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View Full Version : dbx Driverack pa+, do yours introduce a hiss to the tweeter?



panduro
05-28-2011, 03:42 AM
hi all, need help:o:

my diy front ht speakers consists of 12" bass jbl le120h1-s, 6,5" midrange jbl gs726 and high freq. 1" compression driver jbl 2426.
power comes from 2 carver av 705x consumer poweramps(5x125w each). only rca inputs.

crossover is a dbx driverack pa+.

my tweeters has a small hiss when only connected to the poweramp and the poweramp is not connected to the dbx. this doesnt bother me.

but:

when i connect the poweramp to the dbx the hiss becomes much louder, its like leasening to a seabreeze:crying:

i only sitt 6 feet away, because of roomsize!

it doesnt influence the hiss if the dbx is connected to my pre-amp or not.


do you pa+ users have the same problem? or do you have any ideers that maybe can help me?

ps sorry for the bad enghlish.

JBL 4645
05-28-2011, 07:32 AM
Hiss is a sound frequency when you think about it logically?

I have the same issue as everyone else that has Behringer DCX2496 so this isn’t just one product name that has the same issue.

How loud do play the HF 80db or higher?

I set the amp level at lower level because that’s only going to amplify the hiss until a film or music is playing over it!

The hiss would be centred on narrow frequency response if you placed the EQ and targeted on the hiss and cut back only its going to affect the film or music by reducing a small narrow range of the highs no problem. Place second EQ and target the frequency with cut on dbx and boast it up that’s one of tackling.

You need the second EQ on the inputs only use EQ on dbx to cut down the offending hiss use the Q at narrow then cut down on db level on frequency if the his is still audible widen the Q a little bit until the hiss has gone.

Then boast for the loss on the input with matching EQ or Behinger FBQ2496 because the frequency of the hiss might be around between 3 KHz and 5 KHz and you’ll need to slide frequency up and down on dbx until you have targeted it!

Then use FBQ2496 to find the same frequency and place boast because most 31 band EQ have the bands centred you can’t tailor it to your liking.

Eaulive
05-28-2011, 07:41 AM
hi all, need help:o:

my diy front ht speakers consists of 12" bass jbl le120h1-s, 6,5" midrange jbl gs726 and high freq. 1" compression driver jbl 2426.
power comes from 2 carver av 705x consumer poweramps(5x125w each). only rca inputs.

crossover is a dbx driverack pa+.

my tweeters has a small hiss when only connected to the poweramp and the poweramp is not connected to the dbx. this doesnt bother me.

but:

when i connect the poweramp to the dbx the hiss becomes much louder, its like leasening to a seabreeze:crying:

i only sitt 6 feet away, because of roomsize!

it doesnt influence the hiss if the dbx is connected to my pre-amp or not.


do you pa+ users have the same problem? or do you have any ideers that maybe can help me?

ps sorry for the bad enghlish.

Yes, I have a Driverack PA+, no I don't have a hiss even if I stick my ears on the tweeter.
A properly set gain structure, this is your key to happiness.
The Driverack is a professional piece of equipment capable of outputting more than 20dBu which is much much more than what you need to drive your consumer amp into clipping.

You have to adjust the gains on your amplifier so it starts clipping at about the same level _or just before_ your driverack.

Just to give you an idea, at normal bedroom listening levels I light up the -20dB segment occasionaly, and if I listen to it loud the -10dB is lit up almost solid.

The gains on my amplifier are set to around 9 o'clock and at this level I hear no noise what so ever

In the driverack manual there is a chapter about gain structure, page 33.
Read it and follow it !

Good luck, keep us posted. :)

Eaulive
05-28-2011, 07:44 AM
The hiss would be centred on narrow frequency response if you placed the EQ and targeted on the hiss and cut back only its going to affect the film or music by reducing a small narrow range of the highs no problem. Place second EQ and target the frequency with cut on dbx and boast it up thatís one of tackling.


You need the second EQ on the inputs only use EQ on dbx to cut down the offending hiss use the Q at narrow then cut down on db level on frequency if the his is still audible widen the Q a little bit until the hiss has gone.

Then boast for the loss on the input with matching EQ or Behinger FBQ2496 because the frequency of the hiss might be around between 3 KHz and 5 KHz and youíll need to slide frequency up and down on dbx until you have targeted it!


I sincerely hope nobody follows your ill advice :blink:

allen mueller
05-28-2011, 10:04 AM
I sincerely hope nobody follows your ill advice :blink:
I agree, and also agree a proper gain structure is the key.

JBL 4645
05-28-2011, 12:35 PM
I agree, and also agree a proper gain structure is the key.

I was just thinking out loud! What you think I have the amps for HF up at full to burn the voice coils out along with brittle highs.

panduro
05-29-2011, 06:19 AM
thanks all,

ill hurry up and get my second carver poweramp to the rep shop, last owner took the the attenuator to each channel off:(.

but just tried with the other one, and you sure were right, turning it down took the hiss away, now only a question of seing if it will play loud enoughf.

thanks for the aid.

best regards

panduro

Eaulive
05-29-2011, 08:54 AM
thanks all,

ill hurry up and get my second carver poweramp to the rep shop, last owner took the the attenuator to each channel off:(.

but just tried with the other one, and you sure were right, turning it down took the hiss away, now only a question of seing if it will play loud enoughf.

thanks for the aid.

best regards

panduro

This is the problem when mixing consumer and pro stuff, by turning down the gain on your amplifier you got rid of the hiss, but now your preamp is maybe not going to be able to feed your driverack with enough voltage to take advantage of its full headroom.

Do you have settings in your preamp that allows for higher output level? Do you have balanced outputs?

If you have only RCA outputs you could work around this by inserting some kind of matching device between your preamp and the driverack, example:
http://www.bhphotovideo.com/c/product/217366-REG/Rolls_MB15B_MB15b_Promatch_2_Way_Stereo.html

With this you will increase the consumer output of your preamp to the pro input of your driverack, now I realize it may be not audiophile quality but it was just an example.

Good luck with this :)

panduro
05-29-2011, 09:38 AM
hi again,

my preamp is a Onkyo PR-SC5508 and does have balance in/outs! what does that change?

dont know if i can change the output levet from it, but ill find the instruction manual and find out.

best regards and thanks

panduro

John Relyea
05-29-2011, 12:34 PM
if you are sitting 6 feet away loudness not a problem 10 watts into those high sensitivity drivers will have your ears bleeding john
thanks all,

ill hurry up and get my second carver poweramp to the rep shop, last owner took the the attenuator to each channel off:(.

but just tried with the other one, and you sure were right, turning it down took the hiss away, now only a question of seing if it will play loud enoughf.

thanks for the aid.

best regards

panduro

panduro
05-29-2011, 01:34 PM
I hope so, well not literally, but having more than enough headroom is nice.

thanks

panduro

Eaulive
05-29-2011, 03:52 PM
hi again,

my preamp is a Onkyo PR-SC5508 and does have balance in/outs! what does that change?

dont know if i can change the output levet from it, but ill find the instruction manual and find out.

best regards and thanks

panduro

Usually, balanced outputs means also that the output is of "pro" levels so it should be able to drive your DBX properly.

Check the "nominal levels" section.
http://en.wikipedia.org/wiki/Line_level