DBX-400 and good IC's to do the job right

[jbeckva]

So recently I purchased a DBX-400 program route selector, as I'd like to start getting back into the general taping/recording aspect of our hobby here - Might be a reel to reel in my future radar, as an example.

That was errr.. about a month ago. Hadn't been paying much attention in that period.. no real critical listening sessions as I was also experimenting with digital sources, and specifically using DAC's as preamps with the DBX behind it for switching sources.

Finally half over a cold that's been kicking my butt for the past week, so today it was half past time to do some serious listening. In the process I noticed something.. bass sucked and that was with both WOPL 400's and 700's in play. Soundstage and instrument/voice placement was not as I remembered (when my dang ears were half "clear" before the cold I got over).

Then it hit me - it sure sounded like left and right were out of polarity/phase , like I had swapped the pos and neg outputs on one of the speakers. I then checked and triple checked the speaker lines - definitely hooked up correctly.

So what could it be, I asked myself. Ahhh.. it is that 400, even though it's purpose is strictly signal routing. Yep it does have processor loops and I did have an EQ patched into one, but none of that was in circuit... nothing that SHOULD alter the signal in any way, and yet...

Yanked it, and my bass and soundstage came back. HMMMMM...

So, "and so it begins"... I plan on seeing what I can do to enhance the signal handling in the 400. My thought.. it may be that the circuit has a coupling capacitor - one for each channel. Since caps in series with it do introduce a 90 degree phase shift, and if I do have a pair like that with either one short or the other open, I can see where it would cause the symptoms above.

Has anyone found a schematic for these DBX 400's?? That would be a big timesaver, otherwise I'll need to reverse engineer the one I have. Going to wait til tonight to begin - picks will be provided heheh.

 

[laatsch55]

So, If I put a cap in series with the swamping resistor on my K's crossovers that goes to the mids my mid horns will be 90 degrees out from my bass bins?

 

[fitz43]

So recently I purchased a DBX-400 program route selector, as I'd like to start getting back into the general taping/recording aspect of our hobby here - Might be a reel to reel in my future radar, as an example.

That was errr.. about a month ago. Hadn't been paying much attention in that period.. no real critical listening sessions as I was also experimenting with digital sources, and specifically using DAC's as preamps with the DBX behind it for switching sources.

Finally half over a cold that's been kicking my butt for the past week, so today it was half past time to do some serious listening. In the process I noticed something.. bass sucked and that was with both WOPL 400's and 700's in play. Soundstage and instrument/voice placement was not as I remembered (when my dang ears were half "clear" before the cold I got over).

Then it hit me - it sure sounded like left and right were out of polarity/phase , like I had swapped the pos and neg outputs on one of the speakers. I then checked and triple checked the speaker lines - definitely hooked up correctly.

So what could it be, I asked myself. Ahhh.. it is that 400, even though it's purpose is strictly signal routing. Yep it does have processor loops and I did have an EQ patched into one, but none of that was in circuit... nothing that SHOULD alter the signal in any way, and yet...

Yanked it, and my bass and soundstage came back. HMMMMM...

So, "and so it begins"... I plan on seeing what I can do to enhance the signal handling in the 400. My thought.. it may be that the circuit has a coupling capacitor - one for each channel. Since caps in series with it do introduce a 90 degree phase shift, and if I do have a pair like that with either one short or the other open, I can see where it would cause the symptoms above.

Has anyone found a schematic for these DBX 400's?? That would be a big timesaver, otherwise I'll need to reverse engineer the one I have. Going to wait til tonight to begin - picks will be provided heheh.

I picked one up today at the Post Office. It came with the manual which has a schematic in it. I'll scan it and forward it to you. PM me your email addy. I do it when I get back to Canada later this evening.

 

[Gepetto]

So, If I put a cap in series with the swamping resistor on my K's crossovers that goes to the mids my mid horns will be 90 degrees out from my bass bins?

No it won't Lee...a coupling cap that is sized properly does not add appreciable phase shift.

 

[laatsch55]

Ok...

 

[jbeckva]

No it won't Lee...a coupling cap that is sized properly does not add appreciable phase shift.

Explain Joe... how would it NOT shift the signal 90 degrees?

