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.

That's where the problems with english not being my first language appear!

I don't want to burn my house down! (I live in a block of flats, so a lot of homes would be burned that way, and I don't want to do that! :trouble )
What I meant is that of course I am going to put a mains fuse there (in fact it's already in the power switch), but the question was: I have a mains fuse, do I need the fuses on the +-35V rails? Sorry for the confusion!

I understand your answer as: you don't have to, if your output power is small - but with 50-70W available i think I'm gonna go with the fuses, thanks!

and by the way - should I put the fuses between the power amp section and the +-35V rails of power supply like Rod Elliott shows on his schematic? Is it necessary if I have a fuse between the mains cord and the transformer?

thanks for the tip!  :tu:
I thought you cannot go too big with the power supply caps, but apparently you can. That fixes the problem - now I do have enough 2200uF caps, so I'll solder all the components today and see if it works.

Thanks mexicanyella! I'm not done with my spamming just yet.

I've been kind of busy lately with some non-amplifier stuff, but I've done some things here and there. First of all, I've etched and populated the PCB for the power amp section:

(sorry about the photo quality, but the the camera in my old mobile phone is pretty awful.)

I wanted to get the reverb tank running, but I cannot get the 8ohm:1k transformer anywhere in my country. I don't want to give up so quickly, so I've decided to try the discrete circuit from ESP, figure 6 on this page http://sound.westhost.com/articles/reverb.htm . The bad thing is that this circuit requires a +-35V rails voltage and I still don't have a bench supply, so I didn't know how was I gonna test it.

But hey, I realized that I have a spare +-18VAC transformer from the broken amp, so I thought that maybe I should make myself a bench supply. It wasn't gonna give me +-35V required for this project, but +-25VDC should work at least a bit.

So I've decided to make a simple regulated supply using lm317/337. Here's the schematic:


I've etched the PCB and started populating it, but then I realized that I don't have enough 2200uF caps, so I stopped there:


I don't have any enclosure for this supply yet, I guess that for safety reasons using a plastic enclosure for a PS is not recommended?

I'm afraid you're right phatt, I gave up fighting with the reverb tank way too quickly. But I was really annoyed, because it's third or fourth time I try to make the damn thing work and everytime I fail miserably.

I know that the transformer should be of particular type, I just tried all the transformers I have around and apparently none of them was suitable for this circuit. Right now I'm looking for the 8R/1k transformer, but can't find it anywhere in my country.

I hope it doesn't take me 8 years as everything should be much easier with your help and all those circuits, but I'm going to make this thing work, if only because it pissed me off so much that I cannot leave it unfinished  xP I'm pretty busy with other stuff at the moment, but I'll come back to it as soon as a I get the right transformer for this

sorry for double posting, but I just finished a PCB design for the power amp. I know it's not pretty, but I was just trying to follow some simple rules laid out in the 3886 datasheet - keep the traces short, avoid capacitative coupling by keeping safe distance between +-35V rails and the audio path and also keep the high and low power audio lines separate. I also put the ground paths in the proximity of "high risk" signals. Oh, and all the ground paths meet at one point (BTW, should I make it smaller or shouldn't it make a problem?). I also kept the 100nF power supply caps as close to 3886 as possible.

If you see any terrible mistakes in this design please let me know!

I'm afraid a little cruelty is what this tank needs, because the op-amp drive circuit barely made it move! When I used those little transformers I have the sound was louder, but also distorted as hell.

Other thing is that the clean sound it made was not very good at all. I think it may be mostly because of small power of the driver, but I'm afraid that the tank may not be the best one.

So I think that I'll leave the reverb stuff for the future projects (maybe I'll just make it a standalone box with the mentioned Phabb Reverb drive? I'm not sure if it's worth making the +-35V power supply for the reverb only) and focus on just making the amp work.

So with the preamp done it's time for the power amp - are there any exceptional circuits involving this chip or should I just go with the ESP one: http://sound.westhost.com/project19.htm ?

It would be great if there was some well-designed, ready-to-transfer pcb out there - do you know of any? I can try to design my own, but the power amp section is too easy to mess up by a beginner I think, for example by putting the audio path to close to the rails or something stupid like that.
Or maybe I'll just spend some time googling the design rules for power amps, come up with the design, post it here and you guys will be kind enough to tell me if it's usable or a worthless crap?

