Tube reverb effect

[Nigel Goodwin]

Now I look this message " but connecting a solid state reverb to a valve amp will give the valve distortion to the reverb as well" it´s really a positive point for a guitar player. The problem is not that the reverb effect amplifies the overdrive from the tube amp. The trouble is that the SS reverb device generates its own distorsion. In my opinion a reverb effect must always be linear and have the same sound in the output that the one inserted in the input. No its own overdrive. This is not the case. It generates its own overdrive and it´s not a beauty overdrive, but an ugly one. But it happens to me because the output is very low and if you increase the input signal to have a better output it overdrives. If you put a small signal the sound is OK but the output is too low (I´m speaking about the solid state orange reverb)
View attachment 129080

In which case a valve reverb would be a bad idea, as they add considerable distortion (of numerous types) in their normal operation, even if not over driven. You can design valve amps to give reasonable quality (up there with low-spec solid state amps), but it's not done for guitar amps or reverbs.

Your issue using a solid state reverb is signal levels - you're running at completely wrong signal levels - solid state audio circuits are designed to run at specific levels, valve designs could run at any kind of crazy level. But in both cases you 'should' be able to make either work by adjusting the level controls on the valve amp correctly, which is why they have input and master levels.

 

[rjenkinsgb]

Sorry I don´t understood "before the amp"

I was replying to this part:

This is my amp. What I did in it is to put a dual switch DPDT with two jacks and split the signal before the grid in the 7 tap of the 12ax7. I send this with a jack to the reverb and returned by other jack in the grid. It sounds, but with a little low power. As I said, I dont have a osciloscope to measure the amplitude of signal going out to reverb and returning from it and don´t know how to calculate the impedances. So I´ll try a more simple design.

You say the return signal is too low.

What I was suggesting was, in effect, to add a separate preamp to take the guitar signal and drive the effect loop output, then feed the effect loop return into the original input of your amp, so it has more gain there.

eg. Make the overall amp four stage rather than three by adding an extra first stage, with the effects loop between the first two stages - before the original amp three stages.

 

[Richten]

Hi Nigel. Thanks for your answer.
Yes, but the question is that this model (the solid state) was designed to be used with high gain tube amplifiers. Orange amps are known for its high gain overdrive. And they are clearly tube ones. I think that the question is that this device works better with the specific effect loops of this amplifiers. I think, although I really don´t know, that this loop provides a low level signal to the reverb and amplifies enough it after it returns to the circuit. Or more important, as I don´t have an original one to compare or an orange tube amplifier with a loop, I can´t be sure if it´s all right in my layout.
That would be nice that any seventies orange user could test this.
About the tube model, to use with a tube amp it doesn´t matter a little noise or overdrive. It´s diferent for recording. For this I have a digital reverb or even I could add this in the DAW with virtual reverb. Even could use virtual instruments for live playing, amplifiying it trhough an active monitor. But the question is to have fun building the stuff and experiment how the original devices sounds like.
So, I decided to let the layout of the orange for any one who could be interested. Maybe they find any problem, if it exist. And I will build an opamp based design to use this in front the amp and plug the guitar and other effects in its input. Much more easy to use. Another question is that it works. I wouldn´t be the first time that I build a thing that don´t work. But as I said, its just to have fun and experiment

 

[Richten]

OK!!!! Thanks rjenkinsgb. Now I understood!!!. It´s an good option. I have even thought in add a solid state buffer (buffer is right or may be a booster?). I´ll try to use an ic amplifier based in a lm741 integrated circuit to plug it into the mixer before using a tube one. Is it ok?
I have realized that this model is a little complicated to use and match. Needs a buffer to go to the next device and a preamplifier in front of it. And the tube one will be the same. But maybe perfect for the loop amplifier owners. I hope that this layout could be useful for them.
But more things. I have read from a user that if you use a reverb before the overdrive, the overdrive will hide the reverb effect, so the internal loop could be the best idea. Maybe it´s the reason for the success of the clasical reverb circuits of the Fender twin reverbs and things like that. I´ll plug my digital reverb trhough an real overdrive effect (not vst) and see how it works with the reverb before and after the overdrive.
Anyway, I would prefer a device that you can put over any amplifiers head and use it easily (as i said, the guitar on its input and the output in the amps input). I think that it´s a better design for all those who wants to recycle easily all that old accutronics reverbs and build vintage effects.
Cheers!!

