Custom OT

Discussion in 'DIY' started by m17xr2b, Apr 13, 2019.

  1. m17xr2b

    m17xr2b Friend

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    I'm looking to upgrade the output transformer of a 300B amp and couldn't find any for my requirement.
    Are there any companies that make custom high quality output transformers that will be a noticeable upgrade to say the woo ones?

    Am I mad to request this?
    Primary 2.5K,3.5K,5K
    Secondary 8Ω, 110Ω
    100+mA

    The Tango XE20S might fit the bill but it doesn't have the high impedance secondary and I've come to appreciate with senns and still on the fence if I should drop it.
    The different primaries are for me to experiment and hear for myself what impact it has on sound with different biases.
     
  2. gridmaster

    gridmaster Facebook Friend

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    Pretty expensive and long wait times, but http://www.monolithmagnetics.com/ makes high quality custom transformers.

    I called them once, the technician was very open about discussing the topic of a custom I wanted, gave really good advice.

    Edit: I also believe http://www.tribute-audio.nl/ does customs.
     
    Last edited: Apr 13, 2019
  3. MisterRogers

    MisterRogers Ethernet Nervosa

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    Also, SACThiland / Silk transformers are custom wound. I'm using them in my DG300B, and they're top notch.
     
  4. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

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  5. Zampotech

    Zampotech Friend

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    in Moscow there is a firm which makes fine transformers according to the specification of the customer. They have very good transformer steel.

    http://www.audioalt.ru
     
  6. k4rstar

    k4rstar Britney fan club president

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    Do you know if their sales team speaks English or if they ship outside of Russia? They have some very cool looking amplifiers available.
     
  7. purr1n

    purr1n Desire for betterer is endless.

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    You can still experiment with different biases (within limits) if you go with just 3.5k primaries. Bias is a matter of taste. Almost anything is an upgrade to the Woo OPTs. You don't need a 100ohm secondary - might as well go OTL. Something like a 3.5kΩ to 8Ω would be about right for a 300B or 2A3 into a headphone. Plate impedance of those DHTs is about 1kΩ. x3.5 is the sweet spot. 5k may yield a better damping factor but less power transfer. 2.5k is too low. Don't try to be special or reinvent the wheel.

    Not sure if you can get the Tangos anymore. Even if you can, a colossal waste of money.

    Check out the S-7. 3k3 primary and 4/8 secondary:
    http://www.monolithmagnetics.com/products?q=node/97

    Available in amorphous core too for an additional price.

    Mable audio has an "advanced 300B" transformer which was the basis of the SJR's OPTs. This is the best one I've heard that isn't boutique priced - great bandwidth and even more importantly sounds just right*. Running without feedback, it's less bloated than most 300B OPTs, still has a bit of that rolloff, but immensely powerful and slammin' down low - none of that soft squishy stuff. It reminds me of a bit of the DNA Stellaris; sound. For a China product, not cheap, but better than the double C-core Lundahl I have in my custom 45 and any ElectraPrint.
     
  8. restrav3

    restrav3 Likes Audio-GD

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    The descriptions and the specs for their Amps are some of the weirdest I've ever seen.
     
    Last edited: Apr 14, 2019
  9. m17xr2b

    m17xr2b Friend

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    Is a 45 happy with that primary? Sounds like I'd have to source a 3.5/5 primary to run all three. My end goal is to run the trifecta of DHT.
    Am I asking too much and should just stick with 2A3/300B where the 45 would never run to its full potential without compromises for the other two?
     
    Last edited: Apr 14, 2019
  10. Zampotech

    Zampotech Friend

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    I know they work with international shipping. Postal transportation has a simplified customs.

    Write them. The owner's name is Roman.


    Yes, unusual. They produce unusual DACs. With a discrete implementation of the algorithm PCM53 DAC:eek:
     
    Last edited: Apr 14, 2019
  11. purr1n

    purr1n Desire for betterer is endless.

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    45 tube will need 5k.

    Going with a 5k primary might be easier. Would work with 300B, 2A3, and 45. Not really a huge downside with 300B or 2A3. Maybe less power, but benefit of lower output impedance. You could still go with 3.5k primary though if headphones with higher impedance, just miss goodbye to speakers.

    Keep in mind there is really no such thing as a static 2.5k or 5k primary impedance. It's all ratios and dependent upon the speaker or headphone load.

