Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on November 30, 2016, 09:33:16 am

Title: Parallel loop schematic?
Post by: 12AX7 on November 30, 2016, 09:33:16 am

Does anyone know of a good parallel loop schematic that will work good in a 2204 style amp PRE master? (CF>tones stack or tone stack>master) I have a spare 12AX7 in the amp and having tried several series loops I'm done with them. I need 110% transparency and a parallel loop is the only sure option.

Title: Re: Parallel loop schematic?
Post by: sluckey on November 30, 2016, 09:38:39 am

Search the forum.

Title: Re: Parallel loop schematic?
Post by: 12AX7 on November 30, 2016, 10:22:06 am

I just did, for "loop" and "parallel loop" and found one result...my thread !  :laugh:

Title: Re: Parallel loop schematic?
Post by: SILVERGUN on November 30, 2016, 10:35:54 am

Here's how Mesa did it with a 12AX7 and a MIX control for flexibility.

Title: Re: Parallel loop schematic?
Post by: sluckey on November 30, 2016, 10:49:49 am

Quote from: 12AX7 on November 30, 2016, 10:22:06 am

I just did, for "loop" and "parallel loop" and found one result...my thread !  :laugh:

Really! Try the advanced search, not the quick search. Search for "fx loop". Use the quotes so you search only for the phrase "fx loop". You will find what you seek.

Title: Re: Parallel loop schematic?
Post by: kagliostro on November 30, 2016, 11:03:23 am

The FXLoop on this 5E3 based amp is borrowed from Engl Fireball, and it works fine

http://el34world.com/Forum/index.php?topic=17360.msg173749#msg173749 (http://el34world.com/Forum/index.php?topic=17360.msg173749#msg173749)

look at the end of the thread (the 100k pot is a double pot single shaft connected "reversed", one increases and the other decreases)

(http://i.imgur.com/lx0Onyg.jpg)

Franco

Title: Re: Parallel loop schematic?
Post by: 12AX7 on November 30, 2016, 11:09:47 am

Maybe this isn't gong to work for me. The entire reason i wanted to do this was so the dry signal would NOT be subjected to any other signal path other then is current one w/o a loop. I figured the loop would be where the wet mix is and the dry signal would just be mixed back in with it via a blend pot or whatever. But these 2 examples show the dry signal IS subjected to more amp stages. Thats what i want to avoid but i guess it can't be done?

Title: Re: Parallel loop schematic?
Post by: SILVERGUN on November 30, 2016, 12:10:23 pm

Here's an idea that has probably been tried....
Picture the AB763 reverb circuit. It runs parallel to the dry signal and then gets introduced into the signal chain via a mixing resistor.
Replace the reverb circuit with your effects loop and ....well, maybe
 
Only problem is signal phase will need to be corrected so that when the effected signal joins back into the dry it will be in phase. (would be out of phase if you just inserted either one of our examples)
 
Should work well, but I cant remember ever seeing it on a schematic.

Title: Re: Parallel loop schematic?
Post by: tubenit on November 30, 2016, 03:37:49 pm

Did you look in ARCHIVES which has a lengthy thread about FX loops including parallel loops and schematic and layout information.  It has examples that should work quite well with Marshall topology.

http://el34world.com/Forum/index.php?topic=10208.0 (http://el34world.com/Forum/index.php?topic=10208.0)

With respect, Tubenit