Bottlehead Crack OTL AMP (Kit/DIY) - Official Thread


New tube… I have a couple more on the way …so begins the tube rolling rabbit hole…



Did this change the noise issues you were experiencing?



Actually the noise turned out to be a ground loop with my mechanical keyboards LED lights…as soon as I turn those off, both my tube amps are pretty silent! The Cayin though with the Cayin stock tubes are pretty “noisy”…so I’m looking forward to getting my new tubes for it.

This RCA is nice…it did change the sound it seems brighter, with less low end. But I would need to do some more A/B testing.

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It’s probably more that the tubes (or other elements of the circuit, but probably the tubes) are picking up the radiated switching noise from the PWM drivers for the RGB LEDs in your keyboard then. A ground loop would have to come via what they’re connected to, i.e. the PC/Mac, unless the keyboards have their own PSUs.

Regardless, I’m glad you got to the bottom of it!



ha yeah, it was process of elimination. I determined it was the keyboard, then tried seeing what would happen if I turned off the LED backlighting…and voila! no more buzzing! it is connected via USB B-C into the Mac Mini…

I now need to research PWM drivers and get myself learnt! I kind of want to go back to school/tech school for electrical engineering…it is fascinating! Too bad I dislike math… damn my brain :wink:



PWM is pulse-width modulation.

The hardware that drives RGB LEDs rapidly switches each of the individual R, G and B LED elements on and off to mix the appropriate colors. The relative on-off duty cycle for each color is what drives their relative intensity/brightness. More off-time than on-time results in a dimmer appearance for each color respectively.

So while software tells the hardware what the PWM cycle is for each color channel in each LED, it’s the hardware LED driver we’re talking about here. It is what it is.

USB-C, which implies USB 3.x, is also rather noisy. Early implementations were sufficiently bad that they could knock 2.4 GHz WiFi base-stations out of comission if placed too close.



Yeah I’m having issue with my Magic mouse and lag, and I’m pretty sure it might be this 2.4GHz noise causing it.

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That’s probably something else.

I’m using a Magic Mouse (V2 … which given when you got your Mac is what you should have) in the middle of a bunch of USB 3.0 and 3.1 (mixed connector types) stuff, and it’s 100% non-laggy.

Try unpairing it and then re-pairing it.

How far is the mouse from the Mac Mini?

What’s between the mouse and the Mac?

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Excuse the mess…and cable management… trying to figure out a better way of routing the shared DP port between my two computers.

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Predicition … get that Mac mini laying flat, with no metal between it and the mouse, and your mouse-lag issues will go away.



But…but it looks so cool like that :wink:

I’ll try it tonight! After the lil beast monkey goes to bed

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