Im not looking for the Answer on how to properly setup a DCX. I know all about it. For this discussion, I accept the DCX with no gain control on the amp side, its "good enough" for that situation. The debate isnt about gain structure either its simply about someone thinking the DCX does not increase (attenuate) the signal going into the amp, heck they believe the DCX does not even increase noise levels. I left the last part alone just to show that the DCX easily attenuates the signal by showing the simple measurement of Compression driver hiss increasing 6 dB (measured with a mic/ARTA)...but still the debate continues.
What Im looking for is the technical details on the "the DCX puts a lot of gain between input and output.", How does it put gain between the input and output?
What Im looking for is the technical details on the "the DCX puts a lot of gain between input and output.", How does it put gain between the input and output?
the DCX has a string of opamps that add gain as the signal passes from input to output.
Actually the signal is attenuated at the (analog) input to bring it down from pro level to the input ADC level. Then at the output it is amplified again (IIRC 13 dB) to bring it back up to pro levels which are about 4 times what your regular home hifi expects. So to optimise it for home hifi you'd ideally remove BOTH the input attenuation as well as the output amplification. Both measures would improve S/N ratio.
jan didden
Of course Jan. This is a pro level unit and to use it at it's best you need to adapt it to it's new application environment (home). Even stock, using it as it was intended to be used and applying the appropriate gain/signal levels and attenuation and it is quiet for home use. Modifying it improves it further of course.
OK, count me now as one who endorses the use of attenuation when using unmodified DCX with consumer hifi amplifiers. I've changed my mind on this, though still say it depends on the amp, attenuation was not a good idea with Krell FPB 300 or higher powered Krells, they have low sensitivity and need the extended voltage output of the DCX for full headroom. But with Parasound and Acurus amplifiers I'm using now, I'm finding attenuation to be essential, otherwise there is audible noise and the extended DCX voltage is way beyond amplifier headroom.
I just hooked up a Meguro noise meter to the DCX in my living room and found it has 0.7mV wideband noise (1mhz bandwidth I think) with disconnected digital input. "A" weighted noise goes down about tenfold, still way too high for most home audio use.
Been planning to get DCX modifications, now I see how essential it is.
Here are two posts on this from my blog:
Audio Investigations: Another day, another twofold (6dB) reduction in noise
Audio Investigations: The total noise reduction was achieved through various means NOT
I just hooked up a Meguro noise meter to the DCX in my living room and found it has 0.7mV wideband noise (1mhz bandwidth I think) with disconnected digital input. "A" weighted noise goes down about tenfold, still way too high for most home audio use.
Been planning to get DCX modifications, now I see how essential it is.
Here are two posts on this from my blog:
Audio Investigations: Another day, another twofold (6dB) reduction in noise
Audio Investigations: The total noise reduction was achieved through various means NOT
I use AES/EBU input all the time from a Tact RCS 2.0 preamp, works great, many different ultimate digital sources. I've never noticed input chip bug. You need to select AES/EBU in the first menu that comes up immediately after you press SETUP. Once selected, you get both inputs A and B from the digital input plugged into XLR "A".
Now I have noticed Behringer is sometimes cranky about accepting signals from computers and/or Emu equipment. I seem to recall that some combinations of digital input to Behringer from Emu 0404 might not have worked and wasn't better when 0404 was disconnected from computer. I had been planning to make the 0404 my alternative ADC, but no dice. Now I have a Lavry AD10 instead. 😎
I'd try something not connected to computer and not Emu (not that there is anything necessarily wrong with Emu, insufficient data).
AES/EBU is higher voltage than SPDIF. I believe the Behringer circuit handles either the higher or the lower voltage (send in SPDIF with RCA to XLR adapter) but may well work better with the higher official AES/EBU voltage.
I bought a dvd player and tried the spdif - no dice. I also tried it with my Musical Fidelity X-Ray V8, and that didnt work either. Its not the cables or anything simple like that, Ive tested it all a thousand times. Ive also tried the SPDIF on the 1212, no results. All of the above should have worked - thanks for your help. Looks like shes going to have to go under the knife.
