All-Tube Ambience Schematic (Needs Help!)

[alathIN]

This is what I want to work on next - a fairly straight up Fender style standalone Reverb/Tremolo intended for use in an active effects loop.

The odd-ball add-on is a tape delay. This is far more experimental. And may be dropped or left as a future development if it runs into major problems.

Would appreciate any help or suggestions.

[alathIN]

Same schematic with some corrections and details filled in.

[alathIN]

My main questions:

Do I have the dry signal path correct?
One of my most desired features here is to have very controllable wet/dry mix, and have the "dry" part as transparent/unaltered as possible.

I added some tone pots here and there. I really like having tone control on a reverb.

Would appreciate any feedback or suggestions.

[sluckey]

Tape recording and playback is way more complicated than your rough schematic indicates. Your friend's suggestion to use a hard drive makes no sense to me. I suggest you put this idea on a shelf and do some reading on tape recording theory. Or just get a digital delay pedal for your fx loop. Lot of good choices.

Your reverb circuit output goes nowhere? Take a look at Weber's 5G15T reverb/tremolo unit. Might give you some ideas. Schematic and layout are on this page...

     https://www.tedweber.com/5h15t-c-kt

I'm not suggesting to abandon your basic reverb/trem idea. I just think you may get some ideas by looking at what others have done. Your idea (except for the tape delay) is sound. The idea needs a bit more work. Plan to spend more time on the drawing board than you will spend on the workbench.

[alathIN]

Tape recording and playback is way more complicated than your rough schematic indicates. Your friend's suggestion to use a hard drive makes no sense to me. I suggest you put this idea on a shelf and do some reading on tape recording theory. Or just get a digital delay pedal for your fx loop. Lot of good choices.

Your reverb circuit output goes nowhere? Take a look at Weber's 5G15T reverb/tremolo unit. Might give you some ideas. Schematic and layout are on this page...

     https://www.tedweber.com/5h15t-c-kt

I'm not suggesting to abandon your basic reverb/trem idea. I just think you may get some ideas by looking at what others have done. Your idea (except for the tape delay) is sound. The idea needs a bit more work. Plan to spend more time on the drawing board than you will spend on the workbench.

Re, reverb going nowhere - I realized that later and I think (hope) that I fixed in the schematic in my second post.

I have copied/adapted a bunch of stuff from different places but haven't looked closely at Weber's unit yet - good suggestion.

Re; tape delay - yes I realize this is very experimental and iffy, with a lot of missing details. At this stage it's something I would like to be able to add on later if some of the intermediate steps work out (which of course is not a given). The idea with the hard drive is that the HD disc is a magnetic recording medium that's attached to a cheap reliable motor that can be spun at different speeds. The HDD recording and retrieving system wouldn't work at all and would have to be re-invented pretty much from scratch. But if it could be made to work, it would be a lot more reliable than tape. Yes, there are about 10,000 things to figure out between here and that actually working. Right now the delay circuit is just a "generic place holder" in case that part of the project ever does come to fruition.

At this point I'm wanting to proceed with the reverb/trem part of the project and will post any new refinements I come up with here for feedback.

[alathIN]

So option one is to make the trem in my standalone work the original Fender AB763 way - intermittently grounding the signal as it's going through the unit.

The Hoffman AB763 trem appears to work by oscillating the bias power supply into the signal between the PI and the power tubes. I can't do exactly that, because my effects loop goes in before the PI.

If I understand the Weber revibe correctly, it seems to use two sides of a dual tetrode to create an oscillating power source that feeds into the grids of another dual tetrode, which functions kind of like a preamp, so the signal is alternately amped more or less to create the trem effect.

I'm considering a combination of these ideas.
I was already tempted to put a preamp/gain type stage in this unit. I really like the sound of the EF86 pentode as it's getting saturated and going into overdrive.
This would add a sort of "overdrive" effect to the unit... and an opportunity to make the trem work by oscillating bias power into the signal before the preamp circuit.
The power transformer I have for this project is the same PT you would use to build a Deluxe Reverb amp - so it does have a tap for the 50v bias supply.
Do you think this would work?

