Yes, I'm looking for the smallest sized transformers I can get away with while not unduly compromising performance. I'm looking for the lowest VA rating for a 9v transformer powering a Placid single (for the Buffalo II) and the lowest VA rating for a 15v transformer for powering a Placid bipolar (for the IVY III). I'm trying for a fairly compact layout for a transportable setup.
Am I going down the wrong trail by taking the earlier recommendation of setting the placid for the BII at 350-400mA at ~5.5V and for the placid bipolar at 150mA per rail at 15V to calculate minimum VA rating needed?
Am I going down the wrong trail by taking the earlier recommendation of setting the placid for the BII at 350-400mA at ~5.5V and for the placid bipolar at 150mA per rail at 15V to calculate minimum VA rating needed?
if you are going transportable, why not use battery power? I would think you could survive on slightly less than +/-15vdc, but dont quote me on that. i'm going for fully portable and am using a different output section to achieve this. taking on my first custom PCB to achieve this in a small package, but will be using OPA1632 with some compact discrete diamond buffers.
Brian or Russ, you've probably played with this, how well do you think OPA1632 will cope with a split battery 'bipolar' supply feeding the ref pin of the OPA1632 with the 'center tap' of the battery pack, either passive by just pulling from the middle of the battery, or with a rail splitter.
Brian or Russ, you've probably played with this, how well do you think OPA1632 will cope with a split battery 'bipolar' supply feeding the ref pin of the OPA1632 with the 'center tap' of the battery pack, either passive by just pulling from the middle of the battery, or with a rail splitter.
Using a diamond buffer after an OPA1632 is redundant unless you plan on pushing out more than 100ma or so, because the output stage of the OPA1632 is already a diamond buffer capable of about 150ma. 
As for the batteries I am sure 12V rails would work fine. The 0V (or GND if you will) point is the mid point when the two 12V batteries are in series.
Also 15VA should be fine for both supplies. I would not go smaller.
Cheers!
Russ
As for the batteries I am sure 12V rails would work fine. The 0V (or GND if you will) point is the mid point when the two 12V batteries are in series.
Also 15VA should be fine for both supplies. I would not go smaller.
Cheers!
Russ
yeah by middle of the battery I meant exactly that, literally a battery as in a collection of cells, not a single cell, strangely we call a single cell a battery. so yeah at the mid point of a series of cells is the passive option, but for the reason Russ mentions I was thinking possibly about a charge monitor as I dont want to pull a ref from the middle and ten have '0' be something else entirely and risk offset, but I did read in the datasheet for the OPA1632 that the internal ref is dominant. only reason i'm thinking of using the buffers is because I will be primarily driving VERY low impedance IEMs at 28R, so I want as much current as I can reasonably muster. I am using 20 x AAA or perhaps 16 x AA depending on whether I use i2s input from a modified iriver or cowon X5L, or the spdif receiver. the other option is using an external battery pack and running some SMD super regulators, this would help with evening out the current draw. still in research phase at the moment. thanks for the tips guys, the OPA1632 really is a great little chip I can see why you chose it for the buffalo, its very adaptable indeed. I did find several circuits using buffers though and they were all driving low impedances. I will of course try without, I have some separate versions of the buffers in question made up and was planning on connecting them via pin headers, the PCB is just for the OPA1632/feedback and decoupling/ termination, charge circuit, possible virtual ground, input and output
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I know the loudness is enough, they go loud enough with straight out of an ipod, but I have found that the rather complex load presented by 6 driver (each ear) IEMs benefits a great deal from more current. I know 0 is relative, but I worry about drift and the '0' point not actually being the middle of (for instance) +12vdc and -12vdc and rather being -1.4vdc when related to these 'end points' especially as being such highly sensitive IEMs, even 20 -30 mvdc offset is a bit of a worry.
