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first amp build - choice of pre-amp and some really stupid questions

Started by incurably_optimistic, March 05, 2016, 05:22:41 PM

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incurably_optimistic

I'm using a 2A slow-blow fuse for a 150VA toroidal transformer, I think that's a proper rating (Rod Elliott suggested a 2A slow-blow fuse for 160Va toroid, and he's The Man).

Alright, so I'm slowly finishing the bench power supply board, here's how it looks like right now:


And I've figured out a problem with an enclosure! I didn't have any metal box for the bench supply, but today morning I went to a local market just across the street and some guy was selling a lot of old junk, including an old power supply for a PC, so I bought it for an equivalent of 2$. I didn't really check it, but it looks like it may work, so there's a lot of components to salvage from it, and I got an enclosure for really cheap (with a switch and even a fan!), and that's how it looks like:



In the meantime I have been working on the power supply wiring for my beloved first amp, and this is where I'm at right now:

here's a closer look:



for the AC part connections I used the Faston terminals (is this the correct phase in English?), but I didn't really trust them so I soldered them together just to be able to sleep easily.

incurably_optimistic

hello again!
Just stopping by to say where I'm at right now with my amp:
once again I didn't really have much time lately so the project haven't moved that much, but at least I finished my bench supply! Here's some photos:
that's how it looks on the inside:

I left the fan from the PC supply in place, and even got it working - not sure if it helps dissipate any heat at all, but hey, at least it looks cool!

here's a look at the fan:


after I finished this thing it was terribly ugly, so I decided to make it look less sad. The quickest way is of course using letter-stickers!

it's not that it looks beautiful now, but hey, at least I tried!

and a look from the front:



On another note, I've also finished the power supply for the amp:


It works as it should - with no load it measured +-37VDC, phew!

Since the pre-amp and power-amp are already done, I just have to wire it all together now and the "head" part will be ready - but it's also the part that I dislike the most, so it'll probably take me lots of time! Ah, and I have to get myself a heatsink for the LM3886.

exztinct01

I'm envious  ;)
I haven't even finished my LM1875 amp yet because of family problems.
Although, my first project, the Ruby amp is already done and working, yet uncased. I just finished it yesterday.
It's hard to finish a project when you don't have a personal power drill. I hope I'll be able to buy it soon.

Anyway, your build looks great. I really am envious  :dbtu:
+1
~ Stephen

incurably_optimistic

Thank you! But there's nothing to be envious about - it looks nice because as for now it's just a PS, once I wire everything up I'm afraid it's going to look like a hot mess, "neat wiring" is something I've always struggled with  :-[

Yeah, I know how hard it is to finish - before I started I thought the whole thing wouldn't take me more than month to finish - after all, it's just three simple circuits (PS, preamp and power amp) - I mean, how hard could that be to put it all together? But when I think I'm finally ready to proceed I find out that I'm still missing something - be it a 0,1R 5W resistor, a zener, connectors or something else - it's already been more than 1,5 month and the end still isn't near  ???

Oh, and speaking about Ruby - I couldn't wait for the whole project to finish, so in the meanwhile I made myself a modified version of the Ruby called Noisy Cricket:

I guess it could be less noisy if I put it in a metal enclosure, but whatever, I only use it for playing on my headphones and it works just fine  :dbtu:

Good luck on your project!

J M Fahey


exztinct01

Hey incurably_optimistic, recently, I was actually looking for a pcb layout of the P27 preamp by Rod Elliott. I swear I have read this thread before but somehow at the time I was starting to build the preamp, I forgot you've already done that in pcb. I'm glad I read this thread again. Can you please share your pcb layout of the P27 preamp? I just finished a layout yesterday but it occupies a large area of copper clad and so many spaces are wasted (pcb layouting is just too hard for me right now).
Also, can you please tell me which components you tweaked, removed or added, and what are their new values now. I'm still in protoboarding and testing, so I'll try different values for some components.

Add: Can I also have your pcb layout for your bench supply?
~ Stephen

incurably_optimistic

#36
sure thing! Sorry for not replying for so long, here are the files.

Regarding the bench supply - you probably need to drill a few more holes in the "GND" section from what I remember, also make sure to use a 10uF capacitor instead of 2200uF AFTER the regulator, as suggested by photo! Keep in mind also that the PCB is designed for a specific radiators I had for the 317 and 337. If you want to make some changes to the layout I can post a whole EAGLE project.

As for the preamp - sorry man, I just don't remember the specific values i put in there because I soldered most of the elements right after I took them from my breadboard  :-[ but I don't think I've changed much, maybe a few slight changes in values of caps or resistors here and there to achieve more bass that I like, I don't think I removed any components. But here's the layout I used - I don't think it's any good, I just tried to keep it small, but maybe it'll be of any use to you. Sounded alright when I tested it so maybe it's not that bad after all.

