New Maxx Audio DAC frontend on Pa500 (audio+video)

[alfredokiwi]

Hi all,

On last Saturday I decided to overhaul the Pa500 following a DAC non inverting amplifying configuration. The idea was to add the high equalization feedback network to compensate the roll off of the DAC antialiasing filter (same circuit approach as in R3 please check my blog). At the same time I set again the lows EQs and stereo-image separation (always using feedback components). And final I added another filter pole due the high input impedance of a non inverting stage (300 Kohms approx), this addition was possible avoiding filtering insertion loss due to much filter poles in use (now 7 poles in total).

The reached audio quality on Pa500 after this "stage redesign" using only one op amp stage acting as DAC filter, active EQ compensation and signal gain is stunning... and I want to share the last demos. This idea to overhaul the DAC circuit came due the good results on my Korg R3, that use a non inverting DAC stage configuration. Also on HI-FI forums a non inverting stage is the most faithful configuration on audio amplification.

Notice the high dynamic range reproduction, samples details and nuances. Also check on a soft recording tool the levels from maximal to -75db on fade out, 100% noiseless and very clean DAC reproduction.
All the details of the ROM samples can be heard, a stunning final quality.

Here the last demos, and after this very very happy

<iframe width="100%" height="166" scrolling="no" frameborder="no" src="http://w.soundcloud.com/player/?url=htt ... "></iframe>

Here I played the "Love Ballad" style, notice the dynamic range !! At the beginning starts very quiet reaching maximal dynamic on the drums part. The strings samples quality on first STS is not superb, the second STS and next much better but a bit loud with some "clipping" on the recording (I can notice it after playing back the recording). Is important to set first on each STS instrument the volume parameter before recording !!!.

<iframe width="100%" height="166" scrolling="no" frameborder="no" src="http://w.soundcloud.com/player/?url=htt ... "></iframe>

Very happy with the sounding quality of the new DAC circuit frontend, is the 100% true Pa500 audio without post EQ/effects on the mixer/recording (flat EQ recording at 16 bit 48Khz).

Regards.

[karmathanever]

Hi Alfred

Thanks for sharing your technical knowledge with us - I am afraid you lost me before the end of the first sentence, but I know there will be some who are keen to know this info - so thanks

Pete

[a.schemkes]

WTH are you talking about????

[siebenhirter]

Hallo Alfredo,
what about more informations how to implement these technical modifications?
Schematics and descriptions of the components like the type of user OP-amp would be helpful. Most of us do not know schematic of R3 and what DAC and kind of OP-amp is used.

How to insert only one op-amp-stage into a Pa500 acting as filter, compensator and gain and what components else are necessary to built that additional stage?

Looking the schematic of my PA500 i can see only one OP-amp NJM4580 acting as LPF near the DAC.
Next two op-amp-stages of same type are on another board, acting as mixer for audio-in and as pre-amplifier.

It is comprehensible to get better dynamic by bypassing the mixerstage and changing gain-factors of pre-amplifier NJM4580, headphon-amplifier NJM4556 and TPA3100.
To build in additional components for your final quality of sound it would be helpful to get informations how to realize them concretely.

[Thoraldus]

WTH are you talking about????

Basically the PA500 factory audio output 'suck dead gerbils' and he has done a redesign with significant improvements.

[alfredokiwi]

WTH are you talking about????

Basically the PA500 factory audio output 'suck dead gerbils' and he has done a redesign with significant improvements.

When I checked out the Pa500 headphone output before buying I noticed immediately the low "dynamic range" issue. It takes me a lot of months performing the corrections and research of technical information about DAC stages design. Putting this all together on a post involves time, because the final circuit differs 100% from original design and explaining the last changes is not so easy.

Reaching the best quality is very important on recordings. People spends a lot of money on rack units to reach a better audio, I was one of them. But I learned that on analog stages if quality is affected the degradation of the signal is permanent due the lost of audio information. And the solution is a good circuit stage design from beginning, this is the most important aspect on recordings setups.
When I have a chance I will put all the information of the last circuit changes on my blog at http://www.alfredoblogspage.blogspot.com.ar/

I want to share the last upload, "World Demo" track before and after last circuit bend to show the importance of good audio quality.

<iframe width="100%" height="166" scrolling="no" frameborder="no" src="http://w.soundcloud.com/player/?url=htt ... "></iframe>

<iframe width="100%" height="166" scrolling="no" frameborder="no" src="http://w.soundcloud.com/player/?url=htt ... "></iframe>

Regards.

[a.schemkes]

I can hear the difference very good. Its much "cleaner" more details en instruments stand out much better. Is it only the PA500 that had this weak output stage/DAC convertor?

[Basement Music]

I noticed a lower dynamic range, a much flatter sound on the Korg micro X compared to more expensive Korg units. Could be wrong.

[alfredokiwi]

Only I can give an opinion about instruments that I have at home because is difficult to evaluate only from audio demos the sound quality of other models.
Dynamic range is the key of all attributes on a sound. Most people think that sampling at CD quality or more is the most important, but the attribute that gives a real "fat sound" with presence is the dynamic range or sound level variation. And due leveling and impedance mismatch issues on audio stages design and mixing the sound variation or "dynamic range" can to be affected leading to poor recordings.

Here I have created a video about my R3 synth with a similar DAC circuit bend as in Pa500, to show how well it sounds when audio output reach an excellent "dynamic range".
Please set before watching to 480p quality for excellent audio reproduction. !!!

<iframe width="853" height="480" src="http://www.youtube.com/embed/69hDBcJ5ShE" frameborder="0"></iframe>

Dynamic range plays a key role on recordings. Alan Parsons Project was one of the followers of improved "dynamic range" on his recordings.

[BaliJazz]

Hi ALfredo,
What do you think about PA 600,
Does it have a bad soundtoo ? like PA 500 ?
May be if it is fixed, i wil consider to buy pa 600.

thx

[GXG]

Do you think it might be the same problem with Pa3X ? I heard others complaining about the DAC quality of Pa series .

[fResH_]

KORG, hire this alfredo guy. Obviously he knows and makes better quality things to your own product compared your own staff.