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I would like to install a line out jack so I can feed the 18 watt tone to the power amp section of another amp, using the effects return jack of the other amp. For an outdoor gig I might want the extra oomph. I see different resistor values and different ratios of the higher and lower valued resistors. I'm wondering what experiences people have here.

As a starting point , the JA TMB schematic on the 18 watt site (http://www.rbevins.com/18watt/18watt_tm ... ematic.pdf) shows a 1K resistor across the tip and sleeve in series with a 22K resistor between the sleeve and ground. I have also seen 47K and 470 recommended for those two values, and 100-390 for the smaller one with a value of 2.2K for the larger one. So the ratios of these resistors vary from 22:1 to 5.5:1.

Three questions

1. are their any tone implications in using different values?

2. why is the smaller valued resistor necessary? by having it in place are you providing protection for the OT when there's no load connected to the line out? it seems that the larger valued resistor is what limits the signal passing through the line out connection, what's the smaller one do?

3. would one setup be better than another in protecting the amp from the dreaded "ooops I fired it up with no speaker cab connected" possibility..? seems like there's a range of resistive load imposed when the jack is not plugged into that's anywhere from 2.6K to 23K...or does this not really provide that kind of protection for the OT??

so many questions....

thanks

OK, I just did this for a customer.

1) Don't run the amp without a load ever. A line out is not a substitute for a proper load.

2) Values I used - 22K in series with the input from the 8 ohm lead and 3.3K across the output jack. Same as in the 15 and it worked fine. This is basically a high impedance voltage divider.

3) This was after Output transformer so all the tone was there.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Coco, I'll do it exactly like that.

Yes. Definitely use the Lightning values. They are known to be safe. I don't know where the JA values came from, but they are likely to be a guess...

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--s2
www.s2amps.com
www.category5amps.com

What power rating should I use for the line out resistors?
Thanks
Aharon

1/2 watt or better is fine.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Stephen.
Aharon