Very Bizzarre Problem (analog chain)

[aleatoric]

Edit: Problem Solved.

Setup is Mytek DAC->Sontec MEP-250ex->FCS P3S ME->Mytek ADC

I just got the Sontec today and have a very bizarre problem.

Sontec works great plugged in by itself.

P3S works great plugged in by itself.

When I hook them both together I get a -3.4dB drop on my right "channel" on the P3S but ONLY with the P3S engaged. P3S in bypass all is normal. Really baffled here.

Doing a straight loop from Myteks to the P3S and all is fine, likewise for the Sontec. When hooked together I get this -3.4dB drop when the P3S is engaged.

The P3S is a true bypass unit if that is of any help. Really scratching my head here.

[William Bowden]

If you swap the cabling around does the fault transpose?

The King

[aleatoric]

Originally Posted by William Bowden

If you swap the cabling around does the fault transpose?

The King

Let me try.

You mean like P3S -> Sontec instead of Sontec -> P3S?

[aleatoric]

This really makes no sense at all to me.

- Sontec is fine just by itself or with the P3S in bypass
- P3S is fine just by itself
- Sontec going into an active P3S = a -3.4dB drop from whichever channel on the P3S the Sontec's channel 2 is feeding.

Cabling should not be an issue (I tried swapping cables anyway) because when the P3S is bypassed all audio is still going through all the cables (just not the P3S circuitry). When testing the units individually the other units were still powered up so it is not a matter of power interference or something of that nature either.

Very strange. Perhaps I am overlooking something stupid.

[manman]

If you are using balanced cables there is hot, negative, and ground.

So I'm thinking one unit has "+&ground", but no negative output.

Also try balanced and unbalanced cables.

Try reversing Sontec & FCS P3S ME

I had another RME 800 which i sold, it had same problem, when i tested it did not have negative output. thats where -3db drop comes.

[aleatoric]

Originally Posted by manman

If you are using balanced cables there is hot, negative, and ground.

So I'm thinking one unit has "+&ground", but no negative output.

Also try balanced and unbalanced cables.

Try reversing Sontec & FCS P3S ME

I had another RME 800 which i sold, it had same problem, when i tested it did not have negative output. thats where -3db drop comes.

But why only on one channel? Is there a solution here?

[manman]

Because 1 channel "-" output may be broken stike lol

Test it either with testing equipment or simply by using cables

[aleatoric]

Originally Posted by manman

Because 1 channel "-" output may be broken stike lol

I do not think that is the case. Both units work fine on there own. It is just when I chain them together the problem comes up and only with the P3S engaged.

[manman]

try this testing technique on one channel at a time:

1. get 2 balanced small cables
2. get regular small wires
3. start connecting +,-,ground on Sontec MEP-250ex out --> P3S engaged
4. see if all work properly just with +, just with -, both +&-

I think when you add "-" volume boosts by 3db

[aleatoric]

Making some progress....

Here is some info about this Sontec Output:

Connector:
XLR-Style, Pin1 grounded, Signal on either Pin 2 or 3
Source Impedance:
80ohms, unbalanced function of both the architecture

So it appears the Sontec's output is unbalanced, which I kind of already knew but did not think it would be a problem (and was told by others it should not be).

Here is some info about the FCS P3S's In's and Outs:

• Input Impedance: 20K Ohms balanced, 10K Ohms unbalanced

• Output impedance: 50 Ohms

• Output automatically configures itself for balanced or unbalanced loads. (Pin 3 must be grounded during use with unbalanced inputs)

So it appears the P3S should be able to handle an unbalanced input just fine.

I tried going P3S into the Sontec and there was again a level drop when engaging the P3S but this time it was on both channels. Still scratching my head here and also a bit cranky because I drove 5 hours to pick the Sontec up today. I left Roger of FCS and message and I'll see what he thinks. Any additional help is appreciated.

[manman]

So can you connect manually ground and hot from Sontec going to compressor hot+ground only.

What I mean is: use wires and balanced cables to connect manually.

I'm thinking you are shortening ground and negative: Sontec may shorten negative and ground internally on output.

[aleatoric]

Originally Posted by manman

So can you connect manually ground and hot from Sontec going to compressor hot+ground only.

Not really sure how to do that. Should I open up an XLR connector and snip off the negative so it is just hot and ground?

[Paul Gold]

Originally Posted by aleatoric

- Sontec going into an active P3S = a -3.4dB drop from whichever channel on the P3S the Sontec's channel 2 is feeding.

My guess is that one channel of the Sontec is wired differently than the other since the problem follows the Sontec channel. You may have to open up the box and poke around.

[Adam Dempsey]

Originally Posted by Paul Gold

My guess is that one channel of the Sontec is wired differently than the other since the problem follows the Sontec channel. You may have to open up the box and poke around.

My thoughts as well. And yes, aleatoric, if it's anything like an MES 462 it should be unbalanced in and out, pin 3 hot.

[aleatoric]

FWIW the MEP-250ex is brand new. Still not entirely sure what to make of this because the Sontec runs fine going straight to the ADC. Following it with the P3S and channel 2 has this level drop thing. I'm starting to think that since the P3S automatically detects for balanced/unbalanced that perhaps something with the wiring in the Sontec is telling the P3S that one of the channels is balanced and the other is unbalanced and that is causing the drop in level. Really just a guessing though.

[Adam Dempsey]

Originally Posted by aleatoric

I'm starting to think that since the P3S automatically detects for balanced/unbalanced that perhaps something with the wiring in the Sontec is telling the P3S that one of the channels is balanced and the other is unbalanced and that is causing the drop in level. Really just a guessing though.

