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vox vt series amp fx loop mod

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Post by Sgt. Vimes 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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Sgt. Vimes
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Post by Barry Sun May 25, 2014 10:35 am

"The board requires you to be registered and logged in to view this forum."

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

oh bugger, forgot about that.....

series - vox vt series amp fx loop mod Vt_sim10

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.
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Post by Sgt. Vimes 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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Post by Yamvmax Mon Feb 22, 2021 1:26 pm

Yamvmax :Idk if you're still around. I'm trying to do the vtx mod for looper on my vtx 20. You have any detaled pics?
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Post by Sgt. Vimes Mon Feb 22, 2021 1:33 pm

pm replied to
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Post by Barry Mon Feb 22, 2021 3:49 pm

The Zombie thread lives!! zombie mask

Who's a lucky Newbie then?!

_________________
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Post by Sgt. Vimes Mon Feb 22, 2021 3:54 pm

7 years, bloody hell!
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Post by Yamvmax Wed Feb 24, 2021 3:39 pm

Yes, sorry, back from the dead. Trying to mod a vt20x. Looks different inside.
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Post by Yamvmax Wed Feb 24, 2021 3:45 pm

If i post some pics, someone willing to give some advice? I take all responsibility for electrocution, and amp death😂
Damn, old website, cant post pics. I could upload to my drive folder i guess. I found 2 "test points" on MB. Wondering if they could be an in and out?
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Post by Hohoagogo01 Wed Mar 31, 2021 6:47 pm

Hi! I am new here and apparently about 15 years late lol. I played a Vox AD50VT for about 6 years straight (practice, gigging, etc.) from 05-11. I never knew about adding an effects loop, or that it would really help (didn’t use the internet a lot back then lol). This information would have really helped in getting some different tones. Back then I ended up taking the back off the amp because the stock speaker sucked (I mean it did, trust me I played it enough to know), and removing the back really helped open up the amp’s tone and sound. Ok, so fast forward to December 2019, I picked up another AD50VT cheap because my original one got stolen. I actually did a gig in February 2020 with the new one and it sounded good and just like I remembered, BUT due to Covid, the amp set for about a year (I was playing a Vox stomplab through a CAB M at home during this time). I sold my current Vox AD50VT to my brother (because he loves these amps too, and I am not gigging and still stuck at home playing the Stomplab and CAB M). After speaking with my brother about the effects loop mod, we are going to perform the one listed here, as well as adding one of the new Celestion speakers designed for amp modelling (either the Celestion F12-X200, or the new triple cone one just released) because the stock speaker is just wrong for this amp. These new speakers have a flat response and should really show the amp’s full potential. It’s too bad Celestion didn’t make these back in 2005 lol. With the effects loop and new speaker, the goal is to run a CAB M through the effects loop and do IR’s, and with the new frequency response from the speaker(s), it should really make this a better sounding amp. Of course it will probably need some bracing in the cab, and maybe a little dampening material (and an eq in the loop should help), for the lower bass response. Not sure on how the highs will be considering the new Celestion F-12 HF range is 20,000 hz, and the triple cone HF is 12,000 HZ, but I imagine that reducing the highs on the amps eq (and again, an eq pedal in the loop, or the eq in the CAB M in the loop) will push them down to comfortable levels. I want to mention that there was a guy that was doing an aftermarket effects loop for the Valvetronix amps, but from lots of Googling, and what from what I have read, he stopped performing and selling them a couple of years go. So, finding the material in this thread is pure gold if you own one of these amps. Also, I wanted to note that the ferrite bead listed above is out of production (I mean this thread is pretty old haha), but Amazon has some alternative options for cheap, and it’s really just for RF interference. So, once again I wanted to say Hi! to everyone and looking forward to checking out the forum here. Thanks again for the information listed in this thread, and once we have completed the mods I will check back in and give some feedback on how the amp sounds.


Ps if you own a Valvetronix amp with a tube inside, and you need to replace the 12AX7 (I did 3 times on my original, trust me it got played a lot back then), the stock tube sounds ok. Avoid Groove Tubes (they didn’t last a year the sound was sub par), and go for the Mesa tube (especially if you play lots of metal). Also, read the manual. If the noise gate is not set right, it will sound like the amp is dying on you. 😉
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