Jump to content


  • Posts

  • Joined

  • Last visited

Everything posted by captainbeefheart

  1. I'm also not just designing one amp from the ground up, but two amps that couldn't be more different. This is Chris' amp, he opted for non-traditional chassis which took quite a bit of time to get done. I'm still working on the front panels which will be precision cut for vent/window which I decided on a screen so his daughter and friends won't be tempted to stick their fingers inside but the tubes are still viewable from the front and it will be able to breathe. Heatsinks are for the pass transistors in the power supply and for some top secret parts Again my own circuit which sadly yes takes a lot of time to get performance I find acceptable.
  2. Single ended Class A2 6550/KT88 amp, at 1%THD I'm getting 12 watts RMS, it will push past 20 watts but distortion increases of course. Yes Decware is well over a year waiting list but as mentioned good things come to those that wait. Parts can be a problem getting these days especially if you have custom wound transformers made. Mind you I don't just copy schematics, I design everything from the ground up which takes far more time than just physically building an amp. Especially if you want decent power AND low distortion for single ended, it was a tough task but I did it. I disassembled the amp to paint which is done and I'm just now reassembling it. Here is a pic when I started the tear down process to do the finish paint. Wood is Caribbean Rosewood that I hand picked. Wood is another thing that's tough to get, especially in small sizes needed for custom amps. Paint is BMW Mineral White Metallic and will post finished pic as soon as I finish reassembly. (Next few days).
  3. I agree they wanted to keep the same connections but I also think there could have been a happy middle ground where you keep the same ins/outs yet arrange the components with a little more care instead of how they do it. The way they do it has a clean look with the resistors all lined up in rows but it's not optimal. As for the new design with all triodes and the LTP, the results is why I said it has worse performance yet they claim better performance, you may be correct in that there was something wrong with the amp Amir tested because for what they have to work with they should easily get much better numbers without much effort. I like the addition of the CCS on the tail of the LTP but they chose a pretty poor component as I showed with the graph because their impedance above 10kHz drops like rock, you want a constant impedance over the entire audible frequency range at the very least. With the same amount of tubes, 3 12AU7's they could have used one bottle for a cascode which will behave just like a pentode but with less noise and then DC couple to a shared bottle where one triode per channel is the split load phase inverter. This would the closest to the original and still improve upon it with less noise. The VTA is essentially a Mullard circuit with a triode first stage instead of a pentode but with worse performance. If we are trying to keep the original sonics then the cascode - split load would be the best option. If you want to change it completely then either do the Mullard circuit right or better, just use two dual triodes per channel and do a Williamson circuit which IMHO is a really great circuit. Does anyone have a VTA 70 version in the New England area? I can take some measurements to see if they align with Amirs then we know the one Amir tested wasn't broken. It sort of makes sense something was wrong because you would have to put forth some effort to get that high distortion at only 10 watts with this topology, something is way off balance here.
