attenuator airbrake

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mehfuzhoss
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attenuator airbrake

Post by mehfuzhoss »

Hello,

The 6 position switch is broken on mine. to get maximum attenuation and remove the L pad, what will be the wiring like! I am new to electronics and still trying to figure it out, any suggestions is appreciated.
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Re: attenuator airbrake

Post by JMPGuitars »

If you post the brand and model of the attenuator that would help for a response. If it's a DIY attenuator, then post a link to the schematic.

Either way, those knobs are easy to come by. You could draw it out, and take a few photos of it, then recreate it.
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Re: attenuator airbrake

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Layout attached.
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Re: attenuator airbrake

Post by JMPGuitars »

I'm confused. It looks like the 6-position switch selects the impedance. The giant rheostat should adjust your attenuation. Are you sure the switch is broken? Those switches don't normally break so easily.

Are you sure that switch is wired correctly? The positions are not arbitrary.
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Re: attenuator airbrake

Post by mehfuzhoss »

the switch was played around by my little kid. so now, the 5,6 position is loosey and after 6 it goes around few mms. the fact is i would like the maximum attenuation out of the three big resistors that I have including the rheostat...
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Re: attenuator airbrake

Post by katopan »

Airbrake is the model. Here's one of the many schematics for it:
https://img.audiofanzine.com/image.php? ... _id=300170

Designed for 16 ohm speakers but people do run them at 8 and even 4. Impedance reflected back to the amp changes with different settings, but it works and people like 'em.

The rheostat is the volume adjustment for the highest switch setting "Bedroom". The layout you posted shows the switch in the "Bedroom" position. So if you just want to bypass the switch and hardwire to the highest attenuation setting, solder the green wire on the switch middle (from the input jack) to the blue wire on switch pin 5, and the red wire on the switch middle (to the output jack) to the black wire on switch pin 7.

If you also want to remove the rheostat and have max attenuation from that as well, you'd replace it with a fixed 150 ohm 50W resistor.
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Re: attenuator airbrake

Post by JMPGuitars »

katopan wrote:
Thu 04/23/20 6:20 pm
Airbrake is the model. Here's one of the many schematics for it:
https://img.audiofanzine.com/image.php? ... _id=300170
Oh wow. That's funny. I priced the parts out at Mouser, and it came to $150. I thought that was really expensive until I saw what Dr. Z charges for it. 🙄

I think I paid less than $100 for my 50Watt attenuator that has a speaker motor, and treble boost settings.
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Re: attenuator airbrake

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JMPGuitars wrote:
Thu 04/23/20 9:09 pm
Oh wow. That's funny. I priced the parts out at Mouser, and it came to $150. I thought that was really expensive until I saw what Dr. Z charges for it
Used to be that they could be made for about $105 with parts from Mouser. Those Ohmite rheostats have gone up tremendously.
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Re: attenuator airbrake

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colossal wrote:
Fri 04/24/20 7:26 am
JMPGuitars wrote:
Thu 04/23/20 9:09 pm
Oh wow. That's funny. I priced the parts out at Mouser, and it came to $150. I thought that was really expensive until I saw what Dr. Z charges for it
Used to be that they could be made for about $105 with parts from Mouser. Those Ohmite rheostats have gone up tremendously.
How does it magically work with 4, 8, and 16 ohm loads without specifying the impedance? I assume the amp's impedance has some kind of an affect on attenuation level, but how does this not affect the amp?

Out of curiosity, I decided I'm going to make one and see how it compares to my other attenuator. Hopefully the rheostat I bought on eBay for $23 less is legit. ;)
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Re: attenuator airbrake

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JMPGuitars wrote:
Fri 04/24/20 7:46 am
How does it magically work with 4, 8, and 16 ohm loads without specifying the impedance? I assume the amp's impedance has some kind of an affect on attenuation level, but how does this not affect the amp?

