My DRPA & Gain Structure

Dr. J

Hey Guys -- something is going on with my DRPA. When setting my gain structure I set my mixer up (Pink Noise running thru an input) until my main outputs clip. I back it down slightly and then look at my DR. The DR input lights barely flicker as well as the outputs. There doesn't seem to be anything to adjust on the DR so I noticed on my mixer there is a tiny little trim knob next to my main outputs (On back of mixer). I turned this knob up and it makes no change on my mixer BUT does improve my signal on the DR. I turned it up till I saw a noticable improvement. Here is my hang-up: ALL of the LEFT channel lights aren't as strong as the LEDs on the right(on the DR). Some of them by two LEDs or 10dB. So when this gets to my amps (I run in stereo) the right side clips way before the left side does. I then have to attenuate ALL of the right side inputs on the amps to balance them out. The only other way to balance this out is to use the pan knob on my mixer BUT then my MAIN LEDs are not balanced. Any ideas?

Dr. J

Hey G -- Thanks for the drawings. I also got the link to the D.A.S. RF series tops as well. Yeah they look nice as well.

Dra

Dr. J wrote:

Here is my hang-up: ALL of the LEFT channel lights aren't as strong as the LEDs on the right. Some of them by two LEDs or 10dB. ?

Mixer, DRPA, or both?

DRA

Dr. J

If pan knob on mixer is kept in the center -- my main mixer output LEDs show they are balanced the DR then shows up out of balance. The ONLY way I can get the DR and the amps balanced is by fooling with the pan knob which i don't really want to do or even think my mixer is at fault. I think it is the DR.

Gadget

Run one output from the mixer to one channel of the driverack... then the other... now run the other channel of the mixer into the driverack...is the reading on the input meters the same... or is one side of the mixer channels hotter than the other? If the readings are the same then I would try a soft and hard reset (software issue).

Now, you could take a meter and verify the voltage with pink noise injected into the board (an oscilloscope would be much better... but it's what I would use )to compare the signals out of the board, and DRPA...I suspect the gain control is POST meter on the Presonus board that is why you don't see any affect...

Now, as to the tops... if you were to buy the best components I speced it would cost you about $750 EACH for parts alone...for a comparable speaker around $550/600 that's NOT including ANY labor (whats your time worth old buddy? Last I checked I believe they were $780...and if you noticed the RF 1264 have 4" voice coil woofers and 1.4" exit 3" voice coil horns AND they can be run fullrange! (add to the above another $75-100... or more for crossovers )

Just thought I'd point that out... I think I'd buy the D.A.S now...
G

Dra

Gadget wrote:

Now, you could take a meter and verify the voltage with pink noise injected into the board

...That is IF you have an RMS averaging meter. A typical meter can not read the cresting pink noise. Use a sine tone from the Bink CD (or other souerce). 60 hz, 100 hz, 500hz, doesn't matter.

DRA

Gadget

Won't measure the PEAK value but it would read the average... and it SHOULD be pretty close...

Dra

What I should have said was... it won't read at all. Maybe an analog might. Tone is still the way to go.

DRA

Dr. J

Thanks guys -- I will check it today. G -- I think the D.A.S. tops would be a better deal too. Thanks.

Dr. J

Well just using one side of the DR as my guide (LED's) it is obvious that my right side mixer output is cranked compared to the left. I plugged the right side mixer into the right side of the DR and got +15dBu then moving the cable from the right side mixer going straight to the left side of the mixer (DR side is still right side) I get a zero to +5 dBu. Basically a difference of 10dBu at the outputs. I repeated this again on my other DR just to make sure and got the same result. I tried to use my Multimeter but I couldn't get anything consistent. I emailed Presonus tech support two days ago and still no reply. I found this by re-doing my gain structure since I added more amps to the low end. It seems like it is always something. I have been reading Bob McCarthy's big green book and he is a stickler when it comes to "Signal". Very cool book. He trys to get his signal very linear just like you do when you optimize the frequency response.

Dr. J

Hey another thing. Do you guys have any idea why the output meters on the DR (my DR) are at different levels? In other words: The low is around 0dBu, the mids are at +5dBu and the highs are at +15 dBu. It looks like a 45 degree slope upwards to the right (looking at the meters). Is this OK -- or do we really want the Input meters to match the output meters evenly? Or at least ALL output meters to match evenly.

Dra

Does the output (difference) follow to all input channels on the mixer? Are you certain that the pan is centered?
Download the Binks CD (from the RMF section) and play a tone from CD. You'll be able to check voltage. OH! Make sure that the meter is set to AC, not DC.

DRA

Dra

What source are you using for checking the levels? Mono or stereo? Mono "Y"?

