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Home Theater => Audio => Tubes => Topic started by: dgmate on Feb 25, 2018 at 07:17 PM
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Hi, my cayin tube amp A-50T has a initial 'thug' noise when it is turned on. Then there is a loud long noise that will follow. Nakakainis.
Pls help what's the problem. Any advise?
Any repair shop in Las Pinas or Paranaque?
Thanks in advance
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Try mo kay Rene Rivo or kay John Poscablo.
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Brod may contact nos. Ka nila. Ty very much
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Brod may contact nos. Ka nila. Ty very much
Kay Rene Rivo search mo na lang dito. Kay John P. 0922-827-7301.
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Brod may contact nos. Ka nila. Ty very much
Shop ni sir Rene sa Parañaque: Music Haven
https://www.facebook.com/MusicHavenPH/
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Hi, my cayin tube amp A-50T has a initial 'thug' noise when it is turned on. Then there is a loud long noise that will follow. Nakakainis.
Pls help what's the problem. Any advise?
Any repair shop in Las Pinas or Paranaque?
Thanks in advance
Wow that's DC and it's gonna burn your speakers. Pm me this is JOHN Martin
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parang solid state? call Cayin/Audio Amplified in Libis for expert advice.....after all amplifier nila yan...
+632-6310379
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Wow that's DC and it's gonna burn your speakers. Pm me this is JOHN Martin
Sent from my SM-A720F using Tapatalk
Is DC possible on a tube amp?
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Is DC possible on a tube amp?
yes if the insulation breaks down between the primary and secondary windings of the OPT, but the effect will be immediate, fuse blows and maybe speaker burns out, pero i have not seen it happen before, tbh....
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Is DC possible on a tube amp?
Unfortunately, yes. Insulation is one of the main problems I noted. Corona discharge, arcing, etc etc. The opt is the speaker's last line of defense.
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yes, when you run the tube amp at volume without speakers that can happen..
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Hi Jojo, Tony,
Many thanks for the info. But I believe this is under severe fault that you cannot even
turn on your amplifier.
My take on dgmate problem would be humming (if it is how he describe the noise) perhaps due to defective power supply capacitor.
Is the noise on both channel or single channel, maybe can easily swap the tube and isolate the fault.
Many others fault isolation can be done, but presence of DC at the output for me means...you better buy a new amplifier.
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hum is always a perplexing issue, and there are ways to eliminate them..
in the Dusit show, i always bring with me an isolation and line conditioner to power up our gears..that helps...
but in home settings, it is better to trace the source of noise and do the filtering right at the source...
going back to tube power amps with OPT's, i make is a point to add a zobel network at the speaker jacks, 10 ohm 3 watts in series with 0.01 ufd/630v film caps to avoid the problem of running the amp at volume with no speakers connected...
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Hi Jojo, Tony,
Many thanks for the info. But I believe this is under severe fault that you cannot even
turn on your amplifier.
My take on dgmate problem would be humming (if it is how he describe the noise) perhaps due to defective power supply capacitor.
Is the noise on both channel or single channel, maybe can easily swap the tube and isolate the fault.
Many others fault isolation can be done, but presence of DC at the output for me means...you better buy a new amplifier.
It is truly hard to "guess" what causes dgmate's tube amp to behave like that and at this stage all we can do is speculate. It is up to the hands of the one who will open it up.
But your take is a valid one, if the amp is still working (sans the hum during power up) then it is safe to say that the opt might still be ok. A thorough check of what may have caused it is in order. A failing tube doesn't produce such a behavior but we truly cannot dispense that too.
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going back to tube power amps with OPT's, i make is a point to add a zobel network at the speaker jacks, 10 ohm 3 watts in series with 0.01 ufd/630v film caps to avoid the problem of running the amp at volume with no speakers connected...
That Zobel network will only be helpful at high frequencies dictated by the cap where the opt starts to see the 10 ohm resistor as load, below that all the amplifier sees is an open circuit. This can be helpful to dampen the opt-load circuit as long as it doesn't approach ringing.
Anyways, I strongly urge tube amp users to always, always secure their speaker lines. No speaker, no play. Period.
