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Tube reverb effect

Richten

New Member
Hello friends! I´m an amateur builder of music electronics. I have buid many guitar effects and some tube amps but allways following the original desing. I have a course of telecomunications but I haven´t seen analog electronics (sadly), so I preffer to ask :).
I have succesfully build a solid state circuit for this tank. It´s in spanish, but if any one is interested just ask me:
Could any one tell me please, if there is a short circuit in this design? It´s a tube reverb circuit. I made it and it have a great fallen of voltage when i connect the power supply: from 200vdc to 33vdc in the first tube anode!! The voltage must be aprox. 160vdc. And the transformers warms up. I think that the power supply is not big enough for this circuit, but, as I said, electronics is only a hobbie for my, and maybe I´m mading any mistake. Thank you so much!!
This is the original circuit:

image_37896.jpg
And this is the layout. I used the first triode of the 12ax7 to build the first preamp stage of a 5f1 fender Champ. I Know i might consider about signal levels and impedances, but itst only for experimentation (I´m from spain, so the text is in spanish, sorry):

Reverb.jpgReverb.jpg

And this is the circuit where the reverb originaly is inserted:

OR120schem_74.gif
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
I would suggest it's because of the extremely low anode load of the second triode (in a desperate attempt to try and get a low enough impedance to feed the reverb spring), and because of the high value resistor (33k) feeding power to it. I would suggest the reverb spring needs feeding from a cathode follower

However, I'm quite bemused why you would even want to build a valve reverb?, what's the point?.

I can see the point in a valve guitar amp, where you're wanting low quality and high distortion, but connecting a solid state reverb to a valve amp will give the valve distortion to the reverb as well.
 

schmitt trigger

Well-Known Member
If you have seen old tube schematics, you may remember that voltage readings were labeled at each important node.
Do you have a DMM? If so, measure them and label the voltages in the schematic.
That way we will understand what exactly the excessive voltage drop.

Lastly, it is about semantics but unless you are using a tube rectifier, people call them plates and not anodes.
 

Richten

New Member
Thanks you for your answer. It´s just to compare tubes with solid state. The problem that i´m having with the SS is that I have not enough signal in the output and if I increase the signal in the input it overdrives (and the overdrive of transistors is ugly). But I´ll put a booster in the middle point and if it work I´ll add it with a switch to the unit.
So, probably with a suitable transformer, it must work. Isn´t it? I was using a 12vac 2.5A transformer joined to a 2.5A 9 volts with a voltage regulator for filaments and rectifying the output (I dont remember if it was 280vac or so.. The 12vac one was very warm. It have worked for me with many preamps with two 12ax7 (I play with one of them every day) without problems, but it seems that the consumption of this designg is much bigger :)
Two of that preamps for guitar:
IMG-20200407-WA0006.jpeg
 

rjenkinsgb

Well-Known Member
Most Helpful Member
>Off topic<
people call them plates and not anodes.
Not really, people who incorrectly call Thermionic valves "tubes" call the anode the plate :cool:
>End OT<

Back to the original question:

I thought pretty much the same as Nigel, before seeing his answer; the 33K is totally out of proportion with the 4K7 anode load, and the impedance matching is lousy.

The problem that i´m having with the SS is that I have not enough signal in the output
There is something wrong with that circuit as well, then!

Early, primitive solid-state amps were often bad in comparison to the valve technology of the time, that had already been refined over decades.

However properly designed solid state amps are just as good as any valve amp - and that's been well proven; professional guitarists cannot tell them apart in blind tests, with a number of amps of each type all preset to the similar volume and tone.
 

Richten

New Member
Hello again to all!! Thanks for ans some question some questions:

schmitt trigger

I´ll measure again the circuit voltajes. But before this I wanted to be clear that nothing will be burned. But as I said, there was a huge fall. I´ll di it again anyway. I hope the transformer survives :) (it´s a simple wall transformer, don´t mind). Yes I have seen both words, plate or anode. I hope that i could be understood.

rjenkinsgb

This reverb tank is got a specially high input impedance (1475ohm) compared to the normal 8ohm from the most common tanks. I supose that it´s the reason for the designers to look for a high impedance with the 4k7 and the 470nf 400vdc capacitor. Isn´t it?

