Thanks for the nod ... I guess the takeaway is, "Don't be so lazy. Match HFE at operating temperature and current." Thanks!
Does anyone care to ask an amplifier designer a technical question? My door is open.
I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.
I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
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Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.
I like to tell true stories of my experience with others in this industry.
I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.
On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.
I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.
Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.
I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
.
Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.
I like to tell true stories of my experience with others in this industry.
I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.
On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.
I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.
Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.
845 responses Add your response
In case you are wondering, the 25V rails are to accommodate Quad ESL's. With 75:1 step up transformers (Plitron), the amps can only punch the panels to 3750V, exactly half the level which engages the protection circuit. So I can bypass the protection circuit with impunity, and get a remarably refined ESL sound. |
Hi Roger, I own your RM-10mkii, which is a mysteriously addictive amp. How did you approach low-frequency response? I ask because the bass the amp produces is punchier than any 100-watt solid state I've owned. I have zero knowledge of electronics, so my other question is a simple one of your opinion on newer Russian tubes and their sonics/quality. I might be the only person in audiophile land who actually likes the JJ brand. They seem the most linear and balanced, albeit with a dry top end. Thanks for this forum! |
@terry9 In case you are wondering, the 25V rails are to accommodate Quad ESL's. With 75:1 step up transformers (Plitron), the amps can only punch the panels to 3750V, exactly half the level which engages the protection circuit. So I can bypass the protection circuit with impunity, and get a remarably refined ESL sound. You have my ear. Tell me more about what you are doing. Which QUADS? I am guessing 63s. |
@enobenetto I own your RM-10mkii, which is a mysteriously addictive amp. How did you approach low-frequency response? I ask because the bass the amp produces is punchier than any 100-watt solid state I've owned. I am pleased how many people love the bass of that amp. I think I just lucked out. I designed and prototyped all the transformers myself. The application is unique. Very high voltage, perhaps its that. I gave a talk about it at Burning Amp2018 that outlines the application and compared it to the typical applications http://berkeleyhifischool.com/having-fun-at-burning-amp-2018/ I stock several brands and vintages of EL84s. I do not stock JJ so I can't say much. Im glad you like them. |
@geek101 @ramtubes with Class D switching freq over 450/500 KHz these days do you still think output filtering is an issue?. How do I educate more about this ?. If the issue of filtering not a function of switching freq please correct me. Thanks again. One would want to see the measurements John Atkinson style. There is no other way to know but measure it. If these things interest you Stereophile is your best bet and its a good deal at $14 or so. The filtering is easier the higher the frequency. That does not mean its done right. JA recently reviewed a D amp that had what I assume is pre EQ to make up for the drop. I think it was NAD. Of course there are flaws in that idea because it EQ's for a resistive load. At least one can play with it and choose by ear. |
@terry9 Thanks for the nod ... I guess the takeaway is, "Don't be so lazy. Match HFE at operating temperature and current." Thanks! Have you measured the idle current of each transistor at operating temp in the amplifier? You of course know just to measure the Emitter drop divided by R. How well is it distributed? Then you could put a scope on them at full power and see how equal those are. Dont spread the emitter resistors too much because they might not track and share over full swing. I would make all the emitter resistors the same and do good transistor matching. You might make them a little higher like 0.22 ohm. You won't loose much output. The concept of varied emitter resistors is a thought I have not had. :) |
