All of the usual strengths and weaknesses of a passive preamp would apply:
- No active circuity in the way of the signal, so potential for reduced preamp distortion
- Need to consider impedances of dac output, pot & power amp input (aim for your pot to be at least 10x the impedance of the dac output and no more than 1/10 the impendace of the power amp input)
- Need to consider HF rolloff due to cable capacitance between pot and power amp input (short connection best)
- Check that the system will have sufficient gain (some systems need preamp gain to provide the full range of playback volume required)
- No active circuity in the way of the signal, so potential for reduced preamp distortion
- Need to consider impedances of dac output, pot & power amp input (aim for your pot to be at least 10x the impedance of the dac output and no more than 1/10 the impendace of the power amp input)
- Need to consider HF rolloff due to cable capacitance between pot and power amp input (short connection best)
- Check that the system will have sufficient gain (some systems need preamp gain to provide the full range of playback volume required)
The stock topology has a filter then a buffer stage, one stage for each op-amp. If I were doing what you propose, i'd shoehorn the volume pot between those stages rather than after them. That way you have a nice low output impedance.
If you need a little extra gain, turn the buffer into a low gain stage.
Sheldon
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Hello again! I finally did the transformer outs (UTC A-20's) for Gigaworks DAC. The sound is really uncomparable with opamp out, but i still have a problem with hum in outs (both high and low frequency). Estimated hum level is about -80 dB (or more), and it can be easily heard 1m from my speakers. Does anyone has this problem or maybe my DAC is defective? Is there some power source mods, that could help in this case?
P.S. Now UTC's ground pots are not connected to DACs ground, but,anyway, this connection doesnt helps.
P.S. Now UTC's ground pots are not connected to DACs ground, but,anyway, this connection doesnt helps.
Newb, nearly finished my DAC
Hello to everyone, this is my first post on this forum.....actually its my first post on any forum!
So I've had this DAC V1.1 for some time now. I was inspired to buy it after reading the excellent information in this thread and DiyAudio as a whole. Thank you all.
I have slowly but surely upgraded bit by bit each time getting closer to what I believe to be hi-fidelity.
I am a former owner of a Sondek/Ittok LVII/entry level Linn MC, LK1 with Dirak, LK100 & LK280, Linn Helix 2. All of the Linn equipment was sold in 1999. I just lost interest after hearing Levinson, Krell, Martin Logan etc.
Building/Modding my own DAC has been immensely rewarding. And I am astonished at the sound I have been able to get from this little thing; not so little any more.
I would like to mention that I only know how to solder and have basic electronics to high school level. I just used a bit of creativity and copied things that I have seen high end manufacturers implement.
The mods:
No shared PSU's or transformer windings, each chip has dedicated power.
4 x 50VA transformers [one was faulty and I had to use a spare 18VA in the pic]
5 x LM317 PSU's.
1 x Bipolar LM317 PSU.
Removed all DC blocking caps.
Performed pin 20 mod.
Rebuilt analogue output stage with 1% MF resistors and Wima FKP2.
OPAMP Single OPA627 - bought from Gigawork.
1K resistance in series with Opamp output.
Analogue stage is not grounded at the DAC.
I am rebuilding the Analogue output using the exact values as set out in the CS CS_AN048Rev2 application note. I will also increase supply filtering 2x 330p & 2x 3n3 ceramic disc.
Hello to everyone, this is my first post on this forum.....actually its my first post on any forum!
So I've had this DAC V1.1 for some time now. I was inspired to buy it after reading the excellent information in this thread and DiyAudio as a whole. Thank you all.
I have slowly but surely upgraded bit by bit each time getting closer to what I believe to be hi-fidelity.
I am a former owner of a Sondek/Ittok LVII/entry level Linn MC, LK1 with Dirak, LK100 & LK280, Linn Helix 2. All of the Linn equipment was sold in 1999. I just lost interest after hearing Levinson, Krell, Martin Logan etc.
Building/Modding my own DAC has been immensely rewarding. And I am astonished at the sound I have been able to get from this little thing; not so little any more.
I would like to mention that I only know how to solder and have basic electronics to high school level. I just used a bit of creativity and copied things that I have seen high end manufacturers implement.
The mods:
No shared PSU's or transformer windings, each chip has dedicated power.
