Bottlehead Forum

Bottlehead Kits => S.E.X. Kit => Topic started by: audiblesoundwave on December 19, 2009, 09:10:08 AM

Title: Reducing the gain for headphone section but not to the speakers, possible?
Post by: audiblesoundwave on December 19, 2009, 09:10:08 AM

I am currently using Sennheiser HD-650 with the S.E.X. amp!  It seems to be too much gain.  Around 7:30 to 8 o'clock setting would be fine to my hearing.  Anything beyond that is way too loud!

Is it possible to reduce the gain only for the headphone section?

Thanks,
Milton

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: Jim R. on December 19, 2009, 09:33:46 AM

Milton,

What is your source and what is it's output level?

-- Jim

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: audiblesoundwave on December 19, 2009, 09:39:14 AM

Hi Jim,

The source would be coming from CD, LP, or tuner via a selector switch!  CD is loudest!  Listening the LP and tuner has the same issue which too loud around 7:30/8 o'clock setting on the S.E.X. amp.

Any help is greatly appreciated!

Thanks,
Milton

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: Jim R. on December 19, 2009, 09:50:37 AM

Hi Milton,

As I haven't finished my s.e.x amp yet, I don't know if the situation will be the same for me or not with my 650s.  The range on the volume pot is ok for speakers then?  If so, you might be able to increase the value of the 120 ohm series resistors on the headphone jack, but the experts will have to chime in on that as I've not experimented with that myself yet.

If the volume pot is too sensitive on the speaker output too, then an attenuator on the input jacks will cure both at the same time.

Sorry that I can't be any more specific than that.

-- Jim

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: audiblesoundwave on December 19, 2009, 10:00:26 AM

Jim,

It sounds fine with speakers!  My speakers are at 87db not the recommended 93db or better!

Not sure I can really change the 120 ohm resistor for this issue! 

Thanks,
Milton

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: Paul Joppa on December 19, 2009, 10:14:36 AM

The 120 ohm resistor is connected at one end to the output transformer, at the other end to the phone jack. You can connect another resistor from that point on the phone jack to a nearby ground, which will attenuate the headphone output only. Probably something in the range of 50-100 ohms will do the job. Be aware that this will also reduce the headroom  (maximum possible loudness before distortion) on the phone jack, so you are looking for the best compromise, not just to beat the gain down.

Personally, I'd get some clip leads and experiment with different resistors, then solder in the one that works best - making sure it's easy to remove if you get different headphones in the future.

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: audiblesoundwave on December 19, 2009, 11:07:04 AM

Thanks Paul!

I think I got it but let me try!  Is the resistor go to the side has no wire connected on the headphone jack?  A completed S.E.X. amp has all the wires (from the transformers and the output jacks) connected on one side of the headphone jack; including the ground wires!  Is this a correct understanding?

Sorry Pual!  I am learning the electronic terminlogy as I building and upgrading these Bottlehead tube gears!

Thanks,
Milton

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: Paul Birkeland on December 19, 2009, 12:49:45 PM

I would like to suggest an alternative.  Grab a decent quality DPDT switch, then drill/mount the switch maybe 1" above the volume pot on the chassis plate.  Remove the red leads that go from the RCA jacks to the volume pot, then solder them to the center pair of lugs on the DPDT switch.  Wire the rear pair of lugs back to the volume pot where the red wires originally went.  (Be somewhat careful about not mixing up channels).  Then on the other two lugs, solder a 100k resistor to each lug, and the other end of each resistor to the same locations that the wires went to on the pot.

With the switch position feeding through the resistors, you will get a healthy pad at the input, and with the switch position feeding through the wires, you will get the stock input sensitivity. 

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: audiblesoundwave on December 19, 2009, 02:41:31 PM

Thanks Paul!

Are these two (one for each channel) 100K resistors value fix?  Can I experiment with a different values?  Is there a upper or lower ohm limit to try?

Will 1/2 watt be good enough?

Thanks again,
Milton

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: Paul Birkeland on December 19, 2009, 03:00:27 PM

The 100k resistors are a starting point.  Anything from maybe 33k-470k is suitable to try, and wattage is not at all important. 

Title: Re: Reducing the gain for headphone section but not to the speakers, possible?
Post by: audiblesoundwave on December 19, 2009, 03:54:40 PM

Thanks Paul!

Happy Holidays,
Milton