@terry9 I would use a dual trace scope, make sure the two channels have identical gain, use one emitter resistor on channel 1, call that the reference. Then use channel 2 to see how the others (one at a time) match up at various power levels. I would find the results interesting. Have you also looked at the output transistor current driving the speaker at high levels, high frequencies? Trumpet music, thats a killer? Have you measured the impedance of the primary side over frequency? I have found some stepups have so much capacitance that more of the energy goes into the transformer than the panels. FYI, the 57 and 63 transformers, though different, are very cleverly wound. A torroid typically has lots of shunt capacitance that you have to drive. The QUAD transformer does not. BTW, I am not impressed at all with the Plitron audio transformers. Van Der Veen’s paper seemes flawed to me. He is a great speaker promoting his idea of automatic bias. He believes you can use a gapless tube output transformer to make a practical amplifier. I take great issue with that. I think there are some unasked thus unanswered questions. I would ask him, "what happens when there is a DC offest in the output stage. It will happen when the amp is pushed?" Similarly if you have any DC across your primary the core flux will be off center. I cant say how many mV is ok, but i think at 50 it could be noticed and at 100 mV it might be a real problem. Here’s how to set up your test: Scope ground goes to hot output terminal of course. Im assuming the output stage is emitter follower. Dont forget to float the AC power on your scope. Othewise you will be shorting your output. On my bench I only have one piece grounded. Everything else floats. Even my soldering iron floats because sometimes I solder amplifiers while they are on. There are parts of the circuit that dont much mind. Dont do that with SS amps, the are unforgiving. |
Roger, here’s a question about light loading with the RM-200 Mk.2 amp: With a loudspeaker given a nominal 8 ohm load rating by it’s designer/manufacturer (it measures between 10 and 20 ohms from 20Hz to 20kHz save for the 60Hz-180Hz band, where it dips down to 7 ohms, centered at 80Hz), the RM-200 will of course put out at least it’s rated 100w/ch when connected to the amp’s 8 ohm taps. If it is instead connected to the 4 ohm taps (light loading), what will the amp’s output wattage be? Because of the speaker’s relatively high and even impedance curve, it is not for the flattest frequency response I am interested, but rather the lowest distortion and longest tube life. I realize that with light loading those will be achieved at the cost of less power output from the amp. I have a modestly-sized room, and don’t listen at very high SPL, so am willing and able to accept that. |
So Roger: new production tubes from our old Cold War rivals. Can the Russians really make and sell quality tubes at such low prices? A quartet of 12AX7's for $18 (shipping free!). We did that ourselves back 50-60 years ago. But that was when US tube production was in the millions for the radio/television market! Do Russian mfgr's have to compromise on material quality and less vacuum- pumping to sell at a low cost? |
I have bought a set of 4 Gold Lion (Russian) KT-66's for use in my pair of Heath W5's. $35 a tube! Originals sell for $200+ a tube (UK). They sure do look real nice! I still have the original US Tungsol 5881's in use. I wonder if the Russian ones can stand up long-term to the plate and screen voltages in the W5's? |
Thanks for offering your tribal knowledge to the group. I really like vacuum tube audio equipment. Both Pre Amp and Amp. It just sounds better. (Ha....I have all C-J equipment.) My design question for you is..... I have always wondered if vacuum tube technology was abandoned prematurely (for solid state), and never fully exploited to its full potential? |
Roger, you are being very generous with your time and your expertise. Thank you! You have given me a container load of practical information which only comes from practical experience. Much appreciated! As requested, here are some details of my system. My system is 98% analogue. Phono is integrated with the preamp. Twinned MATs reduce the noise floor. All caps in the signal path are air gap or vacuum, including RIAA. Battery power, filtered. Speakers are 5 (soon to be 6) Quad 2905's. These have been modified for the Plitron step-up, which I will revisit - but that protection circuit is not at all transparent! It desperately wants attention, if not removal. The small disgusting ceramic caps in the phase ladder are being replaced with air gap (teflon is a big improvement on ceramic, but coloured). The larger disgusting ceramic caps are replaced with a chain of RTE styrene F&F caps. Air gap caps are made in the usual way. Amplifier power comes from a big variac driving an isolation transformer, driving power transformers. Rectifiers are Ixys, feeding LCLCLC filters. Theoretically at least, this brings ripple down to the level of intrinsic noise. Amp topology is reminiscent of the newer Brystons, but not close to identical. Transistors are AD, Toshiba, Sanken. All resistors are nude Vishay or DIY nichrome. Theory as well as experiment have led me to suspect that much of what we hear is dielectric-sourced distortion. Accordingly, my caps are air-gap or vacuum wherever possible, styrene when not. Wiring is insulated and protected with unshrunk shrink-wrap, except at the ends to prevent corrosion. Just my poor observations in part repayment for your generosity. Your expertise is highly valued, so anything you have to say is welcome. Thank you! |
