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Old 7th January 2011, 01:21 AM   #2891
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OK now that I am home I took a look at the schematics and a am asuming you are talking about TR1 that feeds IC1 a 9420. Can I hook up the S/PDIF output of a QA350 directly to the chip? Is thare anyway to make it mono and keep the 2nd channel of the "B" input? Thanks Andy
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Old 7th January 2011, 02:51 AM   #2892
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OPPs I meant 8420 not 9420. The output chip of the QA350 is a 8406. I do not have a schematic for it.

Can I run from the output of the 8406 chip "TXP and TXN" in the QA350 to the input of the 8420 in the DCX? Andy
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Old 7th January 2011, 03:03 AM   #2893
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TR1, correct. You should be able to feed the 8420 either thru the transformer or a small cap in each line.
That's what the A input does. You could skip the relay if you wanted to.

Have you tried driving the DCX with a simple RCA to XLR cable? It usually works just fine.

You can route the A,B,C inputs where you want, mono, stereo, whatever.
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Old 7th January 2011, 03:16 AM   #2894
AR2 is offline AR2  United States
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Quote:
Originally Posted by 4pyros View Post
OK now that I am home I took a look at the schematics and a am asuming you are talking about TR1 that feeds IC1 a 9420. Can I hook up the S/PDIF output of a QA350 directly to the chip? Is thare anyway to make it mono and keep the 2nd channel of the "B" input? Thanks Andy
Why would you want to bypass digital transformer? It provides galvanical insulation from the dig. source. If you are running S/PDIF instead AES/EBU than you would need to replace 110 ohm resistor to 75 ohm - termination on the TR1 input. Only cheap units are configured without digital input transformer.

I do not think I understand your question, but digital input is on A and presents A and B digital inputs. Within software you could assign routing to be mono, stereo, or whatever else you like it to be.
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Old 7th January 2011, 03:23 AM   #2895
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Quite true. I don't see any reason to mod it - except maybe to baypass the input relay. Tho it does not seem to do much harm.

If you are sending a mono digital signal then no worries about routing.
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Old 7th January 2011, 07:20 PM   #2896
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Quote:
I do not think I understand your question, but digital input is on A and presents A and B digital inputs. Within software you could assign routing to be mono, stereo, or whatever else you like it to be.
On the block diagram it shows the output of the AES/EBU Digital converter going to the A and B channels after the A/D converters. But it would not matter anyway as I would not be using the A and B channels at the same time. The hole system is going to be mono. Andy
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Old 8th January 2011, 02:55 PM   #2897
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You can change the routing if you want. Feed all 6 outputs with only A or only B, for example.
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Old 8th January 2011, 05:14 PM   #2898
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Thanks Pano; I now see that will not be a problum. Andy
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Old 8th January 2011, 06:30 PM   #2899
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Quote:
Originally Posted by sek View Post
I'm in favor of integrated components and prefer to incorporate the lowest possible amount of ICs with the highest respective quality. LME49720 and OPA1632 come pretty close, considering it's just two SO8 ICs per channel. As I won't get tired of mentioning, I'm even looking for a real necessity to keep the LME49720 anyway.
Sek,

The only common-mode reduction mechanism in the LME49720 section seems to be the attenuator. This might affect the OPA1632.

Is the near-infinite input resistance a requirement? Otherwise putting the LME4970s in 2x inverting configuration seems like a better idea to me.

Do you need the attenuator? Otherwise you might want to consider the topology as used for the OP275s in the CA dacmagic; it gives you common-mode rejection and as an added bonus only one in two opamps is really directly in the signal path.

Or am I missing something and can someone (please, pretty please) tell me why the Shine7 topology is so good?

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Old 8th January 2011, 08:34 PM   #2900
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Originally Posted by Brett View Post
almost all of my sources are SE so I don't see the need to do any more than I am
Thats fine of course. I'm conciously selecting or modifying my gear towards balanced interfaces. But there's no point in insisting on balanced I/O for dedicatedly unbalanced sources.

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I might as well get the balancing done in the 1632 or 4562.
Shure, that's what the part is intended for. At least that's it's common use case, driving an ADC with balanced inputs.

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adding extra circuitry to drive short cables makes no sense to me.
I can dig that, although I have a different opinion about it. It surely makes no sense to do multiple conversion steps just in order to drive a couple of short cables. But only having balanced interconnections still wins over only having unbalanced interconnections, even for short cable runs. That's why my decision is to only build or buy devices that connect in a balanced way in the first place.

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Originally Posted by MatchASM View Post
Is the near-infinite input resistance a requirement?
Hmm, I guess it's not. The stage is intended for regular interfacing, no special versatility for high impedance sources or high gain levels is required.

I'm really looking for a reason to dispense with the input buffers, maybe that's the justification.

Quote:
Do you need the attenuator?
Awww, I probly didn't explain myself clear enough here. By linking to the Shine7 schematic I only intended to deliver a source for my idea. I didn't mean to actually copy the whole circuit, i.e. I only wanted to give credit where credit is due.

The portion I applied here is the instrumentation amplifier configuration with one LME in front of the OPA1632 (instead of another unbalanced opamp), not the attenuator inbetween buffer stages.

Quote:
Otherwise you might want to consider the topology as used for the OP275s in the CA dacmagic
Yes, I'm open for other ideas. Unfortunately I don't know the DACmagic from the insides. Could you point me towards schematics or an analysis.

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tell me why the Shine7 topology is so good
As explained above, I don't think it is (for my project), although I could imagine doing something similar in the analog output stage of the DCX.

The design started as an online forum development. I never understood why they mutually agreed on having five amps in the signal path just in order to be able to make the attenuator "symmetrical".

Well, maybe I'm just a little bit reluctant to use the fully differential amp as the first (input) and only (anti-aliasing filter) stage. But as I see from a lot of evaluation boards and commercial products, there seems to be no reason to be afraid of doing so. That's why I made a modification to the schematic (see attachment).

What does everyone think?
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