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:
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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:
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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!
Nothing wrong with an LM3886 build as a first power amp project,, as long as you use recomended supply setup.
As for preamps,, heck pick one lol. Wise to stay away from glass stuff for now.
A whole lot of great advice and kits here; http://sound.westhost.com/projects.htm
A massive amount of info on those pages and aimed at folks in your situation. hint.
look at **Project 27** a complete 100 Watt Amp build and he sells the kit for same.
Some 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.
Watch out there is a lot of stuff on the net that Claims to work but some are downright dangerous.
That Hood preamp you linked to is not something I would want to use as it has some potential safety issues.
having built a lot of preamps both Glass and SS I can tell you that valve stuff is not really needed for great sound.
If you want Valves you are better off to go the full build,, All Valves. :tu:
Regards that reverb tank; Yes it's likely useable but more work for you.
Again ESP has one of the best circuits for reverb drivers. look at project 34.
Phil.
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?
I was going to suggest the excellent Rod Elliott Op Amp guitar preamp, but you already found it.
It can be built on stripboard/Veroboard or even perfboard , and can (and should) be built and tested on Protoboard first, you can try it before actually designing a board.
Try that with tubes ;)
Tubes are fine but require lethal voltages , more complex supplies (they also require 6.3V for filaments), sockets which must be mounted one way or another, etc.
None a deal killing problem, of course, but starting full SS is way simpler.
Besides, what Forum are you actually posting in today? :lmao:
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!
Yes, +/-12V DC is perfectly fine.
In fact, if unregulated , you will have more than 12V, since preamp consmption is VERY low, about 5 mA .
In an emergency, it can run from 2 9V batteries in series, with center tap grounded , effectively +/- 9V rails.
Not as crazy as it looks, you might build such preamp in a box and carry it in your backpack everywhere, either to get into *any* amp present using your own "known" amp or plain go into a PA Mixer (auxiliary/line input) and have a "Guitar" sound and EQ, even a little crunch, instead of the boring "straight into the desk" sound.
In fact there are a couple "amp in a box" pedals out there specifically designed for such use, such as Marshall DRP1 , Sansamp Classic, Mesa Boogie V Twin (although the last one is tubed) .
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:
(http://s18.postimg.org/jnrr0ko79/preamp.jpg) (http://postimg.org/image/jnrr0ko79/)(http://s12.postimg.org/8nft62gah/preamp2.jpg) (http://postimg.org/image/8nft62gah/)
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.
Double congratulations: one for taking the bull by the horns and doing it at once, the other because your Proto preamp looks real cool. :dbtu:
Now I take one away: I cried when I saw pots and jacks plugged straight into delicate Proto holes :o
Ok, now it's done.
I suggest you get a red Sharpie or something and mark the .... ahem!!! .... "expanded" holes ... no transistor/IC/ceramic cap leg will reliably make contact there.
No big deal, just mark them and in future builds always use the same.
And congratulations again. :cheesy:
You can easily get +/- 15V from LM3886 rails with a couple resistors, capacitors and Zeners.
Will you build a head or a combo?
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:
(http://sound.westhost.com/p27b-f3.gif)
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.
Regards Breadboards and pots; You just need a panel to mount the pots and jump wires back to board.
Here is some of my quick and simple test boards for example.
If you look close some pots that have correct pin spacing are mounted directly onto the BB.
Most of those bits come from me scrounging electronic junk like old TV's and VCR gear,, but a lot of that is now drying up. :'(
The switch on the left hand side is just a simple way to implement a true bypass for A/B testing.
I have used this setup for years now it never really got finished as it's always being altered in some way to accommodate a new brain wave. ;)
Spend a long time on the testing as once you commit to a build it's a lot harder to modify and tweak.
Re metal Resistors,, yes in some cases it can help,, like where you have heaps of gain,,, hi z sections of a circuit yes use metal films.
But keep in mind, even with the best opamps and other pretty colored fancy parts,,, bad layout of PCB can reduce any benefit.
Phil.
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:
(http://s29.postimg.org/k8v1gv7f7/pcb1.jpg) (http://postimg.org/image/k8v1gv7f7/)
then I decided to wire it up to see if it works:
(http://s12.postimg.org/s3z6uar61/12821998_603644419798405_1578496602_n.jpg) (http://postimg.org/image/s3z6uar61/)
and put it in the chassis for my testing convenience (don't worry, it's just a temporary wiring):
(http://s24.postimg.org/l2o4tozkh/12788120_603706336458880_437502097_n.jpg) (http://postimg.org/image/l2o4tozkh/)
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?
