Tube Lab  

@@el_arte about that, and we invested about $60k developing it, only to discover the retail price point was way more than our average customer could afford. So we went back to the design stage and started off with two key criteria - great sound at an affordable price. That led straight to an OTL design, that impressed us enough to continue developing it. We're waiting for a couple of parts and then hopefully we can call the prototype done. Eventually when the Kit business is bigger, we'll release the original headphone amp.

I like OTL amps. They want excellent output capacitors. They often require 2 to 4 output followers in parallel to knock down output impedance to a point where they can be used with 50 ohm headphones. They are easier to design for 150-300+ ohm headphones.

@@el_arte Our first prototype has an output impedance of about 70 ohms and easily drives a pair of Behringer 80 ohm cans, though at 150 ohms you get a slight improvement in the very lowest frequencies, as well as a small increase in power. We're just waiting on some parts to hopefully finalize the design. And yesterday we started on a second prototype that will have an output impedance of about 40 ohms, we'll see if it can drive our 50 ohm planar cans. The first design will probably become part of our "Classic" line and the second one will be for our "Modern Line", which will be significantly less expensive. Stay tuned!

@@jeff3575davison actually I did mention that there's at least 2 dozen ways to limit the inrush, but given we get complaints once the Friday episode goes over 30 minutes, we need to push forward sometimes. As a designer, I'm wary of putting anything in current path, the quality of the power supply design substantially affects the quality of the sound. We just replaced the thermistor in one of our Ebike chargers, somehow it blew it's guts to smithereens. I'm not a fan of the thermistor, but obviously there's a place for them - just not in my designs.

@@tubelab194 perhaps make a follow up video to explain the in's / out's, pro and cons? should make for a good video and compelling rational for their non use?

@@jeff3575davison good idea, but a bit beyond our typical audience. Because we tend to only do episodes about tubes / circuits and related stuff that we can get behind (based on actual experience), we don't normally do negative vids and if we talked about the thermistor it would be one of those.

@@tubelab194 doesn't have to be negitive. If you show both sides and explain why you choose not to use them, really is positive, informative, and educational. It would lend to your viewers understanding of their function. Your viewers are probably quite knowledgeable and and capable, don't underestimate them as those who only replace and swap tubes...

@@garretthead This is one big reason why a properly designed power supply is critical. Many tube amps are designed by borrowing other known designs, with no (zero) actual design work being done. This applies both to hobbyists and commercial manufacturers. We design everything from first principles, checking every component in a design to make sure it's correctly spec'd. This takes both experience and time, and costs money, which is why it's not commonly done any more. Now if an amp has a separate filament switch or a standby switch it should have been designed to NOT over voltage the B+ if the filaments aren't lamped. In a well designed power supply there should always be lots of extra room on the component specifications.

Politely disagree. An amp may have been designed, or even just tested to operate with-in spec for an application, following an intended startup sequence . Then blindly on the advice of a youtube video, someone turns their amps on in the opposite order (ie B+ on cold start) and suddenly the amp is put in a situation it was _not_ designed or tested for. You are right that a lot of amps had questionable designs. Many of those amps happily lived through years of abuse or being operated beyond specs. Now some of those I can think of probably would not survive what you suggest here... at least not many times. I understand your sentiment as an engineer, but pragmatically what you are advising is quite dangerous to many amps... and I wouldn't expect the audience to be able to discern which ones. To suggest intentionally operating other amps not-as-designed because you prefer to design/operate yours this way (for whatever reasons) seems sort of distasteful. I did enjoy some of your content and hope you keep it up. Just something to consider. Cheers.