with JH13, some of the drivers may be presenting a much lower impedance like 4R and others higher than 28R depending at which frequency etc. they sound much better to these ears when given more current, the amp I use with them at the moment (portable) puts out 1.4W into 8R and it sounds much better than my other portables. I still only use it in the 2x gain setting and rarely get past 9-9.30 oclock, but more power reserve and 18V seems to work wonders with them. I will be trying JUST the buffers too, just unity gain, nothing is set in stone and I also like to use my HD600 @ 300R, though the JH13 are my primary objective, the amp section must do well with them above all others. IME andall my reading confirms this, but lower impedance loads take MORE current, not less. any reading I have done lately of datasheets recommends a buffer after the opamp for use with low impedance loads
I must be communicating badly, because you seem to be throwing things back at me that are expressly covered in my posts?? I would have though the fact I mentioned the ref pin and the '0' point (inverted commas) would say that I understood the concept of ground being relative. not being facetious, just wondering if i'm not making myself understood
I worried about drift, so started getting other ideas on the go and doing some reading on exactly how the ref pin works on the OPA1632 a couple nights ago late, I seem to remamber it always takes the mean between its own internal reference and what is fed to the ref pin (I know its more involved than that), but if it reaches a thresh-hold it will then take total control and only use the internal reference at the penalty of reduced DNR
with JH13, some of the drivers may be presenting a much lower impedance like 4R and others higher than 28R depending at which frequency etc. they sound much better to these ears when given more current, the amp I use with them at the moment (portable) puts out 1.4W into 8R and it sounds much better than my other portables. I still only use it in the 2x gain setting and rarely get past 9-9.30 oclock, but more power reserve and 18V seems to work wonders with them. I will be trying JUST the buffers too, just unity gain, nothing is set in stone and I also like to use my HD600 @ 300R, though the JH13 are my primary objective, the amp section must do well with them above all others. IME andall my reading confirms this, but lower impedance loads take MORE current, not less. any reading I have done lately of datasheets recommends a buffer after the opamp for use with low impedance loads
I must be communicating badly, because you seem to be throwing things back at me that are expressly covered in my posts?? I would have though the fact I mentioned the ref pin and the '0' point (inverted commas) would say that I understood the concept of ground being relative. not being facetious, just wondering if i'm not making myself understood
I worried about drift, so started getting other ideas on the go and doing some reading on exactly how the ref pin works on the OPA1632 a couple nights ago late, I seem to remamber it always takes the mean between its own internal reference and what is fed to the ref pin (I know its more involved than that), but if it reaches a thresh-hold it will then take total control and only use the internal reference at the penalty of reduced DNR
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2W into what? this amp will put much more into a higher impedance. but yeah like I said, nothing is set in stone, I only started considering the OPA1632 a couple of weeks ago, initially I was planning on using 4 x AD797 or a fully discrete stage thus the buffers and I have the PCBs left over from another project anyway. and I will be trying just the OPA1632, if I can get away with a lesser part count I will. I need to work on or find a pot with more friction too so the volumite doesnt move in my bag or pocket, probably will just use a washer or something I guess. the problem though is not knowing the output impedance of the sabre, I have written to them about an NDA since this will be the 3rd sabre chip I own, without it its hard to go about tuning an I/V stage except for doing what i'm doing and trying many options.
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are you able to tell what the output impedance of the dac PCB is without breaching you're agreement or is the fact there is little in the way of the output too close to home?
sounds like the OPA1632 may well do OK though, since if it will put out 2w into ?? on +/-15v and i'm quite happy with the way the amp performs putting out 1.4W with +/-9v rails. and my battery supply will be somewhere in the middle
thing is though i'm interested in trying something a bit different as I do tend to prefer the JH13 driven by the FiQuest out of the buffalo32 than straight out of the B32. but that could just be an impedance mismatch/termination issue.
anyway i've taken too much of your time already, looking forward to the release, not too far now?? you on schedule for the revised release date since the system crash?
sounds like the OPA1632 may well do OK though, since if it will put out 2w into ?? on +/-15v and i'm quite happy with the way the amp performs putting out 1.4W with +/-9v rails. and my battery supply will be somewhere in the middle
thing is though i'm interested in trying something a bit different as I do tend to prefer the JH13 driven by the FiQuest out of the buffalo32 than straight out of the B32. but that could just be an impedance mismatch/termination issue.
anyway i've taken too much of your time already, looking forward to the release, not too far now?? you on schedule for the revised release date since the system crash?
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The 0V point is the reference in terms of VOCM. It is relative in the sense that it only makes sense in the context of a positive and negative voltage. It is the rails that would be moving relative to that mid point. They can move anywhere as long as they stay with the ranges set forth in the data sheet. Give it a good read all your questions are answered there. It does not significantly harm the signal for the rails to be a little asymmetrical in regard to VOCM. In fact with battery operation and using it to drive headphones in a balanced configuration I would probably let VOCM float (it has a voltage divider to internally set VOCM). You could then just use a single battery and not worry about the mid point voltage.
As for the battery operation part that really won't make any difference, It just a matter of knowing what might occur.
As for driving headphone, what is required for complex load is damping factor, not boat loads of current. The OPA1632 has superb damping factor as balanced headphone amp. I have been using it this way for years. I have not found anything better yet.
I hope you find the information your looking for.
Cheers!
Russ
As for the battery operation part that really won't make any difference, It just a matter of knowing what might occur.