 

[Nigel Goodwin]

OK!!!! Thanks rjenkinsgb. Now I understood!!!. It´s an good option. I have even thought in add a solid state buffer (buffer is right or may be a booster?). I´ll try to use an ic amplifier based in a lm741 integrated circuit to plug it into the mixer before using a tube one. Is it ok?
I have realized that this model is a little complicated to use and match. Needs a buffer to go to the next device and a preamplifier in front of it. And the tube one will be the same. But maybe perfect for the loop amplifier owners. I hope that this layout could be useful for them.
But more things. I have read from a user that if you use a reverb before the overdrive, the overdrive will hide the reverb effect, so the internal loop could be the best idea. Maybe it´s the reason for the success of the clasical reverb circuits of the Fender twin reverbs and things like that. I´ll plug my digital reverb trhough an real overdrive effect (not vst) and see how it works with the reverb before and after the overdrive.
Anyway, I would prefer a device that you can put over any amplifiers head and use it easily (as i said, the guitar on its input and the output in the amps input). I think that it´s a better design for all those who wants to recycle easily all that old accutronics reverbs and build vintage effects.
Cheers!!

As I mentioned in post #21, it's all about signal levels - a reverb spring only has a certain range it works properly within, so the electronics in the reverb circuit, and in the main amplifier, have to work together to maintain signals at the correct levels.

In the Orange circuit in post #1 there's a volume control before the reverb feed - so you can adjust the level in to the reverb over a very wide range. Then there's a reverb level control at the output of the reverb circuit, but the maximum level obviously depends on the gain within the reverb circuitry.

 

[Richten]

Sure. The problem is that if you decrease the clean signal and increase the reverb signal it begins to feed back quickly. As rjenkinsgb have told, the option could be have a low input signal for not to overdrive the transistors and keep the original sound and increase the output sound. I have thought in decrease the value of the resistors from emiter to ground to increase the gain, but I don´t want to do this without doing it in a right way.
As I can see, the clean signal from the first part of the circuit excites the reverb through the BFY51, and this signal is mixed with the reverb signal recovered in the second part of the circuit. I have added a potenciometer after the BFY51 to go to the reverb to attenuate the signal, creating a DWELL control. It allows to control not just the amount of reverb mixed to the clean signal, but too, the depth of the reverb. I have ommited the resistor going from clean signal to the mixer (it increases the output signal) and eliminated the only reverb switch. Apart of it, increased the value of the treble capacitor to obtain more treble (my pickups are specially dark). At leas,t that´s the way I understand the circuit. If it is wrong I´d appreciate any commentary.
I put the power supply out, in a separate box, because the reverb tanks are extremely sensible to electromagnetic noise and very easily produce hum. That´s the reason why they where all built in very tall boxes. They grab not just its own electromagnetic noise. If you put it over a external amplifier could reflect this too. It have happened to me when I put this over my Fender Princeton Head. Its a point to consider for builders if don´t have experience with this kind of stuff. I tried to made a flat box and finally had to build a separate case for the reverb and put the power supply out. If I would have known before I´d have made a tall box. I hope that this information is useful if any amateur is interested in build one.
As I have said, the model could be used with a relative good quality of sound. I used it into the analog mixer (line level input) with a two 12ax7 tube guitar preamplifier feeding it. It just attenuates a little. It wasn´t a "disaster". But I´d prefer a more simple design and learn things that could be useful for me and other
.
The reveb and the preamp:

 

[shortbus=]

I´ll try to use an ic amplifier based in a lm741 integrated circuit to plug it into the mixer before using a tube one. Is it ok?

Now you've gone and done it!. (As a new member you won't get the full humor of this, but those that have been here for a long time should) AudioG should be swooping down at any time now! Mentioning sound quality and using a LM741 in the same post will get him to chime in. To get the full effect could you please say something like, "I'm from India" or "I buy my parts from Ebay China sellers"?

 

[Richten]

Hello shortbus. !! I´m sure that I´m loosing a lot of things. But I imagine that you don´t like 741 (or just the LM ones).
Anyway I have the two LM301an that I need for the new project.
Maybe tomorrow I´ll do the pcb and look for the components. I´ll post photographs from the new project, and meanwhile I´ll keep looking for a better sound for the Solid State.
The LM741, I´ll do it anyway, at least that you convince me or you tell me that it´s going to burn something. It´s a joke.
Greetings!!

