Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on January 27, 2012, 05:37:38 pm

Title: TOS II Stand Alone Preamp - How to add a Balanced Output ?
Post by: kagliostro on January 27, 2012, 05:37:38 pm

I think that the TOS II is a very interesting amp and is since from TOS I that I've in mind the idea to build a stand alone preamp

from TOS I there were a lot of improvement and the TOS II is really something to be build

In this last time I'm collecting materials and infos as to build my U1 rack TOS II Preamp

thinking about the construction I was wondering to myself what about to add a balanced line output ?

it will be nice to go to a mixer or to a PC audio capture card directly from the preamp

as the output to FX Loop is from a cathode follower of V2b tube or of the mosfet (that is a good solution as to have a low output impedance)

I've think that the way to obtain a balanced output can be achieved by the use of a transformer like this

http://www.tube-town.net/ttstore/product_info.php/info/p3813_Audio-Uebertrager-1-1-2-1-fuer-Line-Signale-LTR-110.html (http://www.tube-town.net/ttstore/product_info.php/info/p3813_Audio-Uebertrager-1-1-2-1-fuer-Line-Signale-LTR-110.html)

here a schematic about a balanced output with that transformer

(http://www.tube-town.net/diy/di-lineout/LineOut.jpg)

but in my case the signal comes from the cathode instead than from the speaker output

also see this

http://www.jensen-transformers.com/as/as021.pdf (http://www.jensen-transformers.com/as/as021.pdf)


I'm not sure how to arrange this thing and need your help

THANKS in advance

Kagliostro

Title: Re: TOS II Stand Alone Preamp - How to add a Balanced Output ?
Post by: PRR on January 27, 2012, 10:10:15 pm

> the output to FX Loop is from a cathode follower

Looks like it is from a high resistance potentiometer?

Title: Re: TOS II Stand Alone Preamp - How to add a Balanced Output ?
Post by: kagliostro on January 28, 2012, 06:34:40 am

Quote

Looks like it is from a high resistance potentiometer?

Yes, you are right, I was considering the TOS II exit (the part that is between the cathode of V2b till the wiper of the pot) the same way of the part of the circuit that starts from the speaker intake till the wiper of the 5k pot

but sure the impedance will not be the same

Kagliostro

Title: Re: TOS II Stand Alone Preamp - How to add a Balanced Output ?
Post by: kagliostro on January 29, 2012, 02:35:42 pm

I've tried to solve the problem in this way

and need your councils about this solution

in green what I've do

I've think to use an ECC82 and in order to use both triodes the idea was try to use the second as substitute for the Mosfet

But I'm unsure about it as I don't want to alter the good tone of the TOS

Thanks for any help

Kagliostro