Post by Owen Y on Sept 26, 2017 16:28:25 GMT 12
I built this in around 2012. It's a design by Thorsten Loesch (nowadays designer for AMR/iFi). When I first listened to DACs, I concluded quite quickly that ‘multi-bit’ DACs sounded more like music to me, than ‘bitstream’ DACs – more dynamic & ‘alive’. The TDA1541 was originally developed by Philips (in 1985) as a high performance stereo DAC. The ‘A’ version was manufactured between 1989-1995. Unfashionable & OOP now, it was (is still?) regarded as one of the best sounding DACs ever made. This chip was used in almost 100 different CD players. The DAC output is to be coupled to a valve analogue output stage. 
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Post by Owen Y on Sept 26, 2017 16:40:13 GMT 12
The schematic:  The CS8412 receiver & TDA1541A chips require +/-5vdc & -15vdc supplies. The valve circuit needs of course high voltage (220-240vdc) together with 6.3vdc heater supplies - I adapted my phonostage PSU circuit with elevated heaters. 'Bread-boarding' the valve stage, using a 5687 twin triode:  As usual with DIY building, the PSU is the trickiest part to get right.
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Post by Owen Y on Sept 26, 2017 16:45:42 GMT 12
I was given an old Micromega CDP chassis (thanks Warryn), which was stripped & dressed up with a new (Kwila?) wood fascia.... (wood is much easier to work with than metal)....  
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Post by Owen Y on Sept 26, 2017 17:03:15 GMT 12
PSU transformers - I decided to try some of those nice R-Core transformers, in this case, supplied by DIYClub.co.hk - around US$20-24 ea at the time, shipped - made in China no doubt. Compact, low-loss, efficient size-wise, low radiated flux fields, low noise. 
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Post by Owen Y on Sept 26, 2017 17:08:37 GMT 12
Laying out the chassis - PSU parts on RHS, digital on the LHS (to be separated by a steel partition divider), valve output stage down the centre. 
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Post by michaelw on Sept 26, 2017 17:11:47 GMT 12
usb ? dsd ? wifi ? 
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Post by Owen Y on Sept 26, 2017 17:12:26 GMT 12
As serendipity would have it, i discovered that my pal Ian was planning to build the same circuit - so in collaboration, we were able to have some nice dble-sided PCBs made for the digital circuit:  
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Post by Owen Y on Sept 26, 2017 17:17:13 GMT 12
usb ? dsd ? wifi ? nope, nope, nope  I2S SPDIF in, via 75 ohm BNC, RCA analogue out.
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Post by Owen Y on Sept 26, 2017 17:20:44 GMT 12
The original ‘non-oversampling’ approach was proposed by R. Kusunoki almost 20 years ago. His analysis was that ‘oversampling’, using a digital filter, creates time-distortions and obscures the potential of the 16bit/44.1kHz DAC. These ideas were commercially developed by Sakura Systems-47 labs.- - and by countless DIYers.
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Post by Owen Y on Sept 27, 2017 9:05:52 GMT 12
Digital board filled (except for the Receiver & DAC chips) - WIMA & ERO MKP metalised polyprop film caps I've had for years in my parts drawer, finally put to good use as decoupling caps on the TDA1541A. Sanyo OsCon alumin caps are the usual recommendation for digital circuits, used for final PSU decoupling here, alongside each regulator IC. The +/-5vdc & -15vdc supplies to the digital board are each shunt regulated though TL431 regulators - a bit of tedious time was spent carefully trimming each regulator. 
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Post by Owen Y on Sept 27, 2017 9:16:28 GMT 12
The DAC current output is fed to 20 ohm DAC I/V resistors, a key component, arguably. In this case the Rs used were hand-wound in 'basket-weave' fashion on vintage radio coil-formers (minimising unwanted capacitance). One of the Amplimo TM3 microphone transformers can be seen alongside, providing 1:15 step-up before the analogue outputs. 
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Post by Owen Y on Sept 27, 2017 9:18:03 GMT 12
Inserting the Receiver chip using anti-static bamboo chop-sticks An AudioNote TRANS-279 digital interface transformer, was used at the SPDIF input 
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Post by Owen Y on Sept 27, 2017 9:51:51 GMT 12
The completed chassis:  
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Pundit
Post by beeman on Sept 30, 2017 3:12:13 GMT 12
How does it sound?
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Post by Owen Y on Oct 2, 2017 8:41:13 GMT 12
Hi beeman - the jury is still out actually, because after firing it up again after a long while....silence. I find that one of the digital supplies is dead & currently ordering a couple of new Rs - it appears that at least one of the cheap wirewound Rs I'd used in the PSU has gone 'open circuit'. Hopefully nothing else faulty or cooked. Arghhh... SS.
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Post by colinf on Oct 2, 2017 9:34:55 GMT 12
Nice! 6sn7 has lower distortion than 5687 in this circuit configuration. If you have another pair of 1:15 Amplimo transformers you can add them in parallel to the 20 ohm I/V resistor, and connect the output to connect to the upper triode 1K grid resistor (+) and anode of the lower triode (-), forming a push-pull circuit with less distortion. The lower transformer needs to be connected in reverse to preserve correct absolute phase and make the push-pull operation happen. You'd need to duplicate the filter inductors and caps, and the 47K resistor, for the upper triode. The gain will increase, so if you want about the same gain the 20ohm resistor could be reduced, lowering distortion even further.
