Adding 1-tube reverb

[tubenit]

So in real world implementation, how does the overall character of the amp's sound and volume change with the dry signal having the life sucked out of it?

Where are you getting the idea the dry signal has "the life sucked out of it"?  Not why you're presuming that? 

I'm not sure I'm understanding your question as you may be intending?  And I'm not sure you're understanding the  schematics I've posted in the first post on this thread.

My experience is the amp sounds pretty much the same except with reverb added. 

The dwell pot is rarely turned down low. The mixing resistors I use are reasonably small 220k or less because the 1M reverb pot (which is not in the dry signal path) plays a factor in the mixing vs. standard 100k Fender reverb pot with 3.3M mixing resistor (which is in the signal path).


Respectfully, Tubenit

[mountainhick]

Thanks Tubenit.

I am confused how the parallel loads added do not suck down the signal.

Am i misunderstanding? An example, 5F1, if you insert a reverb after the first gain stage, it has not only the 1M load of the volume pot, but also the parallel loads of the input divider or dwell pot to ground, plus the reverb recovery/level pot to ground. If those three are 1M each, the parallel load is 330K, which means the resulting signal is 1/3 the AC voltage when it reaches the second gain stage in the original circuit. Some of these schematics show voltage dividers, pot values and pot orientations that create even lower impedances plus attenuation, and as far as I can tell, will send a lot of signal to ground.

If they still sound the same, same gain, same volume, that is wonderful, but I am perplexed.

 respect to you too!

[tubenit]

I've installed one tube reverb on quite a few amp builds. I have never lacked volume in any of the amps whether 6L6,5881,6V6 or 6BM8's.  The reverb doesn't "dull" the amp or kill tone. Quite the opposite.

It is rare that I'd have the volume pot above 4 or 5.  Most of the amps I've built for myself have master volumes (usually a PPIMV) on them also.


So far, it's never been a negative experience for me or for others where I've added a one tube reverb for them.

Take one of the schematics in the first post of this thread and follow the signal chain thru to the speaker. Try using a highlighter pen. Then ask yourself where in the reverb section is the signal being killed in the signal chain?


With respect, Tubenit

[Willabe]

I am confused how the parallel loads added do not suck down the signal.

There are tens on thousands of Fender amps that have a parallel (||) reverb circuit and they don't sound like the dry signal had the life sucked out of it.

[mountainhick]

I've installed one tube reverb on quite a few amp builds. I have never lacked volume in any of the amps whether 6L6,5881,6V6 or 6BM8's.  The reverb doesn't "dull" the amp or kill tone. Quite the opposite.

It is rare that I'd have the volume pot above 4 or 5.  Most of the amps I've built for myself have master volumes (usually a PPIMV) on them also.

So far, it's never been a negative experience for me or for others where I've added a one tube reverb for them.

With respect, Tubenit

That is reassuring to hear, and I guess that if you are not diming your amp that you have more room to move. i.e. you were never going to use the maximum range of your preamp to start with.

Take one of the schematics in the first post of this thread and follow the signal chain thru to the speaker. Try using a highlighter pen. Then ask yourself where in the reverb section is the signal being killed in the signal chain?


With respect, Tubenit

Respectfully, you are missing the point. The added parallel loads when adding the reverb circuit draw down the signal AC voltage at the preceding tube stage. It is the load on that tube's output I am talking about.

There are also losses through the subsequent path due to the voltage divider of mixing resistor over reverb output impedance, whether that is the reverb level pot or when the reverb is turned up full, back though the reverb recovery triode.

I will draw and post some pics and load lines when I have the chance.

[mountainhick]

I am confused how the parallel loads added do not suck down the signal.

There are tens on thousands of Fender amps that have a parallel (||) reverb circuit and they don't sound like the dry signal had the life sucked out of it.

And respectfully to you, I am not arguing to the contrary, but the Fender design adds a post reverb gain stage to make up for these load losses. Look at the typical blackface on through silver etc... There is a gain stage post tone stack to make up for the loading losses from the stack. Then the reverb mix and parallel reverb, then another post reverb gain stage. These single tube reverbs do not add that extra gain stage to make up for the load and voltage divider losses inherent in the addition of the reverb.

[Willabe]

I am not arguing to the contrary, but the Fender design adds a post reverb gain stage to make up for these load losses.

