M-Audio Transit caps & op-amp mods
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Miguel

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I've recently seen some topics regarding the modding possibilities of the M-Audio Transit. From what I've seen, the three possible areas for improvement are:



1. The two 10uF 16V caps in the headphone output (bottom right)
2. The LMV722 op-amp located next to those caps
3. The 100uF 10V cap next to the power supply
(biggest one, next to 3.3V regulator, at the bottom left)

Because of those thread reccomendations, I was thinking to change the two 10uF 16V caps by black gates Nx 22uF 6.3V, the 100uF 10V cap by a panasonic 470uF 16V and the LMV722 opamp by an AD823 (or AD822 if I don't have any other choice).

The main differences between those opamps are:

- LMV722: Dual channel, supply 2.2V to 5.5V, supply current per channel 0.90 mA
- AD823: Dual channel, single supply 3V to 36V, dual supplies ±1.5V to ±18V, supply current per channel 4.2mA
- AD822: Some similarities to 823, worst performance, 0.90 mA

Could you please give me your opinion about it? (I haven't seen any feedback from anyone that already did a Transit mod). Would the AD823 be OK for this application? And the caps? Also, any idea of the best method to de-solder the SOIC op-amp? De-soldering is also tricky, but I can solder SMD components easily.

Thanks.

EDIT: All mods done long time ago, if any is interested in info PM me
 
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pburke

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I've been looking at modding mine, but my mods were focusing on a rather different final goal: clean SPDIF out to my DAC. To achieve that, I'm actually about to disable everything but the USB receiver chip and what's related to the SPDIF output. The mods are going to be in the PSU - schottky diodes, blackgates, etc - possibly all in a bigger case since the good caps won't fit in there. Gets too hot anyway as it is. Then a decent BNC output jack, some Stillpoint ERS paper around the thing, and let's see if it works better.

Peter
 
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Miguel

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Unfortunately I don't have a standalone DAC, so I am interested in mods to enhance the line out. I would like to build one but I'm broke after buying a headphone amp and new cans


People, stay away from head-fi forums - your wallet will complain about it!
 
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Garbz

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When looking at cleaning the SP/DIF output I'd look at some form of digital isolation. Pulse transformers or something like that would work nicely, and yes definatly needs a BNC connector, not even an expensive one. I didn't make any digital mods to mine as my DAC has a usb receiver.

Miguel here's some feedback from someone who's already built one. (that's my pic on the top
).

The output caps are fine. I think that's the same value I used for my mod, and it worked very well. Noticably cleaned the sound all around. This is the first thing you should consider. The blackgate NX series although they are non-polar they have a positive pin and negative. The positive pin is longer. I put mine in the way they came out. But another possible mod includes using 2 of them in opposite polarity on each channel. I've never tried this and I don't think very many people on this forum have either. I think it's called Super-E configuration. But if BG marketingsheets are anything to go by it should give a noticable improvement over using just one cap.

I'm not to sure about moding the power cap though. On the one side the powersupply on a computer is noisy, but on the other side after my mods my transit measured -96.6dB dynamic range, and a -99dB noise floor, which pretty much makes the Codec chip the limiting factor as far as psu noise goes. However i'm sure the opamp would appreciate the extra capacitance.

As far as opamps go the biggest limiting factor is the low voltage (5v) and the single ended supply. The AD823 should work just fine in this case and if my cdplayer mod is anything to go by details should be vastly improved.

The biggest problem in getting chips out is not lifting traces. However it's realy easy to get them out if you intend to throw away the old chips. Just get a large soldering iron with a large flat tip, cover the tip with solder and just hit the side of the chip. About 15 seconds, and a fried chip later it'll just fall off the board. Then it's just a matter of steady hands to get a new one back on.
 
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Jon L

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For AD823, you need the 8-pin SOIC, correct? It'll probably be much better if you plan to drive headphones, but would it make much difference if using Transit as line-out into headphone amp, like I'm doing?

Anyway, I've got an Empirical modded Transit with special line-out mods, using black gates for line-out coupling. Of course, my Transit also has a separate outboard power supply, not taking power from USB cable, various refinements on the board, and bigger PS caps also.

