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Old 1st October 2006, 10:38 PM   #1001
Bricolo is offline Bricolo  France
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that's an interesting point, but it can also be positive:

say that you use it NON-OS, and have a 176kHz clock for the DEM
all the bits will use a 1/44 kHz sampling period, so if you use the DEM at 176kHz (4 times faster) the bits will be switched exactly between 4 of the current miror outputs. since there are 4 mirors on every stage, you get an average of all of them, exactly the average

but I'm wondering the effect it would have on an oversampled system, because you wouldn't have the time to use all the mirors during one sampling period
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Old 2nd October 2006, 11:33 PM   #1002
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Hi EC,

Quote:
The op-amp I/V converters use 4 expensive OPA627's, so I decided to try passive I/V setups using non-inductive 15 Ohm copper wire resistors. Dual resistors were "merged" in a single winding because I use a differential setup. Then I increased the gain of the existing differential amplifiers. The enhancement in perceived sound quality was much more than I had expected.
Finally!
I think that now you can try passive I/V with a TDA1543 DI-DAC, which is one of my plans, in a sort of DDDAC'ed DI-DAC (or DI'ed DDDAC ), with "n" towered DACs.
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Old 3rd October 2006, 09:24 AM   #1003
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Maxlorenz,

unfortunately, I do not have so much time as EC as I relocated homes, so if you have some feedback on the DI setup with the dddac modules, let me know !!

doede
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Old 3rd October 2006, 05:25 PM   #1004
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Hi Doede

For doing this, I need first that EC make some PCB's and then buy the components, specially the TDA1543 DAC chips, (at Thomas' or Doede's site )
* 64 chips for an octal DI-8*DAC towered-DAC. Of course, I can try octal DI-DAC with single chip first and then go to 2->4->8. Or maybe a 16 DAC version to build 4 stories towers

As for the sound...who cares? The picks will be awesome, I'm sure

Regards,
M
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Old 3rd October 2006, 05:30 PM   #1005
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Try PCM56 + MSB adjust + 500 ohm per DAC passive I/V
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Old 3rd October 2006, 10:12 PM   #1006
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Hi stefanobilliani,

Thanks for your reply [post#998]

Are you referring to op-amps like the OPA1632? well I haven't tried them yet, but I will. With the passive I/V circuit I only need a one OPA627 or OPA637 for each channel.

The tube amplifier with differential inputs connects directly to the I/V converters, the op-amp amplifier with differential inputs connects to the I/V converters as well.

I added a photograph of the passive I/V, it's a module that can be placed instead of the dual OPA627 module, so both options OP-amp I/V and passive I/V can be used with the existing PCB. The module contains a dual copper wire I/V resistor (2 X 15 Ohm). The dual copper wire resistor is wound on a small plexiglass tube that is mounted on a IC socket. Due to the mobius loop the resistors have zero inductance.

Yesterday I had some more time to listen to the octal D-I DAC with passive I/V, the results are stunning, I never had this sound quality before, the sound seems to have infinite resolution, it's very transparent. Mid's are full and warm, bass is more accurate then before. Even more details are appearing from recordings, sound completely emerges from the speakers. Then consider I am only using OP-amp output at the moment as the tube output amplifier needs to be modified (higher gain). Can't wait to hear it in mixed mode.
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Old 3rd October 2006, 11:42 PM   #1007
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I don't understand how you can have differential output using one OPA627 per channel. If I understand correctly, you're saying the I/V conversion is passive (using resistor), and then the OPA627 is used for a gain stage, correct? OPA627 only has one output, right? Do you mean you are using OPA627 as a differential amplifier, to convert balanced to single-ended? Could you please explain this, or better yet, post a schematic of the passive I/V section? I want to make sure you understand that I am not being critical here. I just don't understand what you're describing.
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Old 4th October 2006, 10:59 AM   #1008
tubee is offline tubee  Netherlands
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Guido Tent has build a new dac. With resisrtor I/V and tube amplification. I have a 6922 waiting to be used for the same task.
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Old 4th October 2006, 11:16 AM   #1009
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Hi tubee

Quote:
Originally posted by tubee
Guido Tent has build a new dac. With resisrtor I/V and tube amplification. I have a 6922 waiting to be used for the same task.
Are you going to buy (parts) of the kit and build this DAC?

Erik
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Old 4th October 2006, 11:22 AM   #1010
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Hi John

I didn't actively show my face around for a long time, but all this time I accompanyed the thread and the evolution of the DAC. Your positive experience with passive IV conversion gives me new ideas for the output stage, as I am quiet a noob and do not have any experience with active IV conversion.

So you are using two 15R resistors per channel (one for + and one for -) and amplifying this with the OPA627? Have you added any low pass filter, or isn't this required with this DAC arrangement?

Hope to see the PCB's ready, but actually I have some other project to conclude too, so I can wait!

Erik
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