  4. Thanks for your reply I really enjoyed it and I agree with you so I'll clarify my position so it accurately depicts my thoughts on "better" for this specific instance. I do not get hung up on .5% THD with a tube power amp especially if it's lower order harmonic distortion. The transducer will always add far more distortion especially at higher power levels so to me it's moot if the amplifier has .5%THD at 35 watts because the speaker will most likely be something like 8% THD especially at low frequencies, literally 30% THD isn't uncommon at lower frequencies with some speakers at higher output levels. We have UL push pull EL34 output stage, when I look at the original vs the newer front end I can see the logic in that they feel a long tailed pair would be a better phase inverter, this can be true when the loads of the two phases are not equal; e.g. driven near 0v where the grid circuit acts like a reversed biased diode and starts to conduct clamping the voltage. But the amp shouldn't be driven into clipping like a guitar amplifier. The split load phase inverter used in the original is actually a very good phase inverter with great balance. The better option would be to just add one more bottle per channel, keep the split load but use the extra bottle as common cathode drivers to drive the power tubes, ala the Williamson circuit. Although the split is under unity gain, with the addition of the extra common cathode stages after the phase inverter you end up with more gain than with just one stage driving a long tailed pair. The original design is very elegant, the pentode/triode single bottle has a ton of gain in the pentode stage and then the triode section is a very accurate phase inverter. The load they use at the tail has frequency dependent loading problems, at high frequencies the tail is at a much lower impedance. It's just odd the new design has such high distortion at such a low power output, 1% at 10 watts, that's pretty terrible for a push pull EL34 UL amplifier as far as anyone is concerned. The newer design is a clone of the famous mullard circuit, even back then with no active load for the LTP tail they were getting .05% THD at 20 watts!!! Now as I mentioned I really don't get too hung up on vanishingly low distortion but being an engineer for a very long time you learn with little effort where certain designs should end up at in regard to distortion. So seeing a Mullard clone with poor specs tells me the circuit wasn't really designed very well because for what it is naturally the distortion should be much lower. Mind you I'm not saying all good amps have very low distortion, I have single ended pentode amps that have 1% THD at 12 watts so that's pretty bad a push pull amp performs worse when it already has a huge advantage of second harmonic cancellation in the output stage and the fact my single ended amp is second harmonic dominant. So my SEP amp with 1% THD at 12 watts will sound much cleaner because it's second harmonic dominant where the new design of the ST70 is third harmonic dominant, but second harmonic is quite high for a push pull amp telling me the front end is not very linear. Overall I just don't think they did a very good job with what they had to work with.
  5. The original used one triode and one pentode for the front end per channel. The newer design uses three triodes in the front end per channel, I should have stated it this way in that they added another active device in the front end per channel and it didn't improve the performance. I don't think I know him, is he a regular on here?
  6. Screw it, my wife triggered the inner voice of my conscience to kick in and so I just changed the price to $250 including shipping. That covers what I paid for the transformers,chassis, and connectors. The wiring inside is all shielded Mogami and not just standard wire giving this extremely quiet operation. I remember when I made it I waved a transformer under load around the outside of the unit and the shielding works very well, nothing bled into the signal. New price: $250 shipped. When I get finished making the two custom amps I am working on now I'll build another unit with my spare transformers and sell that one also. Or if any diy'ers are interested in the transformers themselves just send me a PM. I'd hate to see these transformers go to waste as they are really amazing sounding and I know for a fact you cannot touch the quality of them for the price.
  7. Here is the datasheet for the transformers
  8. I honestly have no idea how to price these things so don't be afraid to throw an offer at me, I am very reasonable and just hate to see fantastic gear sitting in boxes in a closet not getting used. The older I get the more I worry the kids will just throw all in a dumpster when I croak and that would have me rolling over in my grave. I also don't want to get completely taken advantage of and sell of something far lower than it's worth but I understand there needs to be a happy middle ground. My wife gave me a crazy look and said "someone will pay $400 for that thingy? What's it do?"😆 She doesn't get how expensive high quality audio transformers are especially rare vintage ones. So if anyone thinks I am being unreasonable don't be afraid to PM me about the SUT's, I don't want to price gauge anyone here and only want to be fair. As I said I am only pricing these things from poking around the web for a few minutes. I'll edit the first post to add in "OBO"
  9. I went to look at current production 6SN7 tubes and made this look I am dropping the price to half what a current production one is, $15 each plus $10 for shipping. That's a total of $70/quad or $40/pair Someone will get some great tubes for cheap😁
  10. Here is the style I was contemplating, I can actually make a completely new unit with my extra transformers if anyone is interested that way there I don't have to disassemble the black one in the extruded enclosure. I can also add a switch for different loading options which people may like to experiment with, say 50, 100 and 250 ohms which should cover a wide range of loading options. I have other paint options besides black and can make wooden chassis as well.
  11. The ebay listing transformers are super crusty looking if you ask me, the transformers inside mine are in mint condition and were new in boxes when I got them. Here is some of my extra transformers, you can see how clean they are.
