The Truth Pre Amp Review

[Francis Vaughan]

does that mean we should jail all people who sell vacuum tube amplifiers?

If a new tube amplifier does not meet accepted specification for safety the manufacturer needs calling out. Nobody denies that there have been very poor devices sold in the past. Like anything with a death capacitor. But no device like this has met spec for many decades. Modern tube amplifiers meet modern specs. If you want to look at a modern device that has the capability to kill you stone dead, look no further than a microwave oven. That has the capability to not just electrocute you, it will kill you unrestartable dead. But these devices are built to spec, and are sold in hundreds of millions with no problem.

And up until recently any TV had kill you dead voltages inside. Again, no problem because they were built to modern safety specifications.
Just having high voltages is really not the problem. It is realising that there are well developed safety specifications and that as a manufacturer you have, minimally an ethical, and usually legal, duty to meet them. The Truth does not.

Citing old designs from a time when life was cheap and nobody cared does not excuse a manufacturer operating today. We don't accept this argument in any other part of life, and there in no excuse here either.

 

[Bob from Florida]

Lordy, yes. Those capacitors have a name. They have become known as "death capacitors". Especially in tube guitar amp circles where vintage amplifiers are not consigned to the trash but are prized possessions. They are call this because they have a habit of failing. And when the fail they short out, with a 50/50 chance of bringing the chassis to live. Many of the stories you hear of guitarists being electrocuted on stage are, at their root, a failed death capacitor.

Here is a link to a guitar amp technical site going into some detail on these capacitors.
https://robrobinette.com/Death_Cap_and_Ground_Switch.htm
The author claims no actual deaths can be traced to guitarists being electrocuted. Obviously the potential is there if plugged in backwards and the cap shorts out.

 

[Bob from Florida]

As I mentioned, it's not a particularly safe design, but we should keep things in perspective. Unless it's been modified, a Dynaco ST-70 (and that is still a very popular amplifier) is far worse than this. There is no safety ground. If you don't have the top cage, there is exposed high voltage on the PCB. A Heathkit AA-121 is no better. Quite a few old tube amps operate with the shell of the filter caps at a high voltage potential, and the only thing protecting the user is a layer of 60-year-old cardboard. Don't even get me started on some of the old RF amps sold to hams.

This thing has questionable safety grounding, yes, but there is no exposed high voltage, it uses off-the-shelf Mean Well power supplies (which are certified and are a good brand), and although things aren't great inside, they aren't that scary.

Again, I'm not saying this is right, but it's important to keep things in perspective. There are commercial tube amplifiers available, some of which run plate voltages over 1000 volts (with plenty of current behind it). For those who are saying that the person who built / sold this preamp "should be jailed for safety violation", does that mean we should jail all people who sell vacuum tube amplifiers? The chances of a user coming in contact with a HV supply in a tube amp (broken tube, removing a tube from the socket, catastrophic failure) is probably a lot higher than the chances of the chassis on this becoming hot, and the HV supply in a tube amp is also, in most cases, a hell of a lot more dangerous.

Furthermore... I see knockoff equipment from overseas that is a lot scarier than this. I'm not saying this preamp is right (as I've outlined, there are a lot of things I don't like about it), but let's keep things in perspective.

Absolutely agree - a little perspective can provide some balance. The "Truth" may not achieve technical or safety perfection but is providing some enjoyment to happy customers. Understanding the ground lift switch operation does give the user a choice of whether to use it or even order one without the switch.

 

[solderdude]

The ground lift switch as done in the picture shown is an incorrect way.
Regardless if the enclosure get's grounded from an amplifier or source connected to it the way it was done is incorrect.
The enclosure should always be connected to safety ground (that's the ONLY purpose of the safety ground connection) and the switch should be between the signal ground and the chassis.

Aside from that workmanship is shoddy, the name 'the truth' has no relation to reality (it adds distortion that reaches audible levels) and is way too expensive for such amateur (well amateurs in general make much nicer gear) attempt.

Yes, some people like effect boxes instead of electrical fidelity and yes some may like the sound and some may be charmed by the DIY look.
If that's enough of an excuse to fork out $1k then so be it.

 

[egellings]

My understanding is that those 'death capacitors" were used in series string old tube table radios (no power xfmr) to place the chassis at AC ground without resorting to a direct connection. The power cord plugs weren't polarized then and the radio could be plugged in such that the chassis was hot w.r.t. ground, but at least current limited by the capacitor's leakage & reactance. The caps weren't needed in transformer powered radios.

 

[dfuller]

If a new tube amplifier does not meet accepted specification for safety the manufacturer needs calling out. Nobody denies that there have been very poor devices sold in the past. Like anything with a death capacitor. But no device like this has met spec for many decades. Modern tube amplifiers meet modern specs. If you want to look at a modern device that has the capability to kill you stone dead, look no further than a microwave oven. That has the capability to not just electrocute you, it will kill you unrestartable dead. But these devices are built to spec, and are sold in hundreds of millions with no problem.