Im going to take it in. There is really nothing more I can do to determine if there is a problem. Plus the E-mu 1212m soundcard that is currently feeding analog to my DCX sounds like ****, and I sold my cd player. The cold is setting in, and I just want my stereo to sound good again.
crackle/pop fixed-thanks to forum
I've had a DEQ and SRC since they first came out with excellent results, just bought a used DCX off ebay and major noise/crackle microphonics when I touched the box. I read the forum and noted mention of the ribbon's being an issue, so I opened it up again and all three ribbons are supposed to be glued to the bottom of the cabinet, and had separated. So I pulled off the old glue, and basically just pulled up the ribbons so they aren't mashed down, turned it back on and relative silence. Yeah!
I have a 104 db spker's so did have to attenuate the gain and turn up my preamp which helped a lot- but I'm thinking that actually buying a proper balanced to unbalanced transformer to take the pro-signal down for my analogue preamp and back up to the DCX should solve that and I presume having the proper impedance can't hurt either. Question- I am building a 4 way horn system, so will need another DCX. Is there any difference between a new and older used other than firmware?
I've had a DEQ and SRC since they first came out with excellent results, just bought a used DCX off ebay and major noise/crackle microphonics when I touched the box. I read the forum and noted mention of the ribbon's being an issue, so I opened it up again and all three ribbons are supposed to be glued to the bottom of the cabinet, and had separated. So I pulled off the old glue, and basically just pulled up the ribbons so they aren't mashed down, turned it back on and relative silence. Yeah!
I have a 104 db spker's so did have to attenuate the gain and turn up my preamp which helped a lot- but I'm thinking that actually buying a proper balanced to unbalanced transformer to take the pro-signal down for my analogue preamp and back up to the DCX should solve that and I presume having the proper impedance can't hurt either. Question- I am building a 4 way horn system, so will need another DCX. Is there any difference between a new and older used other than firmware?
A couple of resistors/channel will do the same job for a fraction of the price.
what amps?
Doug- I just finished a tapped horn w/98db sensitivity, am using an old Sony N80ES, also just finished an 80hz conical midbass horn which I'm powering with a Mark Levinson #334, next will be a Radian 850pb 113db sensitive Lecleach 280hz round horn powered by a Yamamoto A08-a 45tube amp w/2watts (just starting that project) and finally a beyma cp 25 to be powered by an old yamaha M-4 amp. So for the critical frequencies, I've got my best amps. I have a few others lying around as well. I'm toying with the idea of adding a 4th amp to my old HSU orig subs to cover just 30hz and below.
Doug- I just finished a tapped horn w/98db sensitivity, am using an old Sony N80ES, also just finished an 80hz conical midbass horn which I'm powering with a Mark Levinson #334, next will be a Radian 850pb 113db sensitive Lecleach 280hz round horn powered by a Yamamoto A08-a 45tube amp w/2watts (just starting that project) and finally a beyma cp 25 to be powered by an old yamaha M-4 amp. So for the critical frequencies, I've got my best amps. I have a few others lying around as well. I'm toying with the idea of adding a 4th amp to my old HSU orig subs to cover just 30hz and below.
resisters
Bret-I appreciate the suggestion. While I'm ok at building the speakers, I don't understand electronics that well. Basically, I am taking a pro XLR out to my Rogue preamp's rca in's by using an XLR to RCA adaptor. I think the problem is that the returning analogue RCA to XLR for the Berhinger DEQ is too low. So if I attenuated the signal to the Preamp, I'm not sure what that would get me. I thought the noise was being introduced from the preamp out to the XLR in. I admit I'm not loving the idea of adding transformer's with their own noise/distortion. If I can solve the issue with just attenuation before the pre-amp- how would you add resistors to the XLR/RCA adapter? I am using a digital AES/EBU out from DEQ to DCX. I'm open to any help/suggestions-thanks again.
