captainbeefheart

The chassis for Chris wasn't a standard DIY chassis. I highly doubt you will see another small time tube amp builder go through the troubles of making a similar chassis. Going outside the box and doing a very different type of chassis isn't something one can just snap their fingers and it's done. It takes a lot of time and effort. I put my blood sweat and tears into these things and it's truly a punch to the stomach that for all my efforts I get flogged by some loser that doesn't even have anything to do with it just because he doesn't like how long it takes to do the work. Whatever, this is really stressful for me which I do not need. If that's how people look at me on here for trying to build them amps then I'm just going to be done with this forum for a while.

I didn't want to get into specifics but since I have to defend myself I'll open you up to the other side of the story. Here's the thing with custom amplifiers, they are custom. One person gave me specific design goals due to their passive arrangement and separating two inputs with different gains structures do to the low output of their phono setup. Then after all that work was done they changed their mind and purchased an active preamplifier that completely changed the design criteria. I liked this idea best since we had more signal at input to work and the active amp can drive lower impedance's, I changed the input circuitry around to take advantage of these things. Well would you know it he didn't like the active preamp and went back to passive preamplifier so I had to go and change the whole front end of the amplifier design again for the third time. Not to mention going back and forth between balanced and single ended inputs. I'm not complaining, this is all part of the process and I'm not mad at the person for making these changes but it's part of the larger picture of time frames third parties should know before they go jumping down my throat. I have gone through this before with people making design changes and I go along with it, that's the whole part of having a custom amp made but don't get mad at the guy designing it for taking longer if you keep changing things on him. Maybe people think it's a 10 minute change on paper but it's not, the entire amplifier needs to be re-designed. It's not just one section of the amp, the whole amp is one composite circuit that works together. With a design goal of wanting ~20db of feedback I had to completely change active devices for more or less open loop gain to allow for the 20db of feedback and to get the targeted sensitivity for full output power for his needs. Now it's one thing to change things in a purely mathematical way for loop gains and feedback but to breadboard and listen to the different designs and choose the best one from a listening standpoint takes a very long time. I have to work things out on paper, work up the simulation and see how things look. Next is change around the breadboard and bench test and finally hook up to speakers and listen. Time, time, time, time, but I was told that they would rather me take the time to get the best results instead of just slapping parts together and getting it out as fast as possible. I mean, that makes the most sense no? Why would you have a custom amplifier made only to rush the entire process because you aren't patient enough to work out something you may have the rest of your life. I'm sure nobody has heard that side of the story have they? No I didn't think so. So unless you have all the facts, comprehend fully what I am actually doing, and not have a bias already in your mind I'm up to nefarious actions then you haven't a clue and should just keep your mouth shut. Now I had to air private details to our amp design process that really wasn't fully necessary but because I'm having to defend myself there you have it.

So we have gone from 7 months now to a year in 3 posts. You're too cute for your own good. Go justice warrior someplace else, us big boys have real things to deal with instead of your ridiculous virtue signaling. I don't care what you or anyone says, it takes me as long as it takes me to do what I need to do to complete the amplifiers. It's not my problem you are ignorant about the whole process and have a distorted view of reality. Since you are only willing to see one side of things and remain ignorant to the other side that's your problem not mine. Let's talk about how silly you are to think you or anyone deserves low cost, fast service, and the best product. You get two of the three typically, sure go pay $6,000 for a single ended 6550 amp that produces 8 watts with 5% THD and you'll get it in a few weeks. Great that's fine, it's a choice. Or, have someone build you a better amplifier, for only the cost of parts which is $1200 but it takes longer. It's called a tradeoff. I wish I had both amps out about a month ago on schedule but things happen in life, sorry you are too ignorant to understand this. So your take is I should just drop everything that keeps a roof over my head just to get the amps out? No. Sorry not going to happen. Or even funnier, you expect me to build someone an amplifier for the cost of just parts and I pay for the parts up front? Wow you really live in a bubble. Why would I take the risk? I take the money up front for the parts because people are known to just up and change their mind and decide they want something else. It protects me from wasting my money and time doing someone else a favor all for them to change their mind and I get stuck with stuff I don't need.

