Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bakerlite on May 10, 2012, 09:39:08 am

Title: Help tweaking balanced Line out.
Post by: bakerlite on May 10, 2012, 09:39:08 am

I am trying to optimise this schem for a balanced line out (from my output which is 8ohm) for my bandmaster.
It takes signal and ground in from the same point at which the speaker is connected.
I have a few questions though -
Will this line out circuit be very sensitive to where the ground is made connection in the amp? for example there is the XLR ground and the end of Circuit Ground, Any reccomendations of where to make these ground connections?
Also - if anyone know of a place that sells suitable transformers and not those hurrendous bad quality ones you find in $15 DI Boxes that would be great!
Thanks

Title: Re: Help tweaking balanced Line out.
Post by: Willabe on May 10, 2012, 12:48:01 pm

Hammond sells them.


                    Brad     :icon_biggrin:

Title: Re: Help tweaking balanced Line out.
Post by: JayB on May 10, 2012, 05:50:16 pm

There is Jensen

http://jensen-transformers.com/ln_in.html (http://jensen-transformers.com/ln_in.html)

I think hammond makes them as well.

Title: Re: Help tweaking balanced Line out.
Post by: HotBluePlates on May 10, 2012, 05:53:26 pm

I'm guessing your line out is to be used when the speaker is not being used? I ask because of what looks like a speaker simulator circuit in between the source and the line out transformer.

Pin 1 on your output jack should probably have a 51 ohm and 0.01uF cap in series, between pin 1 and the amp's chassis or circuit ground. It will act like a ground lift that's on all the time.

The Hammond 109T is 10K:10K, 2w. Look at it as a 1:1 ratio, reflecting back the load you place on its output.

Typically, folks add a 25k pot from the secondary to ground, with the wiper feeding the output jack. That would reflect a 25k load back to the amp's OT secondary, which is presumably in parallel with the speaker. That causes very little loading of the typical 8 or 4 ohm amp output, and still passes plenty of output to your line out.

Title: Re: Help tweaking balanced Line out.
Post by: bakerlite on May 10, 2012, 06:58:29 pm

Thanks folks
Actually its meant to be used when the speaker is plugged in. Good call on the sim yeah . Will any 1:1 transformer work?

Title: Re: Help tweaking balanced Line out.
Post by: HotBluePlates on May 11, 2012, 07:29:13 pm

In general, I think you're probably safe with any 1:1 transformer. I'm thinking you won't need all the bandwidth of the Jensen transformers.

Title: Re: Help tweaking balanced Line out.
Post by: bakerlite on May 11, 2012, 08:07:02 pm

At $25 a piece these look like a good comprimise bang forbuck against a jenesen...
http://www.crimsonaudiotransformers.com/LineIsolator%20Datasheet.pdf (http://www.crimsonaudiotransformers.com/LineIsolator%20Datasheet.pdf)

still for the life of me cant figure out why the circuit is for 8ohm only.