[skibum]

I hooked my multimeter to the RCA output jack and played a 1Khz signal at 0 dB through and measured 0.58 Volts AC on the output....

So I played around with the blue variable resistor while watching my multimeter and got it up to 2.0 Volts.

Now I did play with this variable resistor last time while listening to music and kept getting distortion when I increased the output voltage. My guess is I was at such a low voltage I was hearing distortion at way below 2.0 Volts AC.

??

Means I have been lsitening to my Modded DAC for 10 days now with 0.58 Volts output...

My initial quick listening sounds like the bass is a lot more "tubby" and not as tight....

Maybe needs to burn for a bit longer at the new higher voltage ?

The Dueland caps and Texas Component Resistors do sound sweet though!

Just got a Lundahl LL1572 transformer. That is going in next!

Skibum

 

[marcelnl]

well that tells you not to randomly tinker around in a digital device

Probably needs some time to readjust to the nwe voltage, but I do not expect that it needs a new burn in, maybe your ears need to readjust too....

 

[skibum]

Quote:

Originally Posted by marcelnl /img/forum/go_quote.gif well that tells you not to randomly tinker around in a digital device Probably needs some time to readjust to the nwe voltage, but I do not expect that it needs a new burn in, maybe your ears need to readjust too....

I am convince that I lost some of the magic running at this new higher voltage... I had a 0dB 1Khz signal going through both channels and I was measuring the AC voltage of one of the channels and listening to the 1Khz signal out of the other channel. I could hear the "pitch" of the 1 Khz signal change as I increased the volatage.... ???

I do not have a oscillosope but I am trying to figure out how to get some free software for my laptop that would allow me to see the signal to see if it is distorting.

I found this:

Soundcard Scope

My only input on my laptop is the MIC input (max input of about .1 Volt), so I would have divide the output voltage down with a couple of resistors. I was thinking to connect the output of my DAC to a 100K and a 10K resistor. Then look at the signal across the 10K resistor.

Could putting 110K ohm resistance across the RCA output of my DAC harm anything?

??

Thanks!

 

[marcelnl]

110 k across would definitely not harm your DAC.

 

[skibum]

Quote:

Originally Posted by marcelnl /img/forum/go_quote.gif 110 k across would definitely not harm your DAC.

great - thanks again marcelnl.

I had some time to play around with output voltage. It makes a HUGE difference in sound quality when changing the output voltage.

Should this be happening?

I lowered my output voltage from 2.0 volts AC (measured with a mutilmeter with a 0db 1KHz signal) down to 1.7 and the SQ improved dramatically.

I then played some downloaded FLAC files that appear to be recorded at a very high level and am getting distortion again.....

??

 

[errnst]

I feel i have to add some balance to the recent posts on this forum. People who have problems with their dac sometimes need to post a lot before they can figure out what went wrong. This makes it seem like the dac is troublesome when in fact most folks probably have few such troubles, so you do not hear from them much at all.

For my own sanity, I know a man who really knows cicrcuits. He repairs anything for anybody, usually without a schematic. This is the guy who i have in the back of my mind in case something goes wrong that i cannot figure out. Have not used him for the dac yet, but he is there if i need him. I recommend it to everybody who is new to modifications and electronics to find someone like this, it is very comforting.

It is difficult to understand what is happening based on what is said here, the information is always incomplete. I have scant ideas about what is going on with anyones problematic dac, my approach is to do one modification at a time, then if something goes funny i have a better idea why.

i never applied a scope or a vom or any other test equipment. when i adjusted the blue pot on the dac board, i just used my ears and set it in the middle of the spot where the sound was sweetest.

a variable that you might want to consider is the input voltage from your house wiring, mine measures 125- 130 volts and i adjust it to 115 before the dac. Another problem with mains power is that depending on the time of day, the quality of it varies. Sunday usually is the cleanest day for mains power. This dac likes power conditioner.

Skibum.... i have no idea what is going on with your dac. the kind of distortion you are talking about seems pretty severe, based on what you say, my only guess is that there is a problem with a dac chip or a socket, maybe some bit of trash got in somewhere between the chip and the socket? I think that when the cirucuit heats up it changes something, maybe check all your soldering for a situation that either opens or closes or partially opens or closes a circuit when the unit heats up or pressure is applied.

 

[marcelnl]

could it be that you are playing with the DAC bias voltage, and not with the actual DAC supply voltage?

 

[skibum]

Quote:

Originally Posted by marcelnl /img/forum/go_quote.gif could it be that you are playing with the DAC bias voltage, and not with the actual DAC supply voltage?

I have been adjusting the blue variable resistor located on the DAC board. I attached a photo with a circle around the blue variable resistor I have been adjusting.

To clarify: It appears that all of the CD's that I have burned (I use EAC) play wonderfully. But quite a few of the music files that I have (that I did NOT rip), appear to be recorded at a much "higher" level and I am hearing distortion. I am currently using the digital output of a Squeezebox with the volume set to maximum.

As errnst mentions "when i adjusted the blue pot on the dac board, i just used my ears and set it in the middle of the spot where the sound was sweetest."

