I am glad to see the recent discussion of the options for digital input boards, freerider/selectronic/oettle. I was just getting ready to choose a mod for my DCX. I have a couple quick questions, maybe the experts can clear up my confusion.
It seems all three use the same basic topology of SPDIF converter chip and SRC. Oettle makes the comment that the other boards do not attenuate jitter. Does this mean there is some difference in topology of the circuit or just that the clock used in his design is lower jitter, both better clock and supply PSRR?
The selectronic board has option for second oscillator, what is the purpose and frequency of this?
Thanks
Dave
It seems all three use the same basic topology of SPDIF converter chip and SRC. Oettle makes the comment that the other boards do not attenuate jitter. Does this mean there is some difference in topology of the circuit or just that the clock used in his design is lower jitter, both better clock and supply PSRR?
The selectronic board has option for second oscillator, what is the purpose and frequency of this?
Thanks
Dave
Has anyone tried changing DCX resistors to change gain level?
Hi, I came across a post in DCX Yahoo group of a guy who recommended changing a few resistors in the DCX with the intention to better utilize the ADC processing by reducing the gain when using analog inputs. It appears no one over the Yahoo group has ever done this, so wondering if it is worth exploring or not. The main difficulty is that all resistors are SMD so changing it can be a pain. All comments welcomed. Below is excerpt from the poster.
As I described in a couple of other posts. It should be possible to
improve the output noise of the DCX significantly by reducing total
input attenuation from -15dB to -3dB (effectively, a 12dB increase in
input gain) and reducing output gain by the same amount. This mod
should reduce output noise level by 12dB. The downside is that it will
also reduce max input signal by the same amount. However, with these
gain changes, it should still be possible to input a full scale single
ended input signal to the DCX without clipping the ADC.
Full scale domestic should be +6dBV (2Vrms). Since the ADC can
tolerate +4.4dBV and we would maintain -3dB of input gain, the +6dBV
domestic full scale signal would be fine (espedcially since this would
require the volume control on the hifi to be set to full scale).
The improvement in noise performance comes from reduing the analogue
gain post from +21dB to +9dB. By doing this, the noise of the digital
path (much noiseir than the analogue output filters) will not be
gained up to the outputs. The reson for increasing the input gain is
so that the straight-through gain of the DCX would remain 0dB overall.
Inputs - Taking input A as an example, R75 should be increased to 10k
and R78 to 5K. This will provide an approx 12dB increase in input
gain. Equivalents resistors in inputs B and C should also be changed.
To maintian mic input gain on channel C, R7 should be changed to 1K.
Additionally, if you know that your preamp (or analogue source driving
the DCX) is already AC coupled then C26 and C41 can be removed and
replaced with wire links. C6 must be kept, as it bocks the vmid level
of the ADC, but should be replaced with an equivalent value higher
quality electrolytic (oscons are good imo). Equivalent caps in inputs
B and C can be treated the same. I would keep the caps on the mic path
of channel C as they are.
While you ae in there, C12 could also be replaced with an equivalent
value higher quality cap.
Outputs - Taking output 1 as an example, R34 and R10 (and equivalents
on other channels) should be increased from 499 to 2K. Other users
have recomended removing the mute transistor T1 as well (shoudl
improve THD a little). I'm not sure how much this would affect pops
and clicks at the output but it might be fine.
Hi, I came across a post in DCX Yahoo group of a guy who recommended changing a few resistors in the DCX with the intention to better utilize the ADC processing by reducing the gain when using analog inputs. It appears no one over the Yahoo group has ever done this, so wondering if it is worth exploring or not. The main difficulty is that all resistors are SMD so changing it can be a pain. All comments welcomed. Below is excerpt from the poster.
As I described in a couple of other posts. It should be possible to
improve the output noise of the DCX significantly by reducing total
input attenuation from -15dB to -3dB (effectively, a 12dB increase in
input gain) and reducing output gain by the same amount. This mod
should reduce output noise level by 12dB. The downside is that it will
also reduce max input signal by the same amount. However, with these
gain changes, it should still be possible to input a full scale single
ended input signal to the DCX without clipping the ADC.
