My-very-first-gadget (tm)

Hi everyone,

Actually i'm a bit scared about this first post, because i know i am venturing into a brand new territory for me. I have no experience with electronics other than fixing a cable here and there, and i am not particulary good at it either. Soooo....

I know there's some beginners guides around, but it still seems very complicated, and the tech-talk usually throws me off very early in the reading. Besides, i would hate to spend an awful lot of money on projects i never should have started in the first place.
Once, as a kid of course, i "fixed" my mommas stereo. Since then i have not dared to unscrew anything except my computercase to install a new card...

There.. I think that's settled now. I know absolutely nothing about electronics, but i am willing to learn.

My long-term goal is that someday, i would be able to make a Gyraf G9 or some other high-end device for my studio, but for now i was thinking of something simple (the DI box perhaps?).. Reeeaallly simple! And cheap too, if it turns out i'm all thumbs with a solderer (soldering machine? Ah, english is not my first language, so sorry about that!)..

So, besides from getting all kinds of books off the library, what should i start with? (I'm a learning-by-doing kinda person.. Books dont suit me that well, i'm afraid..)

Start here:

http://www.groupdiy.com/index.php?topic=1277

Then just stick around and keep reading...

Yeah, thats where i started.. I ended up even more confused, and actually a bit discouraged about me trying out some DIY.
Searching for "newbie" and "beginner" on the forum actually gave me a little more hope about my future projects.
I'm still a bit hooked on the passive DI box that people have been talking about, and with my (poor) diagram reading skills, it seems like a pretty simple device.. The Green preamp looks nice, but it's probably too big a project to take on as a novice..

Well.. I'll follow your advice and see if i can avoid getting lost in all that info. :green:

It's called a soldering iron in english. I hear Weller makes good ones. The Radioshack ones are almost impossible to do a good job with in my experience. You should read Eddie Cilletti's articles on soldering for a good introduction. Search here: http://www.tangible-technology.com/

[quote author="Family Hoof"]It's called a soldering iron in english...[/quote]

Right, thanks! I actually knew that, just couldn't remember it at the time!
Anyway, i've been reading, taking notes, finding a provider for the various bits and pieces, looking at diagrams ect. and i am pretty confident that i actually can do this stuff if i just take it slow to start with.
After reading some more, i got pretty hooked on the Green Pre. A lot of people use this as a DIY pilot project as far as i can see. The DI box would be simple, but i could really use another pre or 2, so that could probably inspire me to finish the job as well :green:

> Ah, english is not my first language, so sorry about that!)..

Your english is fine. Better than most americans write their own language. If you can't think of the english word for a thing, use French or German-- it always sounds good in english. Or Danish: lots of Danes around here will translate.

> no experience with electronics other than fixing a cable here and there, and i am not particulary good at it either.

Building a Green or Gyraf is like fixing 300 cables, except many more ways to connect them wrong. If you can't make a good solder joint, get a good soldering iron and good solder and practice. Fix every wonky cable in the studio (that's how I started, and I still use some cables I fixed 30 years ago).

While newbies have built Greens, I think there should be something like the old one-tube radio. A very simple yet very useful design that could be built on brass tacks in a board, and explained in a paragraph. Would anybody build it, or just sneer "That's too simple to be good!"?

1 valve radio?!!!!
Spill the beans!! :shock:

chef

If you want to learn to solder without risking to destroy expensive pcb's and components you could do what I did;

Buy a good soldering iron/station and get an old broken stereo or some other electronic device and spend some hours trying to get some components off the pcb's and on again without making too much of a mess. You can also buy some stripboards and try to solder some of the pieces from that first project on these. It's great fun and you dont have to be carefull so you can try out different ways of soldering stuff without breaking expensive gear.

The stereo you use should be old. The newer gear is full of surface mount components and those are smaller and more difficult to solder right.

if you play guitar here is a simple project I designed and gave to Aron for a beginner project at his site.

http://www.diystompboxes.com/forums/stompboxforum/

Look in the beginner project

There are a few things going on in that circuit that can interact with a guitaer in a nice way. Transistor Hfe and how the Hfe changes with Ic can make a difference.


I have thought it might make a fun DI with a EF and transformer added after the gain stage and using a zener regulated supply from the 48V. It was designed for 9V.

Hi Sylle,

And welcome to "The Lab"..!

You're right, we should have some projects for "absolute beginners".

I was thinking maybe a line driver/splitter for guitar/bass. Those always come in handy..

Jakob E.

I would say that a few stompbox projects couldn't hurt. The thing is, there are several very good DIY stompbox pages out there already:

http://www.diystompboxes.com/pedals/index2.html
http://www.muzique.com/schem/projects.htm
http://www.generalguitargadgets.com/

The more stompboxes, the better, I say. :green:

[quote author="PRR"]> While newbies have built Greens, I think there should be something like the old one-tube radio. A very simple yet very useful design that could be built on brass tacks in a board, and explained in a paragraph. Would anybody build it, or just sneer "That's too simple to be good!"?[/quote]

How about a one-tube preamp?


As for one-tube radios: believe it or not, there's a whole subculture devoted to one-tube regens. I know I've seen a couple of websites.

New York Dave's preamp design would make an excellent first project. Keep in mind, though, that it has a gain of about 39dB front to back (assuming a 1:10 input xformer). That means its input clipping point will be about -24dBu, good for ribbons and dynamics, low for condensers. So if you plan to use it with condensers, build a couple of in-line pads too. You can always not use them if you want a little clipping to thicken the sound.

