Build Your Own Clone Message Board

For those of you who asked when I posted the build in the 'show-off' thread, here is the layout for this tiny little amp. Minimal parts, minimal fuss, good sound, and works great with effects:



C1: .1uF
C2: 4.7uF
C3: .001uF
C4: 220uF
C5: .68uF
R1: 10K
IC: NJM2073D
Volume Pot: B100K
Tone Pot: B10K

Find the smallest little enclosure you can and enjoy!

That is, hands down, the coolest layout artwork I've ever seen.

How the hell did you do that?

It's a mixture of photoshop, a scanner, and too much idle time on a Sunday morning!

I was gonna say that ...

Very sweet. Do you need anything other than garden variety power values for the resistors and caps or is this running @ 9V?

It runs off 9V, but I typically use a 12V wall wart since it was handy. I've been using Nichicon's "Audio" electrolytic cap series and I think I like them. Whether I can tell the difference or not is another story since I have yet to A/B the builds. Other than that, poly film for smaller cap values, and whatever is available the the LED's inline resistor.

I wonder if this would work okay with some type of dirt circuit as a preamp? I'm thinking a Rat or a Bluesbreaker or something. Could also do a Valvecaster for that hybrid sound.

Or maybe even have the dirt circuit on a bypass switch to emulate a two-channel amp?

Just throwing out some ideas.

It actually sounds golden when I play it with my BYOC OD II in front, so maybe that's a way to go . . . but because I am easily amused by lights I'm working the valvecaster angle right now.

I tried a JFET preamp and it really didn't add much to the sound. In fact, when played with effects (and, how else would you??) it sounded much better sans preamp. I'm thinking the valvecaster is the solution to that, but all I have to test with are a 12ax7 and a 12ay7 both of which are well-documented as unacceptable subs for the 12au7. I ordered a few on e-bay and now I'm waiting . . .

I'm also working on a variable gain control, but my prototypes aren't playing nice. This is where the LM386-based mini amps have the advantage over the NJM2073D - they have a built-in gain control. I have a lot to learn about how op-amps really work.

Maybe you can help me - one of the issues I have been havaing with the valvecaster is that the damn valve eats up so much current. I've tried resistors to limit the current to each section of the circuit but they almost immediately start to melting. I also tried a voltage regulator but that draws to much amperage, I think.

Any ideas on the best way to power up the whole kit and kaboodle with something like a single 18 or 24V wall wart?

What I meant, and maybe you got this, was to use an overdrive circuit inside the same box. So it would be like a complete little amp that gets dirty. Most small practice amps that have an overdrive "feature" sound like ass.

I was thinking that a 3pdt toggle switch could be used to pull the overdrive section into and out of the circuit. Kinda like clean/crunch channel switching on a bigger amp. Set the overdrive's volume to something fixed so it doesn't sound so lopsided when it's pulled out.

Tremolo would be cool to add as well. But the box will have to get bigger for that.

Do you think that would work?


I don't know if you can drop the current and still get a decent sound. When the Valvecaster craze first hit over at DIYstompboxes, a lot of complaints were resolved by using a beefier power supply (in terms of current).

The 2037 datasheet indicates that it will run fine up to 15v. A 12au7 is good for a lot more than that. So I'm thinking that at 12v 1.0a+ power supply would do the trick. But I'm certainly no expert on these matters. I just tinker...mostly without a disastrous outcome.

Yeah, I think I got you on the overdrive front, and I agree with you. It would make the amp a cooler toy, for sure, and a lot more versatile. I actually just got my 12au7 in the mail so I will try hooking that up tonight and see if it resolves the valvecaster issue. Otherwise I think I'll take your suggestion and just go with a standard overdrive - got any small, low-power type circuits to recommend?

Thanks for the suggestions on this, by the way, I have been hitting a little bit of a brick wall with it and some new thinking is exactly what it needs!

I'm interested to see where this goes, as I would like to try out this amp and see what you wind up with for a dirt section. Please keep posting progress!

