Help with Reverb/Tremolo wiring Gibson GA15-RVT

[Firestorm]

Pin 1 (blank)
Pin 2 (bare braided wire connected to socket shield)
Pin 3 (ground to reverb off)
Pin 4 (ground to reverb and tremolo off)
Pin 5 (to + tremolo switch)

IS THIS CORRECT

Not quite. I don't know what you mean by "Pin 2 (bare braided wire connected to socket shield)." The braided wire gets soldered to Pin 2. That's it. Socket shield?

Pin 3 is not a ground. Pin 4 is.

The schematic shows SPST switches. They may have used DPST. No matter. On each switch, one terminal (or set of terminals if DPST) gets connected to ground: Pin 4. On the Trem switch, the other end is connected to Pin 5; on the Reverb switch, the other end is connected to Pin 3 through the center conductor of the shielded cable.

[Firestorm]

Know when I had no footswitch installed and the reverb was working I noted that I was unable to vary the reverb at the reverb pot...

is that correct I would have assumed that I should be able to vary the reverb...it seemed to make no difference whether I had the reverb input plugged into the tank or not...that doesn`t seem right to me..

Something not right there. Check the continuity of the pot terminals: One end should be at ground; the other end should have continuity to R7; the wiper should have continuity to V3, Pin 2. If you've lost the ground connection, the pot won't do anything.

[devilsindetails]

OK...let's back up just a bit the bare braided wire running off of pin 2 is connected to what? How can it be a plug shield ground if it's not connected to anything? It's just a two inch length of bare braided wire.

[devilsindetails]

I don't see any center conductor on the braided wire!

[devilsindetails]

Here's the foot switch wiring diagram again. Ok, so pin 3 isn't really a ground but it does go to the off terminal end of the reverb switch and is bridged to the off terminal of the termolo right?

[devilsindetails]

[quote="Firestorm"}] Something not right there. Check the continuity of the pot terminals: One end should be at ground; the other end should have continuity to R7; the wiper should have continuity to V3, Pin 2. If you've lost the ground connection, the pot won't do anything.[/quote]

Thanks, I'll check that....I really appreciate your patience Firestorm...I had no idea something that at first blush looks so simple could be so damm frustrating to troubleshoot!

[Firestorm]

OK...let's back up just a bit the bare braided wire running off of pin 2 is connected to what? How can it be a plug shield ground if it's not connected to anything? It's just a two inch length of bare braided wire.

The schematic shows a two-conductor wire going from Pin 3 to one of the reverb switch terminals. One conductor (the center one, assuming someone hasn't changed the wire) makes those connections. The other conductor (the shield) is connected to Pin 2 and nowhere else. What have you got in your footswitch?

[devilsindetails]

The schematic shows a two-conductor wire going from Pin 3 to one of the reverb switch terminals. One conductor (the center one, assuming someone hasn't changed the wire) makes those connections. The other conductor (the shield) is connected to Pin 2 and nowhere else. What have you got in your footswitch?

I only have three wires coming through the chord into the footswitch...red, black and grey......

I think this lies at the heart of my tremolo problem...my question remains however if the shield wire is connected to pin 2 on the plug end where is the other side of the braided wire connected to? Or does it simply terminate at the inlet of the pedal enclosure, unconnected to anything?

[Phil_S]

Here is a picture of the switch from my GA17-RVT, which is the same setup as far as I know. The red and black go to the tremolo. The braid and white go to the reverb. There is a length of bare solid wire that bridges the two swtiches and terminates on the same terminal as the braid (reverb switch). When previewing the post, clicking on the photo blows it up to larger than life and it looks very clear to me. I think the key here is the braid/shield.

I thought about cleaning out the dust bunnies but decided that I'm not fixing what isn't broken. Please excuse my poor housekeeping.

[devilsindetails]

Something not right there. Check the continuity of the pot terminals: One end should be at ground; the other end should have continuity to R7; the wiper should have continuity to V3, Pin 2. If you've lost the ground connection, the pot won't do anything.

Ok, checked pin connections for continuity at Reverb pot and found the wiper was intermittent to V3 Pin2...bad solder joint...resoldered and reverb pot is now working.

Now back to this damn footswitch configuration.