Thanks for all the replies and nice words!

That makes sense Enzo, I've never had a reverb pedal of any sort, but that's the same way I used the delay pedals - I put the distortion before them in the pedal chain (who doesn't like that "fading distortion" sound when you switch off the dist. with the delay still on?) and it sounded better that way. Thanks for the link to that Peavey schematic, I'll take a closer look at how it's done in the commercial amps.

Regarding that bench supply - that sounds like the exact thing I need (or I'm going to need in the near future), unfortunately I'm out of money at the moment, so I'll probably write you a PM next month if you have any left!

I've just searched the PhAbbTone and I realised that I've never owned a EQ pedal so i think I'll give it a try after I'm done with this amp! Is the performance of the circuit better with the bipolar supply than with a single 9V supply (more headroom or something)? If so, does it make sense to use some kind of charge pump (maybe icl7660 or something) to get a 9-0-9 from a single 9v supply?

So I'm just in a process of protoboarding the drive and recovery circuit for my reverb tank (figures 2 and 3 from this link http://sound.westhost.com/project34.htm ) but I've just realised that it may not work that great for me, because the tank I have is apparently a high impendance one - I measured the DC resistance of the tank and it was around 60ohm, which would suggest that this is a 600ohm input impendance tank.

Apparently to drive such a tank you need a discrete circuit and something close to lm3886 rails voltage - if the one I'm breadboarding right now doesn't work well, i'm afraid I'll have to wait with the reverb part until I'm done with the power supply, which is less than optimal for me.

EDIT I forgot that I have some small transformers that I salvaged from broken laptop power supplies and wall warts - I'll try using them if the circuit doesn't drive the spring enough!

that's a good idea to have a panel just for breadboarding and testing, I'll make sure to get one in the future!
I'm kind of jealous of the setup you have there (the bench power supply and thise panels), the voltages of the supply are adjustable right? Guess I'll have to build myself one of those bench supplies.
BTW - what exactly is this prototype?

I spent last night on experimenting with different cap/resistor values and opamps and I found one setting that I like the most - I increased the amount of bass by a little and increased the gain of second op-amp stage, also decided to use 5532 instead of tl072.

Once I figured out the sound I like I opened EAGLE and started designing a PCB for the preamp. I finished and etched it today and here's the final effect:


then I decided to wire it up to see if it works:


and put it in the chassis for my testing convenience (don't worry, it's just a temporary wiring):


Surprisingly, it worked from the first try! So I guess I can say that the preamp part of the job is done.

Before I go with the power amp, I want to try to get the reverb tank working, so tomorrow I'll breadboard myself one of those drivers http://sound.westhost.com/project34.htm and see how they work.
But if I get them working, where should I put them in the amp topology? Before or after the preamp? My guess would be before the preamp, is that correct?

Thank you! I have to admit I fried one output transistor when I accidentally attached its emitter directly to the -12V rail instead of 2,2k resistor but shhh!

Whooops, I really didn't think about the implications of plugging the pots and other stuff directly into the protoboard! No wonder I broke so many of those (on the other hand I got zillions of them at the discount at the local store where they cost me about 1$ each but yeah, I see I shouldn't have done that). Now I think that for the future projects I'll just use this breadbord on the front of the first photo exclusively for mounting the offboard elements like pots, jacks (as I like having them firmly attached to something instead of hanging on the wires) and i think the other one will be fine, as there's only one pot in there. But yeah, kind of stupid of me (in my defence I had never done that until I saw someone on the internet mount the pots like that and I thought "what a great idea!"  :lmao:).

You're right, Rod Elliot posted a power supply schematic on his webpage on the 100W amp that does exactly what you said, gets 15V from the rails of the power amp with Zeners, resistors and capacitors:

It was designed for the discrete power amp, but it's gonna work as well with the lm3886 I guess.

I haven't yet decided on whether to make a head or a combo. If I make a head then I'll have to make a separate cabinet as well, because I don't have one, I own a combo amp only - and I wouldn't want to buy a cab, because what is the point of making a DIY amp head if you don't have a DIY amp cabinet?
I'm not planning to gig with this amp, so I think combo would make a more practical and easier/cheaper to make amp. So you made me think about this subject and I think I've finally made a decision - I'll go with combo.