Full scale domestic should be +6dBV (2Vrms). Since the ADC can
tolerate +4.4dBV and we would maintain -3dB of input gain, the +6dBV
domestic full scale signal would be fine (espedcially since this would
require the volume control on the hifi to be set to full scale).
The improvement in noise performance comes from reduing the analogue
gain post from +21dB to +9dB. By doing this, the noise of the digital
path (much noiseir than the analogue output filters) will not be
gained up to the outputs. The reson for increasing the input gain is
so that the straight-through gain of the DCX would remain 0dB overall.
Inputs - Taking input A as an example, R75 should be increased to 10k
and R78 to 5K. This will provide an approx 12dB increase in input
gain. Equivalents resistors in inputs B and C should also be changed.
To maintian mic input gain on channel C, R7 should be changed to 1K.
Additionally, if you know that your preamp (or analogue source driving
the DCX) is already AC coupled then C26 and C41 can be removed and
replaced with wire links. C6 must be kept, as it bocks the vmid level
of the ADC, but should be replaced with an equivalent value higher
quality electrolytic (oscons are good imo). Equivalent caps in inputs
B and C can be treated the same. I would keep the caps on the mic path
of channel C as they are.
While you ae in there, C12 could also be replaced with an equivalent
value higher quality cap.
Outputs - Taking output 1 as an example, R34 and R10 (and equivalents
on other channels) should be increased from 499 to 2K. Other users
have recomended removing the mute transistor T1 as well (shoudl
improve THD a little). I'm not sure how much this would affect pops
and clicks at the output but it might be fine.
If you put a two-resistor attenuator on the output connector, you can attenuate level. At the same time you attenuate noise from both the DSP/DAC as well as the output analog processing. Better, easier, cheaper.
jd
Rereading that, it seems Frank Oettle has detailed commented on those relative merits. If there is anything unclear why not mail Frank directly? He's a nice guy open to discussions, and he is not commercially involved.
jd
Actually there are two different mods:
1. CS8420 replacement because of ‚dull sound’ problem:
improved PLL operation because of improved power supply
improved max. sample rate 192 kHz
improved SRC (AD1896)
2. Low jitter Clock (24.576 MHz) replacement for DACs and DSP
for improved sound quality (also with analog input)
Please see attached table (hopefully you can see it?):
Comments:
a, Power supply data for Selectronic kits is based on the assumption they use LM1117 regulators. If they use LM2936 please use data for the Freerider design.
b, The Oettle design uses only one clock oscillator for 100% sync operation of PLL, SRC, DSP and DACs for improved jitter operation. Typically this common clock works with a 192 kHz sample rate input (instead of 96 kHz for the original CS8420) but guaranteed are 178 kHz only. If you have real 192 kHz data source an optional oscillator can be mounted but this is not synchronous any more. It’s recommended to use sample rate of data source (e.g. 44.1 kHz for CD) and not to up sample data to avoid unnecessary sample rate conversion.
c, The clock input device on the DSP board is a 5 V type.
d, With long cabling jitter and noise values get worse.
upsampling
Hi,
thank you for the useful document.
I have a question about upsampling: you say that it should be avoided, but I have heard of different schools of thought, like
Behringer Ultramatch PRO SRC2496 test
I do not have a direct experience, so I would really like to hear about yours in order to have a more clear idea of the matter.
Thank you,
Ciao
Paolo
Hi,
thank you for the useful document.
I have a question about upsampling: you say that it should be avoided, but I have heard of different schools of thought, like
Behringer Ultramatch PRO SRC2496 test
I do not have a direct experience, so I would really like to hear about yours in order to have a more clear idea of the matter.
Thank you,
Ciao
Paolo
I fear one answer causes 10 questions
I had a quick look at your link. I have to admit I didn’t read it in detail because it wouldn’t be my approach at all but the switch is really cool, isn’t it.
Best would be to have only one common low jitter clock close to the DACs with a data source (e.g. CD-player) which is 100% synchronous to this clock.
