captainbeefheart

I'm in full agreement about hearing and our age, as long as it's low levels my hearing is still fairly good but I think I just care less about chasing the dragon. I'm happy if it sounds good and that's good enough. I just like to fiddle with electronics and get my geek on. I suspect it's the physical construction properties causing the sonic difference between metalized and foil. They are physically much different and I'm almost certain the foil will have higher series inductance since the metalized achieves greater capacitance given the same amount of film due to greater surface area coverage and getting the plates much closer together. Type of leads factors in also etc... The parasitic properties is what can drive you bonkers when comparing capacitor types. I usually draw out an equivalent model of a capacitor and all it's properties and then fill them in as I measure each property. I may still have some old papers with measurements but they won't be for capacitors you guys are using, they would be for capacitors of long ago. Mostly the change between paper and film and the hybrid "di-films" was when I was very interested in this stuff. Then progressing and getting Tantalum or other polymer types to attain a reference book where if I needed a certain property for a given application I can quickly flip through the book and find what I needed. The datasheets from the companies just were not enough information sometimes to make a thorough model of the circuit.

Impressive!! Are Sonicaps also foil types? It would be prudent of me to also factor in the parasitic properties of each physical capacitor. Clear and easy example would be series inductance, it's part of the summation into ESR and it's certainly possible to have more losses at high frequencies given different constructions and the exact same dielectric. That one property will also change the resonant frequency location. These factors are true for any capacitor, I was strictly talking about the sound difference between just the different dielectrics but of course you are correct in that there are many variables of a capacitor that in an application will behave differently.

I googled, it's a polypropylene capacitor. So are you saying the Theta caps sound different than all other polypropylene caps and you can pick them from a blind test against all other polypropylene capacitors, including other foil PP types?

Sorry for my ignorance, what's a PPT Theta build?

Just because they are authorized doesn't mean they are any better than other Polyester capacitors. The only valid arguments I have been interested in are metalized polyester vs foil. The foil caps are not self healing and all the research I've done has led to when new there isn't going to be a sound difference between the two, if the metalized types have self healed then they also have lost surface area from creating the "holes", this means the value in capacitance will drop and ESR increase. But in retrospect if the self healing types healed then it's logical to say the foil cap would have just failed short. Metalized types can be viewed as needed to be tested or just replaced every 1/4 century possibly. There really can't be a difference in sound because the difference in sound comes from the dielectric properties, using the same dielectric will yield the same sound. Some dielectrics are very non-linear, like Ceramic. One can place their scope in x-y mode, sample the voltage and integrate the current and you'll get a slight curve on your scope, the more linear the dielectric the straighter the line. So capacitor dielectric linearity can be really the only thing I can think of that people an hear between capacitor types. Paper capacitors are actually very linear, the only capacitor I liked better than polyester in a Klipsch crossover is a paper type. I have the original polyester caps in my La Scala's and some new polyesters in my Heresy's. I'll be changing the La Scala's soon and not sure which direction to go, stay original or go paper? I'll probably end up selling my La Scala's because the older I get the harder they are to move around and the room they are in currently is only temporary per order of the "boss". This has me leaning towards polyester and then in the future swap my Heresy caps to paper types. When we moved and downsized the home my office/audio room is much smaller and the La Scala's just lost a lot of their magic. They do much better in a large room. I switched to Heresy's in my office and wow they just fit perfect, much better imaging and overall balanced sound. So it looks like I'm living with my Heresy's for a long time so I plan to swap to paper and see if things improve further. It will be extremely subtle of course and a possibility of not even an improvement but I won't know until I try it and I can always swap back if I don't like it. Some things to consider. For the capacitor to have an effect it needs to have the signal across it's terminals. This means it needs to be of high impedance; i.e. near the crossover frequencies where they start to act as filters. For the tweeters in an AA 2uF is about 13 ohms at 6kHz, this impedance will drop as frequency rises and the effect the dielectric has diminishes. Mind you the maximum current for the K77 is going to be 1/2 an amp, so you may end up with maximum of 6.5v across these capacitors at 6kHz. In reality it's going to be much much lower currents so maybe 200mV across them. When I was testing capacitors to look for non-linear behavior I was pushing near 100v across the capacitor to see it.

The email one has much better information and details, should be the original article I believe from 1951 for hifi not guitar amps.

@Curious_Georgedid you receive the email I sent you on the article about "Extended Class A". If yes what do you think?