No, make the tone first, then reverberate the sound. The difference is like echos that are distorted as opposed to distorted sounds that echo.
Look at solid state amps in general, see how they are put together. Start simple, compare a Peavey Blazer and a Peavey Rage. Same exact amp, but the Blazer has a reverb added. They use the same board, one leaves off the reverb parts. You can look at how the reverb was added in on the schematic. Same schematic for both units.
http://bmamps.com/Schematics/Peavey/Peavey_Blazer,_Rage_(4-95)_Schematic.pdf
By the way, I have some bench supplies, and am in the process of selling off my shop. For small circuit development, I have a Heath that would be ideal. Dual 0-20vDC plus a 5v DC. Current and voltage meteres and adjustable current limits. And tracking. If you have any interest, send me a PM.
Congratulations again on actually protoboarding it, designing the PCB, etching it and building the whole project. :dbtu: :dbtu: :dbtu:
That it actually worked on first try is just the icing on the cake ;)
Lots of people on Forums ask and get answers, but then don't actually go all the way to the end. :tu:
Agree with JMF,, you are obviously keen,, I can tell by all the holes in the board you have already built a lot of PCB,s :dbtu:
Regard my circuits on those BB's the bottom one is nothing,, just to show the idea But the top one (with the battery) is one of my early attempts at a decent tone control.
I've built a lot of stuff and most of it would never win awards but that one is one of my few success ideas that actually worked way beyond my expectations.
Just search for PhAbbTone on here as I've posted that schematic a few times the latest version is PhAbbToneV4. The circuit on the BB is the earlier circuit,, the later V4 has better sig/noise performance. It's dead easy to build and can be run as a pedal (battery) circuit or run from a 12-0-12 VDC Supply. Feel free to test it out. :tu:
Phil.
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!
Well, if you don't mind being pestered by the "Society Preventing Cruelty against Reverb Tanks" , you can search here and build the Phabb Reverb, spring crushing drive from a +/-35V rails :o discrete power transistors dedicated power amp.
Reverb deeper than the Marianas Trench.
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?
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!
Quote from: incurably_optimistic on March 08, 2016, 04:07:35 PM
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?
I admire you entusiasium but maybe slow up a bit. From reading your postings you are going in guns blazing but you might be missing things. The Reveb built corectly with the right circuit will not distort. That transformer has to be that particular type and is used in this case reverse. (As Rod E explains clearly on his site).
This is the way I built it and once I realized how well it worked I mentioned it to Rod at ESP because He actually helped me create my first attempt (The one JMFahey mentioned above,, thanks for the plug Juan yes the "Maxiverb" was over the top,, :loco) Yes tiss rather complex,, Trans Verb is the better option as it runs from 15 V rails the transformer gives it the missing jump start to drive the tank.
Rod being far more tech savvy with the inner secrets of electronics refined it even further. He did mention that the twin opamp drive needs to be NE5532 for best performance with my design.
(or is it NE5534,, for the dual package?)
If the drive transducer in your tank measures 60 Ohms DC resistance then you should have fairly good clean sound.
Sure ideally it would be better if it was higher but I have driven a Fender Rev tank which measures 60 Ohm so I know it works ok.
Be aware you must use the whole circuit otherwise it may not work so well.
The mixer section Rod suggests on his site is an important part of the sonic result.
Although my circuit looks a bit different the *mixer part* is the same as Rod's, I've just changed the PU end and added a tone cut.
(http://s5.postimg.org/h4g5kk2hj/Ph_Abb_Tverb_Ver2.png) (http://postimage.org/)
pic host (http://postimage.org/)
This is an inside view of the Tverb,,in a 19" rack case that came with the transformer which made the whole build much easier.
(http://s5.postimg.org/weg0rqxzn/Revbuild_01_01_2012_001.jpg) (http://postimg.org/image/weg0rqxzn/)
A little point I've made a few times,, It took me many years to build the Maxiverb,, many of the reverb circuits found in magazines and then ones I found on the internet I have built or at least breadboard tested.
ESP reverb circuit was the first one the worked as one would expect it to work. A lot of the others that made grand claimed turned out to be problematic. Yes it took me about 8 years to get there but I'm glad I took that journey as I've learned so much more about the many aspects of Amplification be cause I persisted and insisted that It must be doable.
But you will find it takes time to find all the hidden secrets..... Hint 8|
Phil.
Look at most any Peavey amp of the last 30 years, and you will almost always see one dual op amp running the reverb pan. it works, it is reliable, it is simple. And they run them on single supply in their tube amps for the most part.
