Help with an active / digital system

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patherb

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Joined 2007
Hi All,
I am in the early phases of designing an active / digital bookshelf system. I am planning on using a squeezbox as a source. I'd like to run the SPDIF output from the squeezebox into a digital crossover / processor. I've investigated a few options here:

Behringer DCX2496 (modded)
Rane RPM 26z
Ashly Protea 3.24CL

Is there any problem going from the SPDIF output of the squeezebox to the AES/XLR input on these? Any good recommendations on cables? Also, it seems like volume control is an issue. I know Selectronic has a 6 channel volume control that could work here. Are there any units where the volume control is integrated? How about the Ashly?

I haven't put too much thought into the amps as there are a lot of pro or home audio options there. As far as drivers, I was thinking about going with a Raal ribbon tweeter and a Scanspeak Revelator mid/woofer.

Any thoughts or opinions especially regarding the crossover / processor are greatly appreciated. Many thank in advance
Jim
 
preiter

preiter

Member
Joined 2006
I use a Roku SB500 feeding a Behringer DCX2496 for a 3-way active system. Any RCA-XLR adapter should work, I made my own cable.

I know it's heresy, but the Roku has a volume control that affects the SP/DIF output, so I just control volume that way.

I use Trends TA-10s for high and mids and a Gainclone for bass. Speakers are Hawthorne Audio Silver Iris Coaxials and Augies.

All in all, it's a nice little system. Surprisingly inexpensive and simple for a 3-way active.
 
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patherb

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Joined 2007
Thanks vm. Will I have any sound degradation by doing the volume control from the squeezebox?

Also, I want to make sure I understand the signal path correctly. I'll be sending an unbalanced digital signal from the SPDIF output of the squeezbox to the AES/XLR of the digital crossover / processor. Then I'll be sending a balanced analog signal from the XLR output on the processor to the XLR inputs on the respective amps (assuming I get amps with balanced inputs). Is my understanding correct?

I've been leaning towards the Ashly. It looks like a nice piece of equipment. Does anyone have any experience with it?
 
preiter

preiter

Member
Joined 2006
patherb said:
Thanks vm. Will I have any sound degradation by doing the volume control from the squeezebox?

Also, I want to make sure I understand the signal path correctly. I'll be sending an unbalanced digital signal from the SPDIF output of the squeezbox to the AES/XLR of the digital crossover / processor. Then I'll be sending a balanced analog signal from the XLR output on the processor to the XLR inputs on the respective amps (assuming I get amps with balanced inputs). Is my understanding correct?

I've been leaning towards the Ashly. It looks like a nice piece of equipment. Does anyone have any experience with it?
Click to expand...

There is definitely sound degradation using the volume control of the squeezebox, whether you can hear it or not is another matter. What it's doing is attenuating the signal digitally. If you set the volume at half, instead of a 16-bit range of values from 0-65,535 you will be getting a 15-bit range of values from 0-32767. Effectively, you lose 3dB of dynamic range every time you halve the signal.

Of course, other methods also cause degradation of sound quality. And there's nothing stopping you from adding a 6-channel, ganged volume control at a later time.

Your understanding of the signal path is correct. You can use amps with balanced inputs, or convert the signals back to unbalanced.
 
preiter

preiter

Member
Joined 2006
You could easily do a variant of the Lightspeed Attenuator.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=80194&highlight=

Modify the circuit for balanced operation (I'm not sure exactly how you do series-shunt attenuation on a balanced circuit, but I'm sure someone does). Then use one pot to control all 6 channels.

Should be one of the cheaper options available and very good sound quality.
 
MikeHunt79

MikeHunt79

Member
Joined 2003
preiter said:
You could easily do a variant of the Lightspeed Attenuator.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=80194&highlight=

Modify the circuit for balanced operation (I'm not sure exactly how you do series-shunt attenuation on a balanced circuit, but I'm sure someone does). Then use one pot to control all 6 channels.

Should be one of the cheaper options available and very good sound quality.
Click to expand...

I already asked about using this for a DCX2496 in the thread, and was told it was a huge task to match 2 channels, let alone 6. :( Shame really, as this would be a great solution.
 
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dwk123

Member
Joined 2002
MikeHunt79 said:


I already asked about using this for a DCX2496 in the thread, and was told it was a huge task to match 2 channels, let alone 6. :( Shame really, as this would be a great solution.
Click to expand...


If you can live with a stepped attenuator style approach where you only use a few discrete attenuation values, the lightspeed stuff can work OK for multichannels. The idea is that you use the selector switch to switch V between different banks of resistors in series with the LDR, with each resistor custom-trimmed for the specific LDR it's matched with. It's a bit involved to do the matching, but if you can live with 4-6 steps it shouldn't be too bad. I still hope to try this at some point, and use digital attenuation to fill in the gaps between coarse steps.
 
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patherb

Member
Joined 2007
I spoke to GeorgeHiFi about getting a Lightspeed LDR to do the job and he told me that it would be too difficult to do the matching for a 6 or 4 channel preamp. He also said that balanced inputs and outputs would make matching too difficult. Any other thoughts? Should I just convert go unbalanced and use the 6 channel volume control from Selectronic?
 
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patherb

Member
Joined 2007
I think my solution may lie in the pro-audio world. I was looking at something like this which migh do the trick:

http://www.tlaudio.co.uk/docs_07/product_07/5001.shtml

It would be a nice way to introduce some tubes into the system too. It would be ideal if it had another pair of channels and a master volume control, but at least I'm starting to see the light. Can anyone see any problems using something like this for volume control?
 
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