Which is why medium to large scale companies have regional service centers, which combine repair, refurbishing, and overall product support in one center. It’s equivalent to a low-yield manufacturing center with a marketing wing (in the local language) attached.
They support local retailers, or have direct customer support, and offer the kind of services manufacturers do, just on a smaller scale. Somebody to answer the phone. A parts warehouse. Several techs to repair or upgrade the product. Somebody to manage the facility and make sure things actually get done, along with inventory and personnel management. In short, at least three to ten people working full-time, along with leased space in an industrial park. It’s equivalent to a small factory, with equivalent monthly overhead costs, too.
Once your company passes the threshold of about five to fifty million dollars a year in sales, yes, opening overseas centers in regional markets makes economic sense. You can afford to hire three to ten new workers on another continent, and train them and point them in the right direction. Opening a regional service center requires a pretty steep investment in time and money.
Otherwise, you are supporting the overseas customers by remote control, with very expensive shipments back and forth, and a certain percentage of those returned products severely damaged in shipment because the customer threw away the original packaging and improvised their own packaging.
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I have a thorough dislike of working with lead-free solder. Nothing flows in a point to point build like a good 2% silver solder. Lately I have been using Wonder Solder for the past year or two and it is just wonderful to work with. Of course, one could use lead-free solder, and pass all the hurdles and build things for shipping in large numbers to the EU. First you get the product off the ground in N. America. We have pretty much free-trade between Canada and the USA, and it is quite easy to make things in either country and ship to the other, duty and tariff-free. My main point above was that it is very expensive to deal with customer support across the pond. If you ship 100 things to 100 people, about 1% of the time something happens. For example, UPS will admit that they have a 4% claims rate. Things happen. No matter how robust you make something, and how thoroughly you test it and the tube set before you ship it, things happen a very small percentage of the time. Or a customer plugs a tube you didn't sell them in there and it grid shorts. This gear is quite robust against serious damage when that happens because in all these years of building things, I have seen all sorts of failures. When a bad tube kills something, I improve designs so that will only blow a fuse instead next time. So these things are quite stable, but still, every now and then things happen. When they happen in N. America it is far cheaper to sort out. You always take care of the customer. It is much more expensive to do so overseas.....
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Yeah, RoHS-approved solder might be a stumbling block, since it requires higher temperatures and a little different technique. We’ll cross that bridge when we get there. Our first goal is getting production under way in Salt Lake City, home of Spatial Audio.
Fortunately, both Salt Lake and Denver have a number of aerospace vendors that make various subassemblies for rockets and satellites.
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Japan has a very good used audio stuff market with Tango, Tamura transformer; Kondo, Acrolink cables; used amplifiers and CD player,... Japanese people sell all this stuff on the internal market. A very few used stuff from Japan is sold internationally , for example, on eBay. And because Japanese people don’t use eBay, all used Japanese audio equipment sold by hucksters - prices on eBay are at least twice higher than in the local market.
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a fascinating discussion… and remarkable in that blind American exceptionalism has yet to …intervene…much.
I spent much of my career working globally…for the largest exporter in the USA.
Aerospace grade….. ;-)
Enjoy the music and i wish all well
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Don, myself, and the team at Spatial intend to be on the straight and narrow when it comes to regulations ... we are not Tesla, Apple, or Microsoft, with armies of lawyers to smooth the path into new markets.
To gain the CE mark (which says that the product meets EU Directives) you can self-certify and no lawyers needed. Its not intended as a trade barrier.
If there are no digital or switching circuits involved, you have exemption from a good number of directives. Beyond that, if good practice for the AC wiring is observed (with a proper AC ground if a metal chassis is employed) and there are no exposed voltages, then you are 95% of the way there. It isn't required that you have a tube cage but if its not shipped with the equipment it must be available as an option. Finally the CE mark must appear somewhere: either on the shipping box, the associated owner's manual or the equipment itself.
Its a good idea to test the equipment for RFI generation, even if there are no RF sources such as switching technology. If you paid attention to Ps and Qs regarding layout and grid stoppers this is likely not an issue.
RoHS must also be observed. For the most part this means lead free solder, but there's a percentage involved so it is possible to use leaded solder. You'll have to review the regulations on that.
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@lynn_olson
What they appreciate is artisan audio made to the highest standards, by artisans of superb taste. Not 1" thick anodized-aluminum front panels with a giant meter in the middle. That only impresses naive Americans who have never worked in manufacturing
I wonder how these Japanese engineers/designers view the products manufactured by Robert Koch (Robert Koda Audio). His approach seems to be a blend of Japanese aesthetic/philosophy and heirloom visual appeal for the North American and European markets. I don’t know how well received his components are in Japan.
Charles
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As Whitestix mentions above, the Japanese have a "purist" esthetic that applies to audio. But it goes much deeper than that. The CEOs and top engineers of Japanese, Korean, Taiwanese, or Chinese companies are not going to be impressed by the latest mass-produced gadget. Hardly. That’s the stuff they make every day, and they make it to very high reliability standards.
