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Old 19th January 2013, 06:49 PM   #11
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Oh excellent! That is good to know.

So if I worked with this transformer output of 16ohms, how capable is it to drive something with a much higher headphone impedance? Like a Sennheiser of 300ohms? What would happen?

And for thought sake, if I would want to switch the secondary of the output transformer to a 'standby' mode so I can swap phones, would I just have a switch to a high value resistor?
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Old 19th January 2013, 06:53 PM   #12
cotdt is offline cotdt  United States
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I don't know about driving high impedance cans, never tried. You certainly can if you build a traditional 2-stage tube amp. It's just an issue of getting enough loudness. High impedance headphones like more voltage swing. A 300 ohm transformer would solve this, or adding a power tube.

If it's an expensive transformer, I would build the switch. Otherwise, it's not a big deal. The conditions for arcing is not there.

Last edited by cotdt; 19th January 2013 at 06:57 PM.
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Old 19th January 2013, 11:52 PM   #13
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super awesome, thats fine by me.

So in terms of Power Supply, how forgiving is the B+ voltage? I want to do a simple unregulated design with resistors and electrolytics. How forgiving is the 200v B request? It looks like it comes close to the max watt line. Is this ok?


And does the 5842 or D3A require floating the filaments a 1/4 of the B+? I am planing to regulate the heater supply to DC and was wondering if there is anything I should be aware of.
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Old 20th January 2013, 12:00 AM   #14
cotdt is offline cotdt  United States
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Lol... I don't understand most of your questions. Unregulated is fine, it just needs to be clean power. You need a choke, maybe two of them. Keep in mind that your power line has over 10% distortion with a bunch of hash noise, and it is your power supply that makes the signal that you hear, so you will be hearing all that noise.

There's no point in using DC heater supply. These are not direct heated triodes. It will be quiet with twisted AC wires to power them. Don't float anything.

Last edited by cotdt; 20th January 2013 at 12:04 AM.
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Old 20th January 2013, 12:59 AM   #15
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lol, at the time, the question made sense in my head. I think what I was trying to say was how forgiving is the B+, in terms of accuracy, but I guess that number will naturally fluctuate all the time when in use. Hence "unregulated"

What do you mean by 10%? Is this what will naturally happen if I go without chokes?
Are chokes something I should really shoot for?
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Old 20th January 2013, 01:30 AM   #16
cotdt is offline cotdt  United States
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The amp is running in pure Class A so the B+ voltage will be perfectly constant. The point of regulation is to filter out the noise. With an unregulated supply, a choke filters out most of that noise. Without either of these, you will hear background hiss. The power supply makes a huge impact on the final sound quality.
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Old 20th January 2013, 05:22 AM   #17
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Sweet!
Ok, so I have one last question;
I would like to have this tube rectified, also I am running into difficulty finding the right power transformer at Edcor that meets the proper ballpark of 180 - 200 V rms.

Is a possible to a bring down the Voltage out of the transformer by being selective with the tube rectifier? Since the amp is running pure Class A with a constant current, I can pick the tube rectifier of my choice to meet the required voltage drop at that current right?
Or was this how people typically used to design their amps.

So this leads me to this somewhat basic question: This SESS amp that I want to build, how much current is it going to draw total?
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Old 20th January 2013, 07:27 AM   #18
cotdt is offline cotdt  United States
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It would draw about 40mA total. A standard CLCLC power supply would work well, with a pair of 10H chokes. Get a 150-0-150 VAC transformer, but with such a light load it will actually be 160VAC. Keep the power transformers a good distance away from the tubes and the output transformers.

Yes you can vary the voltage by using different rectifier tubes, but it will require a 5VAC tap to run rectifier tubes. I would just use solid state rectification and not need the 5VAC tap.

Edit: One more tip, and I learned this the hard way... if you are using a single chassis, get the biggest one that you have space for. Go way oversize on the chassis.

Last edited by cotdt; 20th January 2013 at 07:32 AM.
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Old 20th January 2013, 08:50 PM   #19
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Ah! thats very good to know. The 150-0-150 transformer from Edcor is perfect! It has all the secondaries to make the heater voltages. With the chokes and their DCR values, it should bring down the voltage to the appropriate amount.

Previously I made a pre-amp with a separate box for the power supply and I can totally hear the hum when I move the box in and out. If I combine the chasis for this headphone amp, what is a good rule of thumb for how far away I should place the power transformer and the choke from all the signal material?

And for the power supply, I kinda just want to get away with a 2 capacitors and a inductor in-between, Im thinking 10H. I was thinking of using a 47uf for the reservoir and 100uf for the smoothing. This should be plenty good enough ya?
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Old 20th January 2013, 08:59 PM   #20
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A single 10H should be fine... if it's still not quiet enough, you can add another inductor. 47uF is too high for certain tube rectifiers. Use 4.7uF film capacitor instead.

If you draw less power from the power transformer and rotate it at a certain orientation (where magnetic fields cancel), then you can get away with closer placement of the transformer. 6" inches should be fine.

Don't forget bleeder resistors. It sucks to get shocked by 300V.

Other than that, sounds good!
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