4032E Build

[waltzingbear]

I still don't understand, the +V should not appear at pin 5 or 6

you could see a positive voltage at that point, but it would be after a voltage divider of 1M and 100k from the +V. A bias voltage for the input caps, or about 1.8V

And that only with the rest of the console disconnected.

Alan

[horizonsound]

Hi Alan.

Hopefully not confusing you there, but by +ve I mean audio signal hot, in phase, 0°, and not a positive voltage.

Anthony.

[waltzingbear]

+ve is the power supply

so yes, confusing the issue

[waltzingbear]

for our purposes we shall refer to them as mix buss + and mix buss -

mix buss + connects to pin 5 on 82E26, coming from S5E pins 1/4/7&8/11&12.  LF/LB/RF/RB

mix buss - is 0V in the stock config

in a modified balanced config, it needs a buss with connections to each module, this connection would be a 10k resistor ( I think, I haven't checked the value, its the same as feeds the mix buss +) that connects back to the 0V on that module, if the buss feed has a cap in it this will too in the feed. In other words the exact same configuration as the mix buss + feed.  If external to the mother boards its a long buss wire with 10k resistors to each module or something similar.

this new buss needs a path, there would be 4 return busses. one for each old buss. They could be routed thru S5E 0V connections, like pin 2 or 3 for buss 1. etc.

a picture of S5E might be helpful.

look at the buss cards for the new buss.

this should give you plenty of things to look for.

Cheers
Alan

[waltzingbear]

Also, what is the provenance of this board and did you get an original manual with it?

Rant ON
the manuals for complex pieces of equipment, especially those that are custom made ARE TO BE INCLUDED IN THE SALE OF THE EQUIPMENT.

This looks like a factory job to me and it would have been included in the change sheets and Anthony would not be having this problem.

Rant OFF

Alan

[horizonsound]

Hi Alan,

I picked up the 651 through AES, so would have to go back to them and check if there is any documentation. It was not a complete console, but lots of E series parts. My 26 cards came via Andy.
I have no doubt I'll get to the bottom of it, but it will take some time.
When i get back home tonight I'll summarise the setup of all the parts, but am starting to zero in on some ways to sort it out.

Thanks so far for the input.

Anthony.

[waltzingbear]

As you are in contact with Andy already, see if he can't give you a run down on converting the console the rest of the way to balanced. I think you would like the results.

Its either one way or the other, remove the mods or finish implementing them.

Cheers
Alan

[waltzingbear]

start here

http://forum.sslmixed.com/index.php/topic,1226.msg7511.html#msg7511

http://forum.sslmixed.com/index.php/topic,807.15.html

https://groupdiy.com/index.php?topic=24070.0

[horizonsound]

Hi Alan,

Here is my best attempt at a schematic from the lower buss board, through to the 651, following the S5E quad bus.
There are no resistors inserted or bridged along the route. There are some of the mods on each channel though. A bit of a mix and match of old brown, mod brown, and mod black modules.

It looks like for the bulk of it, that it is still set up as unbalanced for the most of it, and might be easier to go down that path. This console being only 32 channels, I thought i read (thanks for the links) that the balanced option helps the noise floor on larger consoles where it is more susceptible (?)

Michael at AES advised that there is documentation, but in Japanese. Luckily I have a long term friend who's job is to translate technical documents from Japanese. What luck.

Schematic from 82E19 lower bus card to 651 / 26 card


Underside of S5E connector on 82E19 lower bus card


Top view of both upper and lower bus cards


Typical "black" channel with resistor mods

[waltzingbear]

your last photo shows the "coat hanger mod", you see how simple that part is.

what isn't clear to me yet is the path from the lower buss card to S5E. The coat hanger mod feeds pin numbers ? (in the 70s)
Andy seemed to say that the later lower card did not require any mods, so you may be almost there.

regarding my earlier comments on the capacitor needing to be 220 or 470uF, that was a misconception on my part that the cap you were talking about was in series with the 10K resistor, it is in parallel and is an RFI filter. Ignore previous comments.

[horizonsound]

There are two parts to the mod on the channel modules.

The 4 x 15k vertical resistors feeding the cue sends (-) to pins 69, 71, 73 and 76 on the upper edge connector, and then the coat hanger wire which goes from pin 78 (mix 0v) on the lower edge connector, to what seems to be the mix amp- position on pin 10 of the lower edge connector - but the ground trace has been cut to the pin.

[waltzingbear]

I haven't ever looked at a balanced mod, but I would expect the same structure to feed the mix buss -, pin 8 on hte 26 card. One per buss


a word on terminology complexity.
Pins 5/6 is the inverting (-) input to the summing opamp. Pin 8 is the non-inverting (+) input.

mix buss + goes to the inverting (-) input of the opamp. mix buss - goes to the non=inverting (+) input of the summing opamp

this is why its important to use unique terms for the lines.

[horizonsound]

Thanks Alan,

Sure is getting complex here, but am confident a solution is near.

I've run a signal in through the echo return to the LF 26 card, with the 26 card removed, simply to get a clean signal straight on to the mix buss.
The signal passes correctly, and drops about 1v p-p post the 15k resistors, and on to pin 5/6. There is a dc offset of around 0.6v
The echo return level works perfectly, and pans it correctly to the RF slot, and also the LB / RB slots.

When the 26 card is inserted, the signal "disappears" and all i have is the 0.6v dc offset on pin 5/6 - as if something is shorting it on the 26.

See some pics.

26 card connector testing points


26 card

[waltzingbear]

that looks correct

we need to focus on the other input now, pin 8

is what you drew from the schematics or did you verify it as the AS BUILT drawings?

[horizonsound]

As built drawings!

Schematics are slightly different, mainly component values. (i.e. the 10k resistor in lieu of a 1k + 20k trim)

Actually, it’s a 100k fixed resistor from pin 8 to 0v.