Quote from: Enzo on March 09, 2016, 11:14:54 AM
Look at most any Peavey amp of the last 30 years, and you will almost always see one dual op amp running the reverb pan. it works, it is reliable, it is simple. And they run them on single supply in their tube amps for the most part.
Yes indeed they do,, as does my Laney. No doubt some work better than others but the Xformer makes a huge impact on the result.
Obviously you chaps will see far more amplifiers than myself but the ones I've had experience with are not that good. My laney circuit has been modified with a small Xformer and with only slight mods needed to change it the result was a
night and day difference. ;) I always needed to run the reverb knob up past half way to hear any decent effect,, now it's dripping wet at half way on the dial. Past 3/4 it's slapping surf twang. <3)
Phil.
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
This thread is an interesting read, and an inspiring one. Also, your writing suggests that your English is excellent; no apology needed (not that one would be needed anyway if your English was worse). Just saying. Carry on!
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:
(http://s23.postimg.org/8f05fk8ev/12899921_1069274563115357_360261498_n.jpg) (http://postimg.org/image/8f05fk8ev/)
(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:
(http://s10.postimg.org/nq4cuwsp1/schemat.jpg) (http://postimg.org/image/nq4cuwsp1/)
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:
(http://s11.postimg.org/bssnelw27/12442755_1069274393115374_516576972_n.jpg) (http://postimg.org/image/bssnelw27/)
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?
Re the supply circuit; C7 & C8 are way to much,, try 10uF MAX. :tu:
Large Value Caps there can actually cause problems. 8|
Phil.
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.
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?
Mains fuse is a MUST!!!! Fire risk if something major fails. You don't want to burn your house down. 8|
Some transformers have an inbuilt fuseable link but if you are not sure use a fuse. :dbtu:
Regards rail fuses,,,,,Have a look here: http://www.ssguitar.com/index.php?topic=3989.0 (http://www.ssguitar.com/index.php?topic=3989.0)
I've posted a small LM1875 guitar amp down that page.
For a small amp it's not so important,,
That little Casino only has 15VDC rails,,many thousands of LM1875 amps work with no fuse on the DC rails,,, so up to you. xP
Phil.
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!
Use the proper Mains fuse, you need none else since there is only one large "customer" , the power amp, so if it fails primary fuse isn guaranteed to blow.
Separate fuses make sense in multi secondary transformers, where, say, a filament/heater short may not blow the main one, but overheat one small winding until it catches fire ... literally.
Besides that, I hate DC rail fuses (unless it's a single rail amp) because they will never ever blow both at the same time, one will protect the other, and that **guarantees** DC on the speaker, a Very Bad Thing.
Don't ask me how I learnt that, many times. :grr
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:
(http://s14.postimg.org/ebjycrvt9/12380440_614637905365723_1910407156_n_2.jpg) (http://postimg.org/image/ebjycrvt9/)
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:
(http://s15.postimg.org/n5sl73rmf/12895425_614637912032389_1413456450_n.jpg) (http://postimg.org/image/n5sl73rmf/)
(http://s24.postimg.org/aw5vzp6kh/12721885_614637922032388_1795501187_n.jpg) (http://postimg.org/image/aw5vzp6kh/)
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:
(http://s16.postimg.org/65jphx2ch/12899703_614637875365726_1750248728_n_2.jpg) (http://postimg.org/image/65jphx2ch/)
here's a closer look:
(http://s14.postimg.org/rf756hubx/12895331_614637888699058_816191290_n.jpg) (http://postimg.org/image/rf756hubx/)
(http://s30.postimg.org/ln7hcycpp/12900225_614637898699057_753550638_n_2.jpg) (http://postimg.org/image/ln7hcycpp/)
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.
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:
(http://s31.postimg.org/kcweij0zb/zasilacz.jpg) (http://postimg.org/image/kcweij0zb/)
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:
(http://s31.postimg.org/45x052w1j/13059459_631430257019821_1601466018_n.jpg) (http://postimg.org/image/45x052w1j/)
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!
(http://s31.postimg.org/4959ya9x3/13023337_631427693686744_472002021_n.jpg) (http://postimg.org/image/4959ya9x3/)
it's not that it looks beautiful now, but hey, at least I tried!
and a look from the front:
(http://s31.postimg.org/o5lxlnx6f/zasilacz2.jpg) (http://postimg.org/image/o5lxlnx6f/)
On another note, I've also finished the power supply for the amp:
(http://s31.postimg.org/5g93w9nef/13077404_1091321184244028_1893675772_n.jpg) (http://postimg.org/image/5g93w9nef/)
(http://s31.postimg.org/n73bi1jnb/13045595_1091321227577357_979195211_n.jpg) (http://postimg.org/image/n73bi1jnb/)
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.