The question with the solid state design is that is was developed to be used with the effect loop of the orange amplifiers. So, It´s a little dificult to set this with other equipment. For example, plugged directly to a line input it have not enough power. If you plug a guitar directly to the input, it´s got not enough signal (although I have replaced the resistor with a potenciometer and now I can do it). So I use a premplifier to go it. I´m not considering impedances because I don´t have enough information.
So, I can´t compare my device with a original one (There is a very few of them out there!!), but I´d say that it´s all right. The problem is that it´s not as easy to use as the fender models that are designed to plug the guitar in the input and then plug the output to the input of the guitar amplifier.

About the quality of tubes and transistors I agree with you. It seems that in blind test it´s imposible to say wich one is tubes and solid state.
But even it´s true, I have four tube amplifiers, and I have made three model of mosfet amplifiers:
- 50w with IRF540
- 50W with IRFP240 (and complementary)
- 150W with IRFP240 (and complementary) this one:

IMG_20191213_134338.jpg

I have pluged in it my tube preamplifiers. My opinion, and it´s completely subjective:
- The sensation of sound power is very inferior in SS compared with tubes. A simple 4w single ended tube amplifier is got the same power that the 50w and i´d say that the same as the 150w mosfet. I have a Kustom tube 12, suposed to be a 12w (integrated IC LM1875 with a 8ohm celetion super 8 speaker) and it sounds less than the half of the 6v6 single ended 4,5 w (mine) 5F2a princeton. ??????
My DIY princeton

DSC01512.JPG
- The mosfet sound of my amplifier is clean and right (with the same speakers that the tube ones), but it doesn´t have the body and harmonics that the tube ones have.
- For sure, the transistors overdrive sounds so so bad. Not so a 12ax7 overdriven, that sounds really well.

I don´t want polemics, really. It´s just that what I hear is not the same that theory says. I ask you because I don´t understand this diference.

I went a little off the topic, sorry, but I have my experience with tube and SS amps i I´d like to share it with other users.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
but it doesn´t have the body and harmonics that the tube ones have.
You mean it's high quality and not all distortion like the valve one :D

Valve amps have their place, particularly in lead guitar applications, where massive distortion and poor frequency response is often a desirable outcome.

They also sound 'louder' simply because distorted sound appears louder than undistorted sound, and also the fact that the massive distortion increases the power output as well. Simply compare the shape of a sinewave to that of an identical height squarewave, the area under the curve is considerably greater for asquarewave.
 

Richten

New Member
Hi again. I have tested again the SS version and again the same. Good sound but not enough signal in the output (it could be used, but not realy satisfied) As I sayd, I´d need to have an original one to know if it´s a design matter or if it´s a trouble with my design. I´ll try with the tube version. If it doesn´t work maybe I´ll try with a circuit from an electronics magazine. It works with 150 ohm input reverbs. But I have audio transformers. I supose I need a ratio of 1470/150=9.8 ratio. Most near is 32ohm to 4 ohm (an 8 ratio). I could do it but I suspect that very often people don´t mind so much about impedances. The article says "150 ohms or more". I´ll have 150x8=1200ohms of impedance going to the input of the reverb tank. Could try with this.
I´ll test the tube model, and if it doesn´t work maybe I made the magazine model or I take the tank to the drawer :) because I have a good digital reverb and it´s giving me too much troubles. Or maybe I´ll buy a blue accutronics reverb tank with a 8 ohms (15 euros aprox) and have more fun of it. Anyway, is someone is really enterested in reverbs with this kind of tanks, I´ll test it anyway :)
 

