Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Joe6v6 on May 12, 2019, 11:19:11 am

Title: Need to add a Line Out
Post by: Joe6v6 on May 12, 2019, 11:19:11 am
So I need to add a line out to an amp I built. The guy that uses it is hell bent on having an on board line out instead of using a direct out box between the output and the speaker. Ive looked around & I see all sorts of schematics & recommendations for resistor values, but mostly they are for lower wattage amps. This amp uses 4 6l6's so in the 80 watt neighborhood. I did it like the attached pdf shows, I used 470r and 2.2k and it works but seems a little hot, all I can do to test it right now is plug it into another amp. What resistor should I change to drop the output or could I put a pot somewhere & make it variable?  Thanks : Joe
Title: Re: Need to add a Line Out
Post by: shooter on May 12, 2019, 11:30:23 am
you can try the values here as a start, you don't need the tranny.
Title: Re: Need to add a Line Out
Post by: 2deaf on May 12, 2019, 01:48:01 pm
Increase the 2.2K to 4.7K or reduce the 470r to 270r.  Does the OT have more than one output impedance?

For a variable line out, leave the 2.2K and replace the 470r with a 500 Ohm linear pot.  Connect the wiper to the line out jack.
Title: Re: Need to add a Line Out
Post by: Joe6v6 on May 12, 2019, 02:39:34 pm
Quote
Increase the 2.2K to 4.7K or reduce the 470r to 270r.  Does the OT have more than one output impedance?For a variable line out, leave the 2.2K and replace the 470r with a 500 Ohm linear pot.  Connect the wiper to the line out jack.


Thanks - This is what I was wanting to know - Yes the OT has 4-8-16 on a rotary switch. 
Since its in the ballpark now I think I will try a 500 Ohm pot with a 100r resistor so the value will not go below that. 
Title: Re: Need to add a Line Out
Post by: PRR on May 12, 2019, 03:56:51 pm
> seems a little hot, all I can do to test it right now is plug it into another amp

Instrument Input is *hotter* than Line Input.

So you may be done already. You really need to try it on a standard PA console the way it would be trimmed for performance.
Title: Re: Need to add a Line Out
Post by: Joe6v6 on May 12, 2019, 04:24:23 pm
Quote
Instrument Input is *hotter* than Line Input. So you may be done already. You really need to try it on a standard PA console the way it would be trimmed for performance.


Good point - I guess I will let him try it as is & tweak it from there.   .     Thanks
Title: Re: Need to add a Line Out
Post by: 2deaf on May 12, 2019, 04:59:40 pm
Quote from: Joe6v6 on May 12, 2019, 02:39:34 pm
Yes the OT has 4-8-16 on a rotary switch. 

Which output tap you connect the line out to makes a difference with how much voltage the line out has.  As an example with the amp putting out 80 Wattsrms, the 4r tap has 25.3Vp, the 8r tap has 35.8Vp, and the 16r tap has 50.6Vp.  So you can also tweak the line out by keeping the resistors the same and moving to a different tap.