Using a spectrum analysis app on a smartphone can be helpful in sorting out what type of noise you have - I use one called Sound Analyser but there are plenty of others to choose from, just find one that works well with your phone. Measure the background noise in the room first so you have an idea of the environmental noise, then measure the hiss with the amps turned up as you've described. If you start with only the amp that drives the speakers switched on and it's inputs shorted you'll get an idea of how noisy that component is - then you can work your way back up the audio chain by re-connecting pre-amps, phono stage and source, looking at the change in noise profile at each stage.
If any component gives a significant increase in noise at 50 - 60 Hz (or the hamonics at 100 / 120 Hz) then you've got a ground loop hum and using the circuit as described by Rod Elliot at ESP here:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques to separate the audio ground from the protective earth / chassis ground for that component will stop the hum.
If the hiss is broadband white noise then that's likely to be thermal or Johnson noise and could well be coming from the volume pot on the amp. Commercial manufacturers like Denon don't tend to use really high quality parts as they cost too much and can't be justified at the price bracket they're selling the product at. A higher quality pot or even a stepped attenuator may give a quieter background to your music as would replacing carbon comp resistors in the audio path with thin film metal resistors.
In the end there are lots of ways an amp or source component can be improved but the most cost effective way could be to go fully DIY and build something that has really good reviews in these forums
If any component gives a significant increase in noise at 50 - 60 Hz (or the hamonics at 100 / 120 Hz) then you've got a ground loop hum and using the circuit as described by Rod Elliot at ESP here:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques to separate the audio ground from the protective earth / chassis ground for that component will stop the hum.
If the hiss is broadband white noise then that's likely to be thermal or Johnson noise and could well be coming from the volume pot on the amp. Commercial manufacturers like Denon don't tend to use really high quality parts as they cost too much and can't be justified at the price bracket they're selling the product at. A higher quality pot or even a stepped attenuator may give a quieter background to your music as would replacing carbon comp resistors in the audio path with thin film metal resistors.
In the end there are lots of ways an amp or source component can be improved but the most cost effective way could be to go fully DIY and build something that has really good reviews in these forums
The highest possible quality pot will give exactly the same Johnson noise as the cheapest possible pot. If there is no DC present then it is likely that excess noise will be small in either case. Few people use carbon comp resistors nowadays, apart from guitar amp builders looking for distortion and audio builders looking for nostalgia (plus a few who have been told that CC make better grid stoppers).
Perhaps I was wrong to call it Johnson noise then but the comments on commercial pots being selected for a price bracket rather than quality still apply and a cheap pot can very easily be a cause of noise in the system.
Few people building their own stuff will use carbon comp resistors these days - in the commercial products I own (admittedly mainly from the '90s so not cutting edge) I've found little but carbon comp resistors.
Few people building their own stuff will use carbon comp resistors these days - in the commercial products I own (admittedly mainly from the '90s so not cutting edge) I've found little but carbon comp resistors.
I would be extremely surprised to see carbon comp resistors used routinely in any commercial equipment since the 1970s. Carbon film is likely, carbon comp is not. Maybe you are confusing these two quite different resistor technologies?
An expensive pot may reduce noise when the pot wiper is moved, but eliminating DC should reduce this anyway. Unfortunately a lot of designers do not keep DC away from their pots, as they have an irrational fear of capacitors.
An expensive pot may reduce noise when the pot wiper is moved, but eliminating DC should reduce this anyway. Unfortunately a lot of designers do not keep DC away from their pots, as they have an irrational fear of capacitors.
From what tiny amount of actual measured data I've seen, it would seem that the distortion from carbon comp resistors is several orders of magnitude lower than the distortion from the active devices connected to it, and therefore, extremely unlikely to be audible.
I don't expect that this bit of information will have the slightest effect on the popularity of carbon composition resistors, of course.
My private suspicion is that the people who prefer the sound of carbon comp resistors in guitar amps, actually prefer the soft hiss and crackling noises generated by those resistors mixed in with their guitar. Maybe it makes their guitar sound more like the vinyl records or A.M. radio they listened to when they were first inspired to start learning how to play guitar.
-Gnobuddy
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.