Preamp for my MC30 pair, a Sensi needed.

Discussion in 'McIntosh Audio' started by zenarrrow, Apr 18, 2018.

  1. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    Do you think I am not doing them proper justice with them on the floor?
     

     

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  2. damacman

    damacman Blown and Injected Subscriber

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    The best thing about this hobby is experimenting with the gear that you already have in an effort to get the best sound. To that end, you should try the speakers on the floor and then compare that to what you have at present. Let your personal preferences guide you to how your system is ultimately set up.

    FWIW, I used to also use my 14s for tops at my annual 4th of July backyard party. The last year we hosted it, I had a Crown MT2400 driving (16) 12" subwoofers in vented enclosures tuned to 32Hz down low and the 14s driven by an MC2300 up top. Crossover point was something like 80 Hz. I had the 14s on end tables about 20 feet apart with the subs between them and loaded against the patio wall. Everyone was just amazed at how good that system sounded. From 1 to 8PM, we slowly inched up the volume as beers were consumed (+10dB for every 10 beers was the plan). Looking back, it was quite the rig for the party. In 8 hours, we registered some 550 complaints from local residents and Johnny Law paid us 4 visits. Whodathunkit?

    God Bless America.
     
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  3. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    So this is where I was.
    I replaced the 12ax7's in the 30's with tele's.
    Replaced the TAD output tubes to a set of Black plate RCA's.
    Followed advice with the putting the preamp volume at 66% or so and had the gain set all the way down on the 30's and adjusted them up from there, to the point of being at the edge of too loud.

    The issue I was having was the top end was sort of distorted. I could hear the slightest bit of distortion not so much on the instruments but more so on the voices. Even the the instruments were, I guess the best way to describe it "thin"
    An example I listened to Black Water from Doobie Brothers and especially the s's when sung, the would fray at the end, and all the vocals actually.

    Where I am now.
    I started with putting the TAD output tubes back in. Same result.
    I left the tele's in all the 12ax7 slots. Kept the TAD's in.
    Next step was to crank the gain on the 30's back to the fullest. Totally open, and I found I still have plenty of adjustment on my volume with my mx110z.

    The issue seems to have been corrected.
    And I feel that the high end and vocals are a lot more tolerable, and I am not straining and discovering distortions. I noticed myself a lot more at ease not trying to note any fault in the mix at every level.

    I read all day long on this subject on many forums. Seems to be many on each side of this debate.

    The clearest idea I read was that having the least amount of obstruction in the signal path.
    Thus having the gains wide open = clear path.

    Adjusting down introduced a distortion.

    Also, using just the bottom end of the volume on the preamp lessened any sort of issues that may arise, that may become more intensified at increasing higher levels of the preamp.

    I do fully understand that everyone here has a lot more experience with this gear than I have attained on my first 5 days of owning my first mac gear.

    Not to say I won't revisit the ideas laid out for me. But as stated the joy in this hobby is trying and testing out different ideas.

    As a final test at 4 am I have Sade Diamond Life spinning and it is the truest I have ever heard it. I am satisfied with the adjustments I have made and am enjoying the music, not straining trying to pin down what exactly is wrong.
     
  4. 62caddy

    62caddy Trust but verify Subscriber

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    That's very surprising as gain settings of 12:00 provide plenty of gain with my MX110 whether driving an MC2505, MC240 or a pair of MC30s- with my Altec 14s.

    Now, with the other speakers which are 10 dB less sensitive (meaning they need 10x the power for the same volume), I set the gains around the 2:00 mark which is still significantly less than full-on. Again, this is the case for all three amplifiers.

    Full-on gain settings with any these amplifiers is around 0.5 volt while the MX110 output is rated 2.5 volts. Should not need anything close to full on gain settings - especially with speakers as sensitive as the Altecs. Something does not sound right here.
     