Phil S the GA17RVT footswitch wiring has me really confused if you look at the original footswitch wiring schematic I posted and have now re posted the connections are not the same.

There is no braided wire running through the length of the footswitch chord I have and thusly no center conductor. I can only deduce that like me the previous owner simply didn't see any purpose in a shield that runs nowhere.

In your footswitch the braided chord runs to an off pole while the center conductor runs to the on pole and a wired bridge between reverb and tremolo off poles. Would that be a correct understanding of this?

Does your Gibson have a five pin connector...would it be possible to open the plug end and see how its configured in there? ie: what wires are attached to what pins?

What I would really like to see, of course is the footswitch connections of an actual GA15...I'm going to look at the schematics for the GA17 and see if these connections are actually the same.

[Phil_S]

I'm attaching the re-drawn schematic of my Minuteman GA20-RVT, which is more like the Explorer we are discussing. I have the "other" Minuteman, not the schematic commonly floating around the internet. There may actually be a 3rd version, but I digress and will save it for another time. Double click the blow up the schematic. I copied this manually from the one glued inside my amp. I believe it to be accurate and faithful, but I'm human, so please cut me some slack if there is an error. Also, I didn't have every required correct symbol, so sometimes I used what I had that was close.

I labeled the terminals with letters, but kept the orientation, so you can sub the correct numbers. As you can see, only C, D, and E are indicated on the switch side. I think the braid is simply omitted from the drawing. As I understand it, it was commonplace to imply connections that were "obvious."

I tried to open the pedal, but was unable to dislodge the Masonite bottom and the corners of the plastic (?) switch housing started to show stress fractures so I won't be going further with that. The Scout didn't come with a bottom, so I made one of cardboard and could easily see the inside of the pedal on that one. I believe they are the same inside.

I pulled the plug at the chassis and removed the cover. I found 3 wires and the shield connected to the plug. I expect the shield is connected at the reverb switch like you see in the picture I posted earlier.

I have a minor problem (mental block) matching the orientation of the switch to the schematic. The wires are connected in this order: White, Black, Red, open pin, Braid. The White is on the key pin, the one that is further apart from the other 4 pins. I was unable to get a good picture, so sorry. By the rotation, I think the only possible is:
A/1=unused
B/2=Braid (rev)
C/3=White (rev)
D/4=Black (trem)
E/5=Red (trem)

It seems peculiar that the braid and the white are attached in the schematic to a single terminal, but I am reasonably sure that's not actually what is done and I am convinced it is an implied connection not explicitly shown on the schematic.

Aha! I took one more pass at the pictures from my Minuteman and found this partial of the schematic glued to my amp of the relevant part (sorry, upside down). This one shows the shield/braid on terminal 2. I also found one low res photo of the socket inside the amp -- not great, but it shows a bit of buss wire going the chassis.

Regrettably, I'm not anxious to pull the chassis on this amp. It is not so easy to get it out and my bench is quite a mess at the moment, leaving me not enough space and complicating the task. If you are desperate and are able to wait, I will see if I can make the time to do it. Honestly, I think we have enough info here already.

That's my 2¢. Hope it helps. Good luck.

[devilsindetails]

Phil_S...

You've gone to tremendous lengths for me and for all you know I could be a one-hit poster....so thanks very very much...no I don't expect nor want you to go pulling apart anything unnecessarily...I truly appreciate all the trouble you've already gone to.

Thanks to the other few and brave who weighed in on this problem as well.

I've worked on a few tube-based Fenders, Marshall, Garnets etc. and this has to be one of the most exasperating stupid problems I've ever encountered and the Gibson chassis layout leaves much to be desired..to say the least! The tag board isn't even shown on any schematic I've ever seen rendering notations like C15 or R33 pretty much irrelevant to any numbers notated on the tag board.

Just to prove I wasn't being to hard on the ole GA15RVT I've let a few other local guitar DIY and professional techs look at the footswitch schematic and wiring as well and got...5 different interpretations and solutions which tells me I'm not the only one befuddled by Gibson's wonky diagrams and wiring implementation.

I'll give your pedal schematics a try, I've wired this footswitch everyway possible with no success... so you'd think I'll stumble across the right set-up eventually.

