Dual I/V stage implementation for Buffalo II & III

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I would like to start this thread to see if some of you would be interested in having a switchable dual I/V stage for the Buffalo II and III. Those are the DAC designed by TwistedPear Audio.

My thoughts on this is that some people love solid state I/V and some love Tube I/V. If you're like me, depending on the kind of music you're listening you might like one or the other.

What I'd like to propose is some sort of way to have both a Legato/IVY I/V stages from TPA and a third party I/V that could be selected with the press of a button or switch.

Now, I'm currently running a Dual Mono Buffalo II setup with Dual Legato 3.1 and I also have a tube I/V from DVBProjekt (Tube-I-Zator).

I was planning to have a switch board sandwiched between the Legato/IVY and the Buffalo II/III that would do the switching using latching relays. Latching relays to not induce EMI in the signal. And having this board sandwiched in between would allow for shortest traces as possible.

I hope this will bring some great ideas and a possible design. Since I'm no circuit designer, I would like to know if someone with experience would gladly provide help in designing the circuit. If not, I have a good source (a friend) that could do it but timing for him is not good at the moment.

Here's a drawing of what I was thinking

https://picasaweb.google.com/lh/photo/IlyeFJIsIh4JQMBbfT68lw?feat=directlink

There would also be a controller on a different board that would carry the electrical and electronics to switch the relays. I do not want to have any electricity flowing on the I/V circuit aside the balanced audio signals, hence the use of latching relays.

Of course we would need the right measurement of the PCB holes and connectors of both Legato/IVY and the BII/BIII to align things. I have sent a PM to Russ White and asked him for the Gerber files but only containing the holes and connectors alignments. I'm relying on their good heart for this help!

I was thinking of a group buy if enough people are interested!

Let's get this started! :)
Do
 
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Hey Oliver!

I need 6 lanes per DAC (we have two BII/BIII) to connect the BII to the Legato/IVY and another 6 lanes per DAC to go to the third party I/V . In dual mono, please see diagram.

When they're installed, they stack perfectly on top of each others and the pins are aligned making a point to point connection. We'll need at least 4 latching relays, one for each "left and right" of each BII/BIII.

See diagram of what has to happen when using an external I/V in dual mono mode

https://picasaweb.google.com/lh/photo/p8EJfHBwz0b75OIktzE-GA?feat=directlink

I'd like to have the relays as close as possible to the BII and legato as possible.

Please let me know if you have any questions

Thanks
Do
 
even a few cm and a fraction of an ohm will effect the resolution and dnr of the current output of the bII in a meaningful way, i dont think this is a great idea tbh. you should if you can avoid it and must push forward, try to avoid switching the return lines
 
good ears, silver cabling or not, using subpar methods to connect the IV stage like using relays, will singlehandedly remove any advantage gained by having a dual mono dac in the first place

Hi Qusp,

I do appreciate the feedback but if you could also provide some positive feedback, maybe tell us how you would do it instead of just pointing out the bad.

If using relays is not good then there must be tons of people wasting their times building / implementing R2R volume control using relays...

After all, this way of thinking would have never brought us to the moon!

Please don't be a show stopper and see the positive side of anyone interested to use an I/V stage of their liking. I do love the Legato / IVY stages but there's plenty of people that won't give up their tube I/V for SS output...

Lets just be innovative and find ways around this issue.

Thanks for your understanding
 
Do, I'm very interested to hear more on your efforts. I am eagerly awaiting delivery of a Buffalo III board and Tube-I-Zator boards. Have been mulling the benefits of getting a second Buffalo III board for the dual mono configuration. Would love to see some shots of your build?
 
Hi Qusp,

I do appreciate the feedback but if you could also provide some positive feedback, maybe tell us how you would do it instead of just pointing out the bad.

If using relays is not good then there must be tons of people wasting their times building / implementing R2R volume control using relays...

After all, this way of thinking would have never brought us to the moon!

Please don't be a show stopper and see the positive side of anyone interested to use an I/V stage of their liking. I do love the Legato / IVY stages but there's plenty of people that won't give up their tube I/V for SS output...

Lets just be innovative and find ways around this issue.

Thanks for your understanding

you are missing the point, relay volume controls are dealing with voltage, not current and volume controls are designed to lower dnr by their very nature, that is not what you want from an IV stage.

i'm seriously happy you love the sound of your dac, thats what its all about, i really am, but the way i see it building an entire second dac to gain a few db performance and then throwing it directly away before the signal even gets anywhere seems a total waste of time and effort, i dont like to see people make such decisions, so i speak up when called for comment, but hey its your money. i think you could probably get better performance with one dac done properly than making compromises with 2. doing the dual mono thing, the only reason to do it is to squeeze the last bit out of the sabre dac, whether this has anything much to do with great sound is subjective

myself (and btw the way the designer of the sabre dac sees it) short line of sight current paths that keep the phases as close to each other as possible and direct signal returns are to be maintained for good performance from an iv stage with sabre. that simply is not possible with the setup you mention and its not possible with ANY setup that uses relays in the current path, the resistance of the relays will become the IV stage, sabre starts falling out of current mode with <1ohm
 
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you are missing the point, relay volume controls are dealing with voltage, not current and volume controls are designed to lower dnr by their very nature, that is not what you want from an IV stage.

i'm seriously happy you love the sound of your dac, thats what its all about, i really am, but the way i see it building an entire second dac to gain a few db performance and then throwing it directly away before the signal even gets anywhere seems a total waste of time and effort, i dont like to see people make such decisions, so i speak up when called for comment, but hey its your money. i think you could probably get better performance with one dac done properly than making compromises with 2. doing the dual mono thing, the only reason to do it is to squeeze the last bit out of the sabre dac, whether this has anything much to do with great sound is subjective

myself (and btw the way the designer of the sabre dac sees it) short line of sight current paths that keep the phases as close to each other as possible and direct signal returns are to be maintained for good performance from an iv stage with sabre. that simply is not possible with the setup you mention and its not possible with ANY setup that uses relays in the current path, the resistance of the relays will become the IV stage, sabre starts falling out of current mode with <1ohm

Hi Qusp,

Would switches create the same scenario?

thx
pinnocchio
 
Do, I'm very interested to hear more on your efforts. I am eagerly awaiting delivery of a Buffalo III board and Tube-I-Zator boards. Have been mulling the benefits of getting a second Buffalo III board for the dual mono configuration. Would love to see some shots of your build?

