Headphone switcher

floppybootstomp · Post by **floppybootstomp** » Tue Oct 11, 2011 10:39 pm

I put one of these together >> Link to use with my two EL84 push/pull monoblocks @ 10W each.

It works ok but when I turn the volume up I get distortion and the top end hurts my ears, it's kinda shrill.

I used the resistor values (all 3W +/- 5%) for the 20W output and wondered if using resistor values suited to 10W would help matters. I wondered what values for R1 & R3 might be suitable for 10W?

Have tried two sets of headphones, Pjilps Pro-Luxe PX-921's and some new-ish Sennheisser wireless HDR-160's, both of which display same characteristics as mentioned.

floppybootstomp · Post by **floppybootstomp** » Wed Oct 12, 2011 4:37 pm

Nobody? Could anybody offer a view whether changing resistor values might make a difference to the sound?

I thought of maybe making R1 & R3 150R & 68R respectively might make it better suited to a 10 watt output.

Here's a few pix of the thing, the piece of vero is held in place with a couple of velcro squares and the box came from Maplins:

Mike H · Post by **Mike H** » Wed Oct 12, 2011 6:27 pm

floppybootstomp wrote:Nobody?

Only just got here!

Ah I think what's going on here is that that design assumes a transistor amp will be used ~ your valve amp's need 8 Ohms dummy loads to work properly.

So you need 8 Ohms between 'AMP L' (or whichever) and 'GND'.

I've found 10R and 47R in parallel are close enough. The 10R needs to be quite a few Watts rating, mine were 25W aluminium clad. Just in case. The 47R can be 6W or somesuch.

Unless you can find 8.2R 25W, but I haven't seen any for years.

HTH

floppybootstomp · Post by **floppybootstomp** » Wed Oct 12, 2011 6:36 pm

Thanks Mike. Now you mention it, I do recall having read that elsewhere here in the past but it clean slipped my mind... Time to order up some WW's

Mike H · Post by **Mike H** » Wed Oct 12, 2011 6:41 pm

pre65 · Post by **pre65** » Wed Oct 12, 2011 7:10 pm

I have a few 15R Berco resistors. If Tony wants 4 (2 in parallel = 7.5ohms) just PM me with your address.

al newall · Post by **al newall** » Wed Oct 12, 2011 7:37 pm

Yes.
I mentioned this to Rod Elliott some time ago, and he said the design wasn't really intended for tube amps. Doesn't say that on his site though.

Mike H · Post by **Mike H** » Thu Oct 13, 2011 12:39 pm

Mmm, only needs a couple of sentences adding to say what to do in that case.

pre65 wrote:I have a few 15R Berco resistors. If Tony wants 4 (2 in parallel = 7.5ohms) just PM me with your address.

Yep that'll work.

Mike H · Post by **Mike H** » Thu Oct 13, 2011 12:40 pm

floppybootstomp wrote:Now you mention it, I do recall having read that elsewhere here in the past but it clean slipped my mind...

Easy done I totally sympathise

pre65 · Post by **pre65** » Thu Oct 13, 2011 12:51 pm

Resistors have been posted Tony.

floppybootstomp · Post by **floppybootstomp** » Thu Oct 13, 2011 1:14 pm

You sir, are a scholar and a gentleman, I am in your debt.

Thanks

pre65 · Post by **pre65** » Thu Oct 13, 2011 1:16 pm

floppybootstomp wrote:You sir, are a scholar and a gentleman.

Thanks

Tony has not met me yet.

Mike H · Post by **Mike H** » Thu Oct 13, 2011 3:40 pm

And the 'debt' bit I'm not sure about

floppybootstomp · Post by **floppybootstomp** » Sun Oct 16, 2011 2:24 pm

That sorted it, pair of 7.2 ohm dummy loads, thanks Phil.

I am still occasionally surprised and warmed by human generosity.

This is probably a good thing

floppybootstomp · Post by **floppybootstomp** » Sun Oct 16, 2011 2:24 pm

There was a big slow down somehwere, caused me to make double post so I have deleted it.

If you give it a short, sharp, shock.... hey

audio-talk

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