No, that gain stage is for boosting the verb, not the dry signal. (And you are arguing to the contrary.)

Your leaving out that Fender knocks down the dry signal with a 3M3 R before the final verb mix gain stage. If the || verb kills the dry signal by loading it down, why does Fender have to put the 3M3 R in series with the dry signal? Because there's too much dry signal compared to the verb signal. 

Look at the typical blackface on through silver etc...

Yeah, I know what a Fender verb circuit looks like. 

....Then the reverb mix and parallel reverb, then another post reverb gain stage. These single tube reverbs do not add that extra gain stage to make up for the load and voltage divider losses inherent in the addition of the reverb.

They don't need to. Different animal.

Your leaving out that 3M3 series R in the dry signal.

The 1 tube reverb's don't use a 3M3 R, they use a MUCH smaller R there. Like 100K to 330K. That's a huge difference. 

[Willabe]

Bottom line is tubenit has built and when building these 1 tube verbs he has tried different things/values while tweaking them.

I know tubenit well for many years now. I know how much time he will invest in getting an amp, a circuit to sound and work not just well, but as best as can be.

Say what you want, but he's done the work and what he is telling you and what he has gone to the trouble of posting here for the benefit of others, after all his experiments, I'm sure is correct.

Most, if not all of these 1 tube verb's won't get the surf verb that a stand alone verb or a the standard 2 tube verb of a Fender combo amp, but they will get plenty of verb for most purposes.

And they will still have plenty of dry signal on tap. Even when dimed.

[Willabe]

That is reassuring to hear, and I guess that if you are not diming your amp that you have more room to move. i.e. you were never going to use the maximum range of your preamp to start with.

This is wrong in real world use and in assumption.

We've seen many guys build a small combo amp with 1 tube verb or add a 1 tube verb to their existing amp build and no one has ever complained that the amp lakes enough dry signal, at any setting, including full up.   

Respectfully, you are missing the point. The added parallel loads when adding the reverb circuit draw down the signal AC voltage at the preceding tube stage. It is the load on that tube's output I am talking about.
There are also losses through the subsequent path due to the voltage divider of mixing resistor over reverb output impedance, whether that is the reverb level pot or when the reverb is turned up full, back though the reverb recovery triode.

Hummm, and yet there is plenty of dry signal available and plenty of reverb short of surf verb.

You must be missing something? 

I will draw and post some pics and load lines when I have the chance.

You might be better off spending that time building a 1 tube verb amp and seeing how it sounds? 

[tubenit]

I will draw and post some pics and load lines when I have the chance.

If that's useful to you, please feel free to do so.  You seem to be concerned there is something about this circuit that impacts the tone of an amp in a negative way?

Do you have any real life experience with the one tube reverb being added to an amp? 


Respectfully,  Tubenit

[mountainhick]

 You seem to be concerned there is something about this circuit that impacts the tone of an amp in a negative way?

Yes.

Do you have any real life experience with the one tube reverb being added to an amp? 

Yes, two, and more to come.


Thanks for you input Tubenit.

Wilabe, I am sorry it seems I have raised your hackles, wasn't any such intent.

I apologize for posting.

Best to you both.

[tubenit]

Please feel free to share what was negatively impacted in the tone or volume with your experiences adding one tube reverb.
What did you hear differently after the reverb circuit was built in?


My experience has been that it has always worked well for me, given me a tone I liked and I still had plenty of volume. The one tube reverb is not a good choice for Dick Dale surf stuff, but works well for what I am looking for.

And if you could post an exact schematic of how you added the reverb that would be helpful. It may help inform someone on the forum considering trying this as to whether or not they want to experiment with it.


If it didn't work well for you, give some details of what your experience was along with the schematic please. Your sharing that could be useful to others.

With respect, Tubenit

[mountainhick]

Again, sorry I posted. Seems like misunderstanding all around. I am not complaining about your circuits, and no question, I do believe that what you have built suits your needs.

And I am not reporting problems with the one tube reverbs I have built, but they are not in a similar context as retrofit to already existing design.

I am trying to reconcile an electronic puzzle that occurs when these are inserted into already established circuits.

The two I have built are not relevant to that context.

I'll figure it out with my next build which inserts a reverb in an altered Fender deluxe type circuit where it is a retrofit to essentially already established design.

