Questions revolving one tube reverb circuit

[nickb]

Just to keep the thread limping along ...

I think the "one tube" stipulation is a little misleading because there just isn't enough signal at the end of a single recovery stage to drive the PI satisfactorily (YMMV). So there needs to be at least one more stage of amplification of the reverb signal (and often recovering the padded dry signal too). To keep the discussion clear and the circuits accessible I'm interpreting the term "one tube" to mean a typical dual triode of a type typically used in guitar amps. Not some obscure three amplifier valve that needs to be hunted down NOS.

Thoughts?

In addition I understood the OP wanted a high impedance tank (implicitly transformer-less) solution.

[nickb]

No, I am not the owner & have no benefit at any level from the link or forum. I've never received a penny for any help I've done. I have no part of Hoffman's business. Never even gotten a discount from Hoffman on parts.

I have another profession totally unrelated to music, amps or guitars. I am just a hobbyist like most of us.

Just sharing information that others have found useful. Occasionally, someone will say thank you and convey that the information was useful to them. Over 26,000 views were on that Hoffman thread .......... so I thought there might be a chance that someone here would also find it useful to them. Just trying to give back a small portion of the help that so many others have extended to me. Google "one tube reverb" and see what comes up.

It's that straight forward.

With respect, Tubenit

Cool!

[pdf64]

...I think the "one tube" stipulation is a little misleading because there just isn't enough signal at the end of a single recovery stage to drive the PI satisfactorily (YMMV). So there needs to be at least one more stage of amplification of the reverb signal (and often recovering the padded dry signal too)...

Just as a silicon device can be used to bump up the reverb drive signal, one can be used to help out with the recovery gain, eg use the tube's cathode current / bias resistor to power an NPN common emitter gain stage.

[Chuck H]

Just as a silicon device can be used to bump up the reverb drive signal, one can be used to help out with the recovery gain, eg use the tube's cathode current / bias resistor to power an NPN common emitter gain stage.

Ah, but that's my point. That's not a one tube reverb. That's a one tube, one transistor reverb.

But let's put the repeated inclusion of transistors aside for the moment since I'm actually just attacking the misnomer mod phrase "one tube reverb" and I interpret this as including the stipulation of "not a transistor reverb". In other words, I know it's entirely possible to make an all transistor reverb or a tube and transistor reverb more cheaply and efficiently, but that's not the point.

There are very few amp designs that don't already include reverb that have:
1) A summing stage, and...
2) In a convenient location downstream of any potential preamp distortion.

But in the case of these amps you can add reverb with one tube. For every other amp you can't. Many threads about "one tube reverb"s are a total kludge that ends up with a weak reverb signal, a reverb in a less ideal location in a circuit or some concession on the dry signal in order to get a better reverb sound. And these are all unacceptable concessions IMHO. I think the whole "one tube reverb" thing started with mods to amps that will accommodate the above two criteria. You could add one tube. That is, cut one hole, sacrifice nothing in signal quality and get reverb. For some reason amateur designers started thinking you should be able to add reverb to ANY amp by just adding a tube. Well you can't in most cases. A "one tube reverb" is a "two amplifier reverb" but a functional reverb circuit requires three amplifiers. So unless one is working with a circuit that has that convenient third amplifier potential as part of the stock circuit, you can't have a one tube reverb.

I think I'm just tired of clicking on every thread I see about "one tube reverb"s and seeing people work so hard to make a barely functional circuit, then raving about it simply because it IS making SOME reverb. I always want to post and tell them what's wrong, but I know they're not in a position to hear it.

[nickb]

Do you think DC across the coil will cause the core to saturate earlier?

I believe there are 1700 turns in a 4F input coil.

