SE amp with reverb

[Leevi]

I have checked some SE reverb amp schematics and wonder why almost all of them
have an extra amplification stage added to the signal way. Is that really necessary?
The extra stage will certainly change the character of the original sound.


http://music-electronics-forum.com/attachments/6245d1252771722-5f2-reverb-6l6-el34.gif
http://music-electronics-forum.com/attachments/2652d1214457798-5f2_reverb.gif


/Leevi

[shooter]

Is that really necessary?

I like the "driver" tube available, I've tweaked for more gain, more control, (think MV), over drive signal, I've changed it to a CF, all without having to re-drill because I needed it.  If you don't like it, jumper it out!

[John]

The extra stage is to drive the reverb tank. Depending on your circuit, that 3.3M is as low as several hundred K instead. The pots in that "extra stage" are to mix the wet/dry signal. Properly done, it doesn't add much "gain" to the overall circuit.


I've done the spring reverb, and the Belton Brick treated as a reverb tank (put in between 2 valves with cathode follower, etc.) and can't really say I like the spring better than the Brick. But that's just my personal preference.

[Leevi]

The extra stage is to drive the reverb tank. Depending on your circuit, that 3.3M is as low as several hundred K instead. The pots in that "extra stage" are to mix the wet/dry signal. Properly done, it doesn't add much "gain" to the overall circuit.

I mean with the extra stage 1/2 triode that is placed on the signal way before the power tube.
The reverb tank needs its drivers and that's pretty clear.


Compare the following 5F2-A circuits (with reverb/without reverb)
You can see the extra stage V3b in the picture.




http://music-electronics-forum.com/attachments/2652d1214457798-5f2_reverb.gif
http://elektrotanya.com/PREVIEWS/63463243/23432455/fender/fender_princeton-5f2a.pdf_1.png


Leevi

[shooter]

extra stage 1/2 triode that is placed on the signal way before the power tube

V-what?
EDIT: missed this

You can see the extra stage V3b in the picture.

V1 is V1 in both, V2 drives tank, V3a amplifies tank out, V3b does as John stated

[Leevi]

Let's check the following schematic:


http://music-electronics-forum.com/attachments/2652d1214457798-5f2_reverb.gif


V1a and V1b are stages that are part of the 5F2-A circuit
V2 and V3a are reverb drivers
V3b is the extra stage


/Leevi

[sluckey]

I'm only gonna talk about REV 1.4. I assume the preliminary Rev 1.0 has been abandoned because the reverb was not as strong as he would like.

He has used the exact same reverb circuit that Fender used in it's AB763 reverb amps. Notice that 3.3M resistor just prior to V3B grid. Also notice the 220K grid return resistor on V3B grid. Those two resistors form a 15:1 voltage divider that knocks the 'dry' signal down. (The voltage divider is really bigger than 22:1 when you factor in the reverb level and that 470K resistor.) V3B is needed to boost the dry guitar signal back up to the level it was before it was knocked down by that voltage divider. It actually boosts the signal a bit more than needed and this adds some overall gain. That's why the VIB channel of a Super Reverb sounds a little hotter than the NOR channel.

[Leevi]

Thanks for clarification sluckey!

The extra stage is to drive the reverb tank. Depending on your circuit, that 3.3M is as low as several hundred K instead. The pots in that "extra stage" are to mix the wet/dry signal. Properly done, it doesn't add much "gain" to the overall circuit.

Sorry John, I misunderstood your statement


/Leevi

[Willabe]

Depending on your circuit, that 3.3M is as low as several hundred K instead. The pots in that "extra stage" are to mix the wet/dry signal. Properly done, it doesn't add much "gain" to the overall circuit.

There's different ways to add reverb and it depends on how much reverb you want/need too.

Most reverb (parallel side chains, verb is parallel with the main/dry signal) circuits have some signal attenuation for the main dry signal as John pointed to.

In this schemo link you posted there is no dry signal attenuation. I've never seen it done like that. The might have wanted the extra gain?
 
http://music-electronics-forum.com/attachments/2652d1214457798-5f2_reverb.gif

This link you posted is normal for adding verb with dry signal attenuation to balance the verb with the dry signal.

http://music-electronics-forum.com/attachments/6245d1252771722-5f2-reverb-6l6-el34.gif

The output signal from the verb tank is less than the output from a guitars PUP's. So 1 recovery gain stage after the verb tank will not give deep verb. The 2nd (verb) gain stage is called the 'reverb mixer' because it mixes the dry/wet signals together but it also boosts the wet signal back up to the dry signal.

In a Fender,  -The- bench mark for tube/spring tank reverb, the dry signal has 2 stages of gain from the guitar before the verb mix stage, the verb tank's output, less than a guitar PUP, has only 1 stage of gain before the verb mix stage.

They have to cut the dry signal so it doesn't swamp out the wet signal. But it's a balancing act of what amount of wet/dry signal you feed it. 

 

[Leevi]

The following circuit doesn't have any mixer stage. On the bottom is a normal 5E3 circuit
and a reverb implemented with one driver and one amplifier. I have built that and I know that it works.


http://music-electronics-forum.com/attachments/5166d1240227603-5e3-r.gif


/Leevi

[Willabe]

The following circuit doesn't have any mixer stage. On the bottom is a normal 5E3 circuit
and a reverb implemented with one driver and one amplifier. I have built that and I know that it works.

Sure a 1 tube reverb. It works fine, but it doesn't have as much verb as a standard 2 tube verb.

Depends on how much verb you need/want.

[Leevi]

Sure a 1 tube reverb. It works fine, but it doesn't have as much verb as a standard 2 tube verb.

This is the reason why I started this topic so is a simple SE amp somehow a special case that
you need this reverb mixer? My goal is to implement a moderate reverb and keep the basic sound
of the 5F2-A amp as unchanged as possible.


/Leevi

[Willabe]

This is the reason why I started this topic so is a simple SE amp somehow a special case that
you need this reverb mixer?

No.

There's different ways to add reverb and it depends on how much reverb you want/need too.

Sure a 1 tube reverb. It works fine, but it doesn't have as much verb as a standard 2 tube verb.

Depends on how much verb you need/want.

My goal is to implement a moderate reverb......

On the bottom is a normal 5E3 circuit and a reverb implemented with one driver and one amplifier. I have built that and I know that it works.

Seems like like you answered your own question. 

[kagliostro]

Just to show it to you

http://www.offsetguitars.com/forums/viewtopic.php?f=10&t=35226

On the middle of the page there is the schematic

Franco

[Leevi]

On the middle of the page there is the schematic

http://www.offsetguitars.com/personal/sookwinder/cr/champreverb49.jpg


No reverb mixer


I would try to move the reverb connection points one stage earlier (after the volume) and replace the 3.3M with 220K.


/Leevi