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"ART" MP 12AX7 tube microphonium preamp:




 
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Author Topic: "ART" MP 12AX7 tube microphonium preamp:  (Read 20471 times)
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Vortex Joe - N3IBX
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« on: July 30, 2008, 12:48:36 AM »

Does anyone have any experience with the ART (Applied Research Technologies) MP tube microphone preamp? For it's price ($29.99 at Musicians' Friend, etc) you get a mike preamp that uses a real 12AX7 dual triode, a VU meter, XLR and other inputs and outputs, PLUS a 48V phantom supply for powering a condensor microphonium, a 9V wallwart power supply,  etc etc. It just seems too good to be true.

I was thinking of buying it and using it with my Behringer B1 condensor microphonium to warm up the audio of my ART-13 a little bit.

I did a little bit of research, and the 12AX7 tube used in the MP preamp could be a "JJ" or other of Eastern European manufacture, not a Chinese variant as I originally thought.

Another point of interest, is that they're supposed to be made in Rochester, NY USA; not "MADE IN CHINA" as originally thought. Not that it makes much of a difference, because Behringer and other companies who make audio processing gear seem to all be made in China. It's just refreshing to see something (supposedely) made in the USA.

The ART MP is strictly a microphone preamplifier, not a EQ. I just can't get over the astoundingly low price, and wonder of anyone here has any experience with the particular unit I'm referring to. I'm a believer in you get what you pay for. It would seem to me that this particular unit should sell in excess of $100. The 12AX7 tube, VU meter  and wallwart 9V supply would cost in excess of $30 if you went to buy them at a electronics supply house.

You can find a link to it at: http://www.musiciansfriend.com/product/ART-Tube-MP-Studio-Mic-Preamp?sku=180581

This may be a inexpensive way to warm up the audio of a otherwise mundane sounding rig, or to give a little warmth to a solid state rig.

Best Regards,
                  Joe Cro N3IBX

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Joe Cro N3IBX

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« Reply #1 on: July 30, 2008, 08:04:22 AM »

I have used one in recording. It has a cheap Chinese 12ax7 which you would need to replace. Also very susceptible to hum. It (the buzz) was too loud for the track so shelved it. We tried a Groove Tube 12ax7 which was awful. MID and more MIDRange. Then used an old Mullard which was noticeably fuller and nicer but both tubes had noise. The worst thing was the hum. It hummed like a single coil pickup next to a florescent transformer.  I could move it around but never null the noise.

I bet a simple unity gain 12ax7 preamp wouldn't be hard to scratch build that would perform better than this one. $29 is cheap though. A good 12ax7 is from JJ is what? $12? 

The thing is on my workbench now and I promised the owner I would try to find a way to shield or ground out the noise.

The Mullard definitely gave what you want though. Nice tube overtones before any SS amplification.   

By the way, when replacing the tube (It said Made in China on it), be very gentle pulling apart the two piece housing as there are boards on both sides connected by ribbon cable which some heavy fisted tinkerers have ripped apart.

Your mileage may vary....
73
Mark

 
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Vortex Joe - N3IBX
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« Reply #2 on: July 30, 2008, 09:36:06 AM »

Mark,
       I really appreciate your insight into it and sharing your experience. I read in one of the reviews that it had a problem with hum. Not that the supplied tube in it was junque, but what you mentioned only confirmed my suspicions. If I get one I'll replace the existing 12AX7 with a Amperex "Bugle Boy", Mullard, or other more suitable tube with better sonic purity and stability. I've heard the Chinese tubes can go into oscillations and are generally not the best for audio preamp applications, etc. With a single dual triode controlling the thing it would seem reasonable that you'd hear every imperfection or limitation in the tube.

