parallel FX loop

[tubenit]

I've done a number of FX loops on board in amps and made several D'Lator type off board FX loops. 

I've tried series and parallel switches in the past only to find that I did NOT care for the parallel tone and strongly preferred the series.

However,  on the TBM with 5879 OD,  I could not get "the" tone that I wanted in the FX loop using a MXR Carbon Copy delay. I don't know exactly how to describe it but it sounded sort of "artificial" meaning that it was stealing something from the warmth/touch sensitivity of the amp and adding something that I didn't want.

So, I tried this parallel FX loop by simply adding a 470k resistor.  I did try other values from 56k to 560k and found the 470k worked best for me to get the right blend of parallel tone.  Schematics I looked at typically used a 220k with a 500p which I did NOT care for.  I did try paralleling a 150p to .001 cap across the 470k but ultimately left it out. 

Essentially, I simply put a 470k from the send pot to the "in" on the return jack. That's pretty much it.

This seems to add some warmth and more of a "natural/organic" tone to the FX and delay, IMO.  I tried this on two amps and got similar results.  I wished I had better adjectives to describe it but simply put I like this better.

My best guess is this may be a mod that works well with some amps and perhaps not so well with others?   Anyhow, thought I'd share it as I am pleased with the results which were significant enough to A/B and pick out which was which.

With respect, Tubenit

[SILVERGUN]

Funny you mention it, 'cause I was just thinking about this...
You're idea is very similar to the Mesa (Rectoverb- which I own) FX, where they have a 25KL pot there labeled as a MIX control, and no effects send or return level controls...

I haven't done much experimenting with the FX loop,,but with just trying to get a decent delay sound dialed in, I was wondering about options...
I did notice that the send sounded best down around 2-3, and could just be a fixed value,,,because some guys (like me) might try to use the pot as an extra gain control    (and probably overload the input of their pedal)

Mesa also labeled your "effects level" control as the "output level" (master),,,BUT added the SOLO (circled in red) pot as a footswitchable boost that I really like a lot as a way to "step out front" when the time comes.....

I put a young gun guitar picker in front of the 5879 the other day, and he didn't want to get up.....he said "WHAT's THIS???....what's with the sustainnnnnnnnn ?             

[SILVERGUN]

To expand a little more on your thoughts about the use of the delay in the loop,,,
I have an older DOD Echo Plus that has a MIX control built in, and with it connected through the loop of the TBM 5879 I didn't want to turn that mix control past 1....it seemed like as soon as I started turning it away from zero, I was getting plenty of effected signal,,,,

SO, I really think this mod makes a lot of sense.....

Maybe a 500K MIX pot, and dial to taste? 

[tubenit]

Maybe a 500K MIX pot, and dial to taste?

I think that would do it.  The Mesa 25k "mixing" pot definitely would not work for what I wanted.  Not high enough value.

With respect, Tubenit

[SILVERGUN]

Maybe a 500K MIX pot, and dial to taste?

I think that would do it.  The Mesa 25k "mixing" pot definitely would not work for what I wanted.  Not high enough value.

Yeah T ,,,looking at it closer, I guess the 470K is in parallel with the 100K series resistor coming off of the return jack, plus the value that is determined by the placement of the send pot..
So if we did a fixed value send, and eliminated the 100K off the return jack,,,,we could probably just get away with a 100K or 50K "mix" pot

Either way it is a great addition to your circuit, and I'll be adding it shortly......nice touch 

[SILVERGUN]

This seems to add some warmth and more of a "natural/organic" tone to the FX and delay, IMO.  I tried this on two amps and got similar results.  I wished I had better adjectives to describe it but simply put I like this better.

I've got an adjective for you....AWESOME!

Great thinkin' T......here's why it's so perfect.....the TBM sounds incredible with nothing in the loop,,,the loop just adds dimension and gain to the circuit..
And initially, when I plugged in my delay, it felt like a bit of a tone suck, and I had a hard time dialing in a great tone, and had a very limited range of control of useable delay.....and I thought my specific delay pedal must just suck tone...