    Don't forget heater voltages. 300B is 5V. 2A3 is 2.5V, but draws significant current.

    I would advise narrowing the scope. The one thing that does them all usually results in more permutations to try and spread out effort, ending up witu the one thing that does them all in a mediocre way.
     
  12. m17xr2b

    m17xr2b Friend

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    Gold advice, thank you.
     
  13. Tristan Jones

    Tristan Jones Acquaintance

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    Im a little late to the party here, but I would like to offer a few thoughts.

    1: any transformer will be better than the ones woo audio provides. I like the guys at woo audio, so I hate to be harsh, but there is only so much you can accomplish with chinese transformers.

    2: While every company previously mentioned makes very solid transformers, I would also like to point out that Sowter makes excellent transformers and are in your back yard, and they also take custom orders. They are slightly on the spendy side, but you might end up saving so much in shipping that you will probably end up saving money over monolith lol.

    3: If you want a great off the shelf transformer that can be sent to you the day you order it, lundahl makes some great transformers too.

    4: I would NOT swap between a 300b to a 45. Especially in a woo amp. You are talking about very different plate voltages, very different filament voltages, very different everything. Even if you went through and tried to address these issues, you probably wouldn't end up with a good sounding amp.

    The 45 is one of my favorite tubes. If you want to hear one, it is worth building your own amplifier around them.
     
  14. randytsuch

    randytsuch Friend

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    A few years ago I started building a tubelab SE amp, which can be configured for many different DHTs. My original plans were to use 300b and 45's, because I had both, and maybe 2A3. At some point, it got too complicated and I shelved it. Restarted this year, and simplified to only 45's.

    I bought electra print output iron, speced at
    5K @ 50ma to 46 and 300 ohm secondaries approx 2-3 watts, low IMD

    So basically a low impedance and high impedance tap. I am including a switch to let me easily change taps.

    Have had it running for a few months as a breadboard, and really happy with the sound, putting it in a case now.

    But if I was on your side of the world, I'd look at sowter and lundahl iron and the few other europeans mentioned. International shipping gets expensive.

    Another option I saw was to add a resistor to 8 ohm taps, so the output iron sees a lower impedance than the cans, but this wastes power. You should have plenty of power though, unless you run really inefficient cans with a 45 biased low.

    short rant. Seems like the one man, "artist" type iron winders are aging and retiring, so there are fewer options now. I include tribute and onetics in this category.
     
  15. m17xr2b

    m17xr2b Friend

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    What do you think of the 300ohm secondary?

    I really enjoy the high impedance tap ¬150ohm on my amp with HD650/HD580 but I'm still unsure if I like because of the value of because it's using the whole secondary winding of the output transformer where the first tap is a 8 ohm.
    In the end I've ordered the ISO FC20S mostly to play around with different primary options and different operation points. End goal is to compare my current OT with it and get a custom Sowter OT with a high impedance tap to see which I like among different tubes. Would you share the operating point of the your tubes and the input tube you chose? I'm thinking going cascaded 6SN7 in a reichert config.
     
  16. Cspirou

    Cspirou They call me Sparky

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    Lundahl does make off the shelf transformers for high impedance headphones

    6DA27D74-3790-4585-97A0-9ABA4D0A08F5.jpeg
     
  17. randytsuch

    randytsuch Friend

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    The 300 ohm tap sounds good with my Senn HD800's, but I haven't compared the low and high taps on the 800's. I know on my HE500's the high impedance tap seems to run out of juice at higher volumes, and you can hear distortion on some parts of songs. I don't have more efficient low impedance cans to try, at least not good ones.

    Here is a link for the amp I'm building
    http://tubelab.com/designs/tubelab-se/

    It uses a 5842 as the driver tube. He picked this tube as it has enough gain to drive 300b's if you go there.
    I bought his board, so I didn't do any design work, the work involved was deciding which DHT to use, and then based on that pick power and output iron and the other parts to get the right B+ for a 45.
    Long way of saying I didn't plot any curves, or figure out operating points for the driver tubes.

    I can tell you my B+ is about 310V, and I'm using about a 25 ma bias. After I finish casing it up, I'll try changing the bias a bit, but I couldn't tell a difference when I tried either slightly higher or lower before.
    I should also add that I've been using type 46 tubes with a 5 to 4 pin adapter instead of 45's. I have one pair of st shaped 45's to compare at some point.

    Randy
     

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