ntn1 Posted November 2, 2003 Share Posted November 2, 2003 My digital audio setup is very simple: Hughes E86 STB and a DVD player connected to an all digital pre/pro (Sony SDP-EP9ES) though optical and digital coax respectively. The pre/pro is then connected to an analog power amp (Adcom 7400), then to the speakers. When the E86 or DVD player is off, the pre/pro and power amp combination produces absolutely no hiss even with volume is up 100% and ears pressed against the speakers. Only when the E86 or the DVD player is powered on, with nothing playing, there is a mild hiss from the speakers. The hiss level changes with the volume level. How could the digital connection (optical, digital coax) produce the hiss? I appreciate any help. Thanks. Quote Link to comment Share on other sites More sharing options...
lynnm Posted November 3, 2003 Share Posted November 3, 2003 Virtually any piece of audio equipment ( other than speakers ) will produce a certain amount of hiss or noise. The very high efficiency of Klipsch speakers makes them very revealing in this respect. It sounds as if you have narrowed the noise source down to the amp and/or the DVD. Try "floating" the ground by plugging the amp into a 3 prong to 2 prong convertor and from there into the outlet. Sometimes reversing the plug will be helpful. Quote Link to comment Share on other sites More sharing options...
ntn1 Posted November 3, 2003 Author Share Posted November 3, 2003 lynnm, Thx for the response. Pictures of my equipment can be seen here: http://f2.pg.photos.yahoo.com/ph/nicnguye/lst?.dir=/910+with+DD5.1&.view=t The RW-12 subwoofer is on back order. All of my AV components have two-prong connectors, including the Adcom power amp, and all connected to the same power strip. The Earth ground is already floating. I am reluctant to reverse the polarity because the two-prong-connectors are keyed. The hiss is not from the power amp or the pre/pro. As stated earlier, my power amp and pre/pro combination produces absolutely no noise even at 100% volume level. It's when I turn on the DVD player, or the STB that provides digital audio feed that I start to hear the hiss. If it were analog connections, then the hiss would be understandable with ground loop problem. But mine is all digital: Optical, and digital coaxial connections that produce the hiss. How could this be? Thanks. Quote Link to comment Share on other sites More sharing options...
michael hurd Posted November 3, 2003 Share Posted November 3, 2003 Maybe the dac's in the preamp are causing the hiss. Most do produce a little self noise. Try connecting the dvd player with regular analog interconnects, and let the dvd player decode? ( use the dac's in the player) to put out an analog signal. If this cures your problem, the dac's in your pre/pro are causing the grief. Quote Link to comment Share on other sites More sharing options...
formica Posted November 3, 2003 Share Posted November 3, 2003 What might be happening is that the pre/pro may have a type of built in noise gate, activating and deactivating the system when it sees a signal. This would explain why you hear the hiss only when you power on an accessory. You sometimes hear this in recordings where the use of noise gate is common.... but the integration is varied. I agree with the suggestions that this probably because of the noise floor of one of the components and don't believe this is a ground loop problem. Trying the analog inputs is a good idea and the analog input may -or- may-not be treated differently. Rob Quote Link to comment Share on other sites More sharing options...
fini Posted November 3, 2003 Share Posted November 3, 2003 There's always the possibility a mad cat has snuck into the system. You don't have KG4's, do you? fini Quote Link to comment Share on other sites More sharing options...
Rudy81 Posted November 3, 2003 Share Posted November 3, 2003 ntn1: Man, I feel your pain. I just spent the better part of a month trouble shooting my system because of a hiss also. In my case, I was using balanced connections in my pre/pro and amp. That section of the pre/pro has a 6db gain over the unbalanced section. I now use the unbalanced connections and there is no hiss at all. I assume you have in fact a hiss, and not a hum. I know it is a real pain, but you may want to start from scratch. Unhook all your gear and just have the speakers, amp and pre/pro. Listen to them with just those hooked up. ( I imagine you already did that). Then just hook up one thing at a time until you can further narrow down the problem. You might try some good quality interconnects between your dvd and pre/pro. Let us know how it goes. Quote Link to comment Share on other sites More sharing options...
WMcD Posted November 3, 2003 Share Posted November 3, 2003 I am stuck in an analog world, at least no HT receiver, this week. I tried two HT receivers a few years ago. The Sony was quiet enough in a regular mode where there was no digital signal processing. However when I tried the surround modes, all using DSP, there was appreciable hiss (noise). I do use CD players and DVD, which are okay. My read of other posts in the past which descibe circumstances similar to yours, and mine. The DSP circuitry in the HT receiver is the cause. Ground loops, bad grounds, inevitably cause 60 Hz hum, or sometimes 120 Hz hum. All orgininate from our 60 Hz power distribution system. I have no reason to think noise can be caused by them. So reversing power plugs, better grounding, is not going to help. Gil Quote Link to comment Share on other sites More sharing options...
