I just received my Buffalo 3 DAC from the good guys at TP, and have been pondering what to do about an IV stage - so this thread has been an interesting read., mainly because TX seems like a very simple solution, and secondly, becasesI already use a TX output on my Cirrus Logic DAC (I have a CS4398 DAC eval board, which conveniently has take-off points on the board directly from the DAC output, before it goes to the op-amp output stage). So 2 questions:
1. Will my Lundahl 1527XL be suitable to with the Buffalo? It's 1+1:1+1, primary DC impedance = 54 ohm, freq response with 800 ohm source = 10Hz to 150kHz +/- 0.2dB - yes, 0.2dB!
2. I hate preamps, and tend not to use one - I have a source selector, and my phono stage has variable gain so nothing else required, however I do have a passive preamp for my existing DAC. Buit can i build variable gain into the TX output by using a switched attenuator across the primary of the TX - this should act as a voltage divider with the output impedance of the bufffalo (I'll work out the resistor values later). I would prefer to switch just one resistor between the +ve and -ve terminals, rather than bother with switching 2 resistors with an ground at the mid point, seems reasonable to me and if it works then the passive pre-amp is gone!! Good, I like minamalist solutions, not complex engineering.
BTW I should have said - buiold quality of the Buffalo DAC is superb. Thanks to fellows at TP!! I'm looking forward to getting the DAC built up.
1. Will my Lundahl 1527XL be suitable to with the Buffalo? It's 1+1:1+1, primary DC impedance = 54 ohm, freq response with 800 ohm source = 10Hz to 150kHz +/- 0.2dB - yes, 0.2dB!
2. I hate preamps, and tend not to use one - I have a source selector, and my phono stage has variable gain so nothing else required, however I do have a passive preamp for my existing DAC. Buit can i build variable gain into the TX output by using a switched attenuator across the primary of the TX - this should act as a voltage divider with the output impedance of the bufffalo (I'll work out the resistor values later). I would prefer to switch just one resistor between the +ve and -ve terminals, rather than bother with switching 2 resistors with an ground at the mid point, seems reasonable to me and if it works then the passive pre-amp is gone!! Good, I like minamalist solutions, not complex engineering.
BTW I should have said - buiold quality of the Buffalo DAC is superb. Thanks to fellows at TP!! I'm looking forward to getting the DAC built up.
Joe ,I know where you are coming from. But the Sabre DAC is different from any other DAC, not just that it can be used in both modes - but arguably sounds best in Current mode IMO.
If you go back through the posts, see the ones that discusses the lighter tonal balance of the Sabre DAC is Voltage mode.
If you want to use Voltage, then transformer is the way to go. Many have heard me say that many times over, that with a differential voltage output where any DC offset will not be seen by the Primary of the transformer. But the Sabre DAC is not a conventional Voltage DAC.
The Sabre DAC has a much higher output Z than is usual for a Voltage DAC and hence there is reason to point to it as the cause of the light tonal balance when used as such. We need to reduce that Z and also force the DAC into current.
So, Voltage mode, use:
The two resistors force the Sabre DAC into 3.14mA current offset while reducing offset voltage from 1.65V to about 1V. The output will be 1.3V RMS.
But how could this be applied to using Tubes and Current mode.
Pretty much all the post-DAC Tube designs I have seen avoid full-on Current mode. But with the Sabre DAC there is and opportunity if employing above suggestion repeated here:
We can force the Sabre DAC into Current mode by pulling it virtually down to 0V DC and then get an offset current of 8mA. Using the same 1:1 transformer, it now opens up the way to use Current mode with Tubes.
So the above example shows how it can be done.
The point is that the Sabre DAC has flexibilities in the way that no other DAC has and using it in Plain Vanilla Voltage mode can be avoided as IMO it gives worst performance.
