Author Topic: Question power resistors Airbrake attenuator  (Read 267 times)

guile

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Question power resistors Airbrake attenuator
« on: November 30, 2018, 01:51:42 PM »
I want to build the Airbrake and I happen to have 30 Ohm instead of the required 25 Ohm power resistors.
Would this be a problem for the Airbrake? (please see attached layout)
Please teach me.
Thanks
« Last Edit: November 30, 2018, 02:09:18 PM by guile »

ahiddentableau

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Re: Question power resistors Airbrake attenuator
« Reply #1 on: November 30, 2018, 03:40:20 PM »
I'm a little confused.  There are two kinds of power resistors in your layout.  One is tapped, the other is not.  Are you saying you have a 30 ohm normal and a 30 ohm tapped, and that they are the same type as the two shown?

guile

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Re: Question power resistors Airbrake attenuator
« Reply #2 on: November 30, 2018, 03:48:41 PM »
Precisely.

ahiddentableau

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Re: Question power resistors Airbrake attenuator
« Reply #3 on: November 30, 2018, 03:56:42 PM »
According to the datasheet there is no 30 ohm version of the tapped resistor cited in that layout.  Do you have a datasheet for the specific one that you've got?

guile

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Re: Question power resistors Airbrake attenuator
« Reply #4 on: November 30, 2018, 04:04:00 PM »
The only difference is that they are both 30 Ohms instead of the 25 Ohms cited in the layout.
« Last Edit: November 30, 2018, 04:11:56 PM by guile »

guile

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Re: Question power resistors Airbrake attenuator
« Reply #5 on: November 30, 2018, 04:12:05 PM »
Could this be helpfull?:
- Draloric resistor 30 Ohm, 160 Watt, GWS 220.
Datasheet: https://www.vishay.com/docs/21003/gws.pdf

- Draloric tapped resistor  0 ... 30 Ohm 100 Watt, Typ ZWS 100 E
https://www.vishay.com/docs/21010/zws.pdf    (not sure)

guile

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Re: Question power resistors Airbrake attenuator
« Reply #6 on: December 01, 2018, 01:56:29 AM »
maybe the schematic could be helpful?

ahiddentableau

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Re: Question power resistors Airbrake attenuator
« Reply #7 on: December 01, 2018, 10:58:39 PM »
The short answer is that it'll be probably be fine.  Your amp is going to see a little bit more of a load when attenuation is active, but the amount is going to be relatively small.  25 ohms to 30 ohms isn't too much--especially if it's interacting with higher (8 or 16 ohms) loads.  You'll have to recalculate the taps if you want to get the attenuation steps just like the original, but if I was in your shoes I'd probably just build it more or less as is and try it out.  My guess is that you'll be plenty close.
« Last Edit: December 02, 2018, 10:19:37 AM by ahiddentableau »

guile

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Re: Question power resistors Airbrake attenuator
« Reply #8 on: December 01, 2018, 11:11:32 PM »
Thanks.
I will build it and report back !

ahiddentableau

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Re: Question power resistors Airbrake attenuator
« Reply #9 on: December 02, 2018, 10:45:09 AM »
Please do that, since I am planning on building a similar attenuator I'm interested.  Some people seem to really like them (at least for smallish levels of attenuation), others seem to think they sound constipated and dull (but then again that's the same thing the haters say about every other kind of attenuator).  I'd like to know what you think.

guile

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Re: Question power resistors Airbrake attenuator
« Reply #10 on: December 02, 2018, 11:19:45 AM »
Will do!

guile

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Re: Question power resistors Airbrake attenuator
« Reply #11 on: December 06, 2018, 12:37:31 PM »
I have another technical question about the Airbrake. The standard circuit has 100 watt power resistors. Does this mean it works safely for amps up to 100 watts? If so, is this the same for 50 watts resistors --> up to 50 watt amps? Is it in fact the Brake Lite?
I assume it does, but need to be sure.
Thanks
« Last Edit: December 06, 2018, 01:08:24 PM by guile »

thesmokingman

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Re: Question power resistors Airbrake attenuator
« Reply #12 on: December 06, 2018, 03:44:37 PM »
the power rating of resistors is the amount of power they can safely dissipate, the power rating of an amplifier is a root mean square measurement of the continuous power the amplifier can deliver. If you're only attenuating some percentage of the power, then sure you're fine. if you're building this to attenuate a large percentage of power you should probably design around that and increase the dissipation capacity. Speaking of dissipation, you'll need to be providing some forced air ventilation to your new room heater.
once upon a time I was Tornado Alley FX

guile

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Re: Question power resistors Airbrake attenuator
« Reply #13 on: December 08, 2018, 10:55:03 AM »
Thanks