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Nagra Stories Sound-men won’t ever tell


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On 5/1/2023 at 3:09 PM, JBond said:

DHB, Post your finding here so we can follow what happens.



Joseph, the thread 'Nagra IV-S input chain issues' can be found on the group under 'Equipment' and if he posts it there it will snap back as a recent thread, so I reckon it's better there (there being other Nagra related technical questions and answers elsewhere throughout the site) where folks with similar issues will find it easier than on this 'general Nagra apreciation' thread.



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And so ..we meet again, Mr Bond.


A funny thing happened after I picked up the IV-S from Mike Harris (..who said that he’d re-soldered a dry joint on the ‘EQ’ knob, centre front..) ..now, instead of recording only on the RIGHT track ..it records only on the LEFT !


From the great suggestions - in other threads here - of Malcolm Davies and of Richard Thomas, I emailed Kris Jarosz (ex Richmond Film Services ..which once was just down the road from me, but now sadly gone..) and Kris emailed straight back:


“Unfortunately I won't be able to help, I only service digital Nagras.

“If Mike Harris couldn't help,I can't think of anybody else in this country who could.”




So, although I’m not much of an electronic fiddler (capacitors, resistors, diodes, transistors, etc) I’m reasonably good at plain, simple logic, and having pored over the circuit diagrams - thanks again to dela, and to the Nagra Service Manual for the IV-S TC (downloaded from somewhere) - before driving the machine down to Petronel in Kent (a region of southeast England), I’ve been trying to work out just where things are going wrong ..and why.


The manual - for the later IV-S TC - shows that in ’68, I think, the simple 2-position ‘MIKE - LINE’ switch was changed to a 3-position version: ‘MIKES - LINE’ switch, described thus:


“..This three position switch is the main input selection switch. It allows the operator to select between MIC or LINE input on both channels simultaneously or "LINE" input on channel 2 (right)   [..Aha!..]   and simultaneously "MIC" input on channel 1 (left)   [..Oho!]   The upper position allows "LINE" inputs to both channels via connector (41), and the other positions allow selection between "MIC" inputs”.


I have only the 2-position ‘MIKE - LINE’ switch, but I opened up the IV-S and checked, just in case a newer-style switch was delivering mic audio to only ONE channel, with the machine expecting a LINE input to the other channel. Nope. And in any case, it USED TO deliver Left mic sound to channel 1 AND Right mic sound to channel 2 ..simultaneously.


So now, looking at the ‘Synoptic’ circuit diagram, I think I must concentrate on those switches leading into the A16 board (..the Record Amplifier & Oscillator..) which delivers the signal(s) to the two record tracks!  - phew! -


I’ll ask Mike (“mic”?) what he did which reversed the active recording track ..but maybe he doesn’t know, despite his being the only man in the UK who can, apparently, fix a Nagra.


It just occurred to me that as this fault began after I’d opened the deck to look inside ..could it be that in tightening the two ‘hold-down’ screws on the right edge of the machine, that some extra pressure was bending or shorting some contacts on the circuit boards in the UPPER (mechanical) section of the IV-S..?


I’ll open it up again this morning, and run it with the case open, and with no possible ‘locking’ pressure on any circuit boards, and will report back. ..No difference whatever.


But are you sure, Mr Bond, that you really do want me to keep posting this saga here..?


I know that you like photos, so I took one of the inside of the IV-S, where Mike apparently re-soldered a dry joint (so he said) ..but how did he get in there to do that? ..It looks like that means removing at least a couple of amplifier boards ..I’ve asked, and I wait to hear..






This is not a story about a Hollywood sound man’s experiences (..sorry!..) but is my experience of the - I hate to say this - ‘unreliability’ of this particular Nagra. It’s a story of severe Naggravation!


Oh, and now the Modulometer won’t show what sound’s been recorded (..now on only the Left channel, remember..) UNLESS - with the TAPE/DIRECT switch turned to ‘TAPE’ - you then turn up the gain knob(s) in Replay ..just like using Replay in ’Direct’ mode!  ..W-w-what?!


..Nurse! ..Help!  …Doctor!! ..Anyone!!!?


(..With a pile of Nagras on show in a cupboard, you’re lucky. It’s when you USE one - or more - that you get to discover the quirks and aggravations.)



UPDATE -  The reply from Mike ..(about why it now records only on the LEFT and not on the Right:


“..Hi, I was doing a check with an other oscillator board that I had in stock, that only recorded on the other channel. to check the heads, I must have left the wrong board in when I put it back together.

sorry about that.