I am puzzled why the idle current goes down rather than up as it warms. Usually its the other way round because of the negative temp coefficient of transistors.Actually this is pretty common with bipolars. They can get into a phenomena known as 'thermal runaway' if this is not well controlled. However, my latest amps are Class A, and I suspect that a more realistic match is obtained by culling outliers by HFE, then match from VBE using the bias at constant potential and sufficient to generate the operating current. Finally, instead of using matched emitter resistors, I use emitter resistors tailored to the output devices, so that each emitter resistor sees the same potential drop. There's a difference between idle and dynamic operation. Matching the hfe over the range in which the device operates is going to be a better method. Otherwise what will happen is a particular transistor can 'hog' current at higher operating points and it will thus be the thing the sets the distortion of the amplifier at power, especially full power. with Class D switching freq over 450/500 KHz these days do you still think output filtering is an issue?. How do I educate more about this ?. If the issue of filtering not a function of switching freq please correct me. Thanks again. There's lots of information on the web! You might want to read the papers of Bruno Putzey who has done a lot to further the art. The filter is there to filter out the switching frequency, which it cannot do completely. What is left is a sine wave called 'the residual'. Usually the filter is set to about 60-80KHz, so as to avoid phase shift within the most sensitive area of the audio passband, but otherwise get the residual down as low as possible. The higher the switching frequency the easier this is to do- the speaker inductance itself starts to play a huge role at higher frequencies. Mac Turner brought me in to consult on his. What disturbes me about them is that they all get their sound from the IC in the front end. Perhaps some are discrete front ends but I have not seen any.Actually you don't need any ICs in the front end prior to the encoding scheme, if you set things up right. The encoding scheme of course is going to use some sort of chip- our amp for example uses a high speed comparator chip. But the audio signal is applied directly to it. |
@bdp24
As I tell everyone. Light loading can be done on any tube amplifier. If you dont play above 80 dB go to the lowest tap. If you play 90 go one higher, if you play more than 90 you may have to use the high tap to get the volume you desire. This change should be far more apparent than a cable change. 7 ohms on the 8 ohm tap is no problem for the amp but lower taps always perform better technically though how it sounds to you is more important. 4 ohms on the 4 ohm tap produces 100 watts. 8 ohms on the 4 ohm tap around 60 watts. As you go down in taps you spend more time in the class A region. The distortion and damping are much improved. Would be nice if you had a way to measure the peak voltage you require, then much better advice can be given. You can also get at that with a SPL meter at one meter at listening level. Then with speaker sensitivity we can compute it Everyone needs an SPL meter. For $50 its an execellent investment. People spend more than that on a poorly designed high end fuse. Please do not buy premium fuses, TuningFuses are the worst and the others I have not dissected but the people who sell them should be dissected. |
@terry9 @atmasphere Actually this is pretty common with bipolars. They can get into a phenomena known as 'thermal runaway' if this is not well controlled. Ralph, did you perhaps mis-read this. He said the idle goes down not up as the amp warms. This is the opposite of thermal runaway. Terry, do you still hold your idle current goes down as it warms? If so I want to see your circuit. Hey, I'd like to see it anyway. This is unusual. |
Ralph, did you perhaps mis-read this. He said the idle goes down not up as the amp warms. This is the opposite of thermal runaway.Yes- you are correct- totally misread that one. It is pretty weird. I’m wondering how the thermal feedback is accomplished. If its done with an active device, that device might be seeing its hfe drift up as it heats up- thus causing the outputs to shut down more than expected. A schematic would be interesting. Nelson Pass has designed an interesting amplifier based on the old VFET/SIT devices. As solid state goes one of the most musical I’ve heard. https://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-2-a.html It also employs low voltage rails, about 25-28 volts. |
@roberjerman
