Banana Jack Amps: No-Solder, All-Tube Guitar Amp Kits

[Gerry Rzeppa]

Even a child, or my mum, would figure out to plug an IEC lead into an IEC socket and a banana lead into a banana socket. That's all it takes to get a shock from your setup,

Yes, but I child, and I suppose your mum, wouldn't have purchased a Banana Jack Amp kit in the first place. And you have to turn it on, too. I suspect (if it hasn't occurred to the person earlier) it is probably at that moment they will realize they should take care -- they're turning on a device that has loose wires plugged (albeit indirectly) into the wall. I really don't think any of our prospective customers would be fool enough to do as you say.

...and it is not reasonable to expect self-evident connections like that to create a lethal hazard.

There is no hazard when the unit is not plugged in. And it is a simple matter to pull the IEC connector from them amp and set it aside; I've done it dozens, if not hundreds, of times. It's an easy operation, it's a convenient operation, and it renders the entire kit electrically harmless.

But I would further argue that it is reasonable to expect self-evident connections to create a lethal hazard when one of those connections goes into a wall socket. Nevertheless, just to be sure, we add (1) warning labels, (2) cautions on every page of the instructions, (3) and market only to those old and bright and disciplined enough to (a) read and understand Kenn Amdahl's book, (b) actually know what a valve amplifier is, (c) actually desire to own one, and (d) actually desire to construct one. Goodness, Merlin! Exactly whom do you picture spending $270 for the privilege of building one of these?

It needs to be more difficult.

I presume you mean, "It needs to be more difficult to hurt yourself with it" because, as it stands, that's possibly the most ridiculous statement I could ever imagine an teacher (like yourself) saying.

As I've pointed out, it would actually take some very minimal changes to your design to make it pretty safe.

It already is "pretty safe". Safer, in fact, than any other comparable kit on the market. Compare, again, these two kits at the same stage of construction, but this time picture the same person working with each: somebody old and bright and disciplined enough to (a) read and understand Kenn Amdahl's book, (b) actually know what a valve amplifier is, (c) actually desire to own one, and (d) actually desire to construct one:



Are you just yanking my chain here? Why don't we go back to discussing the difference between direct current (where the electrons move in only one direction) and alternating current (where the electrons move in both directions). We were getting somewhere with that discussion...

[merlinb]

Yes, but I child, and I suppose your mum, wouldn't have purchased a Banana Jack Amp kit in the first place.

But a 20-year old male might buy it, and if a child can figure out what to plug in where, then a 20-year old certainly can.

And you have to turn it on, too. I suspect (if it hasn't occurred to the person earlier) it is probably at that moment they will realize they should take care

Nope, because most people aren't used to anything being dangerous when they turn it on. They're not suddenly going to get a clue when they buy your kit.

-- they're turning on a device that has loose wires plugged (albeit indirectly) into the wall. I really don't think any of our prospective customers would be fool enough to do as you say.

Of course they would. Heck, I would. I'm very likely to plug the IEC lead in, and some banana leads, maybe even have the whole thing completed. Then I take a phone call, come back, forget I've left it switched on, unplug the banana leads...  Or maybe I have switched it off but someone else in the household decides to turn on the TV which happens to be near the same outlet, only they flick the wrong switch while I'm holding the banana leads... There's any number of scenarios in which even a competent person could end up holding onto the banana leads coming out of your fuse box while it is live. Legal and moral obligations require you to make the product substantially safe against everyday scenarios.

But I would further argue that it is reasonable to expect self-evident connections to create a lethal hazard when one of those connections goes into a wall socket.

Nope, because nothing any normal person owns, and plugs things into (and is inside an enclosure as each of your modules is), is dangerous when powered from the mains.

Nevertheless, just to be sure, we add (1) warning labels, (2) cautions on every page of the instructions,

How many people read the instructions before trying out their new toy? Hardly any. I know you're going to say "well that's their own stupid fault", and indeed it is, but it wouldn't defend you in court. It would be your fault for not making it immune to basic user error. You can get away with it not being complete-retard proof, but it does need to be fool proof.

Goodness, Merlin! Exactly whom do you picture spending $270 for the privilege of building one of these?

Guitarists, and they ain't known for their technical knowledge  

I presume you mean, "It needs to be more difficult to hurt yourself with it"

Obviously.

It already is "pretty safe".