BUT...after hooking it up like the drawing below, I CAN get a really great sound and use a huge delay sound, but dial it back and MIX IT WITH MY ORIGINAL SIGNAL.....
I gave up the effects send pot and traded it for a mix control, and I'm not looking back....I'm still gonna have to mess with values, BUT this is staying

1000% improvement.....I can't say enough  

Thanks for making me think  

[tubenit]

SILVERGUN,

Hey man,  I really do appreciate your posting the results of your experiment!  It seems to be a very significant improvement for me also.
I'm glad it's working out for you.  I wished I had done this sooner. 

On my FX,  I have a send pot,  fixed return resistor and a level pot in the FX.  Lately, I would have the send at 3-5 and the level at 5-7 (prior to this mod).  With this parallel mod, I have the send pot at 5-7 and the level pot at 3-5.  It gives the amp a "BIG" tone with about  the same amount of delay coming thru.

With respect, Tubenit

[SILVERGUN]

Hey man,  I really do appreciate your posting the results of your experiment!  It seems to be a very significant improvement for me also.
I'm glad it's working out for you.  I wished I had done this sooner.

Well, I really appreciate you posting the idea!

Just to clear it up a little for anyone who might be reading along:
- Before the parallel mod, my entire signal would pass through the delay pedal, and I was at the mercy of the controls on the pedal for the amount of delay to dry signal mix....it felt like it took some of my original tone and squashed it,,,and I had to work very hard on balancing the send level with the return level PLUS the controls on the pedal

-After putting the MIX pot in there, I can crank up the onboard mix control on the delay pedal, and find the sweetspot of the pedal, where the delay is just huge,,,and then blend that effected signal back into my dry signal, and not lose any clarity of the dry signal......T just chose a set value resistor and doesn't need to add a MIX pot

I do realize that this is not a major revelation in the industry,,,but I was able to witness firsthand, the difference between it and the series loop, and it is night and day. IMO.

I'm going to try a 12DW7 in that spot so I can have the 12AU7 triode set up as the send,,,and the 12AX7 half as the return.
I'll let you know how that goes.

Side note:
I also noticed that you had added the cathode bypass cap on the 5879, and I just wanted to let you know that I have done the same thing, and IT too is staying  
I'm working on reducing/balancing the gain in some other spots to balance the switching from clean to OD......and will be adding the SOLO pot  

[tubenit]

I'm going to try a 12DW7 in that spot so I can have the 12AU7 triode set up as the send,,,and the 12AX7 half as the return.
I'll let you know how that goes.

That's a great idea!  I'll be interested in hearing the results of that.

Sometime back, I bought a "reversed" 12DW7 where the 12AU7/12AX7 is reportedly swapped from what is "normal"  I may give that a try and if I do, I'll report if there is anything significantly interesting or positive from it.

With respect, Tubenit

[Geezer]

I tried the 470k mod on my FX loop and....it's a keeper!

Definitely added clarity to my rig, and so simple and easy to do.

Thx guys for the work on (and sharing of) this mod

G

[jojokeo]

I'm thinking it's mainly for use if you have a control pot and/or voltage divider in the fx loop there? So this would help to lower the resistance in the signal path yes?! No?! Yes!? 

[tubenit]

I finally had a chance to try this on my last/3rd amp.   Ironically, there was not much "oh wow" factor using a 470k so I experimented with different values. 

I eventually went with a carbon comp 220k resistor which sounded best to me and did have an " oh wow" factor improvement.

I'm thinking now that each individual amp may have a "sweet spot" that could be found experimenting with resistor values.

So, now I am thinking that SILVERGUN's idea of using a potentiometer may be the best solution. Maybe try a 500k or a 250k first using
alligator clipped wires.

with respect, Tubenit

[SILVERGUN]

T, I kinda glossed over this in reply #4 because I didn't want to make it seem like I was correcting you....

The 470K resistor that you suggested using appears to be parallel to the series resistance already in the circuit, so that's why I came up with the lower value.

The variable is wherever you have the send pot set,,,,so lets say, for example, that pot is on 5 and represents a 50K value.....add that 50K to the 100K resistor coming off of the return jack and see the total of those 2 resistances of 150K as being parallel with the 470K resistor and the combined value is now = 113.7K,,,,so I used a 100K pot and left the 100K resistor in series after the wiper of the MIX pot, so it does not affect the overall resistance value anymore...

And, so far, I haven't wanted to go past halfway on that pot so I am thinking that 50K will provide enough range of MIX for me.

It's a must have mod for me because it really keeps the original tone intact...
Thank you so much for all of your hard work and research!

