Scratching sound in left channel [resolved]

[Kurjok]

Hello!

I completed my crack and have listened to it for a couple weeks with no issues. I installed the speedball a couple weeks ago and it was dead quiet until now. I am experiencing a quiet scratchy white noise in the left channel that does not increase with volume. Sometimes it goes away as well but is present more often than not. It persists even with no source connected. Any help is appreciated!

Thanks!

[Paul Birkeland]

It is possible that during the Speedball installation, some joints in the original build that weren't all the way solid are now a bit noisy.  What we recommend is to plug a pair of inexpensive headphones into the Crack while it is running, then poke around the circuit with a wooden chopstick until you are able to activate the noise by poking somewhere specific.  That will tell you where to focus your efforts. 

[Kurjok]

I should also add when I installed speedball one of my insulators cracked, and I replaced it by cutting a piece of plastic in the exact same shape with a hole. Would this affect the left channel?

[Doc B.]

If you mean the insulator between the transistor and the heat sink, yes, using a different material can be a problem. The insulating material must have a reasonably good heat transfer characteristic. They are generally made from mica or from a silicone based material with reasonably good thermal conductivity. A lot of plastics have really poor heat transfer characteristics. If that is the case the heat sink will not be able to wick the heat and the transistor will overheat after a short period.

[Kurjok]

I just tested this by turning on the amp with my headphones on and the noise is present right away now. I will poke around this weekend when I have time to see if I can narrow it down

[Kurjok]

I could not reproduce the noise quickly poking around. Do you think the insulator between the transistor and heat shrink would specifically be causing this noise? I'd like to avoid ordering one due to shipping cost and time

[Paul Birkeland]

What part of the world do you live in?  These are not necessarily too hard to find, but you may have to buy a part locally that comes with one.

[Kurjok]

I'm in Alberta, Canada. It seems that there are some electronics stores near me. Would this part work? https://www.be-electronics.com/product_p/4661.htm

 Thank you for your continued help!

[Paul Birkeland]

That won't work, it's for a TO-3 package, which is way bigger and differently shaped than a TO-220.
Here's the part you want at that vendor:
https://www.be-electronics.com/product_p/4672.htm 

Here's a list of NTE parts distributors in your province:
http://www.nteinc.com/distributor-locator/alberta.php

Just about all TO-220 packaged NTE transistors come with an insulator, so you may be able to pop out and just buy one without any shipping involved.

[Kurjok]

Great, I will pick one of those up and give it a shot over my break in a couple weeks!

[Kurjok]

So I was listening today and something interesting happened...the sound disappeared once my MacBook was fully charged. I'm not sure if this is just anecdotal or the actual cause of the problem. Thoughts on if this could be causing said sound?

[Deluk]

Interesting. Where is your charger plugged in? Same circuit? The charger maybe noisy when working hard but be quiet when it cuts back to idle. You should be able to repeat the test and then try it again with the charger plugged into another outlet.

[Kurjok]

Oddly enough it's plugged into a different outlet. Could the discharged battery be producing some interference that the amp picks up and amplifies into my headphones? I will test again tonight with my laptop in another room and with the charger unplugged.

[kgoss]

What is the Crack input coming from?  Is it the headphone jack, a toslink adapter going from the headphone jack to an external DAC, or a USB/lightning port feeding an external DAC?  An external USB dac that gets its power from the USB port can pass on power noise from the computer.

Have you tried unplugging the MacBook and running it on battery?
Does the noise consistently stop once the MacBook is fully charged?

[Kurjok]

I have USB running from my PC to a Topping D30 (which has external power - plugged into same outlet as the crack).

With my MacBook running on battery I still get the same noise.

I have only observed this last night as I do not regularly charge my MacBook to full battery. This behaviour does however coincide with the timing of me starting school and consequently using my MacBook again. I will test this again tonight to see if I can reproduce the same outcomes.