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C26 - LOUD at zero volume

Discussion in 'McIntosh Audio' started by 1ontop=, Jun 13, 2018.

  1. 1ontop=

    1ontop= Active Member

    Messages:
    275
    Location:
    Croswell in the Thumb, MI
    I got my C26 preamp back from the shop for an audio update, cleaning and test mid February. I just played my turntable through it a couple of days ago. To my surprise when I cued the LP with the volume all the way down the music was like 9-10 o'clock. This obviously is not window shaking volume but too loud for late night/early morning easy listening. The tt I was using at the time was a Denon DP300F that has a built in ground and standard cartridge. I used both phono 1 and 2 .. same problem. I then tried my Sanyo PLUS Q40 with a Nagoaka MP110 cartridge and grounded properly to the back of thr preamp .. same problem. I contacted the technician (name withheld) that did the work and he suggested the C26 has bleed through problems and possibly my cartridge has very high output and is getting past the gain stage. This morning I tried two low end tt's I had around just to experiment with different cartridges. Still had the same problem.

    To expound further, at the zero volume setting the music sounds weak w/o fidelity. Turning the volume control up to 10 o' clock the volume is relatively the same then bass comes on and the music sounds correct. But I'd like to have that at low volume. The only way to get a low volume listening level is to turn the LOUDNESS control clockwise which in turn mutes the volume to a certain degree but does not have the rich music sound I would hear at a flat setting. Of course, this is not acceptable to me. Any comments or suggestions out there? Thanks.

    addendum: only the PHONO mode has this problem. All others work as they should.
     
    Last edited: Jun 13, 2018

     

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  2. c_dk

    c_dk Addicted Member

    Messages:
    6,311
    Location:
    West Michigan
    I would suspect a issue with the low voltage supply that powers the phono EQ stage since it only happens in phono. I believe it is a further filtered 8 volt supply off the 10 volt supply
     
  3. bastelwut

    bastelwut Member

    Messages:
    76
    Location:
    Franconia
    Had the same problem with my C11.
    After fixing the power supply anything was OK
     
  4. 1ontop=

    1ontop= Active Member

    Messages:
    275
    Location:
    Croswell in the Thumb, MI
    I read your post a week ago and now I am really disappointed. In Nov 2017 I contacted Terry DeWick to service my preamp and he replied with cost and options:

    1- Basic- $45 to $90 for checkout and cleaning only
    2-Option 1 Audiopath update, clean controls, test $150
    3-Option 2 Power supply and ground update $50

    I emailed Terry and stated I wanted Option 1 and Option 2 and also included that info in the box with the preamp I sent him. When the service was finished he emailed my bill only Option 1 was performed. I contacted Terry and asked why he did not perform option 2 and got no response. I accepted the preamp as was and honestly, having been serviced by Terry I did not run it through all modes because .. hey! it was serviced by TD and everything should be fine, right? Refer back to my 1st post.
    So now after waiting several months for service, paying shipping to and fro, I have a C26 preamp with a faulty PHONO section.

    I did contact Terry about a resolution to this problem about a week ago and still waiting for an answer. Terry if you are reading this .. what's the deal ??
     
    Last edited: Jul 14, 2018
  5. MACKIE1975

    MACKIE1975 Well-Known Member

    Messages:
    785
    He is on vacation
     
  6. c_dk

    c_dk Addicted Member

    Messages:
    6,311
    Location:
    West Michigan
    You do not mention what power amp you have this hooked up to.

    The C26, Mac preamps in general, have very high output levels compared to most midfi preamps. The loudness compensation of the C26 is also unique, works completely different than most other preamps and does take some getting used to.

    It is really rare to find a phono stage to be that much higher in level than a cd or tuner.

    It is a real head scratcher.

    Terry has been a tremendous asset to this forum and has been a help to me with a number of RF questions....In that vein I have sent you a PM with my email if you want to have some help with this strange issue.
     

     

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  7. 1ontop=

    1ontop= Active Member

    Messages:
    275
    Location:
    Croswell in the Thumb, MI
    The C26 is used in conjunction with an MC754 power amp and MR 74 tuner.
     
  8. Searing75

    Searing75 AK Subscriber Subscriber

    Messages:
    385
    I am certain Terry will get this straightened out for you.
     
  9. c_dk

    c_dk Addicted Member

    Messages:
    6,311
    Location:
    West Michigan
    While Twii and I have discussed the proper volume control- amp gain control- loudness compensation in previous posts I do not beleve they have touched on the unique loudness of the C26.

    So I just read through the C26 manual in the AKdatabase......Roger did not really highlight it's use in much detail.

    I also note that the C26 with the 5mV output of the MP110 should output 6/10s of a volt at the tape outputs which should be less than the typical max cd output of about a volt.

    Soi guess I would start with setting up your setup to get the "best" balance to your ear with the loudness engaged to get you speakers to sound right to you.

    I would turn down the gains of your 754 until the max volume you expect to use will be with the volume at 1:00 loudness full CCW.....off.

    Does this setting have the right bass, mid, treble balance for your ear? As you rotate the loudness control clockwise to cut the volume does the B,M,T stay in balance to your ear.

    What are your reference high level sources......do they put out the quasi industry standard of 1 volt......for example when I have hooked up my iPod with a headphone to RCA adaptor it is quite obvious it does not put out a volt.....maybe a 1/2 a volt so while it is convenient it certainly can not be a refererence.