4 x 50VA transformers [one was faulty and I had to use a spare 18VA in the pic]
5 x LM317 PSU's.
1 x Bipolar LM317 PSU.
Removed all DC blocking caps.
Performed pin 20 mod.
Rebuilt analogue output stage with 1% MF resistors and Wima FKP2.
OPAMP Single OPA627 - bought from Gigawork.
1K resistance in series with Opamp output.
Analogue stage is not grounded at the DAC.
I am rebuilding the Analogue output using the exact values as set out in the CS CS_AN048Rev2 application note. I will also increase supply filtering 2x 330p & 2x 3n3 ceramic disc.
Attachments
I've got circuit boards arriving next week. With the setup costs and such, I'd like to sell the blank boards for $40. I'm also toying with the idea of offering the three main chips already soldered in place, but I won't have the ability to test the chips in the circuit. Any takers?
IF you want to reserve one, drop me an email at: stokes(at)quadesl.com
Here's some info on the boards on post 3827:
http://www.diyaudio.com/forums/digital-line-level/137976-experience-diy-dac-77.html#post2577669
Sheldon
Hmm soldering SMT's
Hi Sheldon,
I read your posts, I must admit it was my first read. This is a long thread and I gave up at about page 80 or 90 and cherry picked the rest. I think the Gigawork board is compromised and poorly designed but good value.
I like your board design, it addresses all the issues I detected with the Gigawork. I had to cut traces to separate the supply rails for the up sampling board and P6 VA on the 8416. After separating all the power rails the sound quality just went to another level.
PSU work is essential to getting the best out of this set of digital chips, rubbish in rubbish out as Linn like to say. Doesn't matter how good your analogue output/filter stage is what goes in matters more.
If you are still selling your boards, can you give me price details please.
Regards,
George.
Hi Sheldon,
I read your posts, I must admit it was my first read. This is a long thread and I gave up at about page 80 or 90 and cherry picked the rest. I think the Gigawork board is compromised and poorly designed but good value.
I like your board design, it addresses all the issues I detected with the Gigawork. I had to cut traces to separate the supply rails for the up sampling board and P6 VA on the 8416. After separating all the power rails the sound quality just went to another level.
PSU work is essential to getting the best out of this set of digital chips, rubbish in rubbish out as Linn like to say. Doesn't matter how good your analogue output/filter stage is what goes in matters more.
If you are still selling your boards, can you give me price details please.
Regards,
George.
Sheldon - Emailed. I'd love one of your boards too 
GSA - awsome work! I bet it sounds fantastic! I'm beginning to suspect that the PSU is actually of far greater importance than the DAC chip used at the end of the day. Whereas good analogue vinyl playback hangs upon speed stability, precision tonearm and cartridge and setup etc, I think good digital relies entirely upon a decent PSU - it's the foundation of the music. If the PSU isn't great it doesn't matter how good the DAC chip is, at least IMHO
Very neat work too - I'm very envious! Did you have any trouble desoldering the components? I have an earlier black-PCB version (non-USB & non-oversampling) and it was a real PAIN to desolder anything!
- John
GSA - awsome work! I bet it sounds fantastic! I'm beginning to suspect that the PSU is actually of far greater importance than the DAC chip used at the end of the day. Whereas good analogue vinyl playback hangs upon speed stability, precision tonearm and cartridge and setup etc, I think good digital relies entirely upon a decent PSU - it's the foundation of the music. If the PSU isn't great it doesn't matter how good the DAC chip is, at least IMHO
Very neat work too - I'm very envious! Did you have any trouble desoldering the components? I have an earlier black-PCB version (non-USB & non-oversampling) and it was a real PAIN to desolder anything!
- John
I've been building stand alone DACs for a long time, and the power supply sensitivity to the DAC chips varies quite a bit in my experience. The old burr brown ladder DAC chips like the PCM63 seemed to be fairly immune to power supply changes, but the bitstream chips like the Crystal semi CS4328 and CS4390 were very sensitive. I suspect that this chip is also quite sensitive, but I stuck with standard three terminal adjustable regulators with lots of local decoupling. I'd reccomending the linear tech three terminal regulators I your pockets are deep enough.
Sheldon
Sheldon
Hi John,
Thanks for the positive comments, yes your absolutely correct PSU is very important. It was a PITA to do anything involving solder on this board. I cut a lot of the resistors and small components off the board. I managed to remove all the caps and the rest was just hard work!
