Adjusting reverb + fx loop

[SILVERGUN]

In my current build I have used this reverb + fx circuit.
The problem is that the reverb control acts as a master volume because the entire signal flows through the reverb circuit. (when that relay is energized)....the problem with that is that as you increase the level to a point where you don't have a volume drop, you are also increasing the amount of reverb.
That fact is also true with the fx recovery pot, but it is ok there because I can mix in the effect as needed by using the MIX pot.

My question is...
Can I use a mixing resistor between the preamp input and signal output (as pictured and highlighted in red), and will I have a phase issue?

Tubenit, if you happen to read this, have you ever experimented with this idea, or had a similar problem?

[SILVERGUN]

OR, should I do it like this so as not to affect the fx loop?

[Willabe]

will I have a phase issue?

No it shouldn't be a problem with phase because there is no real or absolute phase that you can hear with the reverbs random/multiple signal.


                      Brad                     

[SILVERGUN]

Hmmm....thinking more about it..
I guess the second example I gave would make more sense....
It avoids the potential phase mis-alignment by avoiding the non-inverting cathode fed FX send triode....   right?
 
 

No it shouldn't be a problem with phase because there is no real or absolute phase that you can hear with the reverbs random/multiple signal.

I am thinking in terms of the phase of the signal being 180 degrees out of alignment with the input signal. (in the first example)
 
I think the second example solves it. 
 
respectfully, and still questioning myself and always thankful for your help
  

[SILVERGUN]

Man, I musta been tired last night....

If you look at the second example I drew, the 'mixing resistor' I added performs the same function as the 220K resistor that Tubenit already had there.....and both drawings actually perform the same function because in either switch position the signal always flows through that path.

Duh. 

 

Thanks for not pointing that out and embarrassing me in front of the class Willabe.
I'll take care of that myself.

But I'm still left with the problem. 

[Willabe]

Thanks for not pointing that out and embarrassing me in front of the class Willabe.

Oh yeah, sure, no problem.     

(I never saw it!!!!!      )


                   Brad     

[SILVERGUN]

The solution is going to be in experimenting with the 220K value that T had originally put in there.

I don't need to have infinitely adjustable reverb...just subtle, and probably a fixed 'set it and forget it' value

I just don't like the volume drop when I switch the reverb in.

There's a solution in there somewhere....hoefully I'll find it,,,and if not, just accept a compromise.

[tubenit]

There should be NO volume drop/increase engaging reverb & only volume drop/increase when engaging FX loop.

I'll attach a simple illustration to try to give a visual around this 

With respect, Tubenit

[SILVERGUN]

I never installed the bypass cap on the AT7 driver, so I'm sure that's where I'm losing volume as compared with your original drawing ( I just prefer the way it sounds like that)....and I have no dwell control, just a 1M grid leak before the driver.

I'm hoping that by changing the value of that mixing resistor I can get the dry signal level back up.

I also set the FX loop up to have a slight volume boost, so that when I engage that I'm immediately in 'solo' mode....that worked.

But when I bypass the loop and just run reverb (or even with the fx on) I have made myself a volume drop by deviating from your original drawing, and now just looking for a work-around.

I get the design, and I love your work,,,just tryin to make it work for me.

Amp has a TON of gain, so post OD reverb wreaks a little havoc. 
I followed the #102 pretty closely, and have the loop installed after the OD channel and before the PI.

One of the first tweaks I have done is to eliminate the 4th stage bypass cap, and I have found the OD more manageable and more desireable for the tone I'm going for.

[SILVERGUN]

I'm starting to think that if I make that 220K a higher value, but put a bypass cap across it (similar to AB763 reverb ---3M + 10p), that might get me closer...

I guess I could also try adding the bypass cap to the AT7, but use a 'boost-limiting' resistor in series with it to try to manage the gain.

It's not a huge volume drop, but definitely noticeable.

[tubenit]

As I understand the reverb circuit, it should make NO difference in the volume of the amp whether you have the bypass cap on the 12AT7 . 

