Multichannel I/V stage for Buffalo III?

Crumboo

Member
2007-12-19 12:43 pm
Hi,

I'm looking for a 8 ch I/V stage for use with my Buffalo III dac that I'm putting together. Are there any available options for this? All I/V-stages I've found so far are mono or stereo only. Of course it is possible to use several of them, but maybe there is a neater, not to expensive, solution? Only balanced outputs are required, so no BAL/SE conversion is needed.

Best regards,

Mattias
 
nope, you will have to make your own i'm afraid, but it will basically just be 4 x 2 channel IVs tied together, because thats what it is, there is no short cut if you want an active solution. you will have to take into account the 4 x lower current available per channel, for your choice of IV resistors and filter values.
 

knuisje

Member
2007-04-04 2:47 pm
I developed an ES9016 based dac with 2 I/V converters onboard. I have an expansion board available for 6 additional I/V converters that can be stacked onto the dac board.

At the pictures you can also see the supply and controller boards.
 

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well there you go...

how do you find the 9016? seems just 9018 without external DVDD. seems to just be the same die. do you have much experience with 9018 to compare? the reason I ask is I have started planning my own 9016 board for my subs, as well as a small multichannel to play with. i'm running 2 x 9012 dacs for 2 ways with discrete SS IV stages, but wanted to do something a bit less involved for the subs
 

Crumboo

Member
2007-12-19 12:43 pm
I developed an ES9016 based dac with 2 I/V converters onboard. I have an expansion board available for 6 additional I/V converters that can be stacked onto the dac board.

At the pictures you can also see the supply and controller boards.


Wow, that looks like something I was looking for; thank you. I don't know about the difference between ES9016 and ES9018 either, but do you think that board would work with Buffalo III? Are the connections to the DAC lined up accordingly?

Otherwise; can you share a schematic of the board and BOM so I can do an own PCB layout based on your work?
 
Wow, that looks like something I was looking for; thank you. I don't know about the difference between ES9016 and ES9018 either, but do you think that board would work with Buffalo III? Are the connections to the DAC lined up accordingly?

Otherwise; can you share a schematic of the board and BOM so I can do an own PCB layout based on your work?

I do know the difference objectively, I have the datasheets for both and have been playing with 9012/9018 for years. the output SNR, DNR and THD are lower, roughly 10-15db vs the premium parts, but as far as I can see, this is only created by less pins being brought out and thus more voltages generated internally from other voltages, maybe a slightly different process and smaller die perhaps. but otherwise the part is identical, firmware for 9018/12 should even work with minimal changes if any. operating points, supply voltages, digital filters, MUX, voltage and current on the outputs and operating points are all identical. thats why I think its just the same part, perhaps less discriminating internal element matching as well as the other stuff above brought the lower, nbut still pretty stellar performance.

the board above is a standard opamp based IV, nothing tricky there, look for the es9008 application note, there is a multichannel schematic and good layout recommendations/application note. again it should be able to be applied with decent results.
 

Crumboo

Member
2007-12-19 12:43 pm
the board above is a standard opamp based IV, nothing tricky there, look for the es9008 application note, there is a multichannel schematic and good layout recommendations/application note. again it should be able to be applied with decent results.

Thanks! Is this the one you are referring to?

I assume it is just to use 8 of the schematics in fig. 1. I don't know about the differences between ES9008 and ES9018, are the component values the same for ES9018?

And also (sorry I'm a real newbie of electronics): what does the "offset" to the left in that figure mean?
 
yes thats the one, offset refers to the DC offset. the ESS is a V+ only dac, no neg voltages, so the output swings around a DC offset of Half the AVCC supply voltage. youve probably seen the term AVCC/2 mentioned?

well the idea is you take a feed from the AVCC regulator directly (I run at 3.6v, but the spec is 3.3v) and feed this to a voltage divider to get AVCC/2 and send that to the opamps as pictured to delete the DC offset. you can see this trace if you look closely at the layout, is fed to the opamps in between the + and - power planes on the top layer. track it back to see the voltage divider. its hard to see if you dont know its there. I say again, pay close attention to the recommendations on page 5

yeah the values are still about right, depends on how much gain you want if any. the sabre tends to run a bit hot as far as voltage. I like it that way but it depends on your amps I guess. there are a few things I would do differently for sure, but its a good start. for starters I would run a separate AVCC for left and right and feed it from a dedicated supply instead of taking it from the digital supply. I would also avoid the AD797 unless you know what you are doing, not the easiest chip to get right at low gains and the PCB layout is critical.

pay very close attention to the ground plane, it should be solid uninterupted to the opamps and AVCC should be a solid uninterupted power plane from its reg to the AVCC pins. use as small (size) decoupling caps as you can solder. basically read page 5 many times and dont look at some of the other cheap stereo PCBs on the forum for inspiration...

good luck, I gotta say for an electronics noob, this isnt really the best project to start with and could turn into a pretty large money and time pit.
 
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Crumboo

Member
2007-12-19 12:43 pm
Wow...finally some time to work on this again. :) And more questions...

Also, thank you for your comments earlier!

I had a look at the schematic of the TP IVY III and was thinking about using this (with the parts according to the BOM). Now I wonder: if I don't need single ended outputs, can I just ignore the parts within the red lines in the attached picture (this is just for one channel)? Or are there other modifications that should be made?

IV1_zps29dcf97c.png


Best regards
 

nabussan

Member
2009-12-07 10:02 am
Bonn
Hi pos,
I think Crumboo has managed to build an active I/V stage for his BIII. Do you feel the urge to have one, too? Or are you happy with running your BIII in voltage mode?
In which configuration do you use it, how is it connected to your amps? Do you have a passive RC low pass? Or just a resistor?
 
yes thats the one, offset refers to the DC offset. the ESS is a V+ only dac, no neg voltages, so the output swings around a DC offset of Half the AVCC supply voltage. youve probably seen the term AVCC/2 mentioned?

well the idea is you take a feed from the AVCC regulator directly (I run at 3.6v, but the spec is 3.3v) and feed this to a voltage divider to get AVCC/2 and send that to the opamps as pictured to delete the DC offset. you can see this trace if you look closely at the layout, is fed to the opamps in between the + and - power planes on the top layer. track it back to see the voltage divider. its hard to see if you dont know its there. I say again, pay close attention to the recommendations on page 5

QUOTE]

Qusp/Anybody
I have the standard "evaluation board" IV stage. See schematic below:
http://hifiduino.files.wordpress.com/2013/01/iv.png
Based on Qusp's explanation above, there should be zero DC offset after the IV op amp as it is nulled by the 1/2 AVCC voltage feed to +ve input of the opamp?
On my board I measure 1/2 AVCC Volts on the negative signal opamp input (from the DAC) and the same on the output pin of the opamp. This is the same on all 4 IV opamps.
What could cause this to happen?
Any help or clarification appreciated.

Edit - Apologies for this off topic post.