5E3 Effects Loop/Mods??

[The Ballzz]

First, allow me to admit that although I've built a few amps, I am by no means an "Amp Builder" instead, more of a "paint by numbers" kind of guy. That said, my most recent was a 5E3 from a MojoTone small parts kit, chassis and did it all stock, other than a few substitutions such as turret board construction, a multi tap OT, higher wattage dropping resistors and adding screen resistors. I also opted to use a 12AX7 in V1 instead of the 12AY7.

This is by far the best amp I've ever owned/used/played through, though I find myself wanting to make it just a tad more modern in the "gig-friendly" department. While I don't utilize foot/stomp/pedal/thingies to "define" my sound, I do like to occasionally add a some gentle chorus, reverb and I'm a tap-tempo echo junkie and have never found a boost unit that I like. These items work best in a "proper" loop, instead of in front of the amp, for many obvious and not so obvious reasons. It seems that the later in the signal chain a loop is inserted, the better it sounds for especially to echo, so that overall sound/character/overtones/distortion is more fully developed before being fed into the effects. The best I've ever used was a two amp, wet/dry rig where the effects were fed from a line level tap off the speaker out of the "dry" amp and then into the second "wet" power amp section, avoiding it's preamp. Sadly, hauling, setting up, dealing with such a rig is a royal pain in the arse!

So to make a long story even longer, I have a couple of mods (similar to some on robrob's website, but with a few variations) I'd like to do and would appreciate some advice and guidance. The most important aspect here, is that I want to absolutely be able to get right back to where the amp is now, on the fly, in a live performance situation, as stock form is the basis for my core sounds and I just want to add a few "operational" conveniences to the picture! FWIW, I find my best "core sound" plugged into Bright Hi, no jumper, with the tone wide open, Bright Volume about 9 1/2 (scale of 1-12) and Normal Volume about 6 1/2. I should also add that I have on hand a small pile of specially ordered dual concentric, 1MΩ pots (it seems I have the only ones on the planet) that may help in my endeavors.

First Planned Mod, Effects Loop:

A) On Rob Robinette's website, he shows a passive effects loop inserted just after the normal volume pot and also alludes to also using a Metro ZeroLoss loop instead.
https://robrobinette.com/5e3_Modifications.htm#FX_Loop
My plan is to use either that Metro loop or even more likely the one from Granger as it appears to allow a wider range of supply voltage and has a couple of additional features that the Metro does not:
http://www.grangeramp.com/ufxloop.php
B) Before digging in here, I'm pondering the wisdom/effectiveness/ramifications of placing the effects loop after the next triode stage, in the same location as Rob shows the Master Volume, which I also plan to add to accommodate some of the other mods?
https://robrobinette.com/5e3_Modificati ... ter_Volume
C) I'm guessing that IF this a suitable location for the active effects loop, I'll need to experiment with having said loop either "before" or "after" the Master Volume for best possible operation? This Master Volume pot will likely be one side of a dual concentric that I may switch with a relay system, with the other side of the same pot being used for the Bright Volume pot.​

Second Planned Mod, Cascaded Channels:

A) Again, with references to Rob's great website, I want to add the switchable option of cascading the first two triodes, with having the "non-cascaded" default position plugged/routed into the Bright Hi input, for operation exactly as the amp currently is. This would likely be utilizing another dual concentric pot, with one side as the "Gain" pot for the cascaded mode and the other side as the actual Normal Volume during non-cascaded use/mode.
https://robrobinette.com/5e3_Modificati ... in_Channel
B) I'm making an assumption that the Master vole may not need to be "in circuit" for the non-cascaded mode, but if it is, I could simply use another dual concentric in the tone position with one side as a separate Master and the other side for the tone control.
​
My goal here is to have a nicely functioning effects loop, as late in the circuit as possible and simply a foot switchable choice between cascaded and standard two channel modes. It seems the relay switching and dual concentric combinations could facilitate having the Masters and Volume controls "pre-set" to compensate for the unwanted, added gain at the input to the PI. I don't need a wide variety of sounds/tones, as I do all that with my hands, guitar swaps and pickup settings on the guitar. I simply want the cascade mode for a boost that doesn't change the sound, but just adds a bit of gain and/or overdrive.

Is This Doable, Or Am I On Drugs?
Gene

[pompeiisneaks]

First off, I've not looked at every one of Rob's pages on his site, but every one I've reviewed looks correct to me. Also I've seen when he adds content, before he calls it 'done' he spreads the new pages out to tons of amp guru's for confirmation. I've also heard of quite a few people that have successfully done his mods. I'd say you've nothing to fear from any of them so far as I can tell.

For you specific use case, I'd suggest you post the schematic of the amp you built (I know you mentioned the differences, but having the expected amp and knowing the differences means people can confirm that what you're asking 'will or won't' work.

~Phil

[The Ballzz]

Well Sir,
Here's a schematic with the couple/few "differences" shown, as well as proposed locations for either passive (not likely) or active effects loops. Also a link to the "pre-made" loop I'm considering. The loop draws less than 2ma and would likely get powered from the screen node of the power tubes or the PI node.

http://www.grangeramp.com/ufxloop.php

Deluxe-5E3-schematic copy.jpg

Thank You,
Gene

[pompeiisneaks]

I think the location of the zero loss looks good personally. Also I'd recommend the active loop, as it's going to not have tone loss due to the loop if used. This is the big reason the active effects loop are always preferred. I've never installed one, though so I'm speaking from what I've read etc. The metro loop has had good reviews everywhere I've seen them. Others probably can give more background from real use.

