captainbeefheart

I did not say you have to get a UL certificate, I only stated it will greatly help in a lawsuit. Your only obligation for anyone selling anything is to make sure it is safe. If you happen to make and sell a product that isn't safe and there is litigation, all the plaintiff has to do is show it doesn't follow specific safety standards and they will win the case. The safety standards are little harder to find but they are clearly defined.

This is good advice. The higher power output to the speaker could make a bad connection short out and trip the protection of the amp. It wasn't so much of a suggestion, looking at the specs they say nothing about being able to drive 4 ohm loads. They specify the output power into 8 and 6 ohm loads which tells me it won't be happy with anything lower than 6 ohms when cranking it.

It's rated 160 watts into 6 ohms That's 31Vrms into 6 ohms and a little over 5 amps of current If you have dips down below 6 ohms (most likely you do) and the amp can only deliver 5 amps, the protection will trip before reaching the 31v output into a tougher load like 4 ohms. Delivering 5 amps into a 4 ohm load is 20Vrms. As you can see lower load impedances require more current, the amp will try and reach the rail voltage into the load but if the load is too low it may exceed the output stage current delivery capability and either blow up or go into protection mode.

Sounds like it's going into over current or over temperature protection mode.

Looking at the shots from underneath and inside the amplifier, it does look like they didn't prep that area at all as it looks like the paint didn't adhere good, this is where I can see the fish eye. The outside doesn't look as bad so they probably at least prepped that better but still sprayed unevenly given the orange peel look. Looking through other pictures online it looks like quality control is bad, some units look a lot better than the one Amir tested but in many of the pictures I can see issues, just some worse than others.

Had a chance to look the amp over, I have a few thoughts. First I agree with their stance on Ultra linear, Pure pentode mode done right is better and triode mode is the best of all three except for the reduction in power, no free lunch right. Now a couple of issues on the specs is they do not list a weight or at least I couldn't find how much the amplifier weighs. The other issue is they do not tell us distortion vs frequency at full power. The former worries me for the same reasons the Crimson 275 can't make the power output at full bandwidth due to undersized transformers. The latter worries me because with Pentode mode you need feedback to get acceptable distortion figures. They may not use output to input or 'global feedback' and instead used local feedback around the output stage ala 'Schade' feedback or cathode feedback etc.. If they gave distortion information I would have a better idea if local feedback is being applied. Regardless of distortion I would still be concerned with a high output impedance with no global feedback. Now 40 watts is plenty and not a huge difference to the pentode output of 65 watts so I would just run this amp in triode mode full time for best performance. Even triode output stages can take advantage of feedback so I just do not understand why these companies are so worried about using feedback, most likely to fit a niche of the market for people scared of feedback from either reading incorrect things about it online or from experiencing a product with improperly applied feedback giving a poor impression and coming to a bad conclusion all feedback is bad. Anyone can apply feedback but not everyone has a good understanding of control theory and compensation which leads to many products in the market with bad examples in the application of feedback. I would really need to see a schematic and some further testing to make reasonable analysis of the amplifier.

This is very true! So you are seeing a contamination issue possibly with the paint? It's hard to tell from pictures I know but I don't doubt that could be part of the problem here. I was mainly seeing orange peel and issues from spraying far too much paint on at once.

Ok so it's not only me that sees the paint job as a little on the rough side. I use spray cans to paint chassis and I take care to not get orange peel or runs. It takes a little practice but you can get pretty darn good with a spray can. Even still a little 2000-5000 grit wet sand will smooth it out, once you got a nice paint coat then you clear coat and polish.

