ART MPA Gold Mods

[Mylithra]

Just got an ART MPA gold and the stock unit is pretty rough. I have new tubes for it (Mullard 12AT7) but I havent installed them yet. Was looking into other ways I could Mod the thing and heres what I came up with in the order I would probably do them.

1. replace tubes
2. Try out some different OP amps. The list I have as drop in compatible are:
AD826
AD828 <- *edit: looks to be more of a video product.
LT1355
LM4562
3. The caps were not a brand I recognize and truth be told, I dont think Id really hear a difference at this point by changing them but depending on how ambitious I get, I might go here.

Once I get to step 2, Im going to try and get a hold of all these op amps and try them all. Ill probably make some samples if you're interested. Also, If you can think of other Drop in compatible op amps, Please let me know.

[paully]

Dumb question, but have you tried the user adjustable plate voltage and input impedance settings yet? Might make things more to taste. Maybe you could post what you think is missing or needs correcting 'soundwise'. That would help.

I don't want to sound glib, but other users have found out that this, and the less expensive ART pres, are more useful as effects then as a first-choice mic pres. IMHO, those opinions are validated by the modest price of the unit.

Try going to MusicPlayer Forums: Viewing list of forums , register, and repost on the 'Project Studio' forum. Several guys there own and have discussed this pre.

Best, Paul

[TAVD]

Do it up and report back. I think there's better sounding op amps than the OPA2134. Whether or not you hear an improvement is another story.

[elektrovolt]

I believe that replacing the pots might be a good idea also, as they are cheap and unreliable. maybe a slow-ramp-up mod on the phantom circuit also, as those popping sounds are very loud and annoying

[reprenize]

+1 on this thread, by the way.

here is a pdf on the matter mof modding one of these. i plan to do this some day when i have the patience, as i bought the model with the vu in it. i think they're different. i swapped the stock cheesy looking tube for a nicer looking jj tesla tube but it died on me, even after burning it in at 0db of 1k for 10 hours. now its kind of a... high pass filter.

http://home.att.net/~crazydoc/ART_Tu...dification.pdf

here's a geek talkin about some preamp diy stuff (slightly off topic, but somehow relevant)

How to build your own tube preamp

[Mylithra]

Thanks for the info reprenize, but that PDF is for the Art Tube MP, not the MPA gold.
The Tube MP is an OP Amp based Mic pre with a starved plate tube gain stage.
The MPA gold is similar but the Tube gain stage isnt starved plate. It does actually put out around 180v to the tube so anyone playing with this device, please be careful.
As for the Op Amp replacments, Digikey was out of the LTs. Depending on how the Op Amps I was able to get a hold of, I may end up leaving this chip out.
I did take a meter to the Op Amp voltage pins and they were sitting right around 15v. So please do not try using the AD8606. The AD8066 may be promising but Id have to get a SOIC to SIP converter.
There is a lot of good information in there though.

[reprenize]

oh, i thought MPA Gold is what you get when you're finished modding an MP.
i am even halfway serious!

what about changing caps and stuff? i would refer to that pdf for inspiration there.

are you going to start with one channel at a time so you have some a/b?

how are you going to look at the curves? have a scope?

[TAVD]

ART was great at providing me a schematic when I needed one for my MPA. Get one and give a look. Maybe you'll see something more you can do.

[Mylithra]

Here is a prelilmary report.

I got the new op amps. What I was able to get and test:
LM6172
LM4562
AD826

The AD826 oscillated badly and wont work correctly without some circuit modification. Ive not dug deeper into this yet. It could just be putting together some decoupling caps will solve this.

Both LM chips worked fine without any modification.
Based totally off my ears, the LM4562 sounded pretty much like the OPA2134. There was something significantly different with the LM6172, Id say in the low mid band.

The tubes also made a difference. They seemed to add a little more depth.. Not a lot, but enough to be nice.

Im leaving 1 side un-modified till I get some recordings.
At this point, Im planning to do some Acoustic guitar and some DI bass for AB comparisons. Ill let you know when the files are available.

[Jim Williams]

The AD 826, AD827 are dirty opamps, they should be avoided. The circuit must either have some local cap across the feedback resistor or the chip may oscillate. Some wideband parts don't like being used as followers, like the LM6172 for example. Any opamp change must be viewed on a scope to determine if it's operating in a linear region. Local psu .1 uf ceramic bypass caps must be fitted close to each opamp. Input legs must not run long lengths or phase margin will collapse and oscillations at worst, ringing at best may occur. Audio band parts like OPA2134, AD 8599 are usually safe, the LM4562/LME49720 is a 55 mhz bandwidth part, watch out. The LM6172 is a 100 mhz part.

This is not like swapping the tubes on your old color TV, one can quickly make things worse without knowing it.

Jim Williams
Audio Upgrades

[Joel C]

Hi Jim,

I'm interested in modding my Art MPA Gold too.

After some research, I found one guy who says he successfully swapped out the stock op-amps with AD823AN (PDIP) FET chips with improvement to signal quality:

View topic - ART MPA GOLD


Another source says to find out whether the original op-amps are FET or Bipolar because 'FET op amps have a higher input impedance and lower Ib (input bias current) and replacing a FET with a bipolar can result in increased noise and DC offset.'

Because of this, I'm confused.

Aren't the LM4562 and AD8599 both bipolar chips which should be avoided if the original chips were FET? If so, how is it possible Mylithra using an LM4562 bipolar chip and the other guy with an AD823 FET are both experiencing 'improvements?'