  12. This unit uses very rare vintage RCA 12399 transformers with a gain of 14x (+23db) and works excellent for MC carts with an output voltage of .3mV and up. I no longer use MC carts and if I do in the future I have more of these transformers so I can always just make another unit. The unit is configured for a load of 250 ohms to your cart but I can change this to whatever spec you want. I used 250 ohms because with my Dynavector this gave me no losses and also no ringing or any unwanted nastiness. I have seen some carts that prefer a lower load so again the load isn't set in stone just let me know and I'll change it before shipping out. I was going to make a more fancy chassis with the transformers sticking out the top plugged into sockets before selling but I figured I'd post it as is and then if someone wants a custom chassis we can discuss it. I wanted a small footprint which is why I chose this type of chassis but I have seen other SUT units with this type of transformers and kinda like the look of the transformers outside the chassis, so it's an option for anyone interested. Nothing compared to these transformers, I have used Altec and many modern types and these by far are just unbelievable and can understand why the price of these have gone through the roof. Here is the only pair I found for sale and they want $650 just for the transformers!!! I was looking at other devices for sale using these specific transformers and they are selling for $800. https://www.ebay.com/itm/163967138650?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=163967138650&targetid=4580496732614411&device=c&mktype=&googleloc=&poi=&campaignid=418233788&mkgroupid=1230353745471221&rlsatarget=pla-4580496732614411&abcId=9300542&merchantid=51291&msclkid=d97149dba07611356b9f2bbd4f185aef Asking $250 EDIT: I have no idea how to price selling this and don't want to come across as greedy, so I changed the price to include offers and We'll see what happens. There just isn't a large enough online presence to know what it should sell for or the value of the transformers are. I do think $100 per transformer is a very good deal because the price of high quality audio transformers are VERY expensive.
  13. I went and matched up another quad of these because I had more requests for them after the other 3 quads were sold. Just PM me but there is another for sale thread with the other quad or two pairs.
  14. From Brent Jesse Recording: "These sound as good as the redbase RCA at a fraction of the cost. A bit of pleasant warmth in the midrange, plus some reports indicate the side mounted getter adds ridigity to the plate structure, reducing microphonics. These are a bargain now, but as "fad" NOS tubes vanish, these quality USA performers will be worth their weight in gold."
  15. From Brent Jesse Recording: "Very fine sounding, very rare blackplates from the 1940s. These are virtually identical to the JAN Raytheon VT231 orange label tubes above, but you pocket the savings. Most have the extra plate support rods. These rival the RCA 5692 redbase in quality, and are just as scarce. "
  16. These are a different variation of the GE 6SN7's without the filament string across the top. These are the short bottle types, I think they changed designs for lower noise figures and less gas problems you see from larger bottles. Very good tubes, again I had less of these (20) to match up but made up a nice quad (or two pairs), all screened and tested for usual suspects like all my tubes, no gas, no noise, matched triode sections, matched gain and low distortion. These were higher in distortion compared to the pair of Raytheons I have for sale. The "glow domes" had a little higher second harmonic compared to these. The distortion is about in the middle between the glow domes and the Ratheons. Mind you I'm not talking huge differences but want to give people an idea how they test and may sound depending on the circuit. Open loop these differences will be more noticeable, with say a negative feedback differences in tubes matter less.I typically use the simulated distortion figure as a baseline to go from, the Glow domes were close, slightly higher second harmonic so fairly benign but may give more "warmth", these GE types test pretty spot on to how the simulation tests and the Raytheon pair actually tested lower distortion than the simulation. $100/quad includes shipping $60/pair includes shipping
  17. These are actually extremely nice tubes, they test lower than simulation for distortion so they were either screened or the manufacturing process was dialed in well and on average they are very linear. I had less of these to match up so I was able to make a really nice pair with no noise, triode sections are matched, gain matched and as mentioned they have very low distortion for all sections. These bested the simulated distortion spec which is pretty impressive, I rarely see that. Mind you gain was strong also which double rare, usually when I see higher gain distortion increases but these are actually quite impressive. $60/pair includes shipping Thanks!
