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Old 18th January 2010, 07:33 PM   #2401
SQLGuy is offline SQLGuy  United States
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Quote:
Originally Posted by panomaniac View Post
Or look up a it earlier in the thread for ideas about taking the signal after the first opamp - if you want unbalanced. The feedback resistor could be changed to lower gain, too.
No, I wouldn't do that. The previous stage - the opamp directly after the DAC - doesn't just do balanced to unbalanced conversion, it also does the LP filter to remove ultrasonic conversion noise. Changing the feedback there will affect that filter.
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Old 18th January 2010, 07:38 PM   #2402
Legis is offline Legis  Finland
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Will this parallel resistor with mute transistor reduce hiss? Would 6db reduction in gain be adequte to reduce hiss or do I need something like 12dB? Could somebody tell me in words where the transistor is located and how the resistor should be installed. Just solder it to transistor's legs? What resistors are good for audio? So many questions, try to bare
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Old 18th January 2010, 07:48 PM   #2403
SQLGuy is offline SQLGuy  United States
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That depends entirely on where the hiss is coming from. I don't notice much hiss on my system. I'm running balanced to all my amps, though. In the unbalanced configuration, the DCX adds, I believe, 6dB more gain to the output.

Regardless, though, I think you'll get more noise reduction by reducing the 2.32K resistors in the next stage than by shunting the muting transistors.

To reduce the 2.32K resistors, you'd need to order some 1/10th inch 1/8th Watt (IIRC) SMD resistors. 1% metal films would be ideal. You'd also need to be at least a bit comfortable doing surface mount soldering, to remove the original 2.32K resistors. Using 499 Ohm in place of the 2.32K Ohm will drop the output gain by about 6dB, and will also reduce by 6dB any noise sourced between the preamp volume control (if you're using a preamp) and the DAC's LP filter in the DCX.

I suppose, in a pinch, you could also solder, say, a 650 Ohm 1% metal film resistor in parallel with each of the six 2.32K resistors, to give an equivalent of 507 Ohms.
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Old 18th January 2010, 07:59 PM   #2404
Legis is offline Legis  Finland
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Quote:
Originally Posted by SQLGuy View Post
That depends entirely on where the hiss is coming from. I don't notice much hiss on my system. I'm running balanced to all my amps, though. In the unbalanced configuration, the DCX adds, I believe, 6dB more gain to the output.

Regardless, though, I think you'll get more noise reduction by reducing the 2.32K resistors in the next stage than by shunting the muting transistors.

To reduce the 2.32K resistors, you'd need to order some 1/10th inch 1/8th Watt (IIRC) SMD resistors. 1% metal films would be ideal. You'd also need to be at least a bit comfortable doing surface mount soldering, to remove the original 2.32K resistors. Using 499 Ohm in place of the 2.32K Ohm will drop the output gain by about 6dB, and will also reduce by 6dB any noise sourced between the preamp volume control (if you're using a preamp) and the DAC's LP filter in the DCX.

I suppose, in a pinch, you could also solder, say, a 650 Ohm 1% metal film resistor in parallel with each of the six 2.32K resistors, to give an equivalent of 507 Ohms.
Thanks SQL!

I am too running balanced signal to all my amps. The signal coming from the preamp to DCX is unbalanced though. The hiss is very small but audible, just that kind of hiss what you get when the gain is too high. My amps and preamp are almost inaudible even when listened straight from tweeter, with DCX the hiss can be heard from 1 metre if the room is totally silent. Small thing but worth putting right

Do you remember the codes on the board for those resistors that should be replaced? There are quite a few of them in I/O board. I could have them replaced same time with my DACs when I got to the guy that replaces them. I'll start googling those 1% film resistors.


EDIT: Is this the right kind of a resistor (SMD 0805 type). http://parts.digikey.com/1/parts/817...5499rfkea.html

Last edited by Legis; 18th January 2010 at 08:18 PM.
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Old 18th January 2010, 08:31 PM   #2405
Legis is offline Legis  Finland
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Editing time went out.

I think I found those resistors, they are R11, R15, R19, R23, R27 and R 31, am I right?
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Old 18th January 2010, 08:35 PM   #2406
SQLGuy is offline SQLGuy  United States
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Yes, the resistor numbers, and your Digikey part, are both correct.
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Old 18th January 2010, 09:08 PM   #2407
Legis is offline Legis  Finland
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If the gain is reduced by 6dB, does it also reduce the dynamic range by 6dB. Or does this mod have any other negative side effects?

I think it won't affect DR since both noise floor and signal level will drop by 6dB equally, am I right?
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Old 18th January 2010, 09:23 PM   #2408
krzys is offline krzys  Canada
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Default DCX EQ power

Quote:
Originally Posted by SQLGuy View Post
P.S. To be clear, the big difference in EQ between the two is the the DCX offers a single parametric EQ for each output, whereas the DEQ offers the choice of a 31 band graphic equalizer per channel, or multiple parametric EQ's per channel, or a setup that provides graphic EQ with the ability to change Q and center frequency on each band (a paragraphic EQ).

Cheers,
Paul
I have to correct your statement. DCX offers up to 10 EQ filters (parametric or low or high shelving) for each output but limited by the processing power of its processor ie crossover and EQ together. Depending of the crossover slopes uo to 10 filters per output. You can do quite a lot of EQ with the DCX. I used both but discarded the DEQ when I started to use DRC correction. I made the basic equalization with the DCX and DRC makes the rest with very good results. My DCX is fully modified, ie input and output boards, clock and analogue supply for DACs.
Chris
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Old 18th January 2010, 09:41 PM   #2409
Xoc1 is offline Xoc1  United Kingdom
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This Op amp has 2 499R resistors in series on its -ve input
So Input resistance is 998R
Replacing the 2K32 feedback resistor with a 1K0 would reduce the gain by 7.3db
(see post 2233)
So using a 499R on the feedback would reduce the gain by another 6db making 13db in total.
I don't know if reducing the gain of this stage below unity gain is practical or not?
As to if this reduces the noise floor depends on the gain structure of your system. If you are attenuating the DCX outputs into the amplifiers then reducing the voltage drive probably is not going to make much difference.
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Old 18th January 2010, 09:58 PM   #2410
SQLGuy is offline SQLGuy  United States
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Quote:
Originally Posted by krzys View Post
I have to correct your statement. DCX offers up to 10 EQ filters (parametric or low or high shelving) for each output but limited by the processing power of its processor ie crossover and EQ together. Depending of the crossover slopes uo to 10 filters per output. You can do quite a lot of EQ with the DCX. I used both but discarded the DEQ when I started to use DRC correction. I made the basic equalization with the DCX and DRC makes the rest with very good results. My DCX is fully modified, ie input and output boards, clock and analogue supply for DACs.
Chris
Thanks for pointing this out. The default (apparently) is 1 filter per output, and, until I just went now to re-read the manual, I didn't know that NR stood for number of filters allowed.

What's DRC?

Also, how many filters can you practically use before running out of CPU?

Thanks,
Paul
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