[Mylithra]

The LM4562 and the AD826 is a voltage Feedback OP Amps. They are pin and voltage compatible but may not work as designed based on the circuit around on the Op Amp. The OPA2134 is a fet based Op Amp.

I didn't say I heard an improvement on either of the LM chips, As a matter of fact, I thought the LM4562 sounded pretty much the same as the OPA2134.
The LM6172 had different sound to it but dont necessarily know that its any better or worse than the OPA2134 as the only tool I was using to listen to this was my ears, a pair of matched SDC mics, one on the unmodified channel and one on the modified channel and listened to some acoustic guitar and swapped the channels back and forth . All the statement was intended to say was I plugged in the chip, it passed audio and it sounded different than the stock chip. Not better or worse. Ive not made those determination yet.

The circuit may just be forgiving enough use some of these without modification but till I see it on a scope, I cant give you a definitive answer.

Edit: First clip. http://thesupremeruler.com/downloads/mpagoldtest.mp3
The Setup: Matched pair of Rode NT5s both going straight into the ART MPA Gold, straight into the DA converter. No EQ, compression or effects. One channel of the ART has been modified with the LM6172 but I wont tell you which till later. The Tubes are stock. We'll change the tubes and record an AB from stock tube to NOS Mullard in the coming days.
As for the LM6172, it played fine on acoustic but didnt work so well on Bass DI. The gain was very erratic. The conclusion: This chip wont work properly without circuit modification. Could be as easy as some decoupling caps but till I get more in depth on the circuit, I wont know.

[12Bass]

Joel has notified me that the MPA Gold uses socketed OPA2134s and soldered NE5532s.

I've suggested that a pair of AD825s on a dual SOIC/DIP adapter may be a good replacement for the OPA2134s and the LM4562 (or AD8599) may be a good replacement for the NE5532 (using proper PS decoupling techniques of course). I've found the AD825 to be more open and natural sounding than the OPA2134s - quite a nice sounding chip! And the LM4562 is again more transparent than the older NE5532. One caution is checking the voltages to ensure that they are not above the ± 18V absolute maximum for the replacements, but this is probably fine considering that the OPA2134 is a ± 18V part.

[Jim Williams]

The LM4562/LME49720 is rated at 34 volts max, if you use it with a supply above + - 17 volts it will fail. Use the 22 volt version, the LME49860NA, rated at + - 22 volts. For a single package part, use the LME49870. The new BB OPA211 is a very good sounding part as is the fet input OPA827.

Jim Williams
Audio Upgrades

[12Bass]

Originally Posted by Jim Williams

The LM4562/LME49720 is rated at 34 volts max, if you use it with a supply above + - 17 volts it will fail. Use the 22 volt version, the LME49860NA, rated at + - 22 volts. For a single package part, use the LME49870. The new BB OPA211 is a very good sounding part as is the fet input OPA827.

Jim Williams
Audio Upgrades

Thanks Jim - appreciate the input. I'll have to check out those new chips!

BTW, I was quoting the absolute maximum rating from the spec sheet. I realize that the LM4562 is rated for ± 17V. I've had one in my NAD 3150 for months running at a little over ± 17V with no problems.

[mamm7215]

Any thoughts on the AD823AN's as a direct replacement for the 2134's as previously mentioned? Sounds like it's a cheap straight swap...

[12Bass]

Originally Posted by mamm7215

Any thoughts on the AD823AN's as a direct replacement for the 2134's as previously mentioned? Sounds like it's a cheap straight swap...

While I don't have the preamp in question, I've tried it in other applications and haven't found the AD823 to be too satisfying - sort of brash and lacking detail. I like the AD825 much more, more open and natural sounding. IMO, even the OPA2132 would be preferable to either the AD823 or OPA2134 as it is still fairly musical, but has a bit more detail in the highs. The OPA827 JW mentioned sounds quite interesting, but isn't available at Digi-Key yet.

[mamm7215]

Hmmm, good info thanks. I'd sure like to see a good, easy (as in no other circuit mods) op-amp swap out for these units. The tube swap was good and not that the sound is bad, I quite like mine as is now, but I did the input op-amp swap on my ProVLA (compressor) and it did make a bit of positive diff. with that unit. Less smeary, clearer...

[Jim Williams]

Originally Posted by mamm7215

Any thoughts on the AD823AN's as a direct replacement for the 2134's as previously mentioned? Sounds like it's a cheap straight swap...

Not a cheap swap at $5 each. The 823 also has higher noise than the BB 134/132 series. They are precision opamps, no offsets, rail to rail outputs. They do make great sample to hold amplifiers in digital reverbs due to their fast settling time. I occassionaly use them in mute circuits in consoles where bias current switching is a problem.

Jim Williams
Audio Upgrades

[mamm7215]

[quote=12Bass;2035154] IMO, even the OPA2132 would be preferable to either the AD823 or OPA2134 as it is still fairly musical, but has a bit more detail in the highs.QUOTE]

Thank's Jim. Appreciate your input. So what's the main diff between the 2132 and 2134 and is it an "audible" difference. I guess it helps to know the chain as well, I sing through a modded Apex460 (Peluso cap, cinemag xfrmr, erse audio cap in C8) into my Gold, then into my ProVLA (sometimes, sometimes not), then into my EMU 1820M to Sonar7PE. OK-ish enough chain to benefit from a better op-amp?