Newmarket

Pro Bel Card
« on: November 17, 2017, 09:32:14 AM »
Hi all.
I picked up four pro bel rack cards - basically for the Zero Field type Lundahl Transformers.
But having received them they look in very good condition.
But I can't find out what the card is.
I don't know if they are working or not and with the DIN41612 connector it's not easyy to follow the circuit.
Components seem fairly standard pro audio - NE5532 ; Pos and Neg 3 TO220 regs. Appears to have on board ac rectification and smoothing.
Would be a shame i think to take transformers off before I know what the board function is.
Any input appreciated. Thanks.
« Last Edit: November 17, 2017, 10:06:04 AM by Newmarket »


Newmarket

Re: Pro Bel Card
« Reply #1 on: November 17, 2017, 09:33:13 AM »
2nd photo

Newmarket

Re: Pro Bel Card
« Reply #2 on: November 17, 2017, 09:33:59 AM »
and photo #3:

gyraf

Re: Pro Bel Card
« Reply #3 on: November 17, 2017, 09:49:15 AM »
The ZF transformers are really only fun in-circuit, worthless without the specified actives.

Here's a schematic showing the basic idea (Amek), I have nothing on this Pro-Bel, that seems to be a company specialized in matrixing and such for (oldschool) video editing: https://www.ebay.co.uk/b/Pro-Bel-Switcher-For-Video-Broadcasting-And-Recording/3319/bn_89913?_pgn=3

It looks like there's quite some filtering going on on that PCB. And there's on-board symmetric power supply. And probably those transistors are a high-current output stage?

Jakob E.
« Last Edit: November 17, 2017, 09:57:48 AM by gyraf »
..note to self: don't let Harman run your company..

Newmarket

Re: Pro Bel Card
« Reply #4 on: November 17, 2017, 10:12:43 AM »
The ZF transformers are really only fun in-circuit, worthless without the specified actives.

Here's a schematic showing the basic idea (Amek), I have nothing on this Pro-Bel, that seems to be a company specialized in matrixing and such for (oldschool) video editing: https://www.ebay.co.uk/b/Pro-Bel-Switcher-For-Video-Broadcasting-And-Recording/3319/bn_89913?_pgn=3

It looks like there's quite some filtering going on on that PCB. And there's on-board symmetric power supply. And probably those transistors are a high-current output stage?

Jakob E.

Yes, I was looking to implement the ZF configuration. I'm aware of the concept and Lundahl notes and others but thanks for the AMEK schematic - I hadn't seen that one before.
Pro-Bel - yes longstanding broadcast / video etc kit. Since become absorbed into Snell & Wilcox I believe. I've found some info on similar format Pro-Bel cards but not this one.
Yes +/- 12V voltage rails. Not looked into the metal can transistors but you're likely right about output stage drive...
Thanks for the input.

gyraf

Re: Pro Bel Card
« Reply #5 on: November 17, 2017, 10:46:45 AM »
Here's an example of our local mixing-desk builders NP - their version of the ZFT:

Jakob E.
..note to self: don't let Harman run your company..

PRR

Re: Pro Bel Card
« Reply #6 on: November 19, 2017, 02:28:51 AM »
> probably those transistors are a high-current output stage?

All those same-value resistors.... It kinda has to be a Distribution Amp. 20 R, 10 outputs.

Then the two-pair power transistors make sense as a Bridge (balanced) output.

It shouldn't take a half hour to trace from the regulator IN pins to the edge connector; and from the ZF transformer pins through ~~5K resistors to the edge. At that point you know how to power it and feed it signal. 50:50 chance that "any" two pins near that resistor-heap will be An Output.

It looks to be a 4 Watt output. Assuming near 20Vrms, 0.67W in each 600r load, 6 outputs. I wonder if the resistors are 300 Ohms each- then a Match-Load is 1,200r seen by amp for each 600r output, so it can drive twelve 600r outputs at 10Vrms (enough for any video distribution), and 12 is approximately 10, the number of outputs implied by 20 resistors.

desun

Re: Pro Bel Card
« Reply #7 on: November 19, 2017, 01:25:37 PM »
As said, it's probably a DA, most likely a timecode DA. Still using audio circuits for timecode distribution to this day.

PRR

Re: Pro Bel Card
« Reply #8 on: November 20, 2017, 12:21:15 AM »
> timecode DA.

A sexy zero-field input for time-code?

It's old gear and I'm old in video. Last time I wired video there was a LOT of audio run around. Maybe today that's all ethernet, but back in the day it was robust analog like that.

Newmarket

Re: Pro Bel Card
« Reply #9 on: November 20, 2017, 05:14:55 AM »
Thanks for the input people.
Yes - thinking about it the DA function looks a likely candidate.
Doubtful about the timecode function with the Lundahl transformer - esp the ZF type.
Can't really see that being chosen to ship square waves ? Also I'd be a bit suspect of the noise issues of LTC on a card like this - I'd expect more shielding and possibly dedicated screened connection - BNC etc rather than the DIN41612 connector ?
It's a long time since I was doing anything with LTC / VTC - just sync' stuff for console automation - but I do recall 'audio' type circuits being used to square up LTC code in front of an ASIC on DDA stuff.



gyraf

Re: Pro Bel Card
« Reply #10 on: November 20, 2017, 10:04:41 AM »
..timecode is not squarewave, it's real audio. And transformer isolation is wonderful for this..
..note to self: don't let Harman run your company..

Newmarket

Re: Pro Bel Card
« Reply #11 on: November 20, 2017, 10:47:41 AM »
..timecode is not squarewave, it's real audio. And transformer isolation is wonderful for this..

Not sure what meant here. It's 'audio' in the sense that it can be recorded on audio tape. So it can't be a 'real' squarewave - but then again nothing really is as transition time is always >0 even if it's down to ps.
So it's an FM encoded signal - essentially binary in nature. You don't want to listen to it  >:( or have it bleed onto your audio - special fx excluded  ;)

Agree that galvanic isolation can be useful here though - as it can be for digital logic signals - AES3 ; Ethernet etc
« Last Edit: November 20, 2017, 11:02:20 AM by Newmarket »

[silent:arts]

Re: Pro Bel Card
« Reply #12 on: November 20, 2017, 11:51:19 AM »
LTC sounds wonderful  :D
Trained ears can hear if it is 24, 25 or 30 fps  8)

Newmarket

Re: Pro Bel Card
« Reply #13 on: November 20, 2017, 12:12:43 PM »
LTC sounds wonderful  :D
Trained ears can hear if it is 24, 25 or 30 fps  8)

Can 'Golden Ears' detect Drop Frame ?  ;)

[silent:arts]

Re: Pro Bel Card
« Reply #14 on: November 20, 2017, 01:00:01 PM »
Platinum ears may do?
my ears can detect drop outs for sure  8) ;D