Yes 3 months each amplifier times two is 6 months. They both asked me at the same time so to be fair they are getting their amps at the same time. I told both of them this. At one point Chris told me to just put his on hold and finish Tim's first. The money is for the parts. Do you think I'm going to use my own money to build them amps? You are even more delusional than I thought. How about this. Mind your own business. None of this has anything to do with you yet you are the one complaining about it. I haven't asked one person to send me any money for any other amps so I don't know what you are talking about. Racer may purchase an already built amp from me but I haven't asked for a single penny, I told him to just save up his money and we will talk later. You are like a little girl gossiping about things that bother you when it has nothing to do with you at all. Mind your own business why don't you.

I'm sure Roy or any other Klipsch engineer will verify how long it takes to go from paper to prototype build with a new speaker design. If you think 3.5 months is terrible for spare time work then you have lost your marbles.

You have serious comprehension problems so I'll reiterate for you again. 7 months isn't for ONE amplifier, it's for TWO very different amplifiers. Chris will get his amplifier not far behind Tim, I just put Chris' amp on hold until I finish Tim's for now. So again, a little over 3 months for each amplifier which includes the circuit design and breadboarding, going through multiple iterations until I am pleased with the results. Two completely different chassis designs and layouts. All of this being done in my SPARE time. You haven't the slightest idea of what you are talking about and live in a fantasy world. The ignorance is astounding in that you don't have any clue how any of this stuff works yet you will dictate how long it takes someone to do what I did. You do realize for full time work a new product prototype can easily take up to two years to develop don't you? So 3.5 months per amp in my spare time is actually quite impressive for a complete design of EVERYTHING from the ground up done by hand by me alone.

If people can't talk to you immediately they aren't happy, it's just how things are today with cell phones and the internet. It doesn't mean the person took your money and ran off to Mexico with it. It most likely means they are busy working and not staring at their cell phones.

I know all too well many amplifiers on the market aren't designed great either. I never said anything about his amps being noisy with hum, my point was he clones a lot of WE91A circuits and from experience if you just copy the schematic you will have stability issues with the positive feedback. Those amps aren't easy for a novice to build optimally. That and many errors in his wording like him saying "input sensitivity is 300mA" instead of 300mV. Little things like that tells me a lot. 300mA across even an input impedance of 50k is 15,000 volts. I highly doubt the amplifier requires 15000v to be driven to full power 😂 There isn't much required for good sound. I have had many borderline stable amps with high distortion and other gross discrepancies still sound good enough to use. But by no means does it imply they are great amplifiers. For that we would need some specs and measurements of his builds which he doesn't provide. I'm not telling people to not purchase his amps, I'm only putting things into perspective. He is a clone builder with no knowledge of electronics, he sadly focuses on brand name parts instead of the circuits themselves which is a bad sign in my book. Some of his other builds are much more forgiving circuits which won't have the troubles of say a WE91A but from someone with a ton of experience with electronics I'm here to tell you those amps are not for the faint of heart to clone if you want optimal results. Does his amps function? Yes of course but I'm certain that most of his WE91A clones are going to be unstable and ring like a bell. I'm only saying I won't go to a dentist that his day job is an electrician and just because he has a pair of pliers and has successfully pulled teeth before doesn't make him an actual dentist. Not all his clones are going to be as troublesome of a build, it was just an example and I'm certain a broken clock is right twice a day so yea I'm sure some of his amps he has produced sounds fine. But again I personally would want someone that knows what they are doing. A backyard mechanic might be able to slap some brake pads on your Toyota but do you want him putting a timing chain on a near 500hp S58 engine inside your lovely M3? I doubt it. It might just be me, but if I'm going to spend thousands of dollars on an amplifier I'm going to want something designed by someone competent. I have given multiple examples of why just cloning a circuit many times isn't enough to achieve optimal performance no matter how many expensive boutique parts you throw at it. Any amplifier with a decent amount of feedback will need to have compensation networks worked out, it's something you cannot copy from a schematic unless you build the exact same amplifier with the same exact chassis, layout, and parts. I don't expect the average person to know this stuff which is why I'm taking my time to explain it to anyone willing to read it. This isn't art, it's not a painting that is subjective. Amplifiers are technical devices bound by the laws of physics. Yes anyone can make an amplifier that produces sound but is it optimal? That takes someone with knowledge and experience, sheer will won't get you there no matter how hard you pray to your gods. If I'm going to fork over thousands of dollars for a piece of technical equipment I'm not going to trust someone doing it by the seat of their pants that mixes up mA with mV, I want someone that knows what they are doing. That's all.