No. It may qualify as pretty safe in your own head, but to those who are seeing it with 'fresh eyes' the fuse-box is an obvious death trap. There are very strict laws about mains wiring in products for sale, and for good reason.
The DC side of the circuit is also a bit dodgy. Most small traders don't -and sometimes can't- follow every single rule in the UL60065 document, but the rules about mains wiring they do obey (not least because these rules are actually very easy to adhere to). Your fuse box does not comply; it is basically the same as Mojotone's suicide lead.

Safer, in fact, than any other comparable kit on the market. Compare, again, these two kits at the same stage of construction, but this time picture the same person working with each

You can't keep using that as an agument. Your kit is ready to plug into the wall. The others are harmless until a lot of time and effort has been put in (with the exception of the suicide lead supplied by Mojotone- that is a frightening mistake on their part).

[Gerry Rzeppa]

...the suicide lead supplied by Mojotone- that is a frightening mistake on their part.

And, apparently, on the part of almost every other amp kit manufacturer out there. The same kind of "suicide lead" (as you call it) is found not only on "beginner" or "starter" kits by Mojotone, but on those by Allen Amplification, MADAMP, Marsh Amplification, Mission Amps, MOD KITS, S5 Electronics, Trinity Amps, Victoria Amplifier, Watts Tube Audio, Weber, and a number of others I suspect but couldn't confirm.

The rule for all these kits -- including ours -- is the same, and is not at all difficult: Don't mess with the wires when the thing is plugged in. And all these kits -- including ours -- are electrically inert when they're not plugged in (assuming caps have been discharged; ours discharge automatically).

[vigilante397]

assuming caps have been discharged; ours discharge automatically

I hate to get "off topic" here, but I would like to know a bit more about this. I've worked on too many amps that don't have this feature (*ouch*) and I think it would be a great thing to have, especially since I've been considering getting into amp building. Schematic maybe? 

vigilante397 - turning everything into a learning experience since 2014

[pickdropper]

...the suicide lead supplied by Mojotone- that is a frightening mistake on their part.

And, apparently, on the part of almost every other amp kit manufacturer out there. The same kind of "suicide lead" (as you call it) is found not only on "beginner" or "starter" kits by Mojotone, but on those by Allen Amplification, MADAMP, Marsh Amplification, Mission Amps, MOD KITS, S5 Electronics, Trinity Amps, Victoria Amplifier, Watts Tube Audio, Weber, and a number of others I suspect but couldn't confirm.

The rule for all these kits -- including ours -- is the same, and is not at all difficult: Don't mess with the wires when the thing is plugged in. And all these kits -- including ours -- are electrically inert when they're not plugged in (assuming caps have been discharged; ours discharge automatically).

You've focused on a very limited section of Merlin's post and ignored all of the important points. He addressed the differences between an amplifier parts kit (such as a mojotone) and your building block kit a few different times in his posts (IE: the raw parts in a kit amp are generally harmless until you build the amp, which requires some level of technical expertise).  The same cannot be said for your building blocks amp.  Not only that, but in a traditional kit amp, all of the lethal voltages are contained within the chassis.  If all of the lethal voltages were contained within the sealed cubes, it would be a totally different scenario; but they are not.  One can be shocked on the outside of a finished kit while plugging and unplugging the banana cables, which requires no level of technical expertise, nor is it intuitively dangerous; in fact, it's quite the opposite; it seems like it wouldn't be safe because most folks aren't use to that sort of thing being dangerous (I realize this is basically a repetition of Merlin's well thought-out post).

[pickdropper]

assuming caps have been discharged; ours discharge automatically

I hate to get "off topic" here, but I would like to know a bit more about this. I've worked on too many amps that don't have this feature (*ouch*) and I think it would be a great thing to have, especially since I've been considering getting into amp building. Schematic maybe? 

vigilante397 - turning everything into a learning experience since 2014

You can do that with a bleeder resistor to discharge the caps.

[Giglawyer]

As I've pointed out, it would actually take some very minimal changes to your design to make it pretty safe.

This is really the key.  But he just won't listen.

[Gerry Rzeppa]

assuming caps have been discharged; ours discharge automatically

I hate to get "off topic" here, but I would like to know a bit more about this. I've worked on too many amps that don't have this feature (*ouch*) and I think it would be a great thing to have, especially since I've been considering getting into amp building. Schematic maybe? 

