Yamaha M-85 Slightly Disappointing?

Discussion in 'Yamaha' started by lambord, Mar 14, 2017.

  1. tubed

    tubed Lunatic Member

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    The M-85 powers the QLS-1 at realistic listening levels without coming close to breaking a sweat.
    Picture 291.jpg
     
  2. lambord

    lambord Member

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    90
    Those are some sweet speakers!
    I have to say that for being over 30 years old, this unit looks clean on the inside. Anther concern that I thought about. If this Yamaha can push the 250 etc watts, should the meter on the unit be going up to at least near full? I only saw the lights on the 4 ohm setting going up to around 60 watts. The 250 or what ever watts should be rms, but on any song I play, it is not near that with a direct source input into the Yamaha. Here are some pics if you are interested
     

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  3. avionic

    avionic " Black Knights" Subscriber

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    A healthy M-80/M-85 will do approx 295wpc into and 8Ω load before clipping.
     
  4. pustelniakr

    pustelniakr Silver Miner at Large Subscriber

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    Sounds like someone has been in there and replaced parts with incorrect ones, like ECG or NTE or some other incompetent repair. With an appropriate preamp, you should be able to drive the outputs to pegging the meters. DON'T DO THAT! Correctly functioning, you could easily have an amp worth $1,200+. When these go, they make an expensive mess for repair. If it is working at all, get it to a competent tech as it is right now. Stop using it until you do. Do NOT run it in Auto-Class-A until you get it to a tech for what is what. You will find this amp well worth the investment to get up to full speed.

    Good luck,
    Rich P
     
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  5. avionic

    avionic " Black Knights" Subscriber

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    Yes it should. Meters may be misadjusted.
     
  6. lambord

    lambord Member

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    I played a 1 khz test tone on full volume and meassured the voltage.... the amp speakers meter was on 4 ohms and it read about 7watts, and the voltage output was around 6 volts. My calculations show that 6 volts should be 9 watts ish at 4 ohms. Even if the meters are off a little bit, it still was only putting out 7 watts!! now i will say, it was getting louder when i played music compared to the test tone, but still, something does not seem correct.
     
  7. avionic

    avionic " Black Knights" Subscriber

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    Both channels indicates a power supply issue. Those two narrow APS boards have some TO-220 transistors mounted on them. Check the solder connections on them.Two on each board.
     
  8. petehall347

    petehall347 the brandy coffee man Subscriber

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    if playing 1khz test tone through speakers at 20 watts you wont want to be in the same room . 10 watts is pretty bad .
     
  9. whoaru99

    whoaru99 Epic Member

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    Another consideration is that output is proportional to input. What is the voltage of the test signal going into the Yamaha?

    Testing just for approximate voltage gain does not require speakers connected. Considering the gain of the amp, with the level controls fully clockwise, the voltage out of the amp should be a little more than 29 times the input.

    So, for example, if your test signal input is 1V into the amp you should measure 29V or a bit more at the output/speaker terminals.

    Oh, and you are measuring with the AC setting, right?
     
    Last edited: Mar 15, 2017
  10. lambord

    lambord Member

    Messages:
    90
    Voltage going into amp is .225 volt. I did not have speakers hooked up to the amp when doing testing so i am not sure how loud it was. Checked all power supply solder joints on the two thins boards on top running vertically when looking down at amp. All connections seem to be fine, none being loose or cracked from what I can see, should I unscrew the board and look at other side?
     
  11. petehall347

    petehall347 the brandy coffee man Subscriber

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    0.225×29=6.525
     
  12. avionic

    avionic " Black Knights" Subscriber

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    Not unless you want to unsolder the 6 transistors fastened to the large heatsinks on each board.
     
  13. whoaru99

    whoaru99 Epic Member

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    If you were putting in only 0.225V that completely explains why you were only getting ~6V out.

    0.225 x 29 = 6.5V

    If you want big power out you have to put sufficient voltage in.

    It takes 1.55V to drive the amp to full rated power.
     
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  14. lambord

    lambord Member

    Messages:
    90
    I checked the output from the Tandberg on almost full output and the preamp outs and it was putting out .83V.....So my preamp must not be correctly working, but it is still a little weird that the Tandberg would not amplify the signal to around 1.5V. I will try to listen to the Yamha with the preamp output of the Tandberg later, I have too many people home right now.
     
  15. avionic

    avionic " Black Knights" Subscriber

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    AC or DC ?You should be measuring AC voltage. If AC, your Tanberg needs to be looked at.
     
  16. lambord

    lambord Member

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    I was getting numbers that were all over the board for the voltages, so finally i just stripped down a spare set of RCA's and I got different readings. Sorry for the bad information. My Tandberg is putting out 2.5 V ! This is all the way up and signal is probably clipping or something, at a more realistic level on the knob it is putting out 1.5 V. So the Tandberg is good. I retested the preamp and it is putting out barely 1 V. (.959). So this must be my problem.I connected my Tandberg to Yamaha and much more wattage on the meters, putting out 40V when my tandberg is putting out 1.45V ish. Thank God I didnt overpay for a non working amp haha. Again I cant listen to it right now but I assume this was my problem. Anyone want a preamp that doesn't put out the correct voltages lol?:)
     
  17. petehall347

    petehall347 the brandy coffee man Subscriber

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    did you look up the specs for the pre ?
     
  18. whoaru99

    whoaru99 Epic Member

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    Preamp output also depends on the signal voltage input to it.

    So, if it's a low gain design then you won't get much out with a low input.

    FWIW, 40V @ 8 ohms is good for about 200W.
     
  19. lambord

    lambord Member

    Messages:
    90
    The preamp was a kit that the previous owner made. Now that I opened it up, the soldering job is subpar. Possibly some adjustability with a couple pots on one board inside. My input is my phone, at full volume. I just assumed that this would be a good enough signal, and I have a premium music service that has good quality music so I prefer to use this unless I have my desktop closely, I use a DAC from my desktop to amp usually but I have my computer at college right now.
     

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  20. lambord

    lambord Member

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    90
    Ok, I might need to modify the title of the article haha. The Yamaha is cranking just as expected with the Tandberg acting as a preamp. The meters are going higher than before and it is defiantly louder. I still feel that the Tandberg may have a warmer, more bassy sound but that can all be adjusted with a little EQ, Yamahas in general are known for there audio accuracy so I am sure the Tandberg is just designed to be a little warmer. Thanks for the help narrowing down my problem, I will have to pick up a different preamp or mess around with this current one. Glad my expensive equipment is working correctly. Totally off subject but I assume you would enjoy looking at some other old equipment, this is my fathers setup from back in the day. The amp is not popular but it is an amazing amp (Bendini 100/100), B&W 801, Apt Holman preamp, and some random other input units that we switch once in a while.
     

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    Last edited: Mar 17, 2017

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