Cheers, Joe R.
is it possible to use Broskie's Unbalancer as tube line stage in your advice as
beau2317 does it in this thread
http://www.diyaudio.com/forums/digi...iii-dac-tube-output-stage-18.html#post2972129
Zoran
sorry repost, i think this is the right place for ideas
hi guys
i setup my buffalo to run stereo mode using the Leon's guide. Thanks Leon.
i use qls qa 550 as a source for the I2S inputs. when connected to the sabre. the lock LED is on.
then i use transformer for the output. i connect the out + and out - to the primary of the 600:600 transformer. then connect the ground to the secondary side of the transformer to have the Single Ended out from the transformer.
I does sing nicely. but there is a distorted sound that follow the music. its very obvious when playing vocals and music seems noisy.
All the switches are set to OFF. input voltage is 5.25v and using all tridents.
any idea is really welcomed and appreciated.
regards,
erwin
hi guys
i setup my buffalo to run stereo mode using the Leon's guide. Thanks Leon.
i use qls qa 550 as a source for the I2S inputs. when connected to the sabre. the lock LED is on.
then i use transformer for the output. i connect the out + and out - to the primary of the 600:600 transformer. then connect the ground to the secondary side of the transformer to have the Single Ended out from the transformer.
I does sing nicely. but there is a distorted sound that follow the music. its very obvious when playing vocals and music seems noisy.
All the switches are set to OFF. input voltage is 5.25v and using all tridents.
any idea is really welcomed and appreciated.
regards,
erwin
I have been following this thread for a while now and tried have a number of the described transformer configurations both directly from the Sabre IC and with intermedaite electronics
My current setup is perhaps the best I have heard so I thought I would share my findings.
I am using a legato 2 board with Bal/SE circuitry removed and am feeding the balanced + and - in to a LL1518 (now unavailable but very similar to a ll1517). Sound is cureently excellent in my opinion.
My next step is to remove the coupling caps and modify the PCB so VR1 and VR2 are able to cancel and DC between the + and - O/Ps. I am hoping this should further improve sound and at this point I plan on closeing the box and calling the project complete.
I have also been experimenting with the old Opus DAC module and found the sound very natural when driving a transfomer directly my current setup here is an LL1527 with primary CT going through a 10k res and 22.uf cap in parallel to earth . With an optional 4k resistor across secondaries. (dependant on destination impedance).
I'll try and post some piccy's later.
My current setup is perhaps the best I have heard so I thought I would share my findings.
I am using a legato 2 board with Bal/SE circuitry removed and am feeding the balanced + and - in to a LL1518 (now unavailable but very similar to a ll1517). Sound is cureently excellent in my opinion.
My next step is to remove the coupling caps and modify the PCB so VR1 and VR2 are able to cancel and DC between the + and - O/Ps. I am hoping this should further improve sound and at this point I plan on closeing the box and calling the project complete.
I have also been experimenting with the old Opus DAC module and found the sound very natural when driving a transfomer directly my current setup here is an LL1527 with primary CT going through a 10k res and 22.uf cap in parallel to earth . With an optional 4k resistor across secondaries. (dependant on destination impedance).
I'll try and post some piccy's later.
Joe, I also use a LL1527XL tranny - but primary centre tap is floating. What is the purpose of the resistor/cap connected between the centre tap and ground?
Regards, Paul
It creates an offset current, something you can only do with Sabre DACs and also lowers the Primary impedance - always a good thing.
Try it - you already have the resistors in place -then listen and report back here. Others have said that it improves the tonal balance, making it sound more solid, less light.
Cheers, Joe
In retrospect I dont believe the center tapped soltion on the Opus was ideal as it did introduce a small amount of DC through the primaries, this is obviously best avoided, I have since put a pair of LL1518's on the Opus with no caps or resistors (output caps and resistors on the TP board have been removed) and although it sounds good I do get some severe distortion up to 25/30hz, on a sweep, will go back to the 1527's if I can't tame it.
Regarding the Buffalo/Legato 2 setup; I have got an ll1518 after the Muse output caps on the legato and ideally would like to take the caps out, I am measuring 0.005 v DC between the +and- before the cap and am not sure whether its worth modifying the board to balance this DC out at source with a variable ressistor. If anyone has any experience with this or know's whehter I should do the mod or not please could you let me know
.