I mentioned it to a friend, who brought up a very good question, one that I had as well. If you download the owners manual, you won't see a schematic for the thing, or any that I could find in the manual I looked at. I have to ASSUME that it has a plate supply, and some form of bias supply, if they don't use gridleak bias as I ASSUME they would to keep cost down. Besides, IMHO, there's nothing wrong with gridleak bias. I also noted a lack of an on-off switch so I think the thing runs all the time. Maybe it was designed that way on purpose so they could make a few dollars selling replacement tubes.

I'm very skeptical, and appreciate the advice of a fellow AMfone member rather than someone who posted a review on their site or any other audio site.

I was given a internet provided $10 coupon on anything "Musicians' Friend" has to offer, so it would only cost me $19.95 plus $5 or so for UPS shipping charges. For that price I'll have to give it a try. I just can't understand how it could be offered for so cheap. One site claims they originally offered it in 1995, and that there are 100,000 in use. The one depicted in the link I provided seems to be the third generation version that includes a VU meter where the previous versions did not.

If for nothing else, it might provide a good testbed for checking out various brands of 12AX7 tubes - hi!

Regarding your hum problem, I understand it has a metal case, but question the amount of shielding it has in it. Perhaps you could carefully wrap the ribbon cable in aluminum foil to afford better shielding.

I'm curious, what material is the tube socket made from, or are the socket pins part of the perf board that everthing else is on? Also, do you see any evidence of what could be called a real plate supply for it?

Very Best Regards,
                         Joe Cro N3IBX
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Joe Cro N3IBX

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Vortex Joe - N3IBX
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« Reply #3 on: July 30, 2008, 09:49:07 AM »

We tried a Groove Tube 12ax7 which was awful. MID and more MIDRange. Then used an old Mullard which was noticeably fuller and nicer but both tubes had noise.
By the way, when replacing the tube (It said Made in China on it), be very gentle pulling apart the two piece housing as there are boards on both sides connected by ribbon cable which some heavy fisted tinkerers have ripped apart.

I'm surprised the "Groove Tube" was made in China. I originally thought they were "Sovtek" or "Saratov" provided like anything branded "Electro-Harmonix", etc. I stand corrected!

Groove Tube markets their tube line as budget replacements for the audiophile and musician who uses a tube amplifier, so it only stands to reason that they're probably "Shung Yuang" Chinese replacements that are rebranded. I've seen some very good work out of the ShungYuang factory, particularly with their line of 211's. I read somewhere they bought the original tooling that was used by RCA, and include a rather robust graphite anode like you would see in a VT4-C.
Other examples haven't been so good. They make just about everything; and their quality runs the gamut from absolute garbage to acceptable.
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Joe Cro N3IBX

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« Reply #4 on: July 30, 2008, 02:13:08 PM »

Hey Joe,

Actually, the original tube (not the Groove Tube)  in the thing was marked "Made in China."  The Groove Tube was one out of my collection and quite old, maybe 10 years or so but had not seen alot of use. I will take a look at the socket. Boy, at $20, it is well worth playing with.

I'm not a good enough tech to tell you what kind of bias or robustness of the plate supply.

I will tell you that the noise floor was high with both the groove tube and the mullard, but both those tubes were old from my collection. I've heard the JJ's are good and I have a guitar tube pre-amp with a JJ EC803, which is a 12AU7 I think. It sounds great and very quiet.

We didn't have time to put the ART through the paces. The hum was just too loud. We were using balanced XLR cables so maybe 1/4" cable or by tying the ground to an actual ground it could have been improved.

If you do purchase one, please post your impressions and good luck with it.

73
Mark
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John K5PRO
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« Reply #5 on: July 30, 2008, 05:44:15 PM »

Mark
I would think that for best hum immunity, using the XLR connectors and a balanced audio circuit would be chosen? Going to 1/4 inch phone plugs would unbalance the circuit in a studio.

I got one of these preamps for very cheep (a few bucks) from a SK's shack few weeks ago. I plugged it in, and the chinese 12AX7 didn't light. The tube has no brand name, just made in China stamped on it.

I assume that the plate voltage is very low, used in starved plate mode.

