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#1
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Designing a transformer-coupled DAC
Hi all,
After quite a long absence, I'm starting to get back into messing about with hi-fi again. And, as I've now got a secure e-mail base from which to risk posting messages to the USENET again, here I am! Anyway, to cut a long story short, I've finished making myself a listening room here in Heidelberg and have my normal amplifier (one of the big "20/20"s) set up with a choice of either ESL-57s or Monitor Gold 15s. And yes, pretty much everything else I've built or acquired is racked nearby! However, my main source is still - alas - a Pioneer PDS-901 cd player from my student days. In other words, it's high time I got around to building a proper DAC. Cirrus Logic seems to have some promising all-in-one chips on offer. Right now, I'm quite taken with the CS43112 and CS4397 as they offer 24-bit resolution and differential outputs. This should let me transformer-couple (Lundahl LL1527?) the outputs directly to grids of the 6J5s in my existing amplifier. So far so good. Cirrus Logic further offers the CS8420 which appears to be a combined transceiver / upsampler, meaning that I could use it to decode a standard S/PDIF input into the PCM output the DAC chip needs *and* upsample any given input signal to 24-bit, 96KHz at the same time - an ideal situation for running both chips off an external master clock. Should it be necessary, the CS8420 can also run off a PCM signal - such as that from a CS8416 receiver. Please through some helpful comments or suggestions my way! Best regards from Heidelberg, Russ Sadd |
#2
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"Russ Sadd" wrote in message oups.com... Hi all, After quite a long absence, I'm starting to get back into messing about with hi-fi again. And, as I've now got a secure e-mail base from which to risk posting messages to the USENET again, here I am! Hello Russ, Nice to see you back on RAT:-)) Iain |
#3
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Russ Sadd wrote: Hi all, After quite a long absence, I'm starting to get back into messing about with hi-fi again. And, as I've now got a secure e-mail base from which to risk posting messages to the USENET again, here I am! Anyway, to cut a long story short, I've finished making myself a listening room here in Heidelberg and have my normal amplifier (one of the big "20/20"s) set up with a choice of either ESL-57s or Monitor Gold 15s. And yes, pretty much everything else I've built or acquired is racked nearby! However, my main source is still - alas - a Pioneer PDS-901 cd player from my student days. In other words, it's high time I got around to building a proper DAC. Cirrus Logic seems to have some promising all-in-one chips on offer. Right now, I'm quite taken with the CS43112 and CS4397 as they offer 24-bit resolution and differential outputs. This should let me transformer-couple (Lundahl LL1527?) the outputs directly to grids of the 6J5s in my existing amplifier. So far so good. Cirrus Logic further offers the CS8420 which appears to be a combined transceiver / upsampler, meaning that I could use it to decode a standard S/PDIF input into the PCM output the DAC chip needs *and* upsample any given input signal to 24-bit, 96KHz at the same time - an ideal situation for running both chips off an external master clock. Should it be necessary, the CS8420 can also run off a PCM signal - such as that from a CS8416 receiver. Please through some helpful comments or suggestions my way! Best regards from Heidelberg, Russ Sadd Hi Russ, welcome back. I am no expert on matters digital, but are not the analog differential outputs current source rather than voltage source? If so, one may think a pair of follower buffers be used between the DA outputs and transformer you intend using in order to keep the source impedance driving the tranny low, since that favours low distortion from the tranny. I'd have to see a schemo to better understand... Patrick Turner. |
#4
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Patrick Turner schrieb:
I am no expert on matters digital, but are not the analog differential outputs current source rather than voltage source? It's differential voltage output - and Cirrus has been good enough to post a full set of documentation at http://www.cirrus.com/en/products/pro/detail/P147.html . Best regards, Russ Sadd |
#5