Rudy81 Posted November 3, 2003 Share Posted November 3, 2003 In my limited experience, the ground loop humm is very different from a high frequency hiss usually associated with the electronics of the source. Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted November 4, 2003 Share Posted November 4, 2003 hummm... the digital input produces a hiss when powered up. Turned off, no hiss. I was going to go into some dissertation about how even a "digital black" signal (no toggling of even LSB bits) usually produces some noise in the -90 to -100 dB level, but from your post it sounds like the hiss is there when the component is powered up even if there is no DVD in the DVD player. Okay... One thought - what you might be hearing could be power supply / digital circuit noise propogated through the signal grounds on the interconnects (or the air, for that matter) modulating the output of the preamp or amp. How close are the components? If the Hughs or DVD are close to the preamp, or even amp, I'd try simply moving them further away. If that doesn't work, try getting some ferrite rings you can clamp around the interconnects. You might try DISCONNECTING the source components, and see if you still hear the hiss when you turn them on. If so, that's a clear indication that you have some sort of EMI / RFI problem. Quote Link to comment Share on other sites More sharing options...
ntn1 Posted November 4, 2003 Author Share Posted November 4, 2003 Thanks everyone for responding. It's really a white noise hiss, and not a hum. The level is relatively low enough that it's not noticeable while playing audio, but I prefer to have less hiss than it is now. My all digital pre/pro does not have an analog signal processing section, and does not have analog inputs other than the feedthrough bypass. All the signal processing (volume, filtering, equalizing, etc.) is done in the digital domain. The DACs convert the signal to analog before sending it out to the power amp. I can not test the analog inputs as people have suggested. Thanks to formica & micheal hurd's suggestion, I now realize that my pre/pro does have a "noise gate", and it's the DACs that might causes the hiss. I can hear the relays clicking softly as it detects input signal, probably activating and routing the signal path to the various processing circuitry. At this point, I think the pre/pro is at least 50% of the problem. To the subject of balanced and unbalanced components as Rudy81 has mentioned, I feel this could reduce the hiss if done right. All of my AV components have two-prong AC plugs, so they are probably unbalanced. There is nothing I can do here. Rudy81, What exactly do you mean by the balanced and unbalanced connections? I use standard audio patch cables to connect my pre/pro to the power amp (exact same type for all 5 channels), and optical/digital coaxial cables to connect audio sources to the pre/pro. The optical cable is the one that came with my E86 STB. The digital coaxial cable is home made, using Belden 1694A precision 75-Ohm digital video coax, and Canare true 75-Ohm RCA connectors. I strongly believe it's better than the brand-name cables. I must use the optical connection for the STB, and I must use the digital coax for the DVD. There is no other way to get Dolby digital audio. What else can I do? Ray, Yes, when I turn on the DVD w/o a disc in it, I immediately hear the hiss after my pre/pro detects the supposedly-silent (zero bit level?) PCM stream. I can hear a relay click to route the digital input to the default 2-channel PCM decoder. If there is a disc with DD5.1 on it, the relay clicks again to route the signal to the DD5.1 decoder. And of course, hiss is audible when audio is silent. My DVD & STB are located just above the pre/pro. You can see them in the link I provided in my 2nd post in this thread. I'll try your recommendation eventually to see if things improve. I hope to hear more about balanced/unbalanced components, which I am not familiar with, but heard that it could reduce the hiss noise. Quote Link to comment Share on other sites More sharing options...
hwatkins Posted November 4, 2003 Share Posted November 4, 2003 I too bet on the pre/pro DACS. In my set up the hiss even varies by digital source. Since I have analog inputs I was able to determne that this did not happen (to the same degree) when the input DACS were out of the loop. The flip side - much unlike some reports here, I have never been able to get an absolutely 'quiet' amp. At some point the HF hiss can be made audible if there is a signal going to the speakers. While it may be at near ridiculous SPL, it is there. Good luck on fixing this. Quote Link to comment Share on other sites More sharing options...
Rudy81 Posted November 4, 2003 Share Posted November 4, 2003 ntn1: Some new higher end models are starting to sport balanced connections. That is, connections that use XLR interconnects, large, round 3 pronged connectors. These are generally used by professionals and studios due to superior noise rejection. You would know if you had them. I don't want to get into the details of my hiss problem so as not to hijack your thread. BTW, I too use the Canare RCA interconnect and I am extremely pleased with them. These I made myself to custom length. Quote Link to comment Share on other sites More sharing options...
LarryC Posted November 4, 2003 Share Posted November 4, 2003 Rudy, Aside from the hiss, if you can listen around it, can you tell any sonic superiority from using either the balanced or the unbalanced leads? Thanks -- Quote Link to comment Share on other sites More sharing options...
Rudy81 Posted November 4, 2003 Share Posted November 4, 2003 Don't want to hijack the thread, but here is the answer. In critical listeneing, the hiss is a pain in the neck. You tend to focus in on the hiss. I cannot detect any sonic differance, nor should I unless my unbalanced cables were picking up noise, which they are not. So, in my case, the unbalanced connections are better since I don't have the hiss. In my gear, as in most consumer audio gear that has balanced and unbalanced connections, the balanced section is just taken from the unbalanced digital outputs and converted to balanced electronically. Frankly this just adds more electronics to the signal. In my HALO gear, that electronics adds a 6dB gain to the signal, which when paired with efficient Klipsch, gives me a hiss. I spent quite a bit of time with Parasound tech support and they told me the bulk of the information. My understanding is that in order to have truly balanced connections, the internal makeup of the system must be balanced. Having two separate sections inside a consumer unit would make it price prohibitive. These units are 3K as it is. You can see the thread on this issue in the Technical board under "Noise Floor on Heritage systems" . Quote Link to comment Share on other sites More sharing options...
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