  18. More people were interested in these tubes that got them, the 12 were split up into 3 quads so I wanted to put some more out there for people still interested. Same strict screening and so these are quiet, matched triode sections, gain and distortion. I can split them into two pairs or sell as one quad. I am also posting some Raytheon and different GE versions of 6SN7 so check them out as well. Thanks! $70/pair includes shipping $120/quad includes shipping
  19. Yes sorry I had to go back and look at schematics again to remember the different version of the ACA. The ACA 1.6 is single ended common source type design and it intrinsically has second harmonic distortion without a way to adjust it like with the mini.
  20. @Idontknow Good video! What he could have mentioned which may or may not have helped was the music theory and harmony aspect of distortion, I like bringing this up because it helps explain why some distortion is better/worse than others, he only mentions how far the frequency is away from the fundamental being the reason it's more audible but it's a little more complex than that, as I explained it has to do with harmony between two frequencies, how they interact with each other and how we interpret the two notes together as harmonious or dissonant. For example the 4th harmonic of 1kHz is still the same musical note two octaves up, this means the 4th harmonic (4kHz) although it's further away from 1kHz than the 3rd harmonic (3kHz) is more harmonious and less audible compared to the third harmonic. The 3rd harmonic is a musical 12th which you can think of as a musical 5th. In music chords are made up of triads, three notes of a scalar form, 1-3-5. One major aspect of rock music is the use of the "power chord" which omits the 3rd note in the triad and just leaves you with 1-5 notes. These two notes sound very powerful together, hence the "power chord", it has an aggressive powerful sound to it. So a push pull amp with 3rd harmonic dominant is going to sound much different than a single ended amp with the same amount of THD but the distortion is 2nd harmonic dominant with the SE amp, the latter being much more neutral and cleaner sounding. I don't dismiss the SINAD test scores, I merely use it like any other tool so long as you understand it's limitations as this video points out. Personally for me a DAC is something I will look more at SINAD ratings vs a power amplifier. Another thing he mentioned that I liked is the louder the volume the harder it is to discern these distortion differences, I'd like to add upon his remarks beyond how the ear works but looking more at the larger chain of the signal. The point I'd like to bring up is the distortion from your speakers, the louder you push your speakers they will contribute far more distortion than the amp will so the amps distortion at higher output powers will be far lower and less critical. This is why it's hard to just give anyone an easy rule of thumb on how much distortion is too much, it's just a complex concept that needs to be thought of as such. So I honestly can say without much hesitation that .5%THD where say it's second harmonic dominant is less audible than .1% of higher order harmonics say 3rd and above. I may even go as far as to say 1% of second harmonic is less audible than .1% of higher order harmonics. So it's a matter of just looking deeper into the SINAD score to gain more insight into how good or bad something is. Of course if the device has a very good SINAD score you can just immediately know its very clean. But for a lower SINAD score for a power amplifier you may want to look into the specifics of the amplifier. So say the amp I am interested in tested not so great on the SINAD scale but when looking at the data I see that noise is extremely low and the distortion product is mainly second harmonic then I can say the amp should work just fine with my efficient 105db horns because importantly noise is low which is very important for sensitive speakers and the distortion is 1% at full power but it's second harmonic dominant, well my speakers are efficient so I won't be near max power and so at listening levels I know I'll just have a little bit of second harmonic which we know to be rather benign. When consumers get caught up with SINAD ratings I think they can lose perspective and miss out on gear that they may truly love but with a little insight and a better understanding of what the data is telling us we can gain a better picture of if the SINAD will matter for our application or not. It is complex and confusing, for a very good SINAD score it's safe to say the device performs well but for the gray areas of lower SINAD scores doesn't necessarily mean the device will sound bad, you'll just have to dive deeper into the data or demo the device. This is especially true if you are not one to care much about distortion and especially if you even prefer a little coloration which I do not deem as very important for an entertainment device, we aren't reading MRI scans or doing dialysis for Pete's sake. A recording engineer may want to keep their system as squeaky clean as possible to get an accurate mixing and mastering product but the rest of us end users it's all about entertainment and enjoying what comes into our ears.
  • Create New...