Richten

New Member
Hello Nigel. I Havent seen your answer before the upper post.
No, not really. And I repeat that I know that I have practically no knowledge of electronics, but I speak of my experience. Until the tube ones breaks into overdrive (volume up 4 of 10, for example), in my perception, the sound is more rich, with more body and punch. Even when I plug Hifi sound in the guitar amp input (for example the smartphone with a simple jack).
It´s dificult to explain, but to me, my mosfet amplfiers sounds with less power and more flat that the tube ones.
For example, I made a little concert (amateur :) ) in a public school hall with a single ended el84 tube amplifier and almost clean sound. I´m speaking of a 300
square meter hall, aproximately. And I had no problem to be heard. I take my princeton(6v6 single ended) to 5 or 6 and it really seems that the speaker is going to exploit :) really!!. And it´s not completely overdriven. It´s begining to overdrive or mid overdrive. But I don´t have this sensation with the mosfet amplifiers. But I repeat that maybe it´s just a subjective impression.
I supose that you have tube amplifiers. Don´t you really hear the same? Maybe it´s a question of my especific devices or the way I´m conecting it.
Cheers
 

Richten

New Member
Well, forget about the size of the hall :) :) . I don´t want to say a lie, just calculated in my head. But it was a big hall, from a music school. Like a small cinema. Don´t want to say a number but I supose that you can imagine the size. Imagine a place like this or even a little bigger. Remember that we are talking of 4 wats of clean sound. An amplifier made with a tda2003 or so wouldn´t be heard. I´m quite sure. I have it recorded, but i don´t want nobody to sse my super musical performance again :) . It was a cover of Need Your Love so Bad of Fleetwood Mac and two more songs.

Sorry, it´s not very scientific :). I´d like to have a sond level meter.
salon-de-actos_1464595186.jpg
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
The question with the solid state design is that is was developed to be used with the effect loop of the orange amplifiers. So, It´s a little dificult to set this with other equipment. For example, plugged directly to a line input it have not enough power. If you plug a guitar directly to the input, it´s got not enough signal (although I have replaced the resistor with a potenciometer and now I can do it). So I use a premplifier to go it. I´m not considering impedances because I don´t have enough information.
OK, yes that so-called effects loop circuit is extremely odd; it's labelled Echo and in a way it makes sense for that, as it has a permanent bypass signal.

A normal effects loop isolates the preamp out and power amp in, when an external device is connected, which that does not do - and there is no way of overriding the bypass, if the diagram is correct.

The trick would be to actually use the "Slave o/p" as the effects return - the high value resistors feeding that point should have no effect on a low impedance source, and it also eliminates the signal division effect with the 100K resistors around the other input.

Near twice the level and no mixing, in other words.


ps. No arguments from me about building your own gear, I really enjoy it! I've got two large guitar combo amps already though (and too much stuff in general), so no excuse to build one of those myself..
 

Richten

New Member
Thanks rjenkinsgb.

Yes, it´s really an old hobbie I began with my brother (he studied analog electronics many years ago) I made amps, preamps, effects.... I have a lot of schematics and articles (but not electronics knowledge :( ). I suppose that you too, but if I can give you anything, tell me :)

The question is that I´m not building this design for that specific amplifier. I have only single ended tube amplifiers (P1 extreme, Princeton 5F2a and a rare spanish vintage model called Jobé Sonic). And a tweed deluxe that had an old power transformer that burned (because it was too old)) and broke the tubes and the OT (sad because it was really good). My first build. For that reason I think that I´ll read well the model of the magazine to see impedances and levels to use it as people says "in front" or with line going to the mixer: it is pluging the guitar to the device and this in the amplifier input. I was mading some easy experimentation but It´s too much complicated for me to see impedances inside the circuit, mixing and all that things. But if other members are interested I´d try to adapt this to a 5F2a (if posible) and put all the conclusions here.
The interest is that some people have old accutronics reverb tanks 4fb (high impedance input) and I thought that i could be made a reverb with it using capacitors (500nf 500vdc) instead of transformers for them amplifiers. Solid State or tube. But mainly a "in front version", without loops or inserts, because it should be more easy for all.
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.