I will post pictures of the prototype shortly. Everything will be installed in a nice box. But I'm waiting on Brian and Russ to release the AC2 (Audio controller 2) before I do this, since I want to create a nice front panel using Front Panel Express! :D

Thanks
 
Hi Qusp:

You mentioned the importance of low parasitics in the link from the 9018 chip to the I-V stage, which I fully agree with.

To give that point more attention, I'd like to ask your opinion (or experience) as to how much resistance, capacitance or inductance the link can have before the 9018 performance starts showing signs of degradation.

I've read elsewhere that ESS themselves strongly suggest that the link or current injection point of the I-V stage not exceed 10 ohms impedance, wide-band. But do you think that there will be a steady increase in performance with reduced impedance at the current injection node, or do you think that beyond some point there will be a plateau? As an extreme example, would 0.2 ohm input impedance allow superior performance to 0.6 ohm impedance, or is it that below 1 ohm (or 10 ohms, for that matter), performance differences are more or less inconsequential?

I'd appreciate hearing your thoughts.

cheers, jonathan
 
Hi Qusp:

You mentioned the importance of low parasitics in the link from the 9018 chip to the I-V stage, which I fully agree with.

To give that point more attention, I'd like to ask your opinion (or experience) as to how much resistance, capacitance or inductance the link can have before the 9018 performance starts showing signs of degradation.

I've read elsewhere that ESS themselves strongly suggest that the link or current injection point of the I-V stage not exceed 10 ohms impedance, wide-band. But do you think that there will be a steady increase in performance with reduced impedance at the current injection node, or do you think that beyond some point there will be a plateau? As an extreme example, would 0.2 ohm input impedance allow superior performance to 0.6 ohm impedance, or is it that below 1 ohm (or 10 ohms, for that matter), performance differences are more or less inconsequential?

I'd appreciate hearing your thoughts.

cheers, jonathan

Hi Jonathan,

Did you ever got an answer for that? I'd would really love to do this project but right now I'm kinda stuck not knowing...

Thanks
Do
 
Hi Do: No, I haven't received a direct answer from anyone with hands-on 9018 design or build experience.

What I have been doing is working together with a buddy on a balanced-to-SE I-V converter design for the Buffalo II and III, that eschews monolithic devices, and has built-in DC cancellation and therefore requires no coupling capacitors. The overall topology assumes true differential outputs from the 9018, which means that the quantizer should be run in up to 8-bit mode rather than 9 (unless someone reading this knows how to configure a 9018 for true differential outputs when the quantizer is set to 9-bit operation).

Our present overall design is complex with multiple interlocking variables, and it isn't always easy to deduce that topological fragment A is directly responsible for distortion reduction B or phase improvement C.

Keeping those cautionary words in mind, at least down to about 0.2 ohms (achievable with fairly straightforward, although not necessarily simple topologies), it appears that there are direct and quantifiable improvements in distortion. Further reducing input impedances is requiring weirder topologies, and possibly as a result, doing so seems to be bringing diminishing degrees of distortion improvements.

At the end of the schematic design process we will then need to consider how to package the final circuit into a compact enough form so that the input impedance improvements aren't negated due to excess resistance, capacitance and inductance brought by a circuit that is physically too-large (or runs too hot).

kind regards, jonathan carr
 
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Hi Do: No, I haven't received a direct answer from anyone with hands-on 9018 design or build experience.

What I have been doing is working together with a buddy on a balanced-to-SE I-V converter design for the Buffalo II and III, that eschews monolithic devices, and has built-in DC cancellation and therefore requires no coupling capacitors. The overall topology assumes true differential outputs from the 9018, which means that the quantizer should be run in up to 8-bit mode rather than 9 (unless someone reading this knows how to configure a 9018 for true differential outputs when the quantizer is set to 9-bit operation).

Our present overall design is complex with multiple interlocking variables, and it isn't always easy to deduce that topological fragment A is directly responsible for distortion reduction B or phase improvement C.

Keeping those cautionary words in mind, at least down to about 0.2 ohms (achievable with fairly straightforward, although not necessarily simple topologies), it appears that there are direct and quantifiable improvements in distortion. Further reducing input impedances is requiring weirder topologies, and possibly as a result, doing so seems to be bringing diminishing degrees of distortion improvements.

At the end of the schematic design process we will then need to consider how to package the final circuit into a compact enough form so that the input impedance improvements aren't negated due to excess resistance, capacitance and inductance brought by a circuit that is physically too-large (or runs too hot).

kind regards, jonathan carr

Please let me know when you have this I/V completed

If you need some testers, I have some good gear to test it on.

BTW, someone asked me if instead of using relays to switch the BII/BIII current output to Legato or Tube I/V to use them for switching the power of the desired I/V stage and connect both I/V in parallel at all time. This way we could have really short traces.

The only thing I'm not too sure is if one of the I/V stage is powered off, current will still flow in it and go through passive components. I don't know if this could have an issue with the BII current output...

So basically, have the BII and Legato 3.1 sandwiched together like they're supposed to then run an extra set of cables to the tube?

Thanks
Do
 
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