Author Topic: discrete dac mock up  (Read 24737 times)

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Offline kp93300

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Re: discrete dac mock up--increase current to the zener
« Reply #75 on: February 23, 2012, 05:36:32 AM »

This is as advised by Yeo to increase current to the zener and improve snr of the power supply.
I parallel a 122 resistor to the 1501 resistor next to the label 4k7.
The nett resistance decrease from 1500R to about 680R.
The sound improve quite a bit and reminds me of the 3 transistor mod described by Paul N in the Monica .
For once, I am not always thinking of mod ideas as i listen to the discrete dac.

Music flows better, more detail and more alive !
The noise between tracks is less.

cheers and thanks to yeo.

kp93300


Offline CKL

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Re: discrete dac mock up
« Reply #76 on: February 23, 2012, 11:37:22 PM »
It sings better with a preamp. Still, it seems that the bass is less than Monica3?

Offline kp93300

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Re: discrete dac mock up
« Reply #77 on: February 24, 2012, 04:46:39 PM »
Hi CkL
Try the mod described in the previous post . The bass will improve.
My set up shows a leaner and tighter bass with discrete dac.
It excels in percussion music and is hard to sit still !
The ambience retrieval is the best in my set up so far. Large orchestral pieces are a joy to listen and get one immersed in the music .

cheers

kp93300

Offline kp93300

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Re: discrete dac mock up
« Reply #78 on: February 24, 2012, 04:49:31 PM »
Hi CKL
The heatsink for the Ad 815 may be too big. It sings much better when slightly warm. My heat sink is about the same size but there is no fins.
cheers

kp93300

Offline CKL

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Re: discrete dac mock up
« Reply #79 on: February 24, 2012, 05:35:28 PM »
Thanks! KP, I will try your mod to increase the current.

Offline kkerwin

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Re: discrete dac mock up
« Reply #80 on: February 29, 2012, 04:58:24 AM »
hi all,
i got curious about tony's comments regarding the 5.4v reg on the mojo board. so, i fired up the qa550 to mojo 2 to lundahl transformer combo and set up an a/b listening test between the mojo 2 and the discrete dac, using the qa 550 as the source.  i did test my ph reg and found that it was outputting 4.96v so i figure that's about as close to 5v as it will get   i enjoyed the vibrance of the mojo 2, but appreciated more the clarity of the discrete dac.  in comparison, the mojo 2 has a little bit of "grain" that the discrete dac doesn't.  i adjusted the volume when switching between the two, but even in doing this, it made me wonder if the higher gain on the mojo2 wasn't what was giving it the vibrance that i observed.  in my opinion, the discrete dac is still the better performer for its ease, naturalness and clarity.

k

Offline kp93300

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Re: discrete dac mock up
« Reply #81 on: March 18, 2012, 04:56:40 PM »
Hi
Any more ideas to improve the already excellent  dac ? 
I try different value of the resistor setting the current for the zener in the cap multiplier next to the power input .
4k7 is still the best .
regards

kp93300

Offline CKL

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Re: discrete dac mock up
« Reply #82 on: March 18, 2012, 05:31:20 PM »
H KP,

Do you mean the original 4k7 resistor is the best? No need to increase the current?

Offline kp93300

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Re: discrete dac mock up
« Reply #83 on: March 18, 2012, 05:42:50 PM »
Hi CKl,
There are 2 cap multipliers on board. I refer to the  cap multiplier next to power input.  This cap multiplier has one zener .
The 2nd cap multiplier near to the signal out has a different experience. I wonder is there any explanations from yeo  for this different experience. This cap multiplier has 2 zeners in series ?
CKL , have you tried the simple mod ?
regards

kp93300


Offline yeo

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Re: discrete dac mock up
« Reply #84 on: March 18, 2012, 10:04:48 PM »
hi kp

the first multiplier next to power input, powers the circuitry that does the data formatting. this stage prepares the i2s data to the correct format, ready to output as analog signal. this stage shouldn't have any impact on sound quality.

the second stage which as you noticed, has 2 zener diodes, powers the circuitry which outputs the analog data. this stage, as you noticed as well, has huge impact on sound. any noise/hum at this circuitry can be heard through your speakers.

yeo

Offline CKL

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Re: discrete dac mock up
« Reply #85 on: March 19, 2012, 12:46:42 AM »
Hi KP,

what simple mod do your refer to?

Offline yeo

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Re: discrete dac mock up
« Reply #86 on: March 19, 2012, 01:54:20 PM »
hi ck

from top of this page,


This is as advised by Yeo to increase current to the zener and improve snr of the power supply.
I parallel a 122 resistor to the 1501 resistor next to the label 4k7.
The nett resistance decrease from 1500R to about 680R.
The sound improve quite a bit and reminds me of the 3 transistor mod described by Paul N in the Monica .
For once, I am not always thinking of mod ideas as i listen to the discrete dac.

Music flows better, more detail and more alive !
The noise between tracks is less.


this is for the resistor next to the 2 zener diodes, near the black gates n caps. parallel a 1.2kohm to 1.5kohm resistor across the 4.7kohm resistor to give a bit more current to the zener diodes.

you could use surface mounted resistors or carefully solder in a thru hole resistor.

try it and let us know how it goes.

yeo

Offline CKL

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Re: discrete dac mock up
« Reply #87 on: March 19, 2012, 10:05:57 PM »
I use a trimmer set for 680ohms to replace the 1.5k. The result is very positive. Better bass, treble & sound stage. I wonder it might be better than my optimized Monica3 now.  ;D

Offline yeo

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Re: discrete dac mock up
« Reply #88 on: March 25, 2012, 05:23:54 AM »
hi ck, hi kp

i have another tweak for you guys. actually it's a design error on my part.

there are 2 resistors placed just a bit north of the 2sk170s. the pcb label them as "10k".

this value is way too low. feel free to replace with 270kohm or thereabouts. 390kohm is fine as well.

the ladder circuitry's output impedance is 5kohm. so going into 10kohm is a disaster. i only realized this today...

try it. sorry about this mistake.

yeo

Offline CKL

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Re: discrete dac mock up
« Reply #89 on: March 25, 2012, 07:59:02 PM »
Hi Yeo,

Do you mean both 10k resistors have to be replaced?