It really took forever for the mods to break in, but in this configuration, even with stock LMV722 opamp, the line-out driving either Sonic impact->K1000 or SuperMacro v.3-->Ety's sound Really, really impressive, especially at 96kHz..
 
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Miguel

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Many thanks Garbz & Jon L for your help
it's nice to have some feedback from people that already modded this card. I'll order some back gates for the line out, and the AD823. I don't mind about frying the LMV722 so I'll use your method to remove it


Jon L, you need the 8-pin SOIC version, the soldering job is quite easy if you have some flux. De-soldering is more tricky.

I have been reading about the BG Super-E config (acoustic-dimension site) and seems a nice way to get an ideal capacitor. However, I don't think I will be able to fit 4 caps there (I want to keep all the mods in the original Transit case if possible)

Maybe I'll try the 470uF cap in the PS, because I have noticed a bit more noise when using the Transit with my desktop PC compared with the laptop (amplifying the signal to hear the noise, otherwise it isn't almost noticeable). I guess the difference is due to the laptop battery. Maybe a bigger cap will help. Otherwise, I agree with you, with those benchmarks the codec chip is the limiting factor.

BTW, Jon L, could you please tell me which PS cap is used in your empirical modded Transit (capacitance and brand/model if possible)? Or take a photo of the board, if this is not much trouble? I would like to see it to find more ideas for further mods. In any case, I think these three mods will be more than enough :p
 
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Garbz

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As far as opamps go the AD823 will be much better all round then the existing one. Headphones are generally hard to drive, and need plenty of current, especially low-z headphones. When doing tests with dummy loads, as impednace of the load increases so does performance. The measurements I took were loaded with 100k, I don't use my headphones directly with it so I'm sure it would measure worse if I did.

What i'm saying is yes the improvement for headphones will be great, but the improvements for line out will also be good.

The super E configuration should in theory fit in there. The 22uf black gate caps are relatively short. Mine sit 5mm off the board, and there's still close to 1cm space above them in the case. I sugest maybe try and mount them into the board as high as possible, and then place the 2 others at right angles to them and solder the legs to the other legs, and then the giant triangled sideways T shaped mess into the board.

Should be an easy fit, just replace the opamp first, because it won't be accessable afterwards.
 
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amb

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The AD823 is superior in most specs compared to the LMV722, except that it has double the noise. If low noise floor is an important, then you should take this into consideration.
 
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Miguel

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Quote:

Originally Posted by Garbz
The super E configuration should in theory fit in there.


Thanks, I thought they were bigger and would not fit. I'll order 4 caps, that Super-E configuration seems promising
I also have been looking to the AD823 datasheet, it seems pretty good.

Quote:

Originally Posted by amb
The AD823 is superior in most specs compared to the LMV722, except that it has double the noise.


This was my only concern after looking to the datasheet, as I have quite sensitive ears, and I mainly use UM2 IEMs, which are very sensitive as well (i.e. I can easily hear unwanted noise). AD823 has 16nV/vHz voltage noise compared with LMV722 that has 9nV/vHz both @ 1kHz - 100kHz. I don't know if this will be noticeable as I am not used to read op-amp datasheets.

Do you know any other good quality dual op-amp similar to AD823 with lower noise? (I don't mind if it is a expensive one). I have been trying to find one with no luck so far.
 
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amb

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The AD8066 might be a good candidate. I don't know what's the supply voltage to the opamp within the Transit, but the AD8066 is rated down to 5V (+/-2.5V) and has better specs than the AD823 in most areas. This opamp has low noise, rail-to-rail output swing, very high slew rate and wide bandwidth, good output current capability, but draws ~6.4mA quiescent current per amp, which is quite a bit higher than the LMV722 (0.93mA) or AD823 (2.6mA).
 
