Trouble with DBX 234LX Crossover

[HipoFutura]

Just bought this new a hooked it up. It use XLR connectors and all my amps (tube mono-blocks and Phase Linear 400) use RCA. I bought XLR to RCA adapters at Guitar Center. I'm using the 234XL to move to tri-amp. I previously used a Paradigm X-30 to bi-amp my L100s and subs. I'm testing the hi-freq x-over with a set of properly working 035TIA.

The problem I'm having is that I've just about completely lost gain on the low and hi freq outputs. The mid is strong. The x-over points move when I change the front panel control, but the gain is WAY too low. Could this be related to the RCA to XLR conversion?

Don

[johnaec]

The first thing I'd do is move the amp that's now powering the mids to the lows instead, and vice-versa. If the lows are now the correct volume, I'd say it's a sensitivity mismatch between different amps.

John

[moldyoldy]

Sounds like the common problem with interconnecting balanced pro gear with unbalanced consumer audio. In addition to the differences in cables and connections, levels and impedances vary as well. Consumer line levels are mostly -10dB (.3VAC), while pro gear uses 0dB (.775VAC), or occasionally +4dB. Consumer line outs need to see a high impedance (>10K), while pro line inputs are looking for low-Z sources (<600). You've correctly diagnosed the problem of not enough gain in the line stages. You might try using the"tape out" on your source, which is often at a higher level and more tolerant of Z ranges. The most common method is to buy a unit made for the purpose, for example the Rane BB44X, which is a stereo passive solution (only xfmrs) that provides RCA to XLR (and vice versa) and matches levels and impedance. The Rane tech library has some good info as well.

Be aware that no solution (that I know of) is a perfect interface, you may still have S N/R issues, hum, etc to deal with. Consumer and pro gear aren't like peanut butter and chocolate, that work well when accidentally combined.

[HipoFutura]

Today I will switch the amps around and hopefully confirm the problem.

Moldy, I understand the concept but not the specifics. In the diagram below you can see the line voltages I've taken from the manuals for each piece fo gear. If I understand correctly I'd need about four of the Rane BB-44X converters (1 for pre-amp output, and 3 more for each power amp). That's more complicated/expensive than I'd like to go. Can I build converters given the line specs I have in hand.

The DBX 234XL has the following specs:
Input:
Balanced > 50K Ohms, Unbalanced > 25K Ohms.
Max input level: +25 dbu
CMRR: >40 db, typicaly > 55 db at 1khz

Output:
Balanced: 60 Ohms, Unbalanced 30 Ohms
Max output level: >+20 db into 600 ohms or greater

[duaneage]

I used a similar DBX crossover and had no problems. I used small isolation transformers that I got from Radio Shack between the equipment. They were about 10 bucks each.

Got that idea from this site

[Zilch]

Something else is up. DBX should have no problem driving those 1.0V input amps.

If anything, they should be playing too "hot."

[HipoFutura]

Well, it just got more interesting/confusing. Everything now work perfectly! Today I decided to experiment with switching the amps around. To get a baseline, I turned everthing on as I last left it. When I started the CD it all sounded fantastic. I had changed nothing! This leads me to believe the DBX 234XL does not reconfigure some of the setting until it is recycled (turned off/on). At this point I have all the levels (in/out) set to 0db and the balance between the low/mid/high freq speakers is as it should be. I've had to back off the 2402H amp as there was too much shrill. The PL 400 is a 200 watt RMS per channel amp where the mono-blocks are only 60 watts RMS.

You can't imagine my surprise, and delight! It all sound unbelievable! The combo of two DIY subs, L100s, and 2402Hs is amazing!

I really appreciate all the help, and I apologize for the false alarm! I'll keep a close eye/ear on things to be sure it doesn't revert back at some point. This sort of thing always leave me a bit uncomfortable as I don't have a solid answer.

[Mike Caldwell]

Hello
Check the wiring configuration of the XLR to RCA adapters.
They should be wired so that the tip of the RCA connector is wired to pin two on the XLR connector and the outer sleeve of the RCA is wired to both pin 1 and pin 3 on the XLR.
On most balanced audio equipment DBX included that is the way to correctly go from a balanced connection to unbalanced. On balanced equipment that uses a 1/4 inch tip, ring, sleeve connector when you plug in a two conductor tip, sleeve plug the same connections as described above are made automatically with in the connector.

If using a transformer I would recommend something a little better that what is available from Radio Shack. Those small transformers are at best designed for low level microphone and instrument signal levels and higher line level signals can easily saturate the transformer.

Mike Caldwell