Behringer ADA8000 pre bypass questions

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[quote author="clintrubber"]
Four options: internal 12.288MHz or 11.2896 MHz Xtals for 48/44.1kHz,
or wordclock or optical in (ADAT).
Wordclock uses a 4046 PLL.

Schematics are in the GroupDIY Gmail account:

Go to http://www.gmail.com
Username: groupdiy
Password: thelab
[/quote]

Thanks Peter, I got the schematics.
The internal clocks are simple single-inverter xtal oscillators. An interesting measurement on these would be short term variations (jitter) as well as changes with operating temperature affecting the LRCLK. I'd suggest that the internal clocks are far more stable than using any of the external clock options though.

Another interesting note is that the VA rails are derived using 7805 devices. These are usually far more noisy than the LM317 devices so upgrades to the PSU may be worthwhile, particularly since the AD Vref is also derived from this rail. Having a cleaner, better adjusted Vref on both AD and DA might help. I'd have to open one of these up and stick a CRO on it to see.

Edit: I also noticed that the +/-15V rails are derived using 78 and 7915 devices. Also known as noise generators. Interesting that they get 15V from one 7815 and 17V from the other according to the schematic...


cheers,
Geoff
 
I have some exams this month, but I will post some nice solution for this beast.

The problem:
I can't verify them on hardware, since I don't have this gear.

But I can promise you, the quality will be nice :)
 
[quote author="gswan"]Edit: I also noticed that the +/-15V rails are derived using 78 and 7915 devices. Also known as noise generators. Interesting that they get 15V from one 7815 and 17V from the other according to the schematic...[/quote]

I hate fake-science-sentences like this ... it's like "a 074 is always shitty".

Of course, a 317/337-PSU has a little bit less noise in datasheets, but since we want(ed) to remove the mic-preamp, there is only a line-signal.

A mic-signal sometimes needs to be amplified 200x - okay, then you will detect some noise, but not amplifing normal balanced (!) line-level. There, impedance for sending and receiving circut is more important - and the Behringer-receiver and CMRR/InputBuffer is stupid shit!

If you know, how to create a good PSU, you know the 7815 etc. aren't that bad. You need some more caps, but they're cheap and do their work.

My 10cent.
 
[quote author="JD 'ick' B."]It's worse than that. The ADA8000 uses the AL1101 ADC and the AL1201 DAC, both from Wavefront Semiconductor. These chips are clocked at 48kHz (or whatever WC is), and use an internal PLL/synthesizer to generate a 64Fs(ADC) / 128Fs(DAC) converter clock. Based on the VERY wide capture range (=low-Q VCO tank) and the fact that they're using on-die passives for their clock generator I wouldn't be surprised if the converters added more jitter than that 4046.[/quote]
Ah, nothing is unsuspicious in this box :? :cool:
Thanks for adding this. Nice, so the outcome of the jitter-measurement-contest can be surprising.

Note that this also means that the jitter is only correlated between the two adjacent channels in a (stereo) ADC/DAC, as each of the eight converter chips has its own on-chip clock generator.

JD 'ick' B.
Click to expand...
OK, so I figure the least we could do with a stock ADA8000 is to keep stereo-pairs allocated to channel 1,2 or to 3,4 etc.
(assuming Beh. didn't fumble with PCB-routing :wink: )
 
Jitter is attenuated, if you have good hardware on the backend.
You can set RME cards to do reclocking on the bad data from Behringer.
It's well-known that asynchron-recklocking with a good fresh clock DOES sound better.
 
[quote author="gswan"]I'd suggest that the internal clocks are far more stable than using any of the external clock options though.
[/quote]
Hi,

Can well imagine that, but when looking at the total system one has of course to decide which Xtal is going to be Master Of The Universe...
the one in the DAW (with the SMPS and hostile environment) or the one in the ADA8000 (powered by noise :wink: )

Regards,

Peter
 
[quote author="TobWen"]Jitter is attenuated, if you have good hardware on the backend.
You can set RME cards to do reclocking on the bad data from Behringer.
It's well-known that asynchron-recklocking with a good fresh clock DOES sound better.[/quote]
That's a very bold statement, to say the least. Do you have any references to back this up?

The only scenario where async reclocking might help is if you have a DAC with a high quality clock which is being fed by a jittery digital stream (S/PDIF over TOSLINK comes to mind). In a converter like the ADA8000, with a dubious clock synth which is integrated on the ADC/DAC die, the resulting jitter will corrupt your signal, and there's nothing you can do about it.

