Audio Out for Eumig 824 Sonomatic

[Ethan Knightchilde]

At the setting shown in the photo and pressing the black probe into the 9 o’clock position and the red into the 6 as much as I can (their contacts are not very long compared to the pins on a DIN connector), I get a brief reading of about 18.xxx. Couldn’t get anything from the 3 o’clock position. Those three terminals all definitely have metal contacts inside.

Maybe part of the problem in getting a reading is that the probes for the multimeter are not long or thick enough to make a good contact?

[Steve Klare]

Paperclips are an electronics essential: Insert the wire into the connector to bring the connections out. You can stick one probe on clean metal on the chassis since all the measurements should be to ground anyway. The third prong on the unplugged(!) power cord is also good for this.

(The majority of the paperclips I use these days AREN'T for documents!)

Also, please switch to the 200kOhm range. Even at 50,000 Ohms you would be out of range on the 20k setting.

[Ethan Knightchilde]

Paperclips are an electronics essential: Insert the wire into the connector to bring the connections out. You can stick one probe on clean metal on the chassis since all the measurements should be to ground anyway. The third prong on the unplugged(!) power cord is also good for this.

(The majority of the paperclips I use these days AREN'T for documents!)

Also, please switch to the 200kOhm range. Even at 50,000 Ohms you would be out of range on the 20k setting.

Starts high but settled to about 51.6 with black at 9 o’clock and red at 6 o’clock. No reading with black at 9 and red at 3 o’clock. That’s progress tho!

[Steve Klare]

Ok, let's bring this on home:

"6 O'clock"=Pin 2
"9 O'clock"=Pin 3
"3 O'clock'"=Pin 1

Since your connector is installed upside-down compared to the drawing. (Please check my math here?)

"Starts high but settled to about 51.6 with black at 9 o’clock and red at 6 o’clock"
-so: 51,600 Ohms Pin 3 to Pin 2: that's what I'd expect. This should be a line level output.

"No reading with black at 9 and red at 3 o’clock."
I'm taking this to be an open circuit: if it is, you should see the same indications with the probes just dangling in the air.

The more proper measurement would be 3 O'clock' (Pin 1) to 6 O'clock(Pin 2) but if one is open circuit, they should both be open.

This means that Pin 1 may be installed but not used. Maybe there was some other place they needed pin 1 loaded in the same shell and it was less confusing to have a common part in the big bin with all the pins used loaded.

(It's easier to have all the wiring harnesses at the car factory built with the connector for the convertible top switch than straighten out the fifty convertibles that got just assembled with the sedan harness!)

Here's something else to try (just for fun): measure 6 O'clock(Pin 2) to exposed metal on the chassis and/or the third prong on the plug

[Ethan Knightchilde]

Ok, let's bring this on home:

"6 O'clock"=Pin 2
"9 O'clock"=Pin 3
"3 O'clock'"=Pin 1

Since your connector is installed upside-down compared to the drawing. (Please check my math here?)

"Starts high but settled to about 51.6 with black at 9 o’clock and red at 6 o’clock"
-so: 51,600 Ohms Pin 3 to Pin 2: that's what I'd expect. This should be a line level output.

"No reading with black at 9 and red at 3 o’clock."
I'm taking this to be an open circuit: if it is, you should see the same indications with the probes just dangling in the air.

The more proper measurement would be 3 O'clock' (Pin 1) to 6 O'clock(Pin 2) but if one is open circuit, they should both be open.

This means that Pin 1 may be installed but not used. Maybe there was some other place they needed pin 1 loaded in the same shell and it was less confusing to have a common part in the big bin with all the pins used loaded.

(It's easier to have all the wiring harnesses at the car factory built with the connector for the convertible top switch than straighten out the fifty convertibles that got just assembled with the sedan harness!)

Here's something else to try (just for fun): measure 6 O'clock(Pin 2) to exposed metal on the chassis and/or the third prong on the plug

Agreed. 1,2,3 clockwise starting at 3 o’clock seems correct to me.

I quickly tried red to pin 2 and black to the exposed metal near the lamp housing. Varied a bit but settled around 1.0. I can take the back off a bit later and do it properly.