~Phil

[sluckey]

If you decide to connect a "zero loss eff loop" at the grid of that PI you must use coupling caps. There is a pretty big dc bias voltage at the grid of that PI. If you don't use coupling caps you will upset the bias of the PI and you will also send that dc voltage into your loop circuit.

[The Ballzz]

If you decide to connect a "zero loss eff loop" at the grid of that PI you must use coupling caps. There is a pretty big dc bias voltage at the grid of that PI. If you don't use coupling caps you will upset the bias of the PI and you will also send that dc voltage into your loop circuit.

What would be an appropriate value? Can I assume that I would simply "insert" the loop where noted and add another capacitor between the output of the loop and the PI grid? In what way(s) might this extra cap impact the signal and it's tone going to the PI? Might it be best to "split" the capacitance between the the "pre-loop" and the "post loop" caps, so that the total capacitance is the same 0.02 as the stock coupling cap, let's say like a 0.04 before and the same after the loop? Of course, that would be assuming no capacitance value for the whole loop circuit.
Thank You,
Gene

[pdf64]

22nF would be fine for both, as the corner frequencies for the filters they comprise are in the sub-sonics.

But before you go too far in planning the fine detail of all this out, I think it would be a good idea to check out whether the MV / cascaded gain mods are to your liking. And then whether the switchable cascade is actually feasible (as the margin of stability will be much reduced).
As without sufficient preamp gain and a MV (or a control that acts as a MV), the benefits of an fx loop may be questionable, or a least much reduced.
FYI active fx loops such as the Metro are ususally recommended for insertion in the feed to the MV (rather than after the MV).

[pdf64]

First off, I've not looked at every one of Rob's pages on his site, but every one I've reviewed looks correct to me. Also I've seen when he adds content, before he calls it 'done' he spreads the new pages out to tons of amp guru's for confirmation...

It's a fantastic site, and kudos to rob for getting it done, it must have taken a mountain of work.
But there's a lot of stuff up there, and it doesn't take much looking to find content seems technically questionable to me.
And (as is his right), I seem to recall that even after such issues have been drawn to his attention, he's happy to leave that content up there if he still thinks it's correct.

The point being, the site's content should not be considered 'peer reviewed' / a reliable technical reference, in the way that Aiken or Merlin's sites are.

[The Ballzz]

If you decide to connect a "zero loss eff loop" at the grid of that PI you must use coupling caps. There is a pretty big dc bias voltage at the grid of that PI. If you don't use coupling caps you will upset the bias of the PI and you will also send that dc voltage into your loop circuit.

Please inform the uninformed? I'm not seeing where that "pretty big dc bias voltage at the grid of that PI" would be coming from? Please remember that I'm kind of a "paint by numbers" sort of guy and that I may be missing something obvious.
Thanks,
Gene

[sluckey]

It comes from the cathode. You have a 5E3. Check it with your voltmeter and see.

[The Ballzz]

It comes from the cathode. You have a 5E3. Check it with your voltmeter and see.

Yeah, I'm trying to make most of my plans before digging in, though I do now see/understand it coming from the cathode. DUH on my part!

As far as the cascaded gain stage mod, I will likely forego that for the time being and simply resign myself to finding/using the most transparent buffered boost in front of the amp, as this will also accommodate a longer cable run if needed. While I'd love to do it all on board, in the amp, with a relay switching setup, providing adequate power for the relay system becomes rather cumbersome. Modifying the whole power supply system becomes so invasive that I'd likely be better off just building another amp with these mods already planned into it's design. No big deal, as I love sniffing solder fumes anyway!

I just happen to have a 10 watt 6AQ5/JCM800/2203 build that isn't seeing much use and the iron in it will likely be suitable and robust enough for said build and the current chassis has plenty of real estate! Simply yank the complete turret board out, swap the 7-pin sockets to octals and go to town. I really love the character imparted by the cathodyne phase inverter. While not for everyone, that PI seems to be one of the keys to a 5E3's magic!

The loop experiment will definitely be a go though and fairly simple/convenient as it's a turret board build with all connections (even the jumpers) done above the board! This amp is truly glorious and I want to be able to put right back to where it is, if the loop isn't to my liking!

Thanks Again Folks,
Gene

[dorrisant]

From experience, the Jet City loop is great. I couldn't tell any difference between active or bypassed in a few amps I've installed them in. Much cheaper than the Mojo or Grainger. Input and output trims can be installed as well.

[The Ballzz]

From experience, the Jet City loop is great. I couldn't tell any difference between active or bypassed in a few amps I've installed them in. Much cheaper than the Mojo or Grainger. Input and output trims can be installed as well.

A little info and a source for said loop would be helpful. When I goggle Jet City Effects Loop, the first things that come up are comments about how the ones in their amps suck?

Please Elaborate?
Gene

[dorrisant]

Loop info: https://tubeamparchive.com/viewtopic.php?f=6&t=29741

Yes, you may have to buy the nuts for it separately... still way worth it. I posted a spacing diagram on the last page. I see the links... but personal experience tells me otherwise. I installed this loop with true bypass and can hear absolutely no difference in or out. https://tubeamparchive.com/viewtopic.php?f=9&t=30633

[The Ballzz]

Thanks for the links. I'll likely read them in their entirety, as well as the links within the links. And I've got plenty of nuts, as most of us squirrels do!
Thanks Again,
Gene