Any core material that allows for less copper to get the same amount of inductance is in my book great as it will improve high frequency response. The biggest difference will be in zero feedback amps where you have no negative feedback to increase bandwidth. Of course it's optimal to start out with the best performance before feedback is applied, I think it's less critical with feedback amps, adequate inductance is always important but often with high inductance transformers the top end may roll off earlier than you would like. My buddy made a zero feedback amp with a transformer that had sufficient inductance, low frequency performance was excellent but he was already sloping down well before 20kHz, memory I believe it was around 14kHz where it started to slope down. Of course 20db of feedback will bring things up to above hearing range but he didn't want feedback for whatever reason. I've seen this in other threads of builders also. So yes zero feedback amps definitely don't short change the output transformer.

The original schematic used only 8uF decoupling capacitors and had a tolerance of +50%, typically they were probably much more than 8uF. Modern copies may use precision film caps 8uF that have a low ESR that won't have the dampening ability of a high ESR electrolytic. Another issue is the original had a massive 30H choke and if it's not at least 30H you'll end up with a low frequency resonance too high up that causes the audible motorboat. If one increases the decoupling/filter caps you can use a lower choke and still keep the resonance below 10Hz. Small caps and small chokes don't play nice together, you need either large capacitance and low value choke, or a large value choke and smaller capacitance. Of course high capacitance and high inductance will just push the resonance towards DC. I have never had any issues with any Williamson style amp I've made either but have heard others complain also. It's just from people with little experience in design mixing up the values and circuit without much thought. I see you used 1625 power tubes, fancy!! I wondered about using them but was thinking pentode due to the 3.5watt screen dissipation limit in ultra linear. They are also 12v heaters so 12v front end tubes need to be chosen to keep one filament transformer, 12AU7 would work fine.

@Curious_George would you post your Williamson circuit? If not in email or PM would be great. I love a good Williamson design.

The Williamson circuit I have found almost always sounds good, it's one of the greats especially in it's original Triode output form. The later UL or Pentode versions can be good also but not as good as the triode output original circuit. I too have been on a single ended kick, I was doing the no negative feedback thing and had mixed results. With fully horn loaded speakers reaching 50% efficiency like the Khorn or Lascala etc.. they work fine enough and sound great but with your average 5-10% efficient speaker not so much. Even the Heresy's and Cornwall's can be a tough load for them and it's imperative to use very linear triodes, and the lower the plate impedance of the output triode the better I found the sound was. Lately I switched from SET amps into getting more power out of single ended and going pentode operation with feedback. The downside is you typically need 20db of feedback to get the distortion to low levels and with an output transformer one needs to fully understand control theory and compensation networks to achieve excellent results. I find when feedback is added without analysis of stability the sound can suffer greatly. Square wave testing will show overshoot and ringing especially if you add a little reactance to the bench load like for the real world. Another reason I feel amateur tube amp builders stray away from feedback amps, they don't like the sound of the amp because they didn't go through the effort of providing exact compensation lead/lag networks. They can make all the difference in the world. If you have great OPT, only two stages say using triode output stage, you can get away with 6-10db of feedback and it may not require any compensation. So using a little feedback with triodes is much easier to get good results.

Another reason I tend to gravitate towards using negative feedback is because it makes differences in tubes less critical to amplifier performance. i.e. swap tubes and you are guaranteed to get the same results.

That would be excellent. If you have a mutual transconductance tester that info would also be very useful but just bias current of the power tube should be sufficient and we can assume an average gm for the tubes. I have found some modern tubes tend to be higher/lower in gm than datasheet suggests so they aren't the exact same tube as in the tube days but close enough to call them it by name and function in said circuit. A graph of power out and THD along with bias current would be great. You'll probably see that Svetlana tube is running hotter than the others you tested. If not it could be on the high side for gm or have low rp or both, in that case making it a nice tube choice if they are consistently like that.

Conversely if you have the same bias current through the EL34 then one can assume the transconductance of the Svetlana (and or it has lower plate impedance at given operating point) is much higher than average. Another reason for higher output power is the divider ratio the tube plate and load make together. As bias current increases plate impedance typically is reduced getting more signal out. The simulations I made yesterday assume a tube with an average transconductance (11mA/V) and a very specific operating point or bias current. I could increase the current and produce more power. It's all one composite circuit.

