DIY Airbrake...

[JimboM]

Yet another schematic and layout request! Thanks!

Thanks Mark! I've got it. Greatly appreciated.

[M Fowler]

JimboM,

I'll email you the info right now. EDITED: Information sent.

Mark

[M Fowler]

lotus

Information sent.

Has anyone not received the information they asked for?

Mark

[Teije]

hi i'm marty from Argentina, and I'm looking for an angel so I can build the airbrake.

I'm having a hard time getting the parts for the unit since few shops have them and the really big ones don't have a clue in how to get this parts in english.

Could anyone please make me the favour in looking in this 2 lists of parts and telling me if any will work?

THANK YOU IN ADVANCE

http://www.rodaronline.com/pote/reostats.htm

http://www.rodaronline.com/otros/resist.htm

[rosspix]

I've just ordered the main parts from Mouser (rheostat, power resistors & fittings, switch and enclosure) - came in at around GBP 75, including delivery to the UK. My parts bin should yield some knobs, feet, sockets and fixings.

All being well, the parts should be with me by the end of the week - looking forward to actually building the thing (instead of just researching/talking about it)!

Ross.

[HDeno]

Hey guys,

These resistor values are optimized for a 8 ohms load.. What would e the values for a 16 ohms speaker instead as the 8 ohms version isnt very effective...

[reverbus]

I just finished Airbrake rheostat less. (for use with TW express-ceriatone)
Excellent. I used Hammond chasis 1444-16. Big enough, but some holes were drilled for security reason.
Not yet completely finished (but working), here is how it looks like.

I'd like to mention - BOM for newbees should be more precize.
There is one fixed resistor 25ohm/100W in BOM, but must be adjustable.
I improvised with fixed resistor - ceramic protection was sharpened to find point (wire) of 13ohm.
Also, 8ohm resistor is not mentioned.

Otherwise, thanks guys for additional help.
I always got it when needed. Great community here in "The Amp Garage"!

For those newbees from EU:
Goods were ordered by Mouser, delivered in 4 days (Eu-Slovenia).
Proffesional service and no problems (my first order by Mouser).
If you choose payment "with VAT" and delivery option "Fedex int. priority" + VAT paid by Mouser,
then there are no additional costs (just added VAT for your country).
And VAT is then paid by Mouser (they said delivered from EU-France).
I think this is new option if you order more than 150€ value...good.

[Doug H]

Thanks to everyone who posted the airbrake layouts and schematics.

I just built one and it sounds great. I had the jacks and knobs, got the switch from Mouser, and got everything else (resistors, rheostat, chassis) surplus. Overall cost for me was $35 ( ).

I built the full-blown version with the bedroom controls. That comes in handy with my modded 100W Peavey Windsor. It sounds pretty transparent until you dial the bedroom control down real low. There is a very subtle high freq rolloff on all settings, but I actually like that. Works great for my purposes. I can now run the master vol at 50% or even dime it and get great sound at reasonable volume levels. Works great with my 10 watter too, two or three clicks on the switch is all it takes for that amp.

Thanks again, everyone.

[Travst]

I'd like to get a copy of the layout and any other files, please. Thanks!

bamajawn@gmail.com

[rooster]

reverbus - You just built the Airbrake III, that's what you did. There is another more typical layout that does not invlove the 8 ohm resistor or the 2nd adjustable resisitor. Make sense? I am running the parts you originally bought and am having no problems to speak of - and yes - I do not have the adjustable rheostat.

I am pretty sure that Mark (?) developed the Airbrake III as an idea of his - something beyond the basic Airbrake. I have played one (rawnster's) and it sounds great.

Anyway, let's talk about the impedance of the original Airbrake? Some are saying that it is an 8 ohm device. Well, I am not clear on the Airbrake III measurements but here are the ones I am getting from my AB clone. (Keep in mind that I found and used a 5 position rotary switch so these reading are for the 5 positions only - I do not have the rheostat in place.)

