I was so pleased with my vintage McIntosh MX110 tuner-preamplifier 'resistor adventure' this morning I just had to tell you about it!

As you know, the MX110 Adventure has thrown us a few unexpected curve balls, and in response Ron-san and I have been going through component-by-component to figure out what was going on and optimizing it.

Our first step was to revisit Modification A, where we had replaced the stock 56KΩ Allen Bradley carbon comp phono input resistors at R88 & R90 and R89 & R91 with 47KΩ Tepro metal film resistors.

The R88 & R90 and R89 & R91 phono input resisters have a large influence on the phono stage’s ultimate sound quality, as they are the first resistors the music signal goes through after leaving the cartridge and tonearm.

The Tepros are great resistors, but the change to 47KΩ from 56KΩ was a sonic & musical 'real sound' disaster, so we've gone back to the stock 56KΩ value for input resistors, and have been working through listening to a variety of resistors to optimize the sound & musicality of Modification A.

As I reported during Rafe's & Don's visit, we installed a pair of NOS Allen Bradley 56K Ohm 2W carbon comp resistors on phono input 2, and 56K Ohm Vishay VAR-Series ”naked ladies” z-foil resistors on phono input 1 (above).

The consensus during our impromptu group listening trials was that the NOS Allen Bradley 56K Ohm 2W carbon comp resistors were the best sounding of the two.

From a 'real sound' perspective the NOS Allen Bradley 56K Ohm 2W carbon comp resistors have stomped the other resistors tried in overall musicality, timbral naturalness, their ability to express tone color, as well as the overall musical flow in terms of tempo, dynamics, beat, rhythm, convincing melodies, and getting female vocals to sound their most natural.

The metal film resistors are more transparent and resolving than the Allen Bradley carbon comps, so in those two sonic senses they are better than the carbon comps, but in every other regard they can't touch the the vintage NOS Allen Bradley 56K Ohm 2W carbon comp resistors for 'real sound'.

We're also getting ready to try some NOS 56K Ohm 1/2 watt Shinkoh tantalum resistors (as used on the original Kondo Ongaku amplifier) in a shootout against the NOS Allen Bradley 56K Ohm 2W carbon comp resistors, which we will probably get to next weekend, so I'll report back on that in due time. That Shinkoh-AB comparison will settle the input resistor evaluations, at least for now, and then we'll move on to shaking down the next modification downstream.

It is clear that at this point in our 'resistor adventure' for the MX110, the NOS Allen Bradley 56K Ohm 2W resistors are 'The King' of the Modification A.

McIntosh knew what they were doing when they voiced their vintage MX110 with Allen Bradley resistors, and so far we have not been able to improve upon their choice of resistors.

Ok, all that was a prelude to remind you of where we are at in the MX110 'resistor adventure', and now I want to to tell you about the success I had this morning in the next step of the 'resistor adventure' with my vintage McIntosh MX110 preamplifier.

You might remember that before we changed out the Tepro RA phono input resistors, Yazaki-san recommend we first try changing out the stock 220kΩ Allen Bradley resistors located at R94 & R95, for 1MΩ resistors, to see if that had a beneficial effect on the sound & musicality.

Yazaki-san’s reasoning was, “I checked the circuit diagram of the first stage of phono EQ of Marantz Model 7 and also McIntosh C22. They use the phono input resistor, 47kΩ and the grid resistor, 1MΩ for 12AX7. And the combined resistance is around 44.9kΩ. But MX110, the phono input resistor, 56kΩ and grid resistor, 220kΩ. And also the resistance is 44.6kΩ. When we installed 47kΩ into MX110, the combined resistance is 38.7kΩ. I suppose you have been using MC transformer and the combination of your MC transformer and the input resistor, 47kΩ would be some harmful effect on the tonal character. And so, I have a idea that, how would be changing the resistor R94 & R95 from 220kΩ to 1MΩ … And I suppose there would not be any negative effects about this changing.”

We tried replacing the stock Allen Bradley 220K Ohm resistors at R94 & R95 with 1M Ohm Roederstein resistors (above), and at that time it seem like there was some small improvement by doing that, but it was not enough to offset the performance of the 47K Ohm Tepro RAs in the R88 & R90 and R89 & R91 positions for phono input resistors.

So today I decided that the next step in our MX110 'resistor adventure' was to remove the 1M Ohm Roederstein resistors we tried, and to put back in some Allen Bradley carbon comp resistors to replace them.

In the upper left of the photo above you can see the big Allen Bradley 220K Ohm 2 Watt resistor at R94 that I put into to replace the 1M Ohm Roederstein resistor at R94. The Allen Bradley is huge compared to the tiny Roederstein, so I had to offset it to one side to get it to fit into the crowded innards of the MX110.

In the middle of the photo above is the 1M Ohm Roederstein at R95, which I replaced with the 220K Ohm 2 W Allen Bradley resistor at R95 (below).

Due to the jumbo size of the 2W Allen Bradley I had to offset its position to get it to fit into the MX110's crowded interior.

I turned off the soldering iron and buttoned everything back up on my vintage MX110, and then installed it back into the system for a little listening.

So what was the result of replacing the 1M Ohm Roederstein resistors we tried at R94 & R95 with a pair of vintage NOS Allen Bradley 220K Ohm 2W resistors I had ordered?

Voilà, the sound was transformed in a very good direction!

The sound & musicality improved in the same ways as it did when I went back to vintage NOS Allen Bradley resistors for the phono inputs: much better overall musicality, gains in timbral naturalness, more saturated tone color, as well as improvements to the overall musical flow in terms of tempo, dynamics, beat, rhythm, convincing melodies, and importantly, female vocals sounded even more natural.

I have been listening to music all morning after putting the vintage NOS 220K Ohm 2 W Allen Bradley resistors in at the R94 & R95 positions, and I would say they had as big an overall influence on the sound quality & musicality of the phono stage as did the Allen Bradley resistors on the phono inputs.

Is there a down side to the Allen Bradley 220K Ohm 2W resistors at the R94 & R95 positions? As I noted for the phono input resistors, there is a slight loss in transparency & resolution with the Allen Bradley 220K Ohm 2W resistors compared to the Roederstein metal film resistors, but if you want 'real sound' the vintage NOS Allen Bradley resistors kill the metal film resistors, it's not even close!

What an empowering feeling it is to solder in a couple of new resistors and have a really good musical result!

Here's the moral of our 'resistor adventure' story for my vintage McIntosh MX110Z tuner-preamplifier: Leave the stock Allen Bradley carbon comp resistors in place and don't screw around with them, they are the original 'real sound' resistor.

If 'real sound' is what you want then Allen Bradley resistors will do a better job than any of the metal film resistors we tried at R88 & R90 and R89 & R91 (phono inputs) or R94 & R95.

Jut for kicks I also ordered a pair of vintage NOS Allen Bradley 1M Ohm 2W carbon comp resistors to try at R94 & R95, but that is a story for another day!

Thanks for stopping by!