Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on May 13, 2015, 03:11:23 pm

Title: Lost tread - there was a tread about a simply mod with a FS and a resistor .....
Post by: kagliostro on May 13, 2015, 03:11:23 pm

I'm looking for an old tread where it was discussed a simple mod where (if I remember correctly) a Foot Switch was used to short a resistor

that was on the preamp section (after V1 ??) giving a Boost effect, it was something related to a partition resistor between V1 and V2
(or so seems to me)

May be SILVERGUN posted a schematic or a link to this feature but I'm not able to find the tread

can someone give me help ?

Thanks

K

Title: Re: Lost tread - there was a tread about a simply mod with a FS and a resistor .....
Post by: MakerDP on May 14, 2015, 03:10:39 pm

I'm not familiar with the thread but if you had a typical 470k/470k voltage divider between two gain stages you could have a foot-switchable resistor in parallel with the "R1" series resistor of the divider (the one NOT going to ground.)

For example, 1v of input on the typical 470k/470k divider would yield 0.5v output
Parallel a 470k on top of the "R1" 470k to get a 235k/470k divider yielding 0.67v output -- a nice little boost.

Tweak that paralleled resistor to taste.

Is that what he was doing?

Title: Re: Lost tread - there was a tread about a simply mod with a FS and a resistor .....
Post by: kagliostro on May 15, 2015, 12:27:37 am

Ciao MakerDP

thinking about the circuit surely it will be something as you say

but I have interest also to re-read the tread

anyway many thanks for the answer

Franco

Title: Re: Lost tread - there was a tread about a simply mod with a FS and a resistor .....
Post by: chocopower on May 15, 2015, 07:12:10 am

I think a better way is using 2 resistors in serie to ground.


This way you can use an standard footswitch without relay.


You can put a pot wired as variable resistor so you can dial the boost level






             

Title: Re: Lost tread - there was a tread about a simply mod with a FS and a resistor .....
Post by: chocopower on May 15, 2015, 07:12:11 am

I think a better way is using 2 resistors in serie to ground.


This way you can use an standard footswitch without relay.


You can put a pot wired as variable resistor so you can dial the boost level

Title: Re: Lost tread - there was a tread about a simply mod with a FS and a resistor .....
Post by: kagliostro on May 15, 2015, 11:32:29 am

Many Thanks Chocopower !

---

I've just find the old tread I was looking for :grin: :grin:

http://el34world.com/Forum/index.php?topic=15080.msg144992#msg144992 (http://el34world.com/Forum/index.php?topic=15080.msg144992#msg144992)

(http://hiwatt.org/Schematics/DR_Pre2InputJP.gif)

Franco