What they appreciate is artisan audio made to the highest standards, by artisans of superb taste. Not 1" thick anodized-aluminum front panels with a giant meter in the middle. That only impresses naive Americans who have never worked in manufacturing,
What impresses them is genuine American aerospace-grade quality, if circuit boards are involved, or artisan hand-tuned point-to-point circuitry. And they are not impressed by magazine reviewers, since they have an insider’s view of the publishing industry, and are very aware of how American marketing works.
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I was only 11 at the time, but I was dazzled by the private tour of Kurobe Dam. It’s size of Hoover Dam and freaking huge. The dam was nearly finished when we visited as guests of Kansai Electric, and we took this strange little Elves railway deep, deep into the mountain. We got out of our mini-train carriage into a brightly lit station with gleaming tiles, and directly opening into a modernist office area, with desks and office furniture.
Rather than office windows looking outside, there was a massive expanse of glass overlooking the turbine hall, from three stories up. I assume the control room was in the floor underneath us ... didn’t get to see that, but we did go to the main turbine hall. Two were up and running, the third Hitachi-made unit was on a crane, and there was a vast and deep concrete pit for #4, yet to arrive. All new and the walls all done in gleaming white tile, not bare concrete. Basically, an office and power station deep in a mountain, with a very quiet thrum as enormous quantities of water flowed through the penstocks into the turbines. You could just barely feel it.
We left by another route and saw the ultra high tension power lines coming out of the mountain, There was a faint glow around the wires from corona discharge and a sound like crickets from overhead.
Dad drew our attention, as we left on the micro train out of the very deep valley, that all this was being built 15 years after the most overwhelming defeat in history, with nearly every Japanese city in smoking ruins, and tens of millions on the verge of starvation. A scant 15 years later, a Japanese-made technological wonder that put Hoover Dam in the shade. It left quite an impression.
I have to give Dad credit. As Economic Attaché, he wangled some spectacular tours while we were overseas. Kurobe Dam. A Japanese steelworks at full blast. A visit to the 8-reactor carrier Enterprise. A visit to a factory assembling magnetic-core memory. An aerial tour of Hong Kong on a four-engine Super Constellation as the FAA aligned Kai Tak’s landing systems.
Although he was a diplomat with a Masters in Economics, he was a big fan of technology, the more spectacular, the better. If you want Big Tech, Asia’s the place.
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Very interesting discussion about gear sold on one side of the Atlantic and that sold on the other side. Reading the British hifi magazines, I have always been curious why they and the Europeans fancy such different gear than we do in the US. Naim and Hegel are two EU brands that have deeply penetrated the US audio market, as well as the venerable Linn TT's. With Lynn's erudition, I now understand why that is the case.
As I am sure Don can attest after his renovation of lots of vintage HK and Marantz gear, a boatload, literally, of these vintage tube amps made their way to Japanese audiophiles for decades. Don't flame me for saying this, but the Japanese have a purist view of a lot of things, including architecture, gardening, city planning, vital mass transit, delicate and inventive cuisine, etc etc. It comes as no surprise to me that the Japanese clamor for the best audio gear on this side of the pond. Kondo Audio Note is a prime example of their aesthetic. We all learn from one another.
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I saw Kurobe Dam while it was under construction by Kansai Electric. The underground power station, deep under the mountain, is like sometime out of a Bond movie set. Two of the generators were running while the third was suspended from a crane. The fourth was an immense concrete pit.
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About 12,000 naturalized immigrants a year, it turns out, out of a population of 123 million. Not enough to offset a population loss of about a half-million to a million a year.
Returning to the original question, Asian companies are a lot more export-oriented than US companies. They have far more experience exporting to North America and the EU, and are expert in making "localized" versions.
Japan is also interesting because half the country is 50 Hz (Tokyo), and the other half (Kobe/Osaka) is 60 Hz. Asynchronous 50/60 Hz Grids. In a sense, even the internal market is an export market, since there are two power frequencies.
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My son lives in Japan and has worked and lived there for the last 4 years. ??
but any kind of immigration is nearly impossible. Visit, yes, but don’t stay. This is a demographic problem with a rapidly declining population and no effective guest-worker program.
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Japan is interesting. Unlike the USA, it looks outward to the world (Americans by and large don’t know or care), but any kind of immigration is nearly impossible. Visit, yes, but don’t stay. This is a demographic problem with a rapidly declining population and no effective guest-worker program.
What makes the USA unique is that it only imports 12% of its economy, less than nearly any other nation, and half of that are imports from Mexico and Canada, which are effectively domestic markets. Get rid of those two and it is 6% or less.
It is self-sufficient in energy for the foreseeable future, and for the history of the country has always exported food to the rest of the world. The USA has never had a food famine in its entire history, which is unique as far as I know. So Americans are pretty insular compared to most other nations, and only the larger companies have any awareness of the ins and outs of selling to non-North American markets.
