Im building a small 5 watt amp as a summer project and originally decided to not put in reverb (tank, not solid state) because of the cost. I didn't want to have to pay for more tubes and components because I was already over budget. Would it be possible to place the tank in between the pre amp tube and power amp tube? Pre amp tube would be the driving stage and the power tube would be the recovery stage. Could this work?
Schematic:
I would only have one volume pot for the reverb. Nothing fancy.
Would I have to buy a new output transformer too? I've read about reverb tanks and their impedances.
Any help is appreciated. Thanks
Schematic:
An externally hosted image should be here but it was not working when we last tested it.
I would only have one volume pot for the reverb. Nothing fancy.
Would I have to buy a new output transformer too? I've read about reverb tanks and their impedances.
Any help is appreciated. Thanks
No. You might be able to have the preamp tube drive the reverb pan, but the return signal would be very weak for the power tube to use. But even if that worked, you would wind up with ONLY the reverb sound and none of the plain guitar sound.
A compromise would be to have the verb tank driven by a solid state driver, you would need to take signal from after first stage preamp tube, bring it to a small chip amp through the spring verb and recover the return with a SS buffer. Then its remixed with original signal prior to driver stage. You would need also a separate little power transformer supply to run the solid state stuff but 12V supply enough.
It still keeps costs low, and you would not need additional tubes or different transformers for the tube stages. If you are not certain you want to do it that way, run the preamp stage out through a 1/4'' jack on the chassis, and same for a return.
Then you can build it ''outboard'' later, attached inside the bottom of a combo amp or something. And it will still sound like a spring reverb, because it is!
It still keeps costs low, and you would not need additional tubes or different transformers for the tube stages. If you are not certain you want to do it that way, run the preamp stage out through a 1/4'' jack on the chassis, and same for a return.
Then you can build it ''outboard'' later, attached inside the bottom of a combo amp or something. And it will still sound like a spring reverb, because it is!
Or this: drive the reverb with the output of the amp - along with your speaker. Then take the reverb return and send it through a small recovery amp into the preamp.
Wow Enzo that is cool thinking..Hey a load is a load right? ;-) I guess look at the verb tanks that won't soak up too much of your power...?
Something like that has been done, see the Fender Champ 12 schematic, http://www.prowessamplifiers.com/schematics/fender/champ_12_schem.pdf where the reverb tank is driven straight from the speaker out, but the main problem is to reamplify the weak recovered signal (as Enzo noted) but much worse is to find a proper point to reinject it together with the regular guitar sound.
That requires a much more complex amp than the regular Champ (why they called "Champ" a complex multi mode amp, with 12W coming from a 6L6 and driving a 12" speaker, let alone having Reverb, is way beyond me).
To boot, the signal taken from the output is injected back at an earlier stage, amplified, fed again to said earlier point, in circles.
Does the word "feedback" come to mind?
I'm an inveterate experimenter and tried that ........ it did work, sort of, but I got crazybtrying to adjust the exact gain level.
A little lower, reverb was very weak; a little higher and it howled uncontrollably.
I'd suggest you check how Reverb is added in similar simple amps , usually with a dual Op Amp, think TL072 or similar, and add that just after the Champ Volume control, where signal is still not too large.
Or build a standalone Reverb, your choice, and use it between Guitar and Preamp input, like any pedal.
This almost 50 y.o. Reverb adapter circuit , published in Popular Electronics but straight based on datasheet circuits suggested by Accutronics, Popular Electronics January 1968 was my first commercially successful product, I sold tons of them starting in 1969, to add reverb to amps lacking it.
And the text shows how to interface them to SS and Tube amps 😉
I suggest you drive this circuit from the Champ volume control slider and feed the next preamp tube grid, using 100k mixing resistors.
You can't connect it between preamp out and straight power tube grid, signal there is way too high.
You can build it "outside" , test it, and only when happy with results fix it inside the Champ chassis.
Or add some crude effects loop and build Reverb as a standalone box.
Transistors used are obsolete but modern equivalents are easy to find, they show the (old style) PCB, suggest a mini chassis , how to power it from an SS power amp supply (you'll need 20/24 V DC) , etc.
That requires a much more complex amp than the regular Champ (why they called "Champ" a complex multi mode amp, with 12W coming from a 6L6 and driving a 12" speaker, let alone having Reverb, is way beyond me).
To boot, the signal taken from the output is injected back at an earlier stage, amplified, fed again to said earlier point, in circles.
Does the word "feedback" come to mind?
I'm an inveterate experimenter and tried that ........ it did work, sort of, but I got crazybtrying to adjust the exact gain level.
A little lower, reverb was very weak; a little higher and it howled uncontrollably.
I'd suggest you check how Reverb is added in similar simple amps , usually with a dual Op Amp, think TL072 or similar, and add that just after the Champ Volume control, where signal is still not too large.
Or build a standalone Reverb, your choice, and use it between Guitar and Preamp input, like any pedal.
This almost 50 y.o. Reverb adapter circuit , published in Popular Electronics but straight based on datasheet circuits suggested by Accutronics, Popular Electronics January 1968 was my first commercially successful product, I sold tons of them starting in 1969, to add reverb to amps lacking it.
And the text shows how to interface them to SS and Tube amps 😉
I suggest you drive this circuit from the Champ volume control slider and feed the next preamp tube grid, using 100k mixing resistors.
You can't connect it between preamp out and straight power tube grid, signal there is way too high.
You can build it "outside" , test it, and only when happy with results fix it inside the Champ chassis.
Or add some crude effects loop and build Reverb as a standalone box.
Transistors used are obsolete but modern equivalents are easy to find, they show the (old style) PCB, suggest a mini chassis , how to power it from an SS power amp supply (you'll need 20/24 V DC) , etc.
Nice reference JM, I kind of had in mind a 1W chip amp or something, for the driver..I have been thinking along the lines of a build-out also with an opto based tremolo and using SS based oscillator control to save one tube.
I didn't invent the idea, Hammond organs and some others did that decades ago. They did have a separate speaker and amp to play the reverb sound, but the reverb drive was right off the main amp output.
A reverb pan will suck very little power from an amp, it isn't like a speaker that has to move a lot of air.
yes, you would still need a small return amp stage, but that is maybe easier than having not only the return stage but also a new drive stage. Then again as you propose, a little drive circuit is not really very complex. Powering it is maybe the hardest part, ther are no low volt supplies in a Champ.
Feeding the reverb back into the preamp is not as much a feedback risk as it may seem. The signal coming out of the reverb pan is not in any particular phase relation to the dry signal. So it cannot repeatedly loop through and howl.
JMF suggested an op amp, and Peavey has used a single dual op amp, typically a 4558, for both drive and recovery, for years in their tube amps. Pick any one of them and look at their circuit. it works well and reliably. Classic 30 uses this with a single 30v supply, as an example.
A reverb pan will suck very little power from an amp, it isn't like a speaker that has to move a lot of air.
yes, you would still need a small return amp stage, but that is maybe easier than having not only the return stage but also a new drive stage. Then again as you propose, a little drive circuit is not really very complex. Powering it is maybe the hardest part, ther are no low volt supplies in a Champ.
Feeding the reverb back into the preamp is not as much a feedback risk as it may seem. The signal coming out of the reverb pan is not in any particular phase relation to the dry signal. So it cannot repeatedly loop through and howl.
JMF suggested an op amp, and Peavey has used a single dual op amp, typically a 4558, for both drive and recovery, for years in their tube amps. Pick any one of them and look at their circuit. it works well and reliably. Classic 30 uses this with a single 30v supply, as an example.
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