My father who ownes a Audio Research Ref Two and just got back from listenig to one of the transformer coupled pre-amps at JC Audio. He walked in the door and told me he was going to sell his preamp and for me to sell my pre-amp. He couldn't believe the difference it made. There must be something to this transformer coupling. He has hardly listened to his Reference since re hooking it up after bringing it back. I am heading over there tomorrow and will advise. A friend of ours just told us about this cool site. Wow is it fun.... I haven't slept in two days just reading all the cool stuff.
Transformer coupled / Capacitor coupled
Just a question from my curiosity. I remember someone recently mentioned here that capacitor coupled pre-amp sounds better and is more expensive and rare, than transformer coupled ones. Could someone elaborate, as to the difference of those two and how each design works and why either sounds better? Thank you!
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Hi Clueless, My recollection of the effects of capictors vs transformers during my radar repair days was that if you want to alter the shape of a waveform, eg, a square wave (which may appear simple, but is rather complex) use a capacitor and if you want to pass it on unaltered use a transformer. We took great joy in taking a nice square wave and converting it into a saw tooth waveform by adding more or less capacitance in either series or parallel: shape-shifting if you will. Music as rendered by an analog electical waveform is extremely complex where the slightest alteration in voltage is the essence of the artistic intelligence. When I think of how a capcitor can make a square into a triangle, I am little surprised at my reality. Which is, I prefer transformer coupling to capacitive coupling: the ear is the finsl determinant. Materials have a profound effect on both sides of the equation. With respect to transformers, core saturation, hysteresis, relationship of the windings in the primary to the secondary...and I guess that is where the art of design begins. Just my $.02, Jim. |
Thanks peter: >"There is a world of difference between the transformer volume control that Thorsten is talking about in this article and the use of transformers in the output of a pre-amplifier" No argument from me. Some of discussion was going to passives and what are essentially volume controls which are a perfectly legit way to go in some systems. I put the word "pre" in parenthesis in my post for that reason. It is obviously not a preamp in any normal sense of the word other than it "pre"cedes the amp. I was just trying to point to one take on using transformers in that part of the chain in one sentence. You folks make nice stuff. Cheers I remain, |
Dear Clueless, There is a world of difference between the transformer volume control that Thorsten is talking about in this article and the use of transformers in the output of a pre-amplifier. Take the M3 for example, it uses an output transformer driven by a single 5687 with the two halves wired in series, it has a 33:1 step down ratio, an output impedance of about 4 Ohms and a bandwidth from about 8 Hz to over 150kHz minus 1 dB, for all intents and purposes that is at least 3dB above and below any audio signal it is likely to be presented with. Due to the enormous gain (hence the high stepdown ratio) the line stage does not limit neither the dynamic nor the frequency envelope of the signal it is presented with, which is why a good transformer coupled pre-amplifier sounds so free, easy and uncluttered. Transformer volume controls have many great advantages when correctly designed and wound (which I might add is not a simple matter), however there are several key problems implementing them into a pre-amplifier circuit, 1.) The input impedance is typically too low to be driven directly from a normal no-feedback high gain pre-amplifier stage. a.) This means that you either have to apply feedback to the gain stage which defeats the sonic advantage the transformer volume control provides. b.) Or you have to drive the input winding on the transformer volume control with a driver transformer from a no-feedback tube gain stage to get the full benefit. This is not an inexpensive solution! 2.) The frequency/phase behaviour of the secondary windings MUST be very similar, otherwise each step on the volume register will sound different. This requires enormously accurate winding and interleaving, also not inexpensive. 3.) The overload/saturation behaviour of the mumetal core is very critical, again you require a large mumetal core to get the best results and they are cheap either. There are other issues. All in all, transformer volume controls are unquestionably the way forward to achieve the greatest sonic performance, but they come at a price and none of the "passive" implementations I have seen or read about sofar achieve this aim. Hope this helps. Sincerely, Peter Qvortrup |