DO you have a schematic of this thing? I contact ART's support line, and they never replied for this.

John L
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Vortex Joe - N3IBX
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« Reply #6 on: July 30, 2008, 11:00:52 PM »


DO you have a schematic of this thing? I contact ART's support line, and they never replied for this.

John L
K5PRO

John,Mark,
             I want to see the schematic to see what it has, or lacks thereof. To come up with even a small plate supply to power the tube and everything it comes with, I just don't know how they do it. If I come up with a schematic or when I get the thing and actually try it out, I'll post my impressions and any pros and cons. Ditto on the brand tube that's in there and it's tested emission on my TV7. I'm particularly interested in how they bias the 12AX7. Gridleak would be my guess. Maybe nothing at all............

Regards,
            Joe N3IBX
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Joe Cro N3IBX

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« Reply #7 on: July 30, 2008, 11:48:50 PM »

I've used an "original" Tube MP (not the one with the meter) for a long time.  Beats me what the schematic looks like or which brand of toob sounds best .. one review I came across mentioned Tesla, but I never bothered to twiddle with it.

I bought it years ago because it was available where I went shopping and it was cheap.  I've had no noticeable issues with noise or hummmmmm (using the XLR connectors) with either an RE-20 or PR-40, or several other mics I used to have around here. 

Grant/NQ5T

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Vortex Joe - N3IBX
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« Reply #8 on: July 31, 2008, 01:46:26 AM »

Hello Grant,
               I don't know if it's a panacea for the hum, but I would think that balanced input to balanced output (and XLR to XLR) would be the best way to go. At least you'd have some control over thsese issues.

From what's been said on the board here, it soulds like the hum is related to poor internal shielding. Maybe it depends on ones' partucular choice of mucrophones and application.

Regards,
           Joe Cro N3IBX
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Joe Cro N3IBX

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« Reply #9 on: July 31, 2008, 09:52:33 AM »

Now that I think about it, XLR is best in that it lifts the ground from the audio. The third pin of the XLR is ground so I guess the case was shielded.

Maybe the audio Xfrmrs are cheap.  I do like the idea of a tube shaping the audio before any solid state device.

Maybe its me, but I can listen to my rig for hours through a tube audio amp, an old mono EICO and speaker. But listening through solid state amps, it is much more fatiguing to my ear. The noise and distortion seems painful so I can't listen as long.
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Vortex Joe - N3IBX
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« Reply #10 on: August 01, 2008, 02:03:50 AM »

Hello All,
           The ART tube preamp arrived today. Only two days from Kansas City,Ks. via UPS, and no shipping damage!

I got home late so I didn't have a chance to check it out, though I did unpack it to take a look to see what I got. It's a smallish thing that appears well made. I stand corrected in my one of my earlier emails in that it appears to be made in China, not Rochester,NY as originally stated. This confirmed my one suspicion. When plugged in, the 12AX7A tube does glow, as does the VU Meter. The meter light is so bright you could practically read it from across a large room. It has a "OPL" MOSFET type limiter, and a indicator lamp that will change from green to red when the limiter is in operation. It's power requirement is 9V@700ma, and the supplied wallwart is rated at 1 amp, which is over spec. No complaints with it thus far, but I haven't tried it out yet. I'll post more in a few days when I put it through it's paces. All of the switches and controls seem reasonably made with a decent "feel" to them. The pots have a nice sweep without any binding, and the pushbutton switches seem to actuate and have a reasonable "click" to them when depressed.

A couple of nit picks: The 1/4" female jacks are plastic, not metal, as are the male and female XLR connectors. This could be a source of hum or poor shielding as someone previously stated.

There is a manual, but no schematic as previously stated. I had hoped a schematic would have been included, but they state there are no user servicable parts albeit the tube. Hmmmmmmmm.

