Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Hello.

I've been lurking on the forums as a guest for a while now and finally built up the courage to ask some questions. Please don't bite and please bear with me while I give you an idea of where I'm coming from.

I'm a noise maker (via guitar) and enjoy poking and prodding things that I probably shouldn't. I have some previous experience using a soldering iron for simple circuits, and can follow layouts to wire up guitar electronics. However, the workings of amps currently mystify me. I can read the schematics for an amp, but I don't really understand what is going on (i.e. why are those resistors there in parallel to those capacitors, etc.) So, I'm interested in putting together a frugal practice amp to hopefully learn something.

Right now I either plug my guitar into my computer or plug in to a small Fender practice amp (don't remember the model off hand), so just about anything will be an upgrade. This also means I need an amp and some type of speaker cabinet, preferably both DIY. I've done some searching on my own, but I'm at a loss for where to start.

Anyways on to my desires. Feel free to tell me I'm asking for too much from a simple project.

To start out, I want a practice amp that is so clean, the sound waves shine as they leave the speaker. In my mind, a good practice amp will allow me to get a feel for the frequency response of the pickups and also give me a good idea of what a pedal is/isn't capable of. In the future I'd like to have good, switchable distortion, dirt, whatever, but that's a long way off.

I looked into the ROG Ruby, but I've seen some concerns that it doesn't have much headroom. I also found a new design called the mylk[386] amp which is a Ruby with an op-amp booster/buffer (no clue if this is beneficial and/or necessary). I've also seen a number of other SS amps that look overly complicated.

So, first question, what would be a good SS amp build to get me started?

Edit: Forgot to add, I'm looking to use anywhere from an 8 to 12" speaker. So next question would be what size speaker should I be considering?

Hi nipperiodic, welcome.


Oh my.  There are several people on here who could write hundreds of words on the function of each and every component in an amplifier.  Teemuk already has, (http://www.ssguitar.com/index.php?topic=711.0) and you could do worse than start there.

The general process is more like - build something, have a problem and learn about that bit, repeat until satisfied.  Many people who don't know what component does what still manage to build quite satisfactory amplifiers.

Like all small chip amps the Ruby "lacks headroom" in the same way that a moped would lack headroom in the Indy 500 - it just doesn't have a lot of horsepower, one watt out clean maximum.  Try for any louder and you get distortion.  But as a moped is ideal for a trip to the shops for some milk, so amps such as the Ruby are fine for bedroom noodling.

Generally the bigger the speaker the better, particularly if you have an amp with limited power output, but the cabinet it is in is also important and can make the difference between any speaker giving its best, or being crippled by the cab - again, size matters.

Thanks for the welcome Roly. Thanks for the input also. Teemuk's book looks like an enormous labor of love; I'll definitely start looking through it.

I hope you won't mind me picking your brain some more.

So if I'm reading you right, your advice would be to build something and play with it until I'm happy with what I come up with? I can probably do that.

When a Ruby lacks headroom due to only outputting 1W, what is causing the lack of headroom? I get that there isn't enough power, but why does the lack of power cause distortion?

For the speaker, if possible I should plan for a 12" speaker (that sounds like overkill for a bedroom amp)? Also, I know the Ruby is specced for 4 to 16 ohm impedance speakers. How do I determine which impedance speaker to use?

I've seen lots of plans for speaker cabinets and seen the calculators for determining cabinet size, etc. How do I determine which are good designs?

Thanks again. I've been googling this stuff, but the more I try to figure out on my own, the more I can't see the forest for the trees.

As a fellow newbie to amp building, I've received much more from this site than I've contributed. Your questions seem like the kinds of things I was thinking about when I first started learning, so I thought I'd try to answer and maybe contribute something for once (hooray!).


I think what Roly was getting at is that you can copy someone's schematic and put together a working amp without actually having to understand what each individual part is actually doing for the circuit. Sort of a, "Connect this thingy to that doohickey, and you'll have a working amp," kind of deal. After you put something together, you can start to learn how to fix things that bug you about it, like if you want the EQ to sound different or want to adjust the distortion or something. Little by little you'll learn how to correct/change all these things until you actually know what you're doing (more or less).

Teemuk's book was a great read, but definitely a labor of love. I have read through it a couple of times now, along with many, many other pages on how electronics work. And let me tell you, the first time through, I probably only understood 10% of it. If you really want to get a grasp on it, my advice is to just keep reading, even if you don't understand. Eventually you'll read something that reminds you of another thing you didn't understand at the time, and it will suddenly click.



I think I have a grasp on headroom, so I'll give you my non-technical, layman's understanding of how it works. (Keep in mind this is not entirely factually correct; I'm just trying to hopefully get across the concept.) Your amp's power supply will put out a specific voltage, say 10 volts. That means if you want a clean, undistorted signal, the maximum voltage swing that signal can have will be 10 volts. If you try to amplify the signal to 20 volts, the amp can only get to 10 volts, so basically you're clipping off half of the signal, and when you clip a sine wave, that comes through as distortion. So the amount of headroom refers to how much room there is between the max voltage of the sine wave and the max voltage that your amp is capable of. Again, very technically incorrect, but hopefully that will help you get you going when you're reading how it actually works.


https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/clipping/page1.html

If you want to take Berlin you need a plan.  If you are just going for a wander in the electronic wilderness to see what you can find/learn, then just doing stuff is as useful as anything.  Most of us learned by blowing stuff up, and that's just a phase you have to go through.   ;)


It's not the lack of power that causes the distortion, it's trying to make it louder than it's capable of.  Within its ratings, say in a small portable radio or headphone amp it has no shortage of headroom, just as a moped will go smartly from zero to 20MPH.  It only runs into "distortion" when the rider wants to go faster than it is capable of.  {but who would think that a guitarist wanted to be louder?  :lmao: }


Particularly with low power amps the amount of speaker cone area is important, it kind of buys you a bit of extra headroom.  I'd go for an 8 ohm speaker, and all you really need is a box with about 1.4 cubic feet of capacity (around 50 litres), closed or open back.  Don't over-think it, just make it solid and the joins air-tight.


