diyaudio.com has accepted me as user
Back in 2012 I had a website up in DK with DIY hifi amplifiers, speakers and circuit diagrams as well as vintage gear, which worked until 2019. In 2019 people who had gained access to my PC data wanted me to pay for the content, which I refused.
Due to a virus on my old PC, all files and data disappeared, where hackers without a real reason that I knew of, deleted my files.
Because of this I had to remove the remains on the PC myself, I lost all my contacts and connections and gave up on restoring my PC as it was......
Since then I have been working on refining tube preamplifiers and am currently putting together a line amplifier based on the Marantz 7 circuit and The Paravicini 834P phono stage.
But before I get to the point where I can show you a complete DIY amp based on the two mentioned amplifier circuits, I would like to know if there are others here at diyaudio who work with tube preamplifiers and transistor regulated power supplies on amateur basis? I have some info to show for interested hifi people at the link shown:
https://sites.google.com/view/tubeamp-dk/the-aurora
After I completed the ”New” Dynaco Pas 3X in 2025, the amplifier has undergone several listening tests in direct comparison with other tube preamplifiers with almost the same circuit topology. The starting point in the test is amplifiers that all comply with high high fidelity standards and a frequency response that far exceeds the limits of human hearing.
Starting from the extra good high fidelity standard, there are many reasons why a tube preamplifier sounds good, since human hearing is not a stationary function, but a sense that changes over time, while the perception that the brain has available when interpreting sounds also changes.
Therefore, well-known pieces of music can be perceived differently by the same person depending on how the brain processes certain sounds and tones that day.
That said, the three tested tube amplifiers have some common features, as they all use audio tubes of the 7025 / 12AX7 type, and that all three amplifiers have been subjected to a critical listening panel of experienced hifi people.
The listening panel preferred “The Aurora” as the most musical amplifier followed by Elrad’s “Röh-1” both with regulated high voltage +B.
Fairness regarding listening quality and testing as well as objectivity will never be neutral, as every person with electronics experience has already formed their own reservations about the amplifiers based on the known circuit diagrams.
Therefore, only the diagrams are presented for review, as well as a link showing how the Dynaco Pas 3X and “The Aurora” are put together.
The German variant “Röh-1” has yet to be recorded and shown on the aforementioned site, while “The Aurora” is freely available.
One parameter that affects the sound signature of the three tube preamplifiers to a greater extent is the power supplies, where the Dynaco Pas 3X is the only one that does not have a transistor regulated supply. All three preamps have approximately 1K in output impedance.
Write back if you find this interesting?
Best regards Kim, DK
Edit: 1. Google offers free space for a amateur site like mine, where more space is allowed for uploading images...
2. I am retired optometrist and autodidact within electronics..there might be errors 🙂
Back in 2012 I had a website up in DK with DIY hifi amplifiers, speakers and circuit diagrams as well as vintage gear, which worked until 2019. In 2019 people who had gained access to my PC data wanted me to pay for the content, which I refused.
Due to a virus on my old PC, all files and data disappeared, where hackers without a real reason that I knew of, deleted my files.
Because of this I had to remove the remains on the PC myself, I lost all my contacts and connections and gave up on restoring my PC as it was......
Since then I have been working on refining tube preamplifiers and am currently putting together a line amplifier based on the Marantz 7 circuit and The Paravicini 834P phono stage.
But before I get to the point where I can show you a complete DIY amp based on the two mentioned amplifier circuits, I would like to know if there are others here at diyaudio who work with tube preamplifiers and transistor regulated power supplies on amateur basis? I have some info to show for interested hifi people at the link shown:
https://sites.google.com/view/tubeamp-dk/the-aurora
After I completed the ”New” Dynaco Pas 3X in 2025, the amplifier has undergone several listening tests in direct comparison with other tube preamplifiers with almost the same circuit topology. The starting point in the test is amplifiers that all comply with high high fidelity standards and a frequency response that far exceeds the limits of human hearing.
Starting from the extra good high fidelity standard, there are many reasons why a tube preamplifier sounds good, since human hearing is not a stationary function, but a sense that changes over time, while the perception that the brain has available when interpreting sounds also changes.
Therefore, well-known pieces of music can be perceived differently by the same person depending on how the brain processes certain sounds and tones that day.
That said, the three tested tube amplifiers have some common features, as they all use audio tubes of the 7025 / 12AX7 type, and that all three amplifiers have been subjected to a critical listening panel of experienced hifi people.
The listening panel preferred “The Aurora” as the most musical amplifier followed by Elrad’s “Röh-1” both with regulated high voltage +B.
Fairness regarding listening quality and testing as well as objectivity will never be neutral, as every person with electronics experience has already formed their own reservations about the amplifiers based on the known circuit diagrams.
Therefore, only the diagrams are presented for review, as well as a link showing how the Dynaco Pas 3X and “The Aurora” are put together.
