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OLD THREAD DAC End by Andrea Ciuffoli

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#1,322
apelizzo said:
I will try it soon on this DAC.

Use TL431 as you LED. It''s like your LED but with three legs where you adjust the voltage. There is no TL431 tuned at 3.8V so it's just matter of adjust it.
It's the same but with better performance I believe. If nobody tried this it doesn't mean it's impossible. Just follow the rule.
Click to expand...

You have tried this?
What exactly do you propose changing? Are you still on about the I/V Board, putting tl431 in place of the R21-24 and R9-12.
 
#1,327
agithegreat said:
You have tried this?
What exactly do you propose changing? Are you still on about the I/V Board, putting tl431 in place of the R21-24 and R9-12.
Click to expand...

No TL431s replace C3,C4,C5,C6,R5,R5 and C8,C9,C10,C11,R17,R18
The`purpose is to improve the function of the capacitor. In other words to make the bias flat in all the frequency spectrum.
In this way unfortunately the tube local feedback is totally eliminated so B+ must be stable.

I tried on another project and it works. Soon I will try on this dac.
 
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#1,328
ksnider1 said:
I didn't 😀, I will look for 350V.

Thanks
Click to expand...

PIO caps can easily handle short term overvoltage. 300V is OK for PIO if you cannot find higher as plate voltage goes to 90 very gently in IV stage. Also 300V capacitor in this position should sound better then a 630V. IMO thicker dielectric in higher voltage capacitors affect the sound performance in this case.
 
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#1,330
After a good listen, i'm very happy with this DAC if anything i would like to brighten up the top end. I'm considering your mod Adamus.

The midrange really is second to non, it's just the high's that let this down, just to add to the transparency. I think this may be a toss up of SS vs Valve though...
For the time being i have it EQ'd and it sounds great. But electrical modding will make me happier than using EQ.
 
#1,331
Quanghao,

It seems you routed a solid DGND groundplane on the top of the board. This groundplane doesn't directly link to the DGND of the +5v Digital. So there must be via on the board that link this ground to DGND. But i don't see them. where are they ? (ex : Cs8414 pin 8) ?
 
#1,336
agithegreat said:
After a good listen, i'm very happy with this DAC if anything i would like to brighten up the top end. I'm considering your mod Adamus.

The midrange really is second to non, it's just the high's that let this down, just to add to the transparency. I think this may be a toss up of SS vs Valve though...
For the time being i have it EQ'd and it sounds great. But electrical modding will make me happier than using EQ.
Click to expand...

If you read back i found the dac quite dark tonally, which essentiallymeans slightly recessed highs as you found.

1st, the LED mod really does get rid of the darkness, or at least it did for me. highs are definately clearer, and the bass tightened up. i found intially the bass was loose, which dominated the sound and made the highs appear recessed, the led mod removed this for me. i always find electrolytics in the cathodes give a very 'tubey' sound.

2nd, if you want an even tighter sound (some would say more 'solid state') then CCS the anode of the 5687. You do need to watch the B+ though, it needs dropping to use a CCS without excessive heat.

3rd, try different valves... thats the beauty of valves. I found the phillips reasonably full and slightly recessed highs. The RCA's much clearer but slightly microphonic.

4th, try different coupling caps on the output of the dac, or bypass with a small quality film.
 
#1,338
Help Please

Brought my system up this AM

Voltages at points on the DAC board are 5+/-0.03V. Negative 4.999 at Pin 1 Ad1865. All 47microF are Oscons. 0.1 bypasses not installed at C22 and C24 but installed elsewhere. (5.5V on each out of +/- Salas and 5.37 on the other Salas)

Used Adamus' LED scheme. All are lit and there is 6.23 filament voltage. HV to Output board is 295V.

No sound.

Red LED on DAC board is off w/o signal. Confirmed pin 28 goes to anode of LED, cathode of LED to 560 ohm resistor, other end of 560 ohm resistor goes to ground. IF I put a LED checker on LED it lights.

I also have 75 ohms between hot and ground of SPDIF signal.

Any suggestions are appreciated.

Thanks

Bob
 
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