When you take your measurements are you also taking bias readings? I doubt it's the brand of tube getting more power, it's more likely the Svetlana has a higher bias current allowing it produce more output power. The more current through the tube the higher the cathode voltage is, in respect to grid they become more negative which allows greater input swing also. Cathode bias is tricky, a tube that biases up hot (more current) will produce more power given roughly the same transconductance health.

I think there is some confusion about these kits and the output transformers. The output transformers are not made in Japan, they are made in China which is why they are so cheap (cheap labor and loose regulations). It's the Z11 lamination's that are sourced from Japan that they use to make the transformers. Don't get me wrong, the transformers tested good so they are sufficient at winding them there in China. Quality core material is very important for transformer performance and so they are advertising they use high quality Z11 lams from Japan which is a good thing. In one test using the same bobbin, same lamination thickness and core size the M6 Silicon Steel gave over 8H of inductance where the Z11 gave 12H. The higher permeability in the core material given the same amount of copper gave better results. I'd like to see some differences in eddy currents and hysteresis plots to further compare core material. Don't lose too much thinking about needing to have this core material over that core material, really it's the application of part that matters. It's the engineers job to use the part in hand in the best way possible, so if you have slightly lower inductance it's not a game changer if you change to a lower source impedance. A quick explanation is we want to load the tube with a specific impedance, say 2500 ohms. The speaker reflects back via impedance ratio the impedance to the tube, so you ask yourself okay what's the problem? The impedance of the primary inductance is in relation to frequency, impedance drops with decrease in frequency. At low frequencies if source impedance isn't sufficiently low, or if inductance isn't sufficiently high, the impedance of the primary inductance may drop far below the reflected load of the speaker and dominate loading the tube down creating excessive distortion. So for 2500 ohms to 8 ohm speaker, gives us an impedance ratio of 312:1 Let's now assume the plate impedance of a triode strapped EL84 is 1800 ohms, which from memory sounds about right if I'm wrong just go with it and please let me know in comments what it actually is, I'm too lazy to look right now. Now lets assume the primary inductance of the 2500:8 output transformer is 10H. Will this transformer give satisfactory low frequency performance? Let's see. The impedance of 10H at 35Hz is 2199 ohms. As we can see at 35Hz the primary inductance is below the target impedance of 2500. Down further at 20Hz the 10H drops to an impedance of 1256, that's half the impedance that we want to load the tube with. Since the inductance impedance and reflected secondary load are in parallel things are actually much worse than it appears. At 35hz the load the tube sees is 2500 | | 2199 which is a total of 1169. So at 35Hz we are actually at half the load we want for the tube. The greater the inductance the better the low frequency performance will be. So why don't we just make the primary inductance as high as possible? It's a tradeoff, typically the more inductance you get the more copper is wrapped around the core to make the large inductance value so then we end up with higher amounts of leakage inductance and interwinding shunt capacitance which kills our high frequency bandwidth. Yikes what a pickle right? For all you smarties out there looking for more information here we go. The plate impedance of the tube, called source impedance and the load impedance create a voltage divider, just like a volume pot. If the plate of the EL84 is 1800 ohms, and we have a 2500 ohm load then we can assume a divider ratio of .58, which means 58% of the signal will get through. What happens if we now have a load of 1169 like at 35Hz? Well we now have a divider ratio of .39 or 39%. We can see that we will be 19% lower at 35Hz vs mid frequencies like 1kHz. Make sense? So to get the best high frequency response you want to choose an output transformer with the right amount of primary inductance that's just enough to work well but not too much to reduce high frequency bandwidth. This is why I prefer to choose a tube that has a low plate impedance, or source impedance because it changes the divider ratio. Say we have a tube with a plate impedance of 600 ohms. With a 2500 ohm load we have a divider ratio of .8 or 80%. With only 10H and a combined impedance at 35Hz of 1169 the divider ratio is .66 or 66%. Much better right? So with the same small 10H primary inductance choosing the right tube to work with it can be a major difference in performance. I also like to choose low impedance tubes because they require a lower load impedance, with a lower load impedance you have less of a turns ratio. This means less copper is needed and so leakage inductance is less and so is interwinding shunt capacitance. A 5k:8 output transformer is guaranteed to have higher leakage inductance and shunt capacitance than a 2.5k:8 transformer, typically. This is why the McIntosh output transformer has such high bandwidth, they split load the tube so impedance needed is halved greatly reducing the leakage inductance and shunt capacitance. The fact they also bifilar wind them practically makes leakage inductance non existent. Hopes this helps some of the people questioning the mystique around output transformers and what all the specs mean to the application.