Out of curiosity, I decided I'm going to make one and see how it compares to my other attenuator. Hopefully the rheostat I bought on eBay for $23 less is legit. ;)
It gets in the ballpark for all input impedances with the impedance rising with increasing attenuation. Like any attenuator, once the speaker stops moving air, the perceived tone can be affected. Those Ohmites have gotten ridiculously expensive. Here is a plot. The kink you see is where the rheostat kicks in. You can tailor the -dB per click by moving the adjustable taps.

Airbrake.jpg
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Re: attenuator airbrake

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colossal wrote:
Fri 04/24/20 1:56 pm
It gets in the ballpark for all input impedances with the impedance rising with increasing attenuation. Like any attenuator, once the speaker stops moving air, the perceived tone can be affected. Those Ohmites have gotten ridiculously expensive. Here is a plot. The kink you see is where the rheostat kicks in. You can tailor the -dB per click by moving the adjustable taps.
That's roughly what I expected, pretty cool tho. I got the rheostat for $40, which is $23 less than Mouser. None in stock though, that's what inspired the ebay purchase.

This seems like it could also be used as a dummy load. Is that correct, or would it pose any issues?
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Re: attenuator airbrake

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JMPGuitars wrote:
Fri 04/24/20 1:59 pm
colossal wrote:
Fri 04/24/20 1:56 pm
It gets in the ballpark for all input impedances with the impedance rising with increasing attenuation. Like any attenuator, once the speaker stops moving air, the perceived tone can be affected. $23 for a rheostat is pretty good! Those Ohmites have gotten ridiculously expensive. Here is a plot. The kink you see is where the rheostat kicks in. You can tailor the -dB per click by moving the adjustable taps.
That's roughly what I expected, pretty cool tho. I got the rheostat for $40, which is $23 less than Mouser. None in stock though, that's what inspired the ebay purchase.

This seems like it could also be used as a dummy load. Is that correct, or would it pose any issues?
It does a reasonable job of impedance matching, but you can use it for 4, 8, or 16R inputs; trade one thing to get another. I've built them and they sound quite good. You certainly could make a dummy load out of it as well. Have just a dedicated tap to soak the entire load and bypass R1.
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Re: attenuator airbrake

Post by JMPGuitars »

katopan wrote:
Thu 04/23/20 6:20 pm
Airbrake is the model. Here's one of the many schematics for it:
https://img.audiofanzine.com/image.php? ... _id=300170
It's interesting. I got the parts today and started building this. I wired the switch and drilled the chassis. In the process I noticed that the schematic you linked doesn't match the layout, but appears to be functionally the same.

I think I like the idea in your linked schematic better, where the resistor is only connected at all when not in bypass.

Here's a schematic that matches the layout better, but the numbers are dumb:
attenuator.jpg
Thanks,
Josh
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Re: attenuator airbrake

Post by katopan »

Will be interested to hear back what you think of it Josh. I've never used one but they get a good rap from people. It's interesting that although it doesn't present an ideal matched load to the amp, it does a pretty good job with 4, 8 or 16 ohm speakers. Other attenuators are generally matched and only suitable for one speaker impedance.

I've never built one - my attenuators are just a straight up L-Pad, or a full reactive dummy load that I use in a re-amping set up for my bigger amps to get down to TV volumes. All my amps have VVR so that's the key method that gets used. The L-Pad gets used in conjunction with VVR on my 18 Watt and other amps at home. The re-amping set up gets used most often with the Wreck Express. Playing out it's only VVR on any of them.
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Re: attenuator airbrake

Post by JMPGuitars »

I finished it today. I haven't tested it on an amp yet (I tested with a meter and it appears fine).

I simplified the construction of it based on the schematic you linked. If I like how it sounds, I'll create new build docs that are clearer, and accurate.

I'm curious to see how it sounds compared to my MiniMass 50. I like the MM50, but I've seen plenty of people on forums saying how much more they like the Air Brake, so it should be interesting.

I need to record a few demos of recent amp builds, I'll record a demo of this at the same time.

Thanks,
Josh
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