  5. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    As I stated many people on both sides of this debate. I don't think there is a problem, as my amps seem to be pretty evenly matched with the gain. And using both methods I have found that so far this seems to be the best sound for me. It was explained to me and I understand it this way, take an ordinary ss SX 980 Pioneer stereo or an integrated amp, the amps will always be wide open, the preamps in those are what have the controls volume etc. The Mono blocks with gain on them are used when two or more are in a system and one has more gain than the other, which in that case one can turn down the gain accordingly. As I said, I am just starting here and will probably change my methods many times over. but this is working for me right now, as my amps seem pretty equally matched. And the distortion has disappeared.

    Here is a quote or two from another forum on adjusting gain and on the MC30's.


    "You may be thinking that gain and volume are the same things. They're not. Setting the amp's gain to full increases the sensitivity of the amp's inputs. Using the volume control on the preamp then makes use of the quietest part of the preamp's circuitry while at the same time getting full advantage of everthing (headroom, current, dynamic range, damping factor, etc., etc.) that the amp has to offer. Just as the manufacturer recommends: amp on full, preamp controls the volume. The amp will be more responsive, your preamp will be running in its ideal range, and I think you'll be happier with the sound."
    ". . . which is why the amp makers advise running their amps at full gain when using a separate preamp."

    With that being said just as many statements in line with the way you advised as well.
    Joe
     
  6. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    You are far more knowledgeable than I am on every aspect of the McIntosh. I guess I am just trying to tinker with my new toys. I do honestly appreciate all of your help and advice 62caddy. You have been more than helpful and encouraging. I hope that does not go unnoticed. Joe.
     

     

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  7. damacman

    damacman Blown and Injected Subscriber

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    Yeah, no. Research the topic of gain overlap and you'll understand why. Caddy's explanation should get 90% of folks 90% of the way there. Keep in mind the MX110 will be a limiting factor in overall system noise whereas a modern preamp would be several magnitudes quieter.
     
  8. damacman

    damacman Blown and Injected Subscriber

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    Don't overlook that it would take a test tone recorded at 0dB (the highest level possible on a CD) and a high volume setting on the MX110 to achieve said 2.5V. As music is dynamic in nature, it is definitely possible to set the gains on the MC30s to max and never clip the inputs - at least as long as you never played a Sheffield Lab or Telarc recording. You are correct in stating that such high gain settings would both increase the noise floor and reduce the effective range of the volume control on the preamp. Given the sensitivity of the 14s, this would likely be audible from the listening spot wit the volume set to fully CCW on the MX110.
     
  9. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    Well, let me start with a rebuttal, I, soon after the statement, I made about the full gain on the MC30s I noticed an issue with the high end of the music it seemed shrill and almost appears to fall apart on the top end. Especially the So I went back to 62caddy's suggestions. While it seemed to fix the issue for a bit (maybe it didn't) but again I am suffering from the top end being shrill especially the vocals. I cannot seem to shake it whatsoever. I have played with the loudness and messed with the filters. Trying different tubes in the vital spots ( can't recall them off hand) V14 V15 ? And the 6U8 spot.

    I have noticed though, no noise or hum or white noise. The system is quiet only issue is the top end. At times this set up is magical and a very sweet sounding system. Other times other recordings and the top end is falling apart. For instance jazz such as monks dream sounds really good , Sade Diamond Life amazing. But let's say Wilco jesus etc. Song in particular I feel that the top end is completely cut off.

    Again no noise is associated with the amps or preamp. No restoration has been done to the mx110z. Could I have some caps that may be faulty?

    Any advice would be appreciated in which way to proceed , and I would be very thankful. I do have a sheffield lab drum lp. But no equipment to test any thing beyond that.
    Again, any advice would be greatly appreciated.
    I am sorry if I seemed to be not taking 62caddy's advice. Just reading all over the Web and testing different ideas.
    Joe
     
  10. damacman

    damacman Blown and Injected Subscriber

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    Joe - no apology necessary. Given the age of the MX110, it's long overdue for service. Good idea.
     
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  11. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    OK, so I stayed up way too late because I have to work tomorrow and be awake at 4 am.

    But, this is what I have found. I hated to do it but I put the Pas back in the loop to power the MC30's and the shrill was still there (a lot more noise from the preamp too). So tomorrow after work I will plan on putting the ST-70 back in and using the pas and then the MX110z and see what I find. Maybe the shrill is in the MC30's.
     

