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Building the ultimate NOS DAC using TDA1541A
Building the ultimate NOS DAC using TDA1541A
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Old 21st June 2021, 02:46 AM   #7821
abraxalito is online now abraxalito  United Kingdom
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Quote:
Originally Posted by L0rdGwyn View Post
Hello - I am in the very preliminary stages of a TDA 1541A design. I have read good things on Sowter 1465 I/V interface transformers. Anyone has experience using them? They are meant to generate a line-level output with a high-value resistor across the secondary, however seems one could use a lower value resistor and present the TDA 1541A with a smaller load at the cost of output voltage and add a gain stage to the secondary, I'm curious if anyone has experimented with both configurations, thank you
No direct experience with TDA1541A or Sowter transformers however I've been playing with a lot of I/V configurations on my TDA1387 DACs. What I've discovered is that I/V stage noise matters. A higher valued I/V resistor will generally give lower output noise than a lower valued resistor followed by gain. But take care not to exceed the DAC's compliance range.
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Old 21st June 2021, 01:07 PM   #7822
BarG01 is offline BarG01  Hungary
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I bought the bigger/more expensive Sowther and tried to get 60-80mV at the secondary, prior to an analog stage. After a few month exercise I returned to a simple resistor I/V. With transformer I always feel lack of something, and furthermore I did not feel the smoothing effect which others used to mention in respect of transformers.
The I/V resistor has paramount effect on the sound, try AN silver cap tantallum even if you think you can not afford, worth it.
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Old 21st June 2021, 01:59 PM   #7823
L0rdGwyn is offline L0rdGwyn  United States
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Building the ultimate NOS DAC using TDA1541A
Thank you call for the ideas. Resistor I/V certainly is more simple, although I had read a few users here who swore by transformer over active I/V, but now of course, the opposite is true too! Maybe I will need to experiment and try for myself. I'll investigate the active approach as well, there is time to think it over as I need to plan the power supply.

I did read a long article by Thorsten Loesch although I did not see a tube I/V conversion, as I recall he used a resistor I/V followed by a tube gain stage, maybe I was reading in the wrong place. I did see an article from John Broskie with a proposed tube I/V stage with the DAC working into the cathode.

Tube I-to-V

I will keep reading and learning, digital is new design territory for me.
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Old 21st June 2021, 04:45 PM   #7824
wlowes is offline wlowes  Canada
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Default I/V resistor type and value wrt TDA1541a

FWIW, I tried extensive list of alternatives wrt size of resistor and type. All of this pertains to TDA1541a with passive I/V followed by Lampizator tube stage. No experience as it pertains to other DAC chips.

First I followed Fikus recommendation of 100r. When John (ecdesigns) argued for lower value I went to 60r. Better to my ear. Less sharp so some will complain laid back, but overall more relaxed and I believe more natural.

I started with Takman metal film (good). Tried Amtran carbon (terrible). Also tried vintage AudioNote tantallam. (also smeared sound to my ear). Then build hand wound manganin wire and it was like removing dirty glass from a window. I believe Rohpoint would be the commercial option (stupid expensive)

With a 6n2p tube stage after the I/V, I had too much gain. So I tried 32r I/V of non inductive wound Manganin. To my ear this was the most pleasing sound. I have since returned to 60r as I have taken out some gain with a parametric equalizer to smooth speaker performance. With gain limited I needed to raise response away from the noise floor, so 60r ended as the optimal balance.

Last edited by wlowes; 21st June 2021 at 04:48 PM.
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Old 21st June 2021, 06:00 PM   #7825
diyiggy is online now diyiggy
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That is not me speaking : ECC88, 47 ohms resistor max ! Why bother


6N23P if you have not monneyt for a good ECC88 Nos is where I might dig...
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Old 21st June 2021, 06:48 PM   #7826
L0rdGwyn is offline L0rdGwyn  United States
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Quote:
Originally Posted by wlowes View Post
FWIW, I tried extensive list of alternatives wrt size of resistor and type. All of this pertains to TDA1541a with passive I/V followed by Lampizator tube stage. No experience as it pertains to other DAC chips.