I posted my question here wanting to go into the build with better fore-knowledge, but will proceed anyway to find out through my own experimentation.

Carry on.

[tubenit]

You brought up a reasonable question.  It may prove to be a useful insight and/or question for others.  Solid information may help others to make a decision whether to consider this approach or not.


I'm limited in my understanding of electronics and just sorta grasp some of the basics needed to design and build amps. So you may be on to something that I've totally missed.  You're welcome to post any thoughtful information that you may see useful to others.


Most of my values/taste/preferences regarding tone are based on many hrs of simply experimenting til I find what works well for me. Given limited knowledge of electronics, I have to rely on what I'm hearing instead of the math/science to guide me.


Best regards and respect, Tubenit

[pullshocks]

Here is one example of what happens EDIT can happen when inserting a reverb circuit into an existing amp.  This is not a conventional way of analyzing or evaluating, but you might be interested in the results


I’ve got an amp build on the breadboard, very similar to a Blackface Champ.  The preamp follows the Tone King Imperial 20th Anniversary schematic, with V1A unbypassed and a slightly tweaked tone stack.  I also have the V1B cathode bypass cap down at 5 uF.  So not quite as high gain as the Champ.


Running a .1V 1000hz signal into the amp , and out through an attenuator to a Canabis Rex speaker, I get a sound level of 83 dBC.  This test would be intolerably loud without the attenuator.


After adding the 1-tube reverb with 2meg reverb isolation resistor as shown in the attached schematics, sound level dropped to 67 dBC.  Amp settings, mic position, etc. were the same for both tests.


So there is a big volume drop.  But other than that, there is no loss of tone.  Still sounds great, plenty of “life,” just not as loud.


There are any number of schematics out on the web for adding reverb to a Champ.  Most if not all add a recovery gain stage after the reverb isolation resistor and before the 6V6.  From this test I can see why.  It sounds good at low volume practice levels, but that’s all you get.


I don’t have room for another tube.  2deaf/Ten Over designed a LND150 recovery stage that shows promise.

[tubenit]

I am wondering if it would have a volume drop like that simply with the 2.2M isolation resistor in the circuit?  Perhaps it has little or nothing to do with the reverb circuit itself.


Again, as previously mentioned, the isolation resistors I use are of a much smaller value.  Often 150-330k with a 1M reverb pot  vs.  3.3M with a 100k reverb pot.


And to date, IIRC, I have not ever added reverb to a single ended amp.


With respect, Tubenit

[Willabe]

On the 6V6 grid 1, spec sheet says only 100K for total grid resistance, = grid stopper and grid return R's. Fender got away with 250K grid return and 1K5 grid stopper.

That 1M pot and 5K2 grid stopper is too much. It will kill the 6V6.   

[pullshocks]

On the 6V6 grid 1, spec sheet says only 100K for total grid resistance, = grid stopper and grid return R's. Fender got away with 250K grid return and 1K5 grid stopper.

That 1M pot and 5K2 grid stopper is too much. It will kill the 6V6.

Thanks for that info Willabe. It must be a slow death. I have been using it that way for over 20 years.

[pullshocks]

I am wondering if it would have a volume drop like that simply with the 2.2M isolation resistor in the circuit?  Perhaps it has little or nothing to do with the reverb circuit itself.


Again, as previously mentioned, the isolation resistors I use are of a much smaller value.  Often 150-330k with a 1M reverb pot  vs.  3.3M with a 100k reverb pot.


And to date, IIRC, I have not ever added reverb to a single ended amp.


With respect, Tubenit

Yes, I agree the volume drop depends on the reverb isolation resistor.  I quickly popped in a 330K and the SPL difference between reverb and reverb bypass was only about 10 dBC.  But there is still a volume drop, and I think even a 150 k would still show some volume drop, though maybe not noticeable with a push/pull amp.  If your amps sound good with the 150K, I would say your transformer-driven setup is more efficient.  The capacitor-driven circuit I am working with sounds a lot better with 1-2 meg for the isolation resistors, which lead to considerable signal loss, as shown by these sound level readings.  I've got to say, this is a good sounding reverb, and I'm determined to make it work, signal loss and all.  Ampeg must have found the signal loss acceptable, since they used 2 meg in many of their amps with capacitor driven reverb. 