Very nice design.

Peace,
Paul

I am in a similar scenario to Sylle. I had to quit college after I discovered I was colourblind and being a Naval school you would never have been comissioned without a good medical. My electronics experience was totally amateur after that. I am fine on guitar electronics but I want to start doing some serious stuff. I am going to build a G7 with a board from Gustav (ordering today) but in general I think that it may be an idea to follow Mendelts lead and learn how to manipulate an iron correctly. I am a fan of Antex irons. With regard to learning to solder I really recommend Rev. G.C. Dobbs instructions on the inside cover of the Ladybird book "Making a Transistor Radio" I will try and drag out a copy of it as it is good. I like the look of LuLu the Spacecat's Mic pre too, it is real painting by numbers stuff and helps you blow by blow. Here's the link...

http://webpages.charter.net/altaflux/

Regardless of what you end up doing; Good Luck!

I'm gonna build that dave preamp, if I can figure out a way to generate a decent B+ with the power transformers I have lying around!

Also I don't have any decent audio transformers :/

[quote author="tmbg"]Also I don't have any decent audio transformers :/[/quote]

Then build it without the transformers, set the input resistor at 1M, and use it as an instrument preamp. I bet it'd be a dandy, and it'd let you get your feet wet while you look for some nice iron.

Peace,
Paul

What I did was to buy a cheap 12VAC plug in wall transformer, then used an old 220VAC to 9V transformer and wired it backwards. Through a bridge rectifier it gave me 300V for the plate voltage. It was cheaper than using a dedicated transformer.

Plus it freaks people out to see a real tube preamp that uses a wall wart.

CA

Paul, thanks for the kind words about the single-tube preamp. I should emphasize that this is a "circuit idea" (see the verbiage on the schematic), not a tested design. It is similar enough to other circuits I've built, however, that it should work pretty much as predicted.

The 12AV7 seems an unusual choice, but it's a favorite tube of mine lately because it's low-cost and is capable of medium gain with low plate resistance. It's great for those instances where a 12AU7 would have too little gain, but a 12AX7 has too high of a plate resistance. (I rarely use 12AT7 because it's pretty nonlinear, for a triode).

The feedback resistor (100K in the posted example) could be reduced somewhat for less gain. You can't go too far or it will load down the output plate. Increasing the feedback does reduce the output impedance, but there is an irreducible minimum load that a tube can drive to a given level regardless of the amount of feedback. This limit is imposed by the current-handling capability of the tube. But we can play around with it a little if we don't need maximum output capability under all conditions... See below.

If the ability to drive 600-ohm loads is not required, and if an unbalanced output is acceptable, the output transformer can be eliminated if the load impedance is going to be 10K or higher. This will net an increase in level of 12dB, with a maximum output of about +27dBU. You could use more negative feedback, then, for a given net gain.

An off-the-cuff idea for implementing variable gain: change the feedback coupling cap to 2.2uF (or greater) and replace the fixed 100K feedback resistor with 8.8K in series with a 100K pot. At minimum gain--with the pot shorted out--that low value of -fb resistor will load down the plate, but the lying-assed simulator tells me that under those conditions, it can still do about 12VRMS at the output plate before reaching 1% THD.

A reverse-log pot would be preferable, if you can find one in that value. For more precise gain control, a stepped control would be better, but then we're drifting away from the goal of simplicity...

[quote author="NewYorkDave"] The feedback resistor (100K in the posted example) could be reduced somewhat for less gain. You can't go too far or it will load down the output plate. Increasing the feedback does reduce the output impedance, but there is an irreducible minimum load that a tube can drive to a given level regardless of the amount of feedback. This limit is imposed by the current-handling capability of the tube. But we can play around with it a little if we don't need maximum output capability under all conditions... See below.[/quote]

Yes, that's the universal problem of feedback-pair designs: the tradeoff between keeping gain within bounds and keeping loading within bounds.

If the ability to drive 600-ohm loads is not required, and if an unbalanced output is acceptable, the output transformer can be eliminated if the load impedance is going to be 10K or higher. This will net an increase in level of 12dB, with a maximum output of about +27dBU. You could use more negative feedback, then, for a given net gain.

An off-the-cuff idea for implementing variable gain: change the feedback coupling cap to 2.2uF (or greater) and replace the fixed 100K feedback resistor with 8.8K in series with a 100K pot. At minimum gain--with the pot shorted out--that low value of -fb resistor will load down the plate, but the lying-assed simulator tells me that under those conditions, it can still do about 12VRMS at the output plate before reaching 1% THD.

Click to expand...

Maybe. As you say, it's a lying-assed simulator, and I'd want to see a real test before I believed it. My experience has been that a load that low (and don't forget the load it's driving -- if that's 10k then the total load is something like 5k) not only generates distortion at a lower level than most simulators predict, but also generates distortion with a lot of high harmonics, which is quite unpleasant. I think I'd be more inclined to leave the gain higher and pad the input.

A reverse-log pot would be preferable, if you can find one in that value. For more precise gain control, a stepped control would be better, but then we're drifting away from the goal of simplicity...

Click to expand...

Reverse-log? In this application, wouldn't regular log be the way to go? Reverse-log is normally used for gain control only when the pot is in the other end of the feedback chain.

Peace,
Paul

Paul, it looks like you were right regarding the taper of the pot. When I crunch the numbers, I end up with a curve that's certainly closer to log than to reverse-log.



It looks like a 20% log pot (if you could find one) would give the smoothest response. A regular 10% log should work OK, but not as smoothly according to these numbers.