Yes the original uses a 12AX7 which will also effect compensation changes and the sensitivity is certainly too high at 380mV to full power. Many of these old amplifiers were meant to be driven from a crystal pickup directly so they were shooting for a high input voltage sensitivity compared to our modern amps. I Increased the amount of feedback on many of the ones that came in to over 20db, added the lag comp network on the plate of the 12AX7 and changed the lead network cap value. Many of us builders that clone these circuits, well not verbatim just the topology because they have too much open loop gain and don't really like more than 30db of feedback so we change tube types to lower gain, especially if the circuit had a pentode like the hf35 or the original Mullard 5-20. I'll usually triode wire a 6AU6A for the first stage and use a 12AY7 for the phase splitter. I have used all 12AU7's, 12AT7's, EF86 in triode mode for the first stage and many more. I was partial to the triode wired pentode input and the 12AY7 LTP, it was one of the better combinations I tried. The issue with UL when sharing the same winding as the plate is when the plate swings down near ground with 43% taps especially the screen gets pulled down with it and makes the tube weak in this region of operation. Of course this happens at higher output levels and doesn't show very well on regular bench testing a sine wave against an constant load. Normal dips in impedance at bass frequencies down near half the original impedance the power tube can't supply enough current in that low screen power of operation when the plate pulls it down near ground. Look at a curve tracer when the screen is at only 50v, all the curves get squished together and compressed, then when the load halves the load line goes much more vertical on the current axis. Drawing it up shows how non optimal the load line is against the squished curves. With a nice stiff regulated screen supply in pentode mode this doesn't happen. So in the real world with real loads a well designed pentode amp often will outperform an UL amp in the higher power region. One neat experiment that showed how negative feedback is one of the major reasons for performance in transistor amps is making a +/- 300v supply and using two 12AX7 tubes in an opamp type configuration. When setting the feedback resistor to achieve a gain of 40db distortion wasn't measurable from my equipment with near 150v peak to peak output. The other advantage of transistors is complimentary pairs which tubes just cannot do ever, we will always only have NPN type devices with tubes. I always wanted to try that 12AX7 opamp circuit as a front end stage to drive a big single ended triode output stage that requires lots of swing. But it never happened due to it being kinda ridiculous. But if we can remove the driver distortion from these types of amps then deal with local feedback around the output triode then we could achieve very low distortion levels for the entire amplifier. Oh well something to play around with in the future.

Yup, the natural order of progression where fine tuning is at the end. I was discussing the highly cloned Western Electric circuits like the WE91A, naturally there is substantial high frequency roll-off starting around 10kHz which is why they added positive feedback to increase the high frequencies. Practically all clones will be unstable if you just copy the schematic verbatim. I have actually heard one Japanese builder claim that the amps should have major ringing and stability issues as it's part of the sound. I think the engineers at WE were not striving for that outcome, they worked the values to fit their specific amplifier with specific components and specific layout. Similarly with the later 40's-60's push pull designs and global feedback implementation. Many builders just use the values given on the schematic which typically won't hurt anything, they are just not optimal and can certainly be improved upon with drastic improvements many times. Just like the Mullard 5-20 or Eico circuit, the common cathode gain stage, long tailed pair inverter, and push pull finals typically UL, with 20db of feedback they perform very well. I have gone as high as slightly over 30db of feedback with the original Pentode input stage but the amplifier is just too sensitive and much harder to get excellent square waves. Most of us now just go with a triode for the common cathode input stage and a medium mu LTP inverter. Still gives excellent open loop gain for plenty of sensitivity and still allow for 20db or more of feedback. It's a tried and true design that gets built a lot to this day because it just works like glue. It's one of the great tube amplifier circuits! s

I was going to say I could look through my notebooks and try and find the Eico values for the networks but since yours is a clone with different output transformers it would be useless. I can walk you through making the bode plot. It's actually pretty easy once you get use to what to see on the scope for an ellipse pattern. it's one of the next plateau type things in amplifier designs. After I got the hang of it feedback is no longer a trouble maker and the designs will yield excellent square wave results.

