Purpose of the resistors and capacitors on output here?

[Garbz]

Quote:

Originally Posted by flecom so then how do tube amps work?

I'm sure some transformers can be used for DC blocking. In the case of every output transformer used for driving a balanced line I've seen the data sheet says DC is bad, and I have such a transformer!

Quote:

Originally Posted by flecom no matter what there is gonna be a dc offset cause most dac's have dc on their output...

Actually most DACs overcome this by putting their own ground reference voltage out. The differential input of the I/V stage will then swing everything in reference to ground. In this case though there's definitely offset.

Anyway I think you misunderstand what I mean by transformer:http://www6.head-fi.org/forums/showt...light=balanced

 

[nikongod]

its *only* 10 uf, you can easily get film caps in that value, why subject yourself to an electrolytic?

 

[Garbz]

lol because the mod was done with using existing size constraints in mind. It was also done a long time ago when I was less knowledged about things. At this point any 1uf cap would do there since the input impednace of my amp is insanely high.

Mind you the black gate NX-HiQ fairs very favorably to film caps. I doubt there is a night and day difference.

 

[flecom]

instead of spending so much money on those tx's why not just replace the akm dac on your sound card with a similar akm dac with balanced outputs?

 

[Garbz]

This has gone way off topic.

Firstly the xformers have been built.
Secondly they sound great.
Thirdly the DAC may not be pin compatible, then again we're outside of the realm of using the same case for the soundcard to fix XLR plugs on it.

Also the transformers have input and output selection, decouple the signal so there's definitly no ground loops, and I use them with my CDplayer not just with my computer.

Finally and most importantly all these mods have already been done so there's no point in arguing the cost factor to me, this thread was simply about what the passive components AFTER the dc blocking electrolytic cap do, with the possibility of loweing output impedance.

I'd like to add that the system as is sounds fantastic, the only reason i was considering this is because there's no good movies in the cinema, my turntable hasn't arrived yet, and my soldering hand is getting twitchy.

 

[rickcr42]

Quote:

This has gone way off topic.

so time to get 'er back to something of value yes ?

Quote:

Firstly the xformers have been built. Secondly they sound great. Thirdly the DAC may not be pin compatible, then again we're outside of the realm of using the same case for the soundcard to fix XLR plugs on it.

dealing with spec sheet readers and not folks who build,try and listen so don't sweat it man.

Quote:

I'd like to add that the system as is sounds fantastic, the only reason i was considering this is because there's no good movies in the cinema, my turntable hasn't arrived yet, and my soldering hand is getting twitchy.

and unless an all out assualt on the high end can be "improved" (or butchered

) with some small amount of research

First up is the actual AKM CODEC chip.When in doubt always check the manufacturers data sheet to decipher what exactly is going on here

Product page : http://www.asahi-kasei.co.jp/akm/en/...84/ak4584.html

Data sheet : http://www.asahi-kasei.co.jp/akm/en/...584/ek4584.pdf

Eval Manual :http://www.asahi-kasei.co.jp/akm/en/...84/ekd4584.pdf

The output stage is obviously a unity gain buffer to get a lowered output impedance but looking at the specs (3V P-P) you can lose that entirely !
Toss the whole shooting match and replace the passive section with the circuit in figure 3 of the data sheet.

so the 10uF becomes 22uF (Single 22 0r 2x10uF polyfilm caps).The WIMA MKP-4 polypropylene good here if fits in the size restraints http://www.inter-technical.com/datasheets/MKP_4.PDF.
The resistor to ground is now 10K (vishay,beyschlag,generic MF) and the inline resistor to 220 Ohm.This last is not a critical value nor is the resistance high so thermal noise not a factor so shoot for resistor "sound" here as your main guide.
Riken carbon,really expensive Tantalum or even a NOS Allen-Bradley should help with the "Digitalis" sound of the device.That takes care of the Analog section...................next up would be power supply improvements

BTW-losing the output stage is a common Sigmal-Delta DAC chip upgrade.The voltage is already plenty high,the filters usually internal to the chip so all you need is a DC blocking cap and cap bias resistor (the resistor to ground) to get the voltage OUT clean and without the added sonics of an active stage which does no more than lower the impedance a bit.Not important for normal length cable runs in the real world

 

[chris719]

Careful when removing anything after a current output DAC, generally this would be the I/V converter. Although this particular one isn't as you can see from the datasheet.