DRA

Dr. J

Pan is centered for sure. Do you mean like all input channels translate the same result? Meaning it could be -- the one channel (ch16) I have been working with........ Never tried a different channel. I could not find my Bink CD (Full Test one) I was only able to use the pink noise disk I have. I am pretty sure it is the mixer and not the DR. The DR gets an uneven INPUT signal. So it is coming in the the DR lopsided and then it shows the same on its way out. I will have to try the other input channels on the mixer. Ok -- i will try the test tone with the meter and see what I get. Dra -- put what probe where. Like the Red probe on pin 2, black on pin 3, 1? I am not very handy with a multimeter.

Dr. J

Dra wrote:

What source are you using for checking the levels? Mono or stereo? Mono "Y"?

DRA

My source is a CD player connected into the channel input with a Pink Noise Cd. I have used the stereo adapter as well as a mono adapter. I see no change only that it takes more gain to achieve the clip point with (I don't remember which one) mono or stereo adapter.

Dra

Dr. J wrote:

My source is a CD player connected into the channel input with a Pink Noise Cd.

Try swapping left and right, just to eliminate a hot side from the CD player.

Dr. J wrote:

Do you mean like all input channels translate the same result?

Yes

Dr. J wrote:

put what probe where. Like the Red probe on pin 2, black on pin 3, 1? I am not very handy with a multimeter.

The easiest thing to do (if you have one) is make an open ended mic cable (no male end). Plug in the female end to the mixer outputs. If you have aligator clips they work best to leave connected. If not, just strip enough wire to wrap the leads. Connect (if I remember right) to shield and (+) or shield and (-). Either of these will give you half signal (like 2v at -0- output). If they are not the same, you have a balance problem. (+) and (-) together will give you 4v at -0-. I think. It doesn't matter which probe (red or black) goes where, for your purpose.

DRA

Gadget

Hey another thing. Do you guys have any idea why the output meters on the DR (my DR) are at different levels? In other words: The low is around 0dBu, the mids are at +5dBu and the highs are at +15 dBu. It looks like a 45 degree slope upwards to the right (looking at the meters)

What are the gain settings for the different xovers? Are they all -0-db or are you adding gain or cutting the gain of any of the xover points?

So the meters show both channels @ the same level? If so then the fat channel really isn't affecting anything anyway but perhaps it's before that... but from the block diagram I suspect that the balance line drivers could be at fault? Zero the fat channel and make sure you don't have any sub groups routed to the mains...or any aux returns sending...or efx returns to the mains...

G

Dr. J

Hey G -- on my DR I get about +15dB on the input meters. So from there I look over to the output meters and I barely hit +5dB on the subs, +15dB on the mids (It matches the Input) and I get +20dB on the highs. Aren't these supposed to be in balance with the inputs? If I raise the outputs on the SUB XO 6-7dB I can get it to match the input. On the highs I have to lower the output gain by about 6-7 dB to match the inputs. This is the only way for me to balance the signal. I don't have a problem doing this because I will set my frequency response with Smaart to make sure my magnitude levels are even (inputs on the power-amps). I guess I don't understand how these differences got that way since this is all before the power-amps. And yes, on the Presonus -- ALL Fat Channel EQ's, gates, compressors, limiters are off. Only a single input channel assigned to the mains with No panning whatsoever.

I did what DRA said to do with the 1K test tone using a volt-meter and sure enough there is a difference from the right output to the left output on the mixer. The right side was twice as strong as the left. I am sending the board back for repair. I honestly have no idea how long this has been going on.

Any thoughts on the output gains on the DR?

Dr. J

GADGET WROTE:
What are the gain settings for the different xovers? Are they all -0-db or are you adding gain or cutting the gain of any of the xover points?

Yes -- every output is currently at -0- dB.

Gadget

Yo J...
You didn't tell me what the individual crossover gains are set at... select the xovers... toggle through the screens and tell me what the gain setting is for the HI, mid and lo outs it'll be in the lower right hand corner of the screen...

Dr. J

Yeah I listed them above your post. They are all set a ZERO dB. Lows = 0dB, Mids = 0dB, highs = 0dB Straight across.

Gadget

Ok... so I'm blind 8) I have EARNED that distinction! with years of abuse! You know... after I got the 260 and hooked up the GUI it became obvious that the meters were not all that useful... the ballistic characteristics were slow, and inaccurate... and not very useful to me... I suspect the nature of the different frequencies affects the meters differently...as long as the amps are getting a usable signal then all is good... remember it doesn't matter if you change the gain @ the xover or the amps... the xover frequency changes as well..
G

Dr. J

Ha -- you know this past year I have found myself squinting more and more. I think my eyes are starting to fail me. All those years of staring at an instructor doing power point presentations on a big screen that was NEVER in focus! Oh well -- I still got my ears. OK --- so I doesn't matter whether I change the gains internally on the crossover or if I keep them at 0dB and level it off at the amps. Thanks G!