I'm thinking off the shelf, or at least kit form. A related question, what are the ideal characteristics for such a PSU?
What I look for is the best isolation from the mains. So this tends to mean either lots of mains side filtering (CM chokes and the like) or as physically small a trafo as possible (giving lower capacitance to mains) with less extreme filtering. Or - another alternative - use trafos on the output to break any ground loops which makes the system less susceptible to mains-borne hash.
Avoid toroidal transformers (because they have higher inter-winding capacitance) and switched mode supplies (because they generate their own CM noise).
Avoid toroidal transformers (because they have higher inter-winding capacitance) and switched mode supplies (because they generate their own CM noise).
Do you mean an off-the-shelf supply or suggestions for DIYing one?
The X8 is my reference DAC now, I can't think of any more mods as its a really satisfying listen, nothing remotely annoying in the sound which would make me search for something to change
Mind if I ask you what other DAC's you've listened/compared it to? Im very intrigued, and have been following your comments about the TDA1387
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Its been a long while since I listened to any commercially available DACs so I doubt I'll be able to give you any point of reference. About 5 years ago I was using an Asus Essence soundcard but couldn't go back to that now - even with the mods I did to it.
<edit> When I wrote 'X8 is my reference' I was implicitly including all the mods I've done to it, which are plentiful, not all of which I have mentioned on here. They include ferrite bal-SE transformer output, LC filtering on the DAC's supply, raising the DAC supply to 6V, running the DAC chips 4+4 balanced with digital inversion, improving the PSRR of the shunts, additional reservoir capacitance, 5 pole LC quasi-elliptic filter for reconstruction duty, 2nd order passive NOS droop correction, single transistor transimpedance stages on DAC current outputs. Just about the only mod I've tried in the past but not included here is reducing the DAC's bit clock to 1.4MHz.
<edit> When I wrote 'X8 is my reference' I was implicitly including all the mods I've done to it, which are plentiful, not all of which I have mentioned on here. They include ferrite bal-SE transformer output, LC filtering on the DAC's supply, raising the DAC supply to 6V, running the DAC chips 4+4 balanced with digital inversion, improving the PSRR of the shunts, additional reservoir capacitance, 5 pole LC quasi-elliptic filter for reconstruction duty, 2nd order passive NOS droop correction, single transistor transimpedance stages on DAC current outputs. Just about the only mod I've tried in the past but not included here is reducing the DAC's bit clock to 1.4MHz.
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I can give some loose comparisons with some commercial/off-the-shelf DACs. Most of my listening takes place on my desktop, as it's the closest thing to a "man cave" that I have. I'll go through my "DAC progression" so you can see where I'm coming from.
For several years, I used a Cambridge Audio DACMagic (the original). While I had this, I briefly tried a HiFiMeDIY es9023 async USB DAC. I preferred the DACMagic, though in terms of value (i.e. performance normalized by cost), I'd say the HiFiMe was the winner.
I also briefly flirted with the Muse tda1543 x4 DAC available on ebay for around $50. I didn't like it. That was my first NOS experience. There were tons of mods listed for that DAC, I only attempted one of the simplest. My recent experience with the 1387 has me thinking maybe some more patience would have resulted in a different conclusion.
Next up was the Emotiva Stealth DC-1. Initially, I thought it was great, a decent step up from the DACMagic. But, over time, I started to notice that I was always turning the music down when listening through it... and then I finally put my finger on it: it's giving me listening fatigue. As far as I can tell, no one else in the world has this problem with the DC-1. If you look at the thread I started on the Emotiva forum, they are blaming my TPA311x amps, even though no other DAC (including Emotiva's own XDA-1) has ever given me fatigue with these amps. I've basically put this one in the closet for now. It's either indeed bad synergy with my system, or it has some actual problem. It could be great if I can get rid of the fatigue.
Next up is the Gustard DAC X-12, which is es9018-based. I received this right around the same time as I did the first mod or two to the tda1387 x8. Initially, the bass was weak on the tda1387x8 compared to the X-12. However, once added capacitance to the digital power supply and to pin7 of the tda1387 ICs, the bass was noticeably better.
This is where I'm at now, the Gustard versus the tda1387x8. To be honest, I spend most of my time listening to the tda1387x8. It's not night and day different than the X-12, but there's something I can't quite put my finger on that makes me prefer the TDA1387. Maybe it's simply the "magic" of NOS? Note that I'm not set up to do any kind of rapid A-B switching. I have to literally shuffle cables around, then update output settings in my player. I have to work from "aural memory".
