Re: Info or schematics for BBC AM9, AM7, UN4/6, AM1/57 Modules anyone?

So i've been working on the modules today.
Had a proper look at the EQs.
Its passive but sounds great!
Will be good for mastering and fine eq tuning.

I'm going to use an AM7/4 for the gain stages. Which need +/- 24VDC

Which brings me to the PS2/49 power supply unit.
Now i cleaned it up and tested as much as i could before powering it up.
Turned it on (whilst hiding under the desk :-[) and it gives off a fairly loud hum.

I have no schematic or pin out for it.

Theres four output pins connected.
I'm getting +48, -48, 0, and 0.
I was expecting +/- 24v so does this mean it uses a floating ground reference and i should link a couple of terminals?

some pics anyhow
the eq guts,



PSU

mrclunk said:

Which brings me to the PS2/49 power supply unit ...

I'm getting +48, -48, 0, and 0.
I was expecting +/- 24v so does this mean it uses a floating ground reference and i should link a couple of terminals?

Click to expand...

Yes, you tie down the positive. I do this on the back of the rack - if you don't, you get +24v down your unbalanced output screen!

The amps want -24v w.r.t. earth. I don't know why you're getting 48v, but the output will be floating at the PSU - what are you referencing your measurements to?

cheers mate, i worked that out just before i left work...
linked pins 12 and 11.

now i need to get rid of the almighty hum. i'll recap it tomorrow but if that doesn't  work it must be the mains transformer i believe. recall reading about loose lams in old transformers vibrating or some thing.

So i got our eqs finished, thought i would update the thread.

PSU.
It was the transformer humming, was physically vibrating. So i swapped it out.
Changed the caps but still loads of ripple. noodled about with the psu for a while but without a schematic i found it quite tricky.
Ended up ripping out the old psu circuit and building a simple LM337 -24V supply into the casing. Quicker than sorting out that rusty old bundle of corrosion.


Line Amps.
Fixed/Recapped/matched the two AM7/4 line amps.
Worth checking the blue 100uf 'Hunts' signal caps in these modules. I had several bad ones.

EQs
Not much to do to these. Cleaned up  the switches and panel. There was a few cold joints, mostly on the inductors.


Found this BBC doc which details some of the stuff discussed in this thread also
www.bbc.co.uk/rd/pubs/archive/pdffiles/monographs/bbc_monograph_46.pdf

thanks for the help peoples ;D

sorry to revive this, but I'm looking for schematics of the AM7/13A line amp. I've been asked to modify 8 of these to 'proper' mic preamps.

thanks,
corneel

Nele said:

sorry to revive this, but I'm looking for schematics of the AM7/13A line amp. I've been asked to modify 8 of these to 'proper' mic preamps.

Click to expand...

PM me your email address. These have tonnes of gain, and IIRC a 10K input impedance which is probably already ok.

We have some modded ones at work with a full gain range control.

i found this on the AM7/13
http://www.bbceng.info/EDI%20Sheets/10243.pdf

I've a rack of these too, be great to turn them into mic pre's.
Reckon u may have to change the input transformer tho. (input impedance = 18k )

Roddy could u chuck the doc's into the gmail account so i can have a butchers also.
ta
paul

I'm curious about these too.  Just ran into a pair of AM7/13A's.  Anyone got schematics?

Thanks
Orin

Bump.

Bump??? 

Cheers
Søren

Thanks Dan.. 

Cheers
Søren

Thank you Dan.

Regards
Orin

Just scored some more ex beeb junk.
Any one have any schematics for :-
effects voice over module: UN4/6
dual meter amp module: AM1/57
thanks
Paul

only just read this thread. i've attached a photo of a photocopy of the schematic from one of the orange books that the BBC compiled for maintenance purposes. these seem to be as rare as hens teeth even within the beeb, sorry i haven't got any more detail than that but my source was incomplete.

Hi guys,
I am quite new here. I have one AM9/23 module and can't find any schematics to connect it.
Would it be OK for you to re-upload the pictures mentioned earlier in the thread ?
that would be fantastic. thanks in advance.
Jean-charles

BBC Bump

Hey Fellas... Going all the way back


Alt this talk about schematics but nobody declares how he likes the units sonically, above all....So has someone used the Am9 in the End and how would you like it??? 

I can get some of these beauties but don't know at all how they sound and what their worth... Does sombody know when they where made and if it is a discrete scheme? Moreover did someone add Gain-Stage succesfully on them AM9/5 Pre's ? What would you say one of these would be woth?

Any help appreciated.

Kenobi said:

BBC Bump

Hey Fellas... Going all the way back


Alt this talk about schematics but nobody declares how he likes the units sonically, above all....So has someone used the Am9 in the End and how would you like it??? 

Click to expand...

Another BBC bump!

I just built one of the AM9 preamps and I'm very impressed with it.
I had the right transformers (six of each) already so it seemed like a no-brainer.

I used elements from both of the AM9/4 and AM9/5 designs...10k log pot for volume control as with AM9/5, TX balanced out and switchable low cut filter from AM9/4.
Otherwise they are basically identical. A couple of component values are slightly different and the AM9/5 has a 100R resistor on the -24v rail and an extra 100uf cap from -24v to GND, but that's it.

I've not given it a proper test in the studio yet, but talking through it sounds very full and nice, I can't hear any obvious distortion or nastiness of any kind and even at full gain, it's incredibly low in noise/hiss!

It doesn't have loads of gain, About 55dB according to the tech-sheet...But it's getting plenty of volume out of the ElectroVoice 635A I tested it with, Should be perfectly fine for most dynamics and condensers.

For anyone else who wants to build one, Here's a Mouser basket containing everything for one channel, except transistors (I used NOS Ti 2G308's) and transformers;
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=f88add42e3

I'm 99% sure everything else is in that basket, But you may want to double check against the schematic before ordering.

*Edit* - AM9/4 Schematic attached to post.