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
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:
(http://s31.postimg.org/itmmjanrb/13046069_1091936714182475_830537215_n.jpg) (http://postimg.org/image/itmmjanrb/)
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!
:dbtu:
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?
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.
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:
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
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 :)
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?
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
True, $10 gives you a very good, already calibrated and housed voltmeter.
Doubt a homemade one can be made for such a low price.
"Economies of scale".
Quote from: J M Fahey on May 02, 2016, 04:51:01 PM
You'll lose audience (I think) if you fill page after page of obscure (for us) code and what you expect it to do, including endless "version mods" :trouble, but a nice finished project for a voltmeter or any other useful add on , including a PCB design and easy to download and burn code , a fully finished and tested package, will in fact be welcome. <3)
Just open a new thread for it so those interested can have all together in one place :)
Sure thing - I won't bother you with any posts about this until I'm done with the whole thing (but hey, the code will be awfully simple! You can measure 0-5V using AD converter, so you have to bring the voltage down using a voltage divider and then view it on LED display ;) ).
Quote from: exztinct01 on May 02, 2016, 05:41:54 PM
don't power supply wires, pots wiring, need insulated wires too?
Damn it, of course they do, what I meant was shielded wires - I always confuse those words for whatever reason.
Both of you are probably right and I think this will be an overkill, but when I think about it, I think I prefer to have the meter built in the enclosure - it takes less space, you don't need to connect it every time you want to use the supply - it'll just be more convenient for me. And it's just a fun thing to do! Most reasonable people (that doesn't make amps for a living) would probably buy a pre-made guitar amplifier instead of wasting time and money on a DIY thing, but that's not why we're here on this forum ;)
About the price - as we all probably have a lot of resistors and capacitors (and this project will call only for a few) the only components you really need to buy are micro controller atmega8 (I think it costs around 1$) 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
:) 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
Welcome back!
I finally bought myself a little dremel tool for cutting metal which allowed me to (almost) finish my project!
The head section of the amp is more or less ready. I didn't have a shielded wire at hand so I used a regular wire for all the wiring, but once I get myself some I'll surely fix it - however, the noise doesn't seem to be an issue so far. I may make some shielding for the preamp in the future if I feel like it. I don't have a dedicated guitar speaker, so I just connected it to the speaker from my stereo system - sounds quite nice, and it's going to sound only better with a real guitar speaker!
I live in a block of flats so I couldn't really test it at anything close to full volume, but after an hour of low-to-mid volume playing the heatsink didn't really get warm at all, so I think it's a good sign for the things to come. I think that heatsink should be enough for a single LM3886, right?
I haven't yet decided whether it's going to be just a standalone guitar head or a combo amp, so the speaker wiring is just temporary for test purposes, don't rip me for that! :trouble But here are some pictures (click to make it larger):
(http://s33.postimg.org/4dfv7lajv/13342246_654322128063967_758962486_n.jpg) (http://postimg.org/image/4dfv7lajv/)
(http://s33.postimg.org/ai9pxbru3/13393441_654322124730634_1174562823_n.jpg) (http://postimg.org/image/ai9pxbru3/)
(http://s33.postimg.org/wkdsclgh7/13341953_654322114730635_824280006_n.jpg) (http://postimg.org/image/wkdsclgh7/)
I'm sorry exztinct01, but I cannot record any sound clips, because I don't have a microphone :( It's all good though, because I'm a terrible guitar player so you don't have to listen to my terrible attempts to catch a clean chord :lmao: however, when I'll figure out a way to record a sample with a good audio quality I'll make sure to invite a friend who can play well and post something here.
I tried it with a guitar plugged straight into the amp and with a modded tubescreamer I made and it sounds fine either way :dbtu:
mine still squeals when I add a distortion pedal in front of the preamp. I'll try putting the distortion after the preamp and see if it minimizes noise.
Did you reduce the gain of your preamp from Rod's original 27db?
no, I left the gain settings more or less unchanged.
I haven't yet tried it with master pot cranked up at maximum, I did however max the "volume" (or "gain") pot and noticed no squeal. Did you test your amp with different guitars? Sometimes a noisy/high output pickup + a lot of gain = squeal, so grab another guitar and see if the problem persists.
does the schematic of the p27 preamp have the supply bypass caps for the opamps or should I add it?
I didn't put 0.1uF caps there
or maybe Rod put it there but different values?
it's C11 on this schematic:
(http://sound.westhost.com/p27-f1.gif)
in case you are asking about my layout for the preamp - yeah, I forgot to put it on the board, but it works fine as it is.