You can apply a lag network to any amplifier circuit regardless if it never had one to begin with, more times than not it will greatly improve stability. I have added them to lots of vintage amps including Eico. Some circuits will have an RC network or just a cap from plate to ground, it does the same job as plate to power supply node since the node will have a low impedance to ground anyway through the filter cap. Same with adding a zobel network at the output, if an amp didn't have one and the specific circuit will benefit from one I'll add it in a restoration/repair. It can be on either side of the transformer but I typically use the secondary side because capacitance is cheap. In the old days it was probably cheaper to use a small value ceramic cap on the plate side instead of a higher value paper/polymer cap on the secondary. On many vintage amplifiers these networks were omitted as the amp was "good enough" for most easy loads. When something comes my way I don't just try and put the circuit exactly to the schematic, I improve upon the design to make the amplifier better. Many of my friends or anyone that's handed me an amplifier greatly appreciates the extra care to improve upon things and often times it's an audible improvement.

I'm not cloning a simple circuit pal where I just need to build the amp. I design the circuit from the ground up which I know you have zero experience with so you may want to just zip it. Now that the circuit has been worked out I can skip the entire design stage which takes the longest time, all that is needed it so build the amp and send it. I don't care what people do, I'm just offering if Shakey gives a good review of the amp and others are interested I'll make them one. Sorry for being nice. There was an interest in high powered single ended tube amplifiers that perform very well, much better than others being sold for $6,000 like Bigger Ben. I take great care and pride in designing something that will perform well and have no interest just pumping out garbage amps that only look nice just to make a profit. If you have no patience and want an amp immediately go on Music Direct. If you want a custom amp from me just start a conversation. I also had some health set backs but that has been more on the building side of things. I also have a day job and don't do this full time for money, it's just a passion of mine. I know more about circuits in my pinky finger compared to most of the hacks selling amps out there. If you want a quick hack job go for it, if you want something special that will last the rest of your life I'm right here.

That's good, you were just creeping up into the audio frequency spectrum with the resonant frequency. If you do run into any issues just increase the capacitance if you want to keep using the same chokes. -20db of feedback should be plenty to get great results. I add the lag network first then the lead network. The lead network is the cap across Rfb, it breaks upwards and will flatten out the response after the lag network (typically in the plate circuit of the first stage) is added. The quickest way I have found to accurately find the amplifier breakpoints is with a 45° Lissajou figure on the scope. With it in X-Y mode place the scope leads to amplifier input and output to measure phase difference. Increase frequency until you get the desired rise/run 45° ellipse pattern on the screen, write down the first breakpoint frequency. Keep doing this until you find all the amplifiers breakpoints by 45° intervals. Once you know where the breakpoints are we then know gain margin and phase margin of the open loop amplifier circuit. I can explain this better if you want but I have found most people just sort of make a guess at comp networks and adjust until square wave response is better. I had the hardest time doing it that way and hated it so I wanted a more definitive way of knowing the exact phase response of the amplifier and to calculate out the feedback networks to get me about perfect right out of the gate. Sometimes I do go back and move the lag network up if feedback didn't add enough bandwidth or down if the results didn't give me the stability I wanted and there is enough frequency bandwidth to do so.

Min builds lots of Western Electric circuits, many the 91A model which due to such low open loop bandwidth (starts to roll-off at 10kHz) uses some positive feedback to increase the high frequency response. In almost all cases I have seen this circuit produce instability and needs to be fine tuned for any sort of decent performance and stability. There are lots of guys that copy these old WE circuits, some do a fantastic job because they thoroughly understand the circuit and can make changes to or slight adjustments to values for optimal and stable performance. Many of these circuits, although look simple can be tricky to implement and build properly.

