choosing a resistor

[wwmhf]

Hi,

The previous owner of my Bottlehead amp did not use headphones and he took out the resistors across the headphone jack. Since I use headphone exclusively, I would like restore the original circuit by putting those resistors back. My trouble is that I do not have 120 ohm resistors. Instead I have the 100 ohm and 150 ohm. I have a few questions:

1. How critical are those 120 ohm resistors across the headphone jack?
2. What should I expect if I use the 100 ohm resistors?
3. What should I expect if I use the 150 ohm resistors?

Thanks in advance.

[Paul Birkeland]

Which headphones do you plan to use mainly?

[wwmhf]

I will mainly use a Sennheiser HD650

[Jim R.]

How do they sound to you now?  Do you have enough range on the volume control, or is it really touchy?

-- Jim

[wwmhf]

I noticed that the resisters were missing because my headphones sounded too loud. I have to turn the volume knob to a very low position to listen.

I have tried three resister values:

100 ohms: works, sounds OK
150 ohms: works, sounds OK
180 ohms: works, the amp looses some details.

I think I can live either with 100 ohm or 150 ohm resister, but I really like to know a little more about the characteristics of these resisters.

Thanks

[Paul Joppa]

I'm working on a short white paper about this subject. Ping me with your email address and I'll send a draft copy - I haven't found a way to send attachments through the PM facility.

[wwmhf]

PM was sent.

[Jim R.]

Sorry, meant to reply but I was running a beta of my screen reader and it wasn't cooperating with my web browser.  Looks like you'll have a very complete and educating answer coming your way .

-- Jim