attenuator airbrake

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Re: attenuator airbrake

Post by colossal »

JimbpGaff wrote:
Tue 05/12/20 2:58 am
Great info.

not sure if I missed it in the threads but is this for a 16 ohm load and how much attenuation will it give.
Jim
As Josh said, the attenuator will "work" for 4 and 8 ohm loads, but is best suited for 16. See the first page of this thread for a plot of impedance vs. attenuation.
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Re: attenuator airbrake

Post by JimbpGaff »

Can I use a different value Rheostat ?
The 150 ohm 50 watt is hard to come by at the moment in the UK as they all seem to be on back order until the end of the year.
Jim
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Re: attenuator airbrake

Post by colossal »

JimbpGaff wrote:
Wed 05/20/20 12:36 am
Can I use a different value Rheostat ?
The 150 ohm 50 watt is hard to come by at the moment in the UK as they all seem to be on back order until the end of the year.
Jim
You can. Lower values will limit attenuation. Higher values will increase it at the expense of increasing impedance.
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Re: attenuator airbrake

Post by JMPGuitars »

colossal wrote:
Wed 05/20/20 8:05 am
JimbpGaff wrote:
Wed 05/20/20 12:36 am
Can I use a different value Rheostat ?
The 150 ohm 50 watt is hard to come by at the moment in the UK as they all seem to be on back order until the end of the year.
Jim
You can. Lower values will limit attenuation. Higher values will increase it at the expense of increasing impedance.
Limiting attenuation isn't a bad thing, since there will be less tone sucking that way. BUT there's limited options in that price range. I looked at alternatives, and they get pretty expensive. The RJS125E for example is 125 ohms, and $80. Some other variations were hundreds of dollars.

Personally I got a couple of the RJS150Es on eBay for $40 a piece. There is a seller in the UK selling the 150 also, but not as cheap. The 125 is available on there too, but I dunno about in the UK.

Thanks,
Josh
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Re: attenuator airbrake

Post by JimbpGaff »

Thanks Josh

Just found the one on ebay for $77.00.

A lot of money in these difficult times .

I will have to do some thinking .

The pure resistor attenuator is a cheaper option, But.....
Jim
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Re: attenuator airbrake

Post by JMPGuitars »

JimbpGaff wrote:
Thu 05/21/20 1:52 am
Thanks Josh

Just found the one on ebay for $77.00.

A lot of money in these difficult times .

I will have to do some thinking .

The pure resistor attenuator is a cheaper option, But.....
Jim
Yeah, it's not cheap. But it's only $14 more than Mouser sells it for if you can't wait for people to have it in stock. On the other hand, you could build this attenuator without the rheostat, and use the switched section until a better deal on the rheostat becomes available. You can increase the resistance for the lugs and have the switched section attenuate at higher levels in the meantime.
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Re: attenuator airbrake

Post by JimbpGaff »

Thanks Josh.

I will do some thinking .
Jim
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Re: attenuator airbrake

Post by crgfrench »

I'm building a Trainwreck-style attenuator right now and I decided to draw up 4 possible wiring possibilities as schematics. All 4 of these are electrically identical and it is the same circuit. the only difference is the wiring sequence in which R1 is connected in the circuit. I drew all 4 in bypass mode.

Josh posted my #1, "Attenuator Type 1" on 4/29/20 and I don't know the source; its R1 sequence is: Input, R1, Lorlin Switch Pins, "A" (On the Lorlin switch), then Ground.

Mehfuzhoss posted my #2, "TDPRI Layout" on 4/22/20 and I drew up the schematic from that layout; its R1 sequence is: Input, "A", Pins, R1, then Ground.

Katopan posted my #3, "JMP/Audiofanzine Layout" on 4/23/20 and I drew up the schematic from that; its R1 sequence is: Input, Pins, "A", R1, then Ground.

There is a fourth possibility I haven't ever seen, so I drew up #4, "Not Seen in the Wild". Its R1 sequence is Input, R1, "A", Pins, then Ground.

The R2, cap and rheostat structure is common to all four of these wiring possibilities.

[I noticed Josh drew his layout with pin 7 going to the wiper, it was just easier (and electrically the same) for me to draw 7 to the leg in the schematic.]
Trainwreck Airbrake Wiring Possibilities.png
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Re: attenuator airbrake

Post by crgfrench »

I drew up wiring diagrams for all 4 of these schematics, and I like the JMP/Audiofanzine setup the best -- mainly I like the simplicity of daisy-chaining pins 11-5 on the switch. Here is my wiring diagram for that. Note, if you align the centers of the switch and the Rheostat, and face pins 6/7 at the rheostat, the switch knob pointer will point at the pot control when selected (nice from a user interface perspective). With jacks on the short side and resistor mounts on the long sides, the switch and pot will be the only things poking through the face of the enclosure, which is nice for graphics. Mine is going inside a combo cabinet and I added an external speaker out jack to the output.
Attenuator Layout.png
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Last edited by crgfrench on Mon 08/03/20 6:46 pm, edited 2 times in total.
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Re: attenuator airbrake

Post by crgfrench »

I cleaned up that Audiofanzine schematic a bit. You can use 6, 11 and 16 Ohm taps on R2; I decided to use 5, 11 and 17.
Screen Shot 2020-08-01 at 10.59.38 AM.png
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Re: attenuator airbrake

Post by crgfrench »

Here is the same circuit that JMP built and that I drew from the Audiofanzine picture. I found this schematic on The Amp Garage, it was posted by bnwitt, Sat May 07, 2011 at 11:15 pm in the "Airbrake schematic or layout" thread. This is identical to my schematic of the JMP layout, just a slightly different visual.
AirbrakeSchematicAmpGarage.png
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Re: attenuator airbrake

Post by crgfrench »

Honey Hush!
20200805_135133.jpg
20200805_134724.jpg
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Re: attenuator airbrake

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