Take a look here:

http://www.modkitsdiy.com/sites/modkitsdiy.com/files/product_files/mod_102_schematic_0.pdf

That 220k resistor just to the right of the power transformer at the bottom of the schematic is the "bleeder" resistor. It doesn't do much to normal operation because very little current goes through it -- the total resistance of the rest of the circuit being so much smaller. But enough current does go through it to drain the big capacitors of their charge when you shut the power off (or unplug the amp).

Here's the schematic for our vacuum-tube rectifier module (flow is from right to left):



The 220k resistor is the bleeder. You can see it "strapped" to the capacitor here:



And here's the schematic for our solid-state rectifier module, with a two larger capacitors connected in a "pi" formation (again, flow is from right to left):



The bleeder is the 220k resistor at the far left. You can see it in the module here (the capacitors are both in the "can" on top of the module, 32uf instead of 50uf as indicated on the schematic):



You can also discharge capacitors by touching a stiff, insulated wire to both ends, but you may get a spark doing it that way.

[Gerry Rzeppa]

...in a traditional kit amp, all of the lethal voltages are contained within the chassis.

Once again, I must insist on comparing apples to apples. In the photo below, on the left, we have a Banana Jack chassis -- not a finished amp. On the right we have a Mojotone chassis -- not a finished amp. High voltages on the Banana Jack chassis are inaccessible without removing a cable, and the danger areas are clearly color colded (red: danger; yellow: caution; green: safe); on the Mojotone chassis, high voltages are fully exposed at various (and not at all obvious) points, with no special indication:

If all of the lethal voltages were contained within the sealed cubes, it would be a totally different scenario; but they are not.

Such a configuration would defeat the whole purpose of the project. We want a "tube amp breadboard" that can be easily rearranged so the student can experiment without soldering, de-soldering, and re-soldering.

One can be shocked on the outside of a finished kit

Not our finished kits. Those look more like this (with all the banana cables fully enclosed):



You're talking about a finished chassis ready for testing, experimentation, and modification. Just like the open Mojotone chassis on the right, above -- only more convenient.

...plugging and unplugging the banana cables... requires no level of technical expertise... nor is it intuitively dangerous; in fact, it's quite the opposite; it seems like it wouldn't be safe because most folks aren't use to that sort of thing being dangerous (I realize this is basically a repetition of Merlin's well thought-out post).

"Most folks" aren't going to have a Banana Jack chassis sitting around the house. The people we are targeting are people old enough, smart enough, and disciplined enough to (a) read and understand Kenn Amdahl's 217 page book, cover to cover; (b) know what a valve amp is; (c) want to own a valve amp; (d) want to construct their own valve amp; and (e) have $270 to spend on it. Such are not "small children" and "uninformed mums". And they will be no safer with other tube amp kits; less safe, actually (because they'll have to deal with the unmarked and unobvious danger areas in the chassis on the right, above, not to mention hot soldering irons).

[pickdropper]

Actually, many people are familiar with banana plugs because their hifi equipment uses it.  I know many people that are not very knowledgeable about electronics but have had no issues connecting their speakers to their hi-fi receiver using cables terminated with banana plugs.  For the layperson, I think banana plugs are largely associated with harmless, low voltage audio connectors.  For engineering professionals, they are more known for their use in test equipment.

As you've repeatedly said, the purpose of the kit is to have a breadboard of sorts for tube amps.  This implies that it will be used as a teaching exercise with the acrylic cubes exposed but not in a final chassis.  To put it in a final chassis would negate one of its primary listed purposes. I get the argument you are trying to make, but I believe it's disingenuous. 

With a tube amp kit, it is not designed to be used with an open chassis, it's design is for it to be enclosed in a headshell, where the lethal voltages are contained.  Sure it can be operated in the open, but that is not it's intended usage.

I don't expect we are going to agree on this (even if all of us keep writing the same arguments over and over).  Would you consider calling a UL certification lab and asking them to look over the design?  They could likely give you an expert opinion on what you are bound to change (if anything) according to the law of the land.  You could make your tube amp kit argument to them as well.

[Ice-9]

When I was 10 years old all I wanted for Christmas was an Elektor hobby electronics kit, Now my parents having no clue about electric or electronics could have went out and bought me that kit, which of course would have been safe running as it did from a little battery. I didn't get one Christmas as it happened.

Roll on 38 years, Gerry is planning in principal of selling a high voltage valve amp as an electronics  learning kit.
Now little Jimmy aged 10 tells his parents about this great amp that is an educational tool and as he plays a little bit guitar this would be so cool to have. His parents have no clue about amps and guitars other than 'Hey these must be like hifi's and TV's and other audio video shit, so no problem' Parents have little or no knowledge of what its all about but think it's ok as it was on the net etc etc.

