Jump to content
wdecho

Class D

Recommended Posts

John, thanks for shedding light on the proper grounding of the balanced connections and shields. I’ve played around with using input transformers to convert from unbalanced to balanced inputs, and even though the results were great, I like using the single ended inputs with the amp in BTL mode. The sound is more forward and lively to my ears and my wife’s ears. I had Patricia Barber’s Café Blue playing last night, when the hambone (i.e., body percussion) track “Manha de Carnaval” came on, and my son whose hearing and pitch are very good remarked that it sounded like the musicians were in our living room. The pace, rhythm and timing of this amp module is really impressive. 

 

I finally got around to setting up my Kenwood PC400U belt-idler wheel drive turntable (think Thorens TD-124), and my Audio Research PH5 phono stage today. That was a real treat to listen to some records I’ve bought in the last several months. This amp in my system is really engaging. 

  • Like 1

Share this post


Link to post
Share on other sites
11 hours ago, John Warren said:

 

To be honest WD, I limit my time on forums to this one.  In fact, in my little world, I'd rather just buy an EVM and measure it with various front end designs.  I like the one you've selected and think I might pick up a couple of them.

 

FWIW, If you're after the best in performance I'm a fan of balanced inputs.   The Whitlock paper shows how to handle them.  The drain wire from the shield shouldn't sink to the audio signal 0V.   There's RFI, DC and 50/60Hz noise on that line so why "inject" that into the small signal reference?  The RC filter handles both.  The signal reference is the 0V audio small signal reference (i.e. the power supply GND), the chassis and power supply GND connect via star grounding.  The TPA board schematic does not appear to make any distinction between the grounds so I'm assuming they're all sinking to a common copper layer on the board.  If that's the case, then hybrid grounding can't be implemented  which is fine if you consider the purpose of the board.

  

Mr. Warren, 

    The quote beneath your name in your icon iz prime, considering this discussion.

             Jfc

 

Share this post


Link to post
Share on other sites
9 hours ago, rhing said:

John, thanks for shedding light on the proper grounding of the balanced connections and shields.

 

I hope that was the case! and thank you.

Share this post


Link to post
Share on other sites
9 hours ago, JBCODD said:

Mr. Warren, 

    The quote beneath your name in your icon iz prime, considering this discussion.

             Jfc

 

 

You've been warned! 

  • Like 2

Share this post


Link to post
Share on other sites
On 12/16/2017 at 6:27 AM, John Warren said:

 

To be honest WD, I limit my time on forums to this one.  In fact, in my little world, I'd rather just buy an EVM and measure it with various front end designs.  I like the one you've selected and think I might pick up a couple of them.

 

FWIW, If you're after the best in performance I'm a fan of balanced inputs.   The Whitlock paper shows how to handle them.  The drain wire from the shield shouldn't sink to the audio signal 0V.   There's RFI, DC and 50/60Hz noise on that line so why "inject" that into the small signal reference?  The RC filter handles both.  The signal reference is the 0V audio small signal reference (i.e. the power supply GND), the chassis and power supply GND connect via star grounding.  The TPA board schematic does not appear to make any distinction between the grounds so I'm assuming they're all sinking to a common copper layer on the board.  If that's the case, then hybrid grounding can't be implemented  which is fine if you consider the purpose of the board.

  

Time for an exacto knife or dremel tool? I'm not deep into this project yet but I do have the EVM board procured. I'm thinking there has got to be a way to separate  that input shield ground from the power ground(If necessary)and then implement your own star ground topology.

Share this post


Link to post
Share on other sites

What am I missing?  Texas Instruments configured the 3255EVM to operate in DIFF or SE modes.  Switching from SE to DIFF requires the relocation of jumpers.  I’m assuming that TI understands the grounding issues, which are taken into consideration in the conversion from SE to DIFF modes.

 

I’ve connected my Pono player to the EVM using SE mode with excellent results.  I’ve also connected the balanced outputs of my Pono player to the DIFF inputs of the EVM, also with excellent results.  IMO, the DIFF/balanced sounds better.

 

In either configuration, there is NO NOISE at idle coming from any of the efficient Klipsch, or Klipsch based, speakers at my disposal.  The silence between albums is almost palpable, as is the silence between cuts.  The is no hint of noise in either mode with the 48v Mean Well grounded to the 3255.

 

Absent a hum or ground loop issue, isn’t all this grounding debate akin to calculating fairies dancing on a pin?  Is it naive, or wrong, to assume that TI knows what it’s doing, and that any more stringent grounding requirements would be spelled out?

 

Please believe the foregoing is genuinely offered in the spirit of gaining knowledge.  It is not meant to sarcastically imply a specific answer.

  • Like 1

Share this post


Link to post
Share on other sites

^Cool. You are much further along with your project then I am. I am hoping for the same noise free results.

