Hello
Just bought an ML-9 in very good shape, all original, no hum through the speakers. But it has a very loud transformer noise. It is a combination of hum and rrrrrrrumble 🙂. Sometimes it nearly disappears, but then it comes back. I looked inside, and the trans is a huge toroidal job enclosed in a black round case. Being held by 5 bolts to the bottom, all tight. Any info on possible fixes?
Thanks in advance
Mark
Just bought an ML-9 in very good shape, all original, no hum through the speakers. But it has a very loud transformer noise. It is a combination of hum and rrrrrrrumble 🙂. Sometimes it nearly disappears, but then it comes back. I looked inside, and the trans is a huge toroidal job enclosed in a black round case. Being held by 5 bolts to the bottom, all tight. Any info on possible fixes?
Thanks in advance
Mark
If the hum varies a lot then its probably caused by harmonics (distortion) of the incoming supply. Big toroidals are notorious for this.
You could have a play around with a DC blocker to see if that improves things but I wouldn't hold out that much hope tbh:
Mains DC and Transformers
You could have a play around with a DC blocker to see if that improves things but I wouldn't hold out that much hope tbh:
Mains DC and Transformers
Interesting. Thank you. But it's the only amp that I get this hum with. My previous Classe amps didn't hum or growl. Would an isolating transformer help? I have a big 29A variac
Yes try the variac.
One of the problems of toroidal power supply transformers is their sensitivity to line over voltage causing core saturation.
See what happens when you offer the transformer a lower line voltage through the variac.
One of the problems of toroidal power supply transformers is their sensitivity to line over voltage causing core saturation.
See what happens when you offer the transformer a lower line voltage through the variac.
DC
Thank you. Interesting subject, I'm learning something new.
I measured DC on my mains, I got 60mV. On Variac, the noise is greatly diminished at 110vac, and louder at 125vac (that's what I measured last night on my mains), but is lower than when amp is plugged directly into the mains. I've tried another ML-9 about six months ago, it had problems with audio, but the transformer was dead quiet. This one sounds great with DC offsets 4mV left/1.5mV right) but hums :-( I wonder if that Emotiva DC buster ($99 on Amazon) will help?
Rgds
Thank you. Interesting subject, I'm learning something new.
I measured DC on my mains, I got 60mV. On Variac, the noise is greatly diminished at 110vac, and louder at 125vac (that's what I measured last night on my mains), but is lower than when amp is plugged directly into the mains. I've tried another ML-9 about six months ago, it had problems with audio, but the transformer was dead quiet. This one sounds great with DC offsets 4mV left/1.5mV right) but hums :-( I wonder if that Emotiva DC buster ($99 on Amazon) will help?
Rgds
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Caps
Hi
Is it possible that the huge filter caps are going and cause the trans work harder? There is a faint hum present in the speakers if you put your ear right against them...
M
Hi
Is it possible that the huge filter caps are going and cause the trans work harder? There is a faint hum present in the speakers if you put your ear right against them...
M
Dare I say this 😱 but imo mega expensive gear like this should be devoid of these kind of issues.
Huge caps cause the conduction angle of the diode bridge to become less... think about it... if the energy drawn is constant and you have a small value cap, then the voltage on the falls quickly between each half cycle... result is a higher ripple voltage. The upside is that the bridge starts to conduct earlier on the upswing of the next half cycle to replenish the cap. So it takes longer and currents are lower. A massive cap gives low ripple voltage but the same energy has to be put back. That means the bridge conducts for far less time but the currents are correspondingly higher. So yes, in that sense the transformer works harder and any copper and iron losses start to make their presence felt.
That said it should all be specified to work under those designed conditions.
Huge caps cause the conduction angle of the diode bridge to become less... think about it... if the energy drawn is constant and you have a small value cap, then the voltage on the falls quickly between each half cycle... result is a higher ripple voltage. The upside is that the bridge starts to conduct earlier on the upswing of the next half cycle to replenish the cap. So it takes longer and currents are lower. A massive cap gives low ripple voltage but the same energy has to be put back. That means the bridge conducts for far less time but the currents are correspondingly higher. So yes, in that sense the transformer works harder and any copper and iron losses start to make their presence felt.
That said it should all be specified to work under those designed conditions.
Well, "eeek" is a good way to put it, but this thing is now 30 ys old 🙂 I'd say it held up pretty well with all original parts. What I meant, is not weather or not large caps will make the trans work harder vs the small ones, but if the caps need replacing due to age, would they cause the trans to misbehave without producing big hum in the speakers?
Its impossible to guess the state of play of the caps without actually dangling a scope across them and having a look at the ripple. I would say that aged caps would give the transformer an easier time because the E.S.R. (equivalent series resistance) will increase as the cap (any cap) deteriorates and that in turn will tend to reduce the peak currents drawn from the transformer.
Whether excess ripple from a deteriorated cap would be audible via the speakers depends entirely on the amp itself and how immune the circuit is to noise on the rails. For example an opamp would reject massive amounts of ripple and noise before it began to affect the output... power amps vary somewhat though. Some are good and some poor.
