Re: Running an amplifier without load

As a general rule plugging in headphones disconnects the speakers so should be fine.

It would be a pretty poor design if the amplifier is damaged where no speakers are connected, or when one fails.

A crackle when you change the control suggests that DC is also getting through from a failed/failing capacitor, presumed an electrolytic one.

If not used for a while I would run for a while to reform the electrolytics or consider replacing them.

It's generally OK to run solid-state audio amplifiers without a load. Valves and/or RF are a different matter.

More like Old Women's Talk.

Go ahead.

Headphones generally don't provide much of a load, as they tend to be connected through resistors to limit accidental ear damage.

With transistor amplifiers, there will be no problem running without a proper load. Valve amplifiers will usually generate high voltages when unloaded due the the output transformer inductance, so never run one of them without a normal load connected. You either have to go a long way back in time or have spent vast amounts of money on a trendy amplifier to encounter one of these. A 1974 tuner-amp is not going to contain valves.

By the way, even a small DC leakage through volume pots will cause a vast amount of crackle when they are moved, so look for leaky electrolytics coupling the volume controls if switch cleaner doesn't fix things.

No, as others have mentioned it was an issue with older/valve amps.

That was true of valve amplifiers with output transformers, but is not true of transistor amplifiers.

Most of my designs ran extensively with only an oscilloscope as load until I was sure they were stable :-)

No. Even if this 1974 Tuner Amp contains audio output transformers it wouldn't be a significant issue.

As for the headphones - there could be a problem if the headphones were put in place of speakers. Attempting to drive headphones with, say, 10W of audio could damage the headphones - and maybe your hearing.

If the amp has a headphone socket, use of that might not significantly load the speaker outputs - if that was an issue.

If you feel that there's a concern - keep the speakers in circuit and use some earplugs or, safest of all, substitute Resistors of suitable resistance and energy rating as speaker loads and hear what is happening via mid- resistance (say, 32ohm) headphones - and headphones NOT totally on/over/in your ears.

Old Wive's Tales, indeed.

(that was the expression I couldn't recall last night ;<{ )

Good luck with finding "TV tuner cleaner, BTW. That ID went out with the Ark - not to mention with those seriously dangerous turret tuners. Contact Cleaner is the current moniker. WD40 is not recommended.

Sigh. Hoe many ampliiers have yoi put on test.

Thats why in general you drive then through100 ohm resistors

It would be if it was a pre 1960 valave amplifeirss

There is a grain of truth in it. As you would know if you had any idea of electronics

I just looked -- wear something to protect your eyes while looking at this.

This is a science-y way to do cleaning.

"Access denied"

Geolocation issue?

That's interesting. Potentiometers are effectively sealed units, so fail by the track becoming damaged in some way, whereas faders are open to whatever can get onto the track. I'll bet that most of the "dirt" on faders is from cigarette smoke and tar. Looking at old films of recording studios often shows a fug of smoke in the room!

More than enough. Though little time spent on "ampliiers", "yoi" know

Gosh! I never worked on "valave amplifeirss" (Back in the Pram time?)

Ill-tempered Tosh

Most (rotary) pots that I have encountered are *not* (fully) sealed.

(I would say that both are 'potentiometers' - the faders are linear, the others are rotary. A pot is an 'adjustable potential divider', regardless of the form)

There are 'posh pots', sealed, polymer track etc. but the vast majority of rotary volume controls, particularly of half a century ago, are not these. The rotor is on the opposite side of the track to the spindle, that side is covered by a metal shield which is cut away around the three terminals. Not sealed.

The earliest faders, by the way, were rotary, operating over about a fifth of a circle. The knob moved over an arc, and they were usually mounted 'backwards', so that maximum volume was at the end nearest the operator, so that the graduation marks near maximum level could be clearly seen. The very best were not potentiometers at all, but multipole switches, with poles at 1dB intervals.

As someone who has used valve amplifiers, I know that some drive a conventional loudspeaker via an output transformer, and some drive a speaker where the speaker itself has the winding that gives the output valve its working DC voltage. The first would be perfectly happy without a speaker or headphone load, the second wouldn't.

Having said that, I don't imagine anything made as recently as 1974 would have the second configuration. The only one I have encountered of the second category was of 1930s vintage.

This is the only type I have encountered.

In the absence of compressed air, if I hold the pot with the opening underneath and use a very narrow tube to squirt the switch cleaner in, then an abundance of switch cleaner so that it pours back out, followed by turning the pot back and forth continuously while the remaining switch cleaner evaporates does seem to get rid of any dirt on the pot track.

In message <10d2i47$2f4oa$ snipped-for-privacy@dont-email.me, Peter Able snipped-for-privacy@home.com writes

Thank you all for the many useful comments. Not sure where I got the bit about running an amp without load. Hi Fi News many years ago, I suspect. Yes, my amp is transistor, not valve.

Removed the chassis from the case for the first time this morning, and was quite impressed at how little dust was inside. Failing memory - the major problem was not volume, but the five position rotary input selector (AM, FM, FM Stereo, Phono and Aux), which worked, but required very careful fiddling to get both channels working simultaneously. Sprayed and rotated the knobs earlier, and will give it a while to dry before powering up and testing.

Thanks again,

In message snipped-for-privacy@binnsroad.myzen.co.uk>, Graeme snipped-for-privacy@nospam.demon.co.uk> writes

Update

Having now tested using headphones (which, as has been suggested, cut off the speakers), all seems to be well, listening to R2 on FM and FM Stereo, no crackle from the volume pot and, more importantly, positive use of the selector switch, which is open wafer (I think) and easy to spray.

Given it another spray or two, much twiddling of the knobs, and will now leave to dry properly before testing with speakers - a pair of Marsden Halls, same age as the amp.

Regarding leaking capacitors, I assume this refers to leaking in an electrical sense, which I have no idea how to test. Having said that, any I saw looked fine in a physical sense, and any crackling seems to have gone.

Thank you!

Put a DC voltmeter across the outer terminals of the pot while the equipment is turned on with no sound source. Any reading at all means something is passing current into the pot, either through its input or output coupling capacitor. Turn the pot between maximum and zero to check which.

Some designs may not have either or both capacitors, using DC feedback to an earlier stage to eliminate any standing DC at the pot and/or using DC coupling into the next stage.