vox vt series amp fx loop mod

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vox vt series amp fx loop mod

Post by Sgt. Vimes on Sun May 25, 2014 8:08 am

Don't know if any of you guys use these amps, but I do and like it a lot, only major downside is the lack of an fx loop probably because of the built-in effects, well here's a nice little mod to remedy that.
http://www.valvetronix.net/forums/simple-fx-loop-only-for-the-vt-series-amps-t3756.html?forum_uri=simple-fx-loop-only-for-the-vt-series-amps&sid=6a028f4207e5d6ced1658d64c35745b6

I did this mod midweek and is simple, works a treat too!
I can now use my phaser and analog delay pedals post pre-amp where I need em, Iwas considering buying a new amp just for the loop...saved me ££££.
I have a few of each of the components ( capacitors, ferrite beads, resistors also tons of heatsink tubing) if anyone wants to have a pop at the mod?

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Re: vox vt series amp fx loop mod

Post by Barry on Sun May 25, 2014 10:35 am

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Re: vox vt series amp fx loop mod

Post by Sgt. Vimes on Sun May 25, 2014 10:43 am

oh bugger, forgot about that.....



This places the loop in series before the existing headphone jack, leaving the existing headphone and mute circuit intact unchanged. It involves altering only a couple of wires inside the amp and is geared towards the technically skilled with good soldering skills, you will need to drill, solder and assemble parts.

VT simple loop only.jpg
    VT simple loop only.jpg (833.79 KiB) Viewed 373 times



VT LOOP ONLY PARTS
1 - 22? 1 watt resistor                                                                        .20
1 - 220UF 25 volt capacitor                                                              2.00
2 - Neutrik NMJ6HC-S 1/4" stereo switched solder jack (1.50ea)    3.00
1 - 12” - 6 conductor 22 gauge stranded cable                           1.00
1 - Ferrite bead FB43-287-RC                                                          .50
1 - 3” - 1/4” red heat shrink tubing                                                     .20
                                                            ESTIMATED TOTAL           $6.90

BEFORE YOU START, DISCONNECT THE POWER CORD (A/C power source) FROM YOUR AMP!

We will assume you have the proper supplies, tools, skills and know how to take your amp apart correctly. If you do not know how, search this forum for posts that go over this:

Before removing the amp back, take a pencil and draw a light line around the cover’s opening at the chassis, marking the chassis exposed area for easier placement of components.

Remove the amp chassis from the cabinet (mark any wires for their placement and connections that will need to be disconnected). Locate and position the two new jacks (send and return jacks can be horizontal or vertical and next to each other) at the rear of the chassis inside the pencil lines and where they will not interfere with anything inside or outside the amp. Once the proper location is determined mask off the amp’s electronics and drill two 7/16” holes for the jacks (careful not to let any drill shaving get into electronics).

Turn the amp so the large open end (length wise) is facing you. Locate the indicated headphone board and wires indicated. Cut the RED wire about 1" away from the headphone board’s small connector, label the RED wire side attached to the headphone board RETURN, label the other side of the cut RED wire SEND. Bare the insulation on the left side WHITE wire about 1" away from the large connector on the headphone board, label this wire GROUND.

Modify the two stereo jacks into mono jacks for the SEND and RETURN by pushing the ring common terminal (the one with the contact switch arm) out of the jacks, leave the other terminal (has no contact switch arm on it) as a junction post. Using the wires inside the 6 conductor cable, strip two 1/2” long pieces of wire insulation off of the red wire and install the insulation on each wire lead end of the 22? 1 watt resistor, install the resistor to the RETURN jack’s junction post terminal (ring) and continue the other end of this resistor to the SEND jack’s junction post terminal (ring).

Strip two 1/2” long pieces of wire insulation off of the red wire and install the insulation on each wire lead end of the 220uf capacitor, install the 220uf capacitor’s POSITIVE (+) leg to the SEND jack’s junction post terminal (ring) and continue the NEGATIVE (-) leg of this capacitor to the send jack’s TIP common terminal.

Attach a RED wire to the RETURN jack’s junction terminal (ring), continue this wire to the headphone board’s SEND wire (RED wire), trim it to length (allow some slack in the wire) and solder it to the headphone board's SEND wire (red wire), insulate this connection.

Attach a ORANGE wire to the RETURN jack’s TIP common terminal, continue this wire to the headphone board’s RETURN wire (RED wire), trim it to length (allow some slack in the wire), slide the ferrite bead onto the wire and secure about 1” from this end using heat shrink tubing, strip the end of the wire and solder it to the headphone board's RETURN wire (red wire), insulate this connection.

Attach a ORANGE wire to the RETURN jack’s TIP normally closed terminal, continue this wire to the SEND jack’s TIP normally closed terminal, trim it to length and solder.

Attach a GREEN wire to the SEND jack’s SLEEVE common terminal, continue this wire to the RETURN jack’s SLEEVE common terminal, continue this wire to the headphone board’s GROUND wire.

When you are sure all connections are correct, put your amp back together, you’re done.

Sgt. Vimes
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Re: vox vt series amp fx loop mod

Post by Sgt. Vimes on Sun May 25, 2014 10:48 am

Didn't ask Retrobob's (from the valvetronix forum) permission to do this, so if yer seeing this bob, please and thanks.

It's ok to use a non-polarized capacitor for this and the resistor can go in either direction....i think  Smile

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Re: vox vt series amp fx loop mod

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