DIY Audio

Ove's first DAC
Using TDA1541A

Some background

I recently discovered and modified a Marantz CD65II player and saw that the player is soon become to be an extinct player because the hardware isn't any longer with us.
Hrmm... someone says, there is a lot of new hardware that is better. My reply is, offcource, but I have heard a lot of stories and tales about Philips efforts when it comes to this genuine 16 bit DAC. There is also a wast majority of people liking the sound of this allmighty queen of all 16 bits DAC.

Everyone seems to have good word for it. I know, It's madness to pay a fortune for a S2 crown version of the TDA1541A but It's about the same happening with the allmighty queen of tubes, the double triode ECC803S. I have myself had the opportunity to buy a sleve cheaply and was amased how much money I got when selling it on E-bay. It's like "Everyone whant's this, it is no longer in production" and finally ... I want it. Then the market prise rises to the hypes border, which could be very high. :-D

-OK, Back to the picture above. This is a kit bought from Ebay and China or Hong Kong (AnalogMetric) They are very forced and professionell and even though I have discoverered some problem with the schematic they are willing to help. Kikitronic is the Ebay shop for that company for the moment. They have copys of very old constructions and some on the DIY Audio forum claims that they steal property. I have not decided what to think in these matters yet.

Updated 9 feb 2010 ... and under progress
This page is written in the meantime I research and test my findings. Some of the text have been ripped or edited and altered along these days. I also present it as a kind of "blog" to this project. Please press F5 button now and then, so you get the latest updates refreshed to your browser.
Also,because english is not my native languish I try to change and do the best I can to keep all the information at this page understandable.

It'll be my pleasure if some you find my research of value.

More then one year has passed since I bought this kit and I have still not finished this project. I'm glad I didn't. Why spoil all the fun there is to learn and do modifications to this kit.
The kit is good and the sound is very good but I have now had time to really test things out under some days with lots of testing, listening and modding. I wanted to do some of the mods described on different places on the net when it comes to get the most out of this DAC.

There is another lunatic out there, even more crazy then me, who is modding and testing this kit right now. It's Mr. Fikus or the man who is "tubing" all his DAC's, the lampizator man. He call this DAC the green DAC but this is the same kit allright, even though my PCB is blue.

Anchors on this page, and in following order:

My reference equipment for all listening tests on this page

My first DIY Headphone amp and my belowed Sennheizer HD650

This is my first DIY headphoneamplifier i did 2 years ago. I got very good help and learned alot from the DIY audio forum member Nico Ras. It's a class A amplifier with very high bandwith. The headphones is, hands down, the best there is for the money I would say. They are also very good for OTL tubeamps because they have 300 ohm impedance which make it easier to drive. I use them in my livingroom for my second DIY headamp, with tubes.

Philips CD614 as transporter

I use this old Philips player as the CD transporter and use the SPDIF to my DAC's input receiver, which is the Crystal CS8412. It has one of the better transports and is also a spare part for my Marantz CD65II. The CDM4/19. The player has a A-B button which you can use to repeat snippets. Perfect when you want to do long tests with the test CD i have made. It's also good for practising the guittar and want to copy that Eric Clapton lick exactly right. I bought it for 1.5 $ at an Internet auction. Good deal don't you think?
The amp on top of the player is another DIY project, the Kleinsmidt 10A.

Visual analyzer software a DIY measuring interface and M-Audio audiophile soundcard.

These days we have computers to do nice FFT measurings. This is what I use. Sometimes I also use the Rmaa software for amplifier testing. Lately I have also tied it with my DAC testing. You generate a Testsignal (wav -file) from inside the Rmaa software. Then you burn that file to a "music" CD and run the record test.
Picture above is DUT for one channel of the tubed I/V amplifier later down this page. Below is the reference for this setup. The first graph show worse numbers then it is on the measurings futher down because I had to use the inbuilt amplifier in my measuring interface. But the scope-cables and cheap RCA phono and linecables are the same as in the tests below. The second graph, -60dB is exactly how it's setup but without the tested DAC. I'm not telling you this is the best test setup in the world but it gives a good hint on whats going on and you could also compare the different approaches for the I/V stages on this page. The two CD signals, 0dB and -60dB, i got from Pedja Rogics site and burned on a plain CD.


reference -0dB


reference -60dB



Running the DAC without oversampling

The never ending question among DIY people is if you should run your DAC without oversampling or with it. And also NOS or NON OS vs. reclocked over sampling. After several days of listening and shifting back and forth I decided to stay NOS, in other words without oversampling. The sound was better. There was a kind of glare or grainy but silky or smeared highs the NOS didn't have. I think that this is what most people say about NOS. It's not that much upper highs. The diference is not large but it's there, maybe more or less depending which DAC kit you have. There are measurings elsewhere on my site showing the difference in the upper highs.
As a matter of fact there was win win everywhere going NOS. But to fully understand that read on. The NOS for me hangs very much together with the reclocking option you can read about in the next subject.

