That's @stephe personal design, with a special driver tube and special Schade feedback, and she chose UL, and she did all of the research and design and testing, and she is planning to sell it, and I don't want to modify it. It's her design and her property and I respect that.
I gave it an admirable try. I didn't give up easily.
Gold! My boss in my previous life used that phrase (Lucche vrag horoshego, in Russian). 30 years have passed, and still actual today.
Come on, let's keep trying.
Would you contemplate a push-pull? I know you have SE transformers, but you are going to replace them. You could build a simple push pull with 4 tubes (stereo, ECL86 for example), 8 to 10W, very good sound. It should be not difficult to build a small aluminium plate to adapt 9pin sockets to the octal holes.
Would you contemplate a push-pull? I know you have SE transformers, but you are going to replace them. You could build a simple push pull with 4 tubes (stereo, ECL86 for example), 8 to 10W, very good sound. It should be not difficult to build a small aluminium plate to adapt 9pin sockets to the octal holes.
I already have three and another in progress. One ST70 series ii (EL34 PP UL), one ST35 (EL84 PP UL), and one "Huaji Audio" (EL84 PP pentode) that is absolutely fantastic to the point where I am building a second one in another thread. That will total four.
This project would have been amplifier #5, which I need like I need like another hole in the head, but I thought it would be interesting as a single-ended pentode.
Since everything here may benefit others in the future, if anyone wants to try to pursue and test the parallel triode driver option, this is where another member here (and at AK) arrived after many pages of individual discussion. That member knows who he is, and I want to say thank you again for all of the one-on-one mentoring and tutoring over the past few weeks. It has meant a lot to me, and without people like you, people like me wouldn't have a chance. Here is a possible parallel triode driver schematic where anyone in the future might want to pick up where I left off.
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But it's not new, unique or proprietary, and she would never claim it to be so. Valve amplifiers have been built and discussed since before we were born, and here we are, still discussing them. It's often hard for curious people to weigh the relative importance of a barrage of new facts and strategies, and that requires a step backwards into deeper basics, but building a valve amplifier from a schematic is dead simple.
I'll be helping my Godchildren, 16 and 15, to make a guitar amp this summer. Safety first, then soldering, maybe even some metal work and some wood work (their pops is a finish carpenter). Ballerinas, rock bands, amplifier builders, why not?
Regarding concerns about a special driver tube, 12AX7 is dirt ordinary (I've got more than a hundred myself) and octal type 6SL7 is "plug in compatible except for the plug". Regarding so-called "Schade" feedback, I don't think it's optimal, but it is robust and forgiving, so a good choice for early DIY builds. If, later, you decide to experiment with other variations, you'll have an excellent, working, platform.
All good fortune,
Chris
6SQ7 driver last time I checked. I'm not infringing on or modifying her design to be SEP. It's hers.
https://www.skunkiedesigns.com/6sq7?pgid=kv1sk1f9-ab84f699-13e0-4956-9df7-ac862a75e3f2
🤣
I think most of us often ask ourselves the same question, "why do I need another .... for?", and it relates to tube amps, cars, another refrigerator etc. I can only answer for myself, and it is very simple: making tube amps is fun 🙂.
Going back to output transformers, you do not need to break the bank to get something decent, here is one from China that I bought a while ago from "Amplifiers and Transformer store" on Aliexpress (9Vrms/8ohms):
The -3db at 20Khz is exactly what they advertised. But what surprised me was the low frequency response, it was pretty good for £25 each.
The -3db at 20Khz is exactly what they advertised. But what surprised me was the low frequency response, it was pretty good for £25 each.
Single-Ended amps are so simple, this thing will work if it's wired correctly, even if it's not the "best sound ever." Check @Suncalc's 6L6 Spotted Alder amp, it's a pair of 6L6 driven by a single octal tube, almost exactly what you're going after. 6SN7 might need a preamp to fully drive the output, 6SL7 if you don't want use a preamp.
Matt likes the U/L but all you've gotta do is add one more filter stage in the power supply, to create a node for the screen supply. Try to get those screens ~10v lower than the plates. Guess you'd want some NFB too.
Matt likes the U/L but all you've gotta do is add one more filter stage in the power supply, to create a node for the screen supply. Try to get those screens ~10v lower than the plates. Guess you'd want some NFB too.
I want to clear something up here. What are you talking about "it's hers"? I published all these schematics online as 100% open source in the hopes people would build them, use this as a launching point for their own changes or at least as a learning experience. The amp I am working on to sell? Yeah it's also open source, I am documenting every detail of the design and build process, will publish a BOM and expect the only people who will buy finished products are the folks who don't have the skills or the time/motivation to build one themselves.