The speakers should be silent (no hum) with nothing connected to the amp and shorting plus fitted to the inputs.
Whether excess ripple from a deteriorated cap would be audible via the speakers depends entirely on the amp itself and how immune the circuit is to noise on the rails. For example an opamp would reject massive amounts of ripple and noise before it began to affect the output... power amps vary somewhat though. Some are good and some poor.
The speakers should be silent (no hum) with nothing connected to the amp and shorting plus fitted to the inputs.
Thank you Mooly
So I think it's the trans itself. I will put a DC bocker on line in a couple of days, but have no high hopes for it
So I think it's the trans itself. I will put a DC bocker on line in a couple of days, but have no high hopes for it
Hi Mark:
I just refurbished a Crown DC-300A II which had a 60Hz hum that was audible from several feet away without loudspeakers connected. I also assumed it was the transformer. Vibration was obvious to the touch from the transformer, but even more so from the large power supply capacitors. After replacing the power supply caps the hum was virtually eliminated to my happy surprise.
I owned a No. 23 back in the day and loved it. If your ML9’s big power supply caps are OEM, they are long past due for replacement. That of course goes for the other electrolytics in the amp as well. Good luck! 🙂
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Mark,
Did you fix the problem with the Mark Levinson ML-9? I have one on my bench with the same problem. I tried a DC blocker, Variac, Inrush protector and disconnected the power cords to the bridge rectifier. No result. My conclusion is a loose part inside the transformer. So no solution. This is a complicated transformer with a lot of windings. PS does anybody have a technical manual for the ML-9?
Please send me an email with your email adress so I can send you the schematic and bias precedure. I still have one of these beasts in perfect condition and was wondering the value of these amps today.
For clarifying this exactly you need a variable autotransformer like this:
Variable Autotransformers | Product categories | ALDETRONICS Your Online Shop For Variable Transformers, Variacs, Isolation Safety Transformers, Power Supplies
When the humming noise abruptly disappears at a certain input voltage, the blocking DC value of your DC filter was too low.
Then you need a DC blocker with more than a single diode - i. e. two or three diodes for each electrolytic cap - go to
DC-Blocker - Scintilla-buizenversterkers
and post 159 under
dc filter
When the humming noise gradually disappears with decreasing values for the primary voltage, your assumption is correct and a new torodial transformer (e. g. from Tauscher or Plitron) is necessary.
Please let me know your observation after check out this.
An other question:
Under which thread here on diyaudio was upload the circuit diagram of this power amp ?
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LS-9 and a DC blocker
After some digging in the power supply i found a build in DC blocker in the Mark Levinson LS-9. This means that a humming power transformer almost in every case means a defective transformer. The secondary side is simple. As far as i can see there is a symmetrical 85 Volt for the amps.
The primary side is another matter. Apart from 110/220V windings there are some more to power the protection circuit. When things are wrong on an output of an amplifier (DC, perhaps current) there are some resistors put in serie to limit the power supply and prevent a big current to flow through your speakers. there is a relais and a thyristor used in the circuit.
a schematic or reverse engineering will bring some light on the matter. To be continued.
After some digging in the power supply i found a build in DC blocker in the Mark Levinson LS-9. This means that a humming power transformer almost in every case means a defective transformer. The secondary side is simple. As far as i can see there is a symmetrical 85 Volt for the amps.
The primary side is another matter. Apart from 110/220V windings there are some more to power the protection circuit. When things are wrong on an output of an amplifier (DC, perhaps current) there are some resistors put in serie to limit the power supply and prevent a big current to flow through your speakers. there is a relais and a thyristor used in the circuit.
a schematic or reverse engineering will bring some light on the matter. To be continued.
Same buzz/noise/growl for me
Hi everyone,
Does anyone have found any solutions for this noise problem ?
My ML-9 is doing this.
I felt that the right side is hotter than the left !
Hi everyone,
Does anyone have found any solutions for this noise problem ?
My ML-9 is doing this.
I felt that the right side is hotter than the left !
If you can, put varnish in the transformer.
The laminations and windings could have developed a gap, if there is vibration that tells you there is a gap.
The gap will lead to localized heating and failure.
I have used motor winding (Insulating) varnish to fix humming in tube light chokes and battery charger transformers.
And definitely old caps need inspection and/or replacement .
The laminations and windings could have developed a gap, if there is vibration that tells you there is a gap.
The gap will lead to localized heating and failure.
I have used motor winding (Insulating) varnish to fix humming in tube light chokes and battery charger transformers.
And definitely old caps need inspection and/or replacement .
Tik hai !
I'll try the varnish.
I have attachhed the noise I hear. If it can help to identify.
I've seen it's mainly 100 and 200 Hertz.
Thank you
I'll try the varnish.
I have attachhed the noise I hear. If it can help to identify.
I've seen it's mainly 100 and 200 Hertz.
Thank you