(Sure, there's a theoretical solution. If the cycle-to-cycle clock jitter can be measured with high precision (not possible on the chips used in the ADA8000), and if the inner workings of the converter chip are predictable enough (think SDC state machine here), and if the analog input data was perfectly Nyquist filtered, then it might be possible to undo some of the effects of ADC clock jitter in the digital domain. Then again, measuring the jitter requires a jitter-free clock, so why not use that as the sample clock in the first place ?)

JDB.
 
[quote author="clintrubber"][quote author="gswan"]I'd suggest that the internal clocks are far more stable than using any of the external clock options though.
[/quote]
Can well imagine that, but when looking at the total system one has of course to decide which Xtal is going to be Master Of The Universe...
the one in the DAW (with the SMPS and hostile environment) or the one in the ADA8000 (powered by noise :wink: )[/quote]
There's one way to find out.

JDB.
[don't mean to sound like a broken record, but for a converter box with 'normal' ADC/DACs I would say use the clock in the converter. Once again those pesky Wavefront chips are the unknown factor]
 
A solution:

1. substitute internal clocks to Tent / Kwak and link them directly to the converters and transmitter/receiver (in simple)
2. substitute converters with Cirrus
3. keep transmitter and receiver
4. substitute the input buffer with professional ones (I have one, which I can offer soon)
5. pull up the new VCO to Wordclock-level and send it out to other converters (as a master-clock) - I've already created sthg. like this, publishing it soon!

Okay, in the end it sounds like: Ripping everything out of ADDA8000, but keep the Wavefront-Chips only, since you can't get them for DIY :)

But the result will be "nice"
 
[quote author="jdbakker"]don't mean to sound like a broken record, but for a converter box with 'normal' ADC/DACs I would say use the clock in the converter. Once again those pesky Wavefront chips are the unknown factor][/quote]

No, they're well-known (datasheet):
Receiving a crystal-derived 48kHz on WDCLK, and audio data on all 8 input channels, the jitter was measured to be 630ps typical on OPDIGOUT.
Click to expand...

Since all ADAT-deviced need to use Wavefront's chips, are ALL these devices that bad??
 
[quote author="TobWen"][quote author="jdbakker"]don't mean to sound like a broken record, but for a converter box with 'normal' ADC/DACs I would say use the clock in the converter. Once again those pesky Wavefront chips are the unknown factor][/quote]
No, they're well-known (datasheet):
Receiving a crystal-derived 48kHz on WDCLK, and audio data on all 8 input channels, the jitter was measured to be 630ps typical on OPDIGOUT.
Click to expand...
[/quote]
That's the OPTOREC, the ADAT receiver, I presume. I was talking about the synthesizer in the Wavefront ADC/DAC chips that are used in the ADA8000.

Nevertheless >600ps is a lot of jitter, especially for a 24-bit system.

[quote author="TobWen"]Since all ADAT-deviced need to use Wavefront's chips,[/quote]
Says who ?

JDB.
 
[quote author="jdbakker"]
That's the OPTOREC, the ADAT receiver, I presume. I was talking about the synthesizer in the Wavefront ADC/DAC chips that are used in the ADA8000.
[/quote]

Who cares about ADC/DAC jitter, if the receiver and transmitter have > 600ps of jitter????

[quote author="jdbakker"]Says who ?[/quote]

Simple: Wavefront has licensed ADAT for their chips only, Alesis has the patent ...
This is a "hack" - nothing more.
 
[quote author="TobWen"][quote author="jdbakker"]That's the OPTOREC, the ADAT receiver, I presume. I was talking about the synthesizer in the Wavefront ADC/DAC chips that are used in the ADA8000.
[/quote]

Who cares about ADC/DAC jitter, if the receiver and transmitter have > 600ps of jitter????[/quote]
As far as I am aware, we were talking about the ADA8000 in this thread. Within that context, OPTOREC jitter only matters if you sync on ADAT/Lightpipe, not if you sync on WC or internal clock. To paraphrase your earlier statement: who cares about OPTOREC jitter when you're not syncing on ADAT.

Now, again within the context of the ADA8000, the jitter from the on-chip ADC/DAC clock synthesizer is something you can never get away from, no matter what clock source you select, be it ADAT, external WC or internal clock.

(and sure, you can take an ADA8000 and throw away everything but the case and the ADAT transmit/receive chips, but then you're likely better off starting from scratch)

[quote author="TobWen"][quote author="jdbakker"]Says who ?[/quote]
Simple: Wavefront has licensed ADAT for their chips only, Alesis has the patent ...
This is a "hack" - nothing more.[/quote]
Many jurisdictions' patent laws have exceptions for research/hobbyist purposes, and there's not much stopping you from implementing a (better?) ADAT transceiver in a CPLD/FPGA, as long as you don't sell it, export it to a stricter jurisdiction or use it as a major part of your commercial enterprise. (Disclaimer: I'm paraphrasing, and I am not a patent lawyer. This is not legal advice!).

