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Quad PCM58 current-out SE/balanced board

Orders now are open for Quad PCM58 Iout boards, ready built and tested or as a bare-board kit of parts. This board is not a complete DAC, it requires an external I/V stage. PM me while not forgetting to include your chosen payment method and location so I can quote you inclusive of fees and shipping.

When developing the 'Dark LED' I/V stage I prototyped a number of DAC chips to feed it and it was the PCM58 that won out in our listening. According to its datasheet, the PCM58 is the lowest noise multibit DAC chip available - later generations (including PCM63, PCM1702 and PCM1704) haven't been able to improve on its idle channel noise.

The quad PCM58 current out design has discrete regulators fed from IR LEDs for the DAC chip power rails and accepts I2S input. To create a complete DAC you'll need an interface board on the input (S/PDIF, Toslink or USB) and for generating the output, an I/V converter. The intended use case is with the 'Dark LED' module - the power rails are the same for the two PCBs, +/-18V. Using 0R resistor options the PCM58s may be configured in single-ended mode or alternatively, balanced with an on-board phase splitter. Multiturn pots are included so you can trim the 4 most-significant bit weights of the DACs assuming you have suitable measurement kit. If you don't have that kit, I'll leave those trimmers off the board by default so as not to disturb the factory trimming of the DACs.

Physical dimensions: 100mm * 100mm, max height 20mm. Fixing centres : 95mm * 95mm, M3 holes.

PCM58_promo3.png



Price for a quad PCM58 built and tested unit is : 700RMB (~USD100) to include 4 recycled PCM58 DAC chips which are fitted in turned-pin IC sockets.
for a bare-board kit, including 4 DAC chips the price is 580rmb. We'll be putting up the stuffing guide shortly.

If you already have your own PCM58s the price for the board without DAC chips is 500RMB and I'll supply the sockets unsoldered unless requested otherwise. This is because many recycled PCM58s have disfigured legs which are rather tricky to fit into sockets when they're soldered down due to the nearby components.

Our preferred payment method is via Wise which typically adds a 2% fee. Our receiving currency is CNY, alternatively USD or Euro. PayPal may also be used, in USD but will attract higher fees, 5.5%.

Shipping is in addition and depends on your location and speed of service. Courier (FedEx, TNT, DHL) typically takes 8 - 10 days and e-packet four to eight weeks. Not all locations can be serviced by e-packet though.



What else is needed to turn the Quad PCM58 into a fully operational DAC?

You'll need an input interface board to feed an I2S input to the Quad PCM58 over 3 wires (no MCLK is required). The popular gold-standard USB interface chip CM6631A though is typically not compatible with this board as in stock form it outputs a BCLK of 128fs at 44k1 sample rate whereas we require a 64fs BCLK. If you buy the CM6631A card through us we can perform the firmware upgrade needed to make it compatible. Your output stage (I/V stage) could be as simple as a couple of opamps, configured in transimpedance mode. A low-noise, high speed one is preferred. The ideal I/V from the SQ perspective would be a discrete one like 'Dark LED' customized slightly to run from a unipolar input current. Seeing as the PCM58's DAC internals are unipolar, it generates a bipolar output current through the provision of a secondary fixed current source which adds half the full-scale peak-to-peak output current (1mA). This is the function of the BPO pin on the DAC (pin5). Seeing as this additional current source adds noise it is best to avoid using it if the I/V stage can handle a unipolar input current, which the Dark LED can, given a change to two resistors (R1 & R2). When the BPO pin isn't being used the 0R resistors R7,R30,31 & 32 are not fitted, nor are C7,C14,C20 & C27 which decouple the BPO current source.

You'll also need a well regulated low noise power supply of dual rail +/-18V rated at at least 150mA An LM317 and LM337-based board will be sufficient as the PCM58s have their own regulators. If you already have a single winding AC supply (an AC wall-wart) then 18VAC at 10-20VA would be in the right ballpark. Use a half-wave rectifier so you get both rails from a single winding or alternatively, a centre-tapped trafo. I don't recommend using switching supplies due to issues with common-mode noise, its very hard to filter out unless you're using balanced connections to your amp or pre.

Speaking of balanced mode, the board may be configured into being a 4 channel (L+,L-,R+ & R-) system at 1mA peak per channel or a 2 channel, 2mA peak per channel solution with the four DACs configured in two paralleled pairs. In balanced mode you'll need 4 channels of I/V. The configuration is handled by 0R resistor on the jumper 0R resistor locations U16-U18 and R33,R34.

PCM58_promo.jpg
PCM58 Guide rev.jpg
 
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How much would a complete pcm58 dac with dark led i/v stage and a usb to i2s board including interconnect cables cost please.Delivered to Sussex,UK by cheapest delivery method,thanks Mick.I do not need the trimmers and would prefer to use Paypal.Would a balanced version need two dark led stages.
 
The PSU is an LM350/LM337 pair fed from zener diodes for the main +18/-18V rails and another LM350 for the input stage rail. This latter rail we customize according to the input board being used, typically its 5V.

The input side uses half-wave rectification so as to be able to generate both polarities from a single trafo winding (18-24VAC) then follows the rectification with CLC filtering. At the output of the regulator there's another filter, LC to help with reducing the regulator noise.
 
Me likey your setup JKiriakis!

@abraxalito,
Is the pictures psu from your shop?
I’ve been resisting, but this DAC has strong pull…plus I have the Dark I/V already😉.
Writing to issue a recognition for Richard. DAC+Dark LED I/V playing, super dynamic, detailed, powerful.

Now, need to find a proportionately solid chassis.

Hats off, thanks very much, completely pleased.

Jim