The Audio Note, EAR (E11??), the big Jadis and Atma-Sphere (P-2) preamps are the only high-end audio transformer-coupled units out there to my knowledge. Transformer-coupling is common in professional tube gear, particularly from the 50s and 60s. This is because the equipment had to match to the 600 ohm balanced line standard (which is still very much around today). Tubes coupled by output coupling capacitors would never be able to play any bass driving a 600 ohm load! We built the P-2 (discontinued when it was replaced by the MP-3) so it could drive the 600 ohm standard as well. The nice thing about the 600 ohm standard is that it ameleorates the role that interconnect cables play in the sound of the system, which is why the standard has been used for the last 5 decades by the professional recording and broadcast arts. Its always been a puzzle to my why audiophiles are so slow to embrace the same standards, despite having the same concern about cable qualities. This has spawned the high-end audio multi-million dollar/year cable industry. We're an OTL manufacturer, but we've been a major supporter of balanced line technology for the last 14 years (mostly due to prolonged exposure to the recording studio); our preamps support the standard using direct-coupled ouptuts, which is the only other way to do it as capacitors won't work (since no-one would take a tube preamp with an electrolytic output coupling cap seriously...). IMO, its a shame that more manufacturer's aren't wise to what's happening here (sorry for the hype blast). |
Clueless, I believe per the article that the transformer application he is attempting is in a passive device. I think that is why the active transformer coupled pre's don't have that issue. They are 600 ohm instead of the 50k or 100k many actives use. We drive not only a variety of tube amps but the Gamut solid state which has 10k ohm active balanced curcuit with unbelievable authority and resolution. This amp is in stark contrast to the tube amps we drive with input impedance numbers as high as 100-150k. Wide range for a single pre do be able to handle such extremes with no loss of any musical content. His article points out the very reasons passive devices cannot compete in most real world situations. Thanks again for the heads up. I like to stay current on all this cool stuff. Wish you were local. You could attend one of our shootouts:) |
Hi Jcaudio: I agree, if you have a transformer I think you must have impedance issues. A Trany is inevitably a bandpass filter usually about second order or so (12db an octave). In the article TL spends a lot of time looking at impedance matching -loading the source, excessively high output impedance, ect.. and states that "As with all transformers the ultimately realized output bandwidth is very much system and application dependent." Gotta agree with that. I remain, |
The issue is more than just impedance. As capacitors drain during dynamic passages you will hear it as strained or harsh sounding. In addition, many manufactureres use cheap capacitors. That being said even the best have a sonic signature. I will include the post here for you. Browse Sell Learn MyPage Help Learn > Forums > Amps Preamps > 1028269658 Start New Thread | Log out | * Why do the Audio Note preamps sound so much better I took Joe over at JC Audio up on the offer of a shoot out. Actually it was the second time. About nine months ago I went over and had a shoot out between my EVS Nude Attenuators and the Kora triode preamp. I have to give Joe credit he agreed if you could live with the inconvenience and lack of flexibility that the EVS attenuators sounded as good. But I made a bad mistake today. I went over and did the same shoot out with the Audio Note M5. I should have never done this. The M5 made the attenuators sound dry and lifeless. The M5 sounded prettier with much more top in extension without ever sounding bright. It was more transparent and fuller bodied at the same time. And the layering and the soundstageing was just beautiful. This is disturbing to me for I have been a big proponent of passive, especially the attenuators since you even eliminate a set of interconnects and a power cord. Why does this line stage sound so much better. bilbondo@hotmail.com 08-02-02 Responses 08-02-02: info@audionote.co.uk Dear Bilbondo, Why?? Quite simple, in the M5 (and all our other transformer coupled pre-amplifiers, the M3, M6 and M8), there are no impedance mismatches, there is more than sufficient gain to maintain the dynamic envelope of the signal intact combined with a natural (meaning not created artificially by feedback or other trickery!) drive impedance so low as to render the load (the power amplifier input) irrelevant. The disadvantage is cost, you heard for yourself the sonic advantage. Sincerely, Peter Qvortrup info@audionote.co.uk 08-02-02: Rcprince Some will call it tube colorations; it's the classic music vs. accuracy debate. FWIW, I have always preferred components which deliver a realistic reproduction of what I think the recorded performance/musical event sounded like rather than what the master tape sounds like; after all, if you listen to performances from Row J in the orchestra section of a concert hall it'll sound quite different than what you'd hear if you sat where most microphones are placed. I think my Jadis preamp falls in that category, and perhaps the Audio Note does as well. Rcprince (Answers) 08-02-02: Trelja Rcprince hit the nail on the head. As usual. I am a huge fan of Audio Note. No, it is not cheap. But, like