What Bakeacake08 is saying is right, just from a different perspective.   :dbtu:

Thanks for the input and explanations. After reading your explanations and some other things, I think I have a general grasp of headroom. I think what threw me before was guitarists that always seem to be craving more amp wattage while still being fascinated with distortion.

I was all set to begin things and then the holiday season snuck up on me.

Anyways, I want to order some parts and was hoping to get some clarification on what to order. I decided on the mylk[386] amp and have attached a circuit schematic to this post. I also attached a vero board layout I put together (based off one on the mylk amp's web site).

On the vero layout, I've circled my question areas with red circles. If someone cares to chime in on some or all of them, I'd appreciate it. Going from left to right:

1. I want to run this off of a power adapter rather than a 9V battery. How exactly do I rig up a DC jack with on/off switch, and what should the power rating for the adapter be? Also, the input jack (J13) is supposed to be stereo switched; is this still necessary if I have an on/off switch?

2. For the clipping diodes, I'd like to try 3 diode asymmetric clipping. Is there an easy way to squeeze in the third diode at this point?

3. IC1 is specified as any 741 chip. Is there any particular flavor that would be a better choice than something else?

4. I guess this is a decoupling cap. The directions said the values can range from 1uF to 10uF depending on desired application. Can I just pick a value in the middle as a happy medium?

5. I can add some tone controls at this jumper. Should I attempt to add some type of tone control system (the V2 AMZ presence control looks pretty cool), or should I hold off until I put together a working amp?

6. IC2 is the 386 chip. I've seen people complain that the generic chips have problems while the name brands (national semiconductor?) don't have problems. Is this really true? Is it worthwhile to get the higher powered LM386D-4 or is the regular LM386N sufficient?

7. This is the on/off LED. Do I need to add a resistor to get the LED to work? Would a "super bright" LED be too bright on an amp?

8. The directions say that ideally this pot should be 470ohms, but that a 1K audio pot works. Would adding a resistor in parallel to a 1K audio pot to get the value to ~470 be worthwhile to try? I left off a power resistor included in the circuit. Is a resistor really necessary for something this low powered?

9. (There isn't a circle for this one) So I'm coming from the world of guitar wiring and very simple circuits. When I see a ground symbol, I solder to the back of a pot. What is the main grounding point for an amp circuit? I'd like to put this in an aluminum enclosure. What's the easiest way to ground the enclosure? Any other comments/improvements on the circuit?

Hopefully I don't come across as too clueless, but I like to get all my ducks in order before proceeding with things. I think I have a basic idea of what this circuit is doing, but lack the experience to make choices on component values, modifications, etc.

Thanks for the help and happy holidays.

Okay, this is now a mylk[386] amp build thread.   ;)

A good set of questions deserves a good set of answers I reccon.

Quote from: nipperiodic1. I want to run this off of a power adapter rather than a 9V battery. How exactly do I rig up a DC jack with on/off switch, and what should the power rating for the adapter be? Also, the input jack (J13) is supposed to be stereo switched; is this still necessary if I have an on/off switch?

Output power times two plus a bit for a safety margin.  1 * 2 = 2 watts (volt/amperes)

P = EI

I = P/E

2.5/9 = 0.3A, 300mA at 9VDC
2.5/12 = 0.2A 200mA at 12VDC


Unregulated DC plugpacks aren't too flash, minimal cap filtering and poor regulation; a "9V" DC unit may give 12 or more volts off-load.  Adding a large filter cap is a good idea.

When DC is brought in it comes via a co-axial connector which has a normally closed contact that is intended to revert to battery power when the plugpack is unplugged.

The reason that the jack contact is favored for power switching is that it's practically foolproof under gigging conditions.  Power switches can tend to get knocked in transit resulting in a flat battery just when you need the gizmo.

Quote from: nipperiodic2. For the clipping diodes, I'd like to try 3 diode asymmetric clipping. Is there an easy way to squeeze in the third diode at this point?

Maybe.  The extra diode may have to be up in the air a bit, "aeroboard" style, but build the basic unit first, get that going and confirmed, then throw some mods at it.

Quote from: nipperiodic3. IC1 is specified as any 741 chip. Is there any particular flavor that would be a better choice than something else?

No.  The choice of op-amp here is very much a matter of personal taste, so I'd fit a good IC socket for this position so you can easily audition all the different op-amps (and discover that there really isn't much difference).  I'd tend to favour the TL071 for this position, mainly because of its potentially very high input impedance (which means that some guitar pickups will really "sing") and I think I have some somewhere.  A personal favorite is a dual, LM833, if you want noise quiet and very clean.

Quote from: nipperiodic4. I guess this is a decoupling cap. The directions said the values can range from 1uF to 10uF depending on desired application. Can I just pick a value in the middle as a happy medium?

The general rule is that where there is a conflict between a value given on a circuit, and a value given on a layout, the circuit rules.

The mylk[386] circuit shows a main 470uF supply decoupling cap, and a decoupling cap/AC bypass on the half-rail, "V.ref" is 47uF.  For unregulated plug pack operation I'd be tempted to add another 2200uF/18 to 24V on the main rail, and even bump the 47uF up to 100uF - it's not critical, but very generally "more is better", to a point, anyway.  Not critical.  Quite a few microfarads, and enough volts.

Quote from: nipperiodic5. I can add some tone controls at this jumper. Should I attempt to add some type of tone control system (the V2 AMZ presence control looks pretty cool), or should I hold off until I put together a working amp?

