you could look for a EBay seller offering the same Canadian made pot that macparts sells, pay the import tariff and do the standard modifaction to set the loudness tap at 60/40 or

Spend tons of time to save 125 euro.
 
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