Triple Rectifier loop mod: picture of a "bad sounding" work

[DS-1]

Hi guys! In 2007 I've bought a used Triple Rectifier. The dealer told me it has the "loop modified". I supposed it had the common parallel-to-serial mod.

I starting using it and I loved its sound, but I really can't believe its loop makes the amp sound so bad. I mean: when I use the loop, the effects I use sound right, but my general sound, on any channel, losts some frequencies, and add a sort of "saturation" to the sound (I haven't a really clean sound using the loop), with any send\return knobs settings. Without the loop enganged, it sounds amazing.

This morning I decided to open the amp and see what's inside of it. Here a pic of the loop mod:

It seems to be an "not complete" serial mod, as I read in other topics of this forum. Now, I think that considering that these are the effects that I usually run into loop: EH Small Clone, EH Polychorus, Ibanez DE-7 Delay, Boss DD-5 Delay, what should I do?

1. Try to rewire the missing wire and pray for a good working parallel loop;

2. use a better serial mod.

If the point 2 is the way, what kind of mod should I do?

Thanks in advance for the reply!

 

[94Tremoverb]

First, make sure it isn't a headroom or tone problem with the effects pedals - this is quite common with some pedals, as they are often designed for guitar signal levels not the higher loop levels. Connect the send to the return with a straight cable and see if the problem persists - if it does, it's in the amp.

Removing that one wire should not affect the tone, but it's possible that either the FX loop tube (V4) or one of the buffering transistors is on the way out.

If it turns out to be in the effects pedals, try each one at a time to find the one responsible. At least it doesn't look like you have any pedals which digitize the dry signal path, which is a major cause of tone-suck. (The Boss DD-5 definitely doesn't, and I'm pretty sure the Ibanez doesn't either.)

 

[DS-1]

I have tone problems even with only a patchcord from send to return.

I've found a topic in this forum in which the serial mod consists in two (or three, now I don't remember) jumpers, removing the three transistors, too. Should I do that mod, or the one on my Triple is still a correct serial mod?

Now I don't have any other spare preamp tube to try it in the loop. What tube should I buy to replace it? Is there any way to check if the actual tube is correctly working?

 

[94Tremoverb]

You can 'borrow' V3 - which is only used on channels 2 and 3. Compare the Channel 1 tone with V3 and V4 swapped round - if the tone on the channel gets better (and the dirty channels worse, possibly), V4 is faulty. This is a possibility because it's a cathode-follower position (as is V3 actually) and some tubes don't work well in this type of configuration... mostly Russian-made 12AX7s. If you're going to buy any new tube for V3 or V4, make sure you avoid Russian-made tubes, including the Mullard and Tung-Sol 'reissues'. Some of them don't seem to be affected but it isn't really worth the chance. The standard Chinese 12AX7s are fine.

If it's not a tube problem, you may want to go for a more thorough series mod. What's been done is technically a series mod too, but it still leaves the transistors in the signal path.

 

[DS-1]

Thanks a lot for the analysis.

I'll try swapping V3 and V4 and see what happen.

Svetlana or EH 12AX7 should be fine in V3 and V4 position? What do you think about JJ 12AX7 / ECC83S?

About the "alternative" series mod: are you talking about the mod with jumpers, removing the transistors, found here http://forum.grailtone.com/viewtopic.php?f=24&t=36840&hilit=rectifier+loop?

 

[DS-1]

I swapped V3 and V4 and...the amp sound fine, with a patchcord in send\return or even with 2 pedals (an analog Ibanez delay and a Boss chorus).

So I swapped again V3 and V4 and...the amp sound the same: fine, without lossy signal and\or distortions! I don't know if I'm going crazy or what...

I have to say that I haven't tried with my usual setup (Fender Jaguar and the EH Small Clone, EH Polychorus, Ibanez DE-7, Boss DD-5 in the loop) and I haven't tried at the volume I usually use the amp (maybe a high output volume and a high preamp volume can add gain\distortion to the final sound?).

 

[94Tremoverb]

High channel master volume settings certainly can - it's before the effects loop (before the send). It won't be the output level because this comes after the loop. If you get the distortion back at gig volume, try raising the output level and reducing either the channel master or the FX send level to give the same final volume.

A friend of mine had the same problem with his Rectoverb (which doesn't have a send control), so much that he couldn't get the channel masters low enough to stop one of his pedal distorting without getting into that range where the control is too jumpy, so I modded it for him with an extra resistor to reduce the range of the master, which fixed it.

 

[DS-1]

It seems to be the kind of problem I have with my Recto, but with the difference that I can hear a little different sound, with the loop on, even with not so high pre-volume values (I have now my channels volume on 10-11 o'clock, which is honestly not that loud for a Triple Rectifier!)

Tomorrow I'll try putting a switch to instantly move from parallel to serial loop and see if i'll find any differences in sound.

By the way, my Recto with this mod hasn't anymore the "FX LOOP" switching working from the pedalboard.

 

[DS-1]

I added a switch between the pots and the PCB, so I can switch from serial to parallel loop. I've notice that there's no difference in sound with 2 effects in the loop (analog delay and Boss chorus).

The strange thing is that, even with the parallel mode, the FX LOOP on the pedalboard still doesn't work. Should it works like the LOOP button on the old Mark IV? I had one and when I pressed it, the sound returns to be dry.

 

[DS-1]

Test done with my usual pedalboard and guitar (Jaguar with SuperDistortion on bridge position): obviously there's plenty of distortion added to the normal sound, also using parallel loop, even if I set the send pot to a very low level.

Then I tried to connect every single pedal of my pedalboard, and it still has that distorted sound, that I would like to record to let you ear what I mean.

So I suppose there's something about the loop that doesn't work good. Is it possible that one, or both transistors saturate when effects are connected to the loop?

 

[94Tremoverb]

If the loop switching isn't working even when set back to parallel I suspect something may be up with the loop transistors. Does it not switch off at all, or does it go to silent?

 

[DS-1]

I dunno what's the right function of the FX LOOP button on the footswitch. I suppose that it should work like the Mark IV one: the button should "turn off" all the effects and leave only the clean sound.

In my case, nothing happens: pressing the switch doesn't "bypass" the loop, so the sound is still effected.

 

[DS-1]

Does the 2 J175 on send\return can affect the sound in quality? If so, I would like first to do the mod removing the transistors. If the output volume will be to low, I can try to change those 2 transistors.

 

[94Tremoverb]

Do you definitely have the FX loop set to Footswitch on the back panel? If so and the loop is not bypassing, there's something wrong with the switching circuit, or it has been deliberately modded to remove the main disadvantage of that 'crude' parallel mod, which is that bypassing the loop mutes the amp.

Bad JFETs could affect the tone and possibly add distortion, I think - rather than just not working altogether.

 

[DS-1]

Bad JFETs could affect the tone and possibly add distortion, I think - rather than just not working altogether.

It's what I wanna test. Do you think that modding the loop removing the JFETs, doing jumpers seen here: http://forum.grailtone.com/viewtopic.php?f=24&t=36840&hilit=rectifier+loop could decrease the output volume?