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Old 31st May 2012, 05:14 AM   #351
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Hi RC

yes. i have jensen JE 11p1. i tried them as per your setup and still not good. i suspect the board. will try to locate the problem

regards,
erwin
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Old 15th June 2012, 02:55 PM   #352
joefish is offline joefish  United Kingdom
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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.
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Old 25th June 2012, 12:15 AM   #353
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Quote:
Originally Posted by joefish View Post
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).
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
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Old 25th June 2012, 12:31 AM   #354
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Quote:
Originally Posted by hazard500 View Post
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
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Old 25th June 2012, 08:43 PM   #355
joefish is offline joefish  United Kingdom
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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 .
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Old 25th June 2012, 10:42 PM   #356
joefish is offline joefish  United Kingdom
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Bah - I just removed the caps - sounded slightly bright, added a 800ohm resistor across secondaries (had run out of 600s) and now it sounds very nice. It will need a few weeks of listening but hopefully job is now done
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Old 25th June 2012, 11:58 PM   #357
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Quote:
Originally Posted by joefish View Post
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...
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
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Old 26th June 2012, 02:11 PM   #358
joefish is offline joefish  United Kingdom
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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
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Old 2nd July 2012, 02:53 AM   #359
GaryB is offline GaryB  United States
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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 Anybody using the new ESS Vout DAC (ES9022)?
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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File Type: jpg Back.jpg (84.7 KB, 660 views)
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Old 2nd July 2012, 09:18 AM   #360
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Quote:
Originally Posted by joefish View Post
Hi Joe,
I think we have crossed wires...
Ooops! My mistake. Cheers, Joe R.
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