It will make a difference in the amount of reverb but not the volume of the amp.  The reverb is essentially parallel to the signal chain and NOT in series with it.    The 220k mixing resistor with 330k off the 1M reverb pot isolates the reverb well and parallels it with the dry signal.  So the reverb circuit simply adds or lessens reverb but doesn't impact the amp volume.  IF yours is impacting the amp volume, then I think you have something wired incorrectly.

OR I am misunderstanding what you are saying????

The dwell pot is an essential in my thinking & experience.  Even with the one tube reverb design, I usually have the dwell on 5-7 with the reverb pot on 3-4.  The rare times that I did not use a dwell pot, I would use a 560k to 680k resistor and not a 1M resistor.

You don't need relays for the reverb circuit.  In fact, I would NOT use a relay.  Simply short to ground the reverb if you need it off like in a typical Fender reverb design.

with respect, Tubenit

[tubenit]

when I bypass the loop and just run reverb (or even with the fx on) I have made myself a volume drop

Removing the FX loop will change amp volume by either increasing or decreasing the volume depending on how you have the FX pot controls set.  That has to do with the FX loop gain.  It has nothing to do with the  reverb. 

Whether the reverb is engaged or not engaged should not really substantially change the volume at all. It will change the mixture & ratio of the dry/wet signal.

I am starting to think that I am not understanding what you are saying, perhaps????

Tubenit

[SILVERGUN]

As I understand the reverb circuit, it should make NO difference in the volume of the amp whether you have the bypass cap on the 12AT7 . 

It will make a difference in the amount of reverb but not the volume of the amp.  The reverb is essentially parallel to the signal chain and NOT in series with it.    The 220k mixing resistor with 330k off the 1M reverb pot isolates the reverb well and parallels it with the dry signal.  So the reverb circuit simply adds or lessens reverb but doesn't impact the amp volume.  IF yours is impacting the amp volume, then I think you have something wired incorrectly.

OR I am misunderstanding what you are saying????

The dwell pot is an essential in my thinking & experience.  Even with the one tube reverb design, I usually have the dwell on 5-7 with the reverb pot on 3-4.  The rare times that I did not use a dwell pot, I would use a 560k to 680k resistor and not a 1M resistor.

You don't need relays for the reverb circuit.  In fact, I would NOT use a relay.  Simply short to ground the reverb if you need it off like in a typical Fender reverb design.

with respect, Tubenit

OK cool...you are definitiely understanding what I'm saying...

I never thought that I might have mis-wired something 

I did think about dropping that 1M value grid-leak value,,,but opted out because I dropped the bypass cap.

I committed to the reverb on a relay function, but can still back out if it doesn't work out....it doesn't seem to have an adverse effect on the operation,,,but could be contributing to noise/ hiss / etc.

Here's the build thread if you're curious....I guess if I'm gonna eliminate the relay for the reverb, now is the time,,,before I wire up the footswitch receptacle....
http://el34world.com/Forum/index.php?topic=17872.0

The goal is to have a single foot board with three switches on it.
-Clean/ od
-Reverb on/ off
-FX on/ off

If I get rid of the relay switching for the reverb, I'll have to change the way I wire the receptacle, and the pedal, and the wire I use.
But I'm OK with that if it has to be.

I'll see if I can tweak it to useable before I retreat. 
Thanks for your time and help!

[SILVERGUN]

I am starting to think that I am not understanding what you are saying, perhaps????

No,,,you got it....sorry for the confusion..

I just get a slight volume drop when I engage the reverb.

[tubenit]

I am surprised to hear there is a drop in the volume with reverb engaged?   

If you want to have the reverb on a relay, you can simply use the relay to simply short the return triode grid to ground like on a regular Fender reverb.  However, a non-relay spst footswitch would do that also.

I don't think there is a loss of volume with a typical Fender reverb circuit being shorted like in an AB763?  Maybe I never noticed it before??
 