 

[atferrari]

Hello shortbus. !! I´m sure that I´m loosing a lot of things. But I imagine that you don´t like 741 (or just the LM ones).

The actual long list of "LM ones" formed along more than 30 years makes impossible to consider them as a block much less to dismiss them.

 

[shortbus=]

But I imagine that you don´t like 741

Just the mention of a 741 gets a certain member in a tizzy. I have no problems myself, but the same member says he has the best hearing, and made the best audio circuits ever saw by man or beast. Sorry I interrupted your thread with a inside joke shared by many long timers here. But just couldn't help myself.

 

[Richten]

I imagined a thing like that. I just hope that anyone finds interesting the project. I supose that specially instruments players would like to build an old spring reverb. Althought I have seen a beautyful Pioneer spring tube reverb for Hifi. But I don´t imagine now any person using a spring reverb with his Hifi amplifier. Not even a sofisticated yamaha or profesional rack mounting 500 euros stuff like that. I think that it was a little odd even in seventies.
I like all most vintage stuff. I don´t mind if it´s the best or not. I just like it (like all the Maestro effects or the PYE radios). My first build was a push pull tube amplifier all made with recycled parts and a ibanez overdrive with JRC4558, 2sc1815gr y ma150 diodes (like the original one), all of them recicled from old Sony compact amplifiers of 80´s. Many of them grabed from the garbage. I still have a little bag with maybe 30 JRC opamps. They are supossed to be better. Honestly, my ear is not so good. Up from polyester I have problems to hear diferences with a KP or a polyethylene one (I find with ceramics, they are not good for sound) in tube amps. It´s true that I have very low chances to play really loud, and at low volumes it´s harder to see the true. And I suppose that you can see it better when all your equipment is very good. All my equipment is made of cheap copies So I´m not afraid of breaking it.
I hope that there is any one who likes that kind of stuff out there!!

 

[schmitt trigger]

I definitely like glass electronics, both the vacuum and gas filled versions.
My very first project that actually worked was a 5 tube amplifier.

It is not only pure nostalgia or the beautiful warm glow. Designing electronic circuits with such primitive and fickle devices required a special dedication.

I had many musician friends, and I was their official repairman. I am very familiar with the distinct sound of a Fender Twin Reverb amplifier, which came to define the sound of a generation.

Back to your opamp question: My only suggestion would be to use a dual opamp. For the simple reason that it is the most ubiquitous configuration, there are literally hundreds of different part numbers and they all have identical pinouts.
Practically, this means that if you employ an IC socket, you can swap different part numbers and hear for yourself which one you like best.

 

[Richten]

Hello schmitt trigger!
I think that I have read some of your post before, looking for my own projects. Nice! 5 tube mono and HIFI? I´d like to build a model with ef86 in preamp and 6v6 to the power. I don´t know if it´s the design or tubes, but all the ones that I have heard with 6v6 sounds very warm, meanwhile EL84 sonds more clear. My brother gave me 8 EF86 that he have from the time he studied electronics!!

As I have told to rjenkinsgb I have connected again the tube circuit but with an old tube transformer. A weird one that I have to made experiments. It´s a 280-0-280 secondary winding. After the rectifiers (2x1N4007 joint in the negative and the center tap to ground) I measured 370vdc.
Once the tubes are heated, when I plug the circuit voltages falls to 180vdc, in the main vdc point (must be 330vdc). And in the anode of the first triode I must have 170vdc and I have measured 39vdc. No smoke, no smell to burned... So it seems that it´s not that the transformer is not big enough (I had a single ended tube amp working with this transformer until I have bought a good one).
If the circuit have a short circuit must not be a huge one. As I say, no smoke, no smell. Iwill test the components again and take another look to the layout.
I know that it don´t have a good appearance but all the components are tested before doing the circuit. The paperboard chassis is only to avoid an accident.

In paralell I´ll made the IC model. I´ll keep the one that works better but I´ll test all of them.