Regards. Leon

[Phil_S]

I found a good quality soft copy of the GA20-RVT schematic that Gibson emailed to me. I've cropped it for the pedal assembly. The two amps are from the same production era, with identical cosmetic treatment (elephant hide, front panel appearance, badge, grill cloth, etc.) It is more than reasonable to assume the same pedal assembly. The one I showed in the photo is from the Crestline era, which immediately precedes these Whiteface era amps. They are only about 1 year apart in production, though and the cosmetics of the pedals are identical, including the grey multi-conductor wire and the colors inside the grey outer insulation.

This one also shows very clearly the braided shield goes to terminal 2 on the plug. I never looked at it so closely before. It clearly shows that tremolo is off when open and reverb is off when closed.

I suspect when you look inside the amp at the socket, terminals 2 and 4 are bridged and I know that bit of buss wire goes directly to the chassis.

Ordinarily, I'd say that it is correct to wire the shield to ground at only one end, as it is generally intended not as a circuit ground, but as a RF shield, essentially an extension of the chassis. Since we have a visual on an exposed set of switches, it is probably a safe bet that the schematics are not fully complete. Also,I don't believe there is anything about what we see in the photo of the switch assembly that would cause a ground loop, so why not do it that way?

I can fully appreciate that you have several differing opinions on how to wire this. Gibson amps are not known for consistency. If I had this amp on my bench, I'd do it the way it is done on the switch assembly I showed you. You have nothing to lose and everything to gain.

Sorry for bitching and moaning about pulling the chassis. I'd have done it in a heartbeat if the bench was clear. I've pulled this chassis a number of times and even built a jig to hold it steady when out of the cabinet. It's just that I need an area about 3' x 5' open to do it comfortably, which means I've got to disrupt what's there now. I have been wanting to pull the chassis to modify the notch filters on this amp as they are not tuned to my liking, but it has now been a back burner project for at least a year. Let's say I've got desire without motivation.

I'd like to know how it turns out.

[devilsindetails]

Thanks Phil_S..I will let you know...but even your diagram like mine does not actually show the braided terminal terminating inside the footswitch...and there is no connection at the on/pole of the reverb switch?

Terminals 2 and 4 in the chassis are not bridged but go to grounds on the tag board.

The copper wire (buss wire?) pictured on my plug is a temporary replacement for the original wire leading to pin 3. (The original was intermittent). Yes...I have checked all continuity of pins to chassis connections and from chassis connections to circuits.

I'm getting the distinct feeling that I'll have to find another GA15RVT pedal and see exactly how its wired inside the footswitch....but I am going to try all your suggestions. I REALLY APPRECIATE YOU HELP PHIL!

[devilsindetails]

Ok...so I managed to secure another fully-working GA15-RVT...(I tested all of it including footswitch--all working as they should)

Plugged in my rewired GA15-RVT footswitch...and guess what? It works perfectly on the substitute GA15RVT I brought to my workbench.

I would note that my rewired footswitch does not employ the braided shield and it works fine...my observations lead me to conclude that the braided wire at pin 2 is simply to prevent stray RF interference...the braided wire in the substitute GA15RVT footswitch appears to be bridge soldered to pins connected to the exterior metal housing of the pole switches and NOT to either side of the poles on the tremolo and reverb switches.

I don't understand the implementation of this at all quite frankly as I don't see how or what makes this part of any part of the active reverb/or tremolo circuits. I think it's purely for RF....how exactly may come to me after further reflection. What is clear is that whether or not the braided wire is used has no bearing on whether or not the reverb or term circuits will work in a properly working GA15RVT.

That still leaves me with the problem of why I don't have any tremolo on the first amp. I used the known good pedals from both amps and can't activate the tremolo circuit.

I took all the tubes from the known good amp and substituted in the problem amp and there was no change. I took all the tubes from the problem amp and placed them in the good amp and reverb and trem operated properly.

So I have to conclude there is a problem in the circuit. I can get reverb without the footswitch so tank and connections are ok. But if I jumper the reverb pin to ground I lose reverb as I should but don`t get any tremolo no matter how I attenuate the depth and frequency pots.

Any hints of what I should look for next Thanks everyone.