With respect, Tubenit

[SILVERGUN]

I am surprised to hear there is a drop in the volume with reverb engaged?   :

Yeah, I was surprised too....MAYBE I got something crossed up?

If you want to have the reverb on a relay, you can simply use the relay to simply short the return triode grid to ground like on a regular Fender reverb.  However, a non-relay spst footswitch would do that also.:

Great idea,,I didn't think of that.
I was trying so hard to arrange it like the schematic, that I neglected to think outside the box.

I don't think there is a loss of volume with a typical Fender reverb circuit being shorted like in an AB763?  Maybe I never noticed it before??
 

In my experience, there isn't....I just built sluckey's TDR, so it was fresh in my head still....

This one creates a slight drop.(the way I drew it up)

[SILVERGUN]

I went out on my lunch break and looked hard with a magnifying glass and extra light and I found a questionable path to ground for the recovery triodes cathode resistor.

I'm gonna wait until later to fix it so that I can hear the difference to know whether it was the actual problem.

Until then there's no sense in spending anymore time verbally troubleshooting it....It may have just jumped right out at me.

Sorry,,,I really thought I had it all checked....but this one's got soooo many conections, I'm lucky that it actually worked the first time without any troubleshooting. 

[Willabe]

The problem is that the reverb control acts as a master volume because the entire signal flows through the reverb circuit. (when that relay is energized)....the problem with that is that as you increase the level to a point where you don't have a volume drop, you are also increasing the amount of reverb.

When you wrote this I thought you had the reverb circuit in series because of what is highlighted in blue above in your quote. I thought you had some switching going on that put the reverb circuit in and out of the main signal chain because you brought up maybe being out of phase. I thought you were trying to balance the gain/volume over 2 channels. All you posted as a drawing was the 1 tube reverb block by itself so I didn't pick up on what you were trying to say. (A few old guitar amps did have verb in series but it seems they weren't very well liked or they would have kept making them.)

it should make NO difference in the volume of the amp whether you have the bypass cap on the 12AT7 . 

It will make a difference in the amount of reverb but not the volume of the amp.  The reverb is essentially parallel to the signal chain and NOT in series with it.    The 220k mixing resistor with 330k off the 1M reverb pot isolates the reverb well and parallels it with the dry signal.  So the reverb circuit simply adds or lessens reverb but doesn't impact the amp volume.  IF yours is impacting the amp volume, then I think you have something wired incorrectly.

When Tubenit posted the above with a full schemo in another post, then I saw it was a standard 1 tube reverb which as T said is in parallel (a side chain circuit), not in series. So the reverb master volume does not have "the entire signal flows through the reverb circuit".

With a standard 1 or 2 tube parallel (side chain) reverb the way it's set up it can't add volume to the main signal chain. Because the signal that is being mixed back in from the reverb recovery stage is WAY weaker then the main signal.

The main signal at the point where the verb side chain signal is mixed back in has been through 2 gain stages and the verb signal after it has gone through the verb tank, being sent into the verb recovery stage's grid, is less then the signal being sent in to the amps input from the guitar. So the verb recovery stages signal being mixed back in can not overwhelm or add any volume to the main signal. All it has enough signal power to do is 'wash' the main signal with the verb.


                    Brad     

[Willabe]

So the reverb circuit simply adds or lessens reverb but doesn't impact the amp volume.  IF yours is impacting the amp volume, then I think you have something wired incorrectly.

I was thinking the same thing but thought it was maybe in the switching.

What ever it is I know you will figure it out.


                   Brad   

[SILVERGUN]

Thanks for the clarification...

My circuit is wired just like this schematic, with my preamp signal coming into the first relay (labeled preamp), and my signal leaving the loop and going off to the LTPI.

The parallel path is only due to that 220K resistor, and for some reason it ain't working for me. I increased the value to 1M and it made the problem exponentially worse.

My Reverb control (as pictured) acts as a Master volume and completely shuts my signal down at the lowest setting (despite the parallel path). , where I would just like it to turn down the amount of reverb mixed with the dry signal.