Going further on the SINAD test, if you don't believe distortion is a major problem with an amplifier just ignore the SINAD test they do and go by the rest of the review. I personally don't think lower order distortion especially second harmonic is a huge issue so long as it's not above 1% at full power. I believe once you get to 1% it becomes audible, unless it's 1% of all higher order harmonics and then I would never consider it, so type of distortion is important to me. As for the safety I will try and explain. If you have a device that you plan to sell it must be safe even if a fault occurs. You can either double insulate which means that if anything carrying deadly currents can come loose it will never touch the outer chassis that we come in contact with, this is Class 2. The Crimson 275 is not double insulated, if something internal like a wire carrying over 600v comes loose it can come in contact with the metal chassis that comes in direct contact with user putting them in risk of electrocution. The standard for this type of device is to 'earth' the chassis that the user comes in contact with so it will always be at ground potential, if something comes loose and touches the ground reference it completes the circuit and since it's unimpeded current will be enough to blow safety fuse protecting the user. This is Class 1. If someone was ever to get hurt or die from this amplifier it would be put under a microscope for safety and since they do not follow any safety protocols they would be held negligent and lose the case. If they had properly made the amp safe to begin with and pay the short money to have it certified most likely nobody would ever get injured for it unless they themselves did something like open it up or modify it making the company not liable for the injury. It's honestly such common practice for even small companies to get a third party safety certificate because that's how our world woks today, everyone is sue happy but more importantly we rely on these third party certifications to keep businesses honest and producing safe devices for consumers. It protects both parties really, one from negligence and the other from injury. For this company to not get a certificate is literally insane and stupid. They must have talked to a few lawyers and figured alright it's time to cough up the money to fix these things at no cost before we get sued. They are not doing this out of the kindness of their hearts so don't be fooled, they are doing this to avoid negligence. If the unit was 100% safe they would not be offering what they are offering, they would take the same stance they are with the power output and distortion.

They know they majorly screwed up with the safety aspect which is why they are paying shipping both ways to have it fixed at no cost. Look at almost every piece of gear you have and it is UL listed to some safety standard because the company knew enough to first make the product safe to current standards and then have a third party confirm it adheres to safety regulations. If this product went out to UL for a safety certification it would have failed the way it is which makes them negligent. Jim Clark keeps embarrassing himself more and more, does he know that loudspeakers are HARDER to drive than a simple resistor? I don't think he does. Specs are there for a reason. What would happen if you purchased a 4 cylinder car spec'd at 270hp but later found out after purchasing it only can make 120hp? Then the manufacturer comes out and says 'but doesn't the car drive good?". "You don't drive your car on a dyno you drive it on the road". We all know that's BS, we need a standard of testing and everyone seems ok with the standard of testing except Jim Clark as he just doesn't get it. His only response is "it sounds better than amps that cost twice the money". Ok but that has nothing to do with anything, that only means the amp that costs twice the money is also a dud. As far as Amir and his testing and why the Dynaco ends up where it does on the rating list, I will explain. First off they are rating via SINAD which is signal to noise AND DISTORTION, so if the distortion of the amplifier isn't extremely low it gets put at the bottom of the list. Since most tube amps have higher distortion at lower power output levels they of course will look poor on the SINAD test. If you read the article about the ST70 that was tested it was in poor shape by my standards, that amp should have been brought up to snuff by a tech before going out for that kind of public testing.The ST70 isn't one of my favorite tube amps and it's by far not the best but it's a good amp and it still outperformed by far the Crimson 275. It exceeded rated power and bandwidth was good.

When you get the La Scala's listen to them for a bit before adding a subwoofer. I know you probably are against the subwoofer idea but hear me out. I listen to a lot of different music genres but the majority of time it's Classical and Jazz. With music where you do not think you need a subwoofer let me tell you they still can still greatly improve the sound. Do not cross the sub too high, most have a filter adjustment where you want the woofer to begin providing output, try between 40Hz-70Hz to see what works best. For reference La Scala is only good for 50Hz and up. Low A on a piano is 27.5Hz, low E on a 4 string Bass is 41Hz. You do not necessarily need to listen to EDM or Hip-Hop to need a subwoofer, since adding one with La Scala's it has greatly imporoved all music I have listened to especially at lower volumes. It just sounds MUCH fuller. After you are use to the sub try shutting it off, you will notice a big difference and instantly turn the subwoofer back on. My $.02

If anyone is interested in the La Scala speakers they showed briefly in the video they were purchased by Jerry Garcia's mother as the bands first PA system in 66'/67'. Jerry later gave them to the Hell's Angels for their clubhouse system complete with a Sansui amplifier. Pretty darn neat right! https://insheepsclothinghifi.com/grateful-dead-hi-fi-auction/

