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Looking at installing a line out jack on my Trinity plexi, or perhaps taking the lazy way and just making a box to run off the speaker jack with a thru jack/line out jack. My schematic shows a 25k resistor with a 3.3k resistor for the line out. In looking at other posts I found some that show a 26k/3.3k combo and a 22k/3.3k combo. Is this an "in the ballpark" situation or do I need to follow the schematic exactly? I am having trouble even finding a 25k value resistor that is available. Also, has anyone done one of these with a pot to allow some tweaking? Would I need to add a resistor to the wiper to "smooth" the level adjustment?

You will be fine with values that are close. The idea is to get the ratio as close as possible. It does work reasonably well.

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

I tried the values of 3.3k and 22k, and wired them in an Altoids tin. Things seemd to work with amp at minimum volume, but as soon as I turned it up I got a drastic low frequency noise, and the input meter on the effect unit spiked(I am assuming overload). So I have some questions:

1. If I wire the line out as a seperate box, do I need a ground point in the box or do the grounds on the jacks take care of everything? This design comes off the second speaker jack with the amp connected to 8ohm speaker at first jack.
2. From various sources online it looks like I am trying to get the voltage at the line out jack to around a volt. Is this accurate?
3. In trying to figure out my voltage I multiplied watts by ohms and took the square root, in this case 18 X 8 = 144, sq root is 12, for a voltage of 12 volts at the 8ohm pin on the impedance switch. This would give me a ratio of 12:1 for my voltage divider. Do I have that correct for a starting point, or am I underestimating the output power?

If correct, I then did the following.... 3.3k / (22k + 3.3k) X 12 for a result of roughly 1.56 which seems like maybe it's a tad high.

Assuming I have the math correct so far, what do you think of a combination of 2.2k and 26k? That gives me .93. Or perhaps 2.2k and 33k, which gives me .75 and then use the input gain on effect unit if I need more.

You have the idea about right, except there is no buffering so the interaction of the amp to the effect unit is unknown. Those values should be close, but what was originally suggested was too..
You will have to experiment a bit.

The jacks should handle the ground.. There is no need for a separate box for them. We have done this with a jack on the amp chassis.

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

Thanks! I will give it another go.

Stephen,
Just finished wiring up my line outjack with the 2.2k and 33k resistor combination and it works great with the TC rack unit that was giving me issues.
Thanks so much for the help!

Steve

Excellent. While not sophisticated, it works within its limitations.

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