[regenerate]

Anyone tried adjusting mains voltage with a Variac, for AVA amp or AVA preamp?

I'm concerned that the 126VAC I get may be causing a problem with my circa 1987 AVA preamp (Hafler DH-110 chassis)...occasionally the right channel output is ~zero, but then pushing "Tone" button repeatedly can make it pop and then right channel will start working.

Figured it wouldn't hurt to use a Variac to reduce mains AC voltage down to 120VAC or 115VAC, for the amp & preamp.  (ANSI specifies 120V +/- 6V for residential mains in USA, if I'm not mistaken.  But running at 126V as the prevailing baseline also may allow variations above 126V occasionally.)

[Brett Buck]

Anyone tried adjusting mains voltage with a Variac, for AVA amp or AVA preamp?

I'm concerned that the 126VAC I get may be causing a problem with my circa 1987 AVA preamp (Hafler DH-110 chassis)...occasionally the right channel output is ~zero, but then pushing "Tone" button repeatedly can make it pop and then right channel will start working.

   Don't you suppose there's a problem with the switch?  How does high-but-in-the-ballpark input voltage get fixed by cycling a switch?

     Brett

[regenerate]

   Don't you suppose there's a problem with the switch?  How does high-but-in-the-ballpark input voltage get fixed by cycling a switch?

     Brett

[Disclaimer:  I don't know that much about electronics, and know even less about preamp & amp electronics designs.  That's why I throw the question to a forum like this.]

I figured that maybe a capacitor was behaving badly due to excessive voltage over the last few years, and that maybe - just maybe - keeping the mains voltage down to nominal might just help the situation.

I believe the Tone Circuit is completely bypassed when the Tone Control Switch is out, so if I turn on the system in this state, and the RH channel is nearly zero, the switch may be completely out of the circuit anyway - therefore not the issue.

Also, cycling the switch usually does not cause a POP in the sound - but sometimes it does.  The RH channel will come alive - if/when it does - at one of the switch pushin's that also POPs.  This implies to me that there is something electronic (not electromechanical e.g. switch) in the circuit somewhere that is getting jolted by a transient when the switch is cycled, causing that "something electronic" to jolt into operation.

Finally, would a faulty Tone Control Switch allow RH channel to NEARLY zero but not completely zero output?  Cycling the switch sometimes POPs the system and the RH channel level increases a little but not enough, with further cycling perhaps causings RH channel to fully restore = LH.

Maybe the solution is to ship the preamp to Mr. Van Alstine & Co. for troubleshooting.

But I'm also interested in hearing of others' experiences with Variacs.  Anyone?

[NealH]

Variacs add impedance to the line and, that's not typically what you want to use with a modern amplifier that relies on low line impedance to produce its maximum output and transient power.  Granted, raising the voltage that little will add only a smidgen of impedance but, if you have an amplifier that has problem with 126VAC then you need to get it fixed or, get another amplifie because modern amplifers, and even un-modern amplifiers of yesterday don't have a problem with 126VAC.  The standard tolerance spec is usually 10%, and often greater.  

Having said that, adding some impedance will reduce the harmonic distortion reflected by on the input line assuming the amplifier is a capacitive input linear type.  This might have some positive effects depending on your line impedance and other equipment connected to it.  But in general, adding line impedance on modern amplifiers is a no-no.  This will not apply to inductor or choke input power supplies ("L" or "Pi") as is used in some of Musical Fidelity amplifiers.  This type approach represents a more "ideal" approach if you will.   It provides excellent filtering, energy storage and low reflected harmonic content.  But it cost more to implement this approach so many of today's amplifier manufactures eschew this approach and leave the burden of maintaining a clean line on the buyer.

[regenerate]

Granted, raising the voltage that little will add only a smidgen of impedance but, ...

I wonder then, what effect LOWERING the line voltage a smidgen would have, on line impedance?  (In general...)

I want to lower the line voltage to about 115 to 120VAC.

There is some info floating about, regarding electrolytic caps and long-term service vis a vis voltages:  Evidently, it may be beneficial in some cases to reduce voltages, with these components, especially in longer-term service.

Also, the amplifier is not the problem locus, per se - the preamp is the problem child.  Anybody care to comment on preamp interactions with Variac on the line voltage supply?

Further info & comments most appreciated.

[zacster]

The problem sounds more like a dirty contact or a bad solder joint.  The fact that pushing the switch "fixes" it may just be from the vibration, which causes the contact to be made.  Try tapping the top to see if it has the same effect.  Line voltage will not do this.  The method to find this never sits well with me, that is to take a wooden stick and tap around on the inside until you find something that makes it pop.  Visual inspection with a magnifying glass sometimes is all that's needed.

If this thing is designed correctly, the +10% or so line voltage should be handled without any problem.  There is usually headroom built into a circuit, although notably the venerable Dynaco ST-70 has the electrolytic can cap working near its limit, and these frequently fail.

And one more thing:  did you check for a loose tube?  Is it a tube amp?

[regenerate]

The problem sounds more like a dirty contact or a bad solder joint.  The fact that pushing the switch "fixes" it may just be from the vibration, which causes the contact to be made.  Try tapping the top to see if it has the same effect.  Line voltage will not do this.  The method to find this never sits well with me, that is to take a wooden stick and tap around on the inside until you find something that makes it pop.  Visual inspection with a magnifying glass sometimes is all that's needed.