Well just for fun and it's been a while so here goes:

mmf=flux.Reluctance
=> mmf=flux.(Lc/Uc/Ac + Lg/Ug/Ag)

=> N.I = Bc.Ac.(Lc/Uc/Ac + Lg/Ug/Ag)

=> I = Bc.(Lc/Uc + Ac.Lg/Ug/Ag)/N



Lc= Core length
Uc= Core permeability
Ac= Core Area
Lg= Gap length
Ug= Permeability of gap (=1)
Ag = Area of gap
Uo - permeability of free space

and setting

Bc	1	T
Ac	0.0000056	M^3
Lc	0.037
Lg	0.0029	M
Uc	9000
Ag	0.0001072	M^2
Uo	0.000001256
Nc	1700	Turns
Then I=	72.9	mA

I took the dimensions off the tank pictured above.

[Jazz P Bass]

Hoo.

I need that hat in your picture.

[potatofarmer]

Here's another one-tube circuit, using a triode/pentode tube: Channel Road Amplification: Transformerless Reverb Driver

They used the pentode to drive the tank, but I imagine if you could get the triode to drive it well enough a pentode gain stage would do just fine for recovery.

[66 Kicks]

Well just for fun and it's been a while so here goes:

I took the dimensions off the tank pictured above.

The tank in the picture has a transducer found in Accutronics type 8 and type 9. This transducer has a longer core length and gap area as compared to a type 4. The 1700 turns I suggested was for a type 4F tank. I don't have the number of turns for a type 8F tank, but I do have the input impedance so I can calculate the input coil inductance. This inductance is proportional to the square of the number of turns for the input coil. If the dimensions of the 8F coil are the same as the 4F coil and the iron that the coil goes around is the same for both, I can approximate the number of turns for an 8F coil using 1700 turns for the 4F coil. The coil dimensions and the iron are not exactly the same, but if they were the same, an 8F coil would have 1942 turns.

The core area is in M^2, isn't it?

[nickb]

The tank in the picture has a transducer found in Accutronics type 8 and type 9. This transducer has a longer core length and gap area as compared to a type 4. The 1700 turns I suggested was for a type 4F tank. I don't have the number of turns for a type 8F tank, but I do have the input impedance so I can calculate the input coil inductance. This inductance is proportional to the square of the number of turns for the input coil. If the dimensions of the 8F coil are the same as the 4F coil and the iron that the coil goes around is the same for both, I can approximate the number of turns for an 8F coil using 1700 turns for the 4F coil. The coil dimensions and the iron are not exactly the same, but if they were the same, an 8F coil would have 1942 turns.

The core area is in M^2, isn't it?

The 8 and 4 dimensions are the same aside from the length so the inductance to turns estimate will be off. The DC resistance is the same so it is likely that the coils are the same thinking of it from a manufacturing viewpoint. Plugging the new length in it comes out at 72.5mA. Yes of course area is M^2 just a typo.

[nickb]

Hoo.

I need that hat in your picture.

It seemed like a good idea at the time

[überfuzz]

I don't know if I mentioned this higher up in the thread, but I stumbled upon a tube called ecc823/ecc832. It's basically one high gain and one low gain triode paired up. It helped tightened up the reverb circuit pretty much... You all know the technical stuff behind this. :-)

[Enzo]

Yes, half 12AX7 and half 12AU7. One is the 12DW7 that AMpeg used to use. The other is the reverse order. I can never remember which is which.

[überfuzz]

The ecc832 is high gain + low gain, the ecc823 is low gain + high gain. I guess there are similar versions of the 12DW7 tube.

[Enzo]

I wasn't clear, one of them IS the 12DW7. Just as ECC83 IS a 12AX7.

https://tubedepot.com/products/jj-ec...mp-vacuum-tube

Both are the same two triode types, I can never recall which one has the high gain on pins 1-2-3, and which on pins 6-7-8.

[tedmich]

for "no tube reverb" Rod Elliott makes a nice NE5532/transistor circuit,
Spring Reverb Unit For Guitar
which Wombaticus had useful insights on
Using Op-amps as reverb driver / recovery

Rod's excellent reverb pan page
Spring Reverb