I still want to revisit the Emotiva DC-1, against both the X-12 and the TDA1387. I'm waiting until I have a respectable non-class-D amp to test with, to give the Emotiva people the benefit of the doubt. If I still have the fatigue issues with it, I'll send it back to Emotiva and see what they can do with it.
Note I'm also playing with the cheaper USB-powered tda1387 x4 (see my pics a few posts above). With the simple mods I did, this thing sounds surprisingly good. But, by the same token, I think I'm leaving a lot on the table with the x8. I've only implemented the simplest mods: (1) better output opamps (AD845), (2) more capacitance for tda1387 IC pin7, (3) more digital supply capacitance, (4) improved analog-side decoupling. Given what Abraxalito has said, it looks like there's a lot left to gained with further mods.
In short, the TDA1387x8 is now my daily driver, and I enjoy the heck out of it. At the end of the day, it makes me want to turn the music up and spend more time listening.
This echos my sentiments entirely - this DAC (after a long journey in DACs) has moved the focus away from tweaking for me and on to the music. I'm buying more CDs - just a few days ago I bought this boxed set - Amazon.com: Wolfgang Amadeus Mozart, Friedrich Gulda: Mozart: Complete Gulda Tapes: Music
Over on the Wikipedia article about the pianist, Friedrich Gulda they say the sound quality sucks. I really don't know what they're talking about unless they mean there's not much ambience from the hall. These recordings are close-miked and this makes them a challenge for an audio system - very, very impulsive piano playing. But this DAC handles them - piano being the most demanding material and Gulda's piano playing being the most impulsive I've heard (he was Marta Argerich's teacher and she's quite probably the next most impulsive player). A wonderful aural experience playing these.
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I figured that you'd keep on asking for mods until all mine were used up, that would be a good way to get them all documented, in detail
I'm not sure you appreciate just how much hand-holding I need.
I want to ask for more details, but I feel bad about constantly nagging you.But if you're willing... Back in post #125 on page 13 you suggested the following is the next best bang-for-buck mod:
If you still think that's the next best step, can you elaborate a bit? Keep in mind I'm at the "paint by numbers" skill level.
I don't see continuous interest in getting better sound from a design as 'nagging'. Keep the questions coming, it saves me writing long blog posts about the mods
Elaboration is in the schematic shown in post 126 - the two transistors at the bottom of the diagram (Q25, 26) are the suggested current source. Q25's collector is the output - this needs to go to the opamp's output, pin6. The bottom rail is the negative supply for the opamp, the top rail is the positive supply (no connection to 0V here). You don't need the emitter follower (that's inside the opamp for your application) Q35 or its base resistor or the two ferrite beads.
Elaboration is in the schematic shown in post 126 - the two transistors at the bottom of the diagram (Q25, 26) are the suggested current source. Q25's collector is the output - this needs to go to the opamp's output, pin6. The bottom rail is the negative supply for the opamp, the top rail is the positive supply (no connection to 0V here). You don't need the emitter follower (that's inside the opamp for your application) Q35 or its base resistor or the two ferrite beads.
As you wish!
In post 126, you said, "here's the schematic for the classA buffer I'm using (four off) in the latest DAC mods." I added the emphasis - what do you mean by "four off" (of?)? I would assume only two of these circuits are needed, one for each opamp?
And is the attached picture the correct interpretation of what you're saying? Looks like opamp V+ and output basically become jumpered?
Attachments
Hi Malefoda, if you're still following this thread, this is from post #53, back on page 6:
Is that black wire on the bottom of the board for what Abraxalito mentioned back in post #6 on page 1:
And on the topside of the board, it looks like you cut that big trace between the blue and yellow caps, right?
Rather than cutting the trace, would it make any more sense to cut the RCA ground lead, and directly connect that to the transformer ground? Can that be run to chassis ground? Or the the earth pin of the mains?
Also, what are those little SMT capacitors on either side of the black wire on the bottom of the board?
Is that black wire on the bottom of the board for what Abraxalito mentioned back in post #6 on page 1:
And on the topside of the board, it looks like you cut that big trace between the blue and yellow caps, right?
Rather than cutting the trace, would it make any more sense to cut the RCA ground lead, and directly connect that to the transformer ground? Can that be run to chassis ground? Or the the earth pin of the mains?
Also, what are those little SMT capacitors on either side of the black wire on the bottom of the board?
As you wish!
