A Formal ART Tube MP MOD????

[homestudioguy]

Has anybody here ever done a formal MOD on a Tube MP?
Even as minor as changing out the tube would be of interest.
Thanks

[mshilarious]

Sure. Black Lion used to have a mod posted on their site, but I think it's down. I haven't checked in a while.

Anyway, the basics were cap swaps, no value changes that I remember, but some were removed. Actually now I do think the caps in the PSU were increased by a factor or 2 or 4x . . .

Opamp gets swapped for OPA2134 or similar, tube to NOS of whatever brand you like. There was a diode swap in the power supply rectifier to high speed diodes, but that strikes me as very optional. There is also a regulator for the tube heater as I recall, that Black Lion said was +5V and should be swapped for +12V, but I remember checking my unit and the heater was at +12V (and therefore not starved). The tube plate on these babies is +45V as I recall.

That's the best I can remember, I don't have one of these anymore . . .

[Kevin Deschwazi]

Hey MS, is there really any point modding a starved plate design?

[peopleperson]

I'm far from the modmaster, but I switched out the 12AX7 in favor of a 12AU7 and seemed to notice an improvement.

[mshilarious]

Originally Posted by Kevin DeSchwazi

Hey MS, is there really any point modding a starved plate design?

I read comments like that over the years, and I have to respond, of course there is.

One line of reasoning holds that the tube isn't in the audio path, or doesn't generate much gain, etc. Well, in the ART, the tube is definitely in the audio path, but even if not, that would mean that the solid-state section was important, so clearly an opamp swap should help. And it does. If you've never heard the difference between a TL072 and a BB OPA2134 or 2604, I recommend trying it.

Swapping out caps and bypassing them with poly fims usually cleans up the high end.

As for the tube, no I wouldn't spend $50 on a highly prized vintage tube. The good news is there are lots of old 12AX7s on eBay all the time that sell for $5-7 per tube. Spend $20 on a lot of 4 (buy from someone with a tube tester) and there is guaranteed to be a range of flavors, and yes it certainly does matter even with starved plate. The nature of quality of the distortion varies greatly with the tube.

Of course there are limitations. Simple swaps aren't going to fix the MP's tendency to distort in an unpleasant manner when the gain gets too high. That would require a dramatic increase in plate voltage. Fortunately, there is a very simple mod to avoid that: keep the tube gain knob below 75%

[travelin travis]

Originally Posted by mshilarious

The nature of quality of the distortion varies greatly with the tube.

the overall sound of the tube mp can vary quite a bit with a tube change. the tube in my current tube mp is pretty sterile and does'nt distort much. the tube in my old tube mp distorted quite a bit (in a good way) and had a sort of 3d quality to it. it sounded kind of swirly.

here's a thread about modding the tube mp from last year: http://www.homerecording.com/bbs/sho...d.php?t=143763

[Kevin Deschwazi]

Originally Posted by mshilarious

I read comments like that over the years, and I have to respond, of course there is.

One line of reasoning holds that the tube isn't in the audio path, or doesn't generate much gain, etc. Well, in the ART, the tube is definitely in the audio path, but even if not, that would mean that the solid-state section was important, so clearly an opamp swap should help. And it does. If you've never heard the difference between a TL072 and a BB OPA2134 or 2604, I recommend trying it.

Swapping out caps and bypassing them with poly fims usually cleans up the high end.

As for the tube, no I wouldn't spend $50 on a highly prized vintage tube. The good news is there are lots of old 12AX7s on eBay all the time that sell for $5-7 per tube. Spend $20 on a lot of 4 (buy from someone with a tube tester) and there is guaranteed to be a range of flavors, and yes it certainly does matter even with starved plate. The nature of quality of the distortion varies greatly with the tube.

Of course there are limitations. Simple swaps aren't going to fix the MP's tendency to distort in an unpleasant manner when the gain gets too high. That would require a dramatic increase in plate voltage. Fortunately, there is a very simple mod to avoid that: keep the tube gain knob below 75%

thanks

........................

[chessrock]

It's kind of a bad design in the first place, so I'm not at all certain that any modifications are going to necessarily be worth it.

Like MSHilarious says, any time you see TL072s and TL074s ... there's a very good chance it could benefit from switching them out for almost anything else comparable. Might try an opa275 or possibly the burr-browns like MS mentions if you're feeling rich.

For the most part, though, the Tube MP is what it is. I don't think it's meant to be clean, pristine and detailed, so I don't know if a makeover is going to be able to dramatically change that.

.

