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On 9/19/2014 5:54 PM, Jan Myren wrote:
> I am about to record on reel to reel tape and hear some occasional "pop" and
> "hiss" noises. They appear mostly on the left channel and I use to hear them
> a bit on low passages in the music and between tracks. My machine is a Revox
> B77 MK2 and the tapes are brand new RMG LPR 35 tapes.
>
>
> May this be solved by demagnetizing the heads?
> I have never used a head demagnetizer before, but I clean  regularly so the
> heads are not dirty.
>
> I may obtain a TDK head eraser HD-11. Is that any good for my use
>
> Hope to hear from any reel to reel enthusiasts.

Quick question: do you hear the noises only when playing back tapes, or 
are they audible when the tape deck is in "Source" monitoring position?

I ask becaue this can help track down the location of the problem. If 
the sounds are audible when the machine is set to "Source" they're 
probably coming from the output amplidier; if they aren't audible in 
"Source", then the problem is probably in the playback amplifier.

In either case, the problem is probably not magnetizaed heads (but see 
below). It's probably an electrolytic capacitor in the circuit (playback 
or output amp) that is dying and becoming leaky. Probably the simplest 
and most economical way to solve the problem is to replace all the 
electrolytic capacitors with units of the same value and voltage rating. 
Buy caps rated a 105 degrees C., not 85 degrees -- they'll last longer. 
This is known as "shotgunning", and it's cheaper than having someone 
painstakingly check out the machine for leaky caps; just fix 'em all and 
you're good for another ten years or more.

About the heads: the noise is almost certainly not coming from 
magnetized heads. However, the heads may be magnetized anyway; if the 
bad capacitor is at the input of the playback amp, then current could be 
flowing through the playback head and may have magetied it, which will 
damage your tapes in the long run. If you can, get hold of a 
magnetometer an see if your heads are magnetized; if so, demag them.

But first, shotgun the capacitors. Start with the input capacitors on 
the playback amps; if, after you've replaced them, the noises go away, 
then they were the culprits, and you should probably demag the heads. If 
not, you probably don't need to demag. In any case go on and shotgun the 
rest of the capacitors.

Peace,
Paul