First I followed Fikus recommendation of 100r. When John (ecdesigns) argued for lower value I went to 60r. Better to my ear. Less sharp so some will complain laid back, but overall more relaxed and I believe more natural.

I started with Takman metal film (good). Tried Amtran carbon (terrible). Also tried vintage AudioNote tantallam. (also smeared sound to my ear). Then build hand wound manganin wire and it was like removing dirty glass from a window. I believe Rohpoint would be the commercial option (stupid expensive)

With a 6n2p tube stage after the I/V, I had too much gain. So I tried 32r I/V of non inductive wound Manganin. To my ear this was the most pleasing sound. I have since returned to 60r as I have taken out some gain with a parametric equalizer to smooth speaker performance. With gain limited I needed to raise response away from the noise floor, so 60r ended as the optimal balance.
Thanks for the info wlowes, very interesting. In my tube amplifier designs, I have also preferred Riken Ohm carbon film resistors for tonality, I often use them on tube cathodes. If I try resistor I/V first, I thought I would try these out, but I will keep your findings in mind if the sound is not appealing - totally reasonable that different resistor types work better in certain applications. For instance, I once tried using Audio Note tantalum resistors to load the plates of a gain stage, they were highly recommended, but I found the sound very thin and harsh! I've held onto them though as they will probably find their place in another design

Quote:
Originally Posted by diyiggy View Post
That is not me speaking : ECC88, 47 ohms resistor max ! Why bother


6N23P if you have not monneyt for a good ECC88 Nos is where I might dig...
I'm not sure what approach I will use for the gain stage following I/V, lots of good options out there. I think I will have to decide on resistor vs. transformer I/V first as using the SUT will reduce the gain needed in the output stage. I would like to try passive I/V before resorting to active. Also, I have an active I/V DAC already from a company called SW1X, it is uses a pair of PCM56, which inspired me to design my own!
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Old 21st June 2021, 08:51 PM   #7827
diyiggy is online now diyiggy
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Ah , yes, the good PCM56 !I like it a lot !


Seems all the numerous guys that tried before you all those aproaches, given up traffo for I/V purpose and ended at best tubes or silicon either, at best use traffo just as output traffo ! Is it usefull to make the history once again ! Anyway you will find numerous threads here and elswhere about tda 1541, tube I/V with the good resistor type and value, Sowter traffo threads as well, a lot of discrete I/V and non feed back transconductance opa amp...


It's not if someone has found again something new with the TDA1541A !



A part of your problem is not only to reduce noise but also the chosen parts ! there is resistor and resistor, tube and tube, cap and cap, etc ! Choice is also important whithin a layout and technology choice... and digital front end an important part in the final result.
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Old 21st June 2021, 09:11 PM   #7828
L0rdGwyn is offline L0rdGwyn  United States
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Yes, retracing history might be for the best, after all DIYers are very curious, what if some gem was missed along the way? The journey is just as important as the destination I will not make a decision yet, but I might try the transformer just to see, and in any case I think the power supply is the most complex of the design, so that will take time to work out, I will think the I/V stage over as that plan comes together. I appreciate the feedback!
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Old Yesterday, 06:49 PM   #7829
diyiggy is online now diyiggy
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Let your ears decide at the end !


Btw +1 for the Rohpoint wirewound plastic case resistor ! I use it but with solid state. I hope to try E88CC before the end of the years, although I say it so from 10 years maybe ! A dac is a whole, I spent time on the digital front end, parts, pcb and power supply but not enough on the I/V stage ( I use Pedja Rogic pcb with transconductance oap with no feed back. Sounds nice if you choose the parts with care !
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Last edited by diyiggy; Yesterday at 06:53 PM.
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