Help with mod?

famous beagle

Well-known member
This is also pertaining to the mod in my earlier post, but this isn't a simple matter of a lifted trace.

There seems to be some contradictory information in the directions, and I'm wondering if anyone (with much more knowledge than me) can help me out. This is a mod for the ART Tube MP by Black Lion Audio. It's quite old (from 2004), and though I've contacted them about it, I'm doubtful I'll receive an answer.

I’ve attached a PDF to illustrate my question. It relates to what is done to pins 1 and 2 of U1. Here it is:

At the bottom of page 1 on the attached PDF (Note: this isn’t the original page 1 of the mod; I just extracted the relevant pages), it seems to say that the same procedure is performed for both U1 and U2. In other words, the 1k resistor and 2pf capacitor are soldered together and then soldered to pins 1 and 2. (See text encased in red rectangle. The text referring to U1 is in the green oval.)

But then in the list of directions that follow (“Here’s what needs to be done, in order:”), it seems to suggest something different. Here, it says to solder the 1k-2pf RC network to pins 1 and 2 of U2. But then it says to only solder a 1k resistor to pins 1 and 2 of U1. (Again, this is in a green oval.)

Also, the picture on page 3 of the PDF only shows a 1k resistor attached to pins 1 and 2 of U1.

So I’m confused. Am I misunderstanding something? Which is correct? It seems to say two different things, yes?

U1 and U2 are both LM6172 chips.

Thanks for any help
 

Attachments

  • Art Tube MP mod - question.pdf
    785.7 KB · Views: 37
Yeah I’m thinking there may be a typographical error or two there. I’m not sure I can figure it out. But for sure I can’t without the full instruction set and the schematic. Do you have those?

[EDIT]

Like what I’m wondering is if there is an instance in the instructions where “U2” is supposed to be “U1-2”, the second side of U1...but I need to have the full instructions and schematic so I can follow along on the schematic with the instructions.
 
I do have both of those things. Here you go.

Note that this mod is for the original ART Tube MP, whereas the schematic is for the ART Tube MP Studio. I couldn't find the original ART Tube MP schematic anywhere.

I have the MP Studio. From what I can tell thus far, the schematics are pretty much identical. Every part that's been called for in the mod has matched exactly. I think the only difference between the two units is the addition of a VU meter and a limiter on the Studio.

Thanks!
 

Attachments

  • ART Tube MP Modification - Black Lion.pdf
    1.3 MB · Views: 30
  • ART Tube MP V3 schematic (for reference).pdf
    54.9 KB · Views: 26
I have the Tube MP OPL...its kind of in between the original Tube MP and the Tube MP Studio. The Tube MP OPL does *not* have the VU meter, but it *does* have the output limiter (hence "OPL"). I've actually found it to be a great bit of kit to have around. I think it sounds nice for mics and as an instrument preamp and they can be found pretty dang cheap...very portable...a convenient and nice performing problem-solver that's easy to tote around. And the circuit itself is a nice little design...single-ended power supply, discrete interstage on the mic amp, and they used relatively big coupling caps which means potentially better low-end or at least coupling caps aren't going to get in the way on the low-end as much as maybe on some other designs...the trade-off is potential impact on HF performance with a larger electrolytic caps, but they're not unreasonably large in value IMO and the quality and spec of good quality low ESR caps these days make that essentially a non-issue for all intents and purposes.

So here's what I figure with the instructions...there is a relatively harmless typo, and a much more critical omission to a part reference. I refreshed my memory on the circuit design and walked through that with the upgrade instructions you attached, and the instructions do a pretty good job at setting up the what and the why and then the how. Based on the whats and the whys I could then anticipate the hows and then see where they were not consistent with the written instructions. In the green oval on page one of your instruction guide excerpt, and this is just a mention, it references pins 1, 2 & 7 of U1. That should read pins 1, 2 & 3. They are talking about the "first half" of U1, but pin 7 is the output for the second half. pin 1 is the output for the first half, and pins 2 & 3 are the inputs. Then follows the instructions regarding installing the 1kOhm/2pF R-C network between pins 1 & 2 of U1, and interrupting the trace between those two pins. This is a good instruction and what I believe is intended for you to do because they explain above why this modification is recommended and then they say the first half of U1 "also needs" the R-C network...in context this follows the instruction to install the R-C network on U2, so they intend for you to do the same thing to the first half of U1 as they instruct you to do for the first half of U2. As to the green oval on page 2 of the instruction excerpt, this is where I believe there is an omission. I think it is supposed to say "Install 1k-2pf RC network across pins 1 and 2 of U1." They just told you what needs to be done and why and how above on page one. I'd go with that. I, like you, would still wonder and *really* want verification from the designer. But...If it was me I might likely pull the pin and go with what my determination is on this...while still trying to get a response from Black Lion. YMMV.
 
Yeah that's what I think I'm going to tonight. I was making great progress on this thing until I hit that snag.

Thanks much!
 
Back
Top