Jadis, I believe it offers REAL value. That is because it is one of the few marques that can be considered a last purchase. The purchase is made, the component is inserted, and it is simply enjoyed. Hour upon hour, year after year. They are not for audiophiles so much as music lovers. They are not meant to impress in terms of calling attention to themselves. They are components who want music to sound like music; real, natural, organic. To my love for the components of Audio Note and Jadis, I have also found the same thing true of my Blue Circle preamp. Just as Peter described of the AN, I have found in the BC preamp. I doubt I will ever sell my Jadis or Blue Circle components, they are lifetime companions. And, one day, I will also own an Audio Note pre or power amp. Trelja (Threads | Answers) 08-03-02: Jcaudio I would like to thank those members who took the time to take me up on a shootout between passive devices and transformer coupled pre-amps. Thanks again JC Audio (Threads | Answers) 08-03-02: Jdubusc I will concede from the outset that I have a bias, forgive the play on words, for I am an AN owner. The point I wish to make is regarding my experience with two passive preamps: the EVS attenuators and the Placette passive preamp. IMHO, I found them both to be anemic, profoundly anemic, as compared to my Audio Note M-5. The differences were not subtle! Good Listening, Jim. Jdubusc (Answers) Post your response Subject Your response No html, but you may use markup tags You are logged in as Jcaudio |
JC, sorry about my confusion. I guess I am not only half-deaf, but half-blind. Thanks for explanation. Now I understand the difference. BUT, still wonder whether it is just a matter of avoiding impedance mismatch, or something more? I mean, I have never used pre-amp, let alone transformer or capacitor coupled. I know I have to hear for myself and I will someday, but what if the output of the source is high enough, there is not major impedance mismatch, and power amp is more than powerful enough? My half-dead brain cells keep saying, "if there is no spec mismatch, job of driving speakers should be done by the power amp. Pre amp is for less competent power amps, or just for input selector or tone control which of course depends on one's preference." Please forgive me if "Pre-amp or no pre-amp" issue has been discussed many times here. If you could direct me to the thread, I will go there. Thanks again for your help. Ken |
Here is a discussion of a transformer based "pre" by Thorsten Loesch. Heard it in Chicago a few weeks ago but was not able to draw any conclusions. I remain, |
THE THREAD ACTUALLY STATED THE OPPOSITE! Most manufacturers utilize capacitor coupling. Very few use transformer coupling as it is expensive and time consuming. The most unusual feature is line output stage, which is configured as a small power amplifier stage with a 5687WB double triode per channel. An output transformer is then coupled to the output signal which serves as an interface to the power amp being used. This allows the pre-amp to utilize not only two sets of single ended RCA outputs but also a 600 Ohm fully balanced output using a Lemo type connector. This unique way of transformer coupling the output stage means that the pre-amp can be used with any power amplifier whether valve or transistor. Transformer coupled pre-amps are much more expensive but in all the shootouts we have done here are much better. I have attached one of those posts where a passive device (several) were compared to transformer coupled pre's. In addition we have done shootouts with pre-amps that were capacitor coupled costing as much as $15,000. always with the same result. Why do the Audio Note preamps sound so much better I took Joe over at JC Audio up on the offer of a shoot out. Actually it was the second time. About nine months ago I went over and had a shoot out between my EVS Nude Attenuators and the Kora triode preamp. I have to give Joe credit he agreed if you could live with the inconvenience and lack of flexibility that the EVS attenuators sounded as good. But I made a bad mistake today. I went over and did the same shoot out with the Audio Note M5. I should have never done this. The M5 made the attenuators sound dry and lifeless. The M5 sounded prettier with much more top in extension without ever sounding bright. It was more transparent and fuller bodied at the same time. And the layering and the soundstageing was just beautiful. This is disturbing to me for I have been a big proponent of passive, especially the attenuators since you even eliminate a set of interconnects and a power cord. Why does this line stage sound so much better. bilbondo@hotmail.com 08-02-02 Responses 08-02-02: info@audionote.co.uk Dear Bilbondo, Why?? Quite simple, in the M5 (and all our other transformer coupled pre-amplifiers, the M3, M6 and M8), there are no impedance mismatches, there is more than sufficient gain to maintain the dynamic envelope of the signal intact combined with a natural (meaning not created artificially by feedback or other trickery!) drive impedance so low as to render the load (the power amplifier input) irrelevant. The disadvantage is cost, you heard for yourself the sonic advantage. Sincerely, Peter Qvortrup |