Tube Amp Built-in Effects Loop Design

[JRabbit]

Hi all,

I'm new here and apologize if this topic is stale, but I can't find recent posts that address my question. I am designing a tube guitar amp and want to include a proper effects loop. From what I've seen, current boutique tube amp builders don't really specify the input and output levels and don't clutter-up their products with pad switches and send/receive pots - you get send/receive jacks and that's it. Sometimes (Dr. Z) will say the effects loop is "fully buffered", but sometimes it's not. The best information you get is "takes pedals well."

It seems to me you would want to provide a buffered instrument level output signal (-20dbV or 100mV) to ensure compatibility with most if not all pedals, since guitar level inputs are what most pedals look for (especially vintage ones). It would be also be easy to provide line-level output (+4dBu or 1.23Vrms) to accommodate rack effects and other gear. My concern with the lower instrument level output is the potentially high signal to noise ratio coming from the tube amp.

I'm guessing most of today's tube amps put out a voltage level somewhere in between and just stay silent on what you should expect, or warn that you have to play with your pre-amp volume to tweak-in the right balance with your pedals. That seems sloppy to me.

Does anyone have any insight into what commercial tube guitar amps typically offer or what the best approach should be?

[martin manning]

Here's a thread where a member here built a loop design described in Merlin Blencowe's preamp book: https://ampgarage.com/forum/viewtopic.p ... 02#p308202
It has a low impedance send buffer with a level pot, and a recovery stage.

[10thTx]

Lots of information about built in FX loops with layout, schematic, photos, etc...….. here:

https://el34world.com/Forum/index.php?topic=10208.0

With respect, 10thtx

[raveonstevie]

Here's a thread where a member here built a loop design described in Merlin Blencowe's preamp book: https://ampgarage.com/forum/viewtopic.p ... 02#p308202
It has a low impedance send buffer with a level pot, and a recovery stage.

Yep. I installed one of these last night and it’s working like a champ. This place is awesome.

[JRabbit]

Thanks everyone.