I agree, I am thinking the output transformers are actually the same, just one is covered. The power transformers look much different, and the description of the more expensive one is probably from complaints the original transformers ran hot so they offered up kits with larger versions hence the description of the beefed up power transformer. Not sure it's worth the extra $75 though.

One example of transformer design is the McIntosh OPT. In a normal output circuit, using 6L6's in push-pull, the tube load impedance is 4000 ohms. A transformer is needed to match the typical speaker impedance of 8 ohms. This represents an impedance ratio of 500 to 1. The necessary transformer turns ratio is the square root of 500, or 22 to 1. Leakage inductance and shunt capacitance cause high frequency rolloff. It also causes notch distortion in class B operation. The Unity Coupled transformer distributes the load to the output tubes plate and cathode instead of just the plate and effectively reduces the impedance to 1000 ohms. The impedance ratio is lowered to 125 to 1. The turns ratio is reduced to the square root of 125, or 11 to 1. Leakage inductance and shunt capacitance are greatly reduced. By using the bifilar winding technique, leakage inductance is eliminated between primary sections. For the Mcintosh circuit since there is not the normal gain in the output stage from the split loading scheme the front end needs tons of gain. But still because of the design of the output transformer and circuit, the McIntosh amplifiers have very high bandwidth which is unusual in tube amps utilizing an output transformer.

Doesn't matter how they are built, the goal is to get high inductance with low leakage inductance and low inter-winding capacitance. The former gives low distortion at low frequencies and the latter gives greater high frequency extension. There is always a resonance and that should be well above the audio frequency spectrum. There is no free lunch and to get one typically is a trade-off with the other, you need to find a balance. There are also many different techniques and materials. It's a mixture of science and black art, good luck getting winders to tell you their tricks and secrets.

For those that don't know Z11 steel tends to be the darker laminates compared to M6 and has higher permeability. Like for like core and bobbin/winding the Z11 will give greater inductance. Nick and I both have had great experiences with these transformers that come with these cheap Chinese kits. I think they are pretty high quality for what you pay for them which also includes everything for the amp.

The one for $350 indicated the OPT's used Z11, which I believe is Hi-B orient core. So those cores would/could be smaller compared to M6. The output transformers for both amps say "Japan Z11" which is why I was wondering if they are the same, just one potted in the more expensive one. The power transformer for the more expensive one has stated it's 96-60 large iron core, 200 watt rated power and .35mm high flux grain oriented silicon sheets (goss) and looks to be larger than the other amp. The $350 one doesn't say anything special about the power transformer. Curious if the power transformer runs cooler on the more expensive one, as I remembered they ran hot on the kits I have experience with so maybe they beefed them up and that's the increase in cost?

The power transformer looks much larger on the more expensive version. The outputs are potted so hard to compare them by looks. The difference in price is probably due to more expensive output transformers.

Yes much better price but I wonder about the output transformers. The other one had grain oriented silicon steel transformers. If the output transformers are identical then yes it's a much better deal. Have to do some more digging.

Wow I just had a look and those kits they were buying went way up in price!! They were $250 then another $100 shipping. Now it's $429 plus $100 shipping. I was almost going to recommend people get the kit and wire it to your circuit but I don't know if it's a great deal anymore. One will have to crunch what it costs for parts and compare. https://www.ebay.com/itm/251514808784?epid=20010103033&hash=item3a8f7369d0:g:hfcAAOSwX0BhXrej&amdata=enc%3AAQAHAAAA8G1nkR4qErKbT%2BsB1RSRpmn2XSyK0DM8wjFv9kB6BQ6mnJ4V0q0dvjvUAaNWTYOMO8RxyKhdNfock%2BJwKPXYJsyhK5DJyT7XpnRiK293pQaTJIt9r9IYbqP%2FkT2HEfccvzJ7mRibzBfegQ569VcHwVfq%2B6B1Np8%2B4YVaHdBe5aGbjqPiR0QtH92mtoAVKVuq0phxbVW47rlzcXT%2F8XyanPwleSFfXmJ9svsRM1XhTt%2FmvgZ0pUEIp%2Bqezcjio0UoaN%2FSt4R05HhbSWNHkNSq4yPBRhYXKdVzHQazxklMxlHglfL2yXJMPsc8UmHc6PB5KQ%3D%3D|tkp%3ABk9SR6DLyMbbYA