So Roger: new production tubes from our old Cold War rivals. Can the Russians really make and sell quality tubes at such low prices? A quartet of 12AX7's for $18 (shipping free!). We did that ourselves back 50-60 years ago. But that was when US tube production was in the millions for the radio/television market! Do Russian mfgr's have to compromise on material quality and less vacuum- pumping to sell at a low cost? They are doing better and better. Sometimes I send back a whole batch but not so much lately. Low noise 12AX7 are hard to make. Where do you get 4 for $18? Im sure they are not tested for noise or microphonics. Luck of the draw like poker. Sadly the USA makers never got the noise as low as the Europeans. However USA makers were very good at power tubes. Vacuum pumping is not a problem, cathode coating is. They told me when I visited the EI factory. "All we know is we mix up the cathode coating in a tin pail with whatever water and let it sit overnight, its better that way. However we don't know if thats because it sits overnight or perhaps the night watchman takes a leak in the bucket." Im not kidding and that came via Dragona, our translator, right from the head of production. I spent 10 days at that factory. Sad its gone, they were on to something and I wanted to help by offering noise testing which they could not do. I passed on their offer to make me $100,000 worth of tubes, prepaid. they were broke, Good luck seeing those. |
@terry9 I see you have jumped on the bandwagon of expensive parts. I have not yet found them to be superior and they are costly and often fragile. Those resistors especially. I dont see the benefit. As far as dialectric, i understand it well. Let me ask your a question. How much AC voltage (changing voltage) is across a coupling cap in any amplifier? I am still curious about your falling idle current with rising temp. How do you drive the capacitance of all those QUADS. Have you done some measurements on what the combined impedance of the whole setup is? How do you arrange them? |
There are several Russian sellers on EBay that claim to have military (OTK) grade 12AX7's made circa '80 at Saratov. The prices are astonishingly low! I am tempted to buy a quartet. If I remember right, I might have bought a quartet of 6L6's from one of these sellers a few years ago. I will have to search through my tube stockpile to verify this! I recall the boxes had the proper Cyrillic printing. Thought I'd put them in my FenderTwin Reverb! |
RM happy Thanksgiving! RV says hello - told him I recommended your RM-200 for driving some of his speakers....appreciate the insights on MKII having the cap forming switch. I know he and Low share the DBS patent and a few others have started doing that sort of thing internal to amplifiers, preamps, etc. My question is what tube testers are you recommending at sane portable prices... ???? best to you Jim |
@quincy I have always wondered if vacuum tube technology was abandoned prematurely (for solid state), and never fully exploited to its full potential? Vacuum tubes were not abandoned but slowly pushed aside. However the majority of reciever manyfacturers like Fisher, Sherwood, Marantz, Pioneer, Kenwood, Heath, Knight and Lafayette all went to SS sooner than they should have. Of that list I would say only Marantz made good on the change-over in that their early SS gear. Their early SS gear is quite good where the other early SS gear was quite bad. Kudos to Sid Smith who did a very good job to make the Marantz 7T sound as the 7C. However the current value of each does not reflect this because tubes are favored. Both 7s are quite good. Other early SS designers were Dawson Hadley of Marantz, Jim Bongorino of SAE then GAS, Quatre was horrible, Bob Carver offered power and value but not good sound. Crown was ok, Mac Intosh made some great Autoformer SS amps (see my link via my profile) In the early ARC preamps up to and including the SP-6 Bill J stole the Marantz 7 circuit topology, added a very unrelaible, poorly regulated power supply. Bill Johnson did nothing I find interesting and just made things worse in every way as time went on. CJ, I'm sorry, never impressed me. Two Economists do not make an EE. Getting them to talk about circuits is a non conversation. Their amps are pretty classic circuits. Its not that you have anything bad but frankly a Marantz 8 is hard to beat. Really really hard to beat. I cant even say I beat it with the RM-9 but I did give more power. I don't want to over do it but Sid Smith was a far better engineer than any of his contemporaries. A lovely man. I met and interviewed both him and Saul Marantz. Perhaps I should publish the tapes. The tube HK Citation amps have some serious flaws. Who else shall we talk about? The RM-1 was way ahead of its time and I would love to have it reviewed if anyone wants to review legacy products. It is the first preamp to use the 6DJ8, is DC coupled, No output capacitor, response down to 0.1 HZ. Sadly ended by the folding of Beveridge ESLs. I have considered re-introducing just the line stage to sent to John Atkinson. He has never measured a line stage that does what the RM-1 does. Pardon my enthusiasm, but its really special. If you want to give me a list of companies for a yes/no I would be happy to go down it. Some of the no’s will be no, no, no. like Counterpoint who rightly went bankrup. Sometimes the world takes care of itself. Counterpoint was a group of nasty people making a horrible product. In short, some companies made a good transition some not. Current tube amps have some interesting ideas but none that really impress me. |
