XLR distortion..?

[vldr]

Yesterday I connected my arcam C30 preamp to my 2 arcam p1 monoblocks over XLR.

While having a late night listening session I noticed a certain bandwith range (midrange) being heavily distorted.
This happened on 2 sources:
- Fm Tuner connected via RCA to the preamp
- Settopbox connected via toslink to DAC D33 and DAC via RCA to preamp.

Tonight I will remove the XLR's between my preamp & poweramp en switch back to the RCA connections.

- Could the XLR's be the cause?Maybe the mix RCA (from source->preamp) & XLR (pre->power)?
- Have read something about ground loops too, but then I should hear a hum. I don't hear a hum, I heard distortion...

Extra info:
- The amp was playing quietly.. Late night session you know..
- Schematics attached to this thread.

 

[sergeauckland]

Hard to diagnose at long distance, but firstly, is the distortion in both channels or only one? If only one, then it's possible that the balanced output of the preamp or balanced input of the power amp is faulty. If in both, it's pretty unlikely for the same fault to exist in both channels, so I would check that the cables have been wired correctly. Pin 1 of the XLRs should go to the cable screen only. Pins 2 and 3 should go to the two cores, and be a simple straight-through connection.

There's no reason why the RCA connections from the sources and XLR connection to the power amp would cause distortion.

S

 

[vldr]

Thanks for your reply.

It's happening on both channels. I will check on cable connectivity tonight.. Maybe I can post some pics too.
In the meantime someone else though about a gain difference between my phono's & xlr connections..

 

[antcollinet]

Thanks for your reply.

It's happening on both channels. I will check on cable connectivity tonight.. Maybe I can post some pics too.
In the meantime someone else though about a gain difference between my phono's & xlr connections..

What is the preamp? Is it passive?

 

[sergeauckland]

Thanks for your reply.

It's happening on both channels. I will check on cable connectivity tonight.. Maybe I can post some pics too.
In the meantime someone else though about a gain difference between my phono's & xlr connections..

As the preamp and power amp are both of the same manufacturer, any difference in output voltage between the phono and XLR outputs should be exactly compensated by the difference in input sensitivity of the power amplifier inputs. Even if it's not, the only difference will be to require the volume control to be turned down a little. No reason for any distortion.

S.

 

[vldr]

What is the preamp? Is it passive?

Erm, the ARCAM C30 Preamp is an active in my opinion..
I posted the service manual in the previous post.

 

[vldr]

As the preamp and power amp are both of the same manufacturer, any difference in output voltage between the phono and XLR outputs should be exactly compensated by the difference in input sensitivity of the power amplifier inputs. Even if it's not, the only difference will be to require the volume control to be turned down a little. No reason for any distortion.

S.

So i thought, that the C30 & p1 monoblocs, which used to be sold together should be a perfect match.
They do advice though, to connect the pre with the monoblocs with phono's when the distance is < 3 meter. The distance between the units is < 1 meter so i should use the phonos.. But why does it get distorted.. I'm thinking something must be wrong..

 

[antcollinet]

Erm, the ARCAM C30 Preamp is an active in my opinion..
I posted the service manual in the previous post.

Missed that in the OP - sorry. (write 50 times "must not skim read").

 

[daftcombo]

Did you switch back to RCA yet, to check if the distortion is gone?
Perhaps, for whatever reason, something broke in your pre-amp when you installed the XLR cables.

If there's no distortion with the RCA cables, then something must be broken, either in the XLR output of your pre-amp, or in the XLR input of your monoblocks. But before trying with another pre-amp or set of blocks to localize the problem better, try a different XLR cable brand.

 

[vldr]

Did you switch back to RCA yet, to check if the distortion is gone?
Perhaps, for whatever reason, something broke in your pre-amp when you installed the XLR cables.

If there's no distortion with the RCA cables, then something must be broken, either in the XLR output of your pre-amp, or in the XLR input of your monoblocks. But before trying with another pre-amp or set of blocks to localize the problem better, try a different XLR cable brand.

I will try tonight. At the time writing it's 11.50 am in my country. So still some hours to go ;-)

 

[vldr]

Forgot to mention this.
So yesterday i noticed the distortion playing a radio station on my set top box connectec over toslink to my dac & preamp
I then noticed the same distortion playing the same radio station on my arcam analog tuner connected via phonos to my preamp.

I then searched the same track on apple music and played it via ipad, usb to my dac and preamp and did NOT notice the distortion..

 

[sergeauckland]

So i thought, that the C30 & p1 monoblocs, which used to be sold together should be a perfect match.
They do advice though, to connect the pre with the monoblocs with phono's when the distance is < 3 meter. The distance between the units is < 1 meter so i should use the phonos.. But why does it get distorted.. I'm thinking something must be wrong..