@@garretthead to clarify, if your amplifier manual says to start your amp in a certain sequence, then follow those instructions. An example of this would be an older Fender amp with a standby switch. In this case the manufacturer didn't want to afford expensive filter caps, so they avoided over voltaging the caps, by first turning on the filaments, then the high voltage B+. However in modern amps, the cost of those filter caps is no longer a significant concern and most amps are simply turned on with one switch. This gives a significant inrush current, but the designer would have had to allow for this. Unfortunately it probably also leads to the shortest tube life. Less commonly amps have the option to turn on the filaments separately from the B+. As shown on our bench testing the lowest inrush current happens when you first turn on the B+, immediately followed by the filaments. This produces effectively a slow startup and the lowest inrush current and probably the longest tube life. Any designer of such an amp would automatically have to ensure the caps can withstand a higher B+. Everyone who has ever properly designed such a power supply over specs the filter cap rating for this reason as well for longevity. The fact that many modern tube amps are simply older circuits they copied, with no understanding of how they operate doesn't absolve the manufacturer of responsibility for ensuring a safe operating amp. Another common method for dealing with the above issues is to build in a slow start circuit. A thermistor being probably the most common. Not something I like to incorporate in our designs, but nevertheless a valid approach. As you can see there are many different approaches to achieving the same goal, a safe operating tube amp. With a read of your manual and some common sense, this is not complicated. The most important thing is to avoid badly designed, cheap tube gear, which we unfortunately see more and more of.

@@whome8192 It all depends on the tube, we only talk about things we actually know, and the 5U4G is one example in which some Chinese rectifiers clearly can handle more in rush current than quality vintage production. With other rectifiers it could be the reverse, in fact the GZ34 comes to mind, those vintage mullards are beasts and modern production is junk in comparison. We always design a lower value first cap in our power supplies, typically 47uf with solid state rectification. The UF4007 has amazing specs for a wee piece of doped silicone, but why stress it if you don't need to!

@@darrenfoxwell7831 saying all tube amps are sold with cheap tubes may be subjective but I think a lot of people would agree...if comparing them to NOS tubes & especially Rectifier tubes. Rectifier & driver/preamp tubes seem to be much better with New/Used Old Stock. Just my opinion though & I'm not saying all current tubes are bad. The question is are the sonic differences gained by using NOS worth the extreme premium prices these days? Gotta keep in mind that NOS seems to live much longer as well.

@@darrenfoxwell7831 I agree, what we should have said, is almost all new tube amps sold in the last decade or more are supplied with inexpensive Chinese, Russian and Slovakia made tubes. Those tubes in many cases are inferior to 2nd generation vintage tubes made prior to about 1982. This is based on handling ~5-10k tubes per year and more importantly comments from 100's of customers, who on a daily basis ask questions like "why do my preamp tubes sound so harsh or edgy", "can you recommend a power tube that doesn't die 2 months after I plug it in", "my rectifiers are not lasting more than 6 months" and on and on. The problem with a weekly show that's mostly filmed in one take, is it's not always possible to define everything we say in absolute terms and infinite detail - when we do that the show goes past 30 minutes and we get complaints. Most of our viewers understand this and do more research on their own if they're interested in learning more about something. Or ask questions in the comments section.

@@tubelab194 Are you telling me that people who want to learn understand your making untrue statements due to time restraints ? seriously bud I enjoy what you guys do dont get me wrong.Its bad enough how many people on you tube are just selling snake oil with the twenty million overdrive pedals that are the best they have ever heard ever.I just felt you were going down the same path and thought you might like a little wake up call cheers

@@darrenfoxwell7831 possibly if you can provide significant evidence to the contrary. We correspond with customers around the World 7 days a week and the number one complaint is how bad the stock tubes sound. I make a point of never saying anything on Tube Lab that isn't backed up by substantial first hand evidence. Now are there exceptions, of course, but exceptions don't prove the rule. The source of these bad sounding tubes are 3 or 4 factories. JJ located in Slovakia, New Sensor (almost all reissues like mullard, gold lion, svetlana, tung-sol etc) located in Saratov Russia and Shuguang and several smaller manufacturers located in China. All of these tubes are modern versions of vintage tubes and a significant portion sound bad and to make matters worse they don't last long.

@@darrenfoxwell7831 a qualifier or in depth analysis of every single statement we make is not practical, that's what a scientific peer reviewed paper is for. The fact that we can't take that time, doesn't make a general statement incorrect or untrue, just not fully elaborated on. When we think something really needs to be explained fully, we take the time to do so or we make a full Tube Lab on the subject. Remember two of us take a 1/2 day out of our work week to produce Tube Lab, and we take no monetary compensation from RU-vid nor do we accept any review fees or other money whatsoever. Everything we talk about is based on first hand experience.