Anyway, the only thing you need to do with this kit to run it NOS is to take out the SAA7220 chip and put in an IC holder which are strapped like the picture below shows. Picture is from a post by Elso Kwak in a thread in the DIY HiFi forum.


I then got some nasty cracklings in the sound if I didn't load the digital lines with something. It was enough to just measure with an oscilloscope probe and the cracklings dissapeared. So I ripped the clock and divider all out. Read on

With or without reclocking. Master clock

the DAC now is dead silent between tracks. There was a 1.5kHz sinus very low down on the right channel when running OS, you couldn't here it when the music played but it did annoy me. So, I have ripped it all out. The Xtal and the logic for dividing it to the SAA7220. The clock pulses from the onboard clock and logic going to the SAA7220 also looked very ugly on the oscilloscope. More like weak distorded sinus signals then the pefect pulses coming from the CS8412 directly when running master. This is a thing to try if you will listen to NOS but do not want to recklock on this kit, or maybe others as well. Put the CS8412 in master mode. Which means change the pin # M2 to ground instead of 5V. As this kit comes it is jumpered as slave and then the reclocking takes over. The picture below shows how I can switch between those two modes. The label is misleading because this has nothing to do with NOS or OS. I taped that label on before I fully understood the concept. There is also misleading information out there telling you that this has to be done to run this particular DAC in NOS. It isn't, see above. I recomend to run this DAC without reclocking if you want to go NOS.

Anyway, with the ripped out parts and particularly the SAA7220, I could fit another mod on an IC holder in place there. The I2S attenuator mod. described next.


I2S attenuator mod

To the right at the picture below is another IC holder with some attenuator stuff for the digital lines. This is one of the win win situations I mention above. When I allready decided to go NOS I can build my attenuation mod on this IC holder instead of cutting the board so that it would be hard to comeback to where it was.

There is several flavour of this mod floating and I have done oone of them which works great.

Schematic is still to come .... stay tuned.


The attenuator mod attached to an IC holder, to the right, where the SAA7220 should reside if running OS.


External DEM reclocking or syncronizing

There are a lot of discussion on my favorite forum, the DIY audio forum, about this modification. I will not link, you have to search. Even though there are witnesses telling about a "wow" effect I am a disbeliever in this case. Maybe because I didn't have any success with the easier trials. A big blob with several outside logic circuits didn't catch my interrest to the border where the fun and pleasure of trying really could get me a reasonally good effect of a really useful mod. Also when I read some "white papers" from highly regarded engineers how the TDA1541A, and in this case, how the DEM oscillator works in that circuit, I backed of. I will not do any mod here. I do not believe in syncronized DEM clock. Stochastic it is and stochastic it will be, read on.

The oscilloscope measuring point when trying some DEM recklocking sync.

Measuring and modding of the PSU

This is something that can give you better sound. Here under is a picture that gives you an Idé on how crazy I am. I have done so many tests and fiddlings so I can say there is no such thing as "this it what you should do" so that everything gets perfect. You are on your own here but pictures below gives you a hint and I will also tell you where you should look more carefully. It's all about using some more or better decoupling capacitors.

Here are some suggestions on decoupling caps around the OP's and the TDA1541A and also the SAA7220 digital filter if you are going OS.


Around the OP amplifiers

1mH with ferrite beads on each leg, in serie for the plus and minus supply

1mH with ferrite beads on each leg, in serie for the plus and minus supply. This is the other one.

This one goes to the SAA7220. I tried a larger one but the beast draw some current and my Voltage supply wasn't enough with the inductors
I had in my box, so I just put some healthy ferrite beads as support of tking hifh frequency rubbish away.



