2-channel Dual Rectifier Rev. G - Parallel to Series Loop modification

[mungiisi]

I know this is a topic that's been discussed million times through and through, but I noticed that each one of the threads seem to either discuss of the three channel versions or have differences in the modification instructions.

I have a '99 2-channel Dual Rectifier Rev. G with the notorious parallel loop. I'm not happy with it and been thinking a long time of modifying it to series. I approached Mesa's support and they provided me with official instructions. I'll refer them here:

Converting ORIGINAL 2 Channel Rectifier/Trem-O-verb parallel FX Loop to a Series FX Loop.

Parts needed: 1 pc. #12A or 112A Switchcraft ¼ inch jack.

1. Remove effects “Return” jack and the orange 2-inch wire connecting it to the “Blend” POT.
2. Install the 12A or 112A jack in the “Return” position, very securely with a lock-washer inside as it was previously.
3. Move red wire from “Blend” POT to tip connection of the new “Return” jack.
4. Add jumper wire from “Send” jack at the Brown wire (tip connection) to switched contact connection of the new “Return” jack.
5. Make sure “normalling” contact on new “Return” jack works well when plug is removed.

Author: M B 12.03.02

Majority (if not all) of instructions I've seen in this board are instructing to move the orange wire from the "Return" jack to the "Blend" pot and desolder the green wire from "Send" pot. As you can see, these official instructions are a bit different.

I have been also reading that majority of people who have had their amp modified are still having some dry signal drain despite the mod. I would like to know if anyone reading this would've had the modification done in accordance with the Mesa's official instructions AND whether they have accomplished 100% working series loop?

 

[Jay Omega]

I know this is a topic that's been discussed million times through and through, but I noticed that each one of the threads seem to either discuss of the three channel versions or have differences in the modification instructions.

I have a '99 2-channel Dual Rectifier Rev. G with the notorious parallel loop. I'm not happy with it and been thinking a long time of modifying it to series. I approached Mesa's support and they provided me with official instructions. I'll refer them here:



Majority (if not all) of instructions I've seen in this board are instructing to move the orange wire from the "Return" jack to the "Blend" pot and desolder the green wire from "Send" pot. As you can see, these official instructions are a bit different.

I have been also reading that majority of people who have had their amp modified are still having some dry signal drain despite the mod. I would like to know if anyone reading this would've had the modification done in accordance with the Mesa's official instructions AND whether they have accomplished 100% working series loop?

I did the series mod on a Rev G per Boogie's instructions a few months back, I can run a test for you if you'd like. If I understand your question, a good test would be to plug an empty plug into the effects return to see if there is any bleed, did you have something else in mind? I think the way I normally have the amp set is with the effects send and loop active master at noon.

I tried to quickly sketch what I think is being described in the notes below. The schematic is from the tremoverb available online, which I traced to be identical to the Rev G.

You can see from inspection that there is a leakage path through LDR16 (FX loop bypass LDR), albeit small as the LDR will have high off resistance compared to the 47k on V4a grid. Leakage noise will be greatest when FX send is at its highest setting.

I can tell you that with a volume pedal in the loop, there is no sound when it's pulled back and there are no phasing issues with effects in the loop compared with bypassed.

 

[mungiisi]

I did the series mod on a Rev G per Boogie's instructions a few months back, I can run a test for you if you'd like. If I understand your question, a good test would be to plug an empty plug into the effects return to see if there is any bleed, did you have something else in mind? I think the way I normally have the amp set is with the effects send and loop active master at noon.

I tried to quickly sketch what I think is being described in the notes below. The schematic is from the tremoverb available online, which I traced to be identical to the Rev G.

View attachment 1675
You can see from inspection that there is a leakage path through LDR16 (FX loop bypass LDR), albeit small as the LDR will have high off resistance compared to the 47k on V4a grid. Leakage noise will be greatest when FX send is at its highest setting.

I can tell you that with a volume pedal in the loop, there is no sound when it's pulled back and there are no phasing issues with effects in the loop compared with bypassed.