Roll on one week, little Jimmy will never get to be Big Jimmy.

This is not a home hobby electronics kit, Will these be sold to anyone who wants to buy it or will you personally be talking to everyone who purchases the plexi kits.

To be honest most people that buy PC's and laptops should have to take an intelligence test first.

[Gerry Rzeppa]

Would you consider calling a UL certification lab and asking them to look over the design?  They could likely give you an expert opinion on what you are bound to change (if anything) according to the law of the land.  You could make your tube amp kit argument to them as well.

No need to spend a lot of money to be told what I already know. As I've said before, I trust my own judgement on this matter. And since the risk is all mine, well, that's the end of it. The law of the land places no restrictions on components such as ours. Think about it; anyone can buy a power cord with bare wires on one end at Walmart, Lowes, etc; or a 20-amp circuit breaker that can't be installed without opening up a 200-amp service box. Our stuff falls into the same category: components. Use at your own risk. The difference is that our power cord has a connector on both ends, and our fuse and holder comes with warning labels and detailed instructions (with more warnings on every page), etc.

Related aside (from the "be careful what you wish for department"):

I just bought a three-dollar jump rope for my kid at Walmart. It came with a one-page "USER'S GUIDE" that, curiously, says nothing about how to jump rope! The whole page is warnings and caveats and lawyer-speak. See below.



My favorite is #8: "Always wear eye protection when using this product." Which means hundreds of millions of little girls, like this one, are being very unsafe at this very moment:



I wonder if that's inertia making her hair go like that? or did she fuss with her big brother's Banana Jack Amp before coming out to play? Too facetious? Sorry. You guys are wearing me out.

Interestingly, that power cord with the bare ends I mentioned above has no such instruction/warning sheet. Apparently these huge lawyer-infested companies think that's okay. Why? Probably because they know the market for bare-ended power cords (like the audience for tube amp kits) is not the same as the audience for jump ropes.

[pickdropper]

Actually, I got a Mojotone kit a couple of months back.  It came with an IEC power connector and a standard power cable: No bare ends.  I wonder if they've changed because of liability reasons.

The reason the jump rope came with all the legal warnings (which I agree seem excessive) is because corporations usually go to great efforts to protect themselves as much as possible from misuse they could be held liable for.  That's all we we trying to say.

Now, it's possible I am more sensitive to this because I've had to deal with a lot of this lately (FCC, CE, FDA).  There are many legal requirements that I think are excessive and some seem to be written more by politicians than by people knowledgeable about the ramifications, but that doesn't mean that the products being developed aren't bound by them.  And yes, I have spoken with consultants and test labs that helped clarify the muddy waters (well, most of them help clarify).  There's a lot to learn and gut feelings, intuition, and (sadly) sometimes common sense aren't enough to legally protect you.  I don't consider any of the issues brought up in this thread to be of the excessive and silly manner.  I believe there are some real legal liabilities here.

I completely agree that this is your risk to bear.  I will admit to being slightly bewildered that you won't even consider simple changes that could make the product safer, but that is your choice.  As I've said before, I think the product has potential and I hope that it ends up working out for you.

[Gerry Rzeppa]

Now little Jimmy aged 10 tells his parents about this great amp that is an educational tool and as he plays a little bit guitar this would be so cool to have. His parents have no clue about amps and guitars other than 'Hey these must be like hifi's and TV's and other audio video sh*t, so no problem' Parents have little or no knowledge of what its all about but think it's ok as it was on the net etc etc.

So the kit arrives with warning labels on the box, and on the modules, and on every page of the instructions. And Jimmy's parents -- dad utterly irresponsible and mom completely void of any trace of mother instinct -- somehow aren't moved to take a closer look. Don't notice that the thing doesn't look like a typical consumer device, or even a typical guitar amp, but has vacuum tubes and transformers and all kinds of wires in plain sight. Aren't interested in supervising. Don't ask Jimmy any questions, like, "Does that thing plug in the wall?" I'd say Jimmy needs better parents.

Will these be sold to anyone who wants to buy it or will you personally be talking to everyone who purchases the plexi kits.

Do the Mojotone people personally vet all of their customers? How about Weber? Not their problem. Not mine.

To be honest most people that buy PC's and laptops should have to take an intelligence test first.