Listening test with high grade TDA1541A S1

Again I think it's very hard to hear any difference. If someone switched between a S1 crown and a normal on my system, without me knowing, I would have difficulties to hear difference, if at all. I think my S1 sounded more open and airy but when I measure the distortion with FFT the graph says nothing different from the other chips I have, including the R1 version. On the other hand that is the same with the OP's. No difference when measuring THD+n but small individual coloration when switching between them... or am I deluding myself? I really don't know. Maybe I don't have the golden ears everyone else seems to have.

I have now gone to another modification instead of using my S1 crown DAC. Piggybacking another DAC on top of the other


Listening tests with other output capacitors


This kit comes with good 10uF WIMa caps. I have done some listening tests and took them away completely, bypassed, because I have a cap at the input of my headphone amp used for the listening sessions. I couldn't here a difference at all, even if I would like to. So, then it's not any use of trying another one is it? If someone have one he thinks color the sound in the right way and propose to try it I don't think I will. No. I don't like that idée. Giving plenty of money away to get a colored sound. I'll give it a try another time maybe, but not on this DAC.
Maybe I will see the light and also become a capacitor fetishist, some day, but not for the moment.

Measuring caps is fun




Piggybacked TDA1541A

Inspired by my most visited forum about audio, the DIY Audio, I had to try the piggyback style of this DAC. Some have done it with everyting separate, even the decoupling caps. I have got som hints from erin (again another DIY Audio member) to just solder one TDA1541A on top of the other one and he was .... satisfied (like whooah ;-) ).

I have the most free time att nights so.. one of this nights I went for it (zoombie at work the day after... )

I kept the DEM clocks separate as of erins tip. But I also tested a "syncronisation mod" a'la ecdesign (again another DIY Audio member) For now I have the clocks separated again. So no 100pF between the two DAC's leg 16, see explenation below. Stochastic it is and stochastic it will be, read on.

All in all explained:
Bend the legs 16 and 17 out from the upper IC's body and do not solder that legs to the TDA beneath. Then solder a 470pF DEM oscillator cap at this pins. Then, if you would like to try the DEM syncronizing of the two piggybacked DAC's, solder a 100pF cap between pin 16 of both the dac's. The lower DAC allready has it's own 470pF cap at the 16 and 17 legs.
I did a 3mm thick and 10mm x 55 mm cooling aluminum "device" placed in the middle of the two IC's (thermal paste in between). They get warmer then running alone but not very much. You can keep a finger on top of the upper TDA as long as you will and I have learned thats about 45 degrees celcius. When I decide to finsih this DAc I will also put a small heatzink on top of the package.


How does it sound? Well, It's subtle but I'm sure it gives even more dynamic, punch and details. FFT measurings also shows a dynamic gain. There is at least 2-3 dB better dynamic measurings from FFT. I will present the final figures when all of this splitted project is done. When my player is more or less finished.

I believe the errors are less when two DAC's co-operate like this. Stochastic it is and stochastic it will be.


Using a somewhat new approach to use a discreete tube circuit. The CCDA amp

It all started with my first post at DIY Audio with this one.

The first handsketched embryo of the my CCDA I/V amp

It was a success and I have learned a lot from this work. I have worked it trough and for the moment this is the latest schematic which I am using now and which I probably will use when I "box" this DAC for finalisation.

E88CC Tubed CCDA amplifier
Please click to get a larger picture.


In the same thread there are some more pictures of the testings and the evolution to the latest schematic above. From the beginning I used a readymade PCB, All-in-one sollution from John Broskie at Tubecad. I got a nice RIAA amplifier with tubes fast and also a test jig for evaluating what this circuit could do as an amplifier after a DAC, such as the TDA1541A.

In short I dicovered that this circuit can be "calibrated" to give far better THD figures then one could expect in their wildest dreams! In the notes in the schematic above you also find the details. It goes like this: It's of importance that the two triodes work in balance. Equal current in each one of them. But the real eye opener was to adjust the load outside the output capacitor to match what you hang on after this circuit. 10K total load or about 4.1K makes the second overtone fall from 72dB to 87dB! Yes, I was also chocked. Amasing results and very rewarding. That is such a thing that makes this hobby so fun. Everything is not written in stone. You can also dicover somehing that the rest has forgotten.
Please look for the latest testfigures on the testpage of this DAC.