But in most cases (e.g. using different data sources) that’s not possible. So data source and DACs have different clocks. This necessitates a sample rate converter. When using a SRC it’s better to up-sample data to minimize distortion. Also in case of DCX data is processed by a DSP. Here the higher sample rate (96 kHz, 24-bit) is a further advantage.
To my point of view the disadvantage of one sample rate conversion (AD1896: 140dB THD) is negligible compared to the several advantages of a digital crossover.
But each further down- or up-sampling will worsen the sound quality although the impact isn’t such huge.
I finished my DCX. Analog A,B inputs with two unbalanced to balanced transformers connected to A/D converter without any opamp. I made two digital inputs on DCX: one is an SPDIF input, and the other is an USB input with a simple USB-spdif converter.I can select betweenthe two digital inputs with a simple mechanical switch. The output is a passive unbalanced version with Bennic coupler. All analog inputs and outputs have Neutrik RCA.
Attachments
Couple of quick questions with a disclaimer - I've only read a few pages of this mega-thread.
First, I'm thinking about buying one of these vs. a dbx Driverack. Plan would be to use it mostly in my stereo but pull it out for PA use with medium to large size gigs with my band (which would be infrequent). In the stereo I'd use it mostly to replace the passive crossovers in my Klipsch KG 5.5 speakers and to allow me to add in some Ratshack Lineaum tweeters for a little dipole sparkle on the top end. So question one is, this versus a Driverack? Question 1b is would this sound pretty good for that application prior to any mods?
Second question is, I'll probably want to upgrade it, and don't mind doing the work, but I have no skills with SMD stuff, so I'd be looking for drop in replacement modules. Whats out there for this, and how easy is it to do?
Third, I'm expecting that in the end my stereo will sound much better with active crossovers, but anyone out there think I'd be better off getting DeanG or Bob Crites to just build me a passive crossover replacement for the speakers? The plan would be to add a solid state power amp to drive the woofers with the Behringer and continue to use my 40 wpc tube amp to drive the mids, probably with another small solid state amp driving the Lineaums. With passives, I'd continue to just use the tube amp.
First, I'm thinking about buying one of these vs. a dbx Driverack. Plan would be to use it mostly in my stereo but pull it out for PA use with medium to large size gigs with my band (which would be infrequent). In the stereo I'd use it mostly to replace the passive crossovers in my Klipsch KG 5.5 speakers and to allow me to add in some Ratshack Lineaum tweeters for a little dipole sparkle on the top end. So question one is, this versus a Driverack? Question 1b is would this sound pretty good for that application prior to any mods?
Second question is, I'll probably want to upgrade it, and don't mind doing the work, but I have no skills with SMD stuff, so I'd be looking for drop in replacement modules. Whats out there for this, and how easy is it to do?
Third, I'm expecting that in the end my stereo will sound much better with active crossovers, but anyone out there think I'd be better off getting DeanG or Bob Crites to just build me a passive crossover replacement for the speakers? The plan would be to add a solid state power amp to drive the woofers with the Behringer and continue to use my 40 wpc tube amp to drive the mids, probably with another small solid state amp driving the Lineaums. With passives, I'd continue to just use the tube amp.
Quick Answers?
Consensus seems to be that there are minimal performance gains from buying a driverack in audio quality, but there may be a difference in reliability.
Major gains in home audio come from feeding digital directly into the DCX, and then attenuating the output signals with multi channel volume controls.
The DCX is ideal for developing your own crossover. Just dial it in and try it out!
My own DCX came to me old tired and broken (Frying bacon noises)
It has extra insulation under the analogue board, the problematical ribbon cable has been replaced with 26 individual silver plated PTFE wires soldered to the PCBS, Signal capacitors have been replaced with Panasonic FC which are ideal for this purpose, as they are available in sizes that will fit inbetween the input relays, Digital decoupling caps are now Sanyo OSCON. I added one pair of FC 100uf caps to the +/- voltage rail supply for the analogue board.
These mods don't involve any SMD work.
