L-pads?????

[plasmodium]

I like the idea of being able to adjust the level of the tweeter.... a book I am reading suggests using an L-pad to supply an adjustable resistance across and in series with a driver, calls it an L-pad - I am thinking it is similar to a potentiometer, but have never seen one...

does anyone know where to source them from in Australia???

 

[Westrock2000]

You should read my thread, its very similar to your question. Yes an L-pad is just a big pot, but you may have to wire it differently that just in series to avoid any problems.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=7920&perpage=15&pagenumber=1

 

[mrfeedback]

Sign off With A Real Name Ok.....DIYetiquette

You can phone Wes Components - Ph: 02-9797-9866
or phone me (08-9405-9779) - I have the full print copy of the catalogue.
Many older speakers used them.
General regard is that they are not for audiophile usage, but can be useful temporaryily for determination of appropriate level, and then replaced with fixed resistors, or a rotary switch with a set of attenuation values.
Experience dictates that the resistive (nichrome ?) wire that they are made from forms a hard oxide film that causes dynamic contact resistance and thereby roots the sound.
Treatment with something like Caig Deoxit helps very much (even brand new ones), and helps long term ensurability.
Other contact treatments can bugger it up.

Eric.

 

[FrankDIY]

This is exactly what I am doing, I tweak with L-Pad and use fixed resistor for the final version of the board.

 

[mrfeedback]

You should read my thread, its very similar to your question. Yes an L-pad is just a big pot, but you may have to wire it differently that just in series to avoid any problems.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=7920&perpage=15&pagenumber=1

An L-Pad is not a pot - it is 2 variable resistors - one in series, and one in shunt.
The values are configured such that a reasonably constant load is presented to the amplifier, and variable level fed to the load driver.

Eric.

 

[paulj]

Looking for L-pads in Australia

I've come across this old thread - I'm looking for L-pads here in Australia. 100 watt, 8 ohm. Can anyone help?

Cheers, Paul

 

[lucpes]

L-pad is formed out of two resistors, you don't need 100W ratings, 5W or 10W would be more than enough (for the tweeter). Google a 'L-pad calculator' and buy the two resistors

 

[paulj]

Thanks for your advice lucpes. I'll go out and buy the resistors and try some different amounts of attenuation.

A question for you - (excuse my ignorance with circuit diagrams): am I right in assuming the two resistors R1 and R2 are inserted on the "tweeter side" of the crossover capacitor?

Regarding the power handling of the resistors, the tweeters are bi-wired and bi-amped with an amplifier that is 65 w RMS/8ohms per channel. Would you still be happy with 5 or 10watts per resistor?

Many thanks, paul

 

[Andy G]

http://www1.jaycar.com.au/productVi...d2=&pageNumber=&priceMin=&priceMax=&SUBCATID=


This is the fella you want.. and a heap of 5w or 10w resistors

and with a bit of thinking, you can get up to 6 positions with a solid switch between each position......not a variable slide contact !!!

Have fun figuring it out !!!

here's an L-pad calc

http://www.mhsoft.nl/spk_calc.asp#att

 

[paulj]

Thanks Andy! Can you tell me where I put the R1 and R2 [ between the crossover capacitor and the tweeter or on the amplifier side of the capacitor? (All the diagrams I've seen only show the R1 and R2, not the cap, and I'm a beginner!)

Also, will the 10 watt resistors stand up to the power of my amp? There don't seem to be any resistors rated at more than 10 watts on the Jaycar site. Is there any point in "ganging them up" for extra power handling or does this screw up the impedances?

Thanks, Paul

 

[Andy G]

I'm pretty busy at the moment, but if you like I'll draw it up tomorrow for 1dB to 6dB cut on an 8 ohm tweeter, with values to use....and dump it on my web site.....

If I don't get it done by tomorrow evening, send me a reminder email !!!

I thought that Jaycar still had 10w resistors.... but even better are WES components.. they have non-inductive 10w ones.. I'll find the link and post it at the same time.

 

[Andy G]

Job done quicker than I thought !!!

here ya go..

http://users.tpg.com.au/users/gradds/x-os/6wayrotarylpad.jpg

http://www.wagner.net.au/Catalogue/02_13.pdf

I hope that its correct, it was quickly done !!!

I'm sure someone will correct me if its not !!

 

[synergy]

kinda pleased this one popped up today as i'm stumbling through the same problem myself

i need a variable l-pad for my 3 ways that i use to do small house parties with
difference with me however is that i'm running a lot more power! - QSC RMX 2450 at least!

variable because on their own the tweeter ( Eminence APT:80) is about 10dB too high
however i sometimes use subs with them and being able to balance the treble would be of great benefit

i think i'm going to adopt the switch method as i'm worried about any pots burning up

my questions are what sort of power rating should i be after for them, baring in mind i run my amps close to but not at clip?

10w isn't enough surely? the tweeters are rated at 45w at 3.5KHz, 85w at 5KHz

the other drivers are a kappa 15LF and an Alpha 10 - you get the idea - loud, reasonable quality but cheap enough that we can fry them every so often

and does any body know anywhere in the uk i can get non-inducting resistors from?

(running parallel to this is my desire to build a wallins jig but finding 20w 8ohm non-inducting resistors in the uk is proving impossible)

thanks for your help
dave

 

[markp]

A good wirewound resistor of 10 watts will easily handle 100watt peaks in use. Don't worry about using them in a higher powered system unless your average power is over 200 watt to the tweeter alone, remember the resistor is after the crossover so it sees only a fraction of the total power.

 

[synergy]

cool, no ideas on where to get them in the uk i suppose?

the only place i've found that even stocks them around the right values requires you to be trade and have a bulk order

 

[Andy G]

Resistor wattage...

I use PA gear a lot, my own speakers.....

I have cooked a 5w resistor on a PA tweeter ...once

I use 10w wire wounds in my 200w-400w pairs, and they don't even seem to get very warm.

I have doubled up in my bigger pair. (to 20w)..but they are meant to be able to handle 900w !! Again, I have not had any problem with over heating.