Strange, the DAC only works with up,dn,dn,dn or up,dn,dn,up; regardless of whether the upsampling board is used or not.
Ratio
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There is some doubt as to whether the 1636 will handle the level if you need 0dbu outputs. The 1578 certainly will but it doesn't feature the catch word "amorphous". Rakk uses the 1674 at 1:4 with 3KR across the secondary which equates to 94R on each leg of the primary so resistances that high must sound pretty decent still or they wouldn't bother with the transformer I/V. Most people don't need 2V RMS output from their dac and so could reduce the resistor quite a bit for better sound. The 1674, and the 7905, are so expensive though. I have some blank boards to try but haven't had time to order the parts. I'm going under the assumption that 1:4 is barely enough gain and more would be better but I have never read any comparisons of different gains. I have some cheap Edcor transformers to play with at 1:4 and 1:8 to see what gain I really need and then I will order some Lundahls. The PCM1798 with 40R at 1:8 into 20KR amps (32R total shunts on each leg? with the addition of the secondary load) are a little too quiet. Increasing the primary resistors to 160R was plenty loud but very distorted.
That is the same question I am having. How much of the I/V voltage should come from the transformer gain and how much from the resistors? Do higher gain transformers sound inherently less good? Most of what I have read is that the chips sound best with the minimum of voltage on the pins which is why most people end up with a discrete active I/V with high gain. One concern with higher gain transformers is the amplified effect the secondary load contributes to reduce the voltage making the final design fussier about what it is plugged into.
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There is some doubt as to whether the 1636 will handle the level if you need 0dbu outputs. The 1578 certainly will but it doesn't feature the catch word "amorphous". Rakk uses the 1674 at 1:4 with 3KR across the secondary which equates to 94R on each leg of the primary so resistances that high must sound pretty decent still or they wouldn't bother with the transformer I/V. Most people don't need 2V RMS output from their dac and so could reduce the resistor quite a bit for better sound. The 1674, and the 7905, are so expensive though. I have some blank boards to try but haven't had time to order the parts. I'm going under the assumption that 1:4 is barely enough gain and more would be better but I have never read any comparisons of different gains. I have some cheap Edcor transformers to play with at 1:4 and 1:8 to see what gain I really need and then I will order some Lundahls. The PCM1798 with 40R at 1:8 into 20KR amps (32R total shunts on each leg? with the addition of the secondary load) are a little too quiet. Increasing the primary resistors to 160R was plenty loud but very distorted.
Bleh....... I've ordered two cases from them in the past, one painted and one anodized. IMHO they are overpriced and I can't stand the texture of the coarse grain on the surface of the metal. It can be used as a finger nail file it's so bad.
I hate having to manually put holes in cases. It would have been well worth the money (for me) to buy one of the finished cases from Ian.
Try Modushop cases, excellent quality and finish with 10mm fronts. It so happens that the Maggiorato 230mm x 280mm is a perfect fit for these DAC's with an R-core:
modushop.biz
You can ask for the holes to be drilled and front engraved if you supply a drawing but it can be expensive.
$46 shipping for a $33 case; I'll have to pass on that one. It is nice though.
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I get the shipping to US as $35
Also worth trying is THLaudio. Look in the chassis section. You need to email them to get a quote:
http://www.thlaudio.com/indexE.htm
Front panel express do some nice chassis kits that can be cut to your custom size
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I guess I'm just a little bent because I can't get the case that was made for the DAC. It would have saved me a lot of time and hassle with drilling holes (square holes... ugh) and ordering switches. Plus it's all properly silk screened.
I think I'll just use a case I've had sitting around for a few years. It's absurdly large to use for this DAC (16" x 12" x 3"), but I guess it beats paying for something else I won't be any happier with.
Thanks for all the great suggestions Rich.
I think I'll just use a case I've had sitting around for a few years. It's absurdly large to use for this DAC (16" x 12" x 3"), but I guess it beats paying for something else I won't be any happier with.
Thanks for all the great suggestions Rich.
One more here and thats me done:
High-End Solid Aluminum Case for DIY Audio Equipment on eBay (end time 17-Oct-10 10:10:52 BST)
I'ts a bit bling but should just fit the DAC. They also do the best knobs on ebay!
High-End Solid Aluminum Case for DIY Audio Equipment on eBay (end time 17-Oct-10 10:10:52 BST)
I'ts a bit bling but should just fit the DAC. They also do the best knobs on ebay!
Whoa, the knob and feet on that thing are atrocious. The case itself is nice though.
I just can't believe that there isn't more of this stuff on my side of the planet. Actually I can believe it, sadly.
Has anyone thought about using the output relay to short both the output of the op-amp and the input of the amplifier when there is no signal present? This way the signal is never actually passing through the relay contacts.
The relay contacts would short the op-amps output after the output resistors (100R in my case).With no digital signal this would present a 100R load to the op-amp and a 0R short the input of the amp (or preamp, or volume control, etc).
Can anyone see any potential problems with doing this?
The relay contacts would short the op-amps output after the output resistors (100R in my case).With no digital signal this would present a 100R load to the op-amp and a 0R short the input of the amp (or preamp, or volume control, etc).
Can anyone see any potential problems with doing this?
I've heard some people get some strange random noises with the relay bypassed completely. I know with my DIY MicroDAC (DIR9001/SRC4392/PCM1792A) that it can make strange noises if the source (PC) has a hiccup like freezing or shutting down improperly.
I haven't done anything to the DAC yet. I'm waiting for parts for the LPF to arrive before I take the iron to it. I just have LME49720HA in both sockets right now.