Audio quality is now very satisfying.
The last Gig I did was in a local bar playing CD,s A girl was startled by a loud transient, What was that? she said. Answer 'The sound of a drum!'
Consensus seems to be that there are minimal performance gains from buying a driverack in audio quality, but there may be a difference in reliability.
Major gains in home audio come from feeding digital directly into the DCX, and then attenuating the output signals with multi channel volume controls.
The DCX is ideal for developing your own crossover. Just dial it in and try it out!
My own DCX came to me old tired and broken (Frying bacon noises)
It has extra insulation under the analogue board, the problematical ribbon cable has been replaced with 26 individual silver plated PTFE wires soldered to the PCBS, Signal capacitors have been replaced with Panasonic FC which are ideal for this purpose, as they are available in sizes that will fit inbetween the input relays, Digital decoupling caps are now Sanyo OSCON. I added one pair of FC 100uf caps to the +/- voltage rail supply for the analogue board.
These mods don't involve any SMD work.
Audio quality is now very satisfying.
The last Gig I did was in a local bar playing CD,s A girl was startled by a loud transient, What was that? she said. Answer 'The sound of a drum!'
Hi,
first of all: Hello to all of you, this is my first posting in DIY.
At the moment I plan my installation in my homecinema where I want to use the DCX 2496 for EQ the front channels and make the bass management. Therefor I will go analog with 3 Channels (Front/Left/Center) into the DCX and return analog into the home cinema Amp. With the signals from output 4-6 I will connect 2 PA Amplifiers. To make the level adjustment I think about using 2 Samson S-Converts.
But now my challenge:
I would like to make the input tweaks aon the 3 analog inputs by substitution the capacitors. Also I would like to make the "go passive" mod for the 3 output channels.
For both I see some descriptions on Tweaking du Behringer DCX2496, filtrage actif numérique et très haute fidélité, but:
For the input tweak there is only described to change the caüpacitors for Input A/B. Can I also do it for Input C ? What are the 2 related capacitors numbers?
For the outputstage tweak I would mod 3 channels to "go passive unbalanced", and the other 3 ones "go passive balanced". I understand the description, but I do not see where to start? Does anybody made this mod and has some pictures or descriptions? I cannot find the AK4394 described here: Tweaking du Behringer DCX2496, filtrage actif numérique et très haute fidélité as also I cannot find the X13 left in the drawing.
Many thanks for some help.
Kind regards
Liner
first of all: Hello to all of you, this is my first posting in DIY.
At the moment I plan my installation in my homecinema where I want to use the DCX 2496 for EQ the front channels and make the bass management. Therefor I will go analog with 3 Channels (Front/Left/Center) into the DCX and return analog into the home cinema Amp. With the signals from output 4-6 I will connect 2 PA Amplifiers. To make the level adjustment I think about using 2 Samson S-Converts.
But now my challenge:
I would like to make the input tweaks aon the 3 analog inputs by substitution the capacitors. Also I would like to make the "go passive" mod for the 3 output channels.
For both I see some descriptions on Tweaking du Behringer DCX2496, filtrage actif numérique et très haute fidélité, but:
For the input tweak there is only described to change the caüpacitors for Input A/B. Can I also do it for Input C ? What are the 2 related capacitors numbers?
For the outputstage tweak I would mod 3 channels to "go passive unbalanced", and the other 3 ones "go passive balanced". I understand the description, but I do not see where to start? Does anybody made this mod and has some pictures or descriptions? I cannot find the AK4394 described here: Tweaking du Behringer DCX2496, filtrage actif numérique et très haute fidélité as also I cannot find the X13 left in the drawing.
Many thanks for some help.
Kind regards
Liner
I'm at the verge of doing a total mod job on my DCX. This will include janneman's active outputboard, stef1777's power supply (rev1), oettle's input/clock board and replacing the AK4393 DACs for AK4396s. However i think I read somewhere in this (mega long) thread that oettle's board needs a +9V supply and stef1777 power supply doesn't have that. Any tips or solutions on this would be highly appreciated.
Regards
Regards