Interesting headphone amp circuit, especially the relatively
low plate supply voltage.
But I cannot find a specification or characteristics of this tube on the internet.
Can someone be so kind to supply it?
Thanks in advance.
low plate supply voltage.
But I cannot find a specification or characteristics of this tube on the internet.
Can someone be so kind to supply it?
Thanks in advance.
Interestingly its a frame grid tube with a 10 watt plate (TV video amp):
https://frank.pocnet.net/sheets/135/1/12HL7.pdf
I also have little doubt sound-wise that Ale's DHT amp would be the best of the lot. But it's a quite ambitious undertaking, and would be a bit expensive. Coleman reg boards, heatsinks, all that stuff adds up. I'll bet it would be worth the effort and expense.
My amp is downright boring in comparison. It was meant to be very cheap and simple.
My amp is downright boring in comparison. It was meant to be very cheap and simple.
My 2P29L version of Ale,s hybrid amp didnt turn out to be that expensive. Ill do a cost breakdown if anyone,s interested. Also I dont understand what was meant by " the implementation contains some dirty parts" if that refered to my amp..
rongon,
your design is not boring, but excellent.
Zeta4,
I consider diodes, (IC) regulators, current mirrors, gyrators... as dirty parts.
your design is not boring, but excellent.
Zeta4,
I consider diodes, (IC) regulators, current mirrors, gyrators... as dirty parts.
Ron, regarding bass response... did you try decoupling the cathode to B+? With headphones this trick is only usefull on very low ripple supplies. A 10 - 20uF film type would be nice in this position.
Just breadboarded a CCS loaded parafeed 4p1l headamp using Antek toriods as OPTs. Despite speculation about microphony being an issue with these tube, the amp is dead quiet. The sound is quite good too, I might add.
Thanks for your info and encouragement. My EP trannies have an unknown Lpri, but are quite large, about A-470 Dyna ST70 size, so I expect to be happy with the bass.
That sounds pretty interesting hope to see it. At headphone levels the torroids can handle the DC I guess. Since I too have a bunch of anteks and 4P1L's I'd like to try that experiment.
Interesting idea... No, I haven't tried that. That's the so-called "Ultrapath" connection, correct?
Why would an ultrapath connection of the cathode bypass cap result in tighter/more controlled bass response?
The F3 of a HPF of 82R||30uF would be pretty high in frequency, would it not?
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Parafeed connection puts a DC blocking cap between the tube's plate (audio voltage/current output) and the OPT primary coil. The OPT primary coil has no DC current going through it (it connects from the output of the DC blocking cap to ground). That's how a toroid can be used as an OPT in parafeed configuration.
Parafeed-Amplifier Design
A constant-current source ("CCS") can be used as the tube's plate load, instead of an inductor.
An externally hosted image should be here but it was not working when we last tested it.
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It's design from the days of old without cap sizes larger than 10uF. PS is signalground so small cap sizes are enough. With a big electrolyte to ground the AC on the cathode rectifies a little, it shifts the tube bias around. Try it, but use caps rated at HT.
There is a 4.7uF coupling capacitor to block DC through the primary. As it sits I am using a 230:24 volt transformer as the OPT. My phones are 55 ohm giving a reflected impedance around 5k. 230/24=9.58... 9.58 squared equals 91.8. 91.8x55 ohms = 5.048k. Toriods are notorious for parasitic capacitance, killing the upper frequencies. This can be overcome with biasing the tube to pass more current. I haven't done a frequency sweep with this setup (currently biased at 40mA). But my tests with a 6p15p headamp with Anteks indicated that bandwidth was over 40khz or so with bias as low as 30mA. I don't remember the exact results and my frequency generator has limitations. And for those who don't want to fork up the cash for Coleman regulators up front... 2 volt SLA cells can be bought for cheap on Amazon. You will need a charger for them though. For amps that aren't swinging a lot of voltage, I have found that toriods work exceptionally well.
Hi Gentlemen, long no see... 🙂
Reflecting to above design, I found something on the big internet with help of Google. I think the aforementioned design (drawn on black background) stems from this circuit design, right ? Especially when I look at the filename of the black circuit schematics (Aikido).
So at the very end - which one would you build ? (32 Ohm headphones).
In the linked 'original' I very much like the idea of safety resistors, should anything go wrong in the small amp. So I would build the 'safer version' at the very bottom of the page, would you please just have a quick look at it - will it still suit for 32Ohms just as well ? I also like the simple design and the possibility of using different tubes (within range) without altering anything else.
I would then order the tubes and let the fun begin.
Another question to the PSU part: +220V needed (except heating of course which will be separate). I assume I should strive for a stabilized and filtered one than a very bare minimum/simple one, right ? 🙄
(Bare minimum would be: trafo, graetz-bridge, big electrolytic with small film caps on it - and that's all).
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I would build the one I linked, but I guess I'm biased 😀 It is based on Broskies Aikido, but it doesn't use the "aikido"ing, just the active loads.
As far as the PS, I just use a 12V SMPS and a DC-DC boost converter...
Here's a 12V SMPS: New 6A-8A Unit For 12V 100W Switching Power Supply Board AC-DC Circuit Module | eBay
And the DC board: 150W Inverter Boost Board Transformer DC-AC Converter 12V to 110V 200V 220V 280V | eBay
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