BBE 383 users help please - XLR / 1/4" operation

[Fangry]

Hi,

I only just tried - at a gig, of course - running my 383 pre's balanced XLR and unbalanced 1/4" outputs simultaneously, the former to the board and the latter to my power amp. The problem is I got no signal from the 1/4" output. Luckily the house had a DI box that saved my butt and we had a blast.

I've always used the unbalanced jack to run my power amp. I did some troubleshooting afterwards and found that the unbalanced output indeed seems to be muted when I stick an XLR cable in. Both outputs function perfectly on their own, as do the crossover outputs and FX send in any configuration.

Surely this can't be intentional? There seems to be little point in a preamp that can't feed the board and a monitoring rig at the same time. The manual of course dercribes it running this way and has the schematics, but unfortunately I'm not proficient to make heads or tails of them. Seems like a weird symptom to be caused by a fried component, but then again what do I know.

So, a feature or to a repair shop with the pre? Many thanks for any input!

[jnewmark]

I've used the 383 since they first came out, and never had this problem using both the the 1/4 and xlr out. Something is wrong internally.

[Fangry]

Yeah, so I figured. Gonna take a peek inside to see if anything's visibly wrong - probably not - and look for a repair shop. Or look for a cheap DI box.

[Fangry]

Not having a backup I still haven't gotten around to taking the pre to a shop... I did email BBE about the problem and got the following response:

Originally Posted by BBE

Hello,
It sounds like it could be an impedance problem, that would be the only reason both these outputs not work at the same time. http://www.bbesound.com/products/manuals/383_manual.pdf , this is the link to the manual, the schematic is towards the end of the pages.

I am assuming he is talking about an impedance problem within the device, since I don't see how other components in the signal chain could cause this... Hopefully it's something a tech will figure out.

[craig.p]

Just to reinforce what JN said, page 8 of the manual (PDF page 10) shows an illustration of both being used at once.

[Fangry]

Originally Posted by craig.p

Just to reinforce what JN said, page 8 of the manual (PDF page 10) shows an illustration of both being used at once.

Yup, I noted that in my original post. Just thought I'd post an update.

[craig.p]

Whoa, sorry 'bout that, Fangry. I still haven't learned not to skim OPs.....

[runmikeyrun]

I'll echo the others, mine would work simultaneously. Do you like that preamp? I found the EQ weird and was never able to get a really good sound out of it.

[DD_BigBottom]

I looked at the schematics shown in the manual you provided the link to.

According the output schematic, the XLR and 1/4" unbalanced outputs are electronically isolated
from each other, so you "should" be able to use the XLR and 1/4' at the same time with no
problems.

If each output seems to work OK on its own, then it is unlikely that you have any fried components.
There is an op-amp that directly drives the unbalanced output and also feeds the electronically
balanced output circuit. If there were any problems here then it would seem that you would
loose both outputs and not just the unbalanced (main) output.

It is also possible that your unit is not the same as what is shown in the schematic. Some things
to check out is the XLR cable. Make sure it is Balanced and not wired unbalanced where pin 2 or
pin 3 is strapped to ground. If this is the case, then it is possible for the XLR cable to short out
the 1/4" output. Also check out the 1/4" cable and make sure it is good.

The balanced output impedance is 100 ohms and the unbalanced is 100K ohms. If your amp has
an impedance less than 100K ohms then it is possible the BBE is getting loaded down and loose
output. If this were happening, then the unbalanced output would have problems whether or not
the XLR output was being used at the same time.

If the unit is out of warranty, open up the cover and check to see if anything is shorting between
the XLR and 1.4" output.

Hope this helps.

[Fangry]

Originally Posted by DD_BigBottom

Some things to check out is the XLR cable. Make sure it is Balanced and not wired unbalanced where pin 2 or
pin 3 is strapped to ground. If this is the case, then it is possible for the XLR cable to short out the 1/4" output.

Aaaaand we have our winner!

Today I went to the rehearsal place to muck about with the pre, opened it up, didn't see anything out of the place, connected both outputs to the mixer - and whaddayaknow, I get signal on both channels.

Turns out that indeed if you plug an unbalanced cable to the balanced XLR out, it mutes the 1/4" output - probably shorts it out like you said. I can't really tell how on earth I missed this the last time I troubleshot the amp. I probably figured that since the mixer's line input is 1/4", I'd use an XLR to phone plug (TS of course) cable. Silly me.

What's interesting is why I first had this issue at the outdoor park gig we played - the stage crew probably used an unbalanced mic cable or there was an adapter somewhere on the way to the desk that caused this. Odd, given that it's a quite prominent venue in downtown Helsinki that in the summer hosts pro groups of all genres every day. Better put "BALANCED XLR LINE OUT" on the stage map..

Originally Posted by runmikeyrun

Do you like that preamp? I found the EQ weird and was never able to get a really good sound out of it.

It gets the job done. I have no problem with the eq, I much prefer it to say a Fender tone stack as I can actually see what frequencies I am dialing in. Haven't gotten a great sound out of the pre by myself but then again I haven't really tried. In band context I boost the mids and cut through nicely, something I wasn't able to do with my old Ampeg SVPCL which I sold after getting a nice deal on the 383 and made a nice profit.

Anyway, problem solved, it was once again due to user error... It really never crossed my mind that running both outputs unbalanced could cause such behavior. Many thanks guys, especially DD_BB for your thorough answer!

tl;dr: Kids, triple check your cables!

[DD_BigBottom]

AWESOME!

I've been to Helsinki in the winter time to do a sound system install at the Teak/Vas theater.
Most of what I can remember is that it was f'ing COLD and every time I went from outside to
inside, my face felt like it was going to explode.

Glad to hear your rig is Alive!