In the rest of the world, it is Export Or Die, and governments are tightly focused on this, every day. Because essential inputs, like food or oil, come from elsewhere, and are critical to the survival of the population. In the USA, there’s always more. It’s always been that way. Our economic problems are self-inflicted. The idea of HAVING to export is very foreign to Americans, but is no joke in the UK, the EU, China, Japan, and much of the rest of the world.
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@lynn_olson
Gaining entry into Japan is nearly impossible. It can take decades. Even Wal-Mart has barely cracked it, and think of the massive resources they can bring to bear. Tourists are always welcome, but good luck immigrating to Japan, or cracking the local market
Some could arguably accuse Japan as being a closed homogeneous society but out of control illegal immigration will never be a concern for them. Absolutely no way they’d allow such a debacle.
As always good insight Lynn.
Charles
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My father was a US diplomat and head of the Economic Section of the U.S. Consulate in Hong Kong, and held a similar position at the US Consulate in Osaka, Japan. His primary function was smoothing the way for US business overseas, and making sure they didn’t break local law and get arrested (not joking about this). It’s the job of the nearest US Consulate (or Embassy) to fish Americans out of jail when they unwittingly break local law. Most Americans are unaware they are subject to local law when they travel, with the only exception being US diplomats and members of the Armed Forces. They have separate passports ... I myself held a diplomatic passport until I was 18 and returned to the States.
Hong Kong was very unusual being a Free Port, with zero import duty on goods from anywhere in the world. Back then in the Sixties, the only prohibited goods were guns (of any kind), illegal drugs, and gold. Anything else got a perfunctory inspection and went into Hong Kong warehouses for re-shipment to anywhere else in the world.
Thanks to decades of trade agreements with most countries in the world, the USA is very nearly a duty-free zone, with only the lightest restrictions into our markets. The Chinese government greases the wheels even more by providing free shipping for Chinese manufacturers into the US market (yes, really). But shipping back to China is definitely not free, as anyone with a defective Chinese product will discover. That’s why you should always confirm there is a functioning, and fully staffed, repair agency in North America when buying a Chinese product.
Americans cheerfully assume the rest of the world is this way ... LOL, ha ha, no, not at all. Not even slightly. There’s free trade within the EU, but there’s a maze of mind-numbingly complex safety and technical regulations to gain entry into that market. The big Japanese firms have the resources, but they have full-time staffs doing just that. The EU is a beautiful place and delightful to live in, but in terms of trade, it is a walled garden. Entry is possible but the requirements are daunting ... and are designed that way.
Gaining entry into Japan is nearly impossible. It can take decades. Even Wal-Mart has barely cracked it, and think of the massive resources they can bring to bear. Tourists are always welcome, but good luck immigrating to Japan, or cracking the local market.
Every country in the world is different, with different sets of legal hoops to jump through. Some, like Japan, are essentially closed. China is nearly closed, with complex and difficult currency restrictions. Hong Kong and the USA are very much the exceptions, not the norm.
The USA took the political decision after World War II that it wanted to sponsor worldwide free trade, backed up and protected by the US Navy. (The US Navy has 13 nuclear-powered Carrier Battle Groups. Any other country has just one carrier, and they are not nuclear-powered. Think about that for a while.) The US wanted to dissolve the squabbling European empires that had caused two World Wars, and had the economic muscle to do so. This is still US policy.
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@lynn_olson
The unusual thing about the US market is that it is really easy to sell into ... tariff rates are some of the lowest in the world, technical safety requirements are not too severe, and the market is huge and easy to serve. Markets everywhere else are different ... more fragmented, higher tariff barriers, multiple languages, many different technical standards, and other obstacles
What a very good synopsis of what manufacturers face if deciding to officially enter international markets. Good grief!! This is not a cavalier undertaking by any stretch of the imagination. A multitude of serious issues to contend with.
Charles
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Pindac, I should mention when a private party flies into the USA, buys a product here, and returns with it to the UK or EU, that is technically a "grey market" sale. There is usually no legal problem with the new toy, assuming the local duties and VAT are paid ... but usually it is not legal to re-sell in that country. EU countries take a dim view of grey market sales ... while I have no idea how aggressive UK enforcement is. (In the US, the Federal government doesn’t care about grey market sales, but overseas warranties will not be honored by repair shops.)
And warranty support ceases once it is taken out of the North American market. The primary purpose of an overseas servicing center is to provide continuing warranty support, at a quality standard that matches the original manufacturing quality, with the same parts, service manuals, employee training, etc.
(A "black market" sale, of course, is something that is completely illegal to import into the host country, like an AR-15 into the UK, or something like that. Many laws are broken and arrest warrants are issued. "Grey market" means the product has not been tested by the relevant safety agencies, and is not certified for sale in that country. The most common outcome is that it is seized by Customs and is not returned.)
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Hi there, Pindac!
The decision to export out of North America is largely up to Spatial Audio. Don and I are the technical advisors and consultants, but exporting is a business decision. We can suggest and advise, but we do not make the final decision.