@tomic601 My question is what tube testers are you recommending at sane portable prices.. The B&K Dynajet series is fine and still under $100 or less on eBay. The 601 is the one I have. Although I have the big Hickok I find it heavy and slow to set up. ALL you need is an emission tester, not a transconductance tester. I hope to release a curve tracer/tube tester for around $1000 that will do far more than the Hickok standard. It will connect to your computer, draw graphs, match up tubes and measure a whole bunch of things I have found to be important. |
I have bought a set of 4 Gold Lion (Russian) KT-66's for use in my pair of Heath W5's. $35 a tube! Originals sell for $200+ a tube (UK). They sure do look real nice! I still have the original US Tungsol 5881's in use. I wonder if the Russian ones can stand up long-term to the plate and screen voltages in the W5's How high is the plate voltage? I didnt think the W5 ran the tubes hard? The Russian KT66s are fine and the Chinese looked good to me. Lifetime will be an issue compared to the NOS Genelex. Originals are expensive due to supply / demand and how high someone will go. You know the 5881 is a small 6L6 and neither has the plate area of a KT66. Are you having any problem with tube life? What do you think you get out of a pair before the silver gettering is all gone? |
Jumped on the bandwagon? No - Shanghaied. Didn't want to be convinced, but the two-alternative forced choice paradigm left me no choice. Like when your optometrist says, "Better or worse? Better of worse?". Easy to design a single-blind experiment. Did so with resistors and caps. Results were clear with some components always preferred: air-gap and vacuum caps, nude Vishay resistors. A justly famous person's apparent preference, a species of Caddock resistor, had large minimum orders, and so was not part of the test. His other apparent preference, teflon, always scored highly. Agreed, not much AC - but conversely, not much distortion via dielectric absorption is required to degrade a small signal. Confirming idle current falling monotonically with time. Can't post the schematic because it's not mine and it's proprietary. Sorry. Hope you understand, even though it's poor payment for your generous help. Each Quad has its own mono block. Two Quads facing ahead, and two Quads at one radian angles, facing in. A bit like one of Walker's experiments. Think of two sides of a hexagon on the left, mirror image on the right. And two at the back of the room, attenuated, but important. |
@terry9 Each Quad has its own mono block. Two Quads facing ahead, and two Quads at one radian angles, facing in. A bit like one of Walker's experiments. Think of two sides of a hexagon on the left, mirror image on the right. And two at the back of the room, attenuated, but important. Its ok, ive seen plenty of SS amps. The negative temp coefficient is interesting. You sure have a lot of stuff there. It would still like to know what kind of capacitance you are driving at 10Khz and up. As to the capacitor question. In the passband there is 0 Volts of signal across the cap. I'm still in the Polypropylene camp. Best thing for the money. Remember any part I buy is 5 x cost to the final buyer. So I cant buy too many $50 caps expensive resistors. I also appreciate manufacturers who make relaible parts. I have found CJ, Jensen, and others to fail. There is no reason for a coupling cap to fail in this day. The problem with premium caps it the people make them do not have the years of experience that the old timers have. While I could make an amp with all premium parts, sell it for a lot more, I just dont find anything special about these parts. I would only do it to reach into the buyers pocket. |
@terry9 Are you aware that the secondary capacitance of this transformer is 800 pf and the input capacitance of the speaker panel is many times lower? If I multiply that times turns ratio squared i get a primary load of 45 Microfarads. For the transformer alone. Are they kidding? Thats a lot to drive. The QUAD transformers are quite good and much lower capacitance. I dont get these Plitrons at all. Tell me what is wrong with the QUAD transformers? The primary of the Plitron is 0.1 ohm. How low is your dc offet? |
ramtubes OP This is great advise for those here, to learn and understand these Stereophile measurements, it’s crucial to giving good informed advise to others, and to selecting the right stuff for even for themselves. As all decent manufactures use these types of measurements to design build and to test their products as well as all the EE laws that go with them. Anyone who doesn’t use or doesn’t believe in them, should be given a very wide berth as they have no idea what they’re talking about. Cheers George |