With 8 ohm speaker load connected, clicking from bypass to 'max' resistance:

7 - 8.5 - 10.2 - 11.7 - 13.7 ohms

With 16 ohm speaker load connected, clicking from etc.... :

13.7 - 10.9 - 12.2 - 13.3 - 14.8 ohms

To measure the load, just hook your AB up, pull out the plug that is coming from the amp and measure the resistance from tip to ground, pretty simple. The load will vary a bit as you play but nothing too radical.

Any, from what I see, its pretty clear to me that the original AB was made to favor a 16 ohm load. Which actually makes sense because of the typical 4/12 connection KF favored for his Expresses. But then running 8 ohms isn't completely stinky.

I am not clear what the loads are to the amp in the ABIII. Rawnster, are you game to measure yours?

[reverbus]

Rooster, it's clear for me now. What I wanted to say is - layout (or BOM) for newbees may be a bit confusing - which version of AB it is.
But, in general - it's true and it's neccesary to know what you're doing, otherwise we know that wrong impedance settings may cause smoke from amplifier:-)

From what KF said about Airbrake and some explanation from others - AB can match 4, 8 or 16 ohm load. Sure, to correctly match the amp to the load, you'd have to set the output impedance of the amp to different settings, depending on the load connected and the attenuation setting. It's different attenuation level for different load. Bigger att. for 4ohm and smaller for 16ohm.

I'm not at home now, but next week I can measure and post results for my Airbrake III (if this is correct name for rheostatless with 8 ohm resistor).

Regards

[Blank Frank]

I'm hoping to build the Airbrake III as well-- or really just the regular one y'all have built except, like you, I wanna skip the rheo$tat. I don't need bedroom volume, just wanna take some off my stage volume so my singer can still hear herself. A little.

Would one of you recent lucky winners be willing to forward the schematic and layout to smith AT limetea DOT net? I promise to come back and pay it forward to the next poor bastard...

Thanks! This is my first post, btw... next time I come back I'll expect you guys to PM me detailed instructions on how to build an impossible-to-distinguish Matchless clone out of a Proctor-Silex four-slice toaster. For under $15, if it's not too much trouble...

[benoit]

To measure the load, just hook your AB up, pull out the plug that is coming from the amp and measure the resistance from tip to ground, pretty simple. The load will vary a bit as you play but nothing too radical.

Isn't this over-simplifying things a bit? This will give you DC resistance of airbrake+speaker but that's not the same thing as impedance, which also takes into account reactance. I'm not sure how that would be accurately measured. It may be that these measurements still tell us what we need to know - I only know just enough about this to be dangerous.

[rooster]

benoit - Hmm, sometimes this site blows with the posting business! I wrote a nice paragraph or two about all this but it got 'lost'. Frankly, I cannot do it again, no enthusiasm now.....

Any, remember that the AB design confirms that the 25 ohm resistor is always in place in the circuit when any attenuation is engaged. This means that, looking at the numbers, the first 'click' of the AB is speaker only, the next click - and all others - have the 25 ohm resistor in parallel with the speaker load. Using the math to determine the actual speaker impedance then:

25 X speaker impedance (plus the added resistances at each click, .i.e. 6 - 11 - 16 - 25) ), divided by the value of the parallel resistor plus the speaker impedances (X, X+6, X+11, X+16, X+25) = load in theory.....

We get, with the 8 ohm cab:

8 (speaker only) - 8.97 - 10.79 - 12.24 - 14.22

In practice (from original posting):

7 (speaker only) - 8.5 - 10.2 - 11.7 - 13.7

Here's the 16 ohm cab in theory:

16 (speaker only) - 11.7 - 12.98 - 14.03 - 15.53

In practice (from original posting):

13.7 (speaker only) - 10.9 - 12.2 - 13.3 - 14.8



Well, OK, so benoit, I get that you question the actual readings vs. the theoritical impedances but you can see that they are pretty close. And I still would suggest that the 16 cab is a better match for the box but eh, you sure won't hurt anything with the higher load.

[rooster]

Oh, one other thing? Some of you might be wondering why the box works at all?

In case you don't know, even though the impedances are staying in the park, with each 'click' up from bypass, you are introducing increasing resistive loads that are drawing the audio away from the speaker. The amp doesn't know that the resistors are not making sound, in other words, so it spreads its power throughout the chain. So the speaker looses output power and volume in the process.