I suppose if you stick to cloning a known simple no feedback circuit he will do fine but he admits he has zero electrical engineering background and his portfolio is all clones of circuits. This worries me in a few ways, firstly if the amplifier has feedback you can't just copy the compensation networks and expect fantastic results unless you copy the EXACT layout/chassis and EXACT same parts and transformers used. For example anytime I clone a Mullard 5-20 type circuit I have ended up with very different lead/lag compensation network values. Output transformers will have the biggest impact on this and the layout will also change parasitic properties. If you have a simple, zero feedback design that you want him to clone I'm sure he'll do fine, as he states in his website that pretty much anybody can clone circuits and build tube amplifiers that have already been designed from an engineer. Just a note of caution. Personally I wouldn't want a food biologist fixing my car or making me an amplifier as it's not their area of expertise, it's just a hobby to him. I also looked through his portfolio and gut shot images of soldering and layout and he doesn't seem to follow any guidelines. For example he has a large coupling capacitor where he extended the leads of the cap to reach where he needed to go. On any build I have looked at I can see many bad decisions made which are all rookie mistakes. That's fine if you are building yourself an amplifier but if you are shipping amps across the country you should at the very least take some time to study MIL Spec soldering requirements for different component types to learn how to build a rugged piece of equipment. For what he is doing (cloning) that will improve his amps significantly. It would also help if he did take some electrical engineering courses to not just clone but improve upon older designs and make certain the amp is as good as can be. I don't see any specs or measurements. I guess just another fly by the seat of his pants clone builder selling amps that know nothing about electronics. Sorry it just irks me. Any hack that jumps into something head first with zero background knowledge just doesn't sit well with me. I suppose many of the builds he is making are very simple zero feedback old designs.

The only thing I can think of is just pure novelty. People LOVE trying different tubes in their amps, of course some designs with minimal to no feedback can heavily rely upon the active device linearity for it's performance. Schiit engineers probably know that anything sounding different is at first going to be novel and exciting, yay we changed the sound. Some may like it some may not. Since the FET will have Pentode like output curves and the 6SN7 is a Triode they will sound different. It's kinda neat, but also kinda pointless. The older I get the more I just leave an amp alone after I deem it sounding good compared to when I was younger I'd always be modifying and measuring/listening for differences. I guess if the SS plug in devices makes the amplifier experience more enjoyable to you in any way shape or form that's great. I just want to share my experience on what the device is and how it effects the amplifier to better inform consumers to what they are purchasing. Some may read my description and say right off the bat they don't want no stinkin Pentode like curves in their all Triode amplifier.

Each unit is two LND150 depletion mode FET's with their gate, drain, and source pins tied to grid, plate, and cathode pins. There isn't a "dummy" load for the filaments which is good and bad. Good that it saves energy and bad in that with less current draw on the heater winding voltage will increase possibly stressing the other tubes in the circuit. It will have a completely different distortion profile compared to a true 6SN7 so I don't see the allure either.

https://elsmar.com/pdf_files/Military Standards/Mil-Std-2000.pdf

Smart move. Any low powered amplifier I make, mostly single ended amps especially single ended triode amps I always go direct coupled to the output stage. You'll have a much cleaner sound with no bias excursions and blocking distortion often encountered in low powered tube amplifiers. As a bonus being able to drive grid current you'll get higher output powers also. As to who builds them? Not many that I come across so I don't have much to offer in regard to referring you to a specific model of amplifier. Shakey's amp I am making him is DC coupled. If you haven't found anyone after I complete his amp we can talk about making you an amplifier. I love the 45 tube, it was my favorite power triode of the popular types like 2A3 and 300b, it provided the best sound but many choose 2A3/300b due to higher output power but they don't touch the 45 in quality. The only tube I have found to sound better than a 45 is the 4P1L, it swept me off my feet so I swapped over from my critical listening amp running 45's to running the 4P1L and haven't looked back. The 45 glass bottle is more attractive compared to the 4P1L which I know many have made the decision on looks alone but if you are out for just sonic bliss the 4P1L is hard to beat.