Agreed that polypropylene is best for the money. Improvements on polyp are incremental and absolutely not worth it - unless you are a hobbyist who wants to see how far he can go, just because. What I see in Plitron (theoretically) is two things: first, the two plates of the ESL are driven by the same core, so they can be precisely balanced; and second, they offer 75:1 step-up instead of 250:1. Since I committed to 75:1 with 25V rails, going back to 250:1 would involve re-engineering the protection circuits. Rather than that, I would try to build high voltage amps to drive the Quads directly. Wish me luck - and long life! What I hear (subjectively) is that the Plitron 2905's are much brighter than the remaining stock 2905, without sounding harsh. Piano on vinyl sounds quite similar to the instrument upstairs on the modified units. The unmodified unit sounds mellow but imprecise compared to the Plitronned. In fairness I must add that this was accomplished with the help of nichrome wire and a small inductor to equalize primary impedance over the frequency band, as per the Vandersteen data sheets. My DC offset used to be 50mV or less. What it is now is a good question, one that you have prompted me to ask. Thank you. |
@georgehifi Hey George, did you see the review of the Cary SLI-100 in the lastest issue? Why would they be so dumb to send an amp that is going to look so bad on JA's well documented test procedure? Read Dec, pg 91. Read pg 153 for Cary's response. In there their response they say measurements are not everything and an amplifier should sound "intoxication and emotional". "A degree of second order harmonic texture gives the midrange a certain musical.... and expands the soundstange". Pure marketing drivel. Where is Dennis Had when we need him? The whole argument about 2nd harmonic distortion being "benign" totally ignores Intermodulation distortion which is far worse and always higher. If you are listening to a small group, singer, solo guitar a little THD isnt bad. It just creates the octave. My question is "what is the 2nd harmonic of Beethoventh's 9th:". In a full orchestra, with chorus. there is no fundamental to do much with. Some people must think the amplifier has the intelligence to go find the fundamental note and create the octave. Amplifiers arent that smart. They just amplify a time/voltage varient signal. Its not like they are following the score. :) All the specs on this amp are horrible, shameful, disgusting, who designed this? Please go do something else. By John's standard this 100 watt amp reaches 1% THD as 3.2 watts, 3% at 22 watts, finally reaching its 100 watt rating at 10%. You all get this in addition to poor damping, noise and rising distortion even at one watt on both ends of the frequency range. If you want a comparson look at the review of an RM-200 II, an amp at virtually the same price. |
@terry9 What I see in Plitron (theoretically) is two things: first, the two plates of the ESL are driven by the same core, so they can be precisely balanced; and second, they offer 75:1 step-up instead of 250:1. Since I committed to 75:1 with 25V rails, going back to 250:1 would involve re-engineering the protection circuits. Terry, all of this is intended to help, so have a seat and let me inform you of some things going on. These things may alarm you. You may like what you have created better than the original, however you may not if you go back. Here are the problems I encourage you to look into... deeply, with meters, oscilloscope, numbers. 1. 50 mV offeset on 0.1 ohms is 1/2 amp, a considerable problem for both the Plitron and your amp. 500 mA is a significant portion of your 1200 ma idle current. Later we can talk about how saturated your core may be. 2. There is NO advantage in having the two stators driven from the same core. I can almost promise you the leakage inductance on either side of the center tap of the Plitron is far from equal. It would almost have to be unequal if the thing is done in two winds. You do know how torrids are wound? Great videos on YouTube for those who want to see. 3. The two QUAD transformers are likely more matched at high frequencies than the two halves of your torroid. You can easily confirm this by driving them from 10K-20KHz with a dual trace scope, any low level is fine. I believe you will see the two stator drives rise and fall opposite to one another as you sweep the audio range. See at what frequency this starts. Dont judge those transformers on how small they are and how they look. Nor judge the Plitron on its looks, size or marketing. 800 pf in the specs is a red flag for me. That is 45 uF on the primary, which is like 1/4 ohm at the top frequencies. 4. I have built many DD amps and I am listening to a 5200 volt DD now on my ESLs. Perhaps we could talk about a kit for you.I stil make small production runs if you are interested. DD is the way to go then all that other stuff like parallel capacitance, leakage inductance, core saturation all disappear with the transformers which have always been the weak link of ESL speakers. 