trinityamps.com

I have a customer who wants an effects loop. s2 sent a simple schematic that will probably work but I was wondering if anyone has done this? Needs to be passive and simple.

Thanks,

coco

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

Probably?! Only probably?! And just when have I ever let you down?! Oh. That many times, eh? Ummm... Ok. Carry on.

Seriously, if you want passive, that is pretty much your only option. For those who haven't seen it, I will attach the schematic.

Other options are to buffer it by boosting just the send or just the return with a tube or some sort of SS device.

I just noticed I can't attach pics in this forum. Ok. Everyone will have to use their collective imaginations to picture a couple of jacks and a couple of resistors. Can you see it?

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

s2, to post a pic, you need to, click the Img button, enter the url for a picture, then click the Img button again.

Now,

Here's the effects loops of which s2 spoke.

I am wondering the best way to hook this into a TMB, which has two channels going into the PI (Phase Inverter) and not one single input into the PI.

Comments anyone?

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

I am at o means experienced in this matter but I would think the only way to do this on both channels is to use relays and a switch on the back to switch the effects loop on the normal channel or the TMB channel.

I have contemplated this but chose not to use a passive effects loop, due to the signal loss, and tonal change I think would happen.

I will experiment with an active effects loop, using a 12AT7, that will allow wet/dry, mixed, and send and return gain pots.

Of course this is only theory and my views, and when I finish my first build I will start to play with it.

Bob

You could just mix the two channels into the send side of the loop returning the loop to one side of the PI (use a 220k from each channel's volume wiper to the send jack). Then ground the other side of the PI through a .1 cap. I've done something similar for an effect loop. In fact, somewhere on the 18watt.com I uploaded a schematic of the loop I use, which is similar to S2's.

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Richard Johnson
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Playing an insturment doesn't make you a musician, listening does

I'd appreciate a link to that one. I want to check that out. I'm starting to experiment on this one now.

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

Here's a link to the 18watt forum thread.

http://www.18watt.com/modules.php?name=Forums&file=viewtopic&t=3603&highlight=effects+loop

Theres a message about 4 down with a schematic. The loop listed works pretty well, but you might want to adjust the resistor and cap values. The idea is to make the plugged in level the same as the unplugged level.

I have even done one with a .022 (coupling cap) to the send then a .1 to the PI. On this loop I had so much preamp gain I used a 300 resistor to make the unplugged level match the plugged in level.

IMO, that's the hardest thing about a passive loop, getting enough gain into the effect and then getting the level back from the effect. I usually have to gain up the PI a little (although a normal 18 PI has plenty of gain.

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Richard Johnson
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Playing an insturment doesn't make you a musician, listening does

Thanks, now I remember this one. Even printed out a copy of it. I need to study it & see how I'll hook it up.

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

OK, help me out here. I don'twant to make a mess of a beautiful thing. Can you tell me if this is correct?

http://www.trinityamps.com/ForumGallery ... s_loop.gif

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

I got the effects loop to work, but it has dropped the level way down. I reduced the send resistor to half & then to zero and it made a little bit of difference. Should I try cutting the send voltage divider in half say to 100K instead of 220K?

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

coco,

I responded on the 18watt forum. The gist of the response is getting more gain out of the PI. I did this by adjusting the Bias resistor value to 680 and by using a 15k tail resistor. The .1 cap to ground on the opposite side of the PI is also a must. This makes up the gain.

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Richard Johnson
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Playing an insturment doesn't make you a musician, listening does

I just looked at your schematic. Instead of the .01 on the return use a .1. This will keep the bass bigger sounding. Take the Reg volume's output directly to the 220k. It needs to not be attached to the PI on that side at all (pin 7 side). Attach the 470k on the other side to the screen. Then also take a .1 form the screen to gound.

My schematic showed a coupling cap from a triode plate going to the send. You're going from a volume control. So you don't need that .022 on the from TMB line. You only need the cap on the pin 2 input to PI that is on the return; since you're using it for both channels you'll need to compromize between the 100n and .022.

Those changes and the PI changes should make it work pretty well.

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Richard Johnson
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Playing an insturment doesn't make you a musician, listening does

I ended up putting the loop into the TMB channel only as there was too much impact on 'mixing' both. That worked fine. You could of course do two loops, one for each channel. Doing that would save the tone.

Here's what I did:

I used Flying leads from board to send/return jacks and back to PI.

After 0.022 TMB coupling cap to P1, branched off with 47K and 0.01u in series to send jack, and also 68K to PI, pin 2.

From return, 0.01u coupling cap and 68K in series to pin 2 of PI.

I needed BOTH 0.01u coupling caps. Without one in the send, it loaded down way too much.

Looses a wee bit of gain, but barely noticeable - maybe 2db?

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

Stephen,

To me the two hardest parts of the passive loop is preserving a good tone and getting the levels right with the effect in or out. That took me a night of experimentation and I still tweak it a little for every different amp design I make.

Glad to read it's working for you.

So are you using a CHorus pedal in it in honor of KC from the 18 watt forum?

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Richard Johnson
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Playing an insturment doesn't make you a musician, listening does

Well, I have to admit, we did try out the loop with a Chorus and Tape delay. Personally, I preferred the delay .

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

Thought a schematic of what I did would be helpful to some.

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

If you're looking to add an effects loop for a customer and require a passive and simple solution, there are a few options you can consider. One approach is to use a basic insert cable that splits the signal path, allowing you to connect the effects pedals into the loop. This can be achieved by using a stereo 1/4" TRS cable, with one end plugged into the amplifier's effects send and return jacks, and the other end connected to the input and output of the effects pedals. This setup essentially creates a loop where the effects pedals can be inserted into the signal chain. Another option is to use a dedicated effects loop pedal, which provides more control and flexibility over the loop. These pedals typically have separate send and return jacks, allowing you to connect your desired effects pedals in a passive manner. It's worth noting that the specific implementation may vary depending on the amplifier or equipment being used, so consulting the manufacturer's documentation or seeking advice from experienced professionals can be beneficial.