But where does that kind of thing stop?

[Gerry Rzeppa]

...the purpose of the kit is to have a breadboard of sorts for tube amps.  This implies that it will be used as a teaching exercise with the acrylic cubes exposed but not in a final chassis.  To put it in a final chassis would negate one of its primary listed purposes.

Yes, kind of like this:



Of course that was back in the day when you didn't need permission or a license or a lawyer to experiment, explore, and get things done. Back in the day when a modicum of common sense in one's audience could be assumed (be they students, or mothers of students). Perhaps the times have passed me by...

[Govmnt_Lacky]

Wondering if I should look into this. I have a metric CRAP TON of banana jacks at my work that are gathering dust  

Heres a solution to satisfy the masses.... Send me one of your kits and I will report back on it!  I have no problem acting like a kid (ask my wife!)

[tubegeek]

And since the risk is all mine, well, that's the end of it.

The financial risk it seems to me is being borne by the Kickstarter donors. The safety risk, well, since you tell us there isn't any, and since you claim you've been paying attention your whole 61 years on the planet, I guess it doesn't matter, right?

Reading your replies is making me sick. You won't even reach into your pocket to make a consultation, and if the donors fund your project, you won't even cut into your profit margin enough to provide the banana plugs that you concede are safer. You're showing all the earmarks of a sick greedhead.

This is absurd. When (not if) someone gets hurt and you get sued, this thread will bury you. And it might not be a civil liability you are so blithely ignoring. Feel free to reply with your usual nonsense but it doesn't change the truth.

Also you might want to see a different kind of professional about your paranoia. The Elders of Zion, or whoever you think reads this forum, are NOT behind this conspiracy to take a gentle, law-abiding small-town warm-hearted grand-dad and crush his brave entrepreneurial dream.

EdIT: "plugs" for "jacks"

[Gerry Rzeppa]

Reading your replies is making me sick. You won't even reach into your pocket to make a consultation, and if the donors fund your project, you won't even cut into your profit margin enough to provide the banana plugs that you concede are safer. You're showing all the earmarks of a sick greedhead.

Buying for 100 amps at a time, the part cost for a Banana Jack Amp Kit, as described, will be around $200 per kit. And there's a lot of labor: about 320 distinct fabrication/assembly steps (drilling, mounting, soldering, etc) per kit; if we average one minute per operation, that's more than 5 man-hours per kit; at $15/hour, another $75-$80. Add to that testing, documentation (including all those warning labels!), packaging, shipping, and general overhead, and we're looking at a break-even no less than $350 per kit. If we reach our funding goal ($39,000) we'll be left with only about $500 (since Kickstarter and Amazon Payments take about 9% off the top), which will be spent sending out the lesser rewards requested by small-donation backers (keychains, posters, books, etc). This project is not a money-maker for us; it's a labor of love hoping to inspire others to think simply, practically, and outside-the-box. Where's the greed of which you so glibly speak?

[PRR]

> the schematic for our solid-state rectifier module, with a two larger capacitors

100uFd at 220K bleed is a 22 second time-constant.

To 37%.

Starting from say 300V, after 22 seconds you still have 111V, a significant shock.

After 44 seconds, 41V, which is often harmless but above the 25V which recent regulations use as a dividing line.

Takes nearly a full minute to drop below 25V.

[Gerry Rzeppa]

> the schematic for our solid-state rectifier module, with a two larger capacitors

100uFd at 220K bleed is a 22 second time-constant.

To 37%.

Starting from say 300V, after 22 seconds you still have 111V, a significant shock.

After 44 seconds, 41V, which is often harmless but above the 25V which recent regulations use as a dividing line.

Takes nearly a full minute to drop below 25V.

My value was from actual measurements. I suspect the difference (from your calculated value) is that (1) it's not 100uFd in the actual modules, it's (a) 64uf in the one, and (b) just 20uf in the other (nominal, of course -- perhaps more or less due to component tolerances); (2) we're not starting at 300 volts, but 240 volts; and (3) it's not only the resistor that's doing the bleeding (there are other components in those modules; and my readings were taken with other modules connected as they typically would be in such a situation -- you can't charge up the cap(s) without connecting the rectifier module to at least the transformer and fuse modules, and you can't unplug all the banana cables at once with just two hands). We'll do further testing, of course, before a production run; if it appears to be a problem, we'll adjust the resistor and/or the cap(s) appropriately.