As above, get the basic unit fully functional and bug free first, otherwise it's just a troublesome testbed, a constantly moving target playing games with your head.   :duh  :trouble

Quote from: nipperiodic6. IC2 is the 386 chip. I've seen people complain that the generic chips have problems while the name brands (national semiconductor?) don't have problems. Is this really true? Is it worthwhile to get the higher powered LM386D-4 or is the regular LM386N sufficient?

Any version you can get our hands on.  You won't be highly stressing it, and if you do we all had to learn by letting the smoke out.  And a reason to fit a second quality socket for the power amp too - full drive into an accidentally shorted speaker connector - oops!   :-[

It's not about never making a mistake, it's about how you recover from those mistakes - just as in performing playing an instrument.

Quote from: nipperiodic7. This is the on/off LED. Do I need to add a resistor to get the LED to work? Would a "super bright" LED be too bright on an amp?

It appears to have R1/3k3 in series with it.  You select the resistor that gives you the desired current/brightness.  I use Hi-eff LED's in battery gear because the still light up well as indicators on only tenths of a milliamp and save battery power.

Quote from: nipperiodic8. The directions say that ideally this pot should be 470ohms, but that a 1K audio pot works. Would adding a resistor in parallel to a 1K audio pot to get the value to ~470 be worthwhile to try? I left off a power resistor included in the circuit. Is a resistor really necessary for something this low powered?

Depends - on how good your speakers are, and how fussy the neighbours are.  Try what you've got to hand, change it later if you feel the need.  Simple, your build, you're in charge; it's entirely up to you how much notice you take of what I, or others, may say/offer/advise.

Quote from: nipperiodic9. (There isn't a circle for this one) So I'm coming from the world of guitar wiring and very simple circuits. When I see a ground symbol, I solder to the back of a pot. What is the main grounding point for an amp circuit? I'd like to put this in an aluminum enclosure. What's the easiest way to ground the enclosure? Any other comments/improvements on the circuit?

Excellent question.  Grounding is a large topic on its own.

Your naked project has stray capacitance from every part of it to all sorts of surrounding stuff, but mainly to the active side of the local supply mains, 50/60Hz with lots of buzzes, pops, and whines.

These capacitances are very small but the input impedance (AC resistance) of a typical guitar amp should be at least 1 meghom, and this is very susceptible to picking up these weakly capacitively-coupled signals from nearby wiring.

So the trick is to make all these stray capacitances be to the inside of a conductive box that is connected to amplifier ground, and with the lid on it should be (effectively) silent.

I built a stereo mike into a plastic case lined with grounded kitchen alfoil and it worked a treat (and it also had a Hi-eff LED pilot light that ran on 0.1mA!  It was actually in series with the 9V supply to the two electret mic elements, about 50uA each.  That had a power switch, but also very low current draw, and wasn't gig-critical.

{and anyone who gigs without a couple of fresh 9V batteries in his gig bag deserves what he gets.  :grr I don't even use em' but I've always got a couple.}

Thanks for the continued help Roly. :)

This is indeed a mylk[386] amp build now. I think there is going to be some speaker cabinet building thrown in too, but I'm going to try to get the amp squared away first.

So I started putting together a BOM for Tayda electronics, and I have some questions on part choices. I attached the BOM as well as a copy of the vero board in .png format. These questions are more or less in the order of your reply.

1. By far my biggest concern is electrocuting myself. Just to make things crystal clear, a 12VDC, 200mA wall wart will power the amp sufficiently, correct? The amp will be switched on and off by the input jack too, correct? You mentioned a filter cap; what value should I use and where does it go on the board? It is okay to completely do away with the battery power, correct? I loathe 9V batteries for some reason.

2. Unfortunately the mylk site is down, but I remembered to save some of the pages. For the decoupling cap (C9), they wrote "If you are planning  to build the circuit with lower gain and /or using it through a full size guitar speaker you may want to raise the value to 10uf. 1uf is perfect for a tight high gain sound but may leave the clean and semi clean tones a little bit glassy and sharp for your tastes. 10uf sounds great for clean and "just breaking up" Jimi Hendrix tones but may lead to high gain sounds being a bit farty and unfocused." I don't want farty sounds, that's why I thought in between (4.7uF) might be good. Are you saying that I should go with the 10uF cap?

Is the 2200uF cap you refer to here what I should use for the power filter cap from question 1?

3. I was planning on using IC sockets. I've used machine tooled sockets in the past, but saw that there are some cheaper sockets. In regards to quality, you're talking about the machined sockets right?

4. So, without the 3k3 in series, does that mean I can use any LED, or should I change the 3k3 based on what color LED I want? I specced for a red 3mm LED. What size is usually used on amps?

5. Some questions as I put together the BOM.

I specced for 1/4W resistors (except for the power resistor which is 1W). Is 1/4W enough for this application or should I go up to 1/2W?

Likewise, I specced the capacitors for 25V or more. Is this adequate?

I was looking over the parts list I saved from the web site and the output jack is specified as a switched mono jack. What is the purpose, if any, of a switch in the output jack? Can I just substitute a standard (guitar) jack.

Is there any rule for mounting pots, switches and jacks? I mean do I have to worry about pots/jacks/switches being too close to each other? Ideally I'd like the pots, switches, LED and input jack on the front (with room to add two tone controls down the road), but that sounds a bit cramped for a standard enclosure.

Finally, how do I mount the PCB board to the enclosure? Standoffs glued to the box? Is there a good place to buy these?

That's enough to deal with for now. Thanks for reading.

Edit: Whoops >:(. I just noticed I put down the wrong value on the BOM for R9 (power resistor) it should be a 10ohm, 1W, not a 1k. It's actually specced as 8ohm, so hopefully the extra 2 ohms aren't a huge problem.

