Why no discrete DAC output stage PCB's
Oct 29, 2007 at 1:56 AM Thread Starter Post #1 of 14
regal

regal

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There are a lot of really nice DIY amp projects now. The improvements people are seeing by building opamp free amps are stunning.

But the fact remains that 95% of us have opamps remaining in our DAC's. Those that don't have NOS filterless DAC's which have their own issues.

I'm am an engineer but not an electrical one or else I could design a discrete I/V..

Building a complete OS DAC is cost prohibitive. Most of the good DAC chips are hard to come by. But you can buy a used AD1862 based commercial DAC for a reasonable price. I think that the next step for most of us to improve our audio system is a discreet I/V stage.
 
Oct 29, 2007 at 4:00 AM Post #3 of 14
Quote:

Originally Posted by regal /img/forum/go_quote.gif
Building a complete OS DAC is cost prohibitive. Most of the good DAC chips are hard to come by. But you can buy a used AD1862 based commercial DAC for a reasonable price. I think that the next step for most of us to improve our audio system is a discreet I/V stage.


It's not cost-prohibitive by any means. PCM1794 is very readily available, and is in fact what I use in the ezDAC.
 
Oct 29, 2007 at 7:29 AM Post #5 of 14
You can often get boards for the Pass Labs D1 discrete stage on diyaudio. There's stuff for sale on Rokna too iirc

And rbroer stages (based on Jocko's) are quite easily built p2p if you're a bit careful. Check diyaudio too for those
 
Oct 29, 2007 at 11:31 PM Post #6 of 14
Colin Toole (cetoole here) did a design for an I/V stage awhile ago as part of his DAC design. I've done a board layout (actually modified his a bit), and built it but haven't installed it yet. I've also built one of Rudolf Broertjes's (the less-simple TDA1541A I/V), but haven't tried it out other than on the bench. On both of these I had to adjust for the current requirements of the transistors I was using (2SA970/2SC2240), so took awhile to get stable with DC coupling.

Doing your own boards isn't that hard (even double-sided), and P-P wired is also an option... not a good one in my opinion, but could be done. The one at diyparadise is one of Rudolf's designs as well (TDA1543 IIRC).

As was mentioned, a Pass D1 variant is still available on diyaudio (this one requires +/- 30V supplies).

The problem with a DIY universal design is the differing requirements of DAC chips... current or voltage output, etc.
 
Oct 29, 2007 at 11:49 PM Post #7 of 14
I was going to say ... there's someone I know that's working on it.
smily_headphones1.gif
 
Oct 30, 2007 at 9:17 PM Post #8 of 14
Quote:

Originally Posted by regal /img/forum/go_quote.gif
There are a lot of really nice DIY amp projects now. The improvements people are seeing by building opamp free amps are stunning.

But the fact remains that 95% of us have opamps remaining in our DAC's. Those that don't have NOS filterless DAC's which have their own issues.

I'm am an engineer but not an electrical one or else I could design a discrete I/V..

Building a complete OS DAC is cost prohibitive. Most of the good DAC chips are hard to come by. But you can buy a used AD1862 based commercial DAC for a reasonable price. I think that the next step for most of us to improve our audio system is a discreet I/V stage.


Perhaps you should get out more. Forum-wise that is.
 
Oct 30, 2007 at 11:20 PM Post #9 of 14
The zap filter is really meant for voltage out DAC's which I'm not a fan of. It just has a resistor if you want to hook it to a current out DAC.

I researched DIYaudios forums for hours on I/V and can't make sense of any of it.
Plus there are no plug and play boards available.

I don't have the time to tinker, so I'm buying a Borbeleyo Audio I/V. PCB It comes with all the components, even a discrete regulator.

I'll let everyone know how it goes.
 
Oct 31, 2007 at 2:32 AM Post #11 of 14
Quote:

Originally Posted by regal /img/forum/go_quote.gif
The zap filter is really meant for voltage out DAC's which I'm not a fan of. It just has a resistor if you want to hook it to a current out DAC.


No, it has more than that. It has an input to each of the bases of the differential pair that forms the first stage for active i/v conversion. It is simply a matter of configuration.
 
Oct 31, 2007 at 12:56 PM Post #12 of 14
Here's another idea: Greg Ball's discrete opamp


300x200_skpre.jpg


Greg gives instructions how to configure it as an I/V converter or a differential to single ended converter, so should fit most DACs. It contains an onboard power supply with discrete regulators. If it's half as good as his power amps (which I've built) it'll sound fantastic. Uses the same symetrical topology.
 
Nov 3, 2007 at 7:35 PM Post #14 of 14
Hey i was looking into discrete I/V stages for my denon 2900. I have a balanced current output dac. Do I need a pair of stages for each channel or can I configure discrete stage to handle both duties. Alternately, is there any balanced output stages so I can have balanced and RCA out?
 
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