ctechdx

How to build a simple high pass filter?
« on: March 01, 2020, 11:54:13 PM »

I'm having some very low hum in a tube preamp. I did some measures with RMAA and I see there's a high peak on very low frequencies... It goes from 15hz and goes high in 10hz.

Is there some simple high-pass filter I can build only for filter this low hum? A 20hz or even a 15hz hp filter would help. How can I do this?


Murdock

Re: How to build a simple high pass filter?
« Reply #1 on: March 02, 2020, 01:35:23 AM »
I think it would be easier to come up with ideas if you post the schematic of your preamp.
Or do you want to build a standalone filter which you can insert before the preamp? 

gyraf

Re: How to build a simple high pass filter?
« Reply #2 on: March 02, 2020, 04:59:33 AM »
..agree, show us the schematic.

Often this is caused by transformer/output-capacitor resonance

/Jakob E.
..note to self: don't let Harman run your company..

abbey road d enfer

Re: How to build a simple high pass filter?
« Reply #3 on: March 02, 2020, 10:56:45 AM »
I'm having some very low hum in a tube preamp. I did some measures with RMAA and I see there's a high peak on very low frequencies... It goes from 15hz and goes high in 10hz.
Is it really hum? I doubt it. Mains frequency-related hum starts at 50 or 60Hz.
Anything below that should be investigated.
Is it constant? It maybe, as Jakob suggested, sounds picked up by the mic (vibrations, HVAC, tellurics...) and exacerbated by a possible resonance of the xfmr/coupling cap, or a VLF oscillation (known as motor-boating), which is quite frequent in tube devices.
Anyway, without a schemo we can do no more than speculate.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

Related Topics

  Subject / Started by Replies Last post
9 Replies
4531 Views
Last post August 23, 2017, 09:04:10 AM
by gyraf
3 Replies
7089 Views
Last post May 19, 2013, 01:34:47 AM
by EmRR
12 Replies
7278 Views
Last post October 18, 2010, 09:54:48 AM
by johnR
11 Replies
1787 Views
Last post March 23, 2019, 11:24:57 AM
by Rocinante