As Don has mentioned, exports to Europe would have to meet rigorous EU safety standards, and an EU servicing center would be wise. The EU is a big place with many technical and legal requirements that are quite different from the North American market, which has one dominant language, safety standards, and electrical power. If you can sell it in Los Angeles, you can sell it in Toronto, and everywhere in between.
Sure, there are small audiophile manufacturers who import on a "grey market" basis into the EU and the UK. That’s fine until you get caught. Don, myself, and the team at Spatial intend to be on the straight and narrow when it comes to regulations ... we are not Tesla, Apple, or Microsoft, with armies of lawyers to smooth the path into new markets.
Back when I was at Audionics in the Seventies, we eventually surmounted the many EU technical regulations and sold our products into the European market. But it took several years, and we didn’t attempt it until we had significant sales volume in the domestic market. Sure, it’s easy to order a Monolith power transformer with multiple input voltages. That doesn’t make the finished product legal to sell in the UK or the EU.
The unusual thing about the US market is that it is really easy to sell into ... tariff rates are some of the lowest in the world, technical safety requirements are not too severe, and the market is huge and easy to serve. Markets everywhere else are different ... more fragmented, higher tariff barriers, multiple languages, many different technical standards, and other obstacles.
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I have not inquired to the VAC Owners if they are using their Amp's with a Step Up Mains Tranx, or with any other US Imported Audio Ancillaries I have been demo'd.
I am a listener first and foremost.
The offer of the Prototype Amp's will be a great temptation to somebody, the Pedigree of the EE's and made known design intent behind this design alone, should be enough to convince a special experience is to be had. The reports of listening experiences to be found within this thread can only but reinforce, the idea of the purchase being very worthy of a consideration.
In the UK there are excellent Third Party support services for Electronics Support in both Valve and SS, these services are able to be found across the Country. The Services are not unreasonable in their costings, I have only ever seen the waiting time from certain services being the cause to search further afield. I do believe that the the notable trust that has been placed in these very services, along with the idea that receiving EE support is not being too much of a difficulty to achieve, is an instrumental factor in the making way for rarely seen items of Audio Equipment arriving in the UK from a variety of Countries where products have not got a UK support network.
As for overseas shipping, there are lots of Chinese Origin Audio Equipment arriving in the UK, especially Valve Amp's, of which some are requesting multiple £0000's to acquire. I am yet to have seen any horror stories about the Quality of the goods , resulting from their Transportation.
I myself have imported many items of Audio Equipment from Japan and over approx' 10 years, have experienced two incidents where goods arrived with a damage that was not as advertised.
Either a undeclared damage or transit damage was received ?
I will keep looking in on this valuable thread.
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@pindac Would it require a 240 VAC version or have most of the ones you have heard been US market 120VAC ones that someone was using a step up transformer with on your side of the pond? I will say that I have the pair of prototype amps that will go into production other than some cosmetic changes to the cases and panels. The circuit and power supply will not change as they are done. I abuse the amps regularly, putting them on the bench and tweaking something and turning them on and off 10 times in 30 minutes. Nothing has fazed them in 3 or 4 months since their birth. So I am pretty darn confident if they arrive undamaged they will simply just work and be very reliable. I/we wouldn't sell them if they were not very reliable. But shipping overseas is always dicey, even with good packing.
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Hi Don, I have heard a VAC Amp' within the UK, one of the earlier models is owned by a HiFi Group Member who owns a 300B.
Another newer Model VAC is also owned by a Group Member, I am yet to be demo's this one.
I have heard Modwright as well other Brands that are not with a dealer distribution, it is not too strange for products to end up in the UK without the supporting networks behind them.
There is a fair amount of UK Audio Enthusiasts who are willing to look far and wide for their entertainment to be satisfied.
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@pindac that will be up to Spatial Audio Lab. I am going there in late Nov to teach them the builds of amps and matching preamp. There will be a review pair made that will spend some time in the USA next year. After that we shall see. It is not hard at all to spec power transformers with dual windings and make a 220-240 VAC input version and source a proper IEC connector. While I expect both these pieces to be very reliable, the problem with supporting European and Asian markets is shipping cost, and if the customer has a problem of any sort, the shipping costs are enormous to help them out with any warranty issues. If you make 100 units of anything, no matter how reliable, one will either be damaged by a reckless carrier, or some weird problem may arise. The important thing in that case is to immediately take care of the customer, and that is expensive outside of N America. So that will be Spatial's call. It is much more expensive to support markets outside the USA and Canada.
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There are now over the past few months arrived Three 300B Power Amp's within my Local HiFi Group.
Two are from the Designs done by TDP and Andy Groves for World Audio Designs, One of these Two has an upgrade which I believe has Interstage Transformers.
The other is a design from a 'Heart' of Dutch Origin.
I am now becoming re-familiarised with the 300B sonic.
