Twisted Pear Audio Opus DAC

[qusp]

I apologize if this is lost in the middle of this thread somewhere; but has anyone done a direct comparison between a dual mono opus, with dual-mono COD?? I had planned on building a buffalo32, but not only is it near impossible to get one (which shows how wonderful they are) but I really have to pull back on spending since I just ordered JH13 customs. so the plan now is to build one of those 2, the COD with discrete output, volumite and ballsie added when they come back in stock or opus with LCDPS and volumite with trannie or wire up one of my triad audio LLPs as supply. only need the SPDIF (and perhaps optical) currently, but might add USB later. then flip the result when its time to get the buffalo when they are available more freely and I have recovered from the hole i've recently carved in my poor wallet.

thanks in advance

[mourip]

Originally Posted by ShinyFalcon

That's great to hear, mourip!

I plan on going single-ended for a while, and so from what I understand I won't be needing the output caps for the DC offset filtering. Do I have to bridge the caps' pads with something like solder? When I get the Ballsie later on will I need the output caps at the Opus' output?

And lastly, for the transformer wiring, from the data sheet for the rectifier bridge, there are two "power entries" marked ~, which led me to think that it won't matter how you hook up the secondaries, just as long as they're in phase. Am I correct?

For the first question I believe that the oposite is true. As I undertsand it the Ballsie will take care of DC offset and so if you are using the Ballsie you can either pull the OPUS output caps and replace them with a jumper wire or better, jumper the caps while leaving them in place so that you can always reverse the mod easily. I would not use solder to bridge the gap as solder is better used to keep two conductors in constant contact than to be a conductor itself. I would use a short piece of wire.

Regarding the second question. Originally I thought that as long as they were in phase it did not matter but them I saw a post by Brian which seemed to say that it did matter. I will try to find that text or perhaps someone else will weigh in.

You will love the sound. I do and I have not even gotten around to bypassing the OPUS output caps yet! I am using the OPUS/Ballsie single ended to my tube amp...

Best,

Paul

PS. On the TP website there are some forums that have a number of good post that helped me work through the build.

[BrianDonegan]

Regarding the second question. Originally I thought that as long as they were in phase it did not matter but them I saw a post by Brian which seemed to say that it did matter. I will try to find that text or perhaps someone else will weigh in.

As long as they are paired properly, it should not matter. I like to recommend a fixed order only to prevent accidents.

[qusp]

so no input... very difficult to find comparisons; but I think its the COD for me

[glt]

Would this help? PS Audio Discussion Forum | DAC in PWD - How was it decided

[qusp]

well kind-of (thanks). I guess i would like to get a serious upgrade, but also a slightly different flavour to the 8740 that is in my D10. yes I know the implementation is worlds apart, but I do tend to enjoy BB opamps a lot and I like the idea of the discrete I/V counterpoint, as many comments I have seen on the opus have mentioned the I/V stage as being a weak point in an otherwise good design. is there anywhere I can find an original buffalo??

I'm set on getting a TP dac, but still unsure which now that I dont think I can really afford the buffalo32 (only got about $650 I can spend in total including casing. I think I have ruled out the opus though. sorry for the OT in that case but there is little to no discussion on the COD on the forum. it gets a mention here and there, but nothing substantial. one thing though, if I can really drive headphones balanced directly from the buffalo, maybe that could still be the ticket, because at this stage i'm looking to build a dynalo (actually Dynahi) or balanced M^3 as well.

[Beefy]

Originally Posted by qusp

as many comments I have seen on the opus have mentioned the I/V stage as being a weak point in an otherwise good design.

...... the 8740 is voltage out, and the I/V is performed right there on the chip.

[ShinyFalcon]

Got my Opus partially working! My Metronome is letting out static and high pitched chatter, but I can hear it trying to respond to my music changes. Here's my switches/pinout if anyone can pinpoint the problem:

Opus
I2S +
DSD -
DEEMPH -
MODE -
IWO +
DIFFHW -
FSEL O (open?)
MUTE O
OSRO

Metronome
OWL0 -
OWL1 -
OFMT1 -
OFMT0 +
Open
MODE0 +
MODE1 -
MODE2 -

Open
IFMT2 -
IFMT1 -
IFMT0 +
Open
BYPASS -
Open
LGRP -

4:1 Mux
1 -
2 +
3 +
4 -


Mux > Metronome
DOut > D
LRCK > LRC
BCK > BCK
G > G
MCK > None

Metronome > Opus
G > G
D > DIN
LRC > LRCK
SCK > MCK
BCK > BCK

I only have my KSC-75, but sounds very nice so far...

Edit: Will try playing with OSR, seems like that's my problem, leave it open and the Opus won't like oversampling a 192kHz signal...

[mugdecoffee]

Would the jisbos buffers be a good substitute for the IVY stage? I'd like to have a discrete, good quality output stage and the jisbos seems to be economical. Also as a more general questions, does the OPUS or any voltage output dac really need an output stage when connected to an amp? Shouldn't the amp have an input stage that serves a similar funtion?

[Beefy]

We talked about this in another thread...... the y2 thread I think?

An appropriate output stage also acts to filter out high frequency noise from the digital side of the DAC. Not essential, but can reduce the performance of some amps. Jisbos would not be appropriate in this role.

[mugdecoffee]

In the IVY manual, it says the wm8740/1 has an onboard filter and one isn't needed in the buffer. Besides filtering, what purpose does a DAC buffer serve when feeding an amp?

[rds]

Originally Posted by mugdecoffee

Besides filtering, what purpose does a DAC buffer serve when feeding an amp?

Google the word 'buffer' or use the search function here and you will have your answer.

[digger945]

http://www.wolfsonmicro.cn/uploads/d.../cn/WM8740.pdf
http://www.wolfsonmicro.com/uploads/.../en/WM8741.pdf
links I found in the Gamma 2 thread.

[rhester]

Have everything up and running except for Volumite. How do I get the OPUS into software mode and how do I hook up the volumite to the OPUS? I did based on what had read here but couldn"t get it to work Any help?

[qusp]

Originally Posted by Beefy

...... the 8740 is voltage out, and the I/V is performed right there on the chip.

lol, just looked back at this for kicks; I must've been mixing the 2 dacs up and thinking of the I/V in the original buffalo being talked of as having room for improvement. research stage of builds often gets to me with information overload. the ability to draw balanced output pretty much directly from the dac pins in the gamma 2 apparently didnt sink in lol