Bret-I appreciate the suggestion. While I'm ok at building the speakers, I don't understand electronics that well. Basically, I am taking a pro XLR out to my Rogue preamp's rca in's by using an XLR to RCA adaptor. I think the problem is that the returning analogue RCA to XLR for the Berhinger DEQ is too low. So if I attenuated the signal to the Preamp, I'm not sure what that would get me. I thought the noise was being introduced from the preamp out to the XLR in. I admit I'm not loving the idea of adding transformer's with their own noise/distortion. If I can solve the issue with just attenuation before the pre-amp- how would you add resistors to the XLR/RCA adapter? I am using a digital AES/EBU out from DEQ to DCX. I'm open to any help/suggestions-thanks again.
I assume the signal path is preamp - DEQ - DCX - amps.
You want a high analogue signal level into the Behringer digital chain to get you max SNR. This will give a high analogue level out from the DCX, typically enough to overload most domestic amps that do not have input attenuators. It is here that you need to attenuate to get it back to an appropriate level for the amps.
It takes a resistive divider to attenuate the level, basically a fixed volume pot of 2 resistors per output channel of the DCX.
Take the positive o/p of a DCX channel (pin 2) and add R1 and R2 at the RCA end.
The actual values will need to be determined under test depending upon the varying sensitivity and input Z of the amps involved. The total load seen be the DCX can be quite low, say 10k (R1 + R2//Rload : Rload = amp Zin) which should give you more than enough flexibility to adapt for your varying amps.
I am using a lot of different amps with my DCX's and this has worked well.
You want a high analogue signal level into the Behringer digital chain to get you max SNR. This will give a high analogue level out from the DCX, typically enough to overload most domestic amps that do not have input attenuators. It is here that you need to attenuate to get it back to an appropriate level for the amps.
It takes a resistive divider to attenuate the level, basically a fixed volume pot of 2 resistors per output channel of the DCX.
Take the positive o/p of a DCX channel (pin 2) and add R1 and R2 at the RCA end.
The actual values will need to be determined under test depending upon the varying sensitivity and input Z of the amps involved. The total load seen be the DCX can be quite low, say 10k (R1 + R2//Rload : Rload = amp Zin) which should give you more than enough flexibility to adapt for your varying amps.
I am using a lot of different amps with my DCX's and this has worked well.
A few months ago I announced that I will be making PC boards that will hold Lundahl transformers and balanced B1 jFet buffers for balanced output mod from my modified DCX2496. I was tired of having everything point to point and wanted to make it all nicer. Also I did not have buffers, and with the help of my friend Choky, we came to the design that I have published here before. Than My another friend Christian came into the help and he did the PC board design. I sent it to China, waited about 2.5 months, and miracle! Boards arrived today. Here they are in all their glory. They are stunning, black with gold plating!
There is one more board, that I did not shoot and that one will carry output XLRs, RCAs and switches for conversion from balanced to single ended. Regulators are double regulation, dual supply, and third channel is for +5 V supply for my relay volume control that will be housed together in the case with buffers and regulators. Buffers boards are 6 balanced channels, with cap multipliers.I will post my progress. I am supper excited to complete this project!
There is one more board, that I did not shoot and that one will carry output XLRs, RCAs and switches for conversion from balanced to single ended. Regulators are double regulation, dual supply, and third channel is for +5 V supply for my relay volume control that will be housed together in the case with buffers and regulators. Buffers boards are 6 balanced channels, with cap multipliers.I will post my progress. I am supper excited to complete this project!
Attachments
May I give you another ideea to create the 4th way of sub-bass with only one DCX?
In case you are using powered subwoofers (with integrated low-pass crossovers) use the second output of DEQ as the input for them. In this case, for maintaining a consistent relation between mains and subs at volume changes you need to use digital level (+/-15dB) of DEQ.
I'm using such a configuration and for 0dB digital level I'm situated at the "normal" listening level in my room (there are some rare cases when my wife pretests and I need to put an -6dB to have peace in my family).
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