With the recent experiences and the knowing there are certain designers early in their career knowledge been applied to the Amp's, it really does make the idea of listening to the Amp's being discussed in this thread, a experience to be had.
Who knows a Pair may one day be on the UK to be demonstrated.
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Alex, remember, you cannot harm your amplifier if you completely remove the grid-load resistor. With a transformer, runaway from DC instability is impossible. There is always a DC path through the secondary ... as long as the secondary is intact.
If you have an oscillation lurking in there, at some high frequency like 5 to 20 MHz, that's a different story, and unrelated to the value of the grid resistor. 5 to 20 MHz oscillations, even at a very low level, will absolutely make the sound bright and unpleasant. If they are -40 dB down, you will never see them on a scope ... that's no more than a trace width. You need an RF spectrum analyzer to sniff out the little monsters. They look like little spikes rising out of the noise floor (which should be very smooth).
If you suspect this, you need a grid-stopper in series with the grid pin, like 100 to 500 ohms of carbon-comp resistor soldered no further than 1/2" from the grid pin. (NEVER use a wirewound for a grid-stopper.) That will kill self-oscillation.
I would try a grid-stopper first before futzing around any more. The only way you can solidly rule out self-oscillation is use an RF spectrum analyzer that's good to at least 20 MHz, preferably 100 MHz. These things aren't cheap, and only have one use, chasing out RF nasties. Low-level RF oscillations are surprisingly prevalent in high-end audio equipment, with poorly designed regulators as the usual culprit.
Try the grid-stopper first before anything else. After that, play around with various value of grid resistor, including nothing at all. It should not be sounding bright, unless something is wrong.
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In my case, I compared the sound of my amplifier with different IT resistor load. 120K (Kiwame 2W) vs 56K (Alan Bradley 2W).
The sound with 120K resistor was too bright and rough, with 56K tonal balance was more natural and sound was more refined.
But with RC coupling the sound was even less bright vs IT with 56K resistor. I think the resistors material AB vs Kiwame can make a difference too.
I am afraid if I completely remove the load resistor the sound will be even brighter. So I want to try 39K AB 2W resistors (that I have in my stock) to make the sound a little bit warmer.
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Try removing the 56K load resistor entirely and give it a listen. You might like it better. Remember, with conventional signal sources, there is almost no ultrasonic content, so the ringing in the transformer is never stimulated. And getting rid the load resistor has no effect on circuit stability or DC stability, since the grid sees the DCR of the transformer, which is a few K at most. All the grid resistor does is make square waves look pretty. It has no other function.
Its been my experience that allowing an audio coupling transformer to ring will result in brightness, since any signal presented to the transformer can cause ringing (this is easy to demonstrate- try it!). I'd not be surprised if some people mess with the damping to compensate for a weakness in the circuit elsewhere; IME/IMO you're far better off finding those weaknesses, sorting them out and making sure your transformers perform as good as they are able!
The overshoot, as these things go, isn't bad. You might be able to zero in on it a little bit more. The thing is, the more energy the overshoot has, the brighter/livelier the presentation so if you're going for a warmer sound this is something to avoid (you can see here how easily distortion can influence the tonality of the circuit). I would not reduce the loading resistance to the point it rounds the leading edge. A slight bit of overshoot is OK when trying to hit that critical damping value.
In a zero feedback circuit you have no correction to deal with this sort of thing, so you have to sort out details like this and get them right. The reward is greater detail since distortion and detail really don't go hand in hand. You can see by doing this sort of measurement how different power tubes and different speaker loads affect how well the output transformer can perform- and why people might have contradictory observations about how the same OPT and power tube sounds, because the way the transformer behaves changes depending on the speaker load.
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Try removing the 56K load resistor entirely and give it a listen. You might like it better. Remember, with conventional signal sources, there is almost no ultrasonic content, so the ringing in the transformer is never stimulated. And getting rid the load resistor has no effect on circuit stability or DC stability, since the grid sees the DCR of the transformer, which is a few K at most. All the grid resistor does is make square waves look pretty. It has no other function.
Now, in a cap-coupled circuit, it is absolutely necessary, since grid current, as small as it is, has to go somewhere. With transformers, it just goes through the secondary, and the current is so minuscule there is no effect on the core.
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Hi @donsachs and @lynn_olson ,
Here is square wave 1KHz on my amp output:
https://photos.app.goo.gl/jcdjn88Q71WaEvoR9
Output transformer and driver IT have much wider bandwidth compared to input to driver IT. During the measurement the 6sn7 current was 7.2mA. I just increased it to 8.75mA. Load resistor is 56KOhm.
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The problem with two successive stages that are balanced and DC-coupled to each other is that DC drift is a big deal. A 1 volt shift on a 150 volt plate is normally inconsequential, but becomes a serious concern when the grids of the following stage have a 1 volt offset between them ... which is what DC coupling does.
In the post in which I suggested a differential topology, I also suggested several cures for this problem, which I pointed out in that post.