Most of this SE design style I use was gleaned straight from Kegger, which he likely learned from looking at other people's designs. 12AX7 = two 6SQ7 triodes in a 9 pin bottle. You can't get much more common than that tube. I got most of the front end design from that 6SQ7 amp straight out of the RCA manual someone already told you to look at, which you instantly blew off. Just as you have blown off UL as "marketing" and claim a triode strapped output tube sound exactly the same as a pentode, which is complete nonsense. Multiple people have told you a 6SN7 is gonna struggle to drive a UL/pentode EL34 without a lot of extra circuitry and to look at a 6SL7 instead, you blew off that advice as well. The popular Kegger/Blueglow SE amp can easily be used with EL34 tubes, which is pretty much what the 6SQ7/EL34 amp is an adaptation of. You seem to know better and keep posting proclamations, then at the same time claiming your ignorance. You claim you can hear the difference adding a fist full of stuffing into a speaker cabinet, but then say all amps sound the same.
I was willing to try to help, but I feel like what is really going on here is you using this forum to alleviate your boredom by arguing with people. The only reason I responded was this misinformation that these open source schematics I posted are somehow proprietary and off limits for use/change. Again, good luck but I suspect nothing will come of this other than pages are people debating on an internet forum.
Learning something regards amplifiers is a lot like riding a bicycle.
We can read & talk about riding on & on ad absurdum.
But not much happens until we get on the bike & manage to ride it
a few hundred miles.
PS- I did & pedaled several thousand km each year for 45 yrs. Then I got olde.
Still managed 60 km on my 85th, in 3 hrs flat.👍
We can read & talk about riding on & on ad absurdum.
But not much happens until we get on the bike & manage to ride it
a few hundred miles.
PS- I did & pedaled several thousand km each year for 45 yrs. Then I got olde.
Still managed 60 km on my 85th, in 3 hrs flat.👍
g
Yes indeed. Well, it's nonetheless possible to build a good sounding SE amps, even if not with Triodes...
Below my U-KT120 uses two // 12AX7 in SRPP configuration as the preamp stage, and one KT120 in cathode bias, Ultra-Linear connection for the output stage.
The specs are :
Sorry, no THD% measurement for the moment, my PC gear being obsolete awaits replacement...
T
Yes indeed. Well, it's nonetheless possible to build a good sounding SE amps, even if not with Triodes...
Below my U-KT120 uses two // 12AX7 in SRPP configuration as the preamp stage, and one KT120 in cathode bias, Ultra-Linear connection for the output stage.
The specs are :
- nominal power output 12.5WRMS 8R @440hz sinus.
- input sensivity = 0.8VRMS @10.00V output (12.5W).
- bandwidth @12.5WRMS : 10Hz-40kHz@-3dB, 16Hz-23kHz@-1dB
- bandwidth @1.0WRMS : 4Hz-42kHz@-3dB, 7Hz-24kHz@-1dB
- 6dB feedback loop (fine-tunable for calibrating input gain at 800mV ---> 10.00V output).
Sorry, no THD% measurement for the moment, my PC gear being obsolete awaits replacement...
T
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Very nice. Do you have a schematic? You have 2 preamp tubes - do you run one SRPP into the other?
Thanks folks. I'm going to do as I said and put it on the shelf for future use. I have some specific ideas that I wanted to test, and I don't yet have the knowledge, skills, and ability to do so. I'll keep learning and maybe come back to it one day. I may look into some test equipment.
That's interesting. I'll save that link and schematic. Thanks. He also gives a detailed explanation of everything and calculation examples, which is exactly what I need at this point. I learn best by being given examples and detailed explanations with them, as he has done. Others learn better by doing and making mistakes and correcting them.
That's interesting. I'll save that link and schematic. Thanks. He also gives a detailed explanation of everything and calculation examples, which is exactly what I need at this point. I learn best by being given examples and detailed explanations with them, as he has done. Others learn better by doing and making mistakes and correcting them.
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Perhaps I wasn't clear. I will explain. Pardon my wordiness. Some people might find the history and experience over the decades interesting and/or valuable perspective. Many people lived through it. I have time now since I'm not focused on this amplifier any more, at least not until I know more, which will take time. The example "Spotted Alder" amp writeup provided by @dubadub yesterday is a huge help as it explains what was needed, with an example and actual calcs, to finally get me over the hump in my understanding of the driver stage gain and the 6SL7 vs. the 6SN7. It may seem so simple to all of you, but I just figured it out. All new to me. One step at a time.