 

[Gepetto]

Explain Joe... how would it NOT shift the signal 90 degrees?

Series coupling caps are just high pass networks (they are differentiators at frequencies well below Fc), at near zero Hz they will insert 90 degrees phase LEAD (not lag) into the signal being passed. When the high pass Fc is reached then this phase LEAD will be reduced to 45 degrees. At about 5x the Fc frequency the phase lead will be nearly zero, meaning the cap looks like a piece of wire.


Here is an example set up for Fc of 159 Hz (1uF and 1K ohms)




And here is the phase and magnitude response of the circuit.

 

[jbeckva]

I picked one up today at the Post Office. It came with the manual which has a schematic in it. I'll scan it and forward it to you. PM me your email addy. I do it when I get back to Canada later this evening.

You know what? So did I, now that I'm staring at it.....

Interesting... there appears to be nothing but physical switches here. Hey Lee... let me send this over to ya, and you tell me if I'm crazy or not. Interconnects???? hmmmmm...

 

[orange]

It's totally passive, Jer...that's the neato thing about it...if you have something out of phase you need to go back through your sources or check the wiring. and thank you for the 'fix', if you know what I mean...

 

[jbeckva]

It's totally passive, Jer...that's the neato thing about it...if you have something out of phase you need to go back through your sources or check the wiring. and thank you for the 'fix', if you know what I mean...

LOL.. well I woke up this morning.. got out of bed... and then...

Anywhoo.. That's what I figured, but there sure seems to be a difference even with the same IC's involved.

 

[laatsch55]

Ok..

 

[jbeckva]

Ok..

Yeah man I gotta get a 2nd opinion. I had the 200 prior to this and experienced the same. Could it be ... the WOPL uncovering any deficiencies in the signal path, LOL???..

 

[laatsch55]

When the amp is no longer the question mark.....

 

[jbeckva]

When the amp is no longer the question mark.....

Or the pre... which makes it really odd. I'm on the HK Citation 21 all by itself now, and there's a big difference than before.

 

[laatsch55]

Difference with what??

 

[jbeckva]

Difference with what??

How it sounds, compared to having the signal route up and over through the dbx 400... which as we know is all switches, circuit traces, and interconnects (the last I do NOT suspect because I can route the same exact IC's through that there Denon deck, and hear no degradation)

 

[Gepetto]

Or the pre... which makes it really odd. I'm on the HK Citation 21 all by itself now, and there's a big difference than before.

View attachment 15041

You will really notice a difference with a source going straight into the power amp and using the level controls on the front of the PL700B. It will be better than going through your preamp, almost guarantee that. I hate running a preamp but usually succumb to the convenience it offers rather than constantly plugging and unplugging sources into the amp jacks.

Although the DBX is in straight through mode, are there still loads connected to that straight through wire that you refer to?? You said it is capable of doing some level of processing inside it.

 

[jbeckva]

You will really notice a difference with a source going straight into the power amp and using the level controls on the front of the PL700B. It will be better than going through your preamp, almost guarantee that. I hate running a preamp but usually succumb to the convenience it offers rather than constantly plugging and unplugging sources into the amp jacks.

Although the DBX is in straight through mode, are there still loads connected to that straight through wire that you refer to?? You said it is capable of doing some level of processing inside it.

Not inside of it - it has switching to put an EQ in line (two "processor" loops total), and to switch it in both pre and post for the tape monitors. Even with it configured for a straight passthru from input to output, there's still a difference to my ears.

Yeah I know about going straight in... that DAC I have has a separate pair of outputs designed to do just that. But not quite enough "drive" voltage for serious Mach 8 operations when I get the levels matched up.

 

[Gepetto]

Not inside of it - it has switching to put an EQ in line (two "processor" loops total), and to switch it in both pre and post for the tape monitors. Even with it configured for a straight passthru from input to output, there's still a difference to my ears.

Yeah I know about going straight in... that DAC I have has a separate pair of outputs designed to do just that. But not quite enough "drive" voltage for serious Mach 8 operations when I get the levels matched up.

All wires are not created equal Jer...

 

[laatsch55]

Neither are men, women, Presidents........