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Hi @donsachs ,
I changed a load resistor 56K Ohm (Alan Bradley 2W), in my SET amplifier. And still have a 2-3 times bigger overshoot vs Blackbird has. However the sound is more balanced compared to the 120K (Kiwame 2W) load resistor I had before. I'm still waiting for more break-in time.
So far IT compared to RC coupling between 6sn7 and 6f6 - IT sounds more fast, more precise rhythm and pace, faster transient, more clean in upper frequencies. But I don't hear a big difference in terms of low level resolution. The tonal balance is a little colder too. Bass is more fast and controlled but less deep.
Which resistor will you recommend for power supply? Now I use Ohmite gold 10w and Milles 12.
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Scope pr0n. Same pix as earlier, just more zoomed in.
Don Sachs scope photo of Blackbird at 30% power (8 watts) at 1 kHz. Zero feedback, with no grid resistors to "trim" the response.
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A quick note: Don and will not be making the part-Mullard or the suggestions made by others in this thread. The Raven and Blackbird are where our attention is, and that’s where it will stay. Our focus this year, and the next, is getting production moving smoothly, making sure the Raven and Blackbird are reliable as possible, and growing the customer base.
On my part, I’ll be completing the long-awaited "Beyond the Ariel" speaker project over on DIYaudio, with the assistance of Troy Crowe in Canada. I do my best work collaborating with others, and Gary Dahl, Bjorn Kolbrek, and Thom Mackris have made a real difference on that project. I’ve been meditating on an appropriate name for the speaker, and "Phoenix" feels right, considering how many times it has been re-born.
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The problem with two successive stages that are balanced and DC-coupled to each other is that DC drift is a big deal. A 1 volt shift on a 150 volt plate is normally inconsequential, but becomes a serious concern when the grids of the following stage have a 1 volt offset between them ... which is what DC coupling does.
A Mullard sidesteps this by direct-connecting the plate of the SE input stage to ONE driver grid. The other grid (of the driver) is AC-connected to ground through a 0.1uF cap and DC-connected to the other grid via a 100K ~ 220K resistor. As a result, the two driver grids always DC-track each other.
By contrast, if the Mullard input section is replaced with a DC-connected balanced or diff stage, then DC balance and drifting of the first stage becomes critical, requiring a servo circuit to always keep the plates of the input tube exactly matched. No thanks.
The Blackbird is fully balanced, input, driver, and output, with DC balance issues resolved by using transformer coupling. Transformers are incapable of passing DC from primary to secondary, since the coupling is magnetic. Charge/discharge issues associated with capacitors, as well as potential coloration, are also avoided since cap coupling is not used anywhere in the forward path.
The hard part is getting transformers of high enough quality ... this is where working directly with the transformer designer, making them a part of the design team, is essential. These are not off-the-shelf parts.
A minor side benefit is avoiding turn-on pops and clicks, since the circuit remains balanced in all modes of operation, without relying on servos to maintain balance.
As mentioned above, a part-Mullard is great way to build a PP DHT amplifier. Not too complex, a well-known circuit that behaves predictably, and capable of scaling up the driver so it has enough power to motivate DHT grids.
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A Mullard PP 300B works as follows: input tube direct-coupled to a long-tail pair (or CCS) of triode-connected 6V6 drivers. These in turn are connected to a PP interstage transformer with a modest step-up ratio, between 1:1.4 and 1:2. The interstage then drives the PP 300B grids. This would be a non-feedback amplifier, so good power supplies are required. I would imagine a number of the PP 300B amplifiers already on the market use this topology.
I suggested this earlier in this thread; and added to it that with the input circuit also being differential there is additional benefit. A fully differential circuit has harmonic cancellation at every stage of gain; not just at the output. This results in the 3rd harmonic being dominant; it is treated much like the 2nd by the human ear in that its innocuous. But compared to an amp that does not use this topology, the 3rd is at a lower amplitude, and succeeding harmonics fall off at a faster rate (than seen in an SET) on an exponential curve. So the 3rd is thus more effective at masking higher orders and since distortion is lower, the circuit can be smoother and more transparent.
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There's no feedback, and there's gobs of 2nd-harmonic distortion. Parts coloration works for or against that 2nd-harmonic distortion. Also, because power-supply rejection is zero, power supply coloration is right in your face.
Driving DHTs takes two to three times the swing of pentodes or beam tetrodes. This exposes driver nonlinearity as well. Even worse, in some designs, driver and output distortion partially cancels ... but only at certain power levels. So the distortion signature is strongly level-dependent, which is very undesirable.
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@lynn_olson
I expected all SETs to be terrible, but those two were the best sound ever on the Ariels (which are 92 dB/meter efficient). After hearing several other SETs, I was struck how variable they were. A few were superlative,
Lynn,
What do you attribute to this wide spectrum of SET performance from superlative to terrible amongst them? Given their relatively simple circuit, is it primarily part quality (Output transformer?) or power supply quality and design?
