My first McIntosh Rebuild - MC2105

[rolleiman]

Greeting Gang,
Well I am starting my first McIntosh rebuild so wanted to document the questions and advise along the way.
I recently purchased an MC2105 and despite the wonderful packing job the person did it arrived with broken case, glass and glass holding frame.
I am in the information gathering stage at this point. I have two other projects going on so want to put together my parts lists so I can order all at once.
So here begins the journey!

 

[damacman]

Note to self ... Never ship a Mc component in its wood cabinet. 100% chance of damage to the cabinet, unit, or both,

Good luck with the repairs but chassis parts for these amps are getting harder and harder to come by.

 

[kevzep]

Send it back and get you money back....

Any McIntosh product with a glass facia should not be shipped in anything other than the McIntosh Shipping carton, which are still available for any McIntosh product.

Then when you buy the next one, just make sure its shipping in a proper shipping box.

They are a very basic amplifier to work on, there are updates to do to them....

 

[rolleiman]

Input Section Board 043-795

Ok - the journey begins -

I have not listened to the amp as I want to makes the mods to it while I have it apart so will start with the Input section board.
Photo:


Schematic:
View attachment 043-795 Input Section PC Board.pdf

My plan is to do the following:
- c3, c4: 0.47 replace with a matched set of Polypropylene caps
- c5, c6: Board has 640uF, 25V so plan to replace with similar value audio grade like the Nichicon Muze
- c9, c10: 10uF, 25V look like non-polarized coupling caps on the input. Plan to replace with audio grade non-polarized caps
- c11, c12: 100uF, 15V, look like polarized caps and plan to replace with audio grade electrolytic
- R5, R6: 4.7K ohm, 1/2 watt - plan to use a match pair of Metal Film resistors.

Questions:
1) what type of caps are these white capacitors?
2) would you recommend changing any of the transistors
3) would you recommend changing any of the non-signal path resistors
4) several people bypass the electrolytic with a poly that is 10% to 20% of the value. Is this recommended since even though I plan to use audio grade electrolytic?
5) thoughts on above plan?

 

[pgena]

You might be interested in this DIY audio post (starting with #3). I tried it on my two MC2105s - they sound great, and it's inexpensive to implement. I believe the components refer to the MC2100, hence, a couple schematic #s are different, but it's easy to sort them out.

 

[rolleiman]

Thanks

Thank you I will give this a read. Much appreciated. I had a hard time for some reason obtaining many post when I did a search. I am sure I will have some questioms along the way.

 

[rolleiman]

more MC2105 questions

By the way pgena,
- Did you change out any of the transistors or resistors in your unit?
- What capacitors did you decide to go with for your Polypropylene, .1 bypass and electrolytic caps?
- change out any of the terminals or audio input jacks?
Thanks,
Jerry

 

[pgena]

I recently bought all the output transistors and resistors (located on the heat sinks), but I've yet to install - might be overkill. I did change the the 6.3kohm, 5w, 5% resistors on the output boards.
Input board: For the .1uf bypass, I used Cornell-Dubilier 100v (Mouser).
For the input board: C3 & C4 - Dayton audio grade .47uf @ 250v; C4 & C5 - Sprague Atoms 500f @16v; C9-C12 - Nichicon.
Output boards: C1 & C11 Nichicon.
I also used Nichicons for the 47UF bypasses on the 39,000uf caps.
I haven't changed the terminals, but use the right angle spades to banana adaptors (eBay) so that I have banana connections to the speaker wire. I have gold RCA input jacks, but haven't installed them yet. Have fun!

 

[rolleiman]

Thanks pgena,
Guess it is time to get serious about putting together a parts list in the next couple of days. I bet the amp sounds great!
By the way have a couple questions:
- do you know what type the white capacitors are?
- what preamp and speakers do you use?
Once again thanks for your help.
Getting excited about owning and working on my 1st McIntosh. It will be worth the labor of love to bring her back to life.

 

[pgena]

I don't know exactly what type the white ones are, but I read somewhere that they ought to be changed - maybe they're some kind of composite? There are several experts on here who would know. I have two MC2105s, one I use for the two front channels of a 7.1 system. The other MC2105 powers the bottom end in a biamped system, with a vintage MC275 for the high end. The tubed preamp is a Musical Design SP-2B. I use an MEN220 for the crossovers, as well as for its Room Perfect DSP program. The speaker is a JBL Paragon (ca. 1960 build).

