[ebag4]

I am currently running a Bolder analog modded SB3 into a Burson Buffer and then on to my DIY amp4.  I am considering going to an active crossover (namely the Behringer DCX2496) using multiple amps.  My question is, would there be any reason to keep the Burson Buffer if I am adding a stage between it an the amps?  My gut tells me that there would be no reason to since the goal of the buffer is to match the source to the amp but I want to know what you think.

Thanks!
Ed

[zybar]

I am currently running a Bolder analog modded SB3 into a Burson Buffer and then on to my DIY amp4.  I am considering going to an active crossover (namely the Behringer DCX2496) using multiple amps.  My question is, would there be any reason to keep the Burson Buffer if I am adding a stage between it an the amps?  My gut tells me that there would be no reason to since the goal of the buffer is to match the source to the amp but I want to know what you think.

Thanks!
Ed

Ed,

I might be able to answer that question very soon as I am getting my Emerald Physics CS2 speakers and DCX2496 in the next few days.

I'll make sure to post.

George

[ebag4]

Thanks George, I look forward to your observations and comments.

Ed

[Wayne1]

Hello Gents,

I have been doing a fair amount of research into the DCX in preparation of modding it. There are a few items you may want to consider before you go to the DCX.

First off, it is designed to be used with Pro Audio balanced signals on both input and output sections. Pro Audio balanced means 10 volt signal levels. Consumer gear usually means 2 volt signals. The analog modded SB has a MAX output voltage of 1.1. I think you might have, at least a noise problem if you try to run an analog modded SB direct into the DCX without any additional gain. In fact, you may want to have the Buffer modded to increase the gain.

The DCX also puts out 10 volts. This is quite a bit hotter than most consumer gear. You will have to attenuate to the output levels of the DCX.

Everything I have read about the DCX says you want to run the maximum amount of signal into it and then lower the levels post processing. There are many different mods that will be offered for the DCX. Some will allow the input and output levels to be used with consumer gear.

The same problem exists with the digital input. It is designed for the AES standard which uses a larger voltage than the SP/DIF standard. It may work but I have read of some problems people have had feeding SP/DIF into it. There are devices which will convert the SP/DIF to AES. There is also a mod in development to allow SP/DIF to be used directly into the DCX.

There will always be a problem adapting Pro Audio gear to be used in the consumer level. The many mods being designed now are going to help this, but they are not inexpensive to implement and none are really plug and play. Have fun with the DCX, but be aware that difficulties may exist in interfacing a stock Pro Audio product with a modded consumer product.

[doug s.]

i would try using the burson buffer on the output side of the dcx, for the hi-pass amps...

re: the gain issues wayne mentions w/the pro-audio gear, this can be overcome easily w/two-resistor woltage dividers...

doug s.

[ebag4]

George (Zybar), do you have any initial observations regarding how well the DCX2496 works with the Bolder analog modded Squeezebox with and/or without the Burson Buffer?

Thanks,
Ed

[zybar]

George (Zybar), do you have any initial observations regarding how well the DCX2496 works with the Bolder analog modded Squeezebox with and/or without the Burson Buffer?

Thanks,
Ed

Not yet...hang in there.

George

[PaulHilgeman]

Like Wayne, I would recommend using the burson buffer to increase voltage level as high as you can without clipping before the DCX.

I spent about 2.5 years with the DCX2496 and using the analog inputs you need to get near pro-level voltages to make it sound as transparent as possible.  This will make sure that the processing going on, A->D Conversion and D->A conversion occurs at the greatest possible bit depth. 

Then if you are stuck using the analog inputs with your volume control before the DCX2496, you need to make sure that you are using as much of the range of your analog volume control as possible by using voltage dividers on the output (not altering input or output levels on the DCX).  Make sure that your quietest album can get to full volume with your preamp cranked and then a little bit so that you have the most flexibility possible.

The best option is to use a CDP with AES outputs and then a 4-6 channel matched volume control after the DCX2496.  Like this, it sounds good. 

As you are playing with it, obviously listen first, but if things sound flat an un-dynamic you are probably killing off too much of the signal digitally and turning your 16 bit CD data into 4 or 5 bits, which just kills dynamic range and the micro detail on any recording.