I edited my previous post.

Share this post


Link to post
Share on other sites
21 minutes ago, babadono said:

I am hoping for the same noise free results.

I can't see why you shouldn't. This amp is one of most noise free I've had, and it's connected SE.

 

The way I get it is the 3255 chip only has differential inputs anyway. So if you connect the eval board as single-ended, the op-amp before the 3255 chip converts to differential for input to the 3255. If you connect the eval board as differential, the op-amp just acts as a buffer.

 

 

Share this post


Link to post
Share on other sites

FWIWI, my TPA3118 "Wiener" board is equally silent in either SE or DIFF modes, whether powered by batteries or a 19v computer PSU.

Share this post


Link to post
Share on other sites
45 minutes ago, DizRotus said:

In either configuration, there is NO NOISE at idle coming from any of the efficient Klipsch, or Klipsch based, speakers at my disposal.  The silence between albums is almost palpable, as is the silence between cuts.  The is no hint of noise in either mode with the 48v Mean Well grounded to the 3255.

 

Listening tests have practical limits but there's entitlement and it takes more than an audition with speakers.   Look at it this way, your auditions tell you there's no difference between balanced and unbalanced.  So either balanced signals are nonsense OR your noise floor is limiting in both configurations OR your setup is that the advantages of balanced signals aren't that significant.  I suspect it's the last two.  I'll bet you're not running 30' of cable between your hardware or powering it from different power branches off house power.

 

One parameter that I consider important for headphone amps is the maximum spurious free dynamic range.  It's simply the range (in dB) between the peak signal amplitude and the highest harmonic measured in FFT at, say 6kHz.   This requires FFT and super-pure signal sources.  Also changes in grounding are easy to see using FFT.

 

That said, if you're pleased with the results then that's all that matters.  

 

 

 

 

 

 

 

 

 

 

Share this post


Link to post
Share on other sites

Also, what boards have any of you used that are driven from +/- rails?  I have two power supplies here, one +/-40V and one +/-80V that I can use to assemble a test amplifier.

Share this post


Link to post
Share on other sites
Just now, John Warren said:

  Look at it this way, your auditions tell you there's no difference between balanced and unbalanced.

 

Not exactly.  My auditioning tells me there is no discernible noise, whether SE or DIFF.  My auditions also tell me there is a discernible difference in SQ with the DIFF.  The DIFF sounds better.  I'll spare you the usual audiphool drivel to describe the differences.  Nonetheless, I do prefer it in DIFF.  Whether it's due to real superiority or placebo effect, I can't say.

Share this post


Link to post
Share on other sites
5 minutes ago, John Warren said:

Also, what boards have any of you used that are driven from +/- rails?  I have two power supplies here, one +/-40V and one +/-80V that I can use to assemble a test amplifier.

 

I might be able to answer that if I understood what " . . . . driven from +/- rails . . ." means.  Would it be possible to phrase that in terminology that this geriatric recovering lawyer might understand?

Share this post


Link to post
Share on other sites
12 minutes ago, DizRotus said:

 

Not exactly.  My auditioning tells me there is no discernible noise, whether SE or DIFF.  My auditions also tell me there is a discernible difference in SQ with the DIFF.  The DIFF sounds better.  I'll spare you the usual audiphool drivel to describe the differences.  Nonetheless, I do prefer it in DIFF.  Whether it's due to real superiority or placebo effect, I can't say.

 

That's why you really need to have measurements because if you're not sure then it's an issue.  Also, if it is better how do you know it can't be even better?

 

I'm not advocating getting test gear, the point I'm making is listening test leave us with this dilemma.

 

10 minutes ago, DizRotus said:

 

I might be able to answer that if I understood what " . . . . driven from +/- rails . . ." means.  Would it be possible to phrase that in terminology that this geriatric recovering lawyer can understand?

 

I apologize, I'm thinking CL-AB.

 

Any recommendation on a chip amp that can be driven from a +/- 40VDC supply (or +/- 80VDC).

 

 

Share this post


Link to post
Share on other sites
On ‎12‎/‎12‎/‎2017 at 12:11 PM, babadono said:

@mike stehr Yes they will need an additional dropping resistor. What voltage are they made for? If its 12 volts I'm thinking they probably have a 1K internal so an additional 3.3k or 4.7k. You can play with the value a little to match the brightness. You're going to need a 1/2 watt(minimum) resistor.

 

It works. I ended up with 8.2K to match brightness, and I'm using a 1 watt resistor. (what I had on hand)

Share this post


Link to post
Share on other sites
13 hours ago, mike stehr said:

 

It works. I ended up with 8.2K to match brightness, and I'm using a 1 watt resistor. (what I had on hand)

Cool.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×