[spore]

(josep) Which location is the quad opamp at? I may want to try change it out as opamps are pretty cheap and not expensive. I will report back my findings after I changed it.

 

[josep]

It's 'IC5' at the side of the dual opamp... there is not much PCB to see or get lost around

Be careful with it, even with solder pump this is a size a bit 'dog' already to get out and we do not want to damage the pcb traces. If in doubt, cut its pins with a Dremel disc, then desolder the pins (easy, but destructive way as after this the original quad opamp is useless... well its destination was the bin anyway so...).

If you are feeling brave after this, next step is to completely rework the PS: keep in mind those opamps are gettint its -V rail from the internal DC-DC converters (two 7660 chips IC2 and IC9 close to the power input). An external bipolar PSU (+12 and -12V, it can be done with a second battery for example if you are powering already it this way) will IMO bring great/obvious benefits too...

 

[spore]

thanks! I will see what I can find out on the op amp and voltage converter.

 

[T_K]

MC33079P pdf, MC33079P description, MC33079P datasheets, MC33079P view ::: ALLDATASHEET :::

the datasheet for that quad opamp... I don't have time right now but I'll look for a replacement later.

EDIT: a very quick search yielded this

Print Page - Phonostage upgrade question

so looks like this is the upgrade

Digi-Key - OP467GPZ-ND (Analog Devices Inc - OP467GPZ)

it really must be better seeing how it's 12x more expensive

this one is also suggested

Digi-Key - AD8004ANZ-ND (Analog Devices Inc - AD8004ANZ)

 

[davidcotton]

Just a heads up for those in the uk. Acton-gate audio.co.uk have the dac in for £129 delivered! Would say that don't bother using the site to order it (I tried and it bombed out on processing the order which means I don't know if the order was recieved or not, going to phone them but it being the bank holiday means opening hours aren't normal)but give them a ring instead.

Enjoy.

 

[spore]

I have changed the quad op amp at location IC5 to LME49740. LME49740 is also another quad op amp for audio use with ultra low distortion and low noise.

Only potential issue is that LME49740 is pretty sensitive and can oscillate.

Luckily, this was not the case for the MF V-dac. I did not observe any humming or noise after replacement to LME49740. LME49740 is a direct replacement for MC33079 in this case.

The sound of my modded v-dac is now much cleaner and neutral. Some may describe the sound as cold as vocals do not sound warmth unlike previously. There is also slightly more details in the music and bass is well controlled with no booming.

Previously for certain tracks, I can detect a slight boom in certain passages for some songs only when playing but not in this case anymore. Imaging is also slightly improved and sound seems very well balanced and dynamic.

Overall I like this sound better as it is more neutral, clean and balanced. I love my modded v-dac!


P.S. I did not rework the ps as I am satisfied with my external ps.

 

[T_K]

I think I'll put a socket there as well so I can try the different options.

Did you remove those output caps after changing this opamp?

 

[spore]

Nope, I did not remove the caps yet as I have not yet measured the DC offset. I was anxious to fit back everything and test out the sound first. Besides I left my multimeter in my car parked a few blocks away. I may also leave the caps in place since I am quite satisfied with the sound of my modded v-dac.

Please report back your results of using different op amp. LT1359 is also a quad op amp and it has some pretty good reviews. You may want to consider trying this op amp out also.

 

[T_K]

I've ordered an OP467, should have it in a couple days.

 

[T_K]

Will hear it tonight.

 

[josep]

Nice done TK.
After some burning measure the DC offset entering the output caps, probably it is low now (1 or 2 mV) and you can bypass them.
It may be too a good idea to have some filtering cap directly over the opamps pins (ps), all the V-DAC traces are quite short and with the sockets you have a somewhat long PS line here...
Let us know if it is better or not now!

 

[fdhfdy]

is its usb outs oversampleing to 192 as well or just the coxial outs?

 

[spore]

I measured the dc offsets. C3 is having dc values of 4.6mV while C4 is having 12.3mV values. Looks like we cant use any bypass caps here.

My PSU and the v-dac now runs hotter. Guess LME49740 is consuming more power compared to the stock quad op amp.

Does anybody have recommendations for a better voltage converter other than the stock 7660S?

I was reading the v-lab thread and wow there is really some modding done over there. Are there any more cost effective mods for the v-dac?

 

[MatsudaMan]

I put some new caps on mine. Sounds really bad now.

 

[spore]

Did you solder the caps with the correct polarity or did you change the capacitor values?

For me, I noticed the v-dac sounds better after changing the cap. A more noticeable improvement after changing the NE5332 op amp. Its strange that it does not sound good.....How bad is the sound?