 

[rickcr42]

all sigma-delta and the buffer stage doing nothing but mucking up the sound no matter how good the actual chip

 

[rickcr42]

Straying off topic again but just momentarily :

If this opamp "buffer" were used for anything other than simple impedance conversion to drive a cable and was instead an IV stage it would not be used in the same way.
If trying to convert a current to a voltage you need a transimpedance stage and the signal from the DAC output pin would be going to the inverting input of the opamp and not to the non-inverting pin.The way the opamp is presently connected it can be nothing but a voltage gain stage or voltage buffering stage

back on topic

 

[chris719]

I meant in general, not this particular circuit. Don't want any readers to just assume they can start removing parts without consequence off the output of all DACs.

 

[rickcr42]

Quote:

I meant in general, not this particular circuit. Don't want any readers to just assume they can start removing parts without consequence off the output of all DACs.

I personally think it about as bad an idea as it can get to go poking around inside of audio equipment and start wholesale parts upgrades anyway unless there is a minimum of understanding what the circuit actually does and exactly what is or is not an upgrade.
Plugging in "designer" parts just because someone else did or because they "look cool" is a bad plan and a recipe' for bad sound not to mention you can actually fry the gear you are attempting to upgrade.

 

[Garbz]

That's a big upgrade

If I wern't still finalising my DAC i'd even be interested in doing that. What I am interested though is Figure 7 of the data sheet. The upgraded digital out will become important then.

Knowing eactly what this circuit does was the whole point of this thread

That said the stop band attenuation of 75dB should be sufficient to remove the filters entirely. and it probably won't effect the noise floor in the audible band.

 

[rickcr42]

Quote:

That said the stop band attenuation of 75dB should be sufficient to remove the filters entirely. and it probably won't effect the noise floor in the audible band.

it is not the noise floor you need worry about but out of band aliasing noise.It is my guess without pouring over the data sheet everything is all "inside the box" like it is with most modern ADCs/CODECS/DACs.Any conversion from current to voltage (in segmented dacs),any antialiasing and any final output gain stage all in a tidy little "chip" .

That is a blessing for miniaturization and low power draw but a nightmare if truly good sound and user choice is the goal.No access and no way to bypass means you work with the hand dealt and improve what goes to and what comes from the chip leaving :

1-Ouput coupling,possible output buffering but definately not output gain since we already have 3V P-P
2-A clean power source.Here it comes down to decoupling and pure DC power.If anything hates AC line power it is anything digital audio since it reacts to every single piece of crap riding on the line.Unless you need a HV suppy for a tube based output stage purely DC is the best way to go
3-Improved clocking.Many options available but the trick here is small size with large performance gains.

#1 is easy and will have immediately noticeable returns,#2 will require a fairly large expense when you add in the batteries,casing the batteries and building a charging system AND adding a capacitor bank on the output to lower the impedance of the supply and #3 a matter of researching what is available then buying and installing it.(#3 could also be a custom "on board" modification of the present clock but this not simple and requires researching both the CODEC specs and clocking circuits to get what you need).

Is it worth it ? Only you can decide if the potential gains are worth the effort but the opamp removal and passive parts upgrade a no brainer for cheap and fast or put another way "biggest bang for the buck"

 

[Garbz]

hmmm it didn't occur to me to upgrade the clock. But i'll definitly consider it when the DAC is finished. Afterall you only get out what you put in.

When my dac is done i'll focus on making sure this is the lowest jitter Transit in the world

After that i'll be bored. No wait. I'll pay with the I/V stage on my DAC. Stay tuned for questions on transformers for this before christmas

 

[rickcr42]

Quote:

After that i'll be bored. No wait. I'll pay with the I/V stage on my DAC. Stay tuned for questions on transformers for this before christmas

Then there will be the "re" casing and then better connectors and the HUGE lead acid battery power supply with fully automated charging system and .....


I have a DAC that started out in life as a simple little second hand $50 DITB that now has maybe another $400 in parts hanging off it or in the external interface box.Yes it is immensly improved but sometimes when I look at my "creation" I question my own sanity