1.  Never fear, you are not going to electrolux yourself on a wall wart (or even a 32V laptop supply for that matter).

9 to 12 volts, about a quarter of an amp minimum.  If you can find a regulated one so much the better, but you can take on as much (AC plugpack, you rectify, smooth and regulate), or as little (regulated 12V plugpack), or any mix in between, such as unregulated plug pack and add your own regulator between it and the amp, say if hum proves excessive.  Generally speaking with unregulated plugpacks the voltage sag later with higher capacity units, so a 500mA or 1 amp 12VDC unregulated, will hold a higher output voltage for a given current.  This shouldn't be a problem, just be aware voltages may be a bit high on nominal.

If you are only going to power by plug pack then you can switch it how you like, jack switch, toggle sw, or no power switch at all, just plug in/pull out the plugpack.

Whatever else, I've yet to see the DC plugpack that couldn't be improved with a bit of added capacitance, so somewhere between the plugpack and the amp you can add 1000-2200uF/16V cap across the supply.  Can go just about anywhere you can fit it (off-board somewhere I expect).


2.  Now we have a problem here because our project documentation is incomplete and contradictory.  "C9" 10uF doesn't relate to the "circuit" <mylk386Circuit.jpg> ("diagrammatic", actually)

I have to assume that you are talking about the bypass cap on pin 7.  This is to provide filtering against signals on the supply rail and its value is non-critical - "enough".  It's actually optional, but if you are going to put it in make it around 47uF.

LM386 datasheet (http://www.digchip.com/datasheets/parts/datasheet/321/LM386.php)


3.  machined sockets right?
Yes.  Only a small extra expense here, and you can learn what corners you can cut later.  If you plan to audition/blow up a lot of chips, good sockets are a must.


4.  All LED's gotta have some sort of current limiting, they are only forward biased diodes after all.  Typical LED current is 20mA but with Hi-Eff start with around 1mA and vary to taste.  1k per volt of supply, less the LED drop (2-3V typ), say 6k8 to 10k to start, and tweek from there - it's the effective brightness you are really interested in, not the exact LED current to get that effective brightness because you can't define what you want until you see it, then it's just more or less current.  The empirical (https://www.google.com/search?q=empirical) approach - suck it and see.  Anything less than 20mA can be assumed to be safe.


5.  The difference here between 1/8W, 1/4W or 1/2W is mainly physical; the power levels are mostly really low so whatever you've got should do.  The exception is the 1W load resistor on the output.

Caps should generally be rated for the highest expected supply voltage, say around 18V for a 12VDC unregulated plugpack, so 25V caps should be quite sufficient.

The use of a switching jack on the output is normally to turn off the internal speaker when an external speaker is connected (or whatever you want really) and quite optional here.  A simple plain mono socket should do fine.

I've seen components held down with epoxy, I've glued down circuits boards using silicon goo (almost as useful as gaffa tape around the workshop), plastic wall plugs make pretty good standoffs for PCB's.

A tinkerer/builder should have a tastefully stocked junk box (or shed), so much good stuff goes to landfill and can be stripped from dead items and reused, old 'puters often have an assortment of plastic standoffs/mountings for motherboards, CDRom boxes make good audio cases...

Secret to Learning Electronics - Fail and Fail Often - Jeri Ellsworth - YouTube
www.youtube.com/watch?v=xhQ7d3BK3KQ (http://www.youtube.com/watch?v=xhQ7d3BK3KQ)
Invest five minutes of your life in some damn good advice.  {and she plays bass}   :dbtu:

Roly, I think what you mentioned last resonates the most. I'm just going to go for building it according to the circuit diagram. I can sort out capacitors, resistors, and whatever else if the amp doesn't turn out well when all is said and done. I do have some final questions.

1. You mentioned using an LM833 for the preamp. How is the LM833 compatible as a replacement for the TL071 if it is a dual op-amp? Just looking at the pin out, they don't look interchangeable.

2. Google cache to the rescue. I was able to find a more recent image of the mylk diagram (although I think it's the same as what I posted before). I've attached a picture of the diagram with what I've been calling a decoupling capacitor circled in red. It's shown as 1uF. Since the author suggests anything between 1uF and 10uF I'm going to wing it and do 4.7uF. It wouldn't be off by an order of magnitude, correct?

3. By regulated power supply, you mean something like this (http://www.ebay.com/itm/CMVision-UL-Listed-Regulated-Power-Adapter-12VDC-1Amp-for-Camera-LED-Light-/121338828761?pt=US_Surveillance_Accessories&hash=item1c405b97d9), correct? I'm going to give it a go without the added capacitance and see what comes of it. Ideally I'd like the amp to be idiot proof (and by idiot I mean me) in case I accidentally grab the wrong wall wart. For now, I should be able to handle not using the wrong wart.

Thanks again. :)

{circuit attached - 1v0 so comments and corrections welcome.}


1.  Mainly that a soggy carrot is better than a 741 for audio, a TL071 is just fine.  Later if you want to add a tonestack having a second op-amp to hand in a dual is very helpful, but yes, the pinout is different to a single.


2.  You can wing it - winging it is good, gives you a feel.   :dbtu:

But you can get a theoretical prediction; the bigger this cap, the more bottom end will get through (http://hyperphysics.phy-astr.gsu.edu/hbase/electric/filcap.html).

I'm very suspect of the way they show the Master Volume pot wired - places stress on the driving preamp IC when the Master is set low/off.

---

A key point to stress is that when you build your own you are in total command - you don't like it?  Then change it!  :grr It's about the experimentation that we tend not to do on commercial boxes (for lack of documentation, value, etc etc)

---

Seven bucks looks okay.  It will be switch-mode being that small for 1 amp at 12 volts, so there might be some high frequency noise issues, but again, a 2200uF cap in between this and the amp and you'll be laughing.