Here under I show you the latest hardware which probably will be the things going in to the DAC box. First picture also shows the HV powersupply and, to the right, the Current source I use for heating the filaments. Same approach on both things as on my XPP headphone amplifier. I will spare my two readymade and tested superregulators for another project. It's overkill and to no use to the better for a CCDA circuit like this. It just wants clean Voltage. And with the stabilized HV Mosfet regulator on the picture ... it will have that. Even more silent then my supershuntregulators.


How large can the passive I/V resistor be without giving distortion?

I have read in some threads of different forums, that the smaller the resistor you have in an I/V stage, the less dynamics there is and "this" and "that" and ... No I will do my own empirical work this time. I give all readers of this page a tip. Please be critical and try for yourself, because you can not trust all subjective thoughts out there. Not even mine ;-)

Most DIY people doesn't have instruments to measure with. You can not use your ears all alone. You will benefit greatly with a soundcard, PC and FFT software to measure THD and also an Oscilloscope to look for such evil things as self oscillation and other evil things in audio.

I have now tested it out, at least when it comes to THD. There is a limit where the passive I/V resistor could be of a to high value for a clean sound. Even if you compensate with the 2mA CCS which I have done on the two graphs below.
I discovered, trough measurings , that 68 ohm is on the border to be safe and above, 82 ohm for example, is not safe, when it comes to analyse FFT graphs (THD figures). This is for only one TDA1541A. If you have parallelled more you have to half the resistor value for every pair. So if 56 ohm is good for one you have to use around 27 for two 15 for four units and so on ....

Pictures of measurements below is for one TDA1541A chip. First picture -0dB and 82 ohm. Gives about 114mV RMS signal over the resistor Second picture is with 66 ohm which gives about 95mV RMS. This is also a to high value of resistor.

In the schematic for this CCDA tubecircuit above i have sketched 33 ohm. I would recommend 27 - 30 ohms though. This gives 82-87mV. Then you are safe but need a high amplification tube. You could use a lower mu tube such as a 6DJ8 or equivalents but then you will have lower amplification. On the other hand you will get lower output impedance, which is a good thing to have.
For the moment I use the E88CC (more or less the equivalent to 6DJ8) and two piggybacked TDA's and a 27 ohm I/V resistor. It gives me 1.15 V RMS output, superclean sound. The last tests I did with ECC83 I had 18 ohm metalfilm which gave me about 54mV and amplified output 2.4V RMS with a -0dB testsignal, using the second approach of the sketched circuit above , the one without positive feedback. I repeat this was also with two DAC's parallelled.

More about snakeoil ...

By the way. That metalfilm resistor I use measures 1.8uH inductance which is the exact amount the carbon resistor, Allen Bradley have. So much for the "snake oil" in those resistors. They go for high prices at Ebay.... I also tested a wirewound "speaker filter resistor" which had even higher inductance. So be careful to listen to all subjective thoughts about resistors. I have tried the metaIfilm and the Allen Bradley ones and I couldn't hear any difference. But who am I? A DIY guy without golden ears and without a subjective Hifi audio religion to which I hold on to. Pick your choise but also take care of your hard earned money.


82 ohm I/V resistor (one DAC). 114mV RMS. To much THD IMO.


68 ohm I/V resistor (one DAC). This is also over the borderline where the THD starts to raise.

I chimed in at this thread at DIY Audio for mention my findings and also to be a counterweight to the member -ecdesigns-.


Switchable signal paths "on the fly" between OP and Tube circuits

It's very hard to be sure if you do hear progress in sound when modding, testing and listen to your work. So I used Eagle CAD and etched a PCB which I mounted piggyback on top of the four OP IC-holders. On top of that card I have the I/V resistor, CCS circuit and a LP filter for the tubecircuit. There is also two high quality relays so that I can switch between tubed output or SS with the OP's. I have now settled for the lower amplifying device E88CC. So now my DAC gives about 1.15V RMS, both with the LME49710 and the tubes. I have also altered the LPF and feedback on the OP's to match the tube circuit. So when switching there should be very little difference in amplitude or frequency response. Just comparing other signatures which is hard to measure, and even harder to hear ;-). I also have to use a relay at the outputs from the two paths before i send it to the headphoneamp I use for listening tests. Here are some pictures of that work.


References and links to discussions corresponding to the subjects above.




Take care, enjoy, and plese give me comments. And also tell me of your own works and projects.


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