Headphone II questions

[KennyK]

I'm mid-way through building a headphone II kit. A couple of questions have raised themselves due to lack of specifics in the instructions. is there anyone who has built one of these who can share some tips?

1. should the output transformer winding pairs be twisted together like the mains transformer and heater wiring?

2. when I built the PreII there were instructions to ensure that the o/p transformers were fitted 180degrees around to cancel hum, is this also the case with these?

3. there is no specific instruction regarding the phono input signal ground. should it be connected to the earth post or should it be connected to the ground end of the volume pot? the instructions don't even mention the signal ground from the phono sockets.

Thanks in advance

Kenny

[NickW]

Hi Kenny

1) I asked the same question and was advised NOT to twist the wires between the taps together - depends on what o/p impedance you are wiring for of course. I see no problem in twisting the final two, but the intermediates should probably be as short as possible - but long enough to modify in the future should you change your headphones and their impedance - requiring a re-wire of the output transformers......

2) Nothin special is mentioned in the instructions and mine are in-line as per the instructions. I have no problems with this.....

3) I took my i/p connector earth to the third pin of the Alps Pot and then onto the PCB. This was fine.....In the end, whether you earth to a tag on the PCB or direct to the pot, the pot must be wired to earth one way or the other. Therefore, my logic tells me to go from the sockets to the Pot and then on to the PCB.....

For me, the most important question is how to get the wiring from the i/p sockets through to the pot? ......Options:-

1) by way of the Mains transformer (no!),

2) the other way around the o/p transformers (?) - doesn't sound sensible,?

3) or under the PCB ?

I took option 3 making sure that the wire followed beneath the 0V trace on the pcb.....

But I'm prepared to be convinced otherwise...(?)

regards, Nick

[KennyK]

Thanks Nick.

well I've got it finished and all seems well (and sounds great too!)

The Valve 2 triode section anode and cathode voltages are the only ones to be at the 15% limit, all others are well within spec.

Valve 2 Anode (pin 1) reads 87.7 v instead of 102v and the cathode (pin 3) reads 1.022 instead of 0.9v. I haven't checked to see whether it follows the valve or not. If R11 was at the edge of tolerance would that contribute? is it something I should worry about? or should I just stick my free Hifiworld subscription headphones on and enjoy?

[John Caswell]

Hi KennyK,
No don't worry about it, you could get another pair of ECL83s and they could be at the other end of the spectrum, so you finish up chasing your tail.
Sit back and enjoy!

John aka Dr John.

[KennyK]

Thanks John.

I was more curious than anything else - trying to understand a bit more about the circuit.

I'm not sure if getting it working first time is always necessarily a good thing in terms of learning more about valve circuits, though it is confidence building...