Keep the levels inside the DCX2496 as high as possible and attenuate as much as possible after.

-Paul

[NewBuyer]

When fed a digital signal, some digital signal processors (DSP's) can alter the digital signal content past 0dbfs (pre-D/A), which of course results in digital clipping and distortion. I don't know if the DCX2496 operates like those other DSP's -- but if it does, then you might want to be careful about this aspect when used this way. [Does the DCX2496 have a clipping indicator?]

A little digital attenuation pre-D/A can be a very good thing with these DSP's. Paul's warning about "Keep the levels inside the DCX2496 as high as possible..." is very good advice - just remember that the "as possible" part means not too low, but not too high either!

[TomS]

This all makes perfect sense now that those with some experience have chimed in.  Clayton was using a Modwright LS36.5 preamp after the tube DAC, which is both balanced and probably has gobs of output.  I never really connected why he did this until you fella's laid it out so nicely.  I kinda'  like the idea of pumping up the Burson buffer gain or maybe even a balanced (double) buffer version, then attenuating the back side of the DCX (4 or 6 channels depending on how many bass panels/amps).  Seems like you'd need the Didden 6-channel output mod to do it all the right way.  I'd still prefer to go Squeezebox digital out to DCX digital in somehow, if the interface could be worked out.   Let us know how this all works at the Tweek Geek GTG.  Tom

[PaulHilgeman]

I found that it has greater than 15 dB of headroom when coming in with a full bore signal.  It will not clip as long as you reduce the output levels accordingly... i.e. the output stage clips at around pro-levels but the internal signal processing has very good headroom above pro levels.

-Paul

When fed a digital signal, some digital signal processors (DSP's) can alter the digital signal content past 0dbfs (pre-D/A), which of course results in digital clipping and distortion. I don't know if the DCX2496 operates like those other DSP's -- but if it does, then you might want to be careful about this aspect when used this way. [Does the DCX2496 have a clipping indicator?]

A little digital attenuation pre-D/A can be a very good thing with these DSP's. Paul's warning about "Keep the levels inside the DCX2496 as high as possible..." is very good advice - just remember that the "as possible" part means not too low, but not too high either!

[PaulHilgeman]

This all makes perfect sense now that those with some experience have chimed in.  Clayton was using a Modwright LS36.5 preamp after the tube DAC, which is both balanced and probably has gobs of output.  I never really connected why he did this until you fella's laid it out so nicely.  I kinda'  like the idea of pumping up the Burson buffer gain or maybe even a balanced (double) buffer version, then attenuating the back side of the DCX (4 or 6 channels depending on how many bass panels/amps).  Seems like you'd need the Didden 6-channel output mod to do it all the right way.  I'd still prefer to go Squeezebox digital out to DCX digital in somehow, if the interface could be worked out.   Let us know how this all works at the Tweek Geek GTG.  Tom

I have used several CDPs with S/PDIF out through a digital transformer with success.  Sounded fine.  Got the transformer from Phil at BESL.

[JoshK]

If you need some gain, an Aikido line amp could be just the ticket.  Very linear, low distortion, class A and tubes with low output impedance.

[mgalusha]

I'd still prefer to go Squeezebox digital out to DCX digital in somehow, if the interface could be worked out. 

There are plenty of folks doing this. It's not too difficult to change the input from AES/EBU 110ohm to SP/DIF 75R, at least if you're willing to hack the mainboard. The data sheet for the Crystal input chip has a diagram of the suggested "consumer" input, SP/DIF. Basically a 75R resistor and a couple small caps.

Better will be the new input module that Selectronic is releasing in a few weeks. Supports up to 24/192, has better clocks and has both SP/DIF and AEs/EBU inputs.

In either case that's what I plan on. I added an BNC output to my SB for just this reason. I've never used it's digital out but I will with the DCX.

Now if my kit from Jan Didden would just get here...

Mike

[NewBuyer]

I found that it has greater than 15 dB of headroom when coming in with a full bore signal.  It will not clip as long as you reduce the output levels accordingly... i.e. the output stage clips at around pro-levels but the internal signal processing has very good headroom above pro levels.
-Paul

Hi Paul, this is interesting - are you saying the unit can process and output (unclipped) a digital signal which is at greater than 0dbfs? I understood that for a digital signal at above 0dbfs, the waveform information was clipped by definition - but I am by no means an expert on this subject.