If this thing is designed correctly, the +10% or so line voltage should be handled without any problem.  There is usually headroom built into a circuit, although notably the venerable Dynaco ST-70 has the electrolytic can cap working near its limit, and these frequently fail.

And one more thing:  did you check for a loose tube?  Is it a tube amp?

Good advice on tapping around...I may try that.  (Already opened it up but did not see anything obvious.)

The unit in question is an AVA preamp, c.1987, built into a Hafler DH-110 chassis.

10% over nominal voltage...sure, but what I don't know is the voltage profile over time.  I measure 126VAC, every time I measure the line, but if that is (apparently) the "nominal" of this local utility at this location, then the max or peaks may very well be much higher on occasion - and that's not including anomalies like spikes, etc, which of course may be even higher.

Further comments appreciated.  (Including other potential drawbacks to using a Variac)

[zacster]

If you are that worried that line voltage is causing your problems, replace the power supply caps as these will be the first thing to go.  However, you are only losing one channel and this would impact both channels.

Your problem is not line voltage, and a variac as normal operating procedure is a bad idea.  I tried it and it injected some noise into the line.

[regenerate]

If you are that worried that line voltage is causing your problems, replace the power supply caps as these will be the first thing to go.  However, you are only losing one channel and this would impact both channels.

Your problem is not line voltage, and a variac as normal operating procedure is a bad idea.  I tried it and it injected some noise into the line.

What Variac did you try?  (Mfg/model, amperage rating, new or used/old, etc.)  Running what kind of loads etc?

What kind of noise did it inject in the line?  One characteristic of Variacs I've read is that they are supposed to be free of noise, in general.  (Although they will not reduce existing noise or other line problems.)

I read conflicting opinions about using a Variac as normal operating device.  Some say not a good idea, some say perfectly fine if the Variac is good quality/condition and not overloaded, etc.  It helps to evaluate this question if additional relevant factors are also known.

[Wayner]

I don't want to be a stick in the mud...but, why do you want to do weird stuff like plugging HiFi into a variac? AVA equipment has been carfully designed to operate on normal voltage fluctuations and I just don't understand the need for it. I just plug my AVA stuff into the outlet and listen to music. Make your life simpler. Let Frank figure the fringe stuff out, he's good at it.

W

[zacster]

If you are that worried that line voltage is causing your problems, replace the power supply caps as these will be the first thing to go.  However, you are only losing one channel and this would impact both channels.

Your problem is not line voltage, and a variac as normal operating procedure is a bad idea.  I tried it and it injected some noise into the line.

What Variac did you try?  (Mfg/model, amperage rating, new or used/old, etc.)  Running what kind of loads etc?

What kind of noise did it inject in the line?  One characteristic of Variacs I've read is that they are supposed to be free of noise, in general.  (Although they will not reduce existing noise or other line problems.)

I read conflicting opinions about using a Variac as normal operating device.  Some say not a good idea, some say perfectly fine if the Variac is good quality/condition and not overloaded, etc.  It helps to evaluate this question if additional relevant factors are also known.

Why are you so convinced a Variac will solve your problem?   Why do I care?  Get a real power conditioner if you want to lower the input voltage.  A variac is a testing tool.  And voltage isn't your problem.  You'd be blowing up stuff all over the place, not just your audio gear, if voltage was a problem.

[regenerate]

I don't want to be a stick in the mud...but, why do you want to do weird stuff like plugging HiFi into a variac? AVA equipment has been carfully designed to operate on normal voltage fluctuations and I just don't understand the need for it. I just plug my AVA stuff into the outlet and listen to music. Make your life simpler. Let Frank figure the fringe stuff out, he's good at it.

W

I don't have a weird avatar or image to attach to my forum name, so I must compensate by doing weird stuff like experimenting with real things.

Many times I achieve better results in things, by being this weird way.

Other comments still welcome - especially if they address the relevant issue and not me personally. 

[regenerate]

If you are that worried that line voltage is causing your problems, replace the power supply caps as these will be the first thing to go.  However, you are only losing one channel and this would impact both channels.

Your problem is not line voltage, and a variac as normal operating procedure is a bad idea.  I tried it and it injected some noise into the line.

What Variac did you try?  (Mfg/model, amperage rating, new or used/old, etc.)  Running what kind of loads etc?

What kind of noise did it inject in the line?  One characteristic of Variacs I've read is that they are supposed to be free of noise, in general.  (Although they will not reduce existing noise or other line problems.)

I read conflicting opinions about using a Variac as normal operating device.  Some say not a good idea, some say perfectly fine if the Variac is good quality/condition and not overloaded, etc.  It helps to evaluate this question if additional relevant factors are also known.

Why are you so convinced a Variac will solve your problem?   Why do I care?  Get a real power conditioner if you want to lower the input voltage.  A variac is a testing tool.  And voltage isn't your problem.  You'd be blowing up stuff all over the place, not just your audio gear, if voltage was a problem.

Man, must be too much coffee consumed around here...

I AM blowing up stuff all over the place.  I keep the local lightbulb purveyors in business.

I'm not convinced of anything yet.  That's what experimentation is for.  Various opinions based on hearsay and quasi-technical background are not enough, not alone anyway.

But keep em coming.  Especially if they are based on solid facts, and focus on the relevant issue rather than me personally.  (Starting to detect a pattern here...)