Jump to content
Tunes

Buzzing on nagra taudio

Recommended Posts

Any ideas on helping this novice identify noise on my recent used taudio?

I'm trying to diagnose a hum/buzz on both channels on a nagra t audio tape player. The transport is working fine and audio output is strong on both channels but there is a faint mosquito pitched buzz that increases in loudness as volume dial increases. Present on both headphone and via external outputs to audio system.

Have had a suggestion that i may need to look at the power supply filter capacitors. One other thing if you know this machine, is that the buzz stops after a few minutes when the unit has not been touched and switches itself into standby.

Would this indicate a specific area of the power supply to investigate?

Sure hope to identify the culprit as it's an amazing machine otherwise!

Thanks!

Chris

Share this post


Link to post
Share on other sites

tunes: "  Have had a suggestion that i may need to look at the power supply filter capacitors. "

you have had a good suggestion, and here is another:

refer servicing to a qualified technician, no novice serviceable parts inside.

Edited by studiomprd

Share this post


Link to post
Share on other sites

What Mike said.

 

Someone not well enough acquainted with these types of electronics to implement proper, and thorough, trouble-shooting steps is unlikely to be qualified for Nagra repair.

 

However, I'm confident it's one of three things:  1) An aging power supply capacitor, 2) an oxidized connector, or 3) something else.

 

 

Share this post


Link to post
Share on other sites

I am wondering if chris is hearing the 13.5khz fm pilot.  do you have more than one set of heads for the recorder?  are you listening to recordings made with  fm pilot with a set of heads that covers the entire tape (i.e. not allowing a guard band for the centre track) ? 

Share this post


Link to post
Share on other sites

I was thinking pilot also, but then saw the OP's note that the noise cuts out when the machine goes into standby. Implication is that the tape is stopped while he's hearing the noise, before the deck ever times out. 

 

Okay, what happens when a Nagra T goes into standby (we used Studers)? Does a solenoid release? In that case, current load suddenly goes down and the noise stops... which would point to the power supply. But I'd look at the bypass cap around a voltage regulator -- or a regulator chip itself -- as well as the filter electrolytics. Regulators can go into oscillation...

Share this post


Link to post
Share on other sites

I -wish- we had Nagra Ts for sync use. Nah, just a bunch of Studer 810s...   which were a very nice deck, indeed, if a kind of old-based design (dating back to A67 and even Revox A700). 

Share this post


Link to post
Share on other sites

Any analog Nagra is a fairly uniquely complex machine, and the T-Audio was the most complex of all Nagras.  If you haven't worked on late-analog microprocessor-controlled tape machines before this is not a good place to start, unless it's not important to get it working again any time soon.  Unfortunately, there were never that many techs who could really work on a T-Audio--I hope the OP lives near a major city where such a tech might still be working….

 

philp

Share this post


Link to post
Share on other sites

Sounds to me like you are playing back a Nagra Neopilot recording on a Mono head. The "mosquito pitched buzz" is probably the 7kHz modulated 60Hz pilot tone. The mono Nagras used a straight 60Hz pilot tone recorded onto two small tracks in the center of the tape so that when it was played back on a mono head the two signals would cancel each other and not be heard. However, the same system would be heard when played between the two tracks of a stereo head, which is why Nagra developed the FM (frequency modulated) system called the NeoPilot, which was a 60Hz tone modulated at 7Hz, which was silent in the guard band between the two audio tracks.

 

A mono head was available as an additional option on the Nagra T. if you select the stereo playback head, I bet the noise will go away.

 

Glen Trew

Share this post


Link to post
Share on other sites

I was going to ask: what happens when you hit stop? Does the hum go away, or does it continue? If it stops, then I'd bet Glen's analysis is correct and you're hearing Pilotone. If the hum keeps going, then I would expect a power supply/grounding issue.

 

If the noise is embedded in the tape, it would not be rocket science to just capture the tape signal as a digital file, then take a sample of the buzz and knock it out with iZotope RX 3/4 or something like it. 

Share this post


Link to post
Share on other sites

Thank you all for the suggestions!

I swapped in a power supply from another machine that has no buzz/tone and that made no difference so now i am thinking it may not be power supply afterall. There is no separate mono head and the mono led is not on so i am thinking it is not due to mono / pilot tone. Have tried two tapes from two different machines and it's there so i don 't think it's on the tape. When in stop, the tone/buzzing persists. As mentioned, it does disappear after 3 minutes in park if the keyboard isn't used and the machine goes into standby. Maybe grounding issue. It is more of a higher pitched tone / buzz than a low steady hum like i've heard on other gear when ground loop hum has been present.

Chris

Share this post


Link to post
Share on other sites

As mentioned, it does disappear after 3 minutes in park if the keyboard isn't used and the machine goes into standby.

 

 

Like I said above, you have to look at what changes when the machine goes into standby:

 

-  If a solenoid lets go or the motors stop getting power when the noise stops, it's most likely a regulator issue. This isn't necessarily in the power supply box; it could be on a logic board or wherever the current is boosted from logic levels to solenoid/motor levels.

 

-  If something else happens - perhaps the CPU shuts down - then I'd look at grounding or bypassing on the logic boards.

Share this post


Link to post
Share on other sites

Yep, what Jay said. This sounds to me like a board is going into oscillation for some reason. While the Nagra-T's were really great machines for their time, they go back to (I think) 1987-1988, which is a long time ago for an analogue board. After 25 years, caps go bad, solder joints could be suspect, all kinds of stuff can be on the verge of failure. 

 

I do see Nagra-T's for sale once in awhile on eBay, so it might be possible to just buy a second junker machine and use it for parts. 

Share this post


Link to post
Share on other sites

Yep, what Jay said. This sounds to me like a board is going into oscillation for some reason. While the Nagra-T's were really great machines for their time, they go back to (I think) 1987-1988, which is a long time ago for an analogue board. After 25 years, caps go bad, solder joints could be suspect, all kinds of stuff can be on the verge of failure.

I do see Nagra-T's for sale once in awhile on eBay, so it might be possible to just buy a second junker machine and use it for parts.

Marc,

Your description sounds like what happens to us as we age as well :)))

Yes, i have a second parts machine which i am using to try swapping power supply units, also did swap the main audio control logic boards but no difference. I haven't tried swapping the left and right audio boards with the parts l/r boards yet as the noise is present on both channels. Still working through the possibilities ... Thanks for all the suggestions and the follow up comments jay and marc.

Chris

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×