The grounding issue I thought I saw earlier has been repaired and did not change my situation.

What ever it is I know you will figure it out.

Thanks brother,,,I'm working on it now,,,and you know I'll tell you what I find and won't hide it, no matter how stupid it may be. 

[SILVERGUN]

GOT IT!!

The 500k Reverb pot that I subbed in where T had a 1M wasn't providing enough resistance to ground.

I went out and clipped a 470K R in series to ground and that took care of it.....
I had a feeling that was it, but I was being a bone-head. Luckily it's one of the first things I tried.
I'll put the 1M in there where it belongs and call it a learning experience.....I guess I thought that subbing in the 500K would knock the reverb down a little from a different 'angle'.

Sorry for the false alarm and waste of your time and THANKS AGAIN FOR ALL OF THE HELP!!

Yer Pal,
Bone Head

[Willabe]

The parallel path is only due to that 220K resistor, and for some reason it ain't working for me. I increased the value to 1M and it made the problem exponentially worse.

That R does 2 things,

1. It controls the amount of dry signal that goes to the next stage.

2. It helps isolate the verb out put from going back into the verb input.

My Reverb control (as pictured) acts as a Master volume and completely shuts my signal down at the lowest setting (despite the parallel path). , where I would just like it to turn down the amount of reverb mixed with the dry signal.

It has to be wired wrong for it to do what your saying.


     
                  Brad   

[Willabe]

Glad you fixed it but, the value of that pot, if wired like in yours and T's drawing only effects (limits) the verbs plate output.

There's still the 330K R standing in the way of the dry signal going to ground even when the verb recovery pot is turned all the way down to zero.

It was something else.


                      Brad   

   

[Willabe]

Here;


           Brad   

[SILVERGUN]

Glad you fixed it but, the value of that pot, if wired like in yours and T's drawing only effects (limits) the verbs plate output.

There's still the 330K R standing in the way of the dry signal going to ground even when the verb recovery pot is turned all the way down to zero.

It was something else.

Your dead-on right Sir.

I went back out and measured that 330K resistor as 328OHMS

I NEVER do that because I measure every component as I put them in!?!?!?!
Must have put that in the one night I was here til 2AM.

Can't say NEVER anymore. 
Thanks again for hanging in there with me!

That resistor was affecting the entire tone of the amp...I got it right now, and the beast has awoken.

[Willabe]

Yer Pal,
Bone Head

Your NOT a bone head.

The 500k Reverb pot that I subbed in where T had a 1M wasn't providing enough resistance to ground.

I went out and clipped a 470K R in series to ground and that took care of it.....

Is this what you did?


              Brad   

[Willabe]

I went back out and measured that 330K resistor as 328OHMS

      Dooooohhhhh.       

That resistor was affecting the entire tone of the amp...I got it right now, and the beast has awoken.

Yep, that's why ALL the signal, dry and wet went to ground when you turned down the verb pot. You only had 328R instead of 330K standing in the way of ground for the dry signal.


                     Brad     

[SILVERGUN]

 

 

 

 

 

[Willabe]

Have FUN!   


          Brad     

[tubenit]

I just love happy endings!   

[Willabe]

  

Me Too!


              Brad       

[SILVERGUN]

THANKS guys!

I just want you to know that I did quickly realize why the 470K clip in didn't actually "fix" the problem.

Basically, it was because all I was doing was creating a 1M pot with 470K always going to ground, which was masking the fact that the 330K resistor was the wrong value. And giving me a pot that would never go to zero, so, of course it wouldn't act like a master any more.
But, at least it (and a little help from my friend) led me to the real problem.

Fixing the other grounding issue has also seemed to reap benefits. SO I'm actually glad that I went looking, because amp was working fine....just not optimally. Now it's a KILLER!
OD tone pushing slight reverb is a joy to play.


I was so busy playing last night that I never got back to the computer.