Musical Fidelity V-DAC2 - opamp comaptibility - diyAudio
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Old 26th June 2012, 01:47 PM   #1
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Default Musical Fidelity V-DAC2 - opamp comaptibility

I'm wondering if anyone can help with selecting a compatible op-amp, or give guidance on re-working the loading around the op-amps, in the V-DAC2? I've done some Op-amp rolling, but i'm no depth expert on compatibility - i'm an enthusiastic DIYer. Here's what i've done:

Original Musical Fidelity spec in the circuit is a 4-channel 33079 (ST Electronics) followed by a 2-channel 33078 (ST Electronics).

First I replaced the DC Blocking caps by the RCA outputs: 47uF SMD with Nichicon ES 470uF Electrolytics (there is just room inside the case!).

Then to the opamps: I replaced the 2-channel 33078 ouput opamp with 2 x OPA827 on a Browndog. Lovely improvement in detail, whilst keeping the 'musicality'.

Then I got excited and replaced the 4-channel 33079 with an LME49740. But the bass just disappeared - almost like a low frequency filter. Really not sure why (could it be the larger current requirement of the 49740 at 18.5mA, versus the 8mA of the 33079?). So I switched the 49740 to an OPA1644. Bass came back with good detail and spaciousness. However, over time (i.e. a few hours) the sound became relatively fatiguing. Seemed tight and clinical - it lacked the musical warmth, despite representing instruments accurately.

So I decided to switch the 2xOPA827 on Browndog with an OPA1642. Now this should be a happy result, and mostly it is the best sounding so far (i.e. the combination of OPA1644 and OPA1642 in the circuit), but the mid bass has dropped away again - significantly reduced - coming back with deeper bass notes being present, although softer.

Can anyone give me some guidance of whether this is just audio character of this op-amp series, or is there likely to be an incompatibility with the audio circuit leading to the reduction in mid-bass? It was interesting that i saw this effect with both the 49740 and then the 1642, which are both in different locations. I have an OPA1612 ready to test, and i can go back to the ST chips, although they are not my first choice - they are musical but after hearing the depth of detail produced by the others i've been testing, i'm loath to go back! Any ideas anyone?

Will
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Old 26th June 2012, 08:52 PM   #2
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I think i've answered my own question: i went back to the OPA1642, but used 2 x OPA1641 chips instead on a Browndog. Then the solution to the bass: 0.1uF decoupling caps across the supply pins - really sorted the bass and balances the presentation generally.

So, if you're interested in upgrading the V-DAC2 opamps, i recommend the 4-channel OPA1644 and the 2-channel OPA1642, with 0.1uF decoupling caps on the supply pins of each one - sound is more transparent than stock, but maintains that musicality.
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Old 27th June 2012, 04:53 PM   #3
percy is offline percy  United States
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Hi wiland1,
how easy (smd?) do you think it is to completely bypass the analog stage and use custom I/V ? Can you post some pictures so I can see how it looks in that area ?
Also, did you change anything about the power supply ? Or are you using the stock wall wart ?
I am seriously considering this DAC and would like to get some feedback on it.
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Old 27th June 2012, 08:05 PM   #4
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It's a great sound out of the box - i just like tweeking I'm using the stock wall wart supply - i'm sure the V-Dac supply would clean it up further.

Only trouble is that i think those new OPA's are not totally happy - still slightly bass shy and harsh treble now (oscillating). As you can tell, i'm not a pro so cannot answer your questions. Here's a couple of photos:

Click the image to open in full size.

And one of the underside with the dead-bugged PP Panasonic caps on the supply pins

Click the image to open in full size.:

I'll try and take a photo of the whole board from above so you can check it out.

I've got some 4.7uF PP Claritycaps on order now - the VDac Mod thread on the forum suggested this would be a better option than a big Elec Cap. I wonder if that is the reason my bass is not right? I had heard that a big EC is a good solution for signal path DC blocking - it's the small value ones which veil the sound...
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Old 28th June 2012, 10:11 PM   #5
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Here are 3 pics of the board for folks to look at - the three photos effectively stitch together. I've just replaced the 2 x 470uF green Nichicon ES Electrolytics with 2 x 4.7uF Claritycap PP caps from Falconacoustics - they're big and only just fit - and it sounds fabulous. Really clean, natural, balanced sound now, with lots of space around insruments. And it's still running in! So the advice about using PP caps in the signal path appears to be very true - if you can make them fit .

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Last edited by wiland1; 28th June 2012 at 10:14 PM. Reason: wrong pic #1
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Old 24th July 2013, 12:44 AM   #6
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Default ClarityCaps install

Hi wiland1
Did you install ClarityCap, 4.7uf / 250VDC, ESA Series, 25mm D x 33mm L. If so I assume you had to lay them on their side as I measure usable space of 28mm, did you?

Regards,
Marvin
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Old 24th July 2013, 08:56 AM   #7
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Hi Marvin - I cannot remember for sure, so i'll take the cover off and have a look this evening just to be sure - i'll post up another photo for you. What you describe sounds exactly right - i used the biggest ClarityCaps i could get in there

Since the post, i also experimented with the output Opamp and i am pretty sure i ended up with the OPA1662, which sounds beautiful, but let me check.

Will
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Old 24th July 2013, 08:52 PM   #8
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Hi Will, thank you for your response. I would really appreciate the photo as a reference. This morning I ordered from Mouser the OPA1642 and 1644, one each. From PartsConnection I ordered ClarityCap ESA 4.7uf/250v, 2 each.
I have searched all over the WEB and it seems few people have modded their V-DAC 2. So I was really pleased to find your post. I'm not a tech or EE, I just copy from others; so far so good. After I finish with the opamps I'm going to find a way to change the RCA connectors. It seems a bracket would need to be attached to the board were they are are now. There's room to do it. We'll see.

Regards,
Marvin
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Old 24th July 2013, 09:47 PM   #9
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Hi Marvin - I can't tell you what a difference it made to the sound. running an ipod classic through this modded VDAC2 is really stunning. Forgive the state of the board in the pics - it's had a lot of opamps on and off! you can see that the ClarityCaps are tight in the case, but so long as their wires are well anchored by solder on the board (and you will need to drill holes in the board for them), they do not need a bracket - they hover just above the PCB and although they touch the sides of the case, I've never suffered any vibration related issues in the music.

As for Opamps, well this is where I came out: The OPA1654 and OPA1662 are definitely better sounding than the 1644/1642 - you'll have to order them! The 1662 is very musical and detailed. The 1664 was not available when I ordered, so I went for the 1654 and am not disappointed. It's cousin the 1652 is a terrific sounding opamp - slightly warmer than 1662, so I guess I just like the sound of the 1654/1662 combo. The 1642/1644 are fine, but they do not present the music so clearly or naturally by comparison.

Take care when you take out the old opamps - after 3 changes, the solder pads were in a really bad way, so you can see I had to solder a little jumper wire! Best of luck and would love to know what you think.

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Old 24th July 2013, 09:58 PM   #10
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I just re-read your post and you mention the RCA connectors - I did change mine for some nice, chunky Cardas Gold connectors, but they made no discernible difference in the sound and they were a pain to get on and off (for accessing the internals) because they were bolted to that end-plate. I returned to the original MF connectors.
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