Experience with this DIY DAC ?

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#2,822
Fedor said:
Hi guys, I've been reading this thread for long time, and heavily modded my DAC according to the suggestions here. Now I'm using UTC A-20 transformers. And one thing that is bothering me, is 50Hz hum. When DAC is off it is really audible, when it is on, hum is barely audible, at the same volume, but is still there. If I touch both DAC and amp cases it goes away. It is ground loop isn't? Trafos are not connected to ground, + and - terminals go to the RCA which are isolated from case. Maybe I need to isolate whole DAC board and power transfomer from the case?
Bill, if I remember correctly you wrote several posts about this, that we don't need to connect negative terminal to the DAC ground, but what will happen if we do?

Thanks,
Fedor
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If you can remove the hum by touching both the amp and the DAC, I would suspect one of your chassis is not grounded properly. I would try running a separate earth ground to the DAC chassis to the wall. If the amp is also not properly grounded, run a similar ground from it's chassis to the wall. Whenever I isolate audio with transformers I typically star ground the chassis/grounds of all devices at the wall, which maintains shielding by preventing anything from becoming an antenna. Ground loops are not a problem at this point because no current flows through the signal grounds, which is what causes the typical loop hum to begin with.

Perhaps a simpler and potentially adequate solution would be to connect the DAC and amp chassis with a suitable grounding wire...
 
#2,824
I'm hesitant to try to blame any one condition for your problem, as you have stated the problem is not apparent when you use a receiver. It could be that you have the DAC board grounded to the case, which should not be done, and your preamp board is also grounded to its case, which also should not be done. Another problem could be a very high input impedance in your preamp which makes it susceptible to interference.

This stuff can be aggravating, to say the least. I had a DIY power amp that had a slight hum I could not figure out. The boards were completely isolated from the chassis. I tied the board grounds to the chassis with a .1uf cap and the hum completely disappeared. Go figure!
 
#2,825
Hey guys-

Love the thread


I'm going to buy the $119 version of the Gigaworks DAC on eBay. I'm putting the lm4562 opamps in for sure. What else should I be upgrading?

I planned to spend $500 on a DAC - so I'm willing to put in some serious upgrades. I tried to read the whole thread, but that proved to be time consuming. So I was hoping someone could tell me or point me towards any "crucial" upgrades that I should do to put this puppy into the realm of the big boys. Getting rid of caps on signal seems like something I should do for sure - I would just need a diagram to do it (I know my limitations)


Thanks,
Graham
 
#2,826
P.S. I saw some people put VU buffers into this amp. Frankly, I want them because they look cool; however, if they sacrifice any sound quality (I feel like they do if they are at the output of the amp) then I have no problem dropping them. On the other hand - if someone would care to explain the benefit of VU buffers...I'd be all ears.

Graham
 
#2,827
 
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#2,830
Adrculda said:
Hey guys...
im looking to build a pre-amp soon and want to incorporate a dac into it
...
Which onw would you suggest ???
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I would stay away from any NOS DAC's. To me they sound terrible, fake.
I would try one that has an ASRC - like the Gigaworks or raindrop_hui ones. I have no balanced amp so the ballanced DAC would be a waste. But the discrete HDAM stage sounds interesting...
Personally I prefer the TI DAC's in front of CS ones. Didn't listen to the AD1955 so I cannot tell if it is really that good like it is on paper.
 
#2,832
I don't think NOS dacs sound terrible, but they have many shortcomings that are tradeoffs from modern dacs. The new upsampling stuff is getting better with each generation, and is getting closer to the NOS sound without the shortcomings. Many people are highly biased against this technology, I suggest you must try it for yourself and form your own opinion.
 
#2,833
A lot of what has given digital a bad name in audio came from early NOS designs. That's not to say that NOS in of itself is bad, but in my limited experience, the line between good and bad is thinner with NOS than with oversampled DACs.

I do find that oversampled DACs allows filter and analog stage design freedom that NOS does not.

With NOS, you really don't have much in terms of new chip design. That is a good thing and a bad thing. It's good in that you have DIP chips rather than tiny surface mount, but bad thing is that you are missing out on decades of R&D in the digital audio world.

Sheldon
 
#2,834
NOS require a VERY steep filter in the analog part to eliminate any image frequencies. That filter is almost impossible to be done and anyway will introduce phase and ringing problems that will corrupt the signal even more.
OS was developed to push the image frequencies further away from audio band and to allow use of less demanding analog filters. TDA1541 was designed to work in a 4x OS setup.

All the DIY "NOS projects" that I have seen, have NO analog filters or just some one-two pole filters, totally inadequate. I think that some people like those image frequencies that are artificially generated, but I don't. There are horrid IMO...
 
#2,835
More info on the RE marked trafos, if anyone is interested.

Bill Whitlock, pres. of Jensen, responded to my inquiry.
In the 80s Jensen was using Reichenbach Engineering as their assemblers. The pres. of Jensen died in 1989 and that was when Reichenbach tried to steal the ownership of the designs, but were not successful in court. Subsequently, Jensen changed all their production numbers from JE to JT. The RE units are technically the same units, but legally they are counterfeits. Reichenbach was forced out of business and the Jensen defecter involved in the scheme was forced to pay huge damages. Mr. Whitlock would not divulge their name.
 
#2,836
On the same subject, these trafos have become more refined and smoother through usage over the weeks I have been using them. I was not expecting that, being used. Possibly they became saturated from someone checking continuity with a multimeter. They are extremely good trafos.
 
#2,837
SoNic_real_one said:
NOS require a VERY steep filter in the analog part to eliminate any image frequencies. That filter is almost impossible to be done and anyway will introduce phase and ringing problems that will corrupt the signal even more.
OS was developed to push the image frequencies further away from audio band and to allow use of less demanding analog filters. TDA1541 was designed to work in a 4x OS setup.

All the DIY "NOS projects" that I have seen, have NO analog filters or just some one-two pole filters, totally inadequate. I think that some people like those image frequencies that are artificially generated, but I don't. There are horrid IMO...
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Hi.I am interested in Tda1541a sound.Here is the link of OS Tda541 design. eBay.ie: TDA1541A TDA1541 DAC (CS8412 / CS8414, SAA7220) PCB (item 220635669828 end time 10-Aug-10 07:56:15 BST)
But i heard a lot about bad sound of SAA7220.People say they bypass them and tell the sound became better.So why all the commercial pcbs of Tda1541 have OS filter?
And i will also try Yamamoto dac.A person sells its pcbs for 100$ my friend told me.
 
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