Yoholo 25 Watt amplfier - suggestions?

[JKowalski]

I'm working on a LM1875 based 25 watt guitar amplifier. I'm housing it in a data switch box (I have like 10 of those things, this one was larger then the others).

Here are some pics so far. The backplate is a new peice of aluminum I machined (meaning painstakingly by hand, with a file, sandpaper, and a hacksaw ), that covers up the various parallel port holes that are leftovers from the boxes original use. That means I had to drill/file TWO humongous rectangles into different peices of metal... painful! The front mockup looks quite boringly white because I haven't gotten around to drawing artwork for it yet. The LED bar graph in the mockup will be a signal strength indicator, just cause it looks cool! I still need to hunt down a LM3914 for that.



Now, the reason I posted this in it's 1/4-finished state, is that I am designing a preamp at the moment, and was wondering what I should put into it!

If you notice, there are seven knobs total. The leftmost big knob is the volume (of course!), the top three knobs are going to be the bass, mid, and treble of an active EQ, and one of the bottom knobs will be gain. So I have two knobs left, what should I do with them? What other knobs do you guys find most useful (or just plain fun) in an amp?

[newfish]

Hiya.

Nice Box... 

Maybe use one of the extra knobs for an effects send.

...perhaps some sort of crazy ugly-face oscillator?

[teemuk]

Compressor, reverb, phaser, chorus, vibrato... some sort of "power scaling"?

[anchovie]

Contour for one of them (could just be a pot in place of the slope resistor if you're using a Marshall-style tone stack).

FX level if you've got room for send and return jacks in there!

[JKowalski]

Thanks for the ideas so far guys,

No way I can do a send/return. My chassis space is massively cramped. And today I just realized I forgot to do a headphone/line out! I'll have to put that in, of course, and I might just use a 1/8 jack for that. (headphones) I'll see.

I'm probably going to do a three band EQ rather then a passive tone stack. I'm going to play around with each on the breadboard and see which I like better. That's an idea though, a tone control tweaking knob..

Teemuk, your suggestions are way to complex! I do have alot of room, but it's gonna get cramped pretty quickly. You mentioned vibrato, and tremolo just popped into my head - thats an easy addition... I can't believe I never thought about that. Still kind of iffy on that though, anything else?

I'm not sure what you mean by "power scaling"? Elaborate?




Also, if anyone has any schematics for a simple bar graph display driver that doesn't use the LM3914, please share! If I can't find anything simple, I suppose I could order one from digikey.

[Jarno]

I am also building something like this but with a assembled PCB I bought off of eBay, it houses 3 LM3886's for 150watts (it's a bass-amp). Like yours, the enclosure is recycled (something I got during a dumpster dive action). The mains transformer (300VA toroid) is giving me major headaches. Moving the heatsink outside is a good idea, originally I planned to have it inside and add fans, but that's just not going to fit.

[JKowalski]

Yeah, my transformer is going to barely fit as it is. I was originally going to mount the heatsink internally, but then I realized that that would be a pain to cram things in there - I need a big preamp board, a power supply board, the amp board, the switches sticking into the box, and the huge transformer (comparatively, to the box). And don't be fooled, this box is smaller then my hand

The only problem with mounting the heatsink outside that I see in your case is you can't really fan-cool the fins - 150 watts is going to get dam hot, and fans do help considerably, even a small one.

[sean k]

A noise gate is always handy and an orange squeezer makes a simple comp.