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Miguel

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I did a parametric search in TI and Analog.com. I'll show the AD ones as TI seems not to have low voltage low noise ones. The results were:

Part#, Small Signal Bandwidth, Slew Rate, V Noise Density, Vcc-Vee, Iq per Amplifier, Package, US Price

OP290 -20KHz12mV/µs- 1.6V-36V20µADIP$3.03 US
AD8012 -350MHz2.25KV/µs2.5nV/rtHz3V-12V900µASOIC, SOP$2.46 US
AD812 -145MHz425V/µs3.5nV/rtHz2.4V-36V5.5mADIP, SOIC$2.92 US
AD8028 -190MHz100V/µs4.3nV/rtHz2.7V-12V8.5mASOIC, SOP$2.22 US
AD8018 -130MHz300V/µs4.5nV/rtHz3.3V-8V10mASOIC, SOP$2.95 US
AD8652 -50MHz41V/µs5nV/rtHz2.7V-5.5V9mASOIC, SOP$2.40 US
AD8616 -24MHz12V/µs6nV/rtHz2.7V-6V2mASOIC, SOP$1.40 US
AD8606 -10MHz5V/µs6.5nV/rtHz2.7V-6V1.2mASOIC, SOP$1.40 US
AD8058 -325MHz1.15KV/µs7nV/rtHz3V-12V7.5mASOIC, SOP$1.88 US
AD8039 -350MHz425V/µs8nV/rtHz3V-12V1.5mASOIC, SOT$1.41 US
AD8692 -10MHz5V/µs8nV/rtHz2.7V-6V1.05mASOIC, SOP$0.85 US
AD8062 -320MHz650V/µs8.5nV/rtHz2.7V-8V9.5mASOIC, SOP$1.88 US
OP262 -15MHz13V/µs9.5nV/rtHz2.7V-12V775µASOIC, SOP$2.11 US
AD8529 -8MHz2.9V/µs10nV/rtHz2.7V-12V1.2mASC70, SOIC, SOP$1.22 US

They are in descending order by voltage noise. The problem is that I do not know if any of them are good sounding ones
 
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Miguel

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Quote:

Originally Posted by amb
The AD8066 might be a good candidate. I don't know what's the supply voltage to the opamp within the Transit, but the AD8066 is rated down to 5V (+/-2.5V) and has better specs than the AD823 in most areas. This opamp has low noise, rail-to-rail output swing, very high slew rate and wide bandwidth, good output current capability, but draws ~6.4mA quiescent current per amp, which is quite a bit higher than the LMV722 (0.93mA) or AD823 (2.6mA).


I thought about the AD8066 as well, this one would be ideal, but the M-Audio Transit have a 3.3V regulator next to the USB-in so I guess the supply voltage to the opamp is 3.3V (not sure about it). About the supply current, I don't know the impact of it.

I would like to have better electronics knowledge...
 
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amb

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Quote:

Originally Posted by Miguel
the M-Audio Transit have a 3.3V regulator next to the USB-in so I guess the supply voltage to the opamp is 3.3V (not sure about it). About the supply current, I don't know the impact of it.


If the regulator is indeed for the opamp then the voltage is probably too low for the AD8066. I guess that makes sense, since there is 5V coming in over the USB cable, and it gets regulated down to 3.3V.

As for the other opamps from your parametric search, none of them get mentioned in these forums so we're just as clueless about their sound quality...
 
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Miguel

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Quote:

Originally Posted by amb
As for the other opamps from your parametric search, none of them get mentioned in these forums so we're just as clueless about their sound quality...


I posted them just in case anyone knew a good sounding one, I didn't recognize any when I searched for it. Anyway, many thanks for your help
 
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SnoopyRocks

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Quote:

Originally Posted by Miguel
This was my only concern after looking to the datasheet, as I have quite sensitive ears, and I mainly use UM2 IEMs, which are very sensitive as well (i.e. I can easily hear unwanted noise). AD823 has 16nV/vHz voltage noise compared with LMV722 that has 9nV/vHz both @ 1kHz - 100kHz. I don't know if this will be noticeable as I am not used to read op-amp datasheets.

Do you know any other good quality dual op-amp similar to AD823 with lower noise? (I don't mind if it is a expensive one). I have been trying to find one with no luck so far.




16nV/rtHz translates to an SNR of 112.9 dB for a 1Vrms source over the audio band. The input referred noise of the AD823 should not be a limiting factor in this case.
 
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