It's a fairly well educated guess by now. ; ) And it would explain the symptoms.

[aleatoric]

Sontec:

"XLR-Style, Pin1 grounded, Signal on either Pin 2 or 3"

P3S:

"Output automatically configures itself for balanced or unbalanced loads. (Pin 3 must be grounded during use with unbalanced inputs)"

Maybe that is my problem right there. Perhaps I need to make special XLR cables with Pin 1 ground going to Pin 3 ground and Pin 2 connected?

[William Bowden]

Originally Posted by aleatoric

Let me try.

You mean like P3S -> Sontec instead of Sontec -> P3S?

No I meant swapping the left and right cabling around on the input to the FCS (leave the output of the Sontec as it is). Just to try and figure out if its the output of the Sontec or the FCS, ie if the fault swaps channels on the FCS it may be some weird loading of that particular channel of the Sontec).

The King

[aleatoric]

Originally Posted by William Bowden

No I meant swapping the left and right cabling around on the input to the FCS (leave the output of the Sontec as it is). Just to try and figure out if its the output of the Sontec or the FCS, ie if the fault swaps channels on the FCS it may be some weird loading of that particular channel of the Sontec).

The King

Tried it, the level drop follows channel 2 of the Sontec.

[manman]

Did you do the signal testing on and tried hot+ ground configuration?

[aleatoric]

Originally Posted by manman

Did you do the signal testing on and tried hot+ ground configuration?

No I have not. How exactly do I do this. I apologize but I really do not understand the instructions you gave me. Should I open up an XLR cable and disconnect the negative from hitting the XLR connector???

[aleatoric]

Just got off the phone with Burgess. He is stumped too. The EQ is going back to him today, really hoping this gets sorted out.

[aleatoric]

PROBLEM SOLVED!!!

As I was packing up the Sontec to send to Burgess I got a call from Roger of Foote Control Systems. He told me to solder a piece of copper wire from pin 1 to pin 3 on my XLR cables. That did the trick! This is what you have to do if you are running unbalanced outs into the P3S. Now why this was only happening in one channel I am not completely certain but I have a theory. The Sontec outputs are said to run on either pin 2 or 3. Well I think one of the outputs was 2 and the other 3. Not sure which is which but I guess the P3S was identifying one input correctly as either balanced or unbalanced and the other it was not sure how to handle because I had not grounded pin 3 to 1.

I want to thank everyone for their help and also the 3 personal messages I have received wishing me the best of luck getting to the bottom of this. I will write all 3 of you back but right now I'm gonna re-rack everything and get to know this Sontec! In a few days I will probably make a post regarding my impressions on the FCS P3S ME as well as the Sontec MEP-250ex and perhaps some general thoughts on finally going outboard after working digitally for awhile. I have had the P3S ME for about a week now and am in love. Hoping this Sontec leaves the same impression!

[joeaudio]

Hey Mark. Glad you worked that out. I'm also glad to see you starting
with some nice analog processors. It's a shame that you missed the days
of multi room mastering houses. You would knock on the door across the hall and an engineer who had exprerienced something similar would come into your room and (maybe with the help of another engineer or an in house tech) work it out. Now we type a question on a forum.

As long as you worked it out it's all good I suppose.
Don't forget to put the Sontec on your gear list on your site!
Now get on with your bad self.

[Paul Gold]

Most likely the problem is that one channel of the Sontec has Pin 3 tied to Pin 1 and the other channel doesn't. You can test this with an ohm meter.

You should also check absolute polarity if you're into getting that right. With pin 2 hot it should be right though.

[Peakly]

Originally Posted by aleatoric

Edit: Problem Solved.

Nice! Cool you figured it out. I know the feeling. I've been trying to figure out a vocal edit that was driving me nuts, and I just found a solution that is simple and sounds good.

Post something about that compressor. I'd never heard of it till you mentioned you got one.

Mychal

[William Bowden]

Originally Posted by Paul Gold

Most likely the problem is that one channel of the Sontec has Pin 3 tied to Pin 1 and the other channel doesn't. You can test this with an ohm meter.

You should also check absolute polarity if you're into getting that right. With pin 2 hot it should be right though.

+1

I'd open up the Sontec and physically inspect the wiring.

The King

[RogerFoote]

Yup, the FCS comps need pin 3 and 1 tied for unbalanced sources and loads.

Glad it worked out aleatoric, but still strange about the channel differences. Agreed with the previous posters about checking the connections in the Sontec...

Absolute phase is tested on the FCS products here at the factory, so that should be good.

best
Roger

[aleatoric]

Originally Posted by joeaudio

Hey Mark. Glad you worked that out. I'm also glad to see you starting
with some nice analog processors. It's a shame that you missed the days
of multi room mastering houses. You would knock on the door across the hall and an engineer who had exprerienced something similar would come into your room and (maybe with the help of another engineer or an in house tech) work it out.

Thanks for the kind words Joe. Yeah, where is Randy when you need him! Pretty sure I helped you out once or twice with some Sonic stuff during my intern days too. Nothing like multi room studios where everyone can lay a helping hand.

I'm grateful for the excellent and friendly support from both Roger Foote of FCS and Burgess of Sontec today. They were both incredibly helpful. It seemed Burgess and the rest of the Sontec crew were really scratching their heads today until Roger filled me in on the cable solution for unbalanced units going into the P3S. Always cool to get a chance to talk to the head designer behind a unit. Burgess had me laughing on the phone quite a few times.

Absolutely loving the Sontec. Semi-detailed impressions to follow in a couple days along with the P3S in its own post!

[priko]

yes, please post about the P3S ME