[Tone Junkie]

SG so I have been following what you guys are working on here but what you just said doesn't match with your schematic you posted,so I was confused.
Thanks Bill

[tubenit]

The variable is wherever you have the send pot set,,,,so lets say, for example, that pot is on 5 and represents a 50K value.....add that 50K to the 100K resistor coming off of the return jack and see the total of those 2 resistances of 150K as being parallel with the 470K resistor and the combined value is now = 113.7K,,,,so I used a 100K pot and left the 100K resistor in series after the wiper of the MIX pot, so it does not affect the overall resistance value anymore...

You may absolutely correct in how you're thinking about this. 

My thinking (which may be in error) is that since I am using either a delay or a reverb pedal in the active FX ............. & that pedal has all kinds of caps, resistors and other thingamajigs in the circuitry and signal path that the normal application of paralleled resistors to determine resistance doesn't apply.
 

So, in light of that,  I just use what sounds the best to me which is the final criteria for me anyway. 

With respect, Tubenit

[sluckey]

the normal application of paralleled resistors to determine resistance doesn't apply.

That's correct.

And it may be likely that if you put a different pedal in the loop that you could prefer a different value resistor in the parallel path.

[SILVERGUN]

SG so I have been following what you guys are working on here but what you just said doesn't match with your schematic you posted,so I was confused.

The schematic that I posted in reply #5 is the one I'm currently using, and it's a combination of what T suggested and the Mesa schematic...

The last one I posted in reply #12 is T's original post, but I highlighted the resistances that I believe are in parallel, which may be skewing his final resistance value....

Maybe someone else can look at it and tell us if my thinking is on track.....

....and then there was sluckey  
And it may be likely that if you put a different pedal in the loop that you could prefer a different value resistor in the parallel path

So,,I'm thinking pot is a good choice..........let's just go to Colorado and get it over with  

[SILVERGUN]

the normal application of paralleled resistors to determine resistance doesn't apply.

That's correct.

So what does apply?....is there an explanation so I don't just have to feel 100% wrong  

[sluckey]

I think this is a case where you just let your ears determine the correct resistance. I don't think you'll find any electronic theorem to solve for a 'correct' value. What is the definition of 'correct' value anyhow? I bet you're definition would be different than tubenit's definition. And what about the guy that is gonna put a string of pedals in that loop?

The pot is a good idea unless you will always be using the same pedal and don't want another knob to tweak.

I would not go to Colorado just yet though. They are in morning. Be respectful.   

[SILVERGUN]

Thanks again for taking the time to correct my flawed theory..
It's definitely not my intention to run about, spewing mis-information....'specially when it comes to Mr. Tubenit

 

[SILVERGUN]

I have one MAJOR mistake to report:
-In my last schematic (REPLY #5), I had eliminated the FX send pot and opted for a fixed value of 10K in place of that pot...
Well, that value is way too low, and I had come up with it while tweaking an OD tone with everything cranked....with the amp set like that, 10K is OK because there is a huge signal there and 10K knocked it down real good.....
BUT, when switched to a clean channel, there was not enough signal to push past that 10K and it killed the clean tone

- I switched it out for a 33K to simultate a setting of 3 on a send pot, and that appears to be a much better solution,,, IF you're gonna use a fixed value resistor instead of the send pot

[SILVERGUN]

I'm going to try a 12DW7 in that spot so I can have the 12AU7 triode set up as the send,,,and the 12AX7 half as the return.
I'll let you know how that goes.

I got around to trying this last night and even though it wasn't appropriate for the current amp I'm tweaking,,,I could see it being useful for someone who wanted to add an FX loop that ALSO added a gain stage.
It introduced a large gain/volume boost that I just didn't need,,,,now

The return triode is currently biased like a standard 12AX7 gain stage,,,so I think I'm going to try to cool it down with the 12AU7 in there and remove the cathode bypass cap, and use a higher cath. resistor value... ....and see how that sounds....for me

In my certain situation, I have enough gain BEFORE the FX loop, so this MIGHT be a cool way to find the "sweetspot" of that AU7 return triode 

DISCLAIMER--- I am an obsessive tweaker who has been known to ruin perfectly good designs by over-tweaking  ......take what I say with a grain of salt

[jojokeo]

SG, to me that 10k (grid return if outgoing is for another tube effect or just an impedance reference to an effects box) is a very low value and even the 33k or 47k there would be actually really low values loading down a lot of your outgoing signal unnecessarily. Have you tried 1M there or even 470k and found it not acceptable?