AMR-iFi R&D
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Post by colinf on Oct 2, 2017 9:37:49 GMT 12
Oh, and if you can possibly find a TDA1541 crown or double crown high spec chip, the low level and ambient information sounds clearer.
AMR-iFi R&D
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Post by Owen Y on Oct 2, 2017 11:51:52 GMT 12
Probably the only way now to get a genuine TDA1541A S1/S2 chip, would be to dig one out of a high end CDP. This is the E182CC original tube stage implementation - way too much gain for my system... 
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Post by colinf on Oct 2, 2017 12:17:51 GMT 12
Could you use a transformer with a lower turns ratio to get lower gain?
AMR-iFi R&D
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Post by Owen Y on Oct 2, 2017 13:40:17 GMT 12
First I need to troubleshoot the digital PSUs. It's a LM317/337 dual symmetrical +/- raw supply. Feeding local TL431 regs to produce +/-5v and -15v. The + side is dead, due to an open cct R I've identified. Not my forte....
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Post by colinf on Oct 4, 2017 7:00:32 GMT 12
You seem to be troubleshooting it fine!
AMR-iFi R&D
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Post by Owen Y on Oct 4, 2017 8:55:13 GMT 12
Thanks colin.... There's a bit too much supply volts in the + raw supply to the LM317 & the upstream dropper R has failed (a cheap Surplustronics one). One of the downstream dropper Rs to a TL431 also seems to be getting hot now....but that may be due to having pulled the receiver & DAC chips. Just waiting for some new Rs.
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Post by colinf on Oct 5, 2017 7:24:17 GMT 12
Operating the unit without the receiver and dac chips would mean the TL431s are now taking all of the power supply current, since they are shunt regulators. So they could be getting quite hot as they take on the current normally used by the chips. If the resistor(s) feeding the TL431s are getting hot they could be underrated for power rating. They will still dissipate the same power with or without the chips installed.
AMR-iFi R&D
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Post by Owen Y on Oct 5, 2017 8:33:20 GMT 12
Thanks colin - yes my conclusions too. One of the feeder Rs was marginal dissip rating. The LM317 can take 40v in but I have reduced that to minimise h/sink req'd, hence a dropper feeding that too.
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Post by colinf on Oct 5, 2017 11:37:04 GMT 12
Ok. You could always use a power zener diode to drop the voltage feeding the LM regulators. That way you don't need to calculate or experiment with resistor values.
AMR-iFi R&D
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Post by Owen Y on Jun 2, 2020 21:19:10 GMT 12
Hi peno - in reply to your queries elsewhere: The schematic is poor quality I'm sorry, but I have this one saved from an older site, scanned below. 1:15TX - 75H - 75H - 1K - E182CC The shunt networks are: 1nF - 3k9 47k The tube cathode R shown on this schematic is 470R (Edit: corrected value) with no bypass cap. On the other schematic above, the cathode bypass cap is 0.1uF. I can only suggest that, as a TDA1541 NOS DAC rolls off HFs significantly, TL deliberately used a small Ck on the tube stage in order to lift HFs. My impressions were that: 1) This cct sounded rather bright - at least initially with only a few hours use. 2) There is too much gain/output volts (especially with a E182CC tube (a little less gain using a 5687) & possibly the TX could be omitted, or a lower value I/V R as colin suggests. Let me know how your build proceeds  
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Member
Post by peno on Jun 2, 2020 23:57:15 GMT 12
Hi Owen, thank you very much! I've tried to find a better quality schematic for this for a long time! As I said in the PM I've build this DAC earlier but didn't find the schematic any more. All I remember was that it run hot (the PS regulators) in my small enclosure. Now I'll use bigger heat sinks and enclosure. I'll try this first with the 20R I/V resistor and Amplimo step up with ECC82. My preamp doesn't have much gain so maybe I'll get better results. And will try with / without the Ck. If I remember well the I/V resistor could even be bigger if you wont use a step up transformer or use another gain stage. good luck with the PSU problem! And hello all! I'm new here and my first post etc.. Best regards, Pete
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Member
Post by peno on Jun 3, 2020 0:17:28 GMT 12
Just double checking... Isn't the cathode resistor 470R? Not 470K
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Post by Owen Y on Jun 3, 2020 9:56:31 GMT 12
Hello peno & welcome! Of course, the Rk is 470R Keep us informed of your progress - pics please, if you can manage sometime. Cheers.
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Post by foveaux on Jun 3, 2020 12:22:53 GMT 12
Hi Owen, thank you very much! I've tried to find a better quality schematic for this for a long time! As I said in the PM I've build this DAC earlier but didn't find the schematic any more. All I remember was that it run hot (the PS regulators) in my small enclosure. Now I'll use bigger heat sinks and enclosure. I'll try this first with the 20R I/V resistor and Amplimo step up with ECC82. My preamp doesn't have much gain so maybe I'll get better results. And will try with / without the Ck. If I remember well the I/V resistor could even be bigger if you wont use a step up transformer or use another gain stage. good luck with the PSU problem! And hello all! I'm new here and my first post etc.. Best regards, Pete Hiya Pete/peno Good to have you aboard the forum. Looking forward to your input. Cheers, f
"I see music as a lifetime affair." [Rory Gallagher]
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