    Since it seems that using high level type sources is your top priority you should get this right to your ear first
     
  10. 1ontop=

    1ontop= Active Member

    Messages:
    275
    Location:
    Croswell in the Thumb, MI
    Per your instructions , volume at 1:00 .. loudness OFF .. the max volume I would use starts almost instantaneously by increasing the gains from 0 volume. Only in the TUNER and AUX using a CD player does the tone stay consistent while increasing or decreasing the volume and shuts off completely (no sound). In the PHONO mode, again, at low volume sounds like a transistor radio until volume is increased to about 9-10 o clock does the BASS kick in. And with volume turned off sound can still be heard as though turned up to 9-10 o clock as previously stated.

    By using the loudness control on this preamp the B,M,T do not stay in balance to my ear. I do not use the loudness control on this preamp as it is so different from a typical push button loudness control.
     
  11. c_dk

    c_dk Addicted Member

    Messages:
    6,311
    Location:
    West Michigan
    So if I understand correctly you barely have the amplifer gains up at all and get a lot of volume......you must have very efficient speakers. What are they?

    Again these preamps were being traded in back when I started in 1977 so i never sold a new one, but even then the idea was to try to use the volume control between 9:00 and 1:00, expecting most usage would be between 9:00 and 11:00 were the two channels taper would be closest together.

    The only way you could do this was to lower the tuner and tape decks down to the level of the turntable and then lower the gains of the amp to do the same.

    Your phono situation is a real anomaly. I can guess why there might be to little bass but the extremely high volume does not readily make any sense.

    Most listeners find they need the loudness option at low volume settings and with the C26 use the loudness control to lower the volume until they find a happy equilibrium between the two controls.

    I personally was glad to see this awkward setup go away when I got my C32 and for clients the C27 or C29.
     

     

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  12. 1ontop=

    1ontop= Active Member

    Messages:
    275
    Location:
    Croswell in the Thumb, MI
    The speakers I am using are Thiel Model 01 and I am not using the Model 01 Equalizer because the bass response without eq is sufficient for me. Their sensitivity rating is 94 dB 2.83V/1m. The loud response at 0 volume is the same with my New Large Advents and I believe the sensitivity rating is about 87/88 dB.

    As far as the LOUDNESS control on the C26, rather than increasing the BASS .. it diminishes the TREBLE. Think late 50's, early 60's automobile AM radio tone control.

    FWIW, there is no problem with my C27 preamp using the MC754 , my various turntables and Thiel Model 01 and New Large Advent speakers. I know it has a different type of VOLUME control but same LOUDNESS control .. correct?
     
    Last edited: Jul 16, 2018
  13. c_dk

    c_dk Addicted Member

    Messages:
    6,311
    Location:
    West Michigan
    To my memory without pulling the schematic the C27 used a active gain adding, bass more than treble, loudness circuit like was used in the C29 and C32.

    The C26 used a passive network to pull down the treble and midrange to alter the B,M,T balance.

    With all things being equal I do find it strange that the C26 has so much greater output than your C27. The only thing that comes to mind is that at sometime over the last 40 years a linear taper volume control( like used in the C28,MAC1900, MA6100 ETC) instead of the unique audio taper used in the C26, was installed.

    That does not explain the Phono issue being so much louder than your CD player.

    Again all speculation without a bench test.
     
  14. 1ontop=

    1ontop= Active Member

    Messages:
    275
    Location:
    Croswell in the Thumb, MI
    I wish this were true. After all this time I am at a loss to DeWick's indifference to me. At first he tried to diagnose the problem via email and the last I heard from him was "not sure as you are the first to report this problem." I emailed asking him to provide a hands on fix. Even with his vacation time and visit to his mother I sent enough emails that he should have answered one. Given all the attention he gets here on AK I was expecting excellent repair service and customer service. I got neither. Looks like I am S.O.L.
     
  15. Mamrak1

    Mamrak1 AK Subscriber Subscriber

    Messages:
    1,095
    Location:
    Pennsylvania
    This doesn’t relate to McIntosh exactly. I had a similar problem with a Parasound preamp I use in my garage system. The volume knob didn’t control anything and when turned on it was loud. Parasound techs found a cold solder joint on one of the circuit chips. After the resolder job it worked fine.
     
  16. c_dk

    c_dk Addicted Member

    Messages:
    6,311
    Location:
    West Michigan
    If you want to trek across the mitten some Saturday now that my Doc is no longer using a dartboard and my meds have settled down I would be happy to put it on the bench for a free test.
     

     

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  17. 1ontop=

    1ontop= Active Member

    Messages:
    275
    Location:
    Croswell in the Thumb, MI
    Thanks, I certainly appreciate the offer. I will let you know.
     
  18. brentj4

    brentj4 AK Subscriber Subscriber

    Messages:
    794
    Location:
    Charlotte NC
    Sorry to read about your issue. I've owned several McIntosh units Terry has worked on and have been very pleased. As a side note I had a situation where I sold a large Pioneer vintage receiver to a buyer in TN. They had a problem that required a tech. So I emailed Terry and they took it to him. He got them running right away and didn't want to charge for it. I say that is a heck of guy and tech. All the best to you and hope you get your problem resolved sooner than later.
     

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