Dummy load headphone plug for the Crack

Welderboy · 1390

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Offline Welderboy

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on: January 25, 2021, 11:09:02 AM
I'd like to make a dummy load headphone plug for my crack so I can burn in tubes without having the headphones plugged in.

Just wanted to confirm I have this right. Since the impedance on the HD650s is 300Ω and the crack Crack output 0.3W, all I need to do I solder 2x 150Ω 0.5W resistors as show below correct?




Offline Paul Birkeland

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Reply #1 on: January 25, 2021, 11:21:32 AM
You can run the Crack with no headphones plugged in and it will be loaded (heavily).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Welderboy

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Reply #2 on: January 25, 2021, 11:49:57 AM
You can run the Crack with no headphones plugged in and it will be loaded (heavily).

Good to know! I have two new tubes coming in and they HD650s are loud enough that it's a bit of a bother.

Curious, do you know if the above approach would have work correctly? I already bought the plug so I might still make it to remind myself the amp is on and burning in.



Offline Paul Joppa

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Reply #3 on: January 25, 2021, 12:01:00 PM
The phones are 300 ohm per side, so 150 ohm resistors would match. Not that there's any problem with 150 ohms for a break-in load.

If you are breaking in an output capacitor, I think you would want a load so the cap carries some current. I have no evidence one way or the other that current through the cap is important for break-in load, but it is often claimed to be important.

Paul Joppa


Offline Paul Birkeland

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Reply #4 on: January 25, 2021, 12:28:24 PM


Curious, do you know if the above approach would have work correctly?
With no headphones plugged in, the output is shorted, which is a 0 ohm load (plus the ESR of the coupling cap plus its reactance at whatever frequencies might be playing through the amp).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man