Mullard 5-20 circuit's always sound good to me. One of my favorite simple push pull amps that just perform well without any fuss. Of course different tubes but I have heard a lot of different tubes with this circuit and it's the circuit that sounds good. What feedback resistor value are you using and how much does it give you? Just a quick guess I think 4.7k should give you near 20db. I'd keep an eye on the power supply with such a low value choke, you may need to increase capacitance a little more. The resonant frequency is high at 19Hz

Excellent thank you!! As I said someone else that builds speakers will know more. All my speakers except for maybe one pair are closed box not vented/ported. All my experience is with closed enclosures. I think the crux of the matter is using the speaker within it's ratings. Your device you created was probably as much a protection device along with improvement. If you have someone with a very powerful amplifier cranking the EQ of the low bass up as high as possible and pushing the speakers beyond what they are designed to handle then yes you can easily damage the woofer. A band pass filter just isn't necessary if using your speakers within their ability. If this was possibly a pro audio situation Edgar's device would be a much better approach than a band pass filter which was probably it's intended market?

Look at the plot and notice the impedance at the resonant frequency around 48Hz. It rises dramatically to 90 ohms!! In a cabinet, and depending it's design this frequency will shift down lower. An amplifier source impedance, assuming a voltage source is very low, voltage will remain constant vs impedance and current through load will change. At this resonant point the current dramatically gets reduced. For 10 watts at 8 ohms you'll have a little over 1 amp of current. At 90 ohms you'll end up with 1//10 the current at 100mA. Also remember this is a motor. The plot shows greatly reduced sound pressure as the frequency gets reduced below it's Fs. It doesn't really matter if the woofer tries to reproduce the low frequency signal, it naturally puts out far less sound pressure meaning it's not moving in and out as far to push the air. So for the same voltage output for 10 watts (8.9v) into 8 ohms in the frequency region where the speaker is most efficient, say at 200Hz. With the same 8.9v at 20Hz sound pressure is down -28db. e.g. the woofer isn't moving in and out very much compared to the same signal amplitude at 200Hz with a sound pressure output of 100db. So yes the speaker will reproduce those frequencies but with greatly reduced excursion moving less air and less sound pressure output. How can it damage the woofer when; A- there is much less current B-there is much less movement produced in and out.

I have limited experience with the 6Y6, Maynard will know more than me but I forgot to mention that when switching over to pentode operation check the bias, the cathode resistor may need to be optimized for pentode operation.

I'm trying to play catch up and get work done while not push it too much. When I get done later I'll run some simulations of the Sweetie with varying amounts of plate to grid feedback and see what the results are for anyone wanting to experiment with the Sweetie. All one needs to do is remove screen resistor from the plate and connect it to B+ that feeds the output transformer. Looking at the datasheet their curves are for Vg2=135 so it might be prudent to use a 47v zener in series with the screen. The reason for a Zener and not a resistor is with a resistor during signal when the screen pulls more current you'll get a sag across it squishing the plate curves causing transient compression of the power stage. The Zener keeps the voltage drop constant no matter the current pulled by the screen. If you want to get real fancy for optimal results use three 47v zeners in series making 141v string as a voltage regulator. With 3mA of screen current plus a bias for zeners of 20mA, a dropping resistor value of 4.7k should work well with a 250v B+, if you have less B+, say only 210v use 2.7k for the resistor. What happens is 3mA is pulled by the screen and the rest of the current 20mA will pass through the zeners. When the screen pulls more current the current through the zeners is reduced down by that much keeping voltage steady across the resistor. Simple voltage regulator for the screen, 3 diodes and one resistor. For people just experimenting I'd order like 10 of the zeners and start out using them in series like the first method I described. If you like what you hear in pentode mode with plate to grid feedback and want to improve upon it then move on to the screen regulation circuit I proposed in the second method. With the first method the screen isn't really regulated as since the zeners are in series it will always just drop a specific amount in relation to B+, so if the rail moves so too does the screen in proportion. With the second regulated scheme if B+ shifts around the screen will not, it is regulated and stays at the voltage made by the zeners. They are only $0.30 ea https://www.digikey.com/en/products/detail/onsemi/1N4756A/977325