Studer B67 1/4" Popping Sound

[gg85]

I have a fully recapped/serviced B67 (15ips). Everything is great on it but one thing I am noticing is that when I'm calibrating, I can hear popping sounds under the tone. It's more prominent at lower frequencies (can't really hear it at 10k, definitely there at 1k and lower). It happens with different tapes. I'm currently using agfa 468 but it's there with new ATR and 499. Over-bias with agfa is 3.5dB and alignment is 355nWb/m. Heads are in very good condition and everything lines up flat. Mixes sound great off it, but when tracking vocals through it I can hear the pops sometimes. I know for a fact it didn't always do this and I suspect it's something to do with the bias but I have no idea why. Oscillator frequency is at 150kHz and erase is great, I don't hear any previous recordings.

Any ideas?

Thanks!
George

 

[Bo Deadly]

Did you replace the relays?

 

[gg85]

squarewave, which relays do you mean?

 

[Gold]

Those are most likely  “bias rocks”. Try playing around with the amount of bias you are using to reduce them.

 

[gg85]

Thanks Gold, that's exactly what's happening. The only thing is I can't get rid of them. When I max out my bias pot they definitely reduce but they're still there a little, and that's way too much over-bias.

 

[Bo Deadly]

squarewave, which relays do you mean?

If there are relays in the signal path, the contacts can deteriorate and cause static noise. But it sounds like maybe there are no relays? And I would not characterize the noise as "popping". It's more like rustling leaves.

 

[radardoug]

Are you demagging regularly? (Every 8 hours of tape operation).
Check the bias oscillator waveform on a scope, it needs to be really clean.

 

[gg85]

Not every 8 hours but I will demag and get back to you. I do suspect something is up with the oscillator but will have to bring my scope into the studio and check it out. Thanks for the suggestions!