Part of what makes death caps dangerous is that they were often done with caps that were not rated as Y caps (i.e. they would fail short, not open). But you know this, of course.

And up until recently any TV had kill you dead voltages inside. Again, no problem because they were built to modern safety specifications.
Just having high voltages is really not the problem. It is realising that there are well developed safety specifications and that as a manufacturer you have, minimally an ethical, and usually legal, duty to meet them. The Truth does not.

1000% correct. 3-wire power cords with a dedicated ground and proper insulation of high voltage circuits is crucial to consumer safety.

My understanding is that those 'death capacitors" were used in series string old tube table radios (no power xfmr) to place the chassis at AC ground without resorting to a direct connection. The power cord plugs weren't polarized then and the radio could be plugged in such that the chassis was hot w.r.t. ground, but at least current limited by the capacitor's leakage & reactance. The caps weren't needed in transformer powered radios.

They were used in amplifiers with power transformers (i.e. isolated designs) too to reduce buzz. It's a pretty common thing on old guitar amps to remove them and fit a 3-wire power cord with a proper chassis ground. Series filament amps were the really dangerous ones (they're often called "widowmakers" for a reason) because they weren't isolated from mains at all and if you plug the power cord in backwards (or the mains is wired backwards) suddenly the chassis is hot. Really, really dangerous with guitar amps because the strings are connected to chassis ground and if that's hot, the strings are hot.

 

[LTig]

I got zapped with 4kV, threw me around half the room/ Also accidentally put my fingers on a flyback transformer and am still alive.
Got a nasty zap from a not discharged capacitor (300V DC) from a non functioning SMPS etc.
There are people that died because of touching mains though.

... and the problem is that they are not able to tell their sad story in the Internet, so the fact that many people report their survival has no statistical worth.

 

[LTig]

Absolutely agree - a little perspective can provide some balance. The "Truth" may not achieve technical or safety perfection but is providing some enjoyment to happy customers. Understanding the ground lift switch operation does give the user a choice of whether to use it or even order one without the switch.

There is no choice between enjoyment for the customer or safety. The safety standards (we're not talking about perfection) are mandatory, and not adhering to them is plain illegal and in case of a fatality will put the seller into jail.

 

[Bob from Florida]

There is no choice between enjoyment for the customer or safety. The safety standards (we're not talking about perfection) are mandatory, and not adhering to them is plain illegal and in case of a fatality will put the seller into jail.

With all due respect what makes you think safety standards are mandatory. A quick search in UL standards reveals hits as shown below.

Having a UL listed certified unit is not legally required. It is, however, a common practice because many large companies will only buy equipment that has passed the UL safety tests. ... Having a tested product shows that the equipment meets a nationally recognized safety standard.

What "illegality" are you referring to? You may be correct, but please show some proof. Kinda of like in school if you put the answer down to a math question without showing your work. The test always came back marked up in red - "show your work"!

 

[mhardy6647]

In my high school electronics class, we built AM radios which had no mains transformers or any other safety measures. The instructor warned us not to touch our radios at the same time as we touch each other since there was a 50% chance one of our AC plugs were inserted the "wrong" way. Great fun, that.

The "All American Five" vacuum tube AM radio, replete with the AC-DC series string "killer" chassis.
Most if not all of the Baby Boomers in the US grew up (or, perhaps, didn't grow up, as the case may be ) with one, or more, of 'em -- or even worse transformerless designs.
Yeah, natural selection. Not a pretty sight.

A couple of Motorola AA5s from the collection

 

[Deleted member 26571]

Amazing what arm chair engineers will say in a thread. We have ranged from how badly it is engineered to making fun of Ed's last name to say anyone buying this product is stupid. Regardless of how it measures, is built, or looks there is no call for denigration.

Why not? Willful incompetence masquerading as high art deserves to be ridiculed.

 

[NTK]

With all due respect what makes you think safety standards are mandatory. A quick search in UL standards reveals hits as shown below.

Having a UL listed certified unit is not legally required. It is, however, a common practice because many large companies will only buy equipment that has passed the UL safety tests. ... Having a tested product shows that the equipment meets a nationally recognized safety standard.

What "illegality" are you referring to? You may be correct, but please show some proof. Kinda of like in school if you put the answer down to a math question without showing your work. The test always came back marked up in red - "show your work"!

When the ground lift switch is activated (as a switch is provided and easily accessible, operating with the chassis not earth grounded is a normal mode of operation), a single point failure (e.g. the hot AC wire solder connection to the power supply connector pin got detached and lands on the metal chassis) will result in a shock hazard. This clearly does not satisfy the requirements of being a Class I appliance, and therefore is in violation of safety laws in much of the world.