 

[Nigel Goodwin]

As I have told to rjenkinsgb I have connected again the tube circuit but with an old tube transformer. A weird one that I have to made experiments. It´s a 280-0-280 secondary winding. After the rectifiers (2x1N4007 joint in the negative and the center tap to ground) I measured 370vdc.
Once the tubes are heated, when I plug the circuit voltages falls to 180vdc, in the main vdc point (must be 330vdc). And in the anode of the first triode I must have 170vdc and I have measured 39vdc. No smoke, no smell to burned... So it seems that it´s not that the transformer is not big enough (I had a single ended tube amp working with this transformer until I have bought a good one).
If the circuit have a short circuit must not be a huge one. As I say, no smoke, no smell. Iwill test the components again and take another look to the layout.
I know that it don´t have a good appearance but all the components are tested before doing the circuit. The paperboard chassis is only to avoid an acciden

Assuming you're referring to the original circuit you posted?, that was explained way back at the beginning of this thread - and is simply down to been designed incorrectly - as we said then, the 4.7K anode load is FAR too small, and the 33K feed resistor FAR too large, the resultant voltages are as expected.

Looking at antique schematics the standard method seemed to be using a transformer to feed the reverb spring, which makes sense when trying to feed a high impedance source (the valve) to a low impedance load (the spring). The problem of course is where would you find such a transformer?.

 

[Richten]

Perfect Nigel . I tried because I know that there is circuits that works well with this method (470n caps and high impedance tanks instead of the transformers design) A friend of mine (he is audio technician) spoke me about this kind of designs. And I did before the Moody GA-40 circuit, that uses aECL84 and the same option and the reverb worked. Although I think that this kind works worst than the ones made with transformers (I´m not sure). I´m going to leave this project (the tube one).
Now that the questions are solved, I´ll be looking at the thread. If somebody is interested, I´ll put information of the new IC circuit. If not, I think that it all is solved.
Thanks to all!! and cheers.

The PCB for the 1974 LM301an model:

 

[Nigel Goodwin]

Perfect Nigel View attachment 129120. I tried because I know that there is circuits that works well with this method (470n caps and high impedance tanks instead of the transformers design)

The problem is it's not a 'high' impedance spring, not in valve terms - to be fed directly from a valve you should use a cathode follower, so as to provide a relatively 'low' impedance drive.

A friend of mine (he is audio technician) spoke me about this kind of designs. And I did before the Moody GA-40 circuit, that uses aECL82 and the same option and the reverb worked. Although I think that this kind works worst than the ones made with transformers (I´m not sure). I´m going to leave this project (the tube one).

As the 'L' part is a power pentode, presumably that is better able to feed the 'low' impedance spring than a triode is - in fact I see from the circuit that it uses a 2.7K anode load.

 

[Richten]

Ok. I see. And it was ECL84 not 82, as I said. I have changed it in the post .
I did this circuit and it works, if any user is interested, although abandoned it because the vibrato circuit was more complex than the fender ones and I can´t made it sound well. Anotherusers had the same problem with this vibrato circuit. Vibrochamp one is very easy and have a great quality. I prefer them because I have never had a problem with it. I had some hum noise, but it could have be caused by wires, etc. Trying to made the vibrato work well the PCB was dirty and broken, and I have abandoned it. So now I made the projects with eyelet board. Haven´t work enough in the circuit. But reverb works.
Not enough information to say how good are reverb circuit build that way. Although I´ve seen a review of this amp in youtube and it doesn´t sound bad. They are from Australia.

 

[Nigel Goodwin]

Ok. I see. And it was ECL84 not 82, as I said. I have changed it in the post .

Still basically the same thing:

E means 6.3V heater.

C means triode

L means audio output pentode

8 means B9A base.

The last number identifies the specific valve.

Interestingly ECL82 was intended for audio use, the ECL84 (most commonly PCL84 - 300mA series heater) was a video amplifier valve, commonly used in old colour sets as the RGB amplifiers.

However, the rarity and lack of decent quality valves means that a lot of modern designs use the 'wrong' types of valves, as it's a question of what you can get.

 

[Richten]

Yes. To be true, it´s more common to see this kind of designs with ECL82 than with ECL84, at least in the searchs that I´ve made in the net. For that reason I wrote ECL82, because it was in my mind, instead of the ECL84. But really, the most common design are, as you have told, with impedance transformers.
Really, if I´d like a vintage tube spring reverb, just would buy an 4AB reverb tank and build one of those 5G15 or 6G15. It´s really the easiest way and they are not very very expensive. Must be the easiest chance for amateur builders.

Cheers and thanks for the answer Nigel.