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Hiss problem
Zippy2000
Posts: 6
Hi all,
I've recently purchased a Driverack PA+, but I appear to have a hiss problem. Now, I know that this has been discussed before so I did everything to make sure that I wasn’t dealing with a cable or connection problem. Also, I am not really sure how big of a problem this actually has to be, please read below the clarification for this. I would really appreciate your advice on this!
First of all, my setup looks like this:
DAC --> PA+ --> amp boards (3 pieces from classdaudio.com)
What I did to isolate the hiss to the PA:
- Disconnected the DAC: no effect
- Tried different outputs from the PA on any of the three amp boards: same hiss everywhere
- The amps are dead silent without the PA connected to it
- Using the +4db/-10db switch has no effect, same for the pin 1 switch
- Tried three different cables, from cheap ass to higher end, all show the same amount of hiss
- Connected the output of a cheap ass mp3 player directly to one of the amps: also a hiss, but much, much less pronounced then the PA
A few other things to note regarding the hiss:
- The hiss kicks in a few seconds after powering the PA+. First comes a tiny click and then the hiss starts. I assume this is due to some pop&click protection build into the PA
- The hiss is constant and is unaffected by input volume of the DAC
- The hiss is independant of the crossover frequency. If I change the crossover frequency to a very short bandwith or move the bandwith around, nothing happens to the hiss.
- Also the hiss level seems to be independent of crossover gain. Only when I really crank up the gain towards the +20dB area I can hear an increase in hiss volume
A few other things on my setup
- I am running (semi) high sensitivity drivers, around 94db 1W/1m. This of course makes any present hiss more pronounced
- I need to set the input level to pro (+4db) because otherwise I have deafening volumes at already a fraction of the input volume coming from the DAC
- The amp boards I am using have no gain control, they're always maxed out.
This latter thing is I think the problem, and this is also where the solution can be implemented.
This is where I need your advice: can I put an attenuator between the PA and the amp, effectively lowering the output volume from the PA by let's say 10dB. This lowers the hiss to more acceptable levels (maybe even makes it disappear) and I just have to crank up the DAC a bit higher, but as I said before, it currently already provides enough dB's at low ouput volume.
So I assume it's my setup that makes hiss more pronounced and not the PA+. Happy to hear your thoughts / advice on this!
I've recently purchased a Driverack PA+, but I appear to have a hiss problem. Now, I know that this has been discussed before so I did everything to make sure that I wasn’t dealing with a cable or connection problem. Also, I am not really sure how big of a problem this actually has to be, please read below the clarification for this. I would really appreciate your advice on this!
First of all, my setup looks like this:
DAC --> PA+ --> amp boards (3 pieces from classdaudio.com)
What I did to isolate the hiss to the PA:
- Disconnected the DAC: no effect
- Tried different outputs from the PA on any of the three amp boards: same hiss everywhere
- The amps are dead silent without the PA connected to it
- Using the +4db/-10db switch has no effect, same for the pin 1 switch
- Tried three different cables, from cheap ass to higher end, all show the same amount of hiss
- Connected the output of a cheap ass mp3 player directly to one of the amps: also a hiss, but much, much less pronounced then the PA
A few other things to note regarding the hiss:
- The hiss kicks in a few seconds after powering the PA+. First comes a tiny click and then the hiss starts. I assume this is due to some pop&click protection build into the PA
- The hiss is constant and is unaffected by input volume of the DAC
- The hiss is independant of the crossover frequency. If I change the crossover frequency to a very short bandwith or move the bandwith around, nothing happens to the hiss.
- Also the hiss level seems to be independent of crossover gain. Only when I really crank up the gain towards the +20dB area I can hear an increase in hiss volume
A few other things on my setup
- I am running (semi) high sensitivity drivers, around 94db 1W/1m. This of course makes any present hiss more pronounced
- I need to set the input level to pro (+4db) because otherwise I have deafening volumes at already a fraction of the input volume coming from the DAC
- The amp boards I am using have no gain control, they're always maxed out.
This latter thing is I think the problem, and this is also where the solution can be implemented.
This is where I need your advice: can I put an attenuator between the PA and the amp, effectively lowering the output volume from the PA by let's say 10dB. This lowers the hiss to more acceptable levels (maybe even makes it disappear) and I just have to crank up the DAC a bit higher, but as I said before, it currently already provides enough dB's at low ouput volume.
So I assume it's my setup that makes hiss more pronounced and not the PA+. Happy to hear your thoughts / advice on this!
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Comments
As for high gain speakers I doubt that's the issue, my subs are 104dB efficient and the tops are 104/108dB efficient ( proprietary custom horn loaded )and my systems are dead quiet. Even the not so efficient conventional ones.
Most often it's a gain structure/impedance issue when there is noise with a DRPA.
Just to bypass the one from my computer, which is crap.
I've been reading up on impedance mismatch but I am not sure if I fully understand. I see the PA+ has an output impedance of 120 ohm and the amp boards that are connected to the PA+ have an input impedance of 7k ohm. What I've understood is that if you feed a low impedance output into an amp with a high impedance input, the amp could start to draw power from the source which could result into a hum/hiss?
How to solve this?
With respect to gain structure, as I said I do not have volume control on my amps, they're always maxed out which means I have to feed the PA+ a very low input signal. This means the signal to noise ratio is not so good to begin with.
If you run your amps fully maxed out over your high sensitivity speakers, do you still have no hiss at all?
http://tamaudio.com/store/index.php?route=product/product&path=35&product_id=96
Even with nothing connected to the input of the DRPA+ I have the hiss, so i doubt this is the issue.
Yes indeed. So I was thinking of putting something like a ROLLS SLC19 in between the plate amps and the DRPA+, then tune down the volume on the SLC19 untill the hiss is inaudible, then tune up the input level that goes into the DRPA+, effectively increasing the signal to noise ratio.
In the case above the SLC19 substitutes the lack of input sensitivity control on the plate amps.
Even with the volume on the passive attenuators set to about -20dB (this is an estimate, there is no scale on the attenuators), the output headroom is still huge: the lights on the ouput headroom on the drpa+ barely light up, even at pretty high volume levels. This clearly indicates that I had way to much gain coming from the drpa+ into the amp boards.
Anyway, situation solved!