Studer A807 - IEC to NAB?

[Linnovice]

Hi all. I have a Studer A807. It's an ex BBC studio machine to be fed from a mixing desk. ie. It has no meters or adjustment pots. It is also fitted with Bauch boards. My question is this. I notice on other machines that it's possible to switch between IEC or NAB equalisation. On my machine these buttons are labelled 'Remote Replay or Remote Record'. I have found on the control board under the top cover a couple of switches that enable me to calibrate for two kinds of tape (I've had to drill some holes in the top cover to access them). I'd like to be able to set up for both IEC and/or NAB. Would anyone know whether this is possible?
Any guidance would be gratefully received.

[SteveCG]

I've no experience with this machine so bear with me. Can you answer this question:
Is it 15 IPS only or 7.5/15 IPS ?

NAB at 7.5 IPS is the same as NAB at 15 IPS (ie 50 uSec)
IEC at 7.5 IPS is (50 uSec) whilst at 15 IPS it is 35 (uSec)

I was told the record companies preferred to use NAB, whilst the broadcasters preferred to use IEC.

Revox A77s used different record & replay cards for 7.5/15 IPS machines depending upon whether they were sold as being for NAB or IEC with no replay EQ switching. This was unlike the 3.75/7.5 models which could replay (only) switch between 70uSec and 50 uSec at 7.5 IPS, 70uSec being an earlier IEC standard.

So perhaps on the A807 models that could switch between IEC and NAB, it was on replay only?

[Ted Kendall]

Actually, the IEC curve is 70uS at 7.5 and 35us at 15. The DIN curve is the same as NAB, ie 50/3180.

The earlier IEC/CCIR curve for 7.5 was 100uS, and was superseded around 1966.

Agreed, NAB for 7.5 and 15 are the same, 50/3180.

Standard A807s could flip between NAB and IEC rec/rep on just the one switch.

If this is a BBC machine, the likelihood is that this facility was sacrificed to provide the remote functions. Reinstatement could be a software or a hardware task.

IEC was used by the BBC on quarter inch. NAB was more generally used in the record industry, because most American machines were supplied with this EQ and it was convenient to standardise on it - even the BBC used NAB on multitrack machines.

[SteveCG]

Ted, Re: the 7.5 IPS IEC curve. I thought it was 70 uSec 'at one point' but then got reduced to 50 uSec later. I have seen Revox adverts for machines earlier than the A77 extolling the "New IEC standard" - and they meant 70uSec at 7.5 IPS.

At some point in time IEC meant: 3.75 IPS 140 uSec, 7.5 IPS 70 uSec, 15 IPS 35 uSec

Then later:
3.75 IPS 90 uSec, 7.5 IPS 50 uSec, 15 IPS 35 uSec.

Certainly the value of the constants changed over time as tape oxide formulations improved. It all adds to the fun of attempting to play back old recordings accurately...

On recordings I made I explicitly wrote the time constant on the box.

[Ted Kendall]

IEC has been 70uS at 7.5 since 1966. Prior to that it was 100uS.

NAB has been 50/3180 at 7.5 and 15 since the year dot.

DIN adopted NAB at 7.5 and under, but retained IEC (35uS) at 15.

[Linnovice]

Hi Ted, I fear your comment regarding the BBC sacrificing the switching is right. Hence the Bauch boards. I was just hoping someone may have worked with these machines and would know a fix around. It records/plays great, stunning at times. I use it as the workhorse recorder. Problem only comes when playing back on my NAB machines. The recordings tend to be a bit brassy. Perhaps I should just stick to the 'it ain't broke so don't fix it' school of thought.
Just out of interest though Steve, the A807 is a three speed machine, 3.75, 7.5, 15ips and at present I have it calibrated for Quantegy 456 and Maxell XL1.

[Linnovice]

Sorry . . . intuitive text! I meant bassy.

[SteveCG]

Linnovice,

Indeed, I wonder what the 3.75 IPS replay time constant(s) is/are for your machine?

My investigations into this time constant issue told me that the 3.75 IPS value(s) was never as fixed as the higher speeds. It seems that most later domestic machines used 90/3180 - but earlier machines ??

Perhaps Ted can set us right on this point.

[TIMTAPE]

Originally Posted by Linnovice

Problem only comes when playing back on my NAB machines. The recordings tend to be a bit bassy. Perhaps I should just stick to the 'it ain't broke so don't fix it' school of thought.

If anything I think it should be the other way around.NAB repro characteristic rolled off the low bass to compensate for the boosted low bass in record. Are you sure both machines are truly calibrated to their respective standards? If they are you should expect NAB to playback an IEC 1 recorded tape with reduced bass.

[Ted Kendall]

Time constants for 3.75 were a lottery before the NAB 90/3180 prevailed almost universally after 1966.

EMI pre-recorded tapes were advertised as 120uS. Brenell simply doubled the CCIR 100uS standard for 3.75, and again for 1.875 - yes, 400uS! Other manufacturers used 140, still others 180. Mind you, given the state of the art in tape coatings at the time, these variations were probably swamped by other factors. When retrieving Goon Shows from 1950s tapes at this speed, I just wind up the Studer to 131uS (maximum on an A810) and adjust to taste. It works...