So it’s off to Petronel of ‘Audiophiles Clinic’ ..tomorrow!

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Interesting with the channel fault that moved to another channel when another bias oscillator board was installed... It could indicate that the fault is with the bias board, if that is the only parameter that was changed. I have actually had a visiting IV-S which also had problems with a missing channel, and it turned out to be a connector problem on the A16 bias board. When you get the original board back, it is worth testing the record function while manipulating the bias board and its surroundings.


Regarding resoldering the contacts on the filter board, it is not that hard to get the board out (when you know how to do it). You start with removing the filter knob, that is held in place by a locking ring with a grub screw. Once the grub screw is loosened, the knob + shaft can be pulled out, and after removing the two screws in the bottom retaining the module, it can be pulled upwards and out. I would say that it is a logical place to check when a channel is missing, because the switches are a really weak point of the construction. I have a IV-SJ which had really bad switches, and that was messy... On the IV-SJ the filter settings for the two channels can be set independently, making the system even more sensitive. But the two-way knob is a little mechanical masterpiece...


I feel lucky that whenever I have these weird problem, I can always borrow a known-good module from another Nagra and then use that as a somewhat primitive way of narrowing down the problem...

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Many thanks - again! - dela.


Looking at the 'Synaptic' diagram I did narrow it down somewhat to the A16 board, but didn't feel like dismantling that bit of the electronics, so I've suggested to Petronel that he should have a rummage there ..and he has plenty of test equipment, too.


I'll post any further developments over at 'Nagra IV-S input chain issues', as you suggest ..and just post the final outcome - when it's resolved - here.


Thanks again, and g'nite!

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  • 3 weeks later...

First thing is , I would call BULLSHIT ! Study your magnetic tape properties , Reluctance vs. Coersion theory and in order to eliminate distortion ,  blah , blah . blah . . . No one needs to change any components in a Nagra IV-L or Nagra IV-2 Taperecorder to achieve the very best recordings IN THE WORLD . Electronically they are THE ULTIMATE 1/4 inch tape recording machine . Learn your European (England) Tape Biasing "Standard" first of all (which is ALL WRONG) . America settled on 20,000 Hz (pre-emphisis) at a specific EMF level ok ? (also vis-a-vis tape transport speed) . Some of my tapes sounded better at 21,000 Hz Bias . LISTEN to the resulting Playback . No one needs a Scientist to tell you when it sounds best . Put your wee screwdriver onto the adjustment points as described in the Nagra Service Manual (of the Bias Circuit intensity) , and monitor the resulting volume . BOOM > DONE . It's not Rocket - Science ; Yes it is . The 20,000 Hz signal has been appropriated for our certain Ferrous Oxide Molecule Particle Size (which may differ with your stock) . If you just adjust the intensity so as to get the highest volume returned , and then back off maybe about 8 -14 %  you will have the best recorded sound possible for that particular tape stock . You can alter the Bias Frequency slightly and try it again . I have done this , in the field , with no electronic instruments (just by ear) and it works . Crank the needles , run your machine into overdrive distortion , when you want distortion ! British taperecorded  "FILM SOUND" sucks because of this (Pe-emphisis/de-emphisis) frequency 'mistake' . Try yelling in the studio and pretending you're outside . It will sound fake (why ? reflected sound) , also you won't know Lip-Synching when it's done perfectly . Jack Buchanan 65 year old Soundman . Go ahead - respond . But send me 500 bucks first . E-transfer jackbuchanan2@hotmail.com

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Well, I'm sure glad we got that all cleared up. Not sure what I missed or know what post you are referring to, but I think we got away pretty damm cheap under the circumstances. Sounds like you know your stuff.
 I won't ask anything about what you just wrote because of the costs involved, but how much will it cost to ask what your favorite Nagra was and if you have any pictures from back in the day? 

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Er, hmm, where were we?


Well I got back my IV-S from Petronel (..he'd been away, servicing Studers around Europe..) and it now works -b-e-a-u-t-i-f-u-l-l-y- (..and he's backed-off the pinch-roller pressure screw, which was at the limit of its travel, and has adjusted its arm so that it doesn't need that screw-in trimming).


Sounds wonderful - both Record and Play - and I got a Nagra original power supply, as Petronel doesn't like the 'square wave' switching power supplies; he says they can - eventually - spoil or ruin the electronics. I run it on batteries usually, anyway.


I haven't posted any pictures, as it just looks like an ordinary early IV-S (..or IV-S with QGB..) but I'd like to thank everyone here for their expertise, particularly dela, and maybe I'll look in again another time! ..Cheers!

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