Recomended L Pad or resistors?

lbstyling

Member
2008-07-06 10:09 pm
Hi all,

Working on my new speakers with a JBL 2452SL that needs dropping in volume by 20db vs a TD10m as its producing a little too much hiss (Hypex Fusion NCore amp)

The driver is a 150w capable unit (not that I ever expect to be maxing this out)

Do you recommend a L-pad or soldered resistor version? most resistors seam to be much lower power (5w),although its for domestic use, I assume this is not enough to run safely?

Thanks.
 

rayma

Member
2011-04-29 8:37 pm
The type of amp doesn't matter at all. The driver inductance causes its impedance to rise with frequency.
The series resistor then attenuates less with increasing frequency, causing the hf response to rise.
This is why Zobels are used, to keep the driver impedance (and the response) constant.
With an acoustic loop this could be corrected, but it should not happen to begin with.
 
Last edited:
Ah, I see. I hope the OP doesn't mind me getting involved, perhaps it might be of benefit.

I have a MiniDSP 8x8 (unknown output impedance and not even sure if it is relevant?) going to two Parasound Zamps (33k ohm input). One of which needs to be attenuated for compression driver/horns but I am not quite sure how much, yet. How would a pot be implemented?
 

Lojzek

Member
2012-02-10 12:12 pm
Croatia
Normally you connect a potentiometer like VR201, a shot from Zamp schematic. Can you use this pot (Gain L and R on back side?) to your benefit?
 

Attachments

  • Zamp V3 schematic.png
    Zamp V3 schematic.png
    49.9 KB · Views: 42

lbstyling

Member
2008-07-06 10:09 pm
You could put the attenuation at the input of the amp rather than its output. This uses the amp as a buffer. It's what I'm doing at the moment. It's not the only way to do it. In my case this reduces the noise with the level.

If I have understood you correctly, this would not work for me as its the amp producing the hiss.
 
Last edited:

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
Yes. Some are very particular about the low power, low noise amp they choose to drive a compression tweeter for this reason.

Using an L-pad arrangement instead of a single resistor will reduce the effective source impedance driving the tweeter, but it won't likely be enough to prevent response variations sufficiently.

Compression tweeter impedance is often highly varied. High Q artefacts are typically less reliable to quash. Channel imbalance can be an issue. Some would use an impedance conjugate network tuned for each channel. You want to choose carefully how you manage this because you are relying on a secondary effect to maintain performance. Even if you measure each channel and EQ.