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McIntosh - Hints & Kinks Part II

Discussion in 'McIntosh Audio' started by Mike Gibson, Dec 7, 2013.

  1. Mike Gibson

    Mike Gibson Modulator Staff Member Super Mod Subscriber

    Dufur Oregon
    Please use this to add helpful hints you have discovered so that others can benefit from your knowledge.

    Please ask questions such as what caps to use or how do I in the main forum or PM the techs who frequent this forum.. That way this thread will only contain actual helpful hints. The other thread is full of questions about caps, procedures etc. All posts unrelated to actual hints will be deleted so as to keep this thread relevant. Thank you for your cooperation.



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  2. RShackleford

    RShackleford Active Member

    At least one of the older tube amps was released with minor variations of the circuit. For mine, the MC40, the older version of the circuit is the one seen in virtually every schematic found online. I only know about the newer circuit because it's in the printed manual that I have; it has dotted lines and notes referencing the older one.

    The reason it's helpful to know about the newer circuit is that it has fewer components - two fewer capacitors on the main circuit board, and more significantly, one fewer resistor and one fewer capacitor in the power supply. This last item means that it's more feasible to replace the expensive, bulky, and difficult to source multi-section FP-mount can capacitor with a single-section cap (with high enough voltage rating). The power supply just ends up having 4 caps: the two in the voltage doubler, a big one for B+, and one much smaller (so an axial lead part can be used). I am mod'ing my older one to use the newer circuit while I rebuild the pair.

    Presumably the newer circuit is at least marginally superior as well - I doubt the changes were made just to save a few cents on parts (the newer version is still manufactured with the multi-section can).

    The attached snippet from the schematic shows the relevant section; bear in mind that the values of two resistors on the circuit board (R11 and R12) are also different between the two versions (as well as some capacitors not related to the PS).

    NOTE: I just edited to show the complete newer version of the schematic.

    Attached Files:

    Last edited: Sep 28, 2015
  3. Scifi

    Scifi Super Member

  4. Scifi

    Scifi Super Member

    You can monitor the current when turning on electrical equipment to make sure it isn't drawing too much current. A common cause of this problem is leaky filter capacitors. I use a Micronta model 22-161 clip-on type ammeter with a receptacle-plug adapter (see pictures). I also recently got some test sockets (one octal and two nine pin miniature) so I can test voltages without drilling extra holes and adding test sockets to the device and/or opening the device to test it.



    Attached Files:

    Last edited by a moderator: Jan 5, 2014
  5. rbnjr2

    rbnjr2 New Member


    I would like to try a pair of mc30 or mc40 monoblocks to power just the tweeter
    of my proac response D18 speakers. the manf suggests a tube to power them and i am very very curious how they would sound being tube powered. by what you have shared it appears you have a very good amount of knowledge in the tube design of power amps. mcintosh has always built their products with a lot of pride inside and out with quality number one. thank you for sharing and i look forward to owning one of the mc30 or 40 monoblocks.

    thank you.
  6. pcrosewood

    pcrosewood Active Member

    Halifax, Nova Scotia
    Mc 2105

    Is there anything specific I can do to tighten up the bass on my 2105. Are there specific caps,resistors, transistors that could be replaced ? Any and all suggestions would be helpful and I'm really hoping Terry DeWick chimes in.
    Last edited: Sep 3, 2014


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  7. dewickt

    dewickt Will fix about Anything

    Knoxville, TN
    Caps on the input preamp, and main filters, the main filters do the most.
    LPplayer likes this.
  8. pcrosewood

    pcrosewood Active Member

    Halifax, Nova Scotia
    Thank you Terry.
    Last edited: Sep 6, 2014
  9. rpoli2518

    rpoli2518 New Member

    Canada, Toronto
    Hi fellows,
    I have McIntosh mc2200 amp and McIntosh c33 preamp. Right channel is louder then Left. Tried to switch rca output from main on preamp right to left and left to right. The problem switched also. So its preamp, not amp. What section do you think I need to check. The sound is clear but unbalanced. It has amplifier monitor board. Do I need to check it first and what parts?
    Have multimeter only.
    Thanks in advance
  10. duder1982

    duder1982 Active Member

    The east coast of Nebraska
    Good thread.
  11. RadioTech64

    RadioTech64 New Member

    MC2105 Bias Problems?

    Hello everyone. A newbie to the forum here that has read and taken in a wealth of good info already :) Retired 2 way tech who does audio on the side..With that being said I have a head scratcher 2105 on the bench. First of all according to the customer it would randomly blow line fuses,then from what he explained shut down to thermal overload..this is where I enter :) Powered up and found right channel heatsink heating to 85-90° quickly. Checking the output transistors (132-036 and 132-070) found no leakage but gains all across the board. All were replaced with MJ15003 ON/Motorola parts.Good output and no distortion but right heat sink heats over period of an hour to 80° with no signal applied (idle). Sounds like bias issue to me so the driver boards are swapped and only a slight change.BTW Main caps were replaced due to leakage. From what I gather the bias diode is under the driver transistor on the driver board. That checks OK (compared to other side board) but does read more like a dual diode in series. Question here is: is there a good place to measure the bias current ( across the emitter resistors?) without having to install jumpers?

