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Old 5th April 2011, 02:33 PM   #11
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Hello ashok,
Your discrete SS headphone buffer sounds like a pretty nice project with good results, driven by the 6DJ8 it sounds to be “Moskido” like. All that SS is the opposite end of the DIY from the requested Cathode Follower output version. (last comment added to stay on topic)
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Old 6th April 2011, 07:36 AM   #12
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Here's the circuit I used.
RL is the headphone load ( 62 ohms in my case).
The tube is a 6922 and the heater is 6.3 V ac. There are two series resistors across the heater lines. The center point of the two resistors is connected to circuit ground. Hum is not audible in the headphones.
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Old 8th April 2011, 03:41 AM   #13
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Default Listening update

After two days of running in I tried listening to the amp again.
I kept playing several disks with headphones connected while I was busy doing household work etc. So last night I listened again. Something has "run in " !
It sounds perfectly clean now with no hint of the slight 'veiling' that I mentioned earlier. Transistors were not on a heat sink and were very hot. Maybe 60 deg C. But it was that way all of two days with the ambient at about 33 deg C.

So a CFP follower does sound very good and is suitable for low impedance headphones. Will try later with my 32 ohm phones. Don't have anything with lower impedance than that.

Cheers.
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Old 9th April 2011, 04:57 AM   #14
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I will be making a few pcb's sometime later this month or next month. I should have a couple of extra pcb's. In case anyone is interested in having a pcb , let me know now.

Cheers.
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Old 9th April 2011, 11:16 AM   #15
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The measured temperature on the transistor tab was 69 deg C with an ambient of 29 deg C . I added a 60x35 mm aluminum heat sink. 2mm thickness. I also painted it matt black. Temp is about 10 deg lower at 60 deg C.
So if I add a finned heat sink it should probably drop to about 45 deg C.
I'll probably make the new pcb to suit the finned heat sink !
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Old 9th April 2011, 08:53 PM   #16
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At this point it looks like I'm going to do a White Fowler output stage using the confusing 6N6pi or 6H6p. Our prototype appears to drive 32 ohms elegantly enough. The Russian tube part number system is different than, and clashes with that of the rest of the world. Our system also has a 6N6, but it's a dual diode tube. And when they write an N, it looks like our H. Or did I get that all backwards? Suffixes vary too, which may not matter. The Little Dot III headphone amp uses these (not sure which topology they are using) and it seems to get nothing but rave reviews, so I don't have a better idea. I really don't want to have to add more tubes such as paralleling output tubes. I'm including this circuit in a Line preamp project that will have 2 6SN7's and a 6922 already.
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Old 10th April 2011, 10:54 PM   #17
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Quote:
Originally Posted by Humdinger View Post
At this point it looks like I'm going to do a White Fowler output stage using the confusing 6N6pi or 6H6p. Our prototype appears to drive 32 ohms elegantly enough. The Russian tube part number system is different than, and clashes with that of the rest of the world. Our system also has a 6N6, but it's a dual diode tube. And when they write an N, it looks like our H. Or did I get that all backwards? Suffixes vary too, which may not matter. The Little Dot III headphone amp uses these (not sure which topology they are using) and it seems to get nothing but rave reviews, so I don't have a better idea. I really don't want to have to add more tubes such as paralleling output tubes. I'm including this circuit in a Line preamp project that will have 2 6SN7's and a 6922 already.
I may have been wrong about the 6N6pi White Follower being able to drive 32 ohms elegantly. Depending on levels, it may be sort of OK, but if I want quality I'll buy some 300ohm Sennheisers or equiv. I hear the 600's and 650's are hard to beat.
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