QuoteLoad Regulation: ±3% over rated current: 0 - 1 Amp
Output Voltage Nominal: 12 VDC. Current: 1000mA (1A)

Reads as, 12.00V at 1.0 amp DC, rises 3% at no load, 12*1.03=12.36V off-load

In that respect an almost battery-like ideal supply.   :dbtu:  (but what can you scrounge?  Orphan plugpacks are all around us like odd socks and lost biros.)

Thanks for the circuit, Roly. It helps clarify what we were talking about. I now see where the 2200 and 100uF caps for the power supply go. I can handle that mod.

I see that you mentioned VR4 and R5 are of dubious value. I already thought R5 was dubious. Is there a (simple) way to improve the use of VR4 as an attenuator?

I don't seem to have any orphaned 12V or 9V adapters sitting in my junk bin, so I guess I'm stuck buying new.

Thanks for holding my hand through the planning stages. Just wait until I start to actually build something.

If you don't have any in your junk bin you should check out your local thrift store. Not quite but ALMOST as cheap as your own leftovers.

I might hit a trash bin and see what old electronics someone has tossed. I know I've seen old routers and CD players from time to time.

I know I said I wouldn't approach this until after the amp was put together, but I've been mulling over how to put together a speaker cabinet. I thought I could find a broken down amp and scavenge it, but I haven't had any luck so far.

I don't have any access to any heavy duty power tools, so I was thinking of doing something out of the box and having some panels laser cut via online service. The standard seems to be 3/4" thick panels. Would 1/2" ply with some hardwood bracing/battens work and glue and screws, or would it not be rigid enough? It seems like it would be sufficient for my uses, but then again, I've never built a speaker cabinet before.

Quote from: nipperiodicI thought I could find a broken down amp and scavenge it, but I haven't had any luck so far.

I don't have any access to any heavy duty power tools, so I was thinking of doing something out of the box and having some panels laser cut via online service. The standard seems to be 3/4" thick panels. Would 1/2" ply with some hardwood bracing/battens work and glue and screws, or would it not be rigid enough? It seems like it would be sufficient for my uses

Most commercial amp cases were rubbish when they came out of the factory.  They look great outside but they are built down to a price.  It's not hard to build a better case than you can buy (and you can make it exactly how you want).

3/4-inch is overkill (unless it's an 18" speaker for bass, and even then... it would be nice to be able to actually move it when it's built  :o ).  15-18mm (1/2" to 5/8") ply is suitable, avoid composite/fiber/MDF boards, lowest grade is fine if you are going to cover it.  You can never have enough hardwood framing and bracing inside, well you can, but again its easy to get a box really rigid without too much trouble.  It's amazing how much good, near new, timber gets thrown in the skip during shop renovations.   ;)

I've built cabs using only hand tools, but a drill and jigsaw are the minimum power tools, a circular saw of any sort is also helpful.  I run an old reversible drill of a 'puter PSU as a screwriver/undriver which is also very helpful.  But you really only need a bench and some floorspace where you can make a mess.  A straight 12" cab is pretty straightforward, sealed (initially), about root(2)=1.4 to 2 cu ft, or 55 Litres.

Well, I'm now waiting for some parts to arrive so I figured I might as well asks some questions about "features" for the speaker cabinet.

Should I install dual, parallel input jacks for daisy chaining? Not sure I would ever use this, but since I have the option to do it, why not?

Again since I have the option to do it now, should I consider using those fancy speakon type jacks or should I just stick with 1/4" jacks? Always been a little perplexed by the use of 1/4" jacks, since they don't seem very robust.

Edit: Also, do must people roll their own speaker cable for connecting amp heads to cabinets? I can't seem to find inexpensive short lengths of cable for this use.

Thanks, and a belated Happy New Year to everyone.

I have built a few, (3 to be exact) speaker cabinets, and always installed dual parallel input jacks for daisy chaining.
I didn't know if I would ever use the daisy chain feature, but thought better to have it and not need it...
So far I have not needed it...

I used 1/4 inch jacks, considered the Speakon's and figured they are more for pro audio gear PA stuff rather than guitar cabs.

I make my own short cable for connecting the cab to amp.

To be honest... the cabs I built are more like extension cabs for a combo amp that has an extension speaker output, rather than a dedicated cab for a amp head.
(although I'm working on one of those right now)

For my extension cabs I followed the guidelines in this book. >>> http://www.londonpower.com/Speaker-Book (http://www.londonpower.com/Speaker-Book)

Fascinating read, even if you don't build your cab according to his guidelines, it's still well worth buying/reading that book!  <3)

VERY different approach to speaker cabs for guitar! I highly recommend it!  :) (if only for the excellent info it contains, it's still worth it)

Cheers!
Dale

I use XLR's because the are robust, lock in, have very good contact area for carrying current, and the cable clamps work well with light/med weight standard round mains cable.  "Oxygen-free" is a total scam; what you really need is circular mills, cross-sectional area of the conductor (figure 5 amps minimum), and good road-tough covering (which mains cable is).

1/4-inch/6.5mm aren't really up to the duty (fragile, lack cable clamp), and Speakons are expensive overkill.

  Dual bananas are also fairly expensive.
Agree with Roly, XLR are a good option for carrying high current.
There are also 1/4" jacks with 2 tip contacts which helps, but they are not very common.

The problem with 1/4-inch hardware is that it was designed for the telephone system with a power level of milliwatts at 600 ohms impedance.

Double tip contacts are better than single, but in a speaker cab with a 50 watt amplifier the peak current is of the order of 5 amps!  If you have a close look at a jack plug in its socket you soon realise that the total contact area for both the ground and hot is none too impressive, and why 1/4-inch/6.5mm/TRS hardware really doesn't cut it for speaker connections.