Regarding the Buffalo/Legato 2 setup; I have got an ll1518 after the Muse output caps on the legato and ideally would like to take the caps out, I am measuring 0.005 v DC between the +and- before the cap and am not sure whether its worth modifying the board to balance this DC out at source with a variable ressistor. If anyone has any experience with this or know's whehter I should do the mod or not please could you let me know
.
No DC will go through the Primaries, only through the resistors. This was already made very clear early on. I certainly would not recommend anything that would do that.
If one wanted to be pedantic about it, then the two phases will not have the exact same exact 1.65V offset, there will be some minuscule difference. So in a DC connection across those phases into the DCR of the Primary, there will always be a residual DC current. So in your situation, where there is no grounding, that situation still remains. Adding resistors may actually reduce it. The two resistors should be an exact match and thus will increase DC from the DAC, but may well lessen it through the Primary. But then again we are really talking about very low levels of DC current - not a problem that should be a stumbling block.
So again, give it a go. Nothing ventured, nothing gained, and if you don't like it, then reconfigure it back.
Cheers, Joe
Hi Joe,
I think we have crossed wires, I was refering to my earlier post that Hazard commented on:
"LL1527 with primary CT going through a 10k res and 22.uf cap in parallel to earth . With an optional 4k resistor across secondaries."
Your absolutley spot on with the statements you have made on this thread and it was not my intention to appear to disagree with you
keep up the good work.
Cheers
Joe
I think we have crossed wires, I was refering to my earlier post that Hazard commented on:
"LL1527 with primary CT going through a 10k res and 22.uf cap in parallel to earth . With an optional 4k resistor across secondaries."
Your absolutley spot on with the statements you have made on this thread and it was not my intention to appear to disagree with you
keep up the good work. Cheers
Joe
I just finished building a Buffalo III dac with the latest Trident regulators. I use a single SPDIF input module and 75ohm BNC connector. Outputs are transformer coupled using Sowter 1:18.7 transformers model 8347. The output of the Buffalo DAC is loaded with 25ohm resistors. I followed Joe Rasmussen's suggestion and did this with two 12.5ohm resistors (33||20) from + to ground and from - to ground. That combined with the step up of the Sowters gives a "normal" level for the DAC and is the suggested loading for the Soweters. I buffer the transformers with a discrete FET buffer so that there is sufficient drive. I've found that transformer output alone can sound a bit light weight. It's similar to the buffer that Joachim Gerhard suggested in this ES9022 thread http://www.diyaudio.com/forums/digital-line-level/151846-anybody-using-new-ess-vout-dac-es9022-29.html#post2865647
I used 2SK170s cascoded with some higher Idss FETs I had in my junk box.
The whole thing is powered by an R-core transformer I got off of ebay - 120v/240v primary with dual 9v and 15v secondaries. The 9v secondaries are paralleled to drive the digital section and the 15v primaries are rectified and regulated to give +-15v for the FET buffer. The digital section is regulated using a Placid HD shunt regulator from TP audio while the buffer uses LT1086 adjustable regulators. I've only had it working for an hour or so but it sounds pretty good so far. Definitely worth the effort.
I built the DAC in a wooden box damped on the bottom and sides with Dynamat. The bottom is 1/2" baltic birch plywood, while the sides and top are solid oak. Below are a few pictures of the finished DAC.
---Gary
I used 2SK170s cascoded with some higher Idss FETs I had in my junk box.
The whole thing is powered by an R-core transformer I got off of ebay - 120v/240v primary with dual 9v and 15v secondaries. The 9v secondaries are paralleled to drive the digital section and the 15v primaries are rectified and regulated to give +-15v for the FET buffer. The digital section is regulated using a Placid HD shunt regulator from TP audio while the buffer uses LT1086 adjustable regulators. I've only had it working for an hour or so but it sounds pretty good so far. Definitely worth the effort.
I built the DAC in a wooden box damped on the bottom and sides with Dynamat. The bottom is 1/2" baltic birch plywood, while the sides and top are solid oak. Below are a few pictures of the finished DAC.
---Gary
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