Bottlehead Forum

Bottlehead Kits => S.E.X. Kit => Topic started by: ccmccull on September 18, 2022, 01:14:16 PM

Title: DPDT switch + L-pad mod for sensitive headphones & insensitive speakers
Post by: ccmccull on September 18, 2022, 01:14:16 PM

We're supposed to "Experiment" with this amp, right?

I have Grado headphones which benefit tremendously from an L-pad attenuator, as PB suggested in https://forum.bottlehead.com/index.php?topic=13832.0. It works great.

My conundrum is that I want to also drive my low sensitivity Spendor speakers without placing the 10 ohms resistance in parallel with the speakers as PB's design does. The resulting reduced total load impedance isn't that big a deal, but I wanted to try to design something that would remove those 10 ohms for speaker use.

So I added a DPDT switch after the OT. It was easy to drill out a 1/4 inch hole in the top plate beside the phone jack. Switched right it connects the OT directly to the speaker binding posts. Switched left it sends the OT signal through the 8ohm/2ohm L-Pad then on to the headphones.

(Another bonus, this setup removes the possibility of burning up the 2 ohm resistors under weird settings. See the earlier thread for more details on that.)

Thought this idea might be of use to others with similar setups as mine.

Title: Re: DPDT switch + L-pad mod for sensitive headphones & insensitive speakers
Post by: hifitoaster on October 16, 2022, 06:12:31 PM

Would you mind noting which parts you used?

It may also be helpful to know where you purchased them.

Thanks for the helpful post!

Title: Re: DPDT switch + L-pad mod for sensitive headphones & insensitive speakers
Post by: hifitoaster on October 16, 2022, 06:46:15 PM

Maybe these resistors?
https://www.mouser.com/ProductDetail/71-CMF602R0000FKR6
https://www.mouser.com/ProductDetail/71-CMF558R0000FKEK

Title: Re: DPDT switch + L-pad mod for sensitive headphones & insensitive speakers
Post by: ccmccull on October 16, 2022, 08:14:38 PM

I used these 8 ohms
https://www.mouser.com/ProductDetail/594-5093NW8R200J

and these 2 ohms
https://www.mouser.com/ProductDetail/594-5063JD2R000F

For the DPDT switch, the one pictured is something from Amazon. But then I bought this one and it looks to be higher quality:

https://www.parts-express.com/DPDT-Mini-Toggle-Switch-060-338