The body sleeve effectively contacts at only two points, and with the common single hot spring, at only one point on the hot side, and this is a sphere against a plate, the contact area is a pinprick, yet we are expecting it to carry up to five amps.  If you look at such a speaker lead plugs after they have been in service for a while you may see a ring of pitting around the back of the tip ball where this point contact has got hot enough to melt the metal.  {and the 1/4-inch situation is not helped by manufacturers who can't stick to the size standards, so you get plugs that are very tight or won't insert, which get their tips trapped and can't be extracted, etc.}

In the XLR the trick is in the socket where the contact is a sleeve with a pair of helical cuts.  The ribbon thus created wraps intimately around the pin giving a large number of points of contact.

We are even more stuck with 1/4-inch at the input end, but really, they aren't up to this duty either.

Quote from: Roly on January 07, 2015, 03:22:21 AM


The body sleeve effectively contacts at only two points, and with the common single hot spring, at only one point on the hot side, and this is a sphere against a plate, the contact area is a pinprick, yet we are expecting it to carry up to five amps.

This is what I've always found perplexing. The 1/4" jack just never seemed like a good way to transfer power. Although, it has worked for how long now?

I'm certainly not going to be touring with the cab or the amp anytime soon, but I was thinking I might as well attempt to do it right from the outset. Never thought about using XLR jacks. I'll look into them and see what I come up with.

Thanks.

The 1/4-inch/"TRS"/6.5mm/Jack has never been a great connector for anything much, but for most musicians their shortcomings are below the irritation/action threshold, so they go with the flow.

Good quality hardware seems able enough up to a few amps peak (e.g. 50W into 8r), but starts to show signs of pitting as you get up to 10 amps peak.

A lot of the time I've also run a PA as well as a guitar rig and keyboard pit and amp rig, and with so many connectors to deal with jacks where they weren't needed were a pain in the bum needing constant attention to keep them working properly.

There was also the matter of having an extensive low level signal system and a high level signal system with interchangeable connectors, so I adopted XLR's for the speaker system.  The mikes also use XLR's so a mistake is still not impossible, just less likely, but the XLR's are so much more robust and roadworthy than jack plugs; they are hard to break, and they are less prone to picking up dirt on the contacts.

But for low power at home?  meh - 1/4-inch works well enough.

Just wanted to thank everyone again for the help and to add a bit of an update to this. I have a box of components but haven't had time to actually do anything with them yet. Hopefully I'll get some time in the near future to do some finger burning.

However, I did get a chance to get/make parts for a speaker cabinet. My living space just doesn't allow me to do any cutting or sawing of anything anymore, so I decided to go the laser cutting service route. I haven't had time to glue and screw the parts up yet, but I think it will turn into a cool little cabinet. At the very least, it will be unique.

Unfortunately, the service I used doesn't cut 1/2" ply any longer (no service seems to) so I had to go with 1/4" bamboo and lots of bracing. I know it's not standard, but I'm really having a lot of fun working this project out and seeing what comes of it. At least I hope something comes of it.

I designed the cab to sort of kind of look like an 8" tweed champ. There were a lot of ways I could have gone with the design, but I just wanted something simple and relatively cost effective. Not sure about finish yet, but the bamboo looks pretty cool, so I'm contemplating doing some type of wipe on finish. This cab is never going to see heavy duty use on the road, so it shouldn't be a problem. I'll have to get some pictures put up of the pieces when I get a chance.

So the above is a long way of bringing me to my next question, which I think is a fairly important one. Any suggestions for 8" speakers or are there any specs I should pay particular attention to? Speaker specs are a bit dizzying and as expected, every hobbyist seems to have their own idea about which speakers are great. One speaker that looked kind of interesting (although it looks like it's a not a true guitar speaker) is the Eminence Alpha 8A. I even found some clips of some guy using it as a guitar speaker. Anyways, I'm digressing. Any helpful hints?

Power efficiency - dB/W - the more the merrier.   :dbtu:

So, just to make sure I'm understanding you exactly, I want both dB and W to be as big as possible when selecting a speaker?

I'll use an example. So that Eminence speaker I saw comes in a couple of flavors. They are (with specs in the order sensitivity, power rating, usable frequency):

Eminence Alpha 8A: 94dB, 125W, 58Hz - 5kHz
Eminence Alpha 8MRA: 100.9dB, 125W, 400Hz - 4.8kHz
Eminence Beta 8A: 95.1dB, 225W, 78Hz - 4.5kHz

Again these are only examples, but your selection would be the Alpha 8MRA or Beta 8A due to the higher sensitivity and power rating?

Thanks for clarifying.

No, the wattage rating only has to be "enough". It's the sensitivity/efficiency in dB/W that is more important.

The dB rating is dB/W - dB per watt at one metre, generally measured at the 1 watt level.  This is the conversion efficiency of watts into Sound Pressure Level, SPL, sound.

While 94dB, 95.1dB and 100.9dB all appear to be pretty similar they are actually on a logarithmic scale, so the 100.9dB/W unit is actually quite a bit more sensitive than the other two.


As a sidebar; the ultimate SPL, that each driver is capable of has to be multiplied by the ratio of the power limit to the reference level, 1 watt.

The ratio of 1 watt to 125 watts is

dB = 10 log₁₀(P1/P2)

125/1 = 125

log₁₀(125) = 2.09691001

x10 = 20.969dB

So if it makes 100.9dB at 1 metre with 1 watt it will make 100.9+20.969 = 121.9dB at 125 watts.

Similarly the Alpha 8A will make 94 + 20.969 = 114.969dB at 125 watts.

The Beta 8A will make;

log₁₀(225) = 2.35218252 * 10 = 23.52182520 dB

95.1 + 23.522 = 118.6 dB at 225 watts.


The bottom line with a low power amp is that you need all the speaker efficiency, dB/W, you can get, so the Alpha 8MRA.