In the end I don't know if I added anything to the discussion of whether 1 tube reverb sucks the life out of an amp. 

[Willabe]

It must be a slow death. I have been using it that way for over 20 years.

 

[Willabe]

I quickly popped in a 330K and the SPL difference between reverb and reverb bypass was only about 10 dBC.

Do you mean between the reverb and dry signal?

If your amps sound good with the 150K, I would say your transformer-driven setup is more efficient.  The capacitor-driven circuit I am working with sounds a lot better with 1-2 meg for the isolation resistors, which lead to considerable signal loss, as shown by these sound level readings.

So, even with the 330K series R the verb signal was not loud enough compered to the dry signal?

Notice that Tubenit also upped the verb pot to 1M, that will increase the verb signal a lot.

[pullshocks]

Yes.  Reverb bypassed-85 dBC. Reverb in circuit- 75 dBC


I did not change the reverb pot for that quick&dirty test.  I know the pairing of resistor and reverb pot makes a difference.  Last summer, I started out with 150K and 1 Meg and evolved from there, as covered in my earlier thread " 1-tube transformerless reverb breadboard-fest "   I've beeen fortunate to get a lot of help from 2Deaf / Ten Over.  He recommends 1M resistor w/1M reverb pot or 2M resistor w/ 100k pot.


At that time, I had the reverb in a loud LTP + push/pull amp, and did not notice the signal loss effect.

[Willabe]

Yes.  Reverb bypassed-85 dBC. Reverb in circuit- 75 dBC

Do you mean verb bypassed as in dry signal?

This is a confusing way to put it. You 2 signals, 1. un-effected by the reverb = dry signal and 2.  a wet signal = reverb signal.

So it's either dry or reverb.

[Willabe]

I did not change the reverb pot for that quick&dirty test.  I know the pairing of resistor and reverb pot makes a difference.  Last summer, I started out with 150K and 1 Meg and evolved from there, as covered in my earlier thread " 1-tube transformerless reverb breadboard-fest "   

In your 1-tube transformerless reverb breadboard-fest, the Swart/Ampeg 1 tube verb has 100K/1M pot. There's a reason Swart ended up with those 2 values.

I think he uses the same verb circuit for all his amps, SE and PP.

[pullshocks]

Swart  gets  a lot of good comments on their reverb. I’ve never heard one live.  You own one, right?



I have never seen a bona fide Swart schematic. The Guitar.com reverb was supposedly copied from Swart. That’s as close as I’ve ever been able to get.


That article shows the reverb between the preamp stages. Evidently the 100k resistor and 1meg pot work well in that implementation. As far as I can tell (by trial and error) it does not work equally well  with the reverb after the preamp. I never tried 100k but the verb was pretty weak with 150k isolation resistor and 1 Meg reverb pot. 


 

[Willabe]

Yes, I bought a used Swart Antares. I swapped out the type 4 short 2 spring tank medium delay and put in a type 9 long 3 spring tank with long delay. Much better now.

The verb is not as strong/deep as a Fender BF 2 tube verb, but it's pretty strong/deep. Most guys would probably be fine with it. It's just a hair or 2 shy of what I set the verb to on a BF verb amp, which is ~ 2.5 to 3. But it's pretty close, just not quite as deep.

I play pretty clean and I like a bit more verb than most guys, this amp's pretty good for that. The verb helps the guitar sing/sustain a little bit more and gives the sound more depth. 

[Willabe]

That article shows the reverb between the preamp stages. Evidently the 100k resistor and 1meg pot work well in that implementation. As far as I can tell (by trial and error) it does not work equally well  with the reverb after the preamp. I never tried 100k but the verb was pretty weak with 150k isolation resistor and 1 Meg reverb pot.

Yes, this is all about balancing the dry and wet/verb signals.

Tapping the dry signal to send to the verb tank driver stage after 2 gain stages, there's more signal there than if it's tapped after only 1 gain stage.

[FastNBulbous]

This post has impressive legs, and so much great info!

The one thing I don't quite get from the most-shared "18 Watt Minimalist Reverb" schematic is why the Reverb pot is using the center lug as the input and the side lug as the output to the mixing resistors instead of the reverse/a typical voltage divider orientation, like in the Fender reverb.  How is the pot functioning in this configuration and what is the purpose of doing it this way instead of as a voltage divider?