The real purpose of a balanced connection is to reject hum and noise with long cables. For domestic length cables, say up to 10-20m or so, an unbalanced connection is fine, although normally, using a short balanced connection does no harm, and will help reduce the effects of any hum loops. In other words, if you have balanced connections, you might as well use them, as they'll do no harm, and might be beneficial even with short cables.
In your case, I think there's something going on which has nothing to do with the connections being balanced or unbalanced, short or long cables. There may be a fault in the pre-amp output or power amp input circuitry, so needs further investigation. You may want to try going between the phono output and XLR inputs, and vice-versa to see if you can identify where the possible fault lies, or get the units on the bench and apply some test equipment.

S.

 

[vldr]

Mmh, I also think there might have happened something with it.
I have this function generator & scope. Should I feed it a signal and see if what is coming out has the same shape, amplitude will be bigger if I put it louder of course..

 

[daftcombo]

The real purpose of a balanced connection is to reject hum and noise with long cables. For domestic length cables, say up to 10-20m or so, an unbalanced connection is fine, although normally, using a short balanced connection does no harm, and will help reduce the effects of any hum loops. In other words, if you have balanced connections, you might as well use them, as they'll do no harm, and might be beneficial even with short cables.

I thought the same before replacing the 2m RCA to XLR cables between a Little Bear MCII passive pre-amp and Genelec 8030C: using 2m XLR to XLR instead reduced the hum/hiss audibly.

 

[sergeauckland]

Mmh, I also think there might have happened something with it.
I have this function generator & scope. Should I feed it a signal and see if what is coming out has the same shape, amplitude will be bigger if I put it louder of course..

Yes, that would be worth doing, as you should be able to see what's happening to the signal connected either way. By a process of elimination, you should be able to work out where the problem lies.

S.

 

[vldr]

I will check tonight. In a first quick check on the schedule it could easily be the burr brown drv 135UA.
This is the IC which produces the single ended signal in a double balanced one.

Still strange though, that it's exactly on both channels...

 

[vldr]

O boy, what a night..
So I investigated some things...

1. Opened up the C30 pre.

Nothing to see, took a good lock on some soldering points and renewed them.
No capacitors that are bulging, had a few capacitor tests, all of them are within tolerance, ...
XLR connections look nice.
Had a function generator hooked up an checked the sinus output and it did look okay... (see pictures)

Assembled the C30 and put it back in the chain to do some further investigating.

2. Tried 3 different interconnects,

3. Checked XLR cables (see pictures) and changed to phonos

4. Tried another dac

5. Tried another preamp

6. Tried another poweramp, then just tried an integrated arcam.

Everything resulted in the same distorted sound. So the speakers must be blown then? Could not believe that, I never play my speakers loud...
Maybe there was something else that caused them to be blown? But both speakers, in the same way??...

7. Then I was thinking of what i said yesterday. The distortion only appears with a specific radio station (that one that I happen to like the most).
It happens when I listen to it over internet radio (ipad, iphone over usb to dac to....) but also when I listen to it over FM (tuner to preamp to...)
I took a look at the playlist, there was a track playing: Midnight (the hanging tree) remix from Henrik Schwarz - electronic music - of which the bass was heavily distorted. So I took the test, searched on apple music, connected my Ipad to the DAC and played the song, only to notice that the distortion does NOT EXIST... No distortion at all, play it loud, play it silent, no distortion at all.

How is this possible?

I know every radio station ads its own coloration to their broadcast to give their station a unique sound. I think they might have changed it somewhat a week ago, they've started with a "2-week-special: all music from 2000-2010" and I think (not sure) they changed something in their sound signature... Could it be that they did a real poor job on this? Maybe there's something in my stereo frequency response that's not matching with the filtering they use? Or am I getting crazy?
If I listen to the station on my Iphone earbuds or at work over my bose companions I don't think I hear any distortion.. I did hear a new sound signature..

 

[vldr]

And then... it became silent.

I'm putting my hopes on you guys to give me an acceptable explanation.. I won't figure this out.

Maybe I'm just out of my mind? But at least have the decency to tell me then. LOL

 

[vldr]

Update
Took a better look on my speakers. My last potential solution.

Took both woofers out, it' the type of woofer with a midrange tweeter in the middle (don't know the exact name of this type of speaker).
I turned one woofer 45 degrees, thought the inner cone was touching the edge somewhat. Thought turning it and let gravity do it's work might help.

Of one speaker was the positive cable loose, I could pull it from the connection. Soldered it back in place...

Further nothing special to see.

 

[vldr]

Last update: after all, it just turns out my digibox/set top box was causing this distortion.
The only strange thing about it, it's only happening on that specific channel.

Speakers are okay, dac is okay, cables are okay, ... Luckily!