(ed: speelinge)

  Also note the frequency response.  The 8MRA is designed as a mid-range driver with freq. response dropping off below 400hz. 
  This may or may not be an issue, depending on how much low end response you need.
  But, keep in mind, A440 is the high E string at the 5th fret, open low E string is 82.41Hz.   ;)

Apologies Roly, I misunderstood. I thought you meant to take the sensitivity and power ratings and come up with some magic ratio. At least I was correct in assuming that sensitivity was important.

There aren't many 8" speakers with (relatively?) high sensitivity. Hence why I was looking out of the box at the 8MRA? I imagine it still produces at 82.41Hz, just not as loudly. I don't know if that's a good thing, a bad thing, or just something outside the norm. I wouldn't step on a bassists toes if I played in a band. Is the frequency rating really that important?

If I stick strictly with "high" sensitivity "guitar" speakers, really the most readily available speakers are the Eminence 820H, WGS G8C and Celestion Eight 15.

Anyways, I realize I'm doing lots of typing with very little building. Time to take some pictures of the cabinet pieces.

mmmm....yermmm... g1 makes a very good point.

The bandwidth is usually quoted at the "half power point" or 3dB down on the midband response.  With a CR network we expect the rolloff outside those points to be 6dB/octave, but a speaker is a complex resonant circuit and it's important what the resonant frequency f₀ is because below this the response drops, (IIRC) at 24dB/octave - right down a mine shaft.  So this driver might not have much response at all for musically important midband frequencies like A440 or Middle-C256, and could be pretty well inaudible at your open low-E string.

The Eminence BMRA is closed back for simplicity of installation and so can only be used as a midrange driver.
Even without a cabinet ... because the blind/closed frame works like a very very small one.

Now sometimes the exact same speaker comes in a standard open back frame, like a conventional speaker.

Those are very good efficient speakers for instruments with little bass content.

That speaker (even smaller 6"version, open back frame) is used in the diminute ZR lunchbox to get a loud , stage usable amp, in a mini size cabinet.

Amazing:
https://www.youtube.com/watch?v=w5ave1vU4ds

that said, they cheat a lot:

1) the amp actually "has bass" ... up to a point.
The circuit is secret but I found that it's reasonably flat at low volume, but at high power (say above 20/30W ), bass is limited below 200 Hz ... which by the way is a sensible choice.

2) 200W RMS?  :duh :loco :lmao:
Not in their wildest dreams.

It actually is around 60W RMS ... respectable enough.

That said, I like the little beast, very clever design.

See that they test it with a trebly Tele ... don't even dream of plugging your drop tuned 7 string there.

But the idea is very good, perfect for a busy Pro playing weddings and such.

Back to the BMRA, if you find same with open back ... may work for guitar.

FWIW`Celestion also has some similar "midrange"speakers, open backed.

They are just not in the guitar catalog but on the PA one.

Also check Jensen (both standard and MOD series), they might have something interesting.

You search the datasheets and link them here :)

I notice ZT themselves are a bit coy about power;

"Packing 200 watts of power"
"200W Class A/B Power Amplifier"
"Peak Output: 120 dB at 1 meter"

...and don't actually say "RMS".

The "peak" SPL of 120dB wouldn't be all that impressive in a stage amp even if it were sustained.  The moment a sales blurb mentions "peak" you should get suspicious.

There is an old saying about speaker boxes dating from the '50's - "There ain't no substitute for cubic feet".  There is a small industry devoted to trying to convince people that you can get huge sound, bass in particular, from a matchbox.  Well there are good physical reasons to do with the nature of air why that isn't true, and what you are being sold is an illusion.

"Science notwithstanding..." - no Michael Ross of Guitar Player Magazine, science rules okay?

"Pure analog front-end"

As opposed to what?  An analogue front end that has been sleeping around?   8|

It may be a fine little workhorse amp, but it is being let down by being way oversold.

{yeah, yeah, I know, I keep getting told that I evaluate marketing statements that were never intended to be evaluated.}

Well, Mr. Fahey, I'll take you up on your offer. I think I've already zeroed in on the most readily available and best bang for your buck, but I'd still like to hear opinions from the pros. Anyways, some data sheets, in no particular order:

Eminence Patriot 820H http://www.eminence.com/pdf/820H.pdf (http://www.eminence.com/pdf/820H.pdf)
Eminence Alpha 8A http://www.eminence.com/pdf/Alpha_8A.pdf (http://www.eminence.com/pdf/Alpha_8A.pdf)
Jensen Mod 8-20 http://www.jensentone.com/printpdf/45 (http://www.jensentone.com/printpdf/45) *The Jensen links are a little flakey. I had to save the link as a PDF to view the files correctly.
Jensen C8R http://www.jensentone.com/printpdf/30 (http://www.jensentone.com/printpdf/30)
Jensen P8R http://www.jensentone.com/printpdf/14 (http://www.jensentone.com/printpdf/14)
Celestion Eight 15 http://celestion.com/productpdf.php?id=8 (http://celestion.com/productpdf.php?id=8)
WGS G8C http://wgs4.com/g8c (http://wgs4.com/g8c)
Weber Speakers (various 8" clones?) https://taweber.powweb.com/weber/ (https://taweber.powweb.com/weber/) They have all kinds of variations, but no specs. They also offer reconeing of vintage speakers via their eBay store, if an 8" ever pops up. Maybe someone here knows some of the intricacies of their speakers?

They all look pretty similar spec-wise, although the Jensen's seem to be a little low in sensitivity relative to the others. Given its current price, my pick would be the Celestion Eight 15 ($29 shipped), but I welcome someone telling me why I should opt for something else.

Edit: Weird. At least on my computer, my pics seemed to keep this last page from loading correctly. I'll post links to the photos for now.