     

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  12. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    So, I ended up not having to go into work today.

    So I put my ST-70 in place of the MC30's. And what do you know, the shrill is gone, the top end is great again.

    Last night with the MX110z/30's and Pas 2/30's I tried isolating each channel and found that the shrillness was there on each side, not just one channel.

    So I am thinking it has something to do with the 30's. I remember when I first received them that the Pas 2/with the 30's had this issue and naturally thought it had to be the Pas 2 not being up to par with the mono blocks. Then I got the MX110z and same thing, I was convinced it was the preamp. until last night. until today when I tried the MX110z with the ST-70. Here is the description of what the fellow who sold them to me had in his listing.

    "McIntosh MC30 pair,in good working condition,both amps are fully restored,new CE main electrolytic capacitors,new power cords and thermistors added for power supply protection,all coupling capacitors are original capacitors except we found six caps in leaking condition was replaced NOS Sprague Black Beauty caps,some out of spec resistors replaced,MC30 with serial#5E306 and serial#7E946,both amps have rust spot chrome chassis,all lettering intact but do have some age spots,the transformers are all good but do have some rust spots (See Photo's)not perfect but good,both amps have Telfunken 12AX7's ,US version tubes and TAD 6L6GC's all other tubes are US versions,We strive to retain the original sound of these classic gems,All restoration work preformed by the audio experts at Audio Exchange Atlanta,Ga."

    Does anyone have any ideas where it would be a good place to start with looking for an issue with the MC30's? Again, appears to be on each amp. Thanks, Joe
     
  13. TSmith8605

    TSmith8605 Senile Member Subscriber

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    Unless you are clipping the MC30s when playing some of the recordings, it sounds like an issue with some of your recordings not your equipment. Audio distortions in poor recordings will be more apparent with higher resolution electronics.
     
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  14. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    I was thinking that too, maybe I was hearing poor recordings. But I play records with my wife and grown children, and they can hear it too.

    Also, I play recordings I think I know are "good" such as pink floyd Meddle uk pressing and the s's are thin and sounds like my daughter stated like David gilmour had a walnut shell in front of his teeth where is tongue would touch his front teeth during the s's.
    Please excuse my ignorance, but what is "clipping" ? I have heard the term before but never knew what it was.

    Thanks, Joe
     
  15. TSmith8605

    TSmith8605 Senile Member Subscriber

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    You are describing different problems for different recordings, one is shrill, one has no highs, one has smeared es sounds. Since you don't hear the same issue on every recording, the problems are likely in the recordings themselves and are being made more evident by your newer, higher-resolution equipment. If the highs sounded cut off on every recording, you would have an equipment problem.

    Your McIntosh stuff is going reveal much more readily what's on the recording than does your Dyna stuff. That means you will hear more of the music but also hear more of whatever is wrong with the recording. You no longer have to "think you know" you have a good recording based on what you were told by someone, you now can plainly hear for yourself what is a good recording. Also, since you have the new equipment, you might just be paying more attention to the sound quality.

    I have the Sade Diamond Life record also and it is a very good recording. And I am not surprised you hear smeared es's on the Pink Floyd - that could be a problem with the pressing or it may be there on the original master tape from the original studio recording.

    Clipping happens when you turn the volume up louder than you amplifier can handle and so it gets distorted. I don't think you're doing that.

    From Wikipedia: "Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability. Driving an amplifier into clipping may cause it to output power in excess of its power rating. . .

    When an amplifier is pushed to create a signal with more power than its power supply can produce, it will amplify the signal only up to its maximum capacity, at which point the signal can be amplified no further. As the signal simply "cuts" or "clips" at the maximum capacity of the amplifier, the signal is said to be "clipping". The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a sine wave becoming a distorted square-wave-type waveform.

    Amplifiers have voltage, current and thermal limits. Clipping may occur due to limitations in the power supply or the output stage. Some amplifiers are able to deliver peak power without clipping for short durations before energy stored in the power supply is depleted or the amplifier begins to overheat."
     
