Bh dac q

[John Swenson]

There are two sets of firmware on the board: FPGA and XMOS processor.

The FPGA is the "brains" of the whole thing. It is the S/PDIF decoder, buffer controller, output format generator, adjustable oscillator interface, display controller and several others I can't think of at the moment. The firmware for the FPGA is stored in a special flash memory that is soldered to the board. In order to reprogram this flash memory there is a socket into which you can insert a cheap "eeprom". There is a switch on the board that takes the data from this eeprom and programs the FPGA flash. This chip in the socket is only needed when new firmware is being installed. From the factory there will be no chip in the socket. When new firmware is needed the Bottlehead gang will ship you a little chip, you put it in the socket and flip the switch. When it is done you can take out the chip.

Since there is a USB port I could have done firmware upgrades via USB, but there is a big proglem, you need a driver on the computer, which means I have to maintain drivers on every OS Bpttlehead users use, I REALLY did not want to do that! And every time Apple or Microsoft came up with a new version I would probably have to re-write the driver, not on my list of things I want to do forever. So yI decided on ship out something and plug it in, no software needed!

The XMOS processor also has firmware, but it is just for the USB interface, much lower probability of needing updating. As it is this is updated via USB, which unfortunately has the same problem of requiring a driver. It can theoretically be updated over the AUX port, so I might set things up so that any board that we send out that plugs into the aux port automatically updates the firmware for the processor on the main board.

John S.

[mcandmar]

That 1V output with my filter is a temporary thing, by the time it gets into production I'll tweak the output sevel back up to near 2V level.

Oh please do, anything less than redbook levels would mean having to reconfigure everything i own to increase the gain.  It wouldn't do the product any favors at all, i can only imagine the reaction on head-fi if you said it had an iPod level output.

Somebody mentioned the possibility of supporting multiple channels, is there any chance of fully balanced output via an add on card in the future?

[John Swenson]

Doing an external balanced board COULD be done, but it will not be cheap. The best way to do it is with a separate DAC chip for each phase, I can't just add one, it would have to duplicate the: clock circuits, reclocker and have two DAC chips and associated components. Certainly doable, but not dirt cheap.

Whether it gets done I presume is determined by how many people want to pay for it!

John S.

[Paul Birkeland]

Oh please do, anything less than redbook levels would mean having to reconfigure everything i own to increase the gain. 

You can add a Quickie to increase the gain.

is there any chance of fully balanced output via an add on card in the future?

You can add a BeePre to obtain a set of balanced outputs.

[mcandmar]

Doing an external balanced board COULD be done, but it will not be cheap. The best way to do it is with a separate DAC chip for each phase, I can't just add one, it would have to duplicate the: clock circuits, reclocker and have two DAC chips and associated components. Certainly doable, but not dirt cheap.

That sounds like a whole other project then.  I was just curious if the DAC chip had multiple channels that could be used to create two inverted outputs.  For example some ES9018 implementations feed multiple channels into an I/V board to create a balanced output, hence i was wondering if the same can be done via an add on board.

You can add a Quickie to increase the gain.

Yeah but no.

You can add a BeePre to obtain a set of balanced outputs.

Never knew it could do that, interesting bit of kit.

[Paul Joppa]

You can also do a balanced out like the BeePre, matching the impedance to ground of the two sides. Assuming it is feeding a differential input of the next stage, this is perfectly good and meets the definition used for balanced interconnects.

It is not necessary to have equal and opposite signals on a balanced line. That would be push-pull, not the same thing. This semantic confusion is very widespread.

[Doc B.]

At this juncture we are not considering design changes or additions to the DAC. I always want to ask someone why they want a balanced output in the first place, for precisely the reason PJ offers, most audiophiles confuse terminology. There are good reasons to use balanced connections in some cases. I find it helps the bass with speaker connections to transformer outputs of tube amps, though I'm probably the only guy doing that and I can't explain why it seems to do what it does. At line level where the issue usually comes up I seem to prefer the single ended connection made with properly shielded cable over the additional circuitry and components necessary to make inputs and outputs balanced. I will note that we went to some trouble incorporating the ability to use balanced connections on the BeePre and it seems like we mostly hear about people putting extra RCAs where the XLRs are to create more single ended outputs.