[studiomaster]

I had a small question....How good are the ART Pro MPA(2 channel) preamps? Would they sound better than my present Motu 828mkII pre's?

[mshilarious]

Originally Posted by chessrock

For the most part, though, the Tube MP is what it is. I don't think it's meant to be clean, pristine and detailed, so I don't know if a makeover is going to be able to dramatically change that.

.

No, it doesn't. The mod cleans up the distortion quite a lot, but the unit doesn't have much headroom. That would require a much more significant power supply mod.

Re: Pro MPA, I have the Digital MPA and I rather like it. It's not starved plate (unless you want it to be, there is a switch for low plate but I've never used that), comes with BB opamps, and the digital version has nice converters. For the price I think it's a great deal.

[mamm7215]

I've got the MPA Gold (not digital) and the Pro VLA, I just changed tubes out in both. I put in the JJ 12ax7 for the Gold and JJ12at7 for the VLA. Quite a noticeable difference over the stock tubes. I haven't done the op-amp change as I don't want to dive into the surface mount soldering nightmare it would be for me.

[mshilarious]

Originally Posted by mamm7215

I haven't done the op-amp change as I don't want to dive into the surface mount soldering nightmare it would be for me.

The MPA has OPA2134, so there is no reason to swap it. First thing I did when I got mine was open it and look for something to mod, and I quickly decided on only the tubes.

Don't know anything about the VLA.

[mamm7215]

nice to know about the ops, thanks. Of the 2 units, my MPA had cheap chinese tubes stock but the VLA actually had some Electro harmonix 12at7's. A little better than the stock chinese but nowhere near as clean as the JJ's.

[chessrock]

Originally Posted by mshilarious

The MPA has OPA2134, so there is no reason to swap it. First thing I did when I got mine was open it and look for something to mod, and I quickly decided on only the tubes.

Nice.

Any other thoughts? Quality of the caps? Does the power supply seem to be pretty clean / ample? What converter chips does it use? Just curious. Thanks.

.

[mshilarious]

Originally Posted by chessrock

Nice.

Any other thoughts? Quality of the caps? Does the power supply seem to be pretty clean / ample? What converter chips does it use? Just curious. Thanks.

.

Here were my observations when I got it:

Originally Posted by mshilarious

This is a big step up for ART. The PSU has a toroidal transformer, a goodly amount of capacitance (don't know the brand though--Jun Fu?), and heatsinks on all the regulators. It has the usual ART opamp stages around the tube, but this time, they are socketed and BB OPA2134!! The variable impedance control works off a circuit of about a dozen transistors. It is remote from the rear input PCB, and not easily isolated, so I'll scrap my ideas for a transformer balanced input. The other opamps on board are 5532s, I'm guessing those are for the differential input & output.

Converter chip is AKM5394A and it's got a couple of Wavefront chips to drive the ADAT.

The caps probably could be a bit better, but the unit sounds good enough I didn't bother. I bought some NOS 12AT7s, and I dropped one of them in one channel, but I forgot which is which I have a vintage 12AX7 in the other, and either channel on high plate voltage sounds very clean. Someday I will do some more detailed testing on headroom and distortion . . .

After about 8 months of ownership, I still dig it. Only complaint is the input gain and impedance knobs are scratchy, but I haven't tried cleaning them, or maybe there is DC leaking somewhere. Not a big deal for me.

[chessrock]

Wow. That sounds pretty damn nice for a $400 unit.

Just one last question to bug you with ... is this one of the classic ART designs where you can basically bypass the tube by dialing it out of the equation, or is it just the amount of plate voltage that's variable?

Thanks for the observations.

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[mshilarious]

Originally Posted by chessrock

Wow. That sounds pretty damn nice for a $400 unit.

Just one last question to bug you with ... is this one of the classic ART designs where you can basically bypass the tube by dialing it out of the equation, or is it just the amount of plate voltage that's variable?

It essentially has the same gain controls as their lower end units, input gain and +20 switch control the level going into the tube, and separate analog output and digital output controls attenuate the level coming off the post-tube IC stage. So yes, you can choose to saturate the tube or not, with the plate set on high and output at 12:00, saturation starts pretty close to 0dBFS. I don't believe that bypasses the tube, but it keeps gain low enough that it doesn't clip the next stage.

Probably the most clever feature is the VU meter can be set to "tube", so if you want to limit tube character, you can set it so the VU meter stays out of the red.

[chessrock]

Damn. I might have to see about gettin' me one of these. You sold me.

.

[boingoman]

Originally Posted by chessrock

Damn. I might have to see about gettin' me one of these.

.

I think my heart just stopped for a second.