As I said, I need to get some pics of the cabinet up, so here are some blurry pics of the pieces still in their frames. Note that there is protective paper on the pieces which hides the grain of the bamboo.

http://imgur.com/ULqVVOL (http://imgur.com/ULqVVOL)
http://imgur.com/NvNVSfH (http://imgur.com/NvNVSfH)

All in all, pretty happy with how it turned out. I had a chance to dry fit the pieces, and everything lines up about as well as I would have managed with a saw and router. The only booboo is the front panels. I think some gremlins invaded my design software; they are about 1/16" short on one side. I think some creative gluing to the short end will make the mistake unnoticeable though.

Well, I'm a little bummed that no one checked in to see if I ever made any progress with this.

I did finally make some progress. I even have some play by play pictures. Unfortunately, the amp doesn't seem to work, so I need some (explicit) help figuring out what's wrong. I imagine it's something simple that I'm overlooking, but who knows.

When I plug the amp in, nothing explodes or gets hot, but the LED fails to light up. There is absolutely no signal being put out to the speaker.

The only intentional modification I made was Roly's suggestion of buffing up the capacitor's to 2200uF/16V (to replace the 470uF) and the 100uF/16V (to replace the 47uF). The only other peculiarity is I have the speaker connected via alligator clips since I don't currently have a cabinet to plug into. Probably not ideal, but it's what I've got. Speaking of which, what are the little crimp connectors called that you use to connect speaker wires to the speaker terminals?

So if someone can explain what I need to do to troubleshoot, I'd appreciate it. Pictures to follow.

I thought I did a pretty good job with this (I was even a little proud of my work), so it's definitely frustrating that the amp isn't working. Anyways, below are the pictures of the work in progress. Hopefully the pictures don't break my thread again.

Broke the tracks.

(http://i.imgur.com/aSBjiHs.jpg) (http://imgur.com/aSBjiHs)

Added the jumpers.

(http://i.imgur.com/kzMraOR.jpg) (http://imgur.com/kzMraOR)

Added the op-amp sockets.

(http://i.imgur.com/igLI4pi.jpg) (http://imgur.com/igLI4pi)

Added the resistors and diodes.

(http://i.imgur.com/8wF6rNV.jpg) (http://imgur.com/8wF6rNV)

Film caps.

(http://i.imgur.com/Wnq9hfc.jpg) (http://imgur.com/Wnq9hfc)

Electrolytics.

(http://i.imgur.com/xszFqXg.jpg) (http://imgur.com/xszFqXg)

The backside.

(http://i.imgur.com/j8UTWiF.jpg) (http://imgur.com/j8UTWiF)

Op-amps installed.

(http://i.imgur.com/LrOAptq.jpg) (http://imgur.com/LrOAptq)

All the pots, switches, and jacks connected.

(http://i.imgur.com/6R0tUEt.jpg) (http://imgur.com/6R0tUEt)

Well, it is kinda on you to present your results rather than wait to be asked.

Without reading through three pages of an old thread, I am just looking at the previous couple posts.  8" guitar speakers are 8" guitar speakers.  other than to report if one brand blows up a lot, chosing one is always a matter of taste.  My favorite one may not be your favorite, and vice versa.

The little flat blades on the speakers, and the female crimps that fit onto them are called quick disconnects, and also by the brand name Faston.   They come in sizes by width, as well as the size wire designed to be crimped to.  Width is percent of an inch, so the 250 series is .250 inch or 1/4".  Smaller sizes are 205 and 187.  In my drawer I have them called just speaker terminals, but I THINK those are the 205 size, and the 187 being slightly too small.  Readily available from Mouser or similar.

So it sits there dead?  If nothing lights up and no sound is produced, start at the power supply.  Is there any voltage in the circuits?  verify you have mains voltage across the primary of the power transformer.  if that is not there, you have a problem in the power switch, the fuse/fuse-holder, the mains cord, or the mains wiring.

If you are using a batteru or bench supply or adaptor, then verify it is putting out the desired voltage.

 :lmao: I was only kidding about no one asking about the project.

Thanks for the info on the crimps.

I did forget to mention that I switched out the battery for a DC jack and am using a wall wart for power. Don't know how I forgot to mention that.

So the wall wart is rated for 12V and is putting out 12.3V according to my DMM. So I guess it's working.

I'll have a look at the rest tomorrow and try to figure out how to measure/check what you asked for.

Thanks for the help.

Whoa, it works.

Turns out I had the female power jack wired up (in)correctly. A while ago, I was playing with it on a breadboard before putting the amp together and had figured out the pin out with a DMM. When I went to solder it in, I didn't remember how I had it connected, so I followed a picture I found online. Who knew, the internet can be wrong.

Obviously, I haven't had much time to play with it yet. It gets surprisingly loud.

I think the 500K pot for the pre-amp gain is way too much for my needs. Turning it all the way up with the output volume maxed creates a rumbly/buzzy sound.

Switching the power amp gain switch to max (200X) gives a metal sound, while the other two settings (20X and ~52X gain) are just sort of clean and louder clean. Which I guess makes sense and is probably more useful than not.

The top boost/bright switch doesn't really seem to make much of a noticeable difference to my ear.

All in all, I think it sounds pretty good considering it's sitting unenclosed on a desktop connected to a speaker without a cabinet. Especially considering I didn't electrocute myself, start a fire, or blow up anything. There is quite a bit of extra room on the board, so I would still like to add some sort of tone control (because why not). I also would still like to add an extra diode to get asymmetrical clipping (not sure how to fit this in).

Fun project. Definitely learned a bit. Not sure if this really solves my goal of a super clean amp. Sort of interested in trying to put together an amp with the LM833 Roly mentioned earlier.

Anyways, I'm rambling. I need to get the speaker housed and find something to fit the amp into.

I'll say it again, because I can't say it enough. Thanks for all the help.