APS audio transformers

Our Modification process:

In order to properly evaluate the modifications performed on these DAC’s it is necessary to have at least two DAC’s of the same.  First, we take a pair of our best sounding modified DAC’s and A/B in real time to make sure they are identical in sound quality.  Then we perform a single modification on one. For example, we install our APS R2 transformers from the original APS transformers in one of them and then do the A/B comparisons.  If it’s an improvement we do the same to the other unit and move forward.  We repeat this process and do a DC offset adjustment and then the A/B comparison.  We do this for all modifications.  When we do modifications that make no difference we return it back to the previous state and move to the next modification.  We have several experienced listeners do these listening test over several weeks so we all are very sure before moving forward.  We also compare our best sounding unit to other very high-end DAC’s to make sure the change we made are good ones that everyone likes and agrees on.  We do a lot of measurements along the way to make sure nothing sneaks by us and we can verify we are on track with the modifications that make no difference and ones that do. This process can take months.  It took us almost a year to develop the new Rev.2 transformers and our super low impedance discrete analog power supply in the PLUS units.

 

Modifications we found that make no difference in sound quality in the Directstream MK1 are listed below.

1. AC inlet RF filter removal (LC) (You can bypass this with one that has no filter if you install the filter on PC board) This is also an FCC requirement to keep from contaminating other equipment.  We have found this makes no difference in sound quality in the MK1.  The MK2 has the filter on the PC board, not the inlet.
2. Changing the stock Capacitors on the 12v power supply to Audiophile quality.  Makes no difference in sound quality. These are actually very good capacitors with low ESR.  We will replace them if they are out of specification or are in an older unit.  Also in the Signature Series PLUS we us a seporate high quality power supply with top notch audio grade capacitors so changing them in the stock supply makes no sence.
3. Changing the stock regulators make no difference.  however, we do separate the three 5v regulators to feed the different components. one for the Digital input, one for the display and one for the SD card logic circuit.  Remember there are at least two local very high quality discrete regulators downstream on the PC board’s that Ted Smith designed to keep noise and jitter down to the very minimum possible. The stock power supply that feeds the analog board could be improved if we could get the impedance down to a very low value however there are operating program / control circuits on the bottom of the stock power supply making this almost impossible.  That’s why we use our custom-built analog power supply in our PLUS version to feed the analog board.  This is a very low impedance power supply that is oversized with an R-core transformer that is also isolated from the stock power supply. (4 amps worth). 

Note: this list could change based on new available products or devices. We are constantly seeking ways to improve sound quality.

Modifications that make the biggest improvements.

1. Our Rev.2 nickel transformers. Improvement of the original APS Transformers.
2. Polymer Vcom caps for the video opamps power.
3. Replacement of all thick film 1% resistors with super high quality 0.01% thin film resistors.
4. Perform a DC offset tune. Anyone who is familiar with transformer magnetics would know why this is a necessary step.
5. Change the stock rectifier diodes to fast recovery type.  Split out the 5v regulators so one supplies the Digital board, one supplies the display and one supplied the SD card logic circuit.
6. Our custom-built analog discrete super low impedance power supply. (PLUS only)
7. USB shorting plug. (We don’t recommend using the USB input)

Modifications that make little difference however worth doing.

1. RF EMI filtering on some of the IC’s that generate noise.
2. Turn off the screen when not needed.

 

Of course, high end input and AC cables and fuses of your choice to fine tune for your liking.

We hope this helps clear up our process of upgrading and modifications to the Directstream DAC's so our customers get the best sound quality possible.

To see the measurements of the standard vs the Signature Series PLUS, click on the photos in this section.

 

 

In the process of making these MK1 upgrades even better we sometimes have customers that feel we left them out with the older upgrades.

We have decided to give our past customers a discount on newer upgrades we discover. Just ask.

 

APS