While doing the vintage McIntosh MX110 tuner-preamplifier adventure we experimented with several brands of new & NOS metal film resistors in the circuit in various places, but basically I always ended up preferring the vintage 2-watt NOS Allen Bradley carbon comp resistors that Andy Moore had suggested I try.
NOS Allen Bradley 56K Ohm 2W Carbon Comp Resistors.
The vintage 2-watt NOS Allen Bradley resistors had better tone, were more 'colorful', had more natural timbral textures, and generally provided more of an emotional connection to the music, compared to the metal film resistors in most of the circuit locations where we tried them.
Tepro RA 56K Ohm metal film resistors.
The sole exception is the long term testing we're doing with the 56K Ohm Tepro RA metal resistors we're using as phono input resistors on Leo's MX110's PH-1 (below).
Upper right: 56K Ohm Tepro RA's (black) next to 2-watt NOS Allen Bradley's on Leo's MX110.
On George's MX110 we're using the stock OEM Allen Bradley resistors (1/4 watt I think) on the phono inputs for a baseline comparator, and on my MX110 we're using the vintage NOS 2-watt Allen Bradley resistors suggested by Andy.
After thinking about the differences I heard between the sonic & musical balance of the vintage NOS 2-watt Allen Bradley resistors compared to that of the metal film resistors, I decided I wanted to go back to our vintage McIntosh MC30 monaural amplifier resistor adventure and try some of the vintage NOS 2-watt Allen Bradley resistors in place of the Tepro RA's.
The McIntosh MC30 Monaural Amplifier Adventure!
As a refresher, for our resistor adventure with the MC30 monaural amplifiers we had changed out the 2.2K-Ohm feedback resistor in the R13 position, and the 3.3K-Ohm cathode resistor in the R5 position, with Tepro RA metal film resistors (below).
Tepro RA metal film resistors in the MC30 resistor adventure (the 2 black resistors at the center of the photo) .
Given the big influence these two resistor positions have on the overall sound quality of the MC30 monaural amplifiers, I figured the change would be an interesting experiment.
So a few days ago I ordered up the necessary vintage NOS 2-watt Allen Bradley resistors for the 2.2K-Ohm feedback resistors for the R13 positions, and the 3.3K-Ohm cathode resistors for the R5 positions, to make the change, and they were waiting for me yesterday when I got home from the day job.
So out came the soldering iron, out came the Tepro RA metal film resistors, and in went the vintage NOS 2-watt Allen Bradley resistors in their place.
I fired off the the amps and let them warm up for a while, then put on the minty copy of Brasil '65 that had arrived along with the Allen Bradley's, and let 'er rip.
Brasil '65
The change in the overall tonal balance was so large that it caught me by surprise, and my attention was riveted to what I was hearing.
First of all, with the vintage NOS 2-watt Allen Bradley resistors in place of the Tepro RA's, the upper midrange became more forward, and more the soundstage was more 'lit up', which I wasn't expecting at all. I thought it would be the other way around, that the upper midrange would get darker and softer, but that's not what happened.
I wasn't sure I liked what I was hearing from the resistor swap. I played a bunch of albums last night, and I've been playing music all morning, and the Allen Bradley's are settling down now, and smoothing out.
I'm hearing a very interesting mix of sonic & musical attributes from the vintage NOS 2-watt Allen Bradley resistors.
First of all, even though they're more forward and more 'lit up', they also banished the unnatural & unpleasant glare on female vocals and muted trumpets that I was hearing, and I realize now, had mistakenly attributed to the MX110.
Lucinda Williams World Without Tears
Even the overly aggressive Lucinda Williams album World Without Tears lost its edginess, and for all the world sounded like it was an Analogue Productions remaster, with the room awash in compelling music. I got out a bunch of my 'bad actor' albums and played them, and so far the results are impressive, as they have all been rendered musically satisfying by the vintage NOS 2-watt Allen Bradley resistors.
By the way, one of the things I realized with the Allen Bradley's in place in the MC30s, is how really good the Arizona Capacitors Red Cactus capacitors in Modification B of the MX110 are. The Allen Bradley's really allow the Red Cactus's 'sexy girlfriend' persona to come through in spades on World Without Tears!
The vintage NOS 2-watt Allen Bradley resistors are great big things, and there's a lot of carbon in them, so I suspect it'll take them a while to settle down completely. I usually allow about a 100 hours for things to completely settle in, so we'll see what happens.
I like the darker & richer overall presentation of the Tepro RA's better than the more brightly lit Allen Bradley's, but the Tepro RA's handling of female vocals & muted trumpets are a deal breaker for me, and I could never live with that aspect of their performance on a long term basis, so the Allen Bradley's are staying put for now.
The vintage 2-watt NOS Allen Bradley resistors sound different in my MC30s than they did in my MX110, but overall they are more musically satisfying, and open up a much broader range of albums as being musically enjoyable, than do the Tepro RA's. It seems like a bit of a magic trick, actually, and I'm still getting my ears around what they are doing. One thing I do notice with the Allen Bradley's is that they are more timbrally realistic, particularly on the timbral textures of guitars, and provide more of an emotional connection to the music.
The resistor adventure doesn't end here though, as I've got some highly recommended carbon film resistors on the way to try at various locations in the MX110 and MC30s, so stay tuned, I'll have more to say on this topic.
In the photo below you can see the hard to come by 56K Ohm carbon film resistors that I will try as input resistors for PH-1 on my MX110. Like the conductors of Western Electric WE16GA, these resistors have tinned copper leads.
Mystery carbon film resistors with tinned copper leads.
On another note: I'm really impressed with the good folks at Solen Electronique. Only four days after I ordered them, they wound all six custom 6.6mH inductors I ordered and shipped them, and they've even arrived early (below)!
Solen 6.6mH inductors for the A5 VOTT project crossovers.
So with a little luck I'll find time to start bread boarding the crossovers for the A5 Voice of the Theatre project this week! Exciting!
Thanks for stopping by!