[Steve Klare]

If that's really 1.0 Ohms, it's not unexpected.

What does it say if you just touch the two probe tips together?

[Ethan Knightchilde]

I’ve attached photos of the readout for the “standby/no reading” display (“1 . “) and the zero display it settles to when touching the two probes together (“00.0”). With that in mind, touching the chassis with the black probe and terminal 2 with the red yields 1.0 ohms at the 200kOhm dial setting.

[Steve Klare]

OK, the thing to do when you get down into the low readings on a scale is shift gears: try that same measurement in the 200 Ohm range. With this you'll see that same measurement, but with more digits of accuracy.

I'm guessing your "1 ." means your measurement has exceeded 200kOhms (as if at the time the probes were just out in the breeze.). Now, if you were actually measuring a 1 Megohm resistor you could shift up to 2,000 kOhms and see that measurement. When you are up in that maximum range and you see "1 ." you can start to call that an open circuit, especially if you are expecting something much, much lower like 50,000 Ohms.

(In the real world there are no true open circuits or short circuits: just "close enough".)

[Paul Adsett]

So what's the verdict here! Does the Eumig 824 only line output a single audio channel ( left stripe 0R right stripe) at a time ?

[Ethan Knightchilde]

OK, the thing to do when you get down into the low readings on a scale is shift gears: try that same measurement in the 200 Ohm range. With this you'll see that same measurement, but with more digits of accuracy.

I'm guessing your "1 ." means your measurement has exceeded 200kOhms (as if at the time the probes were just out in the breeze.). Now, if you were actually measuring a 1 Megohm resistor you could shift up to 2,000 kOhms and see that measurement. When you are up in that maximum range and you see "1 ." you can start to call that an open circuit, especially if you are expecting something much, much lower like 50,000 Ohms.

(In the real world there are no true open circuits or short circuits: just "close enough".)

It settles around 9.1 or so at the 200 ohm setting.

[Ethan Knightchilde]

So what's the verdict here! Does the Eumig 824 only line output a single audio channel ( left stripe 0R right stripe) at a time ?

No idea at this end. I’m hoping it at least does a mix down!

[Steve Klare]

Hi Paul,

I think Ethan's ohmmeter measurements show that there are only two active pins in that connector. Since one of them has to be a signal return, then there is only one left to be "signal" therefore this machine can't be outputting two channels of audio.

The fact that his schematic has only one opamp amplifying the signal from the head kind of reinforces this theory.

It gets interesting when you look over in the West where the heads are:
.

Now, in my imagination, this is a workable arrangement to get a twin track soundhead. That switch imediately to their East is three positions. Slid upwards it shorts the upper head and allows the lower head only to be amplified. In the middle, it shorts nothing and puts the two heads in series for blended monaural from the two channels. Slid low, it shorts the lower head and allows the upper head only to be amplified. So this should be the right diagram for this machine.

Those two coils in series with each head I believe are a sighting of those famous hum-buck coils out in the wild! (Get your binoculars!)

(Of course these symbols aren't the same ones I'm used to, so I'm interpreting them the way I want to!)

The recording heads are also in the schematic, way down south.

That other schematic for 810D also has two heads, but that's different: they are marked "Super 8" and "Regular 8" because that one is built for both.

[Ethan Knightchilde]

Interesting. The 824 is dual 8 but doesn't have separate sound heads for each gauge.

Anyway, is the suspicion that the DIN output is a mix down of whatever the heads pickup based on the switch for track 1, 1+2, or 2?

[Ken Finch]

The user manuals for the Eumig 810d and the Baur 610 both show which pins should be used for the line out. I run the output from both to my Yamaha audio video amp via a Realistic mixer with no problems. I use standard screened leads for all the interconnects. Soldering DI N plugs can be a bit tricky. Use a small vice to hold the plug which also will act like a heat sink. Ken Finch😉

[Steve Klare]

"Anyway, is the suspicion that the DIN output is a mix down of whatever the heads pickup based on the switch for track 1, 1+2, or 2?"

Yes.