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Old 20th January 2010, 01:46 PM   #2461
Pano is offline Pano  United States
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Legis. Change the opamps if you like. It could be a fun project and might lower the hiss. May even sound better, I have not tried it, so I don't know.

But get your gain structure right and it WILL reduce the hiss. By as much as 20dB, maybe more. You just need some kind of attenuation between the DCX and the amps. Simple.

Don't put the cart before the horse. Get the gain right first, then do the mods if you need to or want to.
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Old 20th January 2010, 02:38 PM   #2462
AndrewT is offline AndrewT  Scotland
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Legis. ..
...get your gain structure right and it WILL reduce the hiss. By as much as 20dB, maybe more. You just need some kind of attenuation between the DCX and the amps. .....
..... Get the gain right first,...
I used between 20 and 30dB of attenuation between the DCX and the Power Amplifiers. The bass and treble drivers could not be heard emitting any noise with the CD player in standby mode.

Without the outboard attenuation and with the full 15dB of on board attenuation, I could clearly hear hiss at ~ 300mm.
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Old 20th January 2010, 03:22 PM   #2463
Pano is offline Pano  United States
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I'm with you, Andrew. My horns are 110dB/Watt and no hiss. Why? Attenuation after the DCX, as it was intended to be used.

Even with modified outputs I need attenuation - just less of it.
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Old 20th January 2010, 03:47 PM   #2464
AR2 is offline AR2  United States
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Legis...

The source of your problem is fairly simple. What you are trying to do is simply not possible with DCX. When I tried DCX for the first time many years ago, I did the same logical mistake, just as you. I was happy camper thinking, why do I need 6 channel output volume control after DCX? I will just go with analog Preamp in front of DCX and that is where I will attenuate signal. The result and hiss was so bad, that I went back to the store to exchange for the different unit. The result was the same, obviously, unbearable hiss.

What you are trying to do is not possible and not good. Forget about analog attenuation in front of DCX and forget about your preamp. Here is the simple test for you. Set up DCX as a simple two channel DAC. No xover, no EQ, just plain full range out. Plug in digital signal to DCX. Do not attenuate outputs on DCX, keep them at 0 dB. On the output, between DCX and amp place pot, let say 100K. Use any speakers that are with passive crossovers so that you could safely run this test. Listen - no hiss.
The result of this will tell you that the source of your hiss is attenuated analog signal at the input. If you are really stuck and has to go with analog signal in, than that signal has to be at full volume, but obviously not to clip input. Analog in is OK, but why you would do that. You are introducing DA (in your CD player) and AD and than DA conversion. Instead just one DA conversion with digital in. Analog input in my mind would make only sense if you are using turntable, tape player or any other analog source. Performing triple digital conversion versus one simply is inferior and less optimal to digital in.

Next, optimizing gain in your amps will further improve your system and enhance the whole experience. Doing all of the mods mentioned will not solve your problem if you are trying to do the same, attenuate the input signal and by digital pots provided in DCX. The most optimal sound that you will get is if you give a full digital in, 0 or few less dB at the input and 6 (or 4) channel analog attenuation at the output.

Now word on mods and kits. Once you realize that you will need 6 channel analog attenuation, than you will see that are not that easy to find and are expensive solutions. That has to have housing, than add any other mods to the opamps, output boards... It easily overcomes the price of DCX itself and is not that easy to find, execute properly... In my mind Jan Diden's solution is the most elegant solution out there. It solves the input and output circuitry, it gives you remote volume for each channel plus global volume control, plus fits in the DCX case. You simply cannot go wrong about it, and in a short time you will be able to enjoy your DCX, unlike what you are going through now.

Hope this helps,
Good luck
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Old 20th January 2010, 04:31 PM   #2465
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Very well put, AR2. Thanks!
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Old 20th January 2010, 05:25 PM   #2466
mige0 is offline mige0  Austria
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I agree to 99,99% too.

The last 0,01% I'd like to point out - just for *my fun* on contrasting and to "trigger interest for some learning fun" for the novice' here.

There *is* good reason to drive stock unit with analog-IN - actually two.

- first you can use volume control of your preamp which may be convenient for one reason or another. I do not totally agree this is a bad thing to do ! - *if* signal to noise (what goes under "gain structure" here) of your chain is optimized first of course. I have done so and IMO it even can outperform the digital-IN (I have posted the reasons and what to do somewhere way back – fun to look up and check out by yourself!)
- second if you go with attenuation *in front* of the DCX there is a small benefit in that you usually do not "hit the ceiling" easily. What I mean with this is that optimizing for S/N is – to some degree – contradictorily to optimising harmonics and intermodulation distortion. (I know people will come along with "loss of resolution" story – but actually this story isn't the full truth either)

So I hope having given some hot arguments to not "just do mod's out of fun" but to take the challenge to "just read and learn about why actually doing something" which is a loooooot of fun in the long run too.....


Keep swingin'

Last edited by mige0; 20th January 2010 at 05:30 PM.
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Old 20th January 2010, 06:29 PM   #2467
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I looked at the article about the broken samplerate converter issue reported earlier.
However I never understood exactly what cases where affected and to what degree. I found the article to be semantically contradicting as I understood it.

What samplerates and bitdepths will most likely trigger the problem and which will leave it alone?
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Old 20th January 2010, 06:47 PM   #2468
Pano is offline Pano  United States
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Well I have a very hard time getting mine to run at 96KHz rate. 16 or 24 bits.
88.1KHz seems to work OK.
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Old 20th January 2010, 10:00 PM   #2469
AR2 is offline AR2  United States
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Quote:
Originally Posted by panomaniac View Post
Very well put, AR2. Thanks!
Quote:
Originally Posted by mige0 View Post
I agree to 99,99% too.

The last 0,01% I'd like to point out - just for *my fun* on contrasting and to "trigger interest for some learning fun" for the novice' here.

There *is* good reason to drive stock unit with analog-IN - actually two.

- first you can use volume control of your preamp which may be convenient for one reason or another. I do not totally agree this is a bad thing to do ! - *if* signal to noise (what goes under "gain structure" here) of your chain is optimized first of course. I have done so and IMO it even can outperform the digital-IN (I have posted the reasons and what to do somewhere way back fun to look up and check out by yourself!)
- second if you go with attenuation *in front* of the DCX there is a small benefit in that you usually do not "hit the ceiling" easily. What I mean with this is that optimizing for S/N is to some degree contradictorily to optimising harmonics and intermodulation distortion. (I know people will come along with "loss of resolution" story but actually this story isn't the full truth either)

So I hope having given some hot arguments to not "just do mod's out of fun" but to take the challenge to "just read and learn about why actually doing something" which is a loooooot of fun in the long run too.....


Keep swingin'
I love when my post stirs up positive and happy response, and inspire you guys to elevate conversation to the next level!

Stay well
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Old 21st January 2010, 03:21 AM   #2470
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I might as well throw in my 2*bits. Yep, the first effort to make is getting the gain structure correct. Most systems have way too much gain which compromises every thing else.
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