The intermittent-grounding type of circuit seems simplest, but I'm wondering if a kind of hybrid plan might work.

[sluckey]

You don't need a bias supply for this project. Keep in mind that the Weber circuit is designed to work with low level instrument signals. But your fx loop works with much larger signals.

[alathIN]

Looking at the three different kinds of tremolos, I think it would be wisest to use the original AB763 type. It's simpler, I already have a lot of the parts, and it's designed to work with the level of signal between preamps and power stage, unlike the others.

I feel like I understand the circuit as a whole, and I understand it needs to connect with the line carrying the signal on its way out of the standalone unit.
But looking at the AB763 schematic, there is a section I don't understand.
I've highlighted it in the image, and attached the full schematic for orientation if needed.


The lead highlighted in pink is the one that comes from the vibrato circuit (ie, will intermittently run to ground).
Based on my understanding, I would be tempted to just hook this directly to the signal path without any further ado (like in my rough schematic below).

Obviously Uncle Leo put some other components in there where the vibrato/trem connects to the signal path - the stuff in the light blue shaded area - but I don't know whether I need them or not.

My impression of what I need to connect the input jack, reverb circuit, dry signal bypass, tremolo, and output jack looks more like this:

I've seen a lot of different values for the resistor and capacitor that are in parallel with the reverb circuit, but I think I understand what they are for. Fender has that resistor at 3.3M. I'd also appreciate any guidance about those values.

[alathIN]

You don't need a bias supply for this project. Keep in mind that the Weber circuit is designed to work with low level instrument signals. But your fx loop works with much larger signals.

Wait.... hold that thought.

I just heard harmonic tremolo today for the first time and it's awesome.

It seems to me it should be possible to make a tremolo that is switchable between "normal" bias trem and harmonic trem.
If I were to use lower amplification tubes, skip the pre-amp stage, and use the AB763 type reverb circuit, would it be possible to adapt the Weber or Hoffman reverb/tremolo design to a level that is appropriate for use in an effects loop?

I did successfully install the Metropolous active effects loop (thanks for the Sluckey assist!) which can compensate for some signal loss or gain...

[alathIN]

You don't need a bias supply for this project. Keep in mind that the Weber circuit is designed to work with low level instrument signals. But your fx loop works with much larger signals.

I've been spending time in research mode for this project. I think one of the problems I started out with was trying to cram all of my interesting ideas into one project, mixing things that are pretty much off-the-shelf circuits with things that are extremely experimental and would need lots of trial and error before even thinking about a final project.

I have learned that I really like BOTH harmonic vibrato and bias-type vibrato.

At this point I think I'm ready to move forward with a "rough plan" schematic - but there are some basic questions to answer - or assumptions on which I am relying. I'd like to check these before proceeding. So, please, if any of the following statements or parts of statements are incorrect, stop me before I move on to the next step.

1) The harmonic vibrato circuit in Fender 6G12 (and others) is designed to work between preamp and phase inverter - therefore it should work in an effects loop

2) It would be possible to switch the low frequency oscillator output to a separate circuit for "non-harmonic" vibrato - instead of oscillating the power tube bias, one could use a preamp-type circuit applying the LFO to the cathode and the instrument (effects loop send) signal to the screen to create a bias-type vibrato.
2a) This would make the resulting signal out of phase with the dry signal or reverb, so it would be desirable to then run the oscillated signal through another triode to flip the phase back.
2b) It would be desirable to use a relatively low-mu dual triode for this to avoid over-amplifying the signal (I was thinking 5751)

[sluckey]

I have learned that I really like BOTH harmonic vibrato and bias-type vibrato.

Have you actually played through an amp with the Fender Harmonic Vibrato? I really believe that after experiencing the Harmonic Vibrator you will throw rocks at the bias vary tremolo.

