Hi there. If you have a quick moment...

Hi folks,

I've got relatively little experience doing DIY stuff. I've built the Hamptone and Tim Ryan's A12. The Paia tube mic pre thing.

The problem is that, after sending the A12 in to get fixed, it still had problems. It tested fine in the panavise, but mounting it in the box, it didn't get phantom power. I remounted it and it worked. I went back two days later and it didn't work. I'm suspicious because the front two chassis holes (seventh circle) aren't big enough to accomodate the size of the attenuators, so it's a weird fit...like the whole face plate bows!

I don't fault Tim at all for any of this, but I'm not sending it back. At this point, I'm sick of the fact that any one who understands mic pres on a base level absolutely has me by the balls.

MY QUESTION: Sorry...I do actually have a question. I want to understand and learn how to design mic pres, so that I can fix my own A12, even if that's six months from now. Is there truly good book(s) about electronics as they relate to audio and amplifier design? I have a giant electronics text that is good; it even addresses amplifiers, but I need something even dumber that also covers basic electronics concepts like reference vs. chassis ground...different types of pcbs...etc, etc. The problem is that I live in a small town, 3hrs. away from any city that might have a competent tech to lean on.

Any ideas, folks?

Thanks. I'm going to figure this out one way or the other!
:twisted:

The short answer to your question is no.

There are tidbits of info on specific audio application but no text that I know of that specifically teaches towards audio (I remember looking when I first started getting interested in this). You really just have to learn the basics of electronics and then experiment with circuits, study schematics, then when you get stuck ask someone with more experience (this forum is filled very experienced people). The audio world is (as someone recently said to me) a "black art" It's an ongoing process of learning from applying theory in experimentation--sometimes it works, sometimes it doesn't.

I realize that that isn't a very sexy answer. But unforunately there are no books called: "Learning how to design a mic preamplifier" But you have the right attitude. Keep at it. Try to learn the basics, and read, read, read, and study all you can.

Ya just gotta hang around here and lurk. If you follow what goes on, you'll get what you need.

Incidentally, if your problem is just lack of phantom, that's nothing to do with the pre at all, just 48V through a switch and two resistors... you don;t need to know a thing about mic pres to fix that problem!

In the PIAA pre that I looked at for a friend, it was just a CMOS oscillator into a diode/capacitor multiplier... that way it generated the 48V for the phantom and the plate on the tube IIRC.

Should be simple to fix unless I misunderstand your post and the problem is more than no phantom. -Make sure that ground is continuous all the way through by the way, otherwise dynamics will work, but phantom won't drive any powered mics.

Keith

> it didn't get phantom power. I remounted it and it worked. I went back two days later and it didn't work. I'm suspicious because the front two chassis holes (seventh circle) aren't big enough to accomodate the size of the attenuators, so it's a weird fit...like the whole face plate bows!

These are not mike-amp design problems: this is basic electricity (like a flashlight) and mechanical problems.

Works/no-works is usually a bad contact. Which is "electrical" but really mechanical (contacts are mechanical joints that happen to carry electrons too).

You can put an amazing bow in some PCBs. I had a Herc video card warped 20 degrees from end to end, worked fine for a decade (may still be working somewhere). But it is a Bad Idea, and when a board relies on mounting-holes for grounding it will give problems that may be very hard to find.

Thanks folks. I saw someone mention elsewhere a book called The Art of Electronics, that featured a student manual as well. Anyone know where I can find these?

The main issue with the A12 (most pressing, anyway) is that when testing, one of the 0v pwr supply leads (in the molex connector) came loose. Now, the pre only hum and you can definitely smell and feel heat from the card. I'm sure I've melted something, and now I'm at the mercy of troubleshooting something I don't understand. Shame on me for even trying I guess, but heck with it...I'm going to understand that goddamn thing and understand what it is I've done to fix it!

As far as grounding attenuators/xlr's to the chassis for operation...that's just strange. For some reason, it seems totally unnatural to me that external components are reactive with the exterior of a chassis. See what I mean? I'm a retard and it doesn't necessarily come naturally to me. Maybe that means I shouldn't try, but like I said...to heck with it.

Again, thanks...

kb

what you want to do is remove all the switches from the cards and possibly remove the xlr connectors as well. mount the switches and pots to the front panel and the xlrs to the rear. THEN cram the card in there and solder everything in place on the card. PCB mount components are nice and are a time saver, but just slapping them on has rarely not created mounting issues for me. If you do it like that, you arent putting any pressure on a solder joint and the card will sit naturally in the chasis without fighting where you thought the parts should go when you mounted them with the card on the vice, a little bit here and there can translate to a lot of pressure on a joint when mounted in the chasis. If you can measure 48v coming off the supply and you arent getting it at the card and all your components are good, its probably a switch not making contact or a solder joint some where along the line.

making a million mistakes and staying persistent is how I learned this shit, specifically how I learned the little tidbit posted above. Keep at it and one day you'll have half a clue and then be REALLY awed by the guys that really know whats going on.

dave

[quote author="thearnicasync"]Thanks folks. I saw someone mention elsewhere a book called The Art of Electronics, that featured a student manual as well. Anyone know where I can find these?
[/quote]
That was probably me. This book has its own website, with ordering information. It may well help you - it has stuff about construction, and in fact covers a lot of the fundamentals of audio design. It's the closest I've seen to a one-stop shop in terms of electronics textbooks. No, I'm not on commission...

But in terms of direct practical help, you could do an awful lot worse than hang around here - it's like having your own competent supertech on hand!

Kelly, what happened? :grin: Sorry to hear you're having such troubles, but with any luck there's been no permanent damage. First, fix the crimps on the power connector. If a wire has come loose, it means the crimps weren't right to begin with. The best thing to do at this point is to pull the contacts out of the housing and solder all the connections. That should fix any intermittent power problems. Second, it sounds as if you've jammed the panel over the shafts without reaming out the excess powder coating. Use a hole reamer or round file in the holes just until you get down to bare metal. The panel and chassis holes are perfectly aligned with the board, so you shouldn't have to use Dave's trick. The tolerances are close, but everything will fit without the panel or the circuit boards bowing. If you still have troubles, let me know.

-Tim

Thanks a lot, everyone. I'm studying each response carefully!

Thanks Tim, but even after fixing the power (molex), and testing for proper voltage on each pin, the pre is still just humming. Can you believe this shit? Also, the pre is noticably warm. I probably blew the op amp again? I'm still getting voltage on the the op amp pins (approx. 18v on each).

I'll keep on this over at the seventh circle site. I just feel like such an idiot that I don't want to bother you with this anymore. I may, though, if I really can't come come up with anything after scouring the world for info.

Again, thanks to everyone.

kb

hey kelly-

take it slow! When I started this stuff there wasnt much about it that was intrinsically obvious to me, realize that you are basically learning a whole new language so go easy, try not to let yourself get too frustrated and you'll be able to make the thing work and when it does, all the agrivation will be worth it.

dave

Tim IS the Tim you want to talk to. :wink: :wink: (7thO) PM him, Maybe That will get to more specific issues about continuity and metering that may solve your fault without you having to send it in to tech support. I received help from tech support (mindprint) that gave me pin to pin continuity or voltages at specific points that should be available to do some trouble shooting. Setup voltages and test voltages etc. Tim, does the kit have setup test notes?