Dr. Z - Air Brake

Tube or solid-state, this section goes to eleven!

Re: Dr. Z - Air Brake

Postby DrNomis » 26 Feb 2013, 04:54

soulsonic wrote:All I can say is that it sure doesn't even begin to match impedances with the amp - if it's turned down all the way with a 16 ohm cab, the amp is seeing around 22ohms; with an 8 ohm cab it's still around 22 ohms... With the bedroom level set to 50%, it about 20 ohms with an 8 ohm cab, etc, etc... Any time you start messing with impedance mismatches like that it's bound to change the sound. Unfortunately, nearly all the commercial attenuators out there do it from one degree to another.




Hi Soulsonic,


You probably know this already, the actual impedance seen by the amplifier will vary alot depending on what the frequency of the signal being fed through the amplifier, at some point the impedance will peak due to reactance (wirewound resistors exhibit inductance) and capacitive effects, this further complicates impedance calculations..... :thumbsup
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.
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Re: Dr. Z - Air Brake

Postby rosetta » 26 Feb 2013, 05:47

hi guys, I'm decided to build this but I can't found 588-RJS150E RJS150E Ohmite Power Rheostats 50watts 150OHMS on stock is on the bill of components, so I wonder If it can be replace for this one Rheostats 50watt 125ohm 750V Std Shaft which is the same but 25ohm less, so the questions are; do I need to use a sitch with a larger ohm value instead? it will work well? is there any issue with temperature?

can it be used with 4, 8, and 16 ohm with no further problems, isn't it? By the way I want to use it with a 45watt amp I'm building.
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Re: Dr. Z - Air Brake

Postby phatt » 26 Feb 2013, 08:44

Hi rosetta,
To the best of my knowledge the rheostat is only in circuit for the lowest setting, it's not used for the other settings.

I very much doubt 25 ohms will alter the final outcome by earth shattering amounts.

Go build it and have some fun. :thumbsup

Phil.
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Re: Dr. Z - Air Brake

Postby rosetta » 27 Feb 2013, 22:41

phatt wrote:Hi rosetta,
To the best of my knowledge the rheostat is only in circuit for the lowest setting, it's not used for the other settings.

I very much doubt 25 ohms will alter the final outcome by earth shattering amounts.

Go build it and have some fun. :thumbsup

Phil.



thanks a lot.
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Re: Dr. Z - Air Brake

Postby mehfuzhoss » 27 Jan 2018, 23:52

Hello,
I am new to this forum. I have a question about the Air brake. I have followed this layout

http://www.andyharrison.net/files/AirbrakeLayout.jpg

Instead of a 2 pole 6 position i used a 2 pole 12 position. i ordered from e bay and they guy sent me the wrong switch :(

However i have connected everything according to the layout except for the the rotary switch. I plugged it in with my amp (Traynor YCV40WR) and seems to work fine. but some of the position on the rotary switch has no guitar signal at all.

My question is should i replace it with a 6 position or else how can I wire the existing 12 position so I will have attenuated signal on each position. the rheostat works just fine though.

Regards.
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Re: Dr. Z - Air Brake

Postby phatt » 29 Jan 2018, 13:00

Without a very clear close pic of the switch it would be almost impossible to help. With some switches you can see each contact move as you turn but if fully enclosed then you will need to do a continuity test of each position to find which terminals are passing signal.
Just get out your multi meter and find all the tabs which have continuity.
sorry, Phil.
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