On another note - does it make any sense to use metal film resistors in the build or is it an overkill? Precisely my question is: is there audible difference in noise levels between carbon and metal film resistors in a diy solid state amp? Or maybe I should use them in audio path only?
I've never really heard any big difference in noise levels when using metal film resistors in pedals, but then I may be just deaf and besides, the amps are really a different beast from stompboxes.

allright, so i just breadboarded the preamp and connected it's output into my stereo amplifier - sounds really good and clean and also overdrives nicely with the volume knob cranked up to 9-10! I used two wall-warts, one of them was regulated so I got -12V from it and another was unregulated,  so overall i have +16/-12V - not bad after all. Here are the pictures:

I have to admit I thought about having two separate boxes - one for the preamp, and one for power amp, but I've decided to put them in one box for several reasons - I'm afraid I don't have a box big enough to fit a +-12V transformer in it so I'd have buy a box. Also the cost increases because I would need two power supplys instead of one. The chassis I have is big enough for a power-amp and a preamp, so I find it the most reasonable solution to put them both together in one box. I think I'll add an additional output after a preamp if I need to connect it to someone else's amp.

In other words - yay, it works! Tomorrow I'll go buy myself power supply parts and maybe design a PCB for the preamp - any precautions like "keep the xxx part away from the yyy part" or "make this trace really wide" I should take while doing so? I know that there are some rules about how to design the power amp and power supply boards, but I don't know about anything I should keep in my mind regarding the preamp.

Quote from: J M Fahey on March 06, 2016, 10:30:06 AM
Besides, what Forum are you actually posting in today?   :lmao:

:cheesy: hey, just this one, I only posted on diystompboxes before but realised that it probably wasn't a perfect place to ask that question so I came here.

Ok, so i think I have decided to build the mentioned Rod Elliot Op Amp preamp + lm3886 power amp, thanks for the suggestions!

I would like to test it on a breadboard first, but I don't have a +-15V bipolar power supply, so I'd have to build a power supply first, mount the transformer, caps, fuse, rectifier and all that stuff in a chassis and then use this power supply to power a breadboard - this doesn't seem like a great idea (I don't have a bench power supply as this is my first amplifier project and I didn't need it for stompboxes). Unless I can use two small current 12V wall-warts that I have laying around to get a +-12V power supply - will it work? I think it should, because this preamp is essentially one op-amp and one transistor so it's not going to consume too much power? Please correct me if I'm wrong.

I'll probably post some photos and some more questions as I progress with the build if it's ok to do such things here, thanks for your help!

thanks for your answer!

QuoteNothing wrong with an LM3886 build as a first power amp project,, as long as you use recomended supply setup

Speaking of recommended power supply, when I google "lm3886 power supply" most results use the transformer with two separate secondary windings, while on the page you linked there is a center tapped transformer http://sound.westhost.com/project04.htm - which one is more preferable here? What are advantages or disadvantages of center tapped / dual winding transformer? I think that the center tapped is cheaper, so I'm leaning towards this option, but if it's a bad idea please prove me wrong.

QuoteA whole lot of great advice and kits here; http://sound.westhost.com/projects.htm

yeah, I've been there before, great website!

QuoteSome where there is also a LM3886 kit as well ,,I think,,, his site is so big I can't see it right now but it's there somewhere.

I think it's this one: http://sound.westhost.com/project19.htm I think I'm going to use the schematic and etch my own PCB for this one as the shipping costs are kind of big.

QuoteThat Hood preamp you linked to is not something I would want to use as it has some potential safety issues.

what are the safety issues? Is it because it's a DIY design that hasn't been widely tested or is there something fundamentally wrong with the design? I have no experience with the valve stuff so I don't see those things.

QuoteIf you want Valves you are better off to go the full build,, All Valves. :tu:

as I said in the post above I'd like to try the valve pre-amp because I've never owned a tube amp, but if it's not worth the hassle then I'll build a SS one!

