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lingDAC - cost effective RBCD multibit DAC design
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Old 12th July 2018, 05:52 PM   #11
rickmcinnis is offline rickmcinnis  United States
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HEARING forward to reading Randy's assessment.
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Old 12th July 2018, 05:54 PM   #12
GORDMUS68 is offline GORDMUS68  South Africa
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Very fortunate to have received one the first version three tier boards with SE output a while back, and also only recently had time to give the boards a quick try. Yes feeling very guilty about getting around to this after a few months - humble apologies Abrax.

Have been putting together a battery supply using Lipo with regulators when time permits between daily grind of course.

For the first 'armature' effort, read ''could no longer wait', I used two Lipo in series which gave me between 7.98 and settling at 7.54 volts for a quick whirl.

The sound quality did not seem to degrade between the two voltages.

What is the typical 'negative' effect to expect when the DAC is supplied at the lower threshold of the 8v (+/- 0,5v) 120ma?

Perhaps I should read a bit more - sorry if this a naive question!
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Old 13th July 2018, 12:24 AM   #13
abraxalito is offline abraxalito  United Kingdom
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Going below 7.5V what will happen is the transistor doing the supply regulation won't regulate any more. Whether anything is audible I don't know, haven't done tests.

Incidentally just a quick mention that the lingDAC picture I put up in post #3 is an updated version (v2) of the design, based on some feedback from you guys and doing my own listening. The five of you who've already got lingDACs have the v1. The biggest change is to the DAC board itself where I've reduced the number of DAC chips down to two and implemented a low-noise, low impedance shunt regulator. The shunt reg makes a substantial improvement to the bass, its by no means subtle.

v2 DAC board schematic added
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File Type: pdf DAC board.pdf (56.2 KB, 206 views)
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Last edited by abraxalito; 13th July 2018 at 12:52 AM.
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Old 13th July 2018, 07:21 AM   #14
GORDMUS68 is offline GORDMUS68  South Africa
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Thanks Abrax - that gives me something to hunt and increase my limited but hopefully expanding understanding. Cheers
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Old 13th July 2018, 01:46 PM   #15
Ken Newton is offline Ken Newton  United States
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Quote:
Originally Posted by abraxalito View Post
Going below 7.5V what will happen is the transistor doing the supply regulation won't regulate any more. Whether anything is audible I don't know, haven't done tests.

Incidentally just a quick mention that the lingDAC picture I put up in post #3 is an updated version (v2) of the design, based on some feedback from you guys and doing my own listening. The five of you who've already got lingDACs have the v1. The biggest change is to the DAC board itself where I've reduced the number of DAC chips down to two and implemented a low-noise, low impedance shunt regulator. The shunt reg makes a substantial improvement to the bass, its by no means subtle.

v2 DAC board schematic added
Richard, what is the intended function of LED5 through LED8, which are attached parallel to the analog outputs of inverted data DAC U8?

-Ken
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Old 13th July 2018, 02:19 PM   #16
abraxalito is offline abraxalito  United Kingdom
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Hi Ken - good question.

The aim there is to give the 'passive' DAC as close as possible the same voltage on its outputs as the active one. In the basic configuration only one DAC's outputs are taken to the I/V stage, the other DAC is there solely as a 'dummy' to balance out the current drawn by the active DAC (the current draw being signal dependent). I figured to get the best cancellation it might be best to give both DACs the same output voltage, but I've not actually gone and verified this.

With the original v1 lingDAC the outputs were held at +4.5V by the I/V stage, this necessitated two green LEDs in series (2.2V each) to get to the desired voltage. On v2 lingDAC the I/V stage holds the output around +1.1V - this needs a single IR LED, the other LED footprint will be fitted with a 0R link.
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Last edited by abraxalito; 13th July 2018 at 02:22 PM.
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Old 13th July 2018, 02:58 PM   #17
randytsuch is offline randytsuch
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Quote:
Originally Posted by abraxalito View Post
Incidentally just a quick mention that the lingDAC picture I put up in post #3 is an updated version (v2) of the design, based on some feedback from you guys and doing my own listening. The five of you who've already got lingDACs have the v1. The biggest change is to the DAC board itself where I've reduced the number of DAC chips down to two and implemented a low-noise, low impedance shunt regulator. The shunt reg makes a substantial improvement to the bass, its by no means subtle.

v2 DAC board schematic added
Can the v1 be modded to a v2?
I'll compare schematics myself, and see how much difference there is.

Randy
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Old 13th July 2018, 03:04 PM   #18
abraxalito is offline abraxalito  United Kingdom
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v1 can be modded to v2 in the sense that the shunt reg can be used to power the DAC chips on v1. Bear in mind that you'll have 4 or 8 chips (can't recall exactly who got which variants of v1, some have 4, some 8 chips) to power so the quiescent current of the shunt needs increasing by a substantial amount. v2 runs with around 40mA through Q6 for 2 DACs, so I'd suggest of the order of 55mA for 4 DACs and 80mA for 8.
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Old 13th July 2018, 04:19 PM   #19
randytsuch is offline randytsuch
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Originally Posted by abraxalito View Post
v1 can be modded to v2 in the sense that the shunt reg can be used to power the DAC chips on v1. Bear in mind that you'll have 4 or 8 chips (can't recall exactly who got which variants of v1, some have 4, some 8 chips) to power so the quiescent current of the shunt needs increasing by a substantial amount. v2 runs with around 40mA through Q6 for 2 DACs, so I'd suggest of the order of 55mA for 4 DACs and 80mA for 8.
Looking at the schematic, probably more than I want to hack in, so I'll likely build a v2 at some point, at least of the DAC board.
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Old 14th July 2018, 01:35 PM   #20
kokoriantz is offline kokoriantz  Lebanon
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I would like to know if the tda1387 is better than tda1543 . I have the intention to put 16 of these in parallel but activated sequentially, to produce a natural 16 level ramp .
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