Or you could just sign an agreement with Wavefront and buy the ADAT chips from Profusion, they'll happily supply small quantities.

JDB.
 
[quote author="jdbakker"]As far as I am aware, we were talking about the ADA8000 in this thread. Within that context, OPTOREC jitter only matters if you sync on ADAT/Lightpipe, not if you sync on WC or internal clock. To paraphrase your earlier statement: who cares about OPTOREC jitter when you're not syncing on ADAT.[/quote]

I just saw you're talking about OPTOREC, that is not correct!
I was talking about OPTOGEN (ADAT-Encoder/Transmitter).
OPTOGEN's PPL (and this one doesn't care, which clock goes in), has jitter of 630ps!!

OPTOREG has 1,26 ns jitter!

[quote author="jdbakker"]Now, again within the context of the ADA8000, the jitter from the on-chip ADC/DAC clock synthesizer is something you can never get away from, no matter what clock source you select, be it ADAT, external WC or internal clock.[/quote]

Please read the datasheets from Wavefront!
OPTGEN has its own PPL, it only wants a FS inserted and does the rest on its own (but it does it dirty!).
 
[quote author="TobWen"][quote author="jdbakker"]Now, again within the context of the ADA8000, the jitter from the on-chip ADC/DAC clock synthesizer is something you can never get away from, no matter what clock source you select, be it ADAT, external WC or internal clock.[/quote]

Please read the datasheets from Wavefront!
OPTGEN has its own PPL, it only wants a FS inserted and does the rest on its own (but it does it dirty!).[/quote]
<sigh>

Please read the ADA8000 schematics and the Wavefront AL1101/AL1201 datasheets. As long as you don't sync on ADAT, AL1401(ADAT TX)/AL1402(ADAT RX) jitter is irrelevant, but AL1101(ADC)/AL1201(DAC) clock synth jitter will impact the signal.

Why would we care about the OPTGEN jitter if that's going to a DAW? As long as the jitter isn't bad enough to close the eye and cause bit errors the DAW doesn't care.

JDB.
 
[quote author="TobWen"]But most of the people will sync on ADAT.[/quote]
Most of the studios I've been to sync on word clock.

[quote author="TobWen"]What do you sync on?[/quote]
If you have a single converter, you should sync on its internal clock and have the DAW slave to it, either through ADAT or the converter's word clock output.

If you have multiple converters, you should make the most critical converter (usually the one converting your vocals, or the one converting signals with the highest amount of HF content) your word clock master and slave your other converters and your DAW to that.

If you have a master clock such as the Big Ben and you're happy with how it makes your converters sound, you should slave everything to that. Be aware that this is not a minimum-jitter solution; some master clocks even add shaped jitter to their outputs (Apogee, I'm looking at you). Then again, if it works for you, use it.

[quote author="TobWen"]The DAW's card internal clock? I don't trust this one, if this isn't a RME :)[/quote]
What exactly is the DAW's internal clock? Its word clock output? Basically you should never sync a converter to a DAW.

RMEs have notoriously noisy clocks, BTW.

JDB.
 
Hi JDB,

Interesthing things about wordclock generators...

I´m using a Swissonic WD8 WC generator/distributor. The RME cards and apogee DA are clocked to the WD8 (as WC generator) when I don´t need to record and the Mytek AD is off, but when I record, I take the WC from the Mytek AD and the WD8 is used as a distributor for the Mytek Clock. What do you think about this config?

Synthi
 
[quote author="synthi"]I´m using a Swissonic WD8 WC generator/distributor. The RME cards and apogee DA are clocked to the WD8 (as WC generator) when I don´t need to record and the Mytek AD is off, but when I record, I take the WC from the Mytek AD and the WD8 is used as a distributor for the Mytek Clock. What do you think about this config?[/quote]
Your recording path looks fine; for playback jitter will be lower if you let the Apogee be master. Then again, like I said you may prefer the 'sound' of your Apogee when clocked from the WD8, in the same way that you may prefer the sound of a higher-distortion tube mic pre over a cleaner IC mic pre.

Personally I am most concerned about jitter in the ADC path. With the DA you may switch between internal and external clock as much as you like to see which sound you prefer; with the AD there is no way to remove the jitter once it's in the recording.

JDB.
 

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