Cool
You're right, in your version of the DAC you're still (for now) using the opamps, so there's only a need for two current sources, one per opamp. However I got rid of the opamps entirely in the last round of modding, when I went over to balanced (4+4). With balanced operation there are twice as many channels, hence the need for four current sources.
No - you replaced the transistor you've (correctly) removed with a wire link whereas I intended it to be left open circuit. The opamp completes the circuit that the transistor was implementing.
I had a strong feeling that I messed something up. Now I've posted two inaccurate pictures in this thread.
At any rate, here's the corrected diagram. Look OK?Attachments
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Sorry, one more question: do these resistors and transistors have any particular requirements? Looks like BC817-40 is a generic name... OK to go with the cheapest, or should it be a certain manufacturer or spec?
Likewise with the resistors: composition, power rating, tolerance?
Making out my Digi-Key cart now.
Thanks!
Likewise with the resistors: composition, power rating, tolerance?
Making out my Digi-Key cart now.
Thanks!
BC817-40 isn't a generic name in this instance, its the precise part I am using and fortunately its got a model in LTSpice. But you're right its not particularly critical - a lower gain (the -40 indicates the highest gain grouping) may indeed perform slightly better.
Not all transistors will perform as well here - I look for a couple of parameters. First is 'hoe' the output impedance, indicated in Spice models by the parameter 'VAF' - we want a high number as ideally a CS has infinite output impedance. Second we don't want the transistor to have a much lower 'hoe' close to its saturation region - this can be seen on the traditional transistor curve tracer plots. I'll post up some pics later to demonstrate what's important. I don't know about Digikey's pricing but the BC817 (its a SOT23, there are leaded equivalents) is one of the cheapest going - I got a reel of them (3k) and the price was under $30 so less than a cent each.
As for resistors - almost anything will do, I'm using 0805 thick film without noticeable problems. I wouldn't advise 0603 as they do get rather noisy at higher values (like 33k). Leaded metal film will likely have better performance but as for whether you'd notice it, I can't say.
Oh btw your new pic is dandy
Not all transistors will perform as well here - I look for a couple of parameters. First is 'hoe' the output impedance, indicated in Spice models by the parameter 'VAF' - we want a high number as ideally a CS has infinite output impedance. Second we don't want the transistor to have a much lower 'hoe' close to its saturation region - this can be seen on the traditional transistor curve tracer plots. I'll post up some pics later to demonstrate what's important. I don't know about Digikey's pricing but the BC817 (its a SOT23, there are leaded equivalents) is one of the cheapest going - I got a reel of them (3k) and the price was under $30 so less than a cent each.
As for resistors - almost anything will do, I'm using 0805 thick film without noticeable problems. I wouldn't advise 0603 as they do get rather noisy at higher values (like 33k). Leaded metal film will likely have better performance but as for whether you'd notice it, I can't say.
Oh btw your new pic is dandy
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Err one tiny question
Hi Abraxalito
I do read your thread on how to turn this humble DAC into a audiophile DAC. Everytime I read it, my heart beats faster and my breath becomes faster. All because I dont really understand half the technical stuff that you are talking. To goes swoosh above my head.
Would you consider selling one of your modified one to me? (smile smile)
Hi Abraxalito
I do read your thread on how to turn this humble DAC into a audiophile DAC. Everytime I read it, my heart beats faster and my breath becomes faster. All because I dont really understand half the technical stuff that you are talking. To goes swoosh above my head.
Would you consider selling one of your modified one to me? (smile smile)
Once I mod them for myself I prefer to keep them as my build standards for myself tend to be rather lower than I'd do if they have to survive shipping. But if you say what mods you want I can order a fresh one up and do them more reliably specially for you, for suitable recompense. PM me to talk about it.
Much of what Abraxalito is doing is also above my level of understanding. But he's also been extremely generous with his time to explain things. I'm basically going through these mods one at a time, trying to learn as I go. I work pretty slowly due to lack of knowledge and also balancing other life priorities. But I intend to take this as far as I can (though I'm 100% dependent on others' help).
Also, the first few mods I did are really simple, as long as you can use a soldering iron, and to me they are a noticeable improvement. So maybe start with those and see what you think?
To the extent of my limited skill, I'm also willing to help out. I try to take pictures and post them, partially because I like seeing pictures of others' work, but I'm also hoping they have some instructive value. I'm trying to give back to the community in some small way.
Just another suggestion for you. If you're not in a hurry and enjoy this kind of work, I think it would be fun to work "together" with someone else at a similar experience level.
-Matt