McIntosh - Hints and Kinks

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Does the Rightmark program have the abillity to"correct" for soundcard issues like some FFT speaker analyser programs do?
 
Looks like no one is interested in this sticky beyond coffee mugs.

Anyone have an opiniun/experience with the Rightmark analyser program?

I am interested in this thread and I am fine with the coffee mug I use currently....although I do like the one Terry has. :)
 
MC2120 issue

Normal has a capacitor in series with the input for preamps that have a DC component in their output, direct bypasses the capacitor and allows even DC to get to the preamp section in the amplifier. Using the direct with a tube preamp can zap the input stage since many tube preamps can put out several volts during warm up.

Terry and all - my MC2120 has one channel failed, and by checking all voltages I could (I have a schematic marked up which I can scan and provide if requested), the only clear dissimilarity L/R is 0.43V out from LM201 pin 6 (output). I believe the good channel has a near zero voltage out at the same pin (-0.008V measured), so I suspect the op amp is bad...

Other symptoms are signal disappearing at the collector of Q202 on the same channel (checked with scope). I get very faint sound out when volume is max.

The reason for quoting the above is that this may have occured when I fed the amp w/out C240. This was with a (capacitor on output) tube preamp.

Thank you very much for your input.
 
Is the PG light on? If so expect bigger issues. IC's #6 output drives PG light transistor

Most common issues in this vintage of amp:

dirty input sensitivity and stereo switches
bad relay contact due to arcing
failed molex pin plug solder connections on driver boards

If you swap boards does the problem switch sides?
 
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It would be nice if a common format freeware program would allow all to publish their mod's measurements, other than just "listening" impressions. This would open up some of these updates for discussion.Those with traditional old school testing measures would then also have a way to display what we discover as we work through repairs and such on these vintage units.
 
both PG lights stay on a solid green.

I will swap driver boards tonight if I get to it - thanks for bringing that back in my radar, it slipped my mind this far.

Will report later. Thanks for pitching in!

P.S. On second thought, pin 8 also exhibits substantial discrepancy: -0.65V / -0.17V, the latter being, I believe, the bad channel. The former is closer to what I see on the schematic too.
 
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When you pull the driver boards you are ready to re-solder the molex connector pins, these are the #1 cause of failure in this series of amplifiers.
 
When you pull the driver boards you are ready to re-solder the molex connector pins, these are the #1 cause of failure in this series of amplifiers.

Will check on the pins. Thanks Terry!

Now - a bit of news, though it doesn't clarify much for me... I swapped the boards, and the trouble seemed to follow the board. BUT: when switching from using my tube preamp to using my iPhone to inject audio into it, the iPhone would remove the problem. I'd put the AI preamp back, the channel would drop again w/ distortion.

The three consequential issues I see are:
- impedance - the lower impedance of the iPhone doesn't trigger some issue with the input stages or the op amp comparator;
- level - the iPhone injects a lower level signal than the preamp, so again the above applies;
- DC at output of the preamp whacking the input stage - I measured DC out with my Fluke and it's in the mV level. Besides, there is a cap right at input.

What gives?
 
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Installation Made Easier

When installing an amplifier onto a shelf, it is made much easier if the shelf and feet of the amplifier has been wiped down with some Pledge or Endust. The oil in Endust/Pledge makes the feet slide a lot easier on a hard surface. Pure Silicone spray (without petroleum distillates) would also be a good choice.

I was going to say "When installing a heavy amplifier like a MC2500..." but then I remembered that there are no lightweight McIntosh amps. *:>)
 
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When installing an amplifier onto a shelf, it is made much easier if the shelf and feet of the amplifier has been wiped down with some Pledge or Endust.

I stick round felt pads for furniture on the legs. They slide very well and I never got any scratches on the rack or floor, and they just give me this sense of cleanliness and ease of moving around... Especially when you have to slide a few dozen pounds on a shelf that's under another shelf while somehow managing the cables in the back...
 
Here is our famous Mod-a-mod that is done to all non digital McIntosh tuners by Richard Modafferi, designer of MR78.


Modafferi Mod
Install Hysteresis Modification
Modify IF amplifier output stage to reduce IF noise radiation at 9th and 10th harmonics of IF (96.3 MHz and 107.0 MHz)
Replace all audio coupling and bypass capacitors in the feedback circuits with High Quality Metalized polypropylene capacitors
Install bypass caps in the power supply (Tube Units)
Modify the Stereo Decoder to improve Stereo Separation
Modify the Stereo Decoder for higher Slew rate and Stereo Separation
Optimize pilot carrier limiter circuit
Change muting and 19 KHz circuits for more reliable muting and stability of the stereo decoder (Tube Units)
Re-route IF cable from IF chassis to detector to eliminate tailbiting at 96.3 and 107.0
Modify Narrow Filter to accept over modulating stations.
Front end modified for higher RF selectivity
Adjust IF gain
Perform complete RF, IF and MPX alignment
Convert to 220 Volt operation - if required
Change de-emphasis to European Standard - if required
Listening check
Install Cardas output connectors
Unit will now exceed original factory specifications
Run performance graphs
Clean chassis, controls, panel and knobs
Unit signed and dated (inside) by Richard Modafferi
Selectivity modification

* * Investment: Tuner Approx. $700, Tuner-Preamps Approx. $900
* * Turnaround Time: Approx. 3 weeks
* * All changes are not applicable to every unit
 
It would be nice if a common format freeware program would allow all to publish their mod's measurements, other than just "listening" impressions. This would open up some of these updates for discussion.Those with traditional old school testing measures would then also have a way to display what we discover as we work through repairs and such on these vintage units.


There is a program available at a modest cost. The problem with an audio analysis program is it takes some time to learn it. I did take some measurements and published them with my MC2500 mods.
 
MCD7008 Wired remote issues.

If the front panel buttons are "dead", remove the two CD4066 ICs at the bottom of the display board and try again. A fault in the wired remote circuit can cause the player to be unresponsive to key presses.
 
All is well with my MX110 now!
Went down to Audio Classics on a day trip and Richard Modafferi and the staff (Gary Butt) took care of everything!

I believe it was a cap issue - now LOTS of bass!

(also a wood cab!)

They (AC) are a class act!
 
MC2200 autoformer buzzing

Does anyone have an idea what would cause an autoformer to hum or buzz loudly even when there is no input of speakers connected? Internal oscillation?
Thanks,
John
 
Most likely bad filter capacitor, though I have never herd an autoformer sing unless I had a signal going in, are the speakers giving any output?
 
There is a program available at a modest cost. The problem with an audio analysis program is it takes some time to learn it. I did take some measurements and published them with my MC2500 mods.

What program did you use? What audio interface? Where did you publish the results?

Thanks,

Steve
 
My friend with the buzzing MC2200 amp decided to to send it for repair. The fellow who he bought it from on ebay would pay half the cost but wouldn't take it back. We'll see what the problem was when he gets the bill back.
 
What about updating the rectifier diodes ? Aren't there faster ones available now ? How fast is the 1N4820?
 
Watch out for diode changes, a fast diode can introduce noise into the system, especially in a preamp or tuner. Most McIntosh supplies are regulated and well filtered, a fast diode will not have any effect on this type of supply. It can have an effect on a power amplifier by helping stiffen the voltage, but again watch out as a fast diode can cause the peak current draw from the power transformer to increase. I have seen this in a 240 where the peak current increased causing solder joints in the power transformer to over heat and crystallize, not a fun job to unpot and re-solder.
 
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