Best Regards,
                  Joe N3IBX
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Joe Cro N3IBX

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« Reply #11 on: August 01, 2008, 12:02:25 PM »

Hi Joe ... 9V ps sounds like other 'tube' preamps discussed here on other threads ... if you get a chance, see if the 12AX7 is actually pinned out or just sitting there ... dead give-aways are presence of op amps and small xfmrs ...beefus
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Ian VK3KRI
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« Reply #12 on: August 02, 2008, 09:42:58 PM »

I think this unit is similar to a number of other 'tube' pres. That is, uses a frontend of a couple of lo noise transistors in front of an op amp , feeding a tube with lo plate voltage to get  exagerated tube distortion, followed by a few more op amps to provide a low impedance out put.   There are probably no transformers in the audio path, which probably add more to the sound of a tube preamp than the tube(s) anyway.

Given that Joe probably has iron stashed away  that people would KILL for  to use in mic pres, I'd say that this unit might provide $29.99 worth of low effort gain,   which is great if that is what you want -Hell, I'd buy one in a pinch, the solid state front end is probably reasonably competent.  However If you want a pure tube pre, I'd say youll have to invest either more money, or time.                                                 Ian VK3KRI

 
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Vortex Joe - N3IBX
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« Reply #13 on: August 02, 2008, 10:31:04 PM »

I think this unit is similar to a number of other 'tube' pres. That is, uses a frontend of a couple of lo noise transistors in front of an op amp , feeding a tube with lo plate voltage to get  exagerated tube distortion, followed by a few more op amps to provide a low impedance out put.   There are probably no transformers in the audio path, which probably add more to the sound of a tube preamp than the tube(s) anyway.

Given that Joe probably has iron stashed away  that people would KILL for  to use in mic pres, I'd say that this unit might provide $29.99 worth of low effort gain,   which is great if that is what you want -Hell, I'd buy one in a pinch, the solid state front end is probably reasonably competent.  However If you want a pure tube pre, I'd say youll have to invest either more money, or time.                                                 Ian VK3KRI

 

Hello Ian,
            Good point! I really didn't need the ART MP preamp, though I could use it with one of my rigs, I looked at it as more of a diversion or "toy" aka: 12AX7 testing platform than anything else. I thought: "what could I loose for the money"?

As it turns out, I decided to hook it up and take it for a roadtest tonight and guess what? It doesn't work! I can hear a mild hum that tells me something is going on inside, but it doesn't amplify any one of over a half dozen different microphones I've tried. I also tried both the 1/4" phono jack AND the XLR inputs and outputs and came up with the same result. No VU meter schwing, no voice, no nothing; albeit a little hum. Rather than take it apart and investigate, I'll call Musicians' Friend on Monday morning and explain my situation to them and request a new one. My testbed was my trusty ART-13, and I tried a variety of impeadances to make sure the problem wasn't on my end.

I'm real curious given the parameters you mentioned with the low noise op amps, what the plate voltage could be to achieve a little distortion and or output from the 12AX7A tube.

I'll post here what happens, and the results of the (hopefully) new unit whenever it happens to arrive. Hopefully, I just got a bad unit and everything will be taken care of.

Mod-U-Later, hopefully with a little audio the next time - hi!
                                                                                Joe Cro N3IBX

PS: I'm starting to re-believe if you want a real "tube" speech amp, build something with a pair of 45's or 56's into a pair or even a quad of 2A3's to drive your modulator tubes!
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Joe Cro N3IBX

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Ian VK3KRI
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« Reply #14 on: August 03, 2008, 12:31:53 AM »


I knew I'd seen this somewhere....

http://bellsouthpwp2.net/b/u/buschjason/tubempstudio.pdf

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« Reply #15 on: August 03, 2008, 01:12:15 AM »


Ian,
     Good going! The schematic Is greatly appreciated! It appears to be just what you said it is, and it appears to run low plate volatge. Just enough to give a facsimile of tube audio distortion, but not a tremendous abount of gain from the tube itself as far as I can see from the schematic.