I also have been doing this but was getting confused when I listened to some albums and was hearing distortion and others I was not. If I stick with CD's that I have personally burned all seems well.

I am trying to understand why some files are at "higher level" and what to do with those files...

Thanks again for the help!
Skibum

 

[marcelnl]

every CD gets mastered to suit the dynamic range of the recording; f.e Stravinsky's firebird starts off with barely audible music, only to end with a symphony orchester (capable of around 110dB) playing at hurricane strenght. In order to make the beginning heard and the end not to clip a compromise to suit that wide dynamic range has to be found, With Pop music the range often is far less wide and engineers frequently choose for the loudest they can go, also in order to make th music seem 'more energetic'.

You could probably adjust the gain in the digital domain, or make sure your DAC can handle them all (probably th ebetter solution as you;d have to digitally remaster your recordings if you do not want to lose data, if I'm not misstaken)

 

[skibum]

Quote:

Originally Posted by marcelnl /img/forum/go_quote.gif every CD gets mastered to suit the dynamic range of the recording; f.e Stravinsky's firebird starts off with barely audible music, only to end with a symphony orchester (capable of around 110dB) playing at hurricane strenght. In order to make the beginning heard and the end not to clip a compromise to suit that wide dynamic range has to be found, With Pop music the range often is far less wide and engineers frequently choose for the loudest they can go, also in order to make th music seem 'more energetic'. You could probably adjust the gain in the digital domain, or make sure your DAC can handle them all (probably th ebetter solution as you;d have to digitally remaster your recordings if you do not want to lose data, if I'm not misstaken)

I found out about "Replay gain" and that solves all my problems but as you mention I would prefer to sort my DAC out so it will just handle everything. I am a bit busy at the moment but as soon as I get some time I am going to play with my new FREE laptop oscilloscope and look at DAC output THD at different output voltage levels and frequencies. This free scope software is GREAT! : )

Just ordered a Mac Mini and M2Tech hiFace interface. Going to try Pure Music Software to start with. Can't wait!

 

[MikoLayer]

hello gang, been away from head-fi for a while, had other things happening in life.

wonder if you guys made any breakthroughs during my absence?

I basically had to set it aside and wasn't able to work on it for a couple of months.

Just a few minutes ago, I finally unscrewed the board from the bottom plate, and immediately noticed there were exactly three spots were traces were cut.

When I say 'cut', I mean literally cut as if it was done intentionally with an exacto knife. There isn't anything that comes to mind that might have caused such precise cuts when I didn't even separate the board from the case up until now.

Could this be a part of the original design / abrupt design changes that were meant to be there? If not, i guess my best bet is getting a hold of some conductive pen tomorrow.

Let me try to take some pics with my phone

Here it is


Now that I think about it, I think the mods went in this order

Output caps -> DIR9001 -> Resistors / Input caps

It was after the output caps mod that I lost the one of the channels (but wasn't aware, as the outputs were shorted and I was hearing dual mono from there on

). Must have been the easiest mod, can't imagine something going wrong there. I was gonna ask if a failed DIR9001 mod could mute one of the channels, but I guess it was happening before I mucked with DIR9001.

 

[marcelnl]

it almost seems that was done on purpose by the manufacturer, as if they designed the PCB and then learned they needed the capacitor and were in need of an additional connection.

These kind of repairs are quite normal in electronics....

 

[MikoLayer]

well the problem I am having now is one of the channels (forgot which one) being rendered completely silent, while the other is perfect. I was given a suggestion to dismount it from the chassis and take a look at the underside of the PCB. Here I am with a clear look at the underside, I can't find anything other than those marked points. They do seem quite intentional though, I was tempted to try joining them with a conductive pen but I was able to resist the urge

do you have any suggestions as to what might be the suspect? I know everything between the output cap and the headphones is not the culprit - if I short the capacitors I get a nice(...) dual mono from both channels.

 

[marcelnl]

did you replace the I/V resistors? a bad soldering or short there could make one channel go silent.

Think you have one of the later versions of the DAC, could you list what you modded and where things went wrong?

 

[MikoLayer]

Yeah sure.

The first mod I did was replacing output caps with bulky mundorf SIO caps. I had to drill some holes on the cover too, which was obviously done at a remote place separate from the sensitive electronics parts

At that time, I noticed when the caps are laid flat against the board, I would get sound from both channels; otherwise, one channel would be muted. Thought that was weird, but couldn't figure out why. Later it turns out that the legs of the output caps were touching each other, thereby duplicating whatever was playing in one channel to another. At the time of the mod though, I assumed everything went well.

The DAC has worked well (or so it appeared to me as I was unaware of the existing problem), so I applied I/V resistor / input caps / DIR9001 mods all in one sitting. tbh I am not so certain in what other they each went, but the end result was loss of one channel as I have described.

We (me and the guy helping me with the mod) were so convinced it was one of the input caps, went thru several spares with more meticulous soldering each time. Then we somehow discovered the way the output caps were sitting before the second mod session was set in - touching each other creating a short circuit.

Still puzzled and unable to solve the issue, we unscrewed the PCB off the chassis completely and haven't found anything out of ordinary on the backside (well except for what's in that pic below).

I guess we will give I/V resistors a shot for the hell of it