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That Zobel network will only be helpful at high frequencies dictated by the cap where the opt starts to see the 10 ohm resistor as load, below that all the amplifier sees is an open circuit. This can be helpful to dampen the opt-load circuit as long as it doesn't approach ringing.
Anyways, I strongly urge tube amp users to always, always secure their speaker lines. No speaker, no play. Period.
Will the zobel network also act as a "leech" in terms of load? Any effect on the sound?
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Will the zobel network also act as a "leech" in terms of load?
First things first. A Zobel network (aka Boucherot Cell) is an R-C network primarily used to compensate for the rising impedance curve of a specific driver. Imagine a regular driver having a specified impedance of 8 ohms but in reality this impedance rises as frequency rises due to the voice coil inductance. This rise in impedance can cause several issues with amplifiers (mostly solid state) being "unloaded" at high frequencies. Oscillation comes to mind.
You are correct that it may "leech", but at high frequencies only (frequency dependent on RC time constant), besides that's the point of using a Zobel network, to act as a load at high frequencies. Putting a Zobel network across a speaker does not alter it's frequency response, it rather equalizes the impedance seen by the amplifier.
Any effect on the sound?
As far as the human ear is concerned, none.
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Well explained. Thanks tukayo. So for an 8ohm driver, in effect (if I understand it well) as the impedance rises because of the inductance, the amplifier "sees" it as more or less 8ohms pa din?
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@Sir Tony & Sir Jojo, applicable yung Zobel Network pag nag Bi Bias setting ano po? Like sa Dynaco ST70.
Sorry sa OT.
Thanks
Sent from my iPhone using Tapatalk
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Will the zobel network also act as a "leech" in terms of load? Any effect on the sound?
it makes the amp more stable with many kinds of speakers attached to it..
amp makers have no idea what type speakers connect to their amps,
the boucherot cell is just a way to anticipate capacitive loading by the speakers...
the effect on sound? you may or may not hear its effect, but for sure your amp will be more stable with it..
jojod said it right, at a certain high frequency where the time constants of the RC network makes the 10 ohm resistor be seen as a load, when the capacitor leg acts like a short circuit...
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@Sir Tony & Sir Jojo, applicable yung Zobel Network pag nag Bi Bias setting ano po? Like sa Dynaco ST70.
Sorry sa OT.
Thanks
Sent from my iPhone using Tapatalk
no, biasing is a different thing...you are setting cathode currents and therefore tube dissipation when you do that...
for push pull, 80% of plate rating is typical, say an EL34 is rated 24 watts, so we bias the tube so that 19 watts or less is being eaten by the plate, for class B even lower at about 10 watts, the trick is to get the lowest bias setting that you can get away with without any noticeable sound degradation...your tubes will live a longer life that way..
for single ended tube amps, it is 100% all the way....like the 2A3 with 15 watts plate rating, so 250 volts plate and 60mA is the sweet spot...
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Well explained. Thanks tukayo. So for an 8ohm driver, in effect (if I understand it well) as the impedance rises because of the inductance, the amplifier "sees" it as more or less 8ohms pa din?
Yes you're right. It flattens the impedance curve of the driver even at high frequencies. The way it works is once you reach the resonant frequency of the r-c combination, only the "r" is seen by the amp as the "c" will be low impedance (or a short) at F=Fr.
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@Sir Tony & Sir Jojo, applicable yung Zobel Network pag nag Bi Bias setting ano po? Like sa Dynaco ST70.
Sorry sa OT.
Thanks
Sent from my iPhone using Tapatalk
No sir, it is an entirely different application. You will see most Zobel networks in solid state amps rather than tube amps. SS amps can go high where no tube amp can go, far beyond what the human ear can hear/detect. This is so because of the nature of the tube amps, it is opt coupled as opposed to direct-coupled solid state.
The by-product of this wide bandwidth types of amplifiers is that the high frequency signals has nowhere to go because of the drivers being high impedance at high frequencies. This high frequency signals needs a place to go, or they can be coupled to the amps input causing oscillations. This is where the Zobel network plays an important role.
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Thanks sir JojoD818 & sir Tony..
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