[SILVERGUN]

SG, to me that 10k (grid return if outgoing is for another tube effect or just an impedance reference to an effects box) is a very low value and even the 33k or 47k there would be actually really low values loading down a lot of your outgoing signal unnecessarily. Have you tried 1M there or even 470k and found it not acceptable?

Good thinkin jojo,
The original design had a 100K pot there, and when I first had a send pot in there I found myself just setting it to 2-3, so I figured I'd just install a fixed value and lose the pot.....
I don't know what made me put 10K in there at first other than the fact that I had everything wide open and it "seemed" to calm things down a bit......we'll yeah, it did,,,,and took some tone with it.
So no, I hadn't tried any other, larger values,,,but I will now.
AND, I'll look at that 82K on the return side as well.....
Part of my problem is that my delay pedal has input AND output volume controls (ahh, the good old days)
Good lookin out  

Nice avatar!

[jojokeo]

SG, to me that 10k (grid return if outgoing is for another tube effect or just an impedance reference to an effects box) is a very low value and even the 33k or 47k there would be actually really low values loading down a lot of your outgoing signal unnecessarily. Have you tried 1M there or even 470k and found it not acceptable?

Good thinkin jojo,
The original design had a 100K pot there, and when I first had a send pot in there I found myself just setting it to 2-3, so I figured I'd just install a fixed value and lose the pot.....
I don't know what made me put 10K in there at first other than the fact that I had everything wide open and it "seemed" to calm things down a bit......we'll yeah, it did,,,,and took some tone with it.
So no, I hadn't tried any other, larger values,,,but I will now.
AND, I'll look at that 82K on the return side as well.....
Part of my problem is that my delay pedal has input AND output volume controls (ahh, the good old days)
Good lookin out 

Nice avatar!

On the avatar I had some old pictures and forgot I used it on another site after Ed brought it up so I thought I'd put it up here. I'd rather use it here than anywhere else actually. My buddy is in the background but the photo's been cropped. BTW, I still have that V too! 

You had a steady load on the signal via the 100k pot in there but w/ the voltage divider set as you say represented possibly 33k or 47k which would've effectively knocked 54% - 67% of it down going by those values. My guess the actual value would be more closer to 82% since you say "2 or 3 on the dial" so what you'd want to do is use two resistors: 18K to ground w/ 82K joining it & the other side to the hot jack. Take your signal output between them (simple voltage divider in other words). If too much signal is dropped then go up to next level by going with 33K & 68K = 67.3% dropped, 47K & 56K = 54% dropped. This way you keep the same load of 100K to the circuit the way it originally was.

[SILVERGUN]

You had a steady load on the signal via the 100k pot in there but w/ the voltage divider set as you say represented possibly 33k or 47k which would've effectively knocked 54% - 67% of it down going by those values. My guess the actual value would be more closer to 82% since you say "2 or 3 on the dial" so what you'd want to do is use two resistors: 18K to ground w/ 82K joining it & the other side to the hot jack. Take your signal output between them (simple voltage divider in other words). If too much signal is dropped then go up to next level by going with 33K & 68K = 67.3% dropped, 47K & 56K = 54% dropped. This way you keep the same load of 100K to the circuit the way it originally was.

Thanks jojo,
I get it now. Thanks for takin the time brother.....
I wasn't seeing the whole picture.
Now I am.....just like the split plate load you showed me way back when....
 

[Tone Junkie]

SG, to me that 10k (grid return if outgoing is for another tube effect or just an impedance reference to an effects box) is a very low value and even the 33k or 47k there would be actually really low values loading down a lot of your outgoing signal unnecessarily. Have you tried 1M there or even 470k and found it not acceptable?

Good thinkin jojo,
The original design had a 100K pot there, and when I first had a send pot in there I found myself just setting it to 2-3, so I figured I'd just install a fixed value and lose the pot.....
I don't know what made me put 10K in there at first other than the fact that I had everything wide open and it "seemed" to calm things down a bit......we'll yeah, it did,,,,and took some tone with it.
So no, I hadn't tried any other, larger values,,,but I will now.
AND, I'll look at that 82K on the return side as well.....
Part of my problem is that my delay pedal has input AND output volume controls (ahh, the good old days)
Good lookin out 
 

Nice avatar!