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  16. TSmith8605

    TSmith8605 Senile Member Subscriber

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    OK, as an experiment, I just pulled out my copy of Pink Floyd's Meddle and played side one. My copy is a 47-year-old pressing that I think I bought when the album was released - I recall getting this record before Dark Side of the Moon was released. This is not an audiophile pressing, it's just what was in the store then. It's on Harvest Records (SMAS-832). It has a small EMI logo on the back and the fine print says: "Marketed and Distributed by Capitol Records . . . " Inside it says: "Recorded at Air Studios, Abbey Road & Morgan Studios - London, 1971"

    In the vocals, on my copy on my Dual 1219 -> C22 -> MC2505 -> OLA, the es sounds are badly smeared - especially on A Pillow on the Winds and San Tropez. Seems like the high hat in the right channel of A Pillow on the Winds is similarly smeared.

    So the es-sound smearing you're hearing on your newer, high-quality pressing is also there on my 47-year plain-jane copy.

    This is further evidence that this is not caused by your electronics. My guess is that the vocal tracks on the original multi-track studio recording were set too high causing the analog tape to saturate - which causes smeared es sounds. Means no future release can cure that smeared-es issue.

    I think if you listen, you'll hear the smeared-es issue with your Dyna stuff as well.
     

     

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  17. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    [
    Thank you very much. I was as I stated thinking maybe I was hearing in fact poor pressings. I am going to do a lot more tests with certain recordings and see if I in fact, are hearing just simply bad recordings. Which would explain a lot. Maybe I have taken the next step into being a true audiophile. I will keep you posted on anything I find. I have googled high end or shrill issues with MC30's and have found very little or even next to nothing. But for right now I do still have the mx110z plugged into the ST-70 until I find the time to do more research and do some more critical listening.

    Again I thank you very much for helping me diagnose my "issue" in fact I love the MX110z, it is beautiful, very clean, and all original. What can I say, I love everything about it, to be completely honest. I also love the vintage tube audio. I am a romantic for sure. And now I love vintage McIntosh gear. This steaming from a very detailed conversation with 4-2-7 about 6 months ago, starting with some great advice from him on my TT to my speakers to my preamp and amp. I know that a new preamp with a new 50th anniversary MC275 per se would probably sound frickin' awesome. But Until I understand the history of the vintage gear, maybe I would never appreciate the new stuff if I never own and experiment with it, if that makes any sense. Again, all the input from everyone is greatly appreciated, and I mean everybody. Cheers, Joe
     
  18. 62caddy

    62caddy Trust but verify Subscriber

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    With a pair of Altec 14s, the sound would have to be insanely loud long before a pair of MC30s would begin to be overdriven (a/k/a clipping). My MC30s develop ~ 48 watts each at 1% THD (just at the onset of clipping) and I would not want to imagine being in the room with that kind of input being applied to the speakers.

    It is also important to bear in mind horn speakers tend to "hot" in the midrange which is not to everybody's taste. Personally I enjoy the Model 14 with certain types of music while with other material, I prefer my Boston T1000s. The loudness switch does seem to help equalize the response of the 14s by accentuating the lows and highs - bringing them closer to the midrange which is more pronounced. The T1000s being closer to flat response, no loudness is needed.

    This is just hypothesizing here- it's difficult to get a clear picture without listening to the system directly. Hard to get a handle on what's going on in this situation.
     
  19. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    I have a question about gain, if you guys don't mind. Just so I can wrap my brain around it. With the 30's they have the gain dials.
    Why with the ST -70 I am using right now is there is no gain adjustment ? And with that being said are they wide open, or a clear path?

    I do too. I have found that with the ST-70 that I am using withe the MX110Z the system sounds amazing . I know the 30's would leave this in the dust.
    As for me I found if I turn off the loudness and tune up the bass and leave the treble at 12 o'clock it sounds really nice to me. If I turn on the loudness it seems to get almost muddy or murky.
     
  20. zenarrrow

    zenarrrow AK Subscriber Subscriber

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    Unfortunately the seller who I bought them from has not responded to a question I asked him last night as to what he has done. Not that enough time has elapsed to judge him of course. So I am waiting to hear from him to find out if the repairs he did were kinda in sync with his system so to speak.
     

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