L-Pad

dtaylorl · 01-17-2011, 08:32 PM

I'm thinking about building an L-Pad attenuator (see the sticky in this forum), but I can't seem to find a good place to buy them as a Canadian. All the online retailers I can find are charging way too much to ship up North. Any suggestions?

Stratopastor · 01-19-2011, 08:47 AM

Believe it or not my church's youth group bought a few of these some years ago. (It's a long story.) You find out how much it would cost me to ship one to Canada from here in the UK, add your estimate of the unit cost. If the bottom line looks competitive to you then I'll post one to you and you make a donation to my church. How's that? (I'm talking mono, 8 ohm, nominal 100 watt but probably only good up to 30 watt for guitar amp applications.)

dtaylorl · 01-19-2011, 07:44 PM

There's a pretty good chance I'll take you up on that offer. Any idea how much it would weigh? Looks like shipping from the UK is based solely on weight which seems unusual to me - here dimensions are just as important. In any case $7-10ish sounds a lot better than almost $20 from the US. I'll also have to double check my speaker impedance. Only looking to attenuate an 8 watt amp, so the 100 watt l-pad should be perfect.

Stratopastor · 01-20-2011, 01:38 AM

weight - it'll take me till tomorrow (Friday) to get my hands on one, but it's really not much.

Amazon.com: L-Pad 100W Mono 1" Shaft 8 Ohm: Electronics

is a comparable item (not the Monacor) and Amazon says it's seven ounces (times 28 for grams)

Stratopastor · 02-02-2011, 09:34 AM

confession time... can't find them - I'm really sorry. Unitil I can contact our former youth worker (left last autumn) none of my staff has any idea where these parts have gone. Like many church buildings it's a warren of spaces, but I have gone right through the attic where I thought the stuff was stored.

dtaylorl · 02-02-2011, 08:07 PM

No worries. I'll probably have to wait a while before buying an L-Pad anyway. If you happen to run across them before then, great. If not, well I guess thats just how it is

. Do you happen to know where you got them from? Are they something you can pick up at a local hardware store or something like that, or do they pretty much have to be bought online?

Stratopastor · 02-04-2011, 09:20 AM

online...

example

Connect Audio Ltd - Monacor AT-62H L-pad attenuator 100w 8 ohm wirewound, Loudspeaker Drive Units and Components

the most likely sources are people who sell parts for loudspeaker cabinets, 'cos they're often used to fine-tune the tweeter output.

dtaylorl · 03-08-2011, 09:28 AM

I'm having a little trouble finding the specs on my speaker. The amp is a Garnet Gnome which apparently is very similar to a Vibro Champ. My research tells me that the Vibro Champ has a 4 ohm speaker. All the L-Pads seem to be 8 or 16 ohm... is there a solution for this?

Major Tom · 03-08-2011, 02:56 PM

Yes. Get an 8 ohm stereo Lpad, which is 2 lpads ganged together on the same shaft. Jumper the 2 lpads together; i.e., run a jumper from each of the 3 terminals of one to the corresponding 3 terminals of the other. Wire it up like shown on the instructions, to either one of the Lpad's terminals. You now have a 4 ohm mono lpad.

dtaylorl · 03-08-2011, 09:03 PM

Great. Good to know.

Stratopastor · 03-09-2011, 05:46 AM

Another idea would be to buy a couple of power resistors and build a fixed attenuator. Here's a site that does the calculations for you... and the resistor values need only be close- speaker impedance is a very nominal idea. Example, to get a third of a watt max from your 5 watt amp, tell it you want 12bB attenuation...

L-Pad (Driver Attenuation Circuit) Designer / Calculator

Naturally you can't adjust this by turning a knob but it's simple to build. I made one for an old Marshall and experimented with various levels of alltenuation - I naively thought, at first, that throwing away half the power would be fine. In fact I could barely hear any drop in volume! I ended up throwing away 95% of the power.... that corresponds to about 13dB, not that the actual dB value matters.

dtaylorl · 03-11-2011, 05:19 PM

Quote:

Originally Posted by Stratopastor

Another idea would be to buy a couple of power resistors and build a fixed attenuator. Here's a site that does the calculations for you... and the resistor values need only be close- speaker impedance is a very nominal idea.

I'll definitely consider that. I *may* have found a place in town that sells L-Pads, if not I'll probably just trying something like this first.

Is there any easy way to determine speaker impedance? My research online doesn't seem to be turning up much, although one site did seem to suggest it may be 8 ohms... I'm attaching an amp schematic, although as far as I can tall theres nothing on it that would indicate output impedance.

Stratopastor · 03-12-2011, 08:31 AM

Well, you could either ask Garnet, or you could disconnect the speaker and measure ohms across its 2 terminals. DC resistance always comes in a little less than nominal impedance. so a 4 ohm speaker will come in at 3 or 3 and half, and an 8 ohm speaker will be 6 or 7. Unless it's printed somewhere on the speaker... :-)

dtaylorl · 03-12-2011, 10:46 AM

First place I checked was the speaker itself or any other indication on the amp... nothing. Is measuring the ohms something that would be done with just a multimeter? I don't actually own one, but I keep running in to situations where one would come in handy so I may just go buy one.

dtaylorl · 03-21-2011, 08:25 AM

Has anyone ever used a Variable Voltage Regulator (VVR) to attenuate an amp? Someone on another forum recommend I consider using one. Information available here. Only slightly more than the L-Pad. My initial thought is to stick with the L-Pad since it looks to me like it would probably be easier to install, but I'd be interested to hear some discussion about how this VVR works.