The schematic will help clear up a lot of mystery and unanswered questions by the manufacturer.

If they'll send me one that actually works, I guess it wasn't a bad buy for a microphone preamp, tube or no tube.

Very Best Regards,
                        Joe Cro N3IBX

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Joe Cro N3IBX

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« Reply #16 on: August 03, 2008, 08:09:24 AM »

I assumed it was for unity gain and not to bring mic level to line level. So not actually an amp but an audio "shaper" i.e. to give tube harmonic structure instead of solid state. Am I mistaken?

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« Reply #17 on: August 03, 2008, 08:28:47 AM »

I assumed it was for unity gain and not to bring mic level to line level. So not actually an amp but an audio "shaper" i.e. to give tube harmonic structure instead of solid state. Am I mistaken?



That's basically what it looks like to me. I had hoped for the tube to actually do the audio amplification, but due to the low plate voltage and the way they have the tube in the system (per the skizmatic) it's more of a enhancer/shaper like you mentioned.
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Joe Cro N3IBX

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« Reply #18 on: August 03, 2008, 02:28:54 PM »

hmmmm ... gottum hunch ... noted 48V plate supply but I believe you said 9V wall wart ...barring a small switching supply (not seen in schizmatic), how are they powering the plate ?  ... do you suppose they are using phantom power from a mixer ? ... may explain why only getting hum ...73...John
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« Reply #19 on: August 03, 2008, 02:37:07 PM »

Schematic posted on reply 14 of this thread, indicates the device receives 9 volts AC from the wall wart.   Has a 6-diode voltage multiplier, then a series regulator to provide the 48 volts for the plate and the phantom circuit.
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« Reply #20 on: August 03, 2008, 04:02:03 PM »

tnx Rick ... only saw amp stuff, my bad...beefus
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« Reply #21 on: August 03, 2008, 06:20:20 PM »

Who needs a 12AX7 anyway?  Use two 6F5's or 6SF5's.  Same amplification factor (100) and the average price from the tube merchants runs about $5 each, n.o.s., made in USA.  Slightly less compact, yes.  Come in metal or glass format.
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« Reply #22 on: August 04, 2008, 12:57:23 PM »

Hi Joe,
One of those cheap ART pre amps along with a cheap MXL mic and a Turtle beach/Santa Cruz sound card made a big improvement in my transmitted Skype audio when down in Mexico. Big difference over standard mic-pre in Computer Grin.
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« Reply #23 on: August 04, 2008, 01:08:23 PM »

Hi Joe,
One of those cheap ART pre amps along with a cheap MXL mic and a Turtle beach/Santa Cruz sound card made a big improvement in my transmitted Skype audio when down in Mexico. Big difference over standard mic-pre in Computer Grin.

Dave,
       I noticed that you can purchase a "MXL" condenshure microphonium at Musicians' Friend" now for the rock bottom price of $49.95. I was real tempted to pick one up to compliment my Behringer B-1 that I paid $99.95 for about 5 years ago when they were all the rage. I simply love the Behringer and would like to have a second one, hence, my interest in the MXL. They have another MXL with a price of $69.95, but the specs look the same with both mics.

Regarding the tube MP mic preamp, I called them today and got a return auth # for the one I have. Hopefully, I get a replacement one that's working.

What were your impressions of the tube MP preamp? Apparently it was a improvement over the one in your sound card, which is good to hear.

Hope you're doing well and good to hear from you!

Best Regards,
                 Joe N3IBX
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Joe Cro N3IBX

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« Reply #24 on: August 13, 2008, 04:35:16 PM »

Hello All,
           My replacement "ART" MP speech amp finally arrived this afternoon. I'll connect it to my ART-13 and post my findings here when available.

This one better work - hi!
                                 
Mod-U-Later,
                 N3IBX
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Joe Cro N3IBX

Anything that is Breadboarded,Black Crackle, or that squeals when you tune it gives me MAJOR WOOD!
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