5. I think you mean the Vanderveen data not Richard Vandersteen. I sincerely doubt there is anything special going on in that torroid. I would have to say that a torroid is a flat out wrong way to make an ESL stepup. I make my own, but not that way. One has to reduce the capacitance not increase it. Torroid winding is the highest capacitance on earth. If you do all this, you will learn a lot. I have been building ESLs since 1976. If you dont know who Harold Beveridge was I suggest you do a little research.Peter Baxandall wrote an entire chapter (in some large general speaker book) just about the QUAD 57 and 63. Well worth reading. I have his chapter in my file and refer to it often. After reading it many times I think Baxandall had a lot to do with, or entierly did the electronics while Walker had the concept of the rings and delay line. Baxandall gives a compete model of both drive systems. Perhaps I shouldn’t say which speaker is the work of art. Please take all this as education, Im just reviewing your good work and adventure so far. I admire you getting as far as you have. BTW 5,000 volt amps are not so difficult as what you have gone through so far with your SS amps. They dont need protection circuits and I wonder why you are still using yours? Do you live anywhere near SF, CA? |
Thank you for your interest, Roger. I take your comments in the helpful spirit in which they were given. You have motivated me to look again at the stock Quads, and think about driving them with my current amps. These amps have proven themselves to be very stable over the years, and don't really need protection circuits in the speakers. I think. So I just may continue to do without. To be clear, I am not using the Quads' protection circuits. Near to SF is relative. Emotionally nearer than geographically. I did post-graduate work at UC Irvine, but then moved back home. I am now 1000 miles away. But what's that to a man with a thumb, as we said in the 60's. I would be interested in a DD amplifier, but I am somewhat frightened of the high potentials. The one thing I know about super-KV work is that it's qualitatively different from sub-KV work. Perhaps you could point me to your website? |
Just wanted to say that it's great to see you participating on the forums. I've been a fan of yours for a while, and my dream setup is using your amps. Because of your whole philosophy towards audio basically, and I'm part Polish too (I'm assuming you are, but with a Ski at the end. I'm pretty sure you are. Lol). I love that you design to be stable, and avoid failure. I don't have time to go through all this right now, but I almost died at the first question. As far as I know. You make tube amps that are easy to use, and are for the long term. That sounds good to me. The fact that they also sound good enough to keep Stereophile A ratings for years means a lot to me too. I wish I lived in California. I would most definitely check out your school. I honestly think it just needs to be pushed more. I'm willing to bet that Burning Amp alone will help. I know you can't just spend, spend, spend, but maybe some directed advertising on Facebook towards people that are very interested in learning electronics would help. You might pick up done young people struggling to afford College? Something different should be tried, either way. Because if the word doesn't get out. No one will ever know. It's that simple. I only found out about the school, because I was on your site, for instance. I think it's a great thing you're offering, either way, and bless you for doing so sir. Can't wait till I have more time to read what you've wrote about biasing in particular, as it's fresh on my mind. What with buying my 3rd tube amp this past week, and still not knowing how to do it, and even worse, not knowing the theory behind it all. So I'll thank you ahead of time for that, and wish you and your family a Happy Thanksgiving. Thank you Andy B. |
ramtubes I think that one comes later for free on line, as I'm such a tight arse, I only read the ones Stereophile drip feeds online for free. But it must be bad to beat the Leben CS300, check out the HF boost because either the output transformers are ringing or the circuit is oscillating. And it's shown in the 1khz square waves as well. To me another one, that should not be passed on final inspection to be sold. https://www.stereophile.com/images/1111Lebfig01.jpg https://www.stereophile.com/images/1111Lebfig02.jpg Cheers George |
@terry9 Thank you for your interest, Roger. I take your comments in the helpful spirit in which they were given. They are not on my website, not really a Music Reference product. More of something I make when someone interesting who is doing something interesting contacts me. We made 4 for a guy in Australia and his friends. I also sold them 8 Acoustat panels and advised them how to set them up. He had been playing with Acoustats for many years and appeard very comfortable with high voltage. Acoustat panels are very useful and flexible and not expensive. The high potentials bother me not at all. Perhaps because I was a TV tech from age 16 through college. 25,000 volts DC in a color tv is just not a big deal. One should be attentive no matter what the voltage. Ive blown up more things with current than voltage. |