The German variant “Röh-1” has yet to be recorded and shown on the aforementioned site, while “The Aurora” is freely available.
One parameter that affects the sound signature of the three tube preamplifiers to a greater extent is the power supplies, where the Dynaco Pas 3X is the only one that does not have a transistor regulated supply. All three preamps have approximately 1K in output impedance.
Write back if you find this interesting?
Best regards Kim, DK
Edit: 1. Google offers free space for a amateur site like mine, where more space is allowed for uploading images...
2. I am retired optometrist and autodidact within electronics..there might be errors 🙂
Last edited:
I know that there are lots of folks here interested in tube equipment with regulated power supplies and all that.
Welcome.
Id like to see more photos and descriptions of your projects.
Welcome.
Id like to see more photos and descriptions of your projects.
Midnightmayhem
That sounds good if I could get advice and additionel info to my future hifi projects.... I have made more DIY hifi things the last 10 years, but some of the files has disappeared as mentioned...
I can promise that you will se more finished projects on my amateur website, as soon as I have gathered erlier info and photos together.
Kim
Ps. sometimes my answers comes with delay.....but I will answer
That sounds good if I could get advice and additionel info to my future hifi projects.... I have made more DIY hifi things the last 10 years, but some of the files has disappeared as mentioned...
I can promise that you will se more finished projects on my amateur website, as soon as I have gathered erlier info and photos together.
Kim
Ps. sometimes my answers comes with delay.....but I will answer
Hi Kim, welcome back to the public side of tube land. Sorry to hear about your misadventures with the hackers that destroyed your previous tube designes and files. So sad and unnecessary.
I looked briefly at your Aurora preamp on your tubeamp-dk website. Very good work. I’m looking forward to see more of your creations. I’m particularly interested in the PAS-3 modification in post#1 above, since I have a clean looking one awaiting modification.
Enjoy your retirement, your tube amps and the musiek.
I looked briefly at your Aurora preamp on your tubeamp-dk website. Very good work. I’m looking forward to see more of your creations. I’m particularly interested in the PAS-3 modification in post#1 above, since I have a clean looking one awaiting modification.
Enjoy your retirement, your tube amps and the musiek.
Hi Francois G
Thanks for your kind words.
I was lucky enough to find an old cardboard box with the remains of what had once been a Dynaco Pas 3X kit. The remains of this Pas 3X kit turned out to be a good amplifier.
It took a long time to find all the pieces, but the result was far better than expected, as you can see on my amateur site
What is special about the Pas 3X in post #1 that you are interested in?
The Dynaco Pas 3X is a really fine amp and good-sounding preamplifier with all the tone controls in neutral position. The poor and quality varying record recordings of the time made it necessary for Dynaco's engineers to design some drastic tone control adjustments. Changes in the frequency response that are not at all necessary with a modern quality CD player or streaming.
All I did was to reduce the massive bass boost from the bass control pots...I left the treble as it was along with the loudness function, which is useless with the number of components used.
Use the Dynaco Pas 3X as it is, and use the tone controls in the neutral vertical position (Dynaco's patent), that is, as little as possible....and you have a line - and phono amplifier in the high-end class...just below "The Aurora" and my German wonder "Röh-1" from Elrad....
Always remember that a preamplifier's power supply plays as much as the amplifier circuit itself
And a little to refresh your memory:
The “Daniel” amplifier was designed by Joe Curcio in 1986 and equipped with op-amps that were located and regulated on top of the anode of that amplifier. I made a layout on CadInt, but was not happy with an op-amp so close to the high voltage +B.
Before I started building a “new” Dynaco Pas 3X preamp in 2024, I went through all the information I could find about David Hafler’s DIY kit, and found this from Joe Curcio:
https://www.curcioaudio.com/Dynaco PAS RIAA EQ Correction Mod.pdf
I also found that there have been rumors about the Dynaco Pas 3X and relatively large deviations from the riaa amplifier, deviations that have been denied by George Ronnenkamp as follows. I think that before you comment on the Pas 3X riaa, you should read the following well-documented review:
https://www.audioregenesis.com/documents/dynaco-pas-phono-stage-analysis.pdf
Next, there are George and Dave Gillespie (who write on audiokarma.org and tronola.com), who work with Dynaco, where both pretty much agree on most things, including modifications of the Dynaco.
George's review concludes that the Dynaco Pas 3X's phono amplifier from 1965 was good back then and it is still in 2025, where the Pas 3X riaa stays well within the riaa norm!
When there are still other riaa amplifier stages that are preferred over the Pas 3X, it may be due to small circuit differences and especially changed and improved power supplies. As previously mentioned, the power supply plays just as big a role as the amplifier circuit itself, as being seen from “The Aurora” and similar.