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Russ Sadd schreef: Hi all, After quite a long absence, I'm starting to get back into messing about with hi-fi again. And, as I've now got a secure e-mail base from which to risk posting messages to the USENET again, here I am! Anyway, to cut a long story short, I've finished making myself a listening room here in Heidelberg and have my normal amplifier (one of the big "20/20"s) set up with a choice of either ESL-57s or Monitor Gold 15s. And yes, pretty much everything else I've built or acquired is racked nearby! However, my main source is still - alas - a Pioneer PDS-901 cd player from my student days. In other words, it's high time I got around to building a proper DAC. Cirrus Logic seems to have some promising all-in-one chips on offer. Right now, I'm quite taken with the CS43112 and CS4397 as they offer 24-bit resolution and differential outputs. This should let me transformer-couple (Lundahl LL1527?) the outputs directly to grids of the 6J5s in my existing amplifier. So far so good. Cirrus Logic further offers the CS8420 which appears to be a combined transceiver / upsampler, meaning that I could use it to decode a standard S/PDIF input into the PCM output the DAC chip needs *and* upsample any given input signal to 24-bit, 96KHz at the same time - an ideal situation for running both chips off an external master clock. Should it be necessary, the CS8420 can also run off a PCM signal - such as that from a CS8416 receiver. Please through some helpful comments or suggestions my way! Best regards from Heidelberg, Russ Sadd Is this what I hope it is? I have been wondering if it were possible to build a tube D class type amplifier. If I have heard right you amplify the PCM stream first and then convert to analog via a tranny? Supposed to be efficient. I hope this thread gets good. I'm listening. Wessel |
#6
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"Wessel Dirksen" schreef in bericht ups.com... Is this what I hope it is? See it as a PP outputstage with the DAC as phase splitter / driver .... Ronald . |
#7
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Russ Sadd wrote: Patrick Turner schrieb: I am no expert on matters digital, but are not the analog differential outputs current source rather than voltage source? It's differential voltage output - and Cirrus has been good enough to post a full set of documentation at http://www.cirrus.com/en/products/pro/detail/P147.html . It appears they have a pair of outputs, each has 2.5mA in the Cmos output devices, but arranged for class AB to cope with driving loads lower than 2k. So I doubt you have to buffer; it already is buffered. There is enough quiescent current in the output amps to keep these working in class A into loads above 2k; 2.5v swing into 2k is only 1.25 mA I change. So any high Z load won't load down the chip. There isn't anything else at the above site which I can understand. BTW, ppl rtrying to go to the above address may have a bother since there is a dot after ".html" in the above address which stops the address working; leave out the dot and it works. Patrick Turner. Best regards, Russ Sadd |
#8
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Ronald wrote: "Wessel Dirksen" schreef in bericht ups.com... Is this what I hope it is? See it as a PP outputstage with the DAC as phase splitter / driver .... He could have all balanced to the tube amp PP output stage. But he'd have to use a gain control someplace. That'd have to be balanced too, but that's no problem using a dual gang pot for each channel, or a DACT 4 gang attenuator for both channels. Then he'd just need an LTP balanced input amp driver, and a PP output stage. If he wants FB there can be balanced FB from the OPT secondary to the LTP cathodes. The only reason why one would use a tranny after the DA converter would be to have a floating pair of balanced outputs or a floating SE output, which should reduce hum. I'd be wary about stray back emfs from the tube circuits to the DA. I'd put in some diode clamps. Patrick Turner. Ronald . |
#10
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"Russ Sadd" wrote
... Cirrus Logic seems to have some promising all-in-one chips on offer. Right now, I'm quite taken with the CS43112 and CS4397 as they offer 24-bit resolution and differential outputs. This should let me transformer-couple (Lundahl LL1527?) the outputs directly to grids of the 6J5s in my existing amplifier. ... Hello Russ. Have you de-mystified your web pages yet? Why transformer coupled? What are the issues with this switched capacitor output? What scares me is the layout and practical implementation, arranging for proper isolation of digital and audio. The "simple" evaluation board, with the two chips, power conditioning and analogue filtering, has four layers. Then there's the control interface to consider. You must be very brave or very clever. Welcome back. cheers, Ian |
#11
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On 27 May 2005 01:52:29 -0700, "Russ Sadd" wrote:
Hi all, Dude, where'ya been? In other words, it's high time I got around to building a proper DAC. Cirrus Logic seems to have some promising all-in-one chips on offer. Right now, I'm quite taken with the CS43112 and CS4397 as they offer 24-bit resolution and differential outputs. This should let me transformer-couple (Lundahl LL1527?) the outputs directly to grids of the 6J5s in my existing amplifier. Please through some helpful comments or suggestions my way! The pin 19/20 and 23/24 appear to be the DAC raw current outputs. For a serious effort, this is where you'll want to start looking. Remembering that current sources are only linear into virtual shorts, you'll want to load these summing junctions with a very low impedance at *all* frequencies, even those *way* above the sample rate. This issue is the downfall of lots of inexpensive commercial stuff. Two popular approaches have emerged: brute-force, shorting the DAC output with a small resistor and amplifying; And, B, some variation on the "grounded-grid" amplifier topo from RF use. Perhaps surprisingly, these are identical from a noise standpoint. Transformers, however, have no practical use here. (Way! too big) Good fortune, Chris Hornbeck "I didn't think this would happen again, with or without my best intentions" -Liz Phair, "**** and Run" from _Exile in Guyville_ Mean blues; not for the faint of heart. |
#12
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Welcome home, Russ. We missed you.
Russ Sadd wrote: Hi all, After quite a long absence, I'm starting to get back into messing about with hi-fi again. And, as I've now got a secure e-mail base from which to risk posting messages to the USENET again, here I am! When I returned, the first impulse of some parties on RAT of whom I had never heard, and who had never once met me, was to say in public that the first business of RAT was to find out my ISP so they could harass it into throwing me off. Some of that gang are still here. I welcomed the Net when it arrived as giving Everyman a voice... I found using an anonymous remailer very tiresome. But Frank B, an American motor engineer working in Germany, showed me how to use proxies and recommended an automatic proxyfinder and this works smoothly (at least on a Mac). Anyway, to cut a long story short, I've finished making myself a listening room here in Heidelberg and have my normal amplifier (one of the big "20/20"s) set up with a choice of either ESL-57s or Monitor Gold 15s. And yes, pretty much everything else I've built or acquired is racked nearby! However, my main source is still - alas - a Pioneer PDS-901 cd player from my student days. In other words, it's high time I got around to building a proper DAC. My own experiences are at: http://members.lycos.co.uk/fiultra/DACjute.htm You can ignore the text as irrelevant to someone who has ESL; it says mainly that DAC work needs a high resolution chain, which you have, and that I found DAC improvements of marginal utility to my pleasure from music, which you are qualified to regard as matter of opinion upon which you could possibly improve; in addition, suitable input and output transformers, which were a pain when I did this a few years ago, are now generally available. For your purposes the important bits are the block diagrams, one of which lists the best components and the other showing that I came to the same conclusion as you, that the Cirrus Logic chips are the best bet. I liked the PCM63 too but they were even further removed from value for money. Andre Jute Cirrus Logic seems to have some promising all-in-one chips on offer. Right now, I'm quite taken with the CS43112 and CS4397 as they offer 24-bit resolution and differential outputs. This should let me transformer-couple (Lundahl LL1527?) the outputs directly to grids of the 6J5s in my existing amplifier. So far so good. Cirrus Logic further offers the CS8420 which appears to be a combined transceiver / upsampler, meaning that I could use it to decode a standard S/PDIF input into the PCM output the DAC chip needs *and* upsample any given input signal to 24-bit, 96KHz at the same time - an ideal situation for running both chips off an external master clock. Should it be necessary, the CS8420 can also run off a PCM signal - such as that from a CS8416 receiver. Please through some helpful comments or suggestions my way! Best regards from Heidelberg, Russ Sadd |
#13
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Please through some helpful comments or suggestions my way! I did some work with transformers driven by DAC chips he http://pw2.netcom.com/~wa2ise/radios...c.htm#transdac |
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