QuoteAs for preamps,, heck pick one lol. Wise to stay away from glass stuff for now.

http://sound.westhost.com/project27.htm on the 100W amp page there is a op-amp based pre-amp design - is it going to work fine with lm3886 power amp? I think so, because the lm3886 shouldn't alter the sound, but then again in the project there is a discrete power amp which may alter the sound and make the whole amp sound good? I don't know

QuoteIf you want Valves you are better off to go the full build,, All Valves

I thought that the pre-amp was mainly responsible for the tone of the sound coming from the amp, do all-valves builds sound better (or at least different) than valve-chip hybrids?

QuoteWise to stay away from glass stuff for now.

What are the reasons that valve builds are more difficult than SS ones? High voltages everywhere, need for careful biasing or some other reasons?

hello everyone!
I posted this thread on diystompboxes site because I was more familiar with that messageboard, but I didn't get any responses (because, well, it's a stompbox board, not an amp one) so I figured that this will be a better place to post this stuff:

Quote
Hello everyone!

This is my first post so i guess i should introduce myself - I've been making guitar pedals for quite some time but I have never worked with amplifiers, so now is the perfect time to change it I guess! And please excuse me for my poor english as I'm from Poland so I apologize in advance for all my mistakes.

I want to build myself a guitar amplifier. As a first project I would have chosen something small, quiet and simple, but I already have a small 8W amp to play at home, so I thought that maybe I could make myself a practice amp loud enough to play in a band setting? I did some searching and googling and it turned out that a LM3886 chip would be perfect as a power-amp section to get something around 50-60W into 8ohm speaker (but please correct me if it's an overkill or wrong on some other level).

I've had an old & broken solid-state amp laying in the basement, so I disassembled it, threw out the board (after salvaging some parts like 2200uF capacitors or LM1875 chip) and now have myself a nice chassis and neatly wired AC section of the amp. Unfortunately, the transformer included in the amp is not powerful enough for me to use it - it only gives +-17V AC and has a max rating of 45VA, so I'll take it out and use it for some other project.

But back to the topic - now that I've decided on using the LM3886 chip as a power section (I've read that it's loud and clean and that's all that you want from the power section of an amp, right? oh, and it has lots kinds of protections from various failures) I have to choose a preamp to go with it, but I don't really have too much knowledge in this area, so I would like to ask you:

what are the good sounding and simple (as this is my first build it's kind of important) pre-amps to use with a lm3886 power-amp? I was thinking maybe of some low-voltage (or maybe high-voltage?) tube pre-amp - I've never owned a tube-amp so this is kind of a dream of mine, but if there are some great solid-state preamps out there I'm open to suggestions!

I would like it to have a clean and distorted channel, as well as some simple tone control (low, mid and high frequncy controls).

I also have an accutronics spring reverb tank taken from some broken amp that I would also like to throw in there.

For example, I found this project - http://pdfelectronics.com/the-hood-preamp/ and it looks nice for me, but what the hell do i know - what do you think about this one?

Let's say I decided to build the preamp from the link above - can I use one big transformer with secondary voltages 24/0/24 AC to get the +-35VDC needed for LM3886 and then use the +24/0 winding for the pre-amp (as the power supply on the schematic indeed uses a mains to 24V transformer)? Or should I use two separate transformers, one for the power amp and one for the pre-amp?

Sorry for this long post and thanks in advance for all the answers!

after not getting any replies I bumped with own thread with another bunch of stupid questions:

Quote
Sorry for bumping my own thread, but I found a schematic for a preamp based on the Fender Twin Reverb amp and it looks really simple and, more importantly, it uses two cheap transformers (one is 12v*0,25A=3W and the second is 12*0,15=1,8W).
Here's the link: http://s198.photobucket.com/user/birdy81260/media/Fender.gif.html
I was thinking about designing the power supply for the whole amp - does it make more sense to use separate power supplies for the preamp (as it uses two small power 230v-12v transformers) and the power amp (bipolar 230Vac primary +-24Vac secondary, power, say, 150VA) or should i use this big transformer to get the +-24Vac needed for the LM3886 and then some other 24V to 230V transformer to crank up the voltage for the tubes? Which solution is better/cheaper/more practical?

I also have a 600ohm accutronics reverb tank taken out from a broken fender amp that I would like to include in this amp, is this preamp powerful enough to drive the tank? If so, then i think i should use some kind of recovery stage, should a single op-amp operating on, say, +-20v be enough for this?

There are a lot of questions in those two posts, so if anyone could answer any of them I would be really thankful!