The complaint may be that there is no cathode follower that brings the output impedance down below 300 Ohm, as from my latest DIY preamplifier with ECC82....but more on that later. If you keep the output impedance of your preamplifier below 220R, "fence wire" (roughly speaking) can be used as a signal cable without loss...see Luxman CO2
Kim
Since English is not my native language, I can see that my linguistic abilities have made parts of my post appear as a direct address to you Francois G....and that was not the intention at all.
So I hope you will read my "a little refresh you memory" as a general invitation to read and listen to all opinions before one go to the inkwell and write one's opinion.
It was just like that.....I hope you didn't take my writing badly?
Best regards
Kim
Hi Kim,
Your command of English as a second (third?) language is outstanding and I appreciated your response. I understood you replied to me initially, but then switched to “general” thoughts regarding PAS-3X to the wider diyAudio audience.
You wrote:
From the thread title, your quoted statement and the photo of the Dynaco PAS I assumed that your thread will deal with new modifications you applied to your PAS. (Apologies if my assumption was incorrect). That piqued my interest, since I have a PAS-3x that needs attention and at least electrolytics and selenium rectifiers replaced.
What specifically made me curious about your PAS-3 in post #1 is the neat connector your installed where the power cord would usually would be. So, I assumed you made power supply modifications and are using an external power supply modifications.
Your command of English as a second (third?) language is outstanding and I appreciated your response. I understood you replied to me initially, but then switched to “general” thoughts regarding PAS-3X to the wider diyAudio audience.
You wrote:
From the thread title, your quoted statement and the photo of the Dynaco PAS I assumed that your thread will deal with new modifications you applied to your PAS. (Apologies if my assumption was incorrect). That piqued my interest, since I have a PAS-3x that needs attention and at least electrolytics and selenium rectifiers replaced.
What specifically made me curious about your PAS-3 in post #1 is the neat connector your installed where the power cord would usually would be. So, I assumed you made power supply modifications and are using an external power supply modifications.
Francois
It's fine that you didn't misunderstod the "you" which should have been "we" in a broad sense.
But I'm glad my English is readable.
Yes, we can look at the modifications to the Pas 3X....I've just changed the things that are about safety when repairing or building amplifiers. There are some very specific conditions that apply when it comes to tube amplifiers and high voltages, but also the general safety when connecting an amplifier to the mains supply.
But overall I have tried to keep this Pas 3X close to Dynaco's layout.
As for electrolytic capacitors and not least selenium rectifiers, time has passed from components that were created in the seventies and eighties, but more on that later.
The size of the Dynaco Pas 3X is not enough for major changes, especially not in the area around the mains transformer, so I had to find an input socket that could be screwed onto a 0.7 mm iron plate, and that the socket did not have to take up too much space in the depth behind the Dynaco backplate. I found two microphone chassis connectors male/female:
https://www.proshop.dk/Audio-kabel/...lETIbZSjfcNEiT7lX0KyGEPrJCK_VqJorkqwWlkwYqjeh
https://www.proshop.dk/Audio-kabel/Pro-Microphone-jack-4-Pin/2993131
The input jack shown may just be there, but be careful to be clear of the Dynaco mains transformer
But the most important thing: There must always be an external chassis fuse right after the 220VAC ~ 230VAC mains lead comes in....don’t use "open" fuse holders inside the chassis. Not Danish Demco Approved! Fuse for the chassis:
https://www.ebay.co.uk/itm/255812046212
The only reason Dynaco kit's could be sold in Denmark was, that the electrical appliance was not assembled!
You should replace the selenium rectifier, which after many years can emit toxic fumes if a hole occurs in the selenium insulation.
If you switch to 1N4007 you should probably expect to put 80 ~ 90 Ohm in series with the output of the two rectifiers, otherwise you will get too high a DC voltage.
Assume that you have a minimum of 405VDC on the first decoupling electrolytic...so you should therefore choose a 33uF/450V input electrolytic. Remember that if you keep 12X4 the max. load 47uF/450V...
I recommend 33uF/450V.
I chose to keep the 12X4 because the power supply plays a role, and because I think the tube sounds better than solid state...I'm sure solid state fans will say that the tube ruins the sound
If you keep the 12X4 and choose to use a new power supply board, as the solution I chose, then all ground wires must be moved from the bottom surface of the mounting chassis to the surface of the same, to reduce length of the high voltage wire...therefore I chose to make a shielded high voltage wire from pin 7 of the 12X4 to the input of the new psu.
Don't switch to exotic film capacitors on PC-6 and PC-5 .... I've tried all capacitors ... including Russian ones from before 2022 .... If it's going to be vintage, the yellow Philips polycarbonate ones are good both sound and temperature stable .... if it's going to be difficult, the German Wima MKP 10 polypropylene ones measure and sound best ... difficult because Wima are radial and all legs have to be extended and insulated to look nice!
Quite a lot ... but you have my amateur site and you can always to ask questions ...
Best regards
Kim