Sound quality has just been elevated to another plane by adding the seperated regulation and transformer windings, still a work in progress as I discovered a few problems along the way. I will document what I have done ASAP.
IMHO to get the best from these chips or any other IC [including chipamps] you need to place them in an ideal working environment, as far as possible. What else can be done to squeeze the last bit of quality from the chip?
We cant make any changes to the IC itself and I wouldn't know how!
How far you go with these things is simply dependant on what level of performance you are aspiring to. There is definitely a law of diminishing returns with "audiophile" electronics.
I am very concious of the fact that the DAC only forms part of the source component "rubbish in rubbish out". I use a PC running Foobar2000 via ASIO drivers into an ESI Maya 44 card with a digital Coax.
ESI - MAYA44
I use WAV files ripped with EAC in its highest accuracy. The ESI card is not set as the windows sound card. The ESI has an output transformer, internal clock, FIFO type buffer and its own power regulation.
Ultimately I will build a dedicated fanless solid state machine only for music playback. Computer Audiophile Pocket Server - C.A.P.S. | Computer Audiophile
Thanks for the positive comments, yes your absolutely correct PSU is very important. It was a PITA to do anything involving solder on this board. I cut a lot of the resistors and small components off the board. I managed to remove all the caps and the rest was just hard work!
Sound quality has just been elevated to another plane by adding the seperated regulation and transformer windings, still a work in progress as I discovered a few problems along the way. I will document what I have done ASAP.
IMHO to get the best from these chips or any other IC [including chipamps] you need to place them in an ideal working environment, as far as possible. What else can be done to squeeze the last bit of quality from the chip?
We cant make any changes to the IC itself and I wouldn't know how!
How far you go with these things is simply dependant on what level of performance you are aspiring to. There is definitely a law of diminishing returns with "audiophile" electronics.
I am very concious of the fact that the DAC only forms part of the source component "rubbish in rubbish out". I use a PC running Foobar2000 via ASIO drivers into an ESI Maya 44 card with a digital Coax.
ESI - MAYA44
I use WAV files ripped with EAC in its highest accuracy. The ESI card is not set as the windows sound card. The ESI has an output transformer, internal clock, FIFO type buffer and its own power regulation.
Ultimately I will build a dedicated fanless solid state machine only for music playback. Computer Audiophile Pocket Server - C.A.P.S. | Computer Audiophile
Attachments
I don't want to toot my own horn, but people had expressed interest in the DAC design I did and discussed earlier in this thread. I just wanted to give people a heads-up that the pro-made boards arrived and I'll be selling the blank boards for $40, and a blank board with the three TSSOP audio chips soldered in place for $85.
Pics and a writeup is here: http://www.diyaudio.com/forums/swap-meet/194469-cs4398-based-dac-blank-boards-sale.html#post2668925
Sheldon
Pics and a writeup is here: http://www.diyaudio.com/forums/swap-meet/194469-cs4398-based-dac-blank-boards-sale.html#post2668925
Sheldon
Hi!
I have this DAC and a pair of jt-11p-1 input transformers (cs4398 chip). I am planning to take the signal from the smurf board, then to my transformers and finally to my tube amp. My plan is to use the following schematics:
Primary:
http://www.jensen-transformers.com/as/as093.pdf
Secondary:
http://www.jensen-transformers.com/as/as089.pdf
My amp. Is a Music Angel (KT88) with a 100K pot.
Is this a good plan or does anyone have some suggestions for a newbie? Any advice is most welcome as I am still dizzy after reading all those pages…
I have this DAC and a pair of jt-11p-1 input transformers (cs4398 chip). I am planning to take the signal from the smurf board, then to my transformers and finally to my tube amp. My plan is to use the following schematics:
Primary:
http://www.jensen-transformers.com/as/as093.pdf
Secondary:
http://www.jensen-transformers.com/as/as089.pdf
My amp. Is a Music Angel (KT88) with a 100K pot.
Is this a good plan or does anyone have some suggestions for a newbie? Any advice is most welcome as I am still dizzy after reading all those pages…
There looks to be some othere models e.x. this one:
DAC PCM2706 (I2S) + CS4398 USB DAC Kit WLX-3 | eBay
DAC PCM2706 (I2S) + CS4398 USB DAC Kit WLX-3 | eBay