TASCAM 414 - random vocal popping/clicking, only on tape playback

[judeseda]

I have been learning and using an old TASCAM 414 mkII unit I got from a friend for about a month now. I've been surprised by its quality and fidelity save for one persistant issue.
There's this medium-pitched popping/clicking sound pervading my vocal tracks. Its features are so:

*This does not occur when recording acoustic guitar with the same mic/input/settings, only happens on vocals
*The pops are not audible in monitoring input, only when listening back to tape directly or with tape cue. I have no idea if it's occured or will occur until I listen to my finished recordings
*The pops are linked to the vocal delivery and phrasing, perhaps responding to some sort of plosive element
*I have learned to on-command trigger these pops by smacking my lips near the mic - the plosive sound while monitoring is barely audible but the resultant pop on tape is very loud, it has an almost-electronic quality to it
*Using a new section of tape does nothing, cleaning the heads does nothing, using a pop filter does nothing, EQing does nothing, this is all analogue.
*The pops are baked onto tape and make it to my DAW when I send the track into my interface

I cannot get it to stop - all my vocal takes are partially unusable - has anyone had this problem or an idea of how to fix it?
Cheers

 

[Jack Saturn]

Can you upload an audio sample of this somewhere so we can have a listen?

 

[judeseda]

Great point! Uploaded a little clip of an isolated vocal track which had some especially bad pops.
Example clip audio

 

[Jack Saturn]

Checked out the audio file. To confirm, this problem was already occurring when you acquired the machine from your friend? I've worked on a lot of Tascam 414 units and I've never heard anything specifically like this, but my hunch is that there is some component that is being repeatedly "woken up" by certain plosive sounds, as you've mentioned.

A few questions:

What is your vocal chain?

Does this issue occur on all tracks?

If you can, try recording a vocal to another device through the same vocal chain, then feed it to the 414 as a line level signal. I'm curious if the popping still happens in that scenario.

 

[Jimnield]

Have you degaussed the heads? Its worth a try and they should be done anyway.
Can you run the vocal mic through a compressor prior to recording?
It might be the dynamics of the vocal causing the noise reduction (dbx?) to freak out.
I had this issue once using a tascam portastudio in a caravan, it was hypersensitive to any electromagnetism. Once indoors, degaussed and properly earthed it was fine.