Airbrake Files

[mehfuzhoss]

I made one of these. I would want to have more attenuation. I have a spare 50 OHM 100 watt resistor that I want to use. Can someone with experience tell me where i should put this one on the circuit! Any suggestion is appreciated.

https://imgur.com/aomu4A8

[pompeiisneaks]

Moved to this forum, it's not a trainwreck, although they're often used with them.

~Phil

[martin manning]

I would expect to find this in the Trainwreck Files section. Airbrake attenuators were made and sold by KF’s company, Trainwreck Curcuits.

[pompeiisneaks]

Oh my mistake, I'd not put that together. I'll move it back!

~Phil

[Dr Tony Balls]

Can anyone explain the calculations of IL and Pout from the Attenuator III file in the original post? Should be simple but there's something i'm missing in my own calculations.

[martin manning]

Like this:

[Dr Tony Balls]

Like this:

MUCH APPRECIATED!!!

[martin manning]

MUCH APPRECIATED!!!

np. Fixed a typo in the text equation for VT.

[deiseldave]

Good morning. I have a question about the adjustable 100W resistors for the Airbrake III. at the beginning of this thread there are both a scheme and layout attached. The layout shows to set terminals on R2 at 6 Ohms, 11 Ohms, and 16 Ohms. whereas the scheme shows resistance values 4, 5, 10, and 6. Can someone explain this? Thanks.

[Littlewyan]

4, 5, 10 and 6 are the resistances between the lugs on the resistor. I would be wary of that design though as I don't think it could handle a cranked 50W amp. Also it won't sound as good as the original Airbrake design.

The original design, although it presents a higher than normal load to the amp, also keeps a bit of a the relationship between an amp and speaker. A speaker's impedance is not constant, it varies with frequency and the Airbrake presents 'some' of this to the amp. That's why the original design sounds pretty good. So you can modify the design to keep it at a fairly constant 8ohm load, but it will sound very flat. Hope that makes sense.

[deiseldave]

Thanks. Yesterday, I built per the scheme, and it works, but degrades tone a little as attenuation is increased. I’m wondering if I can reuse some of the parts to build the “M” or “M2” attenuator on the Marshall forums. I’m still reading that long forum thread. Not sure if the “M2” is improved over “M” or just different.
Thanks again for your response.

[Littlewyan]

M2 is an improved version.
Did you build the original Airbrake or Airbrake III?

[deiseldave]

Airbrake III. I had built it prior to your response.

[Littlewyan]

How much attenuation do you need? As you could try making R1 25Ohm on every setting, which will allow the amp to see more of the impedance curve of the speaker. Should give you back a bit more 'feel'.

[deiseldave]

Thanks. I’m thinking for regular jamming in rehearsal type situations that 6 to 9DB attenuation would be all I would need. However, for night time practice, I would like to have double that available to me.
So if I’m understanding correctly, to modify what I have to what you suggested, I would need to:
Clear switch terminals 8 through 12
Jump terminals 8 through 12 to terminal 7

Is that correct? Any idea on what I can expect for the maximum amount of attenuation in this configuration?
Also, have you built the M2? I’m wondering if I should just change focus and get busy building that. It seems like everyone is pretty happy with that