As for driving headphone, what is required for complex load is damping factor, not boat loads of current. The OPA1632 has superb damping factor as balanced headphone amp. I have been using it this way for years. I have not found anything better yet.
I hope you find the information your looking for.
Cheers!
Russ
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ok I was actually wondering about that, IE whether it would be better to let it float and let the common mode take care of everything. i do understand the reference (I think), but reading the datasheet the other night for the OPA1632 got me thinking about the penalty it mentioned for letting it just use its own 'judgement' of what 0 is but then faced with the possible penalty of feeding it a 0 point that wasnt in the middle got me a bit overwhelmed with all the variables and which would be the better way to go. can I feed Vosc to the OPA1632? because wouldnt letting the 2 chips float result in some kind of mismatch? if the rails move in relation to 0, I dont get that as how is 0 generated other than in relation to the known quantity ie the rails? kind of a chicken and the egg thing. but yes I will give the 1632 datasheet a good read before embarking on any actual design. hoping ESS will reply sometime soon so I can get some more sabre info.
I suppose as long as they DONT communicate the 0 between each other then it just becomes a different arbitrary number, I guess robots really do dream of electric sheep VOSC just gets fed 3v3 as a chunk of whatever voltage is present and it takes the midpoint of this waveform as 0 right? so the rest of the voltage outside of this really is kinda meaningless? with regard to 0 anyway
thanks for the helping hand, as noted this is the first time i've really had to take all of this stuff into account with regard to actually designing my own PCB rather than just assembling or modifying an existing one. just got sick of trying to fit a square peg in a round hole, even though my avatar seems to think its OK I got the COD running portable BTW, sounds really nice and i'm surprised it doesnt get more attention. only running it single ended though as dac only because I started the research for a decent volume control then you announced the b32v2 and this made the volumite a possibility.
also thanks for the info, that will come in quite handy
I suppose as long as they DONT communicate the 0 between each other then it just becomes a different arbitrary number, I guess robots really do dream of electric sheep
VOSC just gets fed 3v3 as a chunk of whatever voltage is present and it takes the midpoint of this waveform as 0 right? so the rest of the voltage outside of this really is kinda meaningless? with regard to 0 anywaythanks for the helping hand, as noted this is the first time i've really had to take all of this stuff into account with regard to actually designing my own PCB rather than just assembling or modifying an existing one. just got sick of trying to fit a square peg in a round hole, even though my avatar seems to think its OK
I got the COD running portable BTW, sounds really nice and i'm surprised it doesnt get more attention. only running it single ended though as dac only because I started the research for a decent volume control then you announced the b32v2 and this made the volumite a possibility.also thanks for the info, that will come in quite handy
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In the meantime, I have spent some time reading the Sabre White Paper posted in the ESS website.
The case for current output mode is (according to footnote 16) to "cancel a slight on-chip resistor voltage coefficient"
The difference between voltage mode and current mode output stage is that in voltage mode the output connects to input of the opamp and in current mode output, the output connects to a resistor.
It seems then that the off chip resistor is the element canceling the voltage coefficient of the on-chip resistor.
Is there is a case then for a simple low value resistor as output stage? (We may not achieve -120 db THD, but perhaps a bit higher than -108) or is this line of thinking totally offbase?
The case for current output mode is (according to footnote 16) to "cancel a slight on-chip resistor voltage coefficient"
The difference between voltage mode and current mode output stage is that in voltage mode the output connects to input of the opamp and in current mode output, the output connects to a resistor.
It seems then that the off chip resistor is the element canceling the voltage coefficient of the on-chip resistor.
Is there is a case then for a simple low value resistor as output stage? (We may not achieve -120 db THD, but perhaps a bit higher than -108) or is this line of thinking totally offbase?
Sorry, but this is not correct.
Using it in current mode means using it into a low (as close to zero as possible) impedance. An opamp is typically used precisely to do this.
Using it in voltage mode means running it into a higher impedance (it does not have to be very high either).
The benefit of current mode (ultra low impedance) is that the voltage the DAC outputs see does not change with current, it does not modulate, so the outputs of the DAC stay where they always are. They always see the same bias voltage. This is why performance is better. It also makes it so that thermal effects are spread evenly.
Cheers!
Russ
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Hi Russ, your experiment with resistors, was that above or below the theoretical -108 db THD in voltage mode?
I have no doubt that IVY III will result in best performance, but I want to get there in stages. (Been using OPUS 8741 since the first time it was released and incrementally added improvements along the way). Thanks...
I have no doubt that IVY III will result in best performance, but I want to get there in stages. (Been using OPUS 8741 since the first time it was released and incrementally added improvements along the way). Thanks...
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