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Chipomatic balanced input RIAA
Chipomatic balanced input RIAA
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Old 30th January 2019, 09:05 AM   #91
Salas is online now Salas  Greece
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Chipomatic balanced input RIAA
Quote:
Originally Posted by vgeorge View Post
In my pcb though offset is very low, 0.15 mV on one channel and 0.50 mV on the other.
You won the IC2 offset lottery straight away it seems
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Old 30th January 2019, 10:00 AM   #92
Salas is online now Salas  Greece
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@dimdim

When doubling the servo resistor's value from 330k to 680k it will make more of near DC attenuation.

I don't know, if you got any SMD resistors collection including that value maybe pick one with the tweezers and replace the original in the wilder channel to see what happens with your offset. If it proves a good move match it to the other channel as well. So they will have the same curve details no matter if it was already 0mV successful.
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Old 30th January 2019, 10:20 AM   #93
Dimdim is offline Dimdim  Greece
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I think I can try some temporary ~680K resistor to see what happens.. I'll keep you posted.
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Old 30th January 2019, 10:53 AM   #94
Salas is online now Salas  Greece
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Yeah, I should have had a coffee first. Around half the R3's original value I should have suggested, not double
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Old 30th January 2019, 12:07 PM   #95
samoloko is offline samoloko  Bulgaria
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Salas,

Would you recommend using AD8429 as diferential summator / buffer In audio stages like http://www.ti.com/lit/ds/symlink/pcm1794.pdf p 20, figure 24 - can we swap LT1028 for better results

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Old 30th January 2019, 01:07 PM   #96
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I wouldn't
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Old 30th January 2019, 02:27 PM   #97
merlin el mago is offline merlin el mago  Europe
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Old 2nd February 2019, 10:30 PM   #98
Salas is online now Salas  Greece
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Default The Agricultural Edition Sessions

So I made a second channel proto board copy and slapped everything on an aluminum L frame complete with crocodile clips grounding and precarious power line arrangements. In contrast to the SMD PCB that DimDim and VGeorge are almost finished with, this must surely be called the agricultural edition.

Had the Folded Simplistic Phono (FSP) nearby, and a friend's second pair of ears who came visiting with few new (thus quiet) records he had just bought. Mainly acoustic blues and classical.

First we played through the FSP. Nails the feeling. Great musicality and naturalness, layering, dynamics, width, depth, focus, splendid sound. Gain 63dB, cart AT33PTG/II straight in.

Then we put the Chipo on but starting with SMPS (IBM 15V laptop adapter to +/-24V DC/DC to RCZ +/-15V dual branch outputs). It showed some potential but the PSU must have been holding it back. Had dynamics still a ghostly thin haze was lurking at the back and a hint of contrived instrumental tone was there. Bass good but not so well driving. No hum no buzz. Looked very clean via FFT on the bench before taking it to the rack anyway. Gain 62dB in combination with Jensen JT-44K-DX step up transformers.

Was time for linear PSU. UltraBiB 1.3 at +/-15V with 200mA current limit set per rail. AC inputs fed from a Selectronic 18-0-18 R-Core (that brand's gone bust). Big difference. More sound jumped out in the room. Rich with many details but non aggressive too. Depth and slam were added. Does not quite have the spot on naturalness or the intricate layering of the FSP but good. For a chipo job very good really. No hum no buzz again but even less audible hiss up close. Not showing less hiss on the FFT in the audio band when using the UltraBiB vs the switching PSU but the hundred's of kHz high and complex noise must have been adding as a total.

Wait, there's more. What about the subjective influence of IC2 2nd stage? Out went the OPA2134 in went the AD823. You bet they are influential. I preferred the AD823. Less bodily but more natural. Noticeably so. Especially on voices freedom and stringed bass phrasing. With the opa a rather pompous sonic, maybe more at home with things like Yello's Toy album that we also gave it a spin. Measurement wise they virtually didn't differ for THD in this job. On noise grass they were alike again, although they got different nVrtHz spec, that's because they are smothered by the input stage's performance anyway.

All in all for such accessible level of effort and cost its a no-brainer. Highly dynamic, quiet, clean, full, and surprisingly smooth. Just always feed it from some type of good PSU.
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Old 3rd February 2019, 02:07 AM   #99
EUVL is offline EUVL  Europe
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Not trying ADA4627 instead ?


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Old 3rd February 2019, 06:11 AM   #100
Salas is online now Salas  Greece
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Not in the agricultural chipomatic. It accepts DIP-8 dual. The SMD board accepts SOIC-8 or DIP-8 dual. For that ADA or for LT1792 evaluations it would take a further SMD PCB spin for two SOIC-8 as IC2 subs.
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