Charles
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And of course a part-Mullard circuit is perfectly acceptable for a PP 300B amplifier. Unlike a PP pentode amplifier, though, you need about two to three times as much voltage swing in the driver, so a Dynaco circuit is definitely not the right choice.
A Mullard PP 300B works as follows: input tube direct-coupled to a long-tail pair (or CCS) of triode-connected 6V6 drivers. These in turn are connected to a PP interstage transformer with a modest step-up ratio, between 1:1.4 and 1:2. The interstage then drives the PP 300B grids. This would be a non-feedback amplifier, so good power supplies are required. I would imagine a number of the PP 300B amplifiers already on the market use this topology.
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Back in 1993 when I was trying many different amplifiers on the newly completed Ariel speakers, I came to the conclusion that a stock ST70 was the minimum acceptable standard for hifi. Most transistor amps fell below this mark, and most tube amps exceeded it. Restored Mullard designs did very well, as anyone might expect.
What I did not expect was the performance of the Ongaku and the Herb Reichert Silver 300B. I expected all SETs to be terrible, but those two were the best sound ever on the Ariels (which are 92 dB/meter efficient). After hearing several other SETs, I was struck how variable they were. A few were superlative, almost otherworldly, but many others were pretty bad. One was so terrible that Karna and I just burst out laughing ... it sounded like a 1960 transistor radio left out in the sun too long. That’s how variable SETs are ... all over the place.
By contrast, a competently engineered Mullard with a decent power supply is almost guaranteed to sound pretty good. And the best ones are superb.
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The octal boards for ST70 are direct fit and do not stress the power supply. You can use the diode replacement for rectifiers, but it sounds different. Basically, the amp is not bad, and a great deal for the money when restored and updated. A decent preamp and some reasonably efficient speakers and a person can have a very pleasing stereo. That said, an ST70 is nothing special because there really isn't room to make it special. I think we agree on that. You might as well start over and do it right without the compromises.
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But many of these classic PP still sound fine! Why? Because feedback or because PP has PS noise cancelation?
Feedback allows the amplifier rejection of that which is not the signal, so generally speaking, yes.
I really liked the 3 6sn7 tube version that tubes4hifi used to sell and perhaps still does. It makes the amp considerably better.
The problem with any mod that adds tubes to the circuit is the extra load on a power transformer that might already be 65 years old. Dynaco strikes me as being pretty precious about their transformer ratings- I don't like to take chances with them, especially in light of their age.
This is just me of course but if I'm going to modify a vintage piece I follow two simple rules. The first is don't add any extra load to the power transformer. The second is don't do anything that does not fit very easily into the existing chassis. Violate these and you're likely better off doing the whole thing from scratch.
The really glaring weakness in the ST70 is it should have been designed with dual rectifiers; as a result the 5AR4 is the most likely tube to fail in the amp. Triode Electronics of Chicago has a beefed up power transformer that is a drop in replacement that allows you to add a second 5AR4, thereby keeping the correct B+ operating point and so not stressing the output transformers as well. But you have to find room beneath the chassis for some 500V filter caps. It starts to get a bit ridiculous- at that point why not just do your own chassis so you can lay out things properly?
If an ST70 is properly refurbished but pretty well the stock circuit, it can be surprisingly good against a lot of modern PP and SET amps. Since it really does not have enough feedback, you have to help it along with good quality coupling caps and resistors in the voltage amplifier and driver circuit. The second thing to understand about this amp is because of its power supply weakness, you really should not push it hard (which is better for sound but also keeping that 5AR4 alive). CE Distribution in Arizona makes a drop in replacement filter can that features an 80uf section, which should be deployed after the choke, for the plates of the power tubes. That's about as much extra capacity as you can safely add to this amp without stressing the 5AR4.
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Actually, the Kootenay, and the the Valhalla amps use a similar circuit for input and drivers (with judicious use of a CCS), and the power supplies are the basis for what we used in the Blackbird 300b amps. We improved the power supply design for the Blackbird, but the same basic ideas are in the Kootenay KT88 power amp and Valhalla 6L6 integrated amps. Long tailed pair with CCS and really good power supplies and iron. As Lynn said, it makes for a really good tube amp. Not the level of the 300b project, but very nice indeed.
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The three-tube 6SN7 circuit board for the Dyna ST70 converts it to a Mullard circuit, with lower distortion and stronger drivers. Since nearly all the ST70 circuitry is on the single circuit board (for both channels), swapping that board basically gives you a new amplifier ... while retaining the power supply, chassis, and transformers. Lots of ST70 variants, since so many were made and are still kicking around. And the output transformers are pretty good.
Of course, if you are replacing the power transformer and upgrading the power supply, you might as well build on a new chassis, and have an all-new amplifier. Nothing wrong with a 6SN7 Mullard circuit and modern power supplies ... that will take you into the $3000 to $10,000 quality bracket right there.
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@donsachs
If you build a vintage amp with the sort of power supply you are using in your SET that vintage amp would sound much better.
