Tuesday, February 9, 2016

McIntosh MC2100 Upgrade - Part 1

McIntosh MC2100 Upgrade

Lately, I have been rebuilding my old McIntosh MC2100 power amplifier. We purchased this while I was in college from an audio salon in Oklahoma City run by an ex-designer of that company, A.P. Van Meter. Purchased in new 1973, it has undergone literally over a thousand hours of  upgrades and redesigns but I am still very happy with its sound so much so that it has kept me from buying another amp. However, the last recapping of the old electrolytic capacitors occurred back in 2005 and they are currently showing audible signs of age. What a better thing to start my new blog with than a rebuild article whose tricks can be ported to other designs?

First, a bit of history. When I was trying to decide which amp to buy, I made the comment, "I want this to be the last amplifier I ever need to buy." and A.P. recommended the MC2100 over the other models in this price range (my wife wanted to trade our car for the 2300 but we disagreed on this point). I also bought an MX-110 tuner/preamp at the time (wish I still had that) rounding out the electronics side for my first voyeur into the high-end realm.

As I mentioned, I always liked the sound of the 2100 but there was one major drawback: it hummed. The signal-to-noise spec was that of an older tube unit of about -85dB and I attacked that issue first by removing the built-in ground loops (this took a while but the results were impressive). The main issue was the chassis mounted RCA jacks and the numerous ground points connected via pop rivets, screw terminals, redundant wiring, and solder tabs.

The Stock MC2100 "underbelly"

Alas, the wiring to-from the output transistors and main power supply was adequate but also nothing to write home about. So also in the first phase was to replace all of the high-current wiring with higher-quality wire. At this time, I chose to eliminate the socket for the driver boards (located between the black heat sinks) and replace the mechanical connections with longer wire and soldered connections directly to the board (yes, I am mad).

The other mods included a regulator for the input PC board, a redesign of the 80V/90V supplies, and new wiring from the RCA input jacks directly to the input PC board (I eliminated the mono-mode function since I never used it). The wiring to the multi-pin round connector was also eliminated.

After an encounter with a lightning strike that caused the primary power transformer to die, I replaced the old E-I design with a toroid and hand wound the 80V/90Vvoltage supply onto it. The fuse was also replaced with a 7A aircraft-grade circuit breaker and small-value polystyrene and Mylar shunts were added in strategic places to help again with lowering noise and improving dynamics. And the tiny #14AWG zip-cord power cord was replaced with something that could handle the peak currents with added noise filtering.

Toroid Upgrade

I tried to use as much of the old sheet metal from the E-I transformer as I could to retain as much of the aesthetics as possible but as you can see in the above image it totally changed this unit's appearance. At this point, the toroid added in my estimation two full octaves of extremely deep bass to the sound giving it a punch and bass clarity that it never dreamed of before. The stock knobs were broken in a move and replaced with a 0-9 dial version to help match channel balance and limit the output and the pots changed to a lower-noise style.

Finally, I changed out the old-style terminal strip speaker connections with contemporary 5-way binding posts choosing not to use the 16-ohm tap. Some may say that doing all of this was crazy and it devalued and altered the name McIntosh, and I agree. But it was my piece of gear to do with as I chose and I valued sonic accuracy over historic design and so the soldering iron went to work.

5-way Binding Post Upgrade

It looks pretty weird but it sounds fantastic. The sound stage is huge in width and depth plus it is dead quiet. So this ends part one of this series. In the next part, I will reveal some of the things I did to upgrade the power supplies that you can also do pretty easily. So don't change that dial...stay tuned for more goodies.

Yours for higher fidelity,

Philip Rastocny