P.S. For those needing coaxial to AES/EBU conversion, could you use the Hosa product for that?

[PaulHilgeman]

No, I think I did a poor job of explaining.

Lets say you want to add 15dB of boost at say 30Hz.

You have a 0dbfs signal at 30Hz coming in.  As long as the output level is digitally turned down -15dB, it will process it without clipping.

I have since sold my unit, but I believe it has some headroom beyond this.  In other words, you might not have to turn the output level down quite that much.

But since all of this is done in the digital domain, you are effectively loosing data in the areas that are not boosted.

That said, the method that they use is pretty good and even 10dB of filtering and adjustment shouldn't be that audible, especially with a digital input.  Analog and digital data is unconverted to 32 bit depth for processing, then converted back to 24 bit depth for D/A conversion before the output stage.

Also if you have one of these, and are using the digital input, the clipping indicator is NOT correct, do not trust it.  Trust your ears, digital clipping is as obvious as clipping gets.  Also, I would recommend making a CD, or digital files of 0dBfs signals in the bass and power bands to make sure you aren't clipping.  You will of course need a passive way to turn the volume down after the output stage though.

Conversion is tough, the requirements for AES3 are tough, SPDIF current is 8mA, AES3 is 64mA or so.  Voltage for SPDIF is 0.5 rms, AES3 is 2-7.  So, obviously the transform is not direct in terms of ohms law there.  But like I said before, I tested with several CDPs and had no problems using a transformer. 

Your digital solution will probably work, but I havent tried it.

This is good reading on the subject:

http://www.rane.com/note149.html

Also DIY with Lundahl parts:

http://www.kandkaudio.com/transformers.html

Or just buy EXACTLY this:

http://www.fullcompass.com/product/264015.html

Hope this all helps

[Davey]

The DCX is confusing at times with regard to the input clipping indicators, but as Paul says, they are not reliable.  0dbFS signals will cause those indicators to flash quite a bit.  However, the clipping indicators on the output channels are reliable.

If the input signal is 0dbFS and the unit is programmed with no filtering or EQ or level adjustments the outputs will not clip.  However, once you apply a crossover filter, say a LR24, the waveform crest factor will change and the unit will clip and light the output clipping indicators.  Of course, if you program some boost or level increase the unit will also clip.  In this type of situation where the input is really "hot" and the volume control is downstream it's best to set the input level controls at about -3db.

A transformer should work fine for using SPDIF inputs....or some fellas use a Monarchy DIP or similar.

I think the only way the DCX2496 should be used is with large input levels that are not volume controlled.  (Multi-channel volume control downstream.)  The specifications (dynamic range, S/N ratio) say this shouldn't be necessary, but practical experience from a few years now has proven to me otherwise. 

Dave.

[PaulHilgeman]

If the input signal is 0dbFS and the unit is programmed with no filtering or EQ or level adjustments the outputs will not clip.  However, once you apply a crossover filter, say a LR24, the waveform crest factor will change and the unit will clip and light the output clipping indicators.  Of course, if you program some boost or level increase the unit will also clip.  In this type of situation where the input is really "hot" and the volume control is downstream it's best to set the input level controls at about -3db.

Ok, so there is zero additional headroom, I stand corrected.

I think the only way the DCX2496 should be used is with large input levels that are not volume controlled.  (Multi-channel volume control downstream.)  The specifications (dynamic range, S/N ratio) say this shouldn't be necessary, but practical experience from a few years now has proven to me otherwise.  Smile

In no so few words, that is exactly what I was getting at.  I could do it in even fewer words, but I will hold back

Thanks Davey,
Paul

[mgalusha]

Or just buy EXACTLY this:

http://www.fullcompass.com/product/264015.html

Makertek has these in stock for $29.95 - http://www.markertek.com/SearchProduct.asp?item=NA%2DBF&off=72&sort=prod

Part #NA-BMX.

[sunshinedawg]

Makertek has these in stock for $29.95 - http://www.markertek.com/SearchProduct.asp?item=NA%2DBF&off=72&sort=prod

Part #NA-BMX.

Are you going to get the na-bmx temporarily and then do the module from Selectronic later?