 

[rolleiman]

White caps on MC2105

Thanks. Sounds like a couple of good systems.
It will be interesting to find out what type the white caps are.
I have my MC2105 parts list almost put together. Once I look at what I need for my TU-717 tuner, I should be ready to pull the trigger on ordering parts.

 

[rolleiman]

MC2105 Diodes

While I have the McIntosh apart, what diodes would anyone recommend replacing on the Input board and the output boards? Transistors?
And if any, what would the replacement parts be that meet or exceed the specs?

My concern is that when replacing the components around the diodes, they my get damaged by heat. I know that it is best to replace these last since they do get degraded do to heat.

Thanks team for the advise.

 

[rolleiman]

MC2105 Multi Value Can Capacitor

Hi all,
I finally got back at my project and thought you might be interested in seeing why it is important to replace old can electrolytic caps. I decided to open up the can and restuff with discrete cans:

 

[rolleiman]

I don't know exactly what type the white ones are, but I read somewhere that they ought to be changed - maybe they're some kind of composite? There are several experts on here who would know. I have two MC2105s, one I use for the two front channels of a 7.1 system. The other MC2105 powers the bottom end in a biamped system, with a vintage MC275 for the high end. The tubed preamp is a Musical Design SP-2B. I use an MEN220 for the crossovers, as well as for its Room Perfect DSP program. The speaker is a JBL Paragon (ca. 1960 build).

Hi Pgena,
Found out white caps are just electrolytic caps.

 

[rolleiman]

MC2105 RCA Jacks

A couple of weaknesses in these units is the poor RCA jacks and the Direct Switch so I intend not to use the switch in direct mode and replaced the jacks with gold plated units.

After disconnecting the cap from the center post, and snipping the ground wire from the jack, I pried out the plug with a pair of pliers. The hole was too small, so I drilled it out progressively with two drill bits. Use caution as the drill wants to grab and you may end up damaging the heat sink inside should the bit get away from you. The hole was still slightly small so used a Dremel to complete the opening. Another Warning - be aware of the metal shavings. They do not bode well with electric circuits.



I also disconnected the bypass wire from the cap so it would not act as an antenna.
Buy the way, why is this .22 uF cap needed anyway? It seems that the .47 uF cap after the potentiometer will block the DC. Can it and should it be removed?

Schematic

 

[rolleiman]

MC2105 Large Power Supply Can Cap Replacement

Probably not necessary to do, but since I am planning on keeping this unit for a long time, I decided to replace the large power supply cans.

Original Value - 39,000 uF
Bottom View - Note the red dots showing thru the chassis. These are pressure escape valves on these large cans should a problem occur. The must never be covered up!
Screws and rectifier circuit removed
Top View after installation: Value - 56,000 uF

I was concerned that the larger value caps would cause too much inrush current thru the diode bridge but was told that they would be able to handle it. Will see?

 

[rolleiman]

Inrush Current
I powered it up today and there was no problem with the diodes handling the current.
Using an MP3 player hooked up directly to the amp it sounded pretty good.

 

[Gregory]

Looking good man!

How did you cut the original cap-cans? with a tube [pipe] cutter? and what method used to reattach can to the base?
What does the Manual describe.. for the INPUT switch?

-Gregory

 

[rolleiman]

Looking good man!

How did you cut the original cap-cans? with a tube [pipe] cutter? and what method used to reattach can to the base?
What does the Manual describe.. for the INPUT switch?

-Gregory

Hi Gregory,
Thanks.
-I cut the original cap can with a Dremel tool and a cutting wheel. The aluminum cuts quite easily and I reattached using two part epoxy. Since I was not able to solder to the existing aluminum tabs, I cut them off, drilled thru the base and connected the leads directly to the solder lugs. I also drilled a whole to feed the ground wire thru the base.
The manual does not say anything about the Input switch.

 

[L-82]

Rollei looks great, fantastic job. To bad your not in Montreal I would bring you my 2105. What would you say the parts cost? How many hours of work did you invest in the rebuild?