Below from: https://en.wikipedia.org/wiki/Appliance_classes

 

[Jmudrick]

Why not? Willful incompetence masquerading as high art deserves to be ridiculed.

Masquerading as high art?? You guys have no who you are talking about or the community this was designed for. Too much time on your hands.

 

[Francis Vaughan]

A quick search in UL standards reveals hits as shown below.

UL certification isn’t a simple safety standard. Which is perhaps a surprise. It is generally an insurance certification. It is there in the name - Underwriters Laboratories. Which is slightly different. UL initially made insurance companies happy as they had some basis for understanding and limiting risk. UL certification on a device is as much about making sure something won’t cause a fire, or anything else that might cause an insurance company to have to pay out.
UL certification isn’t and never was intended as a standard for governments to legislate compliance of. It can and does overlap with legislation. UL certification can mean adherence to the appropriate standards, as it is generally more strict. As a consumer one like to see a UL badge, and in industry you may find policy dictates only UL certified devices are allowed.
UL has broadened its operations and it provides safety consulting. But it isn’t a government agency and it doesn’t provide services or standards for legislation.

 

[Bob from Florida]

When the ground lift switch is activated (as a switch is provided and easily accessible, operating with the chassis not earth grounded is a normal mode of operation), a single point failure (e.g. the hot AC wire solder connection to the power supply connector pin got detached and lands on the metal chassis) will result in a shock hazard. This clearly does not satisfy the requirements of being a Class I appliance, and therefore is in violation of safety laws in much of the world.

Below from: https://en.wikipedia.org/wiki/Appliance_classes

View attachment 133974

First - Wikipedia is being quoted. The source anyone can edit. The country whose laws I am asking about is the United States. Coincidentally this is also where the preamp in question is built and sold. I seriously doubt it is against the law if this type of product were to be made without the chassis grounded. Why would I say that? Well I have owned 3 different pairs of tube monoblock amplifiers that did not have the chassis grounded to earth. Modern commercial amps. All the folks that are condemning this over safety appear to be focused on the ground lift. So here is the question - if the switch is never operated or simply removed and replaced by a ground wire do the safety concerns disappear?

 

[H-713]

First - Wikipedia is being quoted. The source anyone can edit. The country whose laws I am asking about is the United States. Coincidentally this is also where the preamp in question is built and sold. I seriously doubt it is against the law if this type of product were to be made without the chassis grounded. Why would I say that? Well I have owned 3 different pairs of tube monoblock amplifiers that did not have the chassis grounded to earth. Modern commercial amps. All the folks that are condemning this over safety appear to be focused on the ground lift. So here is the question - if the switch is never operated or simply removed and replaced by a ground wire do the safety concerns disappear?

I don't remember there being laws in the US about this, though it doesn't change the fact that it's bad practice. Also, it's pretty well-agreed that you don't trust switch contacts for something like this.

As I kind of hinted at, there are quite a few tube amps (both new and old) that don't ground the chassis to earth. At least that's how it is in the US. Of course, a good majority of tube amps don't have top covers, and if a tube gets broken, you've got something that is more dangerous than a live chassis. Even if present, the safety ground doesn't really do much to protect you in this case.

I always use a grounded chassis in my designs, but anyone who owns a tube amp needs to recognize that tube amps can be dangerous, especially those which use tubes with plate caps.

 

[MakeMineVinyl]

I always use a grounded chassis in my designs, but anyone who owns a tube amp needs to recognize that tube amps can be dangerous, especially those which use tubes with plate caps.

Just out of curiosity I looked around my system at gear either I designed for myself (i.e. not commercial), or any of my other gear, either vintage or current, and the total which has a proper earth chassis ground is......two.......and on one of those I had cut the ground pin off the AC cable. Remarkable that I'm still alive, no?

At least in the US which uses 120V, touching a live wire is more of a personal annoyance to me than a death sentence. Of course YMMV.

 

[dfuller]

The "All American Five" vacuum tube AM radio, replete with the AC-DC series string "killer" chassis.
Most if not all of the Baby Boomers in the US grew up (or, perhaps, didn't grow up, as the case may be ) with one, or more, of 'em -- or even worse transformerless designs.
Yeah, natural selection. Not a pretty sight.

View attachment 133966
A couple of Motorola AA5s from the collection

The interesting part is these can be made safe - all you need to do is add a 1:1 isolation transformer and a 3 prong power cord.

 

[MakeMineVinyl]

The interesting part is these can be made safe - all you need to do is add a 1:1 isolation transformer and a 3 prong power cord.

On the radios we made in high school, the cardboard box the kit came in was used as the box in which the finished radio was used. I wish I still had that thing.

 

[MakeMineVinyl]

Back to our regularly scheduled programming, has anybody here read this dreck?