1) True

2) True but the switching may be easier said than done.

2a) Phase is irrelevant between dry and reverb signals. The reverb tank kinda destroys that relationship.

2b) I use two 5751s in my revibe. But, the oscillator tube needs to be the highest gain triode you can use. I suggest 12AX7 for the osc.

[alathIN]

I have learned that I really like BOTH harmonic vibrato and bias-type vibrato.

Have you actually played through an amp with the Fender Harmonic Vibrato? I really believe that after experiencing the Harmonic Vibrator you will throw rocks at the bias vary tremolo.

No. Never had the chance. Although Webers is just up the road from me - maybe they have a functioning Revibe in the shop....
They featured a real harmonic vibrato and a digital pedal imitation on an episode of That Pedal Show. The real one was astonishing; never heard anthing like it. I was mildly surprised, then not, that the digital version was so dramatically less... dramatic.
Since then I've hunted up every thread on every forum where anyone has done a harmonic vibe build, and listened to a lot of their sound clips.
I hear what you are saying that it's so much richer and more interesting than "regular" tremolo.
My only reservation is what if I want a more subtle effect. Everyone showing off their build, and the TPS guys, was likely using harmonic vibrato at extreme settings. I haven't heard what it sounds like set to "just a hint."

2) True but the switching may be easier said than done.

I'm surprised you see the switching as the big issue. To me, applying the LFO to a preamp type circuit seemed like the most experimental thing about this proposition.
Not knowing any better, I would have just picked a spot right before the LFO joins the instrument signal, thrown in a SPDT switch, and thought it was going to work.

2a) Phase is irrelevant between dry and reverb signals. The reverb tank kinda destroys that relationship.

In my mind there are three signal paths through this thing.
1 - dry signal
2 - reverb
3 - tremolo(s)
I can see where reverb would so change the signal that phase doesn't matter - but my sense is that tremolo and dry could interact strangely if out of phase.

But maybe I don't actually need a dry signal path - "dry" in this case simply being "tremolo speed and depth set to zero?"

[sluckey]

...but my sense is that tremolo and dry could interact strangely if out of phase.

There is only one path and that is the "dry" path, so phase is not an issue. The tremolo effect is simply applied to the dry signal. When the trem is enabled the dry signal is modulated. When the trem is disabled the dry signal is not modulated.

[alathIN]

OK, here's the latest.

These are the three effects I would most like to have with the TC15 amplifier I built. They are all longstanding circuits that have been used and modded many times over.
However, this is the first time I have tried to put them together in one box 

Parts:
1. Fender harmonic vibrato circuit. This is the five-triode version which has the reputation of being easier to de-bug.
2. Fender reverb circuit - basically straight up AB763 Deluxe Reverb, with a few mods borrowed from other places. The reverb tone control is the oddball - I've only seen this once or twice elsewhere, but I do like tone control on reverb pedals. I'd like it to start out bright, and be able to dial back the brightness. I have both an accutronics 2-spring and MOD 3-spring 16 inch tanks on hand.
3. - and this is another oddball - a Marshall cold clipper tone stack feeding into an EF86 (this would usually be two triodes instead of one pentode). This will take a direct instrument signal - it's basically a standalone preamp - but will also be able to use the vibrato and reverb. I like EF86 distortion and I like cold clipped distortion, and I'd like to try the two together. I have heard from the Metropolous forum that people use their zero loss effects loop equipped amps as "standalone power amps" so this should be possible.