On the avatar I had some old pictures and forgot I used it on another site after Ed brought it up so I thought I'd put it up here. I'd rather use it here than anywhere else actually. My buddy is in the background but the photo's been cropped. BTW, I still have that V too! 

You had a steady load on the signal via the 100k pot in there but w/ the voltage divider set as you say represented possibly 33k or 47k which would've effectively knocked 54% - 67% of it down going by those values. My guess the actual value would be more closer to 82% since you say "2 or 3 on the dial" so what you'd want to do is use two resistors: 18K to ground w/ 82K joining it & the other side to the hot jack. Take your signal output between them (simple voltage divider in other words). If too much signal is dropped then go up to next level by going with 33K & 68K = 67.3% dropped, 47K & 56K = 54% dropped. This way you keep the same load of 100K to the circuit the way it originally was.

jojokeo I just wanted to thank I have been trying to understand voltage dividers and how they. I have read quite a bit but in a few simple lines you explained not only so I can understand but have basis to tweek it. I feel another adjustable tone box coming on (LOL).
Bill

[jojokeo]

jojokeo I just wanted to thank I have been trying to understand voltage dividers and how they. I have read quite a bit but in a few simple lines you explained not only so I can understand but have basis to tweek it. I feel another adjustable tone box coming on (LOL).
Bill

Glad it helped Bill. We remember things mostly by visualization so putting things in those terms I find helps a little better when possible.

[jojokeo]

I wasn't seeing the whole picture.
Now I am.....just like the split plate load you showed me way back when...

*properly called: Split Plate Load Resistors (SPLRs) - to minimize confustion over "split load plate" aka cathodyne phase inverter.

Aside from minor value changes look at this comparison:

[Tone Junkie]

I wasn't seeing the whole picture.
Now I am.....just like the split plate load you showed me way back when...

Aside from minor value changes look at this comparison:

I wanna learn what do we get with the split plate loads, it looks interesting.
Thanks Bill

[sluckey]

Rather than the full signal level at the plate, you get a reduced signal level due to the voltage divider. You could even put a volume/gain pot there. Like in this circuit where I needed one full level signal and a variable level signal too.

[jojokeo]

I wanna learn what do we get with the split plate loads, it looks interesting.
Thanks Bill

Aside from lowering the signal via a voltage divider (as there's a number of ways of doing it), it has benefits over the "usual or typical" methods of performing this function. It retains the original signal better w/out losing high end and then possibly the need for treble bypass caps which then creates a shelving effect via a high pass filter network. It also allows the use of less parts while at the same time lowering the output impedance so it's less affected by loading effects.

[Tone Junkie]

Rather than the full signal level at the plate, you get a reduced signal level due to the voltage divider. You could even put a volume/gain pot there. Like in this circuit where I needed one full level signal and a variable level signal too.

Thanks slucky this gave me a nice visual on how to dial in the right amount of signal to help balance things between clean and over drive i dont need to build a whole box just a good pot will do. Measure both sides and Im good to go
Bill
I learn much better with visual aids

[Tone Junkie]

I wanna learn what do we get with the split plate loads, it looks interesting.
Thanks Bill

Aside from lowering the signal via a voltage divider (as there's a number of ways of doing it), it has benefits over the "usual or typical" methods of performing this function. It retains the original signal better w/out losing high end and then possibly the need for treble bypass caps which then creates a shelving effect via a high pass filter network. It also allows the use of less parts while at the same time lowering the output impedance so it's less affected by loading effects.

You see this is really helpfull and you anwered my next question about the need for a treble bypass cap which simplifies the whole process greatly instead of building a whloe box with capds and pots with restisters to cover every possability i might switch between I can do it all with a good 2 watt pot pull from the circuit and measure here is definatly a couple pages going on my wall of knowledge.
The 80,s were really good to me (LOL) and Im forgetfull, you know what I mean  . So I put this kind of stuff were I will look at it all the time .
Thanks Bill

[jojokeo]

a couple pages going on my wall of knowledge...So I put this kind of stuff were I will look at it all the time .
Thanks Bill

I picture something like this?

[Tone Junkie]

Yes