There is a fundamental question that I don't see addressed much in modern writing about loudspeaker design. It used to be very common, in the forefront in fact. That question is how much do you want your speaker to depend on the damping factor of the amplifier? It's a design factor and a choice.
The modern focus on high amplifier damping factor and "voice coil control" by the amplifier really exploded in the 1980's when a majority of people decided that speakers:
- That were very large (say, refrigerator size or maybe half that) were ugly and "impractical"
- Needed to be narrow baffle instead for "imaging" and "sound stage"
- Needed a small footprint to save space in the room and to not stand out visually in the all-white decor living room that was all the rage then
- Needed small drivers for "tight" and "quick" bass response.
Frustrated as heck with all of that stuff, and thousands and thousands of dollars poorer for it, I rejected "modern" speakers and amplifiers of this type and abandoned the modern approach to speaker design. Many people do like that approach, in particular bookshelf speakers, and narrow floorstanding speakers, and that's fine, but it's not for me. For many, it's all they have ever known and therefore it is their only reference, which is sad I think.
In the late 1980's - early 1990's I was left with very, very few options. I temporarily resorted to the Klipsch Heresy ii. I think I bought them in 1988, maybe 1989. That is one example I gave of a speaker that really isn't sensitive to amplifier damping factor. I speak from experience. It's not a modern design by any means. It's about as far from it as you can get. Being dissatisfied with their 50Hz cutoff and having no real choices due to the 1980's modern speaker downsizing + high damping factor epidemic, I resorted to DIY. A few manufacturers finally tried to put larger drivers in their designs, but they got crazy expensive and also failed to impress me as most were still built for extreme damping factors provided by amplifiers like Krell.
An old audiophile friend of mine started working with me on my current speakers while I still owned the Heresy ii. He played the pipe organ his whole life and traveled the world to play some of the largest ones. He asked me one day how people expected a 6 1/2" driver (or two), hopelessly flopping around to try reproduce the sub bass or the sheer, physical impact of a pipe organ realistically. You can feel that physically, and not just the really low notes either. Point taken. The same is true if you go to a small jazz club and listen to live music. You can feel it physically and it's not just due to the loud volume. You also can hear and feel all sorts of extremely low frequency room interactions and thumps and thuds often related to wooden stages that most speakers just can't reproduce. It's one thing that most speakers miss, and I don't like speakers that miss that. I tried to sell him on the small driver + high damping factor approach and he roared with laughter as soon as he heard "damping factor." His solution? Older Bozak speakers the size of a refrigerator, each with four 12" bass drivers, four 6 1/2" midranges, and an array of 4 tweeters (before domes were popular). Cones barely moving. Earth shaking when needed. Damping factor virtually irrelevant. He also had a pair of Electrovoice corner horns with 30" bass drivers. Again, cones barely moving. Earth shaking when needed. Damping factor virtually irrelevant. You could physically feel the performance even at a normal living room volume. You could feel things vibrating. So I asked him about damping factor, and the impedence of the speakers, and the importance of different speaker wires and lengths. He laughed again. He had a variety of amplifiers over the years. He was using McIntosh solid state mostly but also had used various tube amps that he played for me. I don't remember which ones except a Fisher tube receiver that I eventually ended up owning. He played all of them for me many times, and his speakers simply didn't care about the damping factor as we changed amps. They were from an era when most amplifiers had low or very low damping factors and so were designed to handle the damping themselves. So, I went to the public library (no Internet back then! 😵), and I started reading the sound reinforcement design books there, which were from a time pre-1970's when damping factor was low or even very low.
I couldn't have speakers the sheer size of his at the time, so I set out to do as well as I could with speakers that I could still move and afford. My current speakers always were intended to be a half-size test for the full-size version that I never have built due to weight and financial constraints. A set of 18 top notch drivers will put a very serious dent in your wallet, and moving a speaker that is the same size as the kitchen refrigerator is no easy task. Each would in fact be the same size as my kitchen refrigerator. So I built the half size version instead. I have been using those exact same speakers every day for 30 years now, having spent about 4 years doing a lot of design and testing on them before that and building multiple versions when I had access to a woodshop. They rely almost exclusively on the speaker and enclosure to do the damping instead of the amplifier, as described in the old sound reinforcement books.
The approach of designing a speaker to be relatively independent of amplifier damping factor really appealed to me because I always have liked to change amplifiers and damping factor varies widely from amp-to-amp and from frequency to frequency within any amp. So, I had to come up with a design to use modern drivers but with the old school approach of not relying on the amplifier damping factor a whole lot. I did not say that all amplifiers sound the same. That's not what I meant at least. What I meant was that after using dozens of amplifiers, both solid state and tube, with a huge variety of damping factors, I can confirm that the damping factor of the amplifier is not a big issue with the speaker design that I implemented. How can that be so?