GAA_5f2-a_schem.gif
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
Hello Nigel. I Havent seen your answer before the upper post.
No, not really. And I repeat that I know that I have practically no knowledge of electronics, but I speak of my experience. Until the tube ones breaks into overdrive (volume up 4 of 10, for example), in my perception, the sound is more rich, with more body and punch. Even when I plug Hifi sound in the guitar amp input (for example the smartphone with a simple jack).
It´s dificult to explain, but to me, my mosfet amplfiers sounds with less power and more flat that the tube ones.
For example, I made a little concert (amateur :) ) in a public school hall with a single ended el84 tube amplifier and almost clean sound. I´m speaking of a 300
square meter hall, aproximately. And I had no problem to be heard. I take my princeton(6v6 single ended) to 5 or 6 and it really seems that the speaker is going to exploit :) really!!. And it´s not completely overdriven. It´s begining to overdrive or mid overdrive. But I don´t have this sensation with the mosfet amplifiers. But I repeat that maybe it´s just a subjective impression.
I supose that you have tube amplifiers. Don´t you really hear the same? Maybe it´s a question of my especific devices or the way I´m conecting it.
I haven't had a valve amplifier for decades (and not built one since the 60's), although I've repaired quite a few.

I like high quality audio, that sounds like the original recording - not the massively distorted and completely artificial sound from most valve amplifiers.
 

Richten

New Member
Ok. It´s not my idea to polemicize. It was just my opinion. I think that every one must opinate and enjoy what they like. I was just curious about this and sorry if I ofended you in some way.
I like tube amplifiers anyway, specially for guitar.
If you prefer solid state perfect. Nothing to say.
Cheers
 

rjenkinsgb

Well-Known Member
Most Helpful Member
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.
I'd add a preamp stage before the amp as it is there, and use the output of that to feed the effects loop.
You can always adjust gain downwards in the next stages if it's too high; you cannot easily do the reverse.

I seem to remember that the EF86 was considered one of the ultimate audio preamp valves at one time & from a quick search there are dozens of examples of preamps using those. eg.

preamp.png
 

Richten

New Member
Hi rjenkinsgb.
I have recently made a 1957 vibrato with a ef86 as preamp and a ecc82 as oscilator.
The EF86 sounds really pretty for me: clear and high. The 6267 is the same tube (in the photographs)

Sorry, you says after the second triode add a preamp stage and then recover this before the power stage?
The problem is that the SS reverb circuit saturates easily. Or is it´s place before the power stage.
Sorry I don´t understood "before the amp"

IMG_20210115_174347.jpg

IMG_20210115_174405.jpg
 

Richten

New Member
Data from the model of the magazine:

Reverb Input impedance: 47K Guitar pickup impedance: 13.5K
Reverb input level: 100mV to 1V Guitar pickup voltage (depending what you play) 100mV to 1V
Reverb output level: Unity Guitar amplifier input voltage: As I have seen on other forums tolerates well to 1.5 volts
Reverb output impedance: minor than 5K Amp guitar input impedance: haven´t found a number, but yes this text:"Anyway, the inputs are usually the same exact circuit on just about every amp Fender made. 1M resistor to bleed DC to ground, 68k to match up to the tube grid. The impedance is pretty high, and the 1M resistor is a big part of setting the impedance".

So it seems that this Solid State circuit will work for the use Im looking for: plug the guitar on it and it´s output with a common guitar amplifier input.
I´ll try to match the impedance with an audio transformer very near to a 9 ratio (to match 150 to 1475 ohms.

I give thanks to rjenkinsgb for the information, but I´ll try a more simple design. Unless you have an special interest in made a model with a tube loop.

I think that with that data it must work like a "in front" reverb.
And I think that with the audio transformer I´ll match the circuit with the reverb tank.

Again, i hope that it could be interesting for people who needs a reverb (or just want to build one) and have a 150 or a 1475 unit to recycle.
If you have money (they are not very expensive), there is a lot of designs, tube and solid state, for 8 OHm units.

Here is the circuit:

Dibujo.jpg
 

unclejed613

Well-Known Member
Most Helpful Member

Richten

New Member
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)
thumbs-up-192.jpg
 
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