I saw that you're selling kits of these for pretty cheap. Very cool idea!
-shane

Well - here's the first prototype for a preamp. It's not great, but it's a start, and it has some interesting, potentially useful sounds. I plan to tweak it lots more.



* - edit - CJ found an error here and the corrected version is posted below

You're layouts are..the...coolest. I have to try this.

Still new to schematics. What's the red thing that you're grounding after the 9v resistor?
-shane

LED. It's set up so that if the power is on, the LED lights up.

What value do you have for C5 on the original layout at the top of the thread?

.68uF - sorry, I missed that one. I'll edit it now.

Well, I breadboarded the top layout, and I get a spacey, octave fuzz kinda sound. Also, when I strum, the LED dims. Something ain't right.

rnagoda: I notice that the pin connections for the first layout and second layout (with preamp) are quite different. What's going on there?

I should probably take a look at the data sheet.

The pin connections aren't that different, but the input does go to pin 8 in the new versus pin 7 in the old. Everything else should be basically the same (except that I changed some component values).

With a preamp, the sound seems to be better going into 8. Without one it seems better going into 7. This makes no sense at all based on the datasheet (7 and 8 are the positive and negative inputs for one of the op-amps). You can do the breadboard tango a little to see what I mean.

Right now I have the boost-end of an electra circuit running into pin 8 and it sounds very nice. Run it into pin 7 and it it becomes ass-y. But my preamp-less build is the opposite - when I built that I went right into 7, per the datasheet, and it sounds fine.

I am not smart enough to understand the whys and wherefores of this behavior . . . any op-amp experts out there who care to comment?

If the LED is dimming though, I wonder if you have enough amperage? I am running successfully on a one-spot (9V, 1.7A) or 12V, 1A adapter.

In the first one, pin 2 is connected directly to 9v. In the second layout, pin 2 is grounded.

And in the first layout, output is take from pins 1 and 3, while in the second layout, output is take from pins 5 and 7.

Is the little round dot marker showing pin 1 in both layouts?

Oh yes - you are correct. The round dot marker is supposed to show pin 1 and in fact it misrepresents itself . . . crap.

So - in the first layout the pin 1 marker is correct. In the second layout - pin 1 and 3 are the output, pin 8 is the input. I will make the fix for the pin 1 marker.

Here is the correct version:

maybe this is a dumb question, but i was wondering if this could be used as a headphone amp.

Well - I imagine it could, but you'd have to do something about the output to headphones . . . what that 'something' is I do not know, but I've seen some similar builds where it is as simple as an in-line resistor to the headphone out. Never tried it though.

There are a lot of 'headphone amp' builds out there, I think it would be very easy to take a look at those and make the mods to this as you saw fit.

Okay - I've had another go at a preamp for this. Many goes, actually, but most of them sounded terrible.

Here's one that sounded pretty decent - it is a pretty standard booster front-end using a MPSA18 transistor to dirty things up a bit. I made a quick recording with it just to illustrate how it sounds (this is the amp on the breadboard, through an old Ampeg 1x15" cabinet, mic'd with an SM57): http://www.pedalbuilder.com/audio/NJM2073_v02_01.mp3 - for the recording is is straight into the amp for 95%, then some random idiocy involving what was on my pedalboard at the time. If I decide to pursue this particular design I'll make a better recording, but this thing sounds A-freakin-mazing with my OCD.

Anyhow - I'm looking for suggestions on how to improve this. I'd like a good sounding built-in distortion/overdrive for this. I tried a few things with this iteration of it, but it either didn't do anything (clipping diodes) or it sounded terrible (gain pot on the biasing resistor). Ideas?

Layout:

Here's yet another version. Some real improvements here, this one is verified on a breadboard, but I may not have the chance to build it until after Easter:



Large-size drawing here: http://pedalbuilder.com/layouts/NJM2073D_03_01_large.jpg