Do not be scared away from single ended amps, the issue is most just copy schematics from old designs which don't do so well with tough loads. I agree with the statement that you either modify the crossover to look more like a constant resistance or you purchase and amplifier that can drive the tougher loads. The majority of SET amplifiers do not have feedback, I am not in the camp that is against feedback. It's the internal feedback mechanism that makes triodes so linear, it's not external like adding a resistor from plate to grid. The best part about triode amps is the distortion is already low enough that you don't need a lot of feedback to make them better, you just want to get them to be able to control the woofer. For this I like to add a variable damping control that allows you to sweep between different amounts of both positive and negative current feedback sensed directly from the speaker coil current. Of course you can set the control to zero and use the amp without the feature so you have options from normal mode with the control set to zero all the way to a negative output impedance giving better damping compared to even your average solid state amplifier. Then there are push pull designs if you change your mind. One amp PWK pushed to be used with the K-horn is a Brook 2A3 push pull amplifier, I have made clones of these amps with the 2A3 and a less expensive version that uses a 6AV5GA triode wired which has the same electrical properties and linearity as a 2A3. The difference being the 6AV5GA doesn't require such an elaborate heater/filament supply and the tubes themselves are only $5 each for NOS varieties so you can get excellent performance, same as a 2A3 at a lower price tag.

I saw one pop up on usaudiomart a day ago and figured it might be a disgruntled owner selling it off after the confirmed performance review it just sold today for $1750. I am going to keep an eye on the market for one to see how low they drop in price. I doubt it will ever go low enough to where I will purchase one.

Bob in a Cadillac, that sounds about right. I guess I am in good company with Bob taking inspiration from automobiles for paint colors. Have a look where the shadow and light meet, looks to me like orange peel. I don't have one right in front of me to inspect. It's a huge no-no with a car paint job to have orange peel but with an amplifier or anything else for that matter it gives it an almost textured look. I am not negatively putting the paint job down as like I said they may have intentionally painted it that way, I just can't make out if it is indeed is how it looks in pictures. I try and get my paint work on chassis smooth like a car but maybe a little texture isn't a bad idea. You can also see runs down at the bottom where the metal is folded over to meet the bottom cover.

Get a Crimson 275 😜 I think they will be coming down in price on the secondary market real soon.

Maybe it's just an illusion of the paint in pictures, lots of modern paint with metallic base coats have a lot of depth to them. I really like the color of these amps even though I am not a huge red fan. When I see cars with paint I really like I write down the paint code and have them make me up spray cans of it and I use them to paint chassis. I have two from BMW I really like together, a metallic blue and metallic white. I paint the end bells the white and chassis blue. I am a fan of the industrial green color Altec uses but I have heard several people say they hate it. I see the vast majority of gear is either black or silver which makes amps like the 275 stand out against them, the color just has a nice pop to it. I don't know why more companies don't come up with nice color schemes for their equipment instead of the standard black or silver.

The more and more I look at different production units from people I notice the orange peel on the paint job. They must have rushed the painting process and sprayed way too much on instead of light coats. Are all of them like this? JJPTKD does your 275 have bad orange peel paint also?

Sorry to hear you are sending it back, I honestly don't blame you and if I were in your shoes would do the same thing. When trying to get a refund I would certainly stress the safety issues the most as they don't want authorities finding out their product isn't up to the safety standards. I would have to look at the exact statute but the way the amplifier is now it wouldn't pass and get approval if they went for the application approval.

Definitely marginal with the 2.2uF vs 2.0uF. As the plot shows it won't get any brighter, the opposite you let more low frequencies through to the tweeter.

I am always interested in amplifiers I have no experience with. I will check it out thanks!

I hear you, he seems to have a very good attitude about the whole thing and he still likes the amplifier which is all that matters. I am sure he understands he doesn't require the power so the amp's deficiency in power isn't effecting him. I tried telling him that since he likes it and wants to keep it to at least bring it up to safety standards but he isn't concerned. I would just hate to see anyone get hurt, the safety is more concerning for me than the performance of the amplifier.

Not very far removed from how the original Polyesters sounded, and who knows if I could tell the difference in a blind test but I felt the PIO had a smoother sound with instruments like Trumpets and crash cymbals that can get harsh/fatiguing sometimes. I just wanted to keep listening to music with them all night long. I recommend Polyester to be safe but have no qualms telling people to go PIO. The consensus among people are the KBG aluminum foil types get more praise but I couldn't tell any difference between them and the Metallized paper types. Paper is paper and will give the same characteristics in dielectric properties. You can achieve higher capacitance values and better stability with metallized paper types, they are the technically advanced capacitor type. Basically instead of layering paper and aluminum foil they impregnate the paper (or any dielectric) with the metal giving better uniformity and more surface area.

How so? 2.2uF will lower the crossover frequency putting more low frequencies to the sensitive K77 not the other way around.

I completely agree the PIO caps are great in these speakers. Bob is great but he had really poor hearing in his older years. I don't know Al.