@georgehifi I think that one comes later for free on line, as I’m such a tight arse, I only read the ones Stereophile drip feeds online for free. Yea thats all pretty bad and if they were smart that is a good one not a failure on inspection. That kind of response is simply a result of poorly applied feedback. Strangely, given that the damping factor is horrible there isnt much feedback and they didnt manage to pull off even a little. Certainly the work of someone who doesnt care or couldn’t do any better. Notice that the top rings longer than the bottom in the SQ wave. That is because the two halves of the primary do not have the same coupling to the secondary. What a mess, their standards of performance are rather low. Might sound ok at low levels on easy speakers but the low damping will certainly modify the response of the speaker. The bass rolloff is bad too Probably everything is bad. I’ll go read what JA said. Hey, do you have a link to the complete review? I got 29 hits for Leben. A lot of mention for a poorly performing amplifier. Heres another poor performer from Jadis..https://www.stereophile.com/content/jadis-orchestra-reference-mkii-integrated-amplifier-measurements He was kind to measure the distortion vs frequency at just 2 watts on a 50 watt amplifier. Imagine how bad it would be at 10,20,30 watts. |
Hey, do you have a link to the complete review? I got 29 hits for Leben. A lot of mention for a poorly performing amplifier.https://www.stereophile.com/content/leben-cs300-integrated-amplifier-measurements JA does make mention of the ultrasonic resonance, but "maybe" because they're an advertiser, didn't make too big a deal of it. Cheers George |
John Lennon: "All I want is the truth, just give me some truth". Amen, brother! "High End" reviewers like Harry Pearson convinced lots of audiophiles that the measured performance of an amplifier and that amp’s sound are unrelated. That making a "good" sounding amp was more art than science. Yes, the race for as-low-as-possible static-measured distortion did lead to bad audio engineering, but good designers understand that, and perform bench tests that reveal the dynamic behavior of their designs. I can’t count the number of times I have heard an audiophile (or even hi-fi retailer), when presented with evidence of the poor engineering of a component the audiophile likes (or the retailer sells), or worse owns, defend that component by saying something like "Well, it’s the sound that matters". If a poor design, showing obvious performance weaknesses, sounds "good", something is very wrong somewhere. In the mid-80's I was in a hi-fi shop, and the owner was playing a system for a potential customer. I knew the following about that system's components: the tube pre-amp have a pretty high output impedance, and the interconnect cables very high capacitance, especially at the 30' length of the pair in use (from the pre at one end of the room to the mono power amps at the other). I couldn't stop myself from commenting that the combination of those two factors was obviously creating roll off starting at an audible frequency. The retailer responded by saying, you guessed it, "Well, it sounds good". It didn't to me, sounding, predictably, soft and dark. Cymbals were missing their brassiness and sheen, strings lacking life. I slowly learned some consumers, even "High End" ones, believe whatever they're told. The pre-amp was considered Class A, as was the interconnect. How could they not sound good together? |
If an amplifier is class A/B implementation does it not matter to mention the Class A bias i.e how many first watts are class A. Does crossover distortion matter?. If not why and if yes what do Class A/B designers do to make it go away or mitigate it. Generally reading around good Class A/B amps that have high bias seem to be well reviewed. Again interested to learn more about this. |
Keep in mind just because a unit has a XLR input that is no assurance that the input is balanced.A balanced input is no guarantee of better sonics. The devil is in the details. Every audiophile should read Bill Whitlock's AES paper "An Overview of Audio System Grounding and Interfacing" available here https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf |
Thanks for all your help, Roger. You really have opened up a stack of stuff for me to do. Much, much appreciated. Hate to be pedantic, but I think that the 45uF figure should be 4.5uF, which is less of a problem: (75**2) * (800 * 10**-12) = 4.5 * 10**-6. Your other concerns with the Vanderveen (got it right this time?) transformer remain an area of intense interest (and research!) to me. Thanks again! |
Fascinating thread. Thank you! If you dont mind, could you provide a quick list of your favorite (currntly available) tube preamps? I don't need a phono stage. It will need it to accept input from my PS Audio DAC, and to drive my vintage Audio Research (sorry) tube amp. For what it's worth, I do plan to ultimately sell the AR amp and upgrade to a different make... |