Many thanks for extensive information and actual user experience of the Mesa's official mod.

I'd be happy to hear test clips if you can make such. I guess the way you prescribed with an empty plug in the return would be sufficient.

Regarding the amp after the mod, I have couple of questions:

• Can you still use the switch to switch the loop on and off?
• Does the amp work without a patch plug or effects in the effects loop?
• Do the Effects Send and Mix potentiometers work after the mod and if they do, how?

 

[Jay Omega]

Many thanks for extensive information and actual user experience of the Mesa's official mod.

I'd be happy to hear test clips if you can make such. I guess the way you prescribed with an empty plug in the return would be sufficient.

Regarding the amp after the mod, I have couple of questions:

• Can you still use the switch to switch the loop on and off?
• Does the amp work without a patch plug or effects in the effects loop?
• Do the Effects Send and Mix potentiometers work after the mod and if they do, how?

Yes to the first two questions. Effects send pot works but mix does not. Send works the same as before the mod

 

[TRENCHLORD]

I have several that are series-loop modded the OG mesa "lossless" way, like their original rectifiers were for a couple years.

The only difference is we decided on a "send-level bypass" mini-toggle to replace the mix pot. This way you have the option of removing the send-level attenuator while still having the loop and output-control remain engaged. Having it bypassed is basically the same output as having it on max, but it's just a little crisper and more defined. The difference is slight but it cost almost nothing and was a way to make use of the useless mix slot.

I have not noticed any dry-bleed at all, but I've never actually tested for it. Their loops behave and sound exactly like my Multi-Watt Triple loop.

 

[mungiisi]

I have several that are series-loop modded the OG mesa "lossless" way, like their original rectifiers were for a couple years.

The only difference is we decided on a "send-level bypass" mini-toggle to replace the mix pot. This way you have the option of removing the send-level attenuator while still having the loop and output-control remain engaged. Having it bypassed is basically the same output as having it on max, but it's just a little crisper and more defined. The difference is slight but it cost almost nothing and was a way to make use of the useless mix slot.

I have not noticed any dry-bleed at all, but I've never actually tested for it. Their loops behave and sound exactly like my Multi-Watt Triple loop.

Interesting read. Is the "OG Mesa lossless way" mod same what I described in the opening post?

 

[TRENCHLORD]

Interesting read. Is the "OG Mesa lossless way" mod same what I described in the opening post?

All of mine were done by a nearby mesa-authorized warranty tech. He used their schematic so I assume it is the same as you're saying. Lossless Serial Effects Loop was how Mesa originally advertised them iirc,,,and then they went to the parallel shortly thereafter. Nothing wrong with parallel if you just have one pedal, like a chorus or reverb.

 

[mungiisi]

Encouraged by the experiences of you guys I did the mod to my Rev. G Dual Rectifier according to the official instructions I posted in the first post. After brief initial test everything seems to work as supposed. I couldn't hear dry signal leakage either. I can straightaway say that dialing effected sounds is 100% easier now and the amp sounds so much better with effects than before.

I had to use the Switchcraft 12A jack as there wasn't any 112A or 112AX jacks available in my local store. For those who are interested I took before and after photos of my amp, please see below.

The original wiring parallel loop wiring (pre-mod):

The series loop wiring after the mod per Mesa Boogie's official instructions (post-mod):

 

[FlubbyRec]

If anyone wants to get fancy, you can modify a Fender S-1 pot/switch to a 25K lin pot and use it to replace the blend pot. Then you can switch the loop between serial and parallel at will. This will NOT work in a Trem O Verb because the reverb transformer is in the way. If anyone is interested, I'll post a drawing and pics later this week when I open the amp to replace some caps.

 

[painkiller]

Hi
i have done the mod too, but i still get that mad helicopter Noise with my Boss Chorus pedal....i have done it exactly like described.
The only difference i have a Dual Recti Rev. G.
Any ideas? Thanks