Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: Shamsyrup on June 23, 2021, 09:57:53 AM

Title: Mains hum+ FFT graph included
Post by: Shamsyrup on June 23, 2021, 09:57:53 AM: Hi, previously my stock crack had a slight audible hum. I tried resoldering every joint with new solder and cleaned all the pins. Used bigger caps but the issues remained. Surprisingly when I changed the power supply diodes to a single package vishay bridge rectifier the audible hum was gone, well at least with hd600s. But when I use the 600ohm beyerdynamic dt990 I can again hear the slight hum although not as noticeable as before. Same with high impedance iems. The hum does not change with the volume knob. The magnitude remains same no matter how much I turn the volume knob or change the dac volume. My mains frequency is 50hz.

Is there any solution ? Or this is just normal for crack ? Any suggestions are highly appreciated.

Thank you.
Title: Re: Mains hum+ FFT graph included
Post by: Paul Birkeland on June 23, 2021, 04:08:09 PM: Can you post some build photos? Are the mains power outlets where you are earthed?
Title: Re: Mains hum+ FFT graph included
Post by: diynewbie on June 24, 2021, 01:17:18 AM: I would have thought that a 1 khz hum would have been coming from outside of the crack - either something on mains, in the source chain or through the air. Is it common for circuitry like the Crack to generate such frequencies?
Title: Re: Mains hum+ FFT graph included
Post by: Shamsyrup on June 24, 2021, 01:30:40 AM: Quote from: Paul Birkeland on June 23, 2021, 04:08:09 PM
Can you post some build photos? Are the mains power outlets where you are earthed?

Yes I will post pictures as soon a reach home.
Title: Re: Mains hum+ FFT graph included
Post by: Shamsyrup on June 24, 2021, 01:32:04 AM: Quote from: diynewbie on June 24, 2021, 01:17:18 AM
I would have thought that a 1 khz hum would have been coming from outside of the crack - either something on mains, in the source chain or through the air. Is it common for circuitry like the Crack to generate such frequencies?

1khz is the signal I am injecting. Actual hum is 50hz and it's 2nd order harmonic of 100hz.
Title: Re: Mains hum+ FFT graph included
Post by: Paul Joppa on June 24, 2021, 04:54:16 AM: Quote from: Shamsyrup on June 24, 2021, 01:32:04 AM
1khz is the signal I am injecting. Actual hum is 50hz and it's 2nd order harmonic of 100hz.
What is the voltage of that 1kHz input? Is the gain setting at maximum?
Title: Re: Mains hum+ FFT graph included
Post by: Shamsyrup on June 24, 2021, 08:14:22 AM: Quote from: Paul Joppa on June 24, 2021, 04:54:16 AM
What is the voltage of that 1kHz input? Is the gain setting at maximum?
Line voltage is about 1.8volt p2p. Which gain ? The gain of crack or the interface ?

Quote from: Paul Birkeland on June 23, 2021, 04:08:09 PM
Can you post some build photos? Are the mains power outlets where you are earthed?

I have added the pictures of mains connection and grounding. Also attached some more measurements and pictures.
Title: Re: Mains hum+ FFT graph included
Post by: Paul Birkeland on June 24, 2021, 05:24:31 PM: Can you post a picture of the solder and a picture of any flux that you used?