    Also my bias resistors are 27 ohm each side and have aged to 28 and 29 but..I understood normally they are 22 ohm. Is there a specific target current for biasing these amps? BTW there is roughly a DC Offset of .22 on left and .13 on right at idle,but this is an autoformer design so that shouldn't be a major player.

    Sorry for a long winded first post but I want to tell the whole string of events as I know it.

    Any tips,suggestions,or help greatly appreciated!




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  12. Josar54

    Josar54 New Member

    Dear Audiokarma friends, I'm fixing a Mcintosh MC 2300 and am having problems with the design digram of the top cap, could someone give me a scale design or a good photo to make it print to the top.

    Best regards
    Jose Armando
  13. So...MAC4100 here

    Only hums ( unchanging 60hz hum) when something is plugged into one of the inputs

    Plugging an opened ended RCA cable into the Recorder Tape Outs makes the FM audio level jump way up and then FM starts playing competing stations

    What the heck?

    I work on receivers all the time and do NOT see this anywhere else
  14. Scifi

    Scifi Super Member

    People have debated whether or not speaker cable or other cables or wires have an effect on the sound. I found some patents that discuss the quality of copper and silver that look interesting.

    US 4874436 Method for producing high purity electrolytic copper

    US 4964738 Electrical conductor of high magnetic permeability material for audio
    preamp -> amp
    column 3 lines 66+
    Unfortunately, the only metal with higher electrical conductivity than copper is silver, and the improvement in skin depth is only approximately 3 percent--a negligible improvement at great cost.

    US 5099518 Electrical conductor of high magnetic permeability material for audio circuits

    US 5510578 Audio loudspeaker cable assembly
    copper and/or silver column 3 lines 2-3

    US 5523528 Interconnection cable for low frequency signal transmission
    The inner conductors insulated from each other are shielded by a shielding layer made of copper fabric woven of high-purity copper wires or silver plated copper wires (column 1 lines 50-51)

    US 5900589 Silver ribbon cable

    US 6231637 Process for producing high-purity silver materials
    column 1 lines 19-32
    With copper wires having purities on the order of 99.9 wt %, signals cannot be transmitted correctly without phase differences and, as a result, only blurred images or unsharp sounds are produced. To solve these problems, high-purity copper wires produced by working raw materials having purities of at least 99.999 wt % have recently been introduced into the market.Similar effects are exhibited by silver wires that are produced by a process which comprises solidifying silver with a purity of at least 99.95 wt % in one longitudinal direction to yield an ingot, drawing it by either cold or warm working and further working the wire under conditions that will not cause recrystallization.

    US 4582545 Method of producing electrical conductor
    column 1 lines 10+
    As is well known, an electrical conductor is generally made of one of two types of copper: tough pitch copper (TPC) and oxygen-free copper (OFC) The copper is generally worked so as to be circular or rectangular in cross section or in the form of a foil and then recrystallized by annealing at a temperature ranging between 300.degree. and 600.degree. C. to produce the conductor.It has recently been understood that an electrical conductor made of OFC in a transmisison line for a multi-frequency audio signal, particularly, as an inner wiring conductor or a loud speaker wiring conductor of an audio apparatus, is much superior to one made of TPC.

    US 5574260 Composite conductor having improved high frequency signal transmission characteristics
    Use of silver plating
  15. Scifi

    Scifi Super Member

    US 2825766 High fidelity audio amplifier
    McIntosh - looks like MC-30

    US 2860192 Amplifiers

    US 2886655 Amplifier

    US 2929028 Audio amplifier

    US 2980840 Wide band, low distortion, high efficiency amplifier

    US 3153766 Mode of operation of the pentode or tetrode tube in the output stage of an audio power amplifier
    Pio1980 likes this.
  16. Scifi

    Scifi Super Member



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  17. Yamaki

    Yamaki Not For Hire Subscriber

    Hillsboro, Oregon
    Some newly minted McIntosh amplifier owners complain that banana plugs don't fit well, only going in about 1/2 way.

    The newer McIntosh amps, such as the MC252, MC302, MC352, MC452, MC501, etc... have two separate rings on the speaker connector. The top ring is the locking ring. Loosen that one first, then loosen the bottom ring oh so very slightly. Insert the banana end and firmly seat it. Then lock down the bottom ring and lastly, tighten the top locking ring.
  18. jlovda

    jlovda Things I loved from the 60's and 70's Subscriber

    NE Ohio
    Has anyone tried to replace a burnt out bulb in the moving dial pointer? Is the bulb and red filter just pushed down the tube or glued? How did you remove the old bulb? In the MX113 I just acquired, the bulb is working but the bulb and filter are rotated 45 degrees in the tube so the lamp appears off.

  19. Scifi

    Scifi Super Member

    Some more related patents.

    US 5302912 Push-pull audio amplifier with crossover distortion compensation
    pentode ultralinear fig. 3

    US 4532476 Power amplifier capable of simultaneous operation in two classes
    complete absence of crossover or " notch" distortion (abstract)

    US 4713624 Power amplifier with modified dynamic response
  20. Tcomisky

    Tcomisky AK Subscriber Subscriber

    Lawrenceville, NJ
    I changed one in an MX114 to a small blue LED. It was a direct swap. The pic makes it look much brighter than it actually is. I really liked the change.

    AlTinkster92 likes this.

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