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jmillerdoc 22nd May 2011 05:18 PM

Cheap eBay DAC kit....sans OpAmp for simple I/V with resistor?
In reference to this DAC kit:

Crystal CS4398 *2 CS8416 Parallel DAC Decoder DIY Kit | eBay

I am pretty new to the realm of DACs. To date I have built a couple of kits from eBay and swapped OpAmps and that's about the extent of my mods. I have been reading at Audiodesignguide some lately and the idea of replacing the OpAmp with a simple resistor for I/V has interested me. I was wondering if something like this could be done with this kit. If so, could someone help me figure out how to delete the OpAmp and tie a resistor network into this DAC?

I also have a par of UTC A-20 transformers that might also work? Not sure really.

Please remember I am an infant newbe to DACs and digital audio, explanations should be at the most infantile level.

Thanks for suggestions and ideas in advance!

Praudio 22nd May 2011 05:54 PM

Seem to need your UTC-A20; may be it's a good DAC, but with a feedback of 95.3% ????

jmillerdoc 22nd May 2011 10:49 PM


Originally Posted by Praudio (
.......may be it's a good DAC, but with a feedback of 95.3% ????

You are referring to the sellers feedback.....I went back and read all of the negative and neutral. He hasn't had much problems over the past 6 months but it almost looks like this guy just started selling stuff over a year ago and had a run of bad luck with some delivery issues, miscommunications, and a few crappy watches he sold that weren't waterproof as advertised. When I read his feedback from the electronics he has sold lately he has had very good feedback. For $50 or so I think it's worth the risk. I also have PayPal Advantage so I won't lose in the end of I do get a raw deal from this guy.

So, you think the UTCs would work well here? How would you implement them?

jmillerdoc 26th May 2011 10:59 AM


DF96 26th May 2011 11:36 AM

Not all DACs work OK into a resistor, because the allowable signal voltage may be exceeded. They are usually designed to work into a virtual earth at the input of an op-amp, so only a tiny voltage is developed there. Too much voltage can cause distortion in the output current generators. You need to check the datasheet, and see if anyone else has built, measured and listened to something similar.

Fenris 26th May 2011 02:29 PM

The CS4398 is a voltage out rather than a current out DAC. The op-amps on the output are used for filtering and differential to single-ended conversion, not I-V conversion. You can't replace the op-amp with a resistor with this DAC. The UTC transformers would work well in this application - it would allow you to eliminate any DC blocking caps on the output as well as eliminate the op-amps.

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