Let's look at the extremes of damping factor in my case
- If we were to get absolutely absurdly low on damping factor, it might make a subtle difference with my speakers, but even then not a huge one. The speaker and enclosure will still do its job as designed. They mostly take care of themselves. The cones are barely moving even at high volume with test tones all the way down to about 25 Hz. It's shocking really, and people can't believe their eyes. It amazes me sometimes. Pictures are going sideways on the wall and the cones are barely moving. That's control. A well-designed, large, efficient speaker is that way. They also don't ring like a bell. An old test for speaker damping used a battery to listen to the sound for ringing as it is connected and disconnected. No amplifier damping there as there is no amplifier. Just a quick "pop." At 20 Hz my bass drivers completely lose it, but that's a limitation of physics. It's the only point at which a high damping factor really might help compared to a very low one. Fortunately, it has turned out not to be a very big deal. On some music with ultra low frequencies like the Telarc 1812 Overture CD, I do have to be careful as a few times I have bottomed out the voice coils. Oops. Don't do that.
- At the opposite extreme, increasing damping factor to some enormous level also makes little difference since the speaker is already taking care of itself. Controlling something that has already controlled itself isn't a real thing. I have tried these speakers with a variety of transistor amps with huge damping factors over the decades. Just a whole lot more watts not somehow a different bass sound.
Also, I can say honestly that the differences among very high quality amps aren't anything I'd describe as a huge difference. Most people don't want to hear that, but I stand by it. Differences are what I describe as subtle once we reach a point of diminishing marginal return. For example, I had a Threshold class A 50 watt, and my Dynaco ST70 ii, and a Forte 100 watt AB solid state, and the original Adcom GFA-555 AB 200 watt, and a classic Fisher tube receiver, and another amp that I can't remember, all at one time, all with these speakers. I had so many amps that I put them on loan with audiophile friends because I didn't have room for them all. Yes, I coud rank those amps from best to worst. I put the Threshold and the ST70 ii at the top. The Adcom was at the bottom, BUT it definitely wasn't bad in any way. The sound quality difference between the Threshold and the Adcom was not huge. Most people would ignore it and reject the price tag attached to the Threshold. I paid about $1800 plus tax for it used. I think I paid $500 for the Adcom used. A big price difference for not much sound quality difference. So that's what I meant. Then I said that changing op amps in a DAC made more difference, and that is true too.
Now, when you rely so heavily on the speaker and enclosure for damping, you do run into a situation where every little bit of damping material inside, and its specific placement, does make a difference. If you live with the same speaker for 30 years, you can hear it when you change it. Over time, my speaker surrounds stiffen up, and the transient response and bass response begin to suffer. I can hear the transient response, and I can easily measure the bass response because the ports get out of tune and respond at the wrong frequency. I replace the bass drivers every 8-10 years and the mids about every 15 years, and it throws everything out of whack again. I don't measure the ports any more because I can hear it, unless I am doing a total repower. They get out of tune just like a piano. The only way to adjust it is to add or remove a handful of polyfil in the mid cabinet (which is ultra sensitive to it) and a few handfuls in the bass cabinet, where it is contained in acoustically transparent, corrugated accordion-style baffles at the rear of each chamber. In the past I also have resorted to adding wooden blocks to adjust the enclosure volume as needed. Live with a speaker for 30 years and you really get to know them.
So I hope everyone enjoyed the reading. Everyone can totally disagree and call me insane, and that's fine. Everyone can go with whatever works for them. It's a different approach. If anyone hasn't tried the approach I have outlined and likes to build large or very large speakers, well, maybe try it the "old school" way.
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On the contrary, use it as a test board to develop your skills and your future choices.
So much has changed in the past 24 hours, that I may proceed in a month or so. It will take that long to get the proper iron from China if I proceed.
What changed? In the past 24 hours, I found a couple of things about SEP and how to handle it properly, and the awesome link to the 6SN7 and 6SL7 driver calcs from @dubadub helped me get over the driver gain knowledge hump along with the online load line calculator and another member, and then I found some good info and a tutorial on negative feedback and the two resistors involved and the 4 ohm tap and how to approach that. I didn't expect this yesterday. Maybe I have reached critical mass to proceed.
Thanks @dubadub ! 🙂
No : it is a SRPP single stage preamp, with one // 12AX7 as upper tube, and one // 12AX7 as lower tube. The gain remains the same (or just a bit higher) as a single SRPP tube, but the driving impedance is divided by 2.
T