• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Using a passive volume control hooked to amp output for noise reduction

Joined
Nov 7, 2021
Messages
22
Likes
23
I got a second hand Wells Audio amp recently and found out that the volume is insanely high as well as the noise floor for it's 6.35mm output. Pretty much unusable whenever the music stops playing.

I am thinking of using a 6.35mm to RCA splitter from the amp output to a passive volume control like a Schiit Sys then back to a 6.35mm female port.

Another method might be using a cheap 6.35mm adaptor with a resistor built in. However I am worried about potential sound quality deterioration as some claim to have on Amazon reviews.

Anyone have prior experiences on the topic? Many thanks:)

milo.jpg
 

Lambda

Major Contributor
Joined
Mar 22, 2020
Messages
1,095
Likes
861
Why not get a Amp that works properly and has an appropriate amount of gain for your application?


I am thinking of using a 6.35mm to RCA splitter from the amp output to a passive volume control like a Schiit Sys then back to a 6.35mm female port.

Another method might be using a cheap 6.35mm adaptor with a resistor built in. However I am worried about potential sound quality deterioration as some claim to have on Amazon reviews.
You would also increase output impedance
 

Doodski

Master Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
9,092
Likes
8,586
Location
Canada
Whew! this thing has power output for headphones au plenty.
Yes, you need to attenuate that output down. Or get different amp.
I'm pretty sure there are XLR attenuating in-line adapters.
Give me awhile to google it. I can't remember the company that sells them.
milo.png
 

Doodski

Master Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
9,092
Likes
8,586
Location
Canada
This sort of attenuator is what you want. I am not exactly sure what dB attenuation you need. I don't work in dB for the electronics stuff that I do so you'll need one of the other peeps here to advise you if this is enough attenuation or too much. It has 3 switched positions for 15, 20 or 25 dB reduction. @Lamda is correct in that the output impedance will increase significantly but it will get you up and running if that's all you want.

EDIT: and... your headphone amp has a lot of power so the attenuator needs to be able to handle the power output. This should get you started so you can google more information if need be.
 

Doodski

Master Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
9,092
Likes
8,586
Location
Canada
The power and voltage output of your amp is too much for the Shure model I linked you to. You need something with bigger internal resisters.
shure.png
 

Sharpi31

Member
Forum Donor
Joined
May 20, 2020
Messages
83
Likes
167
You can’t attenuate signal between the amp output and headphones using a line level passive preamp - the signal level and impedances are very different from line level audio (eg. signal between DAC and preamp/amp).

You could try to attenuate the signal before the input of your headphone amp - this will work if the problem is excessive headphone amp gain only (in this situation the noise you’re hearing is the noise floor of the source cleanly amplified by the amp). If the headphone amp has a high noise floor (the noise you hear is coming from the amp, not from the source) then you’ll address the gain issue but still have a noise problem.

You could build a high power voltage divider - I haven’t done the sums but I’d guess you’d need 10-20W(?) resistors. Have a look at the circuits used to adapt a loudspeaker amplifier output down to headphone level. This is the only solution I can think of that will do the job between your amp output and headphone, addressing gain and noise (except for transformers, but that gets expensive and harder to calculate - possibly more expensive than buying a new headphone amp that suits your headphones).
 

JayGilb

Senior Member
Joined
Jul 22, 2021
Messages
334
Likes
402
Location
West-Central Wisconsin
This sort of attenuator is what you want. I am not exactly sure what dB attenuation you need. I don't work in dB for the electronics stuff that I do so you'll need one of the other peeps here to advise you if this is enough attenuation or too much. It has 3 switched positions for 15, 20 or 25 dB reduction. @Lamda is correct in that the output impedance will increase significantly but it will get you up and running if that's all you want.

EDIT: and... your headphone amp has a lot of power so the attenuator needs to be able to handle the power output. This should get you started so you can google more information if need be.
That mic attenuator is meant to be used with a mono input signal and unless the internal connections are known, I would not use it in this application.

I'm not sure what the problem is ? The headphone amp has a volume control, unless the circuit topography is flawed, why would he be getting such a high level of noise ?
 

Doodski

Master Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
9,092
Likes
8,586
Location
Canada
That mic attenuator is meant to be used with a mono input signal and unless the internal connections are known, I would not use it in this application.

I'm not sure what the problem is ? The headphone amp has a volume control, unless the circuit topography is flawed, why would he be getting such a high level of noise ?
Poor ground, poor source signal, noisy amp circuitry. Could be many things. One would need to hear the nasty sound and trace it back with a O-scope. I'm going to stay out of this one. I don't know the pin-outs on the headphone XLR connection nor what the attenuation should be. :facepalm::D I'll just be an observer for this one from here on in.
 
OP
S
Joined
Nov 7, 2021
Messages
22
Likes
23
Why not get a Amp that works properly and has an appropriate amount of gain for your application?



You would also increase output impedance
Yeah I might get rid of it considering its very limited usability.
 
OP
S
Joined
Nov 7, 2021
Messages
22
Likes
23
The power and voltage output of your amp is too much for the Shure model I linked you to. You need something with bigger internal resisters.
View attachment 166795
I was considering something like this: Amazon link and might give it a try. Would only waste my 10 bucks if it fails lol. I found a 300 ohm HD800 works alright with the noise floor but a 64 ohm Z1R suffered miserably. Might need at least 500 ohm of extra impedance to lower the noise to inaudible level.
 
OP
S
Joined
Nov 7, 2021
Messages
22
Likes
23
You can’t attenuate signal between the amp output and headphones using a line level passive preamp - the signal level and impedances are very different from line level audio (eg. signal between DAC and preamp/amp).

You could try to attenuate the signal before the input of your headphone amp - this will work if the problem is excessive headphone amp gain only (in this situation the noise you’re hearing is the noise floor of the source cleanly amplified by the amp). If the headphone amp has a high noise floor (the noise you hear is coming from the amp, not from the source) then you’ll address the gain issue but still have a noise problem.

You could build a high power voltage divider - I haven’t done the sums but I’d guess you’d need 10-20W(?) resistors. Have a look at the circuits used to adapt a loudspeaker amplifier output down to headphone level. This is the only solution I can think of that will do the job between your amp output and headphone, addressing gain and noise (except for transformers, but that gets expensive and harder to calculate - possibly more expensive than buying a new headphone amp that suits your headphones).
Yeah and what's horribly designed about this model is the lack of gain control, plus a lack of XLR input. I first encountered huge ground loop noise from RCA cables and later when all devices are plugged into the same strip, the internal noise floor, which is always there even with nothing plugged in.
 
OP
S
Joined
Nov 7, 2021
Messages
22
Likes
23
That mic attenuator is meant to be used with a mono input signal and unless the internal connections are known, I would not use it in this application.

I'm not sure what the problem is ? The headphone amp has a volume control, unless the circuit topography is flawed, why would he be getting such a high level of noise ?
It seems that the gain is set insanely high and nothing short of 200-300 ohms can be used for these. A 64 ohm 100db/mw MDR-Z1R needed like 1 out of 48 steps to reach normal volume and 2 is already pretty loud. I found similar problems with the Schiit Ragnarök 2's 6.35mm output which just can't be used with most mid to lower powered headphones, despite what paid reviews often BS about "Dead silent when no music was played"
 
Top Bottom