+1
Charles
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@alexberger Fine is a relative term. If you improve the power supply in a citation II the amp is greatly improved. That is why the KT88 amps I used to build have FAR better power supplies than vintage amps. If you build a vintage amp with the sort of power supply you are using in your SET that vintage amp would sound much better.
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All classic vintage PP amps from 50-60 have very weak PS in terms of chokes, power transformers and especially capacitors values. If you use the same power supply for SET with no feedback with a such PS will be a disaster. But many of these classic PP still sound fine! Why? Because feedback or because PP has PS noise cancelation?
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Actually I have rebuilt 3 or 4 of the ST70 amps. The best version is to skip the 7199 or 6GH8 types and to one install of the octal driver replacement boards. I really liked the 3 6sn7 tube version that tubes4hifi used to sell and perhaps still does. It makes the amp considerably better. Really in every way. That said, they still run out of steam under load because the power supply is only adequate and there is no room in that tiny chassis to install a better supply. They are great amps for the money. But they are still not particularly great. However, there is little else you will find at that price point to touch it.
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The Dynaco, introduced in the mid-Fifties, took the drastic step of deleting the driver stage and its associated RC coupling, and driving the output tubes from the RC-coupled phase inverter. Although the open-loop performance was quite poor, rolling off around 100 Hz and 7 kHz
Actually the Dynaco has ~ 6Hz LF cutoff (-3dB) running open loop. Its distortion rivaled that of the Marantz 8B which was and is well respected, for a lot less money. You can reduce the distortion easily by obtaining a socket adapter off of eBay, which allows you to replace the 7199 driver tube (which is rare) with the much more common (and cheaper) 6GH8A. No other changes are required.
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Another walk down Memory Lane. This time, we’ll go into the late Forties, when the Williamson burst on the scene. This English design wiped out all other designs in the USA until about 1955 or so, with the exception of the McIntosh and a few others.
How does it work? There’s an input tube, typically a triode like the 6SN7, direct-coupled to a split-load inverter, also called a "concertina" stage. This always has identical plate and cathode resistors, and gain a bit lower than unity. The plate output drives the upper half of the push-pull amplifier, while the cathode drives the lower half. Despite appearances, the voltages on top and bottom are equal and opposite ... provided the total loads match, as well.
The inverter is then cap-coupled to a separate push-pull driver stage, which is sometimes also set up as a differential stage, depending on the resistance presented to the common cathodes. High impedances move it towards a differential stage, with the limit being modern constant-current sources. 6SN7’s were typically used here, with later designs replacing them with 12AU7’s (which typically have more distortion).
The drivers are then RC cap-coupled to the output tubes in the usual way. The drawback of a classical Williamson are the two stages of cap coupling, which can introduce low-frequency instability unless the output transformer has extremely wide bandwidth. The Partridge transformer specified for the original design had one of the widest bandwidths of any output transformer ever made ... but lesser transformers introduced stability problems, sometimes "motorboating" at low frequencies, but more commonly long recovery times from overload.
The Dynaco, introduced in the mid-Fifties, took the drastic step of deleting the driver stage and its associated RC coupling, and driving the output tubes from the RC-coupled phase inverter. Although the open-loop performance was quite poor, rolling off around 100 Hz and 7 kHz, the 20 dB of feedback nicely corrected it, since the input section used a high-gain pentode and there was plenty of "excess gain" to drive the feedback network.
The Dynaco had the advantage of being the cheapest of all to build; a combined pentode/triode, the 7199, took care of the entire front end, and all that was left were a pair of EL34 output tubes and an output transformer. In addition to Dynaco, many receivers used this approach as well. It was simple, saved money, and saved space, which was at a real premium in a low-profile AM/FM stereo receiver.
Receivers in the early Sixties (Fisher, Scott, Sherwood, Harman-Kardon, etc.) all had Bass and Treble tone controls, an AM and FM tuner with two different IF strips, an FM multiplex stereo decoder, a stereo power amp with at least 20 to 35 watts/channel, and last but not least, a stereo phono preamp. All with vacuum tubes, in a very crowded chassis, with marginal ventilation and caps of much lower quality than we have today.
We don’t see many Williamson amplifiers today. The dominant PP-pentode designs are Mullards and Dynacos, depending how price-sensitive the amplifier is. The monster tube amps with 4, 6, or 8 output tubes per channel typically throw in a dedicated cathode-follower section to drive all those grids ... sometimes one cathode follower to drive them all at once, or preferably, each output tube gets its own cathode follower. The RC coupling is then moved to the input side of the cathode follower, and the CF directly drives the grids of the output tube(s). This easily provides independent biasing of each of the output tubes, which is important when that many tubes are used.
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I agree. This is a stable topology, taking full advantage of specialty transformers designed by two of the world’s top designers, and using vacuum tubes that are in current production as well as ample NOS stocks.
As mentioned earlier, it’s a very simple signal path, with only transformers and vacuum tubes, and fully balanced from input to output. Zero feedback, with the audio signal only propagating in the forward direction.
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