EDIT: Oh, and one thing - there's a misleading caption on the bench supply layout - the TRANS-GND pad isn't actually the 0V from the secondary winding of the transformer - it's the MAINS ground that is connected to the chassis. The 0V from the transformer should be connected somewhere to the big ground area in the middle, probably somewhere between the four 2200uF filtering caps.

exztinct01

 
Quote from: incurably_optimistic on May 01, 2016, 06:33:50 PM
EDIT: Oh, and one thing - there's a misleading caption on the bench supply layout - the TRANS-GND pad isn't actually the 0V from the secondary winding of the transformer - it's the MAINS ground that is connected to the chassis. The 0V from the transformer should be connected somewhere to the big ground area in the middle, probably somewhere between the four 2200uF filtering caps.
oh yeah, I noticed that earth isolation assumed as connection to center tap

Regarding the preamp, I'll just follow Rod's suggestions for tweaks in some resistors and capacitors. Also, thanks for the files man. I'll probably just stick with these as I don't really use eagle. I only use fritzing and diylc. I can manage to make some changes in the layout if needed.
Again, thanks  :dbtu:
~ Stephen

incurably_optimistic

I have a few AVR microcontrollers lying around, so I think I'll add a digital voltmeter circuit and a LED screen to the bench supply so I don't have to measure the voltage myself everytime I want to use it. If you're interested I can post the code and schematics when I'm finished with this.


Whooops, I just realised this is getting terribly offtopic and not really solid state amp related - I better get back to the amp wiring (I still don't have insulated wire for the inputs and outputs)  :duh

J M Fahey

Don't worry, we haven't really deviated ... yet  8|

You'll lose audience (I think)  if you fill page after page of obscure (for us)  code and what you expect it to do, including endless "version mods" :trouble, but a nice finished project for a voltmeter or any other useful add on , including a PCB design and easy to download and burn code , a fully finished and tested package, will in fact be welcome. <3)
Just open a new thread for it so those interested can have all together in one place :)

exztinct01

Quote from: incurably_optimistic on May 02, 2016, 02:46:01 PM
I have a few AVR microcontrollers lying around, so I think I'll add a digital voltmeter circuit and a LED screen to the bench supply so I don't have to measure the voltage myself everytime I want to use it. If you're interested I can post the code and schematics when I'm finished with this.
Agree with Juan. I think few people here are into codes and programming. Still, i'm interested since this will make measurements easier, and I do have some microcontrollers but I don't know how to program and I don't think I have the tools for it either unless all it needs is a computer and a software.
Quote
Whooops, I just realised this is getting terribly offtopic and not really solid state amp related - I better get back to the amp wiring (I still don't have insulated wire for the inputs and outputs)  :duh
don't power supply wires, pots wiring, need insulated wires too?
~ Stephen

exztinct01

Just entered my mind, why not buy a cheap multimeter or voltmeter for the sole purpose of measuring output of the bench supply.  8|
I'm using a cheap multimeter and it's pretty accurate when measuring voltage, so I think that will do for me  :tu:
I can attach it permanently to the bench supply
Just a thought, hehe
~ Stephen

J M Fahey

True, $10 gives you a very good, already calibrated and housed voltmeter.
Doubt a homemade one can be made for such a low price.
"Economies of scale".

incurably_optimistic

Quote from: J M Fahey on May 02, 2016, 04:51:01 PM
You'll lose audience (I think)  if you fill page after page of obscure (for us)  code and what you expect it to do, including endless "version mods" :trouble, but a nice finished project for a voltmeter or any other useful add on , including a PCB design and easy to download and burn code , a fully finished and tested package, will in fact be welcome. <3)
Just open a new thread for it so those interested can have all together in one place :)
Sure thing - I won't bother you with any posts about this until I'm done with the whole thing (but hey, the code will be awfully simple! You can measure 0-5V using AD converter, so you have to bring the voltage down using a voltage divider and then view it on LED display  ;) ).

Quote from: exztinct01 on May 02, 2016, 05:41:54 PM
don't power supply wires, pots wiring, need insulated wires too?
Damn it, of course they do, what I meant was shielded wires - I always confuse those words for whatever reason.

Both of you are probably right and I think this will be an overkill, but when I think about it, I think I prefer to have the meter built in the enclosure - it takes less space, you don't need to connect it every time you want to use the supply - it'll just be more convenient for me. And it's just a fun thing to do! Most reasonable people (that doesn't make amps for a living) would probably buy a pre-made guitar amplifier instead of wasting time and money on a DIY thing, but that's not why we're here on this forum  ;)

About the price - as we all probably have a lot of resistors and capacitors (and this project will call only for a few) the only components you really need to buy are micro controller atmega8 (I think it costs around 1$) and a LED display (even less than 1$). When you factor in the PCB, etchant, wires I think it's reasonable to assume the whole thing won't cost more than 5$ so it's not the end of the world.

But I'll finally shut up about this stupid idea I had and get back to amp-related stuff  :dbtu: sorry for littering this thread

exztinct01

 :) to be honest, I prefer diy projects too compared to buying them. But, some things are better bought than built at home.

Anyway, if you're done with the amp, can you please upload a sound clip? or a video clip? It would be nice to hear it in different settings and setup, maybe one with a distortion pedal, or the integrated distortion in the preamp, the clean sound, compression  :dbtu:
I'm not pushing you to do that though, just a request :P
~ Stephen