Following your rule of thumb, I'm thinking the stepdown transformer for your 'phones will be sub-optimal for my 32ohm Goldrings; can you point me to an information source, or perhaps a calculator, that will help me get my head around it. I need to learn rather than just ask.
I have a feeling I rather over-engineered that trafo's core size so that the winding wire for the primary would be robust enough for even a beginner to handle it. So perhaps its still going to give 4ohms or under, but I will re-visit the design calculations in my notebook and check.
Last night I was working on one for 16ohm IEMs on a slightly smaller core (PQ3535) and the DCR wasn't a problem for them - it came out around 0.5ohm which is over-engineered. But that was on paper, I need to measure to double check.
As regards learning about transformers its something that I haven't found concentrated all in one place, rather I've picked up things here and there. So I don't have a link to offer at present. The thread I started about input transformer design will get you started, here - http://www.diyaudio.com/forums/class-d/292658-designing-classd-amp-input-transformer-step-step-guide.html
Last night I was working on one for 16ohm IEMs on a slightly smaller core (PQ3535) and the DCR wasn't a problem for them - it came out around 0.5ohm which is over-engineered. But that was on paper, I need to measure to double check.
As regards learning about transformers its something that I haven't found concentrated all in one place, rather I've picked up things here and there. So I don't have a link to offer at present. The thread I started about input transformer design will get you started, here - http://www.diyaudio.com/forums/class-d/292658-designing-classd-amp-input-transformer-step-step-guide.html
Will have a better look later but first impression is that this board looks quite nice.
They look suspiciously real but they got slightly warm. I thought the 78M05 to be the reason but took no risk and removed them anyway. The Pana caps even have the red date code so all look original and different from the Ebay picture but I will replace them. BTW I think I see why this board is offered so cheap. The thermal pad is not soldered to the PCB although there are pads there (....covered by solder mask). Sturdy PCB quality as I had to heat up to remove the caps but no pad came loose.
Also removed the output connector as it was indeed magnetic. Round DC socket replaced for a connector.
* Board sounded not too bad in standard form.
Also removed the output connector as it was indeed magnetic. Round DC socket replaced for a connector.
* Board sounded not too bad in standard form.
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I believe those Panasonic and Rubycon caps are made in China and they can order those cap direct (or could be manufacturer excess which is dump very cheaply). So most likely its real stuff.
Anyways, I plan to replace those caps as well. I have also ordered Coilcraft 1210 inductor to replace the the existing really flat inductor. Hope they fit as it is 12mm vs existing 10mm.
The sta333 uses 3.3v for its digital supplies. I can't seem to find the regulator for that.
BTW, I also have a Popu d2p on hand burning in.
I have amassed quite a collection of these. Reconfigured as a DAC rather than amp its now my reference digital source, surpassing my previous best of dual differential TDA1387s.
I haven't quite perfected it as an amp yet but I'm getting there slowly...
The D2P is an amp, how do u use it as a dac? If you feed the speaker out into another amp, won't the output swing be too large? Unless you really turn down the volume, but what's the point?
It uses pcm2706 inside which strangely takes usb and spits out spdif instead of i2s into the D2-41051. Whereas the analogue input uses AK5381 and splits out i2s into the D2 ic.
I am using step-down transformers to go from 24V peak down to 3V for feeding to my amp. It also needs more aggressive filtering to keep the carrier out of the output, for that I'm using the same 1210 inductors as you've got for your STA333, only much higher values. Its rather handy having a built-in volume control on a DAC, incidentally I've figured that digital unity gain is at a setting of 80. Above that clipping might happen on peaks.
Regarding the AK5381 if you're intending to use the analog input you might want to take a look at my blog. The designers rather overlooked that the output of an LM2596 isn't really suitable for connecting direct to the analog supply pin of an ADC. Fortunately its not too hard to insert an LC filter to restore dynamics to the analog input.
Regarding the AK5381 if you're intending to use the analog input you might want to take a look at my blog. The designers rather overlooked that the output of an LM2596 isn't really suitable for connecting direct to the analog supply pin of an ADC. Fortunately its not too hard to insert an LC filter to restore dynamics to the analog input.
Oh right, you were taking about using it as a headphone amp.
But can I suggest you try another fairly cheap dac, the ak4495, since you like using transformers. Get one of those cheap ak4495 dac boards, skip all the output stage and regulators. For power, use one lifepo4 battery its 3.3v supplies and 2 x lifepo4 for 6.4v feeding into its analogue pins.
Output stage just use a good old transformer. For me, this setup more than match the Soekris dam1021 r2r dac which I also have.
Your suggestion comes at a good time as only yesterday I placed an order for one of these little players - https://item.taobao.com/item.htm?spm=a230r.1.14.18.uMaZu0&id=528200190230&ns=1&abbucket=13#detail. They're jolly popular on Taobao right now.
So I've made a start on one of my STA boards, stripped it back removing all the parts not required or to be replaced. I thought I would retain the onboard USB, at least for now but if all goes well I'll remove that too and replace it with an 12S input at 88/96KHz to avoid any upsampling/downsampling by the STA chip.
I'm thinking about substituting a low noise 5V supply for the 78M05 too.
I'm a bit concerned about replacing the inductos as I don't think it will be possible to solder the smd 8.2mH Coilcrafts to the board so it maybe necessary to have an off board arrangement, maybe using these;
RFS1317-825KE COILCRAFT, Inductor, RFS1317 Series, 8200 µH, 350 mA, 310 mA, 5.88 ohm, ± 10% | Farnell element14
I will place my order for the replacement parts later when I've had time to think on it.
abraxalito, did you have any further thoughts on the output transformers after this or shall I just stick with Plan A? The transformer cores/bobbins will be in my parts order.
I haven't actually had a listen yet, perhaps I'll give the other, as yet untouched, board a go tomorrow.
Ray
I'm thinking about substituting a low noise 5V supply for the 78M05 too.
An externally hosted image should be here but it was not working when we last tested it.
I'm a bit concerned about replacing the inductos as I don't think it will be possible to solder the smd 8.2mH Coilcrafts to the board so it maybe necessary to have an off board arrangement, maybe using these;
RFS1317-825KE COILCRAFT, Inductor, RFS1317 Series, 8200 µH, 350 mA, 310 mA, 5.88 ohm, ± 10% | Farnell element14
I will place my order for the replacement parts later when I've had time to think on it.
abraxalito, did you have any further thoughts on the output transformers after this or shall I just stick with Plan A? The transformer cores/bobbins will be in my parts order.
I haven't actually had a listen yet, perhaps I'll give the other, as yet untouched, board a go tomorrow.
Ray
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I've gone back to my trafo design spreadsheet yes and found that you'll be under 4ohms total effective DCR with the trafo made to the specs on my blog (having 2000 turns of 0.19mm for the primary).
Incidentally I fitted the Coilcraft inductors on solid wires, proud of the board. The wires having been cut from the countless electrolytics I've been wiring up for my low-impedance power supplies
Incidentally I fitted the Coilcraft inductors on solid wires, proud of the board. The wires having been cut from the countless electrolytics I've been wiring up for my low-impedance power supplies
That's an interesting player, but IMO the ak4495 loses the magic without using the transformer output. I also feed the ak4495 up-sampled data up to 384khz and dsd256, which the ak4495 can take direct.
I had a brief listen to the D2P with the usb input, I think it is a bit grainy with vocals compare to my tube pre + 3116. I will try spdif input later and then will see how I can tweak it.
You'll definitely want to do the tweak to the level shifting caps I detail on my blog. That's a design fault which could easily be responsible for the graininess on vocals you're hearing.