Questions:
1. The 1:1 isolator transformers are intended to avoid ground loop problems wherever there is a patch cable coming from or going to a separate amplifier. I have not heard of this being done with guitar amps, but it's often done in the home audio world - for instance when there is a powered subwoofer connected to a stereo system. The transformers I've found are 135 ohms resistance and 290mH inductance. If this works, they will isolate the effects loop ground from the incoming and outgoing patch cables connection to the amplifier ground. Obviously I am not sure whether or not this will work.
2. I am not confident of the way I have connected these circuits. I'm also not confident whether I have possibly included two different mods that may be incompatible.
3. Several of the components are show with different values in different versions of these circuits. Whenever I've seen an explanation of what the different values do or how they sound, I've chosen accordingly. There are a couple of these values labeled "alt" which means I've seen two values and don't know which to choose.
There are also some values shown as "TBC" - to be calculated. I'm stymied trying to calcuate the value of voltage dropping resistors because in many cases I'm not clear what the current will be at that spot. Would appreciate any help with this.

Also - I have not done all the labelling of tubes (like V1B, V3A, etc). Would like to save that for last, so I don't do it and then mess it up with revisions.

I would certainly appreciate any feedback or suggestions folks are willing to share.

[alathIN]

Follow up to above:
Calculating voltage drop resistor values - what I did was add up the plate current of every tube "downstream" of the resistor in question, and use that value as i in Ohm's law.
If that's the correct procedure, I've got my answer to that question.

[sluckey]

what I did was add up the plate current of every tube "downstream" of the resistor in question, and use that value as i in Ohm's law.

That's a good starting point. Having a handful of different value resistors is also a quick way to fine tune to a particular target voltage. Keep in mind that this stuff will usually work just fine over a pretty wide range of supply voltages. This is an interesting looking project and I think you will have success and fun with it. Would be a great breadboard project.

[alathIN]

what I did was add up the plate current of every tube "downstream" of the resistor in question, and use that value as i in Ohm's law.

That's a good starting point. Having a handful of different value resistors is also a quick way to fine tune to a particular target voltage. Keep in mind that this stuff will usually work just fine over a pretty wide range of supply voltages. This is an interesting looking project and I think you will have success and fun with it. Would be a great breadboard project.

Appreciate your feedback.
If Sluckey is no longer acting like I'm crazy, I'm probably on a better path 😁

I'm a little leery of missing my voltage targets, because I read all over the place how the harmonic vibrato is such a tweaky circuit and will not work if the slightest little thing is off. I hope that's exaggerated.

[jojokeo]

alathIN, you name isn't Alex is it?

[alathIN]

No, Anthony

[alathIN]

OK I think this may be the final or semi-final schematic.

Researching on various websites, getting feedback from various forums, including here.

Changes:
1. Trying Merlin's Ground Lift circuit, supposed to eliminate ground loops and decrease RF interference
2. Love this idea - not mine - hope it works: adding an extra triode to the reverb recovery. Never liked the idea of that great big 3.3M resistor in the dry signal path, so instead of tamping down the dry signal to balance wet/dry, I want to try amping up the wet signal. Suggestion from another forum, again, hope it works.
3. Revised power supply - biggest change is to put the harmonic trem on its own B+ node; maybe not necessary, but the idea was that none of the other circuits would like to have LFO noise in them.

Sluckey you were right; the schematic process has been vastly longer than I expected but I'm glad because I think (hope) I avoided some problems and added some promising tweaks.

[sluckey]

I'll be following this project with lots of interest. Schematic looks doable, except for the hi-gain preamp. Both tubes are upside down and some pin numbers are scrambled.

[alathIN]

I'll be following this project with lots of interest. Schematic looks doable, except for the hi-gain preamp. Both tubes are upside down and some pin numbers are scrambled.

Good eye.

Now, I wonder how I managed to do that?
You'd think it would take some real effort to mess that up.
Anyway, fixed now.
I wonder if I would have blindly followed the schematic, transferred that error to my layout, and actually built it that way?
Or at some point look at it and say, "something not quite right here..."

[sluckey]

I wonder if I would have blindly followed the schematic, transferred that error to my layout, and actually